1 00:00:00,720 --> 00:00:11,190 [Music] 2 00:00:18,600 --> 00:00:16,150 thank you and thank you for inviting me 3 00:00:20,800 --> 00:00:18,610 and letting me be part of this of this 4 00:00:23,260 --> 00:00:20,810 symposium and I should specifically 5 00:00:25,870 --> 00:00:23,270 thank Nakamura sound for inviting me 6 00:00:28,060 --> 00:00:25,880 actually I'm I'm a physical electric 7 00:00:30,580 --> 00:00:28,070 chemist and and before this morning I 8 00:00:32,500 --> 00:00:30,590 never actually thought about the origin 9 00:00:34,840 --> 00:00:32,510 of life so I am not sure if I will have 10 00:00:38,740 --> 00:00:34,850 anything to tell you about the origin of 11 00:00:40,270 --> 00:00:38,750 life but yeah if you don't find this 12 00:00:44,890 --> 00:00:40,280 useful you can you can blame 13 00:00:47,380 --> 00:00:44,900 nakamura-san afterwards since I work on 14 00:00:49,210 --> 00:00:47,390 in the area of electric Italia's and 15 00:00:52,090 --> 00:00:49,220 this is what Nakamura Sound asked me to 16 00:00:54,070 --> 00:00:52,100 talk about and specifically a part of my 17 00:00:57,969 --> 00:00:54,080 group works on on the electric Attalla 18 00:01:00,060 --> 00:00:57,979 C's of co2 reduction and and and the 19 00:01:03,759 --> 00:01:00,070 relation with proton coupled electron 20 00:01:05,109 --> 00:01:03,769 transfer and maybe it's useful to to 21 00:01:07,719 --> 00:01:05,119 explain a little bit of a how an 22 00:01:10,359 --> 00:01:07,729 electric chemist looks at redox 23 00:01:13,359 --> 00:01:10,369 reactions or how we study them so the 24 00:01:15,130 --> 00:01:13,369 way I study redox reactions in 25 00:01:16,690 --> 00:01:15,140 electrochemical cell is that I have an 26 00:01:20,200 --> 00:01:16,700 electrode and the electrode is typically 27 00:01:24,640 --> 00:01:20,210 also that catalyst for my reaction and I 28 00:01:28,150 --> 00:01:24,650 apply a potential using a basically an 29 00:01:30,490 --> 00:01:28,160 electronic feedback a piece of equipment 30 00:01:32,050 --> 00:01:30,500 called a potential stab and with that 31 00:01:35,560 --> 00:01:32,060 piece of equipment I can change the 32 00:01:37,450 --> 00:01:35,570 electrode potential of my electrode from 33 00:01:39,370 --> 00:01:37,460 reducing which would be a very negative 34 00:01:41,500 --> 00:01:39,380 potential to oxidizing which would be a 35 00:01:42,820 --> 00:01:41,510 very positive potential and then I 36 00:01:44,350 --> 00:01:42,830 measure the current that is flowing 37 00:01:46,899 --> 00:01:44,360 through that electrode and that current 38 00:01:48,730 --> 00:01:46,909 gives me the rate of the reaction and in 39 00:01:52,390 --> 00:01:48,740 that way I can generate current voltage 40 00:01:54,580 --> 00:01:52,400 curves of redox reactions and and then 41 00:01:56,020 --> 00:01:54,590 if I study a particular redox reaction 42 00:01:59,020 --> 00:01:56,030 obviously I will need to know where 43 00:02:00,340 --> 00:01:59,030 where let's say the redox potential the 44 00:02:02,980 --> 00:02:00,350 equilibrium redox potential of that 45 00:02:06,670 --> 00:02:02,990 redox reaction is and in typically if I 46 00:02:08,559 --> 00:02:06,680 would reduce co2 I would I would ideally 47 00:02:10,690 --> 00:02:08,569 see some current flowing and and 48 00:02:12,809 --> 00:02:10,700 reduction current in electrochemistry we 49 00:02:15,430 --> 00:02:12,819 consider it a negative current flowing 50 00:02:17,199 --> 00:02:15,440 if I as I make the potential more 51 00:02:18,640 --> 00:02:17,209 negative I would expect some reduction 52 00:02:20,500 --> 00:02:18,650 current to start flowing and then this 53 00:02:22,660 --> 00:02:20,510 current potential curve would would 54 00:02:24,300 --> 00:02:22,670 typically look something like this and 55 00:02:26,230 --> 00:02:24,310 this is then what I'm 56 00:02:28,930 --> 00:02:26,240 electrochemically and if I reduce co2 57 00:02:30,310 --> 00:02:28,940 then I I can make a number of different 58 00:02:32,260 --> 00:02:30,320 products and we've seen some of those 59 00:02:33,940 --> 00:02:32,270 already today and obviously from the 60 00:02:35,770 --> 00:02:33,950 current I can't really tell what product 61 00:02:37,900 --> 00:02:35,780 I'm I'm making I can just tell how many 62 00:02:42,280 --> 00:02:37,910 electrons are flowing in the external 63 00:02:44,560 --> 00:02:42,290 circuit and then I have a number of 64 00:02:46,570 --> 00:02:44,570 important things that I look at I mean 65 00:02:48,910 --> 00:02:46,580 typically we would like this to happen 66 00:02:50,620 --> 00:02:48,920 very close to the redox potential 67 00:02:52,810 --> 00:02:50,630 because my interest is actually not so 68 00:02:55,780 --> 00:02:52,820 much in in the origin of life but my 69 00:02:57,700 --> 00:02:55,790 interest is in seeing if I can use co2 70 00:02:59,380 --> 00:02:57,710 and water and renewable electricity to 71 00:03:00,820 --> 00:02:59,390 make interesting molecules and I would 72 00:03:02,770 --> 00:03:00,830 like to do that as efficiently as 73 00:03:04,540 --> 00:03:02,780 possible and that means that I would 74 00:03:06,970 --> 00:03:04,550 like this to happen as close as possible 75 00:03:09,160 --> 00:03:06,980 to the equilibrium potential that this 76 00:03:10,420 --> 00:03:09,170 typically doesn't happen and it means 77 00:03:11,830 --> 00:03:10,430 that in order to get some kind of 78 00:03:14,170 --> 00:03:11,840 current we need to move the potential 79 00:03:16,720 --> 00:03:14,180 away from the standard redox potential 80 00:03:18,640 --> 00:03:16,730 we call that an over potential and if 81 00:03:20,260 --> 00:03:18,650 that over potential is very small then 82 00:03:22,480 --> 00:03:20,270 basically I have a very good catalyst 83 00:03:23,740 --> 00:03:22,490 and if that over potentials very large 84 00:03:26,230 --> 00:03:23,750 then basically I have a very bad 85 00:03:28,150 --> 00:03:26,240 catalyst and much of what we do in 86 00:03:30,220 --> 00:03:28,160 electric at alysus is to find electrode 87 00:03:32,110 --> 00:03:30,230 materials that that make this over 88 00:03:33,640 --> 00:03:32,120 potential very very small but obviously 89 00:03:35,050 --> 00:03:33,650 I also need to worry about the product 90 00:03:39,130 --> 00:03:35,060 that I makes I also need to worry about 91 00:03:41,560 --> 00:03:39,140 the selectivity now if I would not do 92 00:03:44,140 --> 00:03:41,570 this electro chemically but I need some 93 00:03:46,810 --> 00:03:44,150 other kind of voltage source I would 94 00:03:49,330 --> 00:03:46,820 probably use another redox couple to 95 00:03:51,640 --> 00:03:49,340 basically donate the electrons to reduce 96 00:03:53,050 --> 00:03:51,650 co2 and that would be d let's say the 97 00:03:54,580 --> 00:03:53,060 other redox couple hydrogen would be 98 00:03:56,620 --> 00:03:54,590 would be a good example and obviously 99 00:03:58,240 --> 00:03:56,630 this redox couple needs to have an a 100 00:04:01,570 --> 00:03:58,250 redox potential that is more negative 101 00:04:03,670 --> 00:04:01,580 than the redox potential of the of the 102 00:04:06,670 --> 00:04:03,680 species that I'm trying to to reduce and 103 00:04:09,370 --> 00:04:06,680 and then in in corrosion Theory we don't 104 00:04:11,410 --> 00:04:09,380 basically we define that we we make this 105 00:04:12,910 --> 00:04:11,420 mixed potential where the current of the 106 00:04:15,160 --> 00:04:12,920 oxidation reaction and the current of 107 00:04:16,780 --> 00:04:15,170 the reduction reaction is equal and then 108 00:04:21,849 --> 00:04:16,790 we end up at this sort of mixed 109 00:04:25,120 --> 00:04:21,859 potential where everything happens now 110 00:04:26,980 --> 00:04:25,130 before I move on to try and explain how 111 00:04:28,840 --> 00:04:26,990 these reactions take place and how I can 112 00:04:30,250 --> 00:04:28,850 make good catalyst for this and and how 113 00:04:33,040 --> 00:04:30,260 what is the role of protons and 114 00:04:35,590 --> 00:04:33,050 electrons there's one thing that that I 115 00:04:37,830 --> 00:04:35,600 included as a slide because of the the 116 00:04:40,480 --> 00:04:37,840 talk that we heard this morning 117 00:04:43,270 --> 00:04:40,490 oscillations because that actually turns 118 00:04:46,510 --> 00:04:43,280 out to be my previous life I did a PhD 119 00:04:48,460 --> 00:04:46,520 in in in in studying electrochemical 120 00:04:50,530 --> 00:04:48,470 oscillations and instabilities and 121 00:04:52,390 --> 00:04:50,540 typically what you would expect if you 122 00:04:54,969 --> 00:04:52,400 apply a fixed potential that after a 123 00:04:56,409 --> 00:04:54,979 while you would expect to get a a 124 00:04:57,730 --> 00:04:56,419 constant current a steady state current 125 00:05:00,189 --> 00:04:57,740 or if you apply and this is something 126 00:05:01,930 --> 00:05:00,199 that we can do also with our feedback 127 00:05:03,580 --> 00:05:01,940 electronics we can apply a constant 128 00:05:06,820 --> 00:05:03,590 current and they would expect that the 129 00:05:08,950 --> 00:05:06,830 system develops a stable potential but 130 00:05:10,779 --> 00:05:08,960 this very often doesn't happen and is 131 00:05:12,700 --> 00:05:10,789 typically what what we see is sometimes 132 00:05:14,830 --> 00:05:12,710 that when these curves do not look 133 00:05:17,350 --> 00:05:14,840 sigmoidal like this but develop a branch 134 00:05:19,450 --> 00:05:17,360 where we have a negative resistance or a 135 00:05:22,240 --> 00:05:19,460 negative impedance then we can develop 136 00:05:25,240 --> 00:05:22,250 instabilities and these instabilities 137 00:05:28,180 --> 00:05:25,250 can give rise to oscillations and and 138 00:05:30,610 --> 00:05:28,190 and I show you a few here and these are 139 00:05:33,189 --> 00:05:30,620 really relatively simple reactions this 140 00:05:35,320 --> 00:05:33,199 is the reduction of indium 3 plus on on 141 00:05:36,969 --> 00:05:35,330 a mercury electrode and I will not go 142 00:05:38,350 --> 00:05:36,979 into the details but this was some a 143 00:05:40,480 --> 00:05:38,360 question I think that was asked this 144 00:05:42,250 --> 00:05:40,490 morning if you can develop something 145 00:05:45,219 --> 00:05:42,260 like chaos here you see the current 146 00:05:47,920 --> 00:05:45,229 oscillate in the reduction of indium on 147 00:05:50,020 --> 00:05:47,930 a mercury electrode and and this this is 148 00:05:52,360 --> 00:05:50,030 how we how we drew what is called a 149 00:05:54,129 --> 00:05:52,370 strange attractor from this from these 150 00:05:55,450 --> 00:05:54,139 these oscillations you can see here a 151 00:05:57,279 --> 00:05:55,460 return map I don't know if you're 152 00:05:58,650 --> 00:05:57,289 familiar with this kind of terminology 153 00:06:01,990 --> 00:05:58,660 but what we see here is a 154 00:06:04,420 --> 00:06:02,000 deterministically chaotic oscillation in 155 00:06:05,950 --> 00:06:04,430 the reduction of indium three-plus on a 156 00:06:07,870 --> 00:06:05,960 mercury electrode and this develops 157 00:06:10,270 --> 00:06:07,880 through a series of period doubling 158 00:06:12,040 --> 00:06:10,280 bifurcation and you can have very 159 00:06:13,930 --> 00:06:12,050 complicated oscillations here we see 160 00:06:15,339 --> 00:06:13,940 something that people call bursting 161 00:06:16,570 --> 00:06:15,349 oscillations this is the reduction of 162 00:06:18,730 --> 00:06:16,580 hydrogen peroxide on a platinum 163 00:06:20,110 --> 00:06:18,740 electrode and now we drive this as a 164 00:06:22,629 --> 00:06:20,120 constant current that we measure the 165 00:06:23,860 --> 00:06:22,639 voltage and you see that it seems to go 166 00:06:26,110 --> 00:06:23,870 through two different types of 167 00:06:27,730 --> 00:06:26,120 oscillations one with a very high 168 00:06:30,610 --> 00:06:27,740 frequency and one with a lower frequency 169 00:06:32,379 --> 00:06:30,620 and I don't want to dwell on this but 170 00:06:33,879 --> 00:06:32,389 this this really much of this can be 171 00:06:35,529 --> 00:06:33,889 understood simply from the current 172 00:06:38,260 --> 00:06:35,539 voltage curve where we have a region of 173 00:06:39,909 --> 00:06:38,270 negative impedance that is coupled to 174 00:06:42,010 --> 00:06:39,919 the external circuit and that is coupled 175 00:06:43,560 --> 00:06:42,020 to a slow feedback mechanism which is 176 00:06:45,520 --> 00:06:43,570 very important in these type of 177 00:06:48,120 --> 00:06:45,530 instabilities and in this case the slow 178 00:06:50,709 --> 00:06:48,130 feedback mechanism is mass transport and 179 00:06:51,159 --> 00:06:50,719 actually we showed in a very simple 180 00:06:53,529 --> 00:06:51,169 model 181 00:06:55,360 --> 00:06:53,539 here many years ago and this was during 182 00:06:57,969 --> 00:06:55,370 my PhD that we can understand much of 183 00:07:00,459 --> 00:06:57,979 what is happening in this in this this 184 00:07:02,140 --> 00:07:00,469 implies by simply coupling the the 185 00:07:03,670 --> 00:07:02,150 kinetics that give rise to the negative 186 00:07:04,830 --> 00:07:03,680 impedance to mass transport and that 187 00:07:07,869 --> 00:07:04,840 will give you rise to oscillations 188 00:07:09,189 --> 00:07:07,879 instabilities and all the transitions to 189 00:07:11,200 --> 00:07:09,199 chaos that we see so the chemistry 190 00:07:14,399 --> 00:07:11,210 behind that is relatively simple what we 191 00:07:16,689 --> 00:07:14,409 have here is a very simple in 192 00:07:18,249 --> 00:07:16,699 non-linearity that is coupled to a slow 193 00:07:22,029 --> 00:07:18,259 feedback mechanism and that can give 194 00:07:23,110 --> 00:07:22,039 rise to these type of instabilities but 195 00:07:25,329 --> 00:07:23,120 that is not what I want to talk about 196 00:07:27,540 --> 00:07:25,339 what I want to talk about is about how 197 00:07:29,980 --> 00:07:27,550 to catalyze electron transfer reactions 198 00:07:34,540 --> 00:07:29,990 and one thing you may have noticed if we 199 00:07:36,939 --> 00:07:34,550 if we can allow co2 to let's say CEO or 200 00:07:38,829 --> 00:07:36,949 formic acid or methane or methanol or 201 00:07:40,779 --> 00:07:38,839 ethanol and you will see that these are 202 00:07:42,839 --> 00:07:40,789 things that we can make that this 203 00:07:45,809 --> 00:07:42,849 requires a different number of electrons 204 00:07:48,939 --> 00:07:45,819 and one thing I've learned is that the 205 00:07:50,709 --> 00:07:48,949 overpotential that we typically find to 206 00:07:51,969 --> 00:07:50,719 catalyze a certain reaction depends on 207 00:07:54,489 --> 00:07:51,979 the number of electrons that we're 208 00:07:56,350 --> 00:07:54,499 trying to transfer if we transfer a 209 00:07:58,329 --> 00:07:56,360 single electron and this typically this 210 00:08:00,070 --> 00:07:58,339 is something we would we would model 211 00:08:01,719 --> 00:08:00,080 using a theory that you may have heard 212 00:08:03,820 --> 00:08:01,729 of is a Marcus theory for electron 213 00:08:05,649 --> 00:08:03,830 transfer and the Marcus theory of 214 00:08:08,079 --> 00:08:05,659 electron transfer tells us that the rate 215 00:08:09,999 --> 00:08:08,089 of an electron transfer event depends on 216 00:08:13,029 --> 00:08:10,009 how easy or how difficult it is to 217 00:08:15,279 --> 00:08:13,039 reorganize the environment of the redox 218 00:08:17,320 --> 00:08:15,289 Center basically the solvent if it is 219 00:08:19,329 --> 00:08:17,330 very difficult to reorganize the solvent 220 00:08:21,010 --> 00:08:19,339 then the rate of electron transfer will 221 00:08:23,200 --> 00:08:21,020 be slow if it is easy the rate of 222 00:08:24,519 --> 00:08:23,210 radical transfer will be fast basically 223 00:08:26,139 --> 00:08:24,529 what is saying is the solvent 224 00:08:28,089 --> 00:08:26,149 reorganization or the environmental 225 00:08:30,790 --> 00:08:28,099 Regan ization of the redox Center is 226 00:08:34,240 --> 00:08:30,800 your reaction coordinate that basically 227 00:08:36,159 --> 00:08:34,250 accommodates the electron transfer once 228 00:08:39,459 --> 00:08:36,169 we transfer two electrons things are a 229 00:08:41,259 --> 00:08:39,469 little bit more complicated or maybe I 230 00:08:43,389 --> 00:08:41,269 should say easier because one of the 231 00:08:46,240 --> 00:08:43,399 things that we find from Marcus theory 232 00:08:49,530 --> 00:08:46,250 is it's very unlikely that you transfer 233 00:08:51,819 --> 00:08:49,540 two electrons exactly simultaneously and 234 00:08:53,889 --> 00:08:51,829 and that is because the solvent 235 00:08:56,680 --> 00:08:53,899 basically needs to reorganize too much 236 00:08:59,980 --> 00:08:56,690 and it is practically always more 237 00:09:02,620 --> 00:08:59,990 efficient to to transfer these electrons 238 00:09:04,990 --> 00:09:02,630 one by one so we transfer the first 239 00:09:07,390 --> 00:09:05,000 electron then we generate an intern 240 00:09:10,570 --> 00:09:07,400 idiot and then we transfer the second 241 00:09:12,880 --> 00:09:10,580 electron and once we have to catalyze a 242 00:09:16,030 --> 00:09:12,890 two electron transfer reaction what the 243 00:09:17,980 --> 00:09:16,040 catalyst does it basically allows for 244 00:09:20,140 --> 00:09:17,990 the intermediate to exist and the it 245 00:09:22,710 --> 00:09:20,150 gives this intermediate it generates an 246 00:09:25,750 --> 00:09:22,720 intermediate of the right energy and 247 00:09:27,990 --> 00:09:25,760 this optimization of this intermediate 248 00:09:31,090 --> 00:09:28,000 is really the key to having a good 249 00:09:33,550 --> 00:09:31,100 catalyst and if you get just the right 250 00:09:35,140 --> 00:09:33,560 energy of this intermediate and I'll 251 00:09:37,150 --> 00:09:35,150 show you in a minute what I mean by just 252 00:09:39,370 --> 00:09:37,160 the right energy we can reach a 253 00:09:42,400 --> 00:09:39,380 situation where we have very low over 254 00:09:45,490 --> 00:09:42,410 potential let's say effectively almost 255 00:09:47,830 --> 00:09:45,500 zero and we come to the conclusion that 256 00:09:49,510 --> 00:09:47,840 it is in principle possible to catalyze 257 00:09:51,130 --> 00:09:49,520 two electron transfer actions with the 258 00:09:53,920 --> 00:09:51,140 right catalyst in a way that there is 259 00:09:56,290 --> 00:09:53,930 hardly any over potential that also 260 00:09:59,050 --> 00:09:56,300 means that that catalyst is capable of 261 00:10:01,060 --> 00:09:59,060 catalyzing both the reduction and the 262 00:10:04,570 --> 00:10:01,070 oxidation so in both ways I will refer 263 00:10:07,690 --> 00:10:04,580 to that as reversible catalysis once we 264 00:10:09,370 --> 00:10:07,700 transfer more than two electrons you 265 00:10:11,350 --> 00:10:09,380 could for instance the oxidation of 266 00:10:14,680 --> 00:10:11,360 water to oxygen the oxygen evolution 267 00:10:18,100 --> 00:10:14,690 reaction is a good example it requires 268 00:10:20,170 --> 00:10:18,110 four electrons or six what we what we 269 00:10:21,730 --> 00:10:20,180 see then is that we no longer have a 270 00:10:23,860 --> 00:10:21,740 single intermediate we go through 271 00:10:27,730 --> 00:10:23,870 multiple intermediates in our catalytic 272 00:10:29,740 --> 00:10:27,740 scheme and now we need to optimize every 273 00:10:32,410 --> 00:10:29,750 single intermediate to get our optimal 274 00:10:34,450 --> 00:10:32,420 catalyst and the problem here is those 275 00:10:36,520 --> 00:10:34,460 intermediates are similar and they bind 276 00:10:39,400 --> 00:10:36,530 to the catalyst in a very similar way 277 00:10:40,990 --> 00:10:39,410 that means if we bind one stronger we 278 00:10:43,840 --> 00:10:41,000 will bind the other intermediates 279 00:10:46,829 --> 00:10:43,850 stronger as well and that means that we 280 00:10:49,600 --> 00:10:46,839 cannot optimize all these intermediates 281 00:10:52,540 --> 00:10:49,610 independently they are fixed through 282 00:10:54,610 --> 00:10:52,550 what we call scaling relations and these 283 00:10:57,220 --> 00:10:54,620 scaling relations make it very difficult 284 00:10:59,550 --> 00:10:57,230 to reach a situation where you can have 285 00:11:02,770 --> 00:10:59,560 non zero over potential and that 286 00:11:04,090 --> 00:11:02,780 typically means that for electron or six 287 00:11:05,890 --> 00:11:04,100 electron transfer reactions although 288 00:11:08,530 --> 00:11:05,900 they can be catalyzed by a single 289 00:11:10,240 --> 00:11:08,540 catalyst they practically always have an 290 00:11:12,790 --> 00:11:10,250 over potential it's very difficult to 291 00:11:15,130 --> 00:11:12,800 overcome this is one of the reasons why 292 00:11:17,980 --> 00:11:15,140 it is difficult to do water splitting 293 00:11:18,730 --> 00:11:17,990 and why it is difficult to develop fuel 294 00:11:21,400 --> 00:11:18,740 cells 295 00:11:23,110 --> 00:11:21,410 in a in a fully efficient way because we 296 00:11:24,610 --> 00:11:23,120 have a four electron transfer reaction 297 00:11:26,200 --> 00:11:24,620 there that it's very difficult to 298 00:11:29,740 --> 00:11:26,210 catalyze because it has more than one 299 00:11:33,070 --> 00:11:29,750 intermediate and you will see that that 300 00:11:37,720 --> 00:11:33,080 these ideas also apply to co2 reduction 301 00:11:40,780 --> 00:11:37,730 just the same thing but now in in in a 302 00:11:42,100 --> 00:11:40,790 in a way that maybe you recognize from 303 00:11:43,750 --> 00:11:42,110 that from the Marcus theory in the 304 00:11:46,090 --> 00:11:43,760 Marcus theory we have these different 305 00:11:47,590 --> 00:11:46,100 oxidation states of the system we draw 306 00:11:49,390 --> 00:11:47,600 the free energy as a function of the 307 00:11:51,220 --> 00:11:49,400 reaction coordinate we have these 308 00:11:52,990 --> 00:11:51,230 parabolas this is the initial state of 309 00:11:54,820 --> 00:11:53,000 the system this is the final state and 310 00:11:57,250 --> 00:11:54,830 this is our intermediate state now you 311 00:11:59,620 --> 00:11:57,260 can see that if we try to transfer two 312 00:12:01,050 --> 00:11:59,630 electrons simultaneously the activation 313 00:12:03,340 --> 00:12:01,060 energy here is going to be the 314 00:12:04,510 --> 00:12:03,350 intersection of these two parabolas it's 315 00:12:06,100 --> 00:12:04,520 going to be somewhere here so that 316 00:12:08,530 --> 00:12:06,110 activation energy is very high because 317 00:12:11,500 --> 00:12:08,540 we need to reorganize the environment 318 00:12:14,410 --> 00:12:11,510 too much so it makes sense to find this 319 00:12:16,810 --> 00:12:14,420 intermediate oxidation oxidation state 320 00:12:18,070 --> 00:12:16,820 to generate this extra this extra 321 00:12:21,220 --> 00:12:18,080 minimum here in the potential energy 322 00:12:23,590 --> 00:12:21,230 landscape and now here you see the 323 00:12:25,510 --> 00:12:23,600 activation energy of the separate steps 324 00:12:27,370 --> 00:12:25,520 and now what determines a good catalyst 325 00:12:29,140 --> 00:12:27,380 is not so much actually the activation 326 00:12:32,530 --> 00:12:29,150 energy that we have here but it is the 327 00:12:35,710 --> 00:12:32,540 level of this intermediate energy it can 328 00:12:37,750 --> 00:12:35,720 be high it can be low and what I'm going 329 00:12:41,500 --> 00:12:37,760 to argue with is that the best catalyst 330 00:12:43,750 --> 00:12:41,510 will actually will will place this 331 00:12:46,030 --> 00:12:43,760 energy level here exactly at the same 332 00:12:48,430 --> 00:12:46,040 energy as the initial in the final state 333 00:12:50,310 --> 00:12:48,440 so we generate this flat thermodynamic 334 00:12:52,960 --> 00:12:50,320 landscape that is going to be our 335 00:12:55,720 --> 00:12:52,970 optimal catalyst and that is basically 336 00:12:57,550 --> 00:12:55,730 just an expression of a principle that 337 00:12:59,830 --> 00:12:57,560 is known in heterogeneous catalysis is a 338 00:13:01,720 --> 00:12:59,840 subbatch a principle the catalyst should 339 00:13:03,280 --> 00:13:01,730 not bind this intermediate to weakly it 340 00:13:05,560 --> 00:13:03,290 should not bind it to strongly it should 341 00:13:07,000 --> 00:13:05,570 bind it at an intermediate energy level 342 00:13:09,010 --> 00:13:07,010 that basically means it close to 343 00:13:10,990 --> 00:13:09,020 iquilibrium the energy of the 344 00:13:13,000 --> 00:13:11,000 intermediate has to be equal to the 345 00:13:14,800 --> 00:13:13,010 energy of the initial and the final 346 00:13:18,160 --> 00:13:14,810 state and so that gives us a very clear 347 00:13:19,630 --> 00:13:18,170 quantitative argument of how to find the 348 00:13:20,830 --> 00:13:19,640 best catalyst basically we just need to 349 00:13:22,360 --> 00:13:20,840 find a catalyst that binds that 350 00:13:25,510 --> 00:13:22,370 intermediate with just the right energy 351 00:13:27,220 --> 00:13:25,520 and and nowadays it's possible to 352 00:13:28,720 --> 00:13:27,230 calculate energies of intermediates 353 00:13:30,640 --> 00:13:28,730 using quantum chemistry using density 354 00:13:31,700 --> 00:13:30,650 functional Theory calculations for 355 00:13:33,440 --> 00:13:31,710 instance and 356 00:13:35,300 --> 00:13:33,450 allow you to screen many many different 357 00:13:37,160 --> 00:13:35,310 catalysts and this is a way to search 358 00:13:38,720 --> 00:13:37,170 using the computer to search for a good 359 00:13:40,760 --> 00:13:38,730 catalyst and this is a this is a 360 00:13:43,190 --> 00:13:40,770 strategy that is used very much nowadays 361 00:13:46,310 --> 00:13:43,200 in in heterogeneous catalysis and also 362 00:13:47,660 --> 00:13:46,320 in electric Attalla C's now other than 363 00:13:50,450 --> 00:13:47,670 that we're transferring electrons were 364 00:13:51,770 --> 00:13:50,460 also transferring protons and this 365 00:13:55,280 --> 00:13:51,780 brings basically this brings another 366 00:13:56,930 --> 00:13:55,290 reaction coordinate so what I'm assuming 367 00:13:58,670 --> 00:13:56,940 in many cases that when you're 368 00:13:59,930 --> 00:13:58,680 transferring a proton one electron and 369 00:14:01,700 --> 00:13:59,940 what many people assume in the 370 00:14:03,290 --> 00:14:01,710 literature is it is when you're 371 00:14:05,480 --> 00:14:03,300 transferring both the proton and 372 00:14:07,460 --> 00:14:05,490 electron that this happens concertedly 373 00:14:10,400 --> 00:14:07,470 so we transfer a proton and an electron 374 00:14:12,950 --> 00:14:10,410 conservatively so we go from a to a h 375 00:14:14,690 --> 00:14:12,960 and so to understand the thermodynamics 376 00:14:16,310 --> 00:14:14,700 of this pathway we just need to know the 377 00:14:19,430 --> 00:14:16,320 energy of this initial state and this 378 00:14:21,200 --> 00:14:19,440 final state but you could imagine that 379 00:14:23,300 --> 00:14:21,210 it's possible to have pathways where you 380 00:14:25,880 --> 00:14:23,310 first transfer an electron and then 381 00:14:28,600 --> 00:14:25,890 transfer a proton and this I will refer 382 00:14:31,700 --> 00:14:28,610 to as decoupled proton electron transfer 383 00:14:33,740 --> 00:14:31,710 now there's many many theories on this 384 00:14:36,320 --> 00:14:33,750 beautiful quantum mechanical theories 385 00:14:38,330 --> 00:14:36,330 but but I think the the real issue and 386 00:14:40,190 --> 00:14:38,340 understanding whether you have concerted 387 00:14:41,630 --> 00:14:40,200 proton electron transfer or whether you 388 00:14:44,300 --> 00:14:41,640 have this decoupled proton electron 389 00:14:47,150 --> 00:14:44,310 transfer just follows from very simple 390 00:14:48,830 --> 00:14:47,160 thermodynamic considerations and that 391 00:14:52,250 --> 00:14:48,840 just has to do with the stability of 392 00:14:54,770 --> 00:14:52,260 these four states typically if if these 393 00:14:55,970 --> 00:14:54,780 two states here are high in energy you 394 00:14:57,560 --> 00:14:55,980 could imagine that you will have 395 00:14:59,290 --> 00:14:57,570 concerted proton electron transfer 396 00:15:02,240 --> 00:14:59,300 simply because these two states are 397 00:15:07,520 --> 00:15:02,250 energetically unfavorable but once these 398 00:15:09,830 --> 00:15:07,530 states are favourable once this a likes 399 00:15:11,600 --> 00:15:09,840 to pick up an electron for instance 400 00:15:13,100 --> 00:15:11,610 because it has a favorable electron 401 00:15:15,140 --> 00:15:13,110 affinity and it has a good solvation 402 00:15:16,640 --> 00:15:15,150 energy then you could imagine that you 403 00:15:19,430 --> 00:15:16,650 first transfer an electron and then a 404 00:15:21,020 --> 00:15:19,440 proton and you can make things more 405 00:15:22,940 --> 00:15:21,030 complicated we can start transferring 406 00:15:24,670 --> 00:15:22,950 two protons and two electrons and we get 407 00:15:26,750 --> 00:15:24,680 these kind of square schemes and 408 00:15:28,400 --> 00:15:26,760 typically what people assume in the 409 00:15:32,090 --> 00:15:28,410 literature that things go along this 410 00:15:34,340 --> 00:15:32,100 diagonal but what I'll argue is that in 411 00:15:36,530 --> 00:15:34,350 many cases actually the mechanism follow 412 00:15:38,780 --> 00:15:36,540 something like this where we where 413 00:15:41,990 --> 00:15:38,790 somewhere in the mechanism we decouple 414 00:15:44,810 --> 00:15:42,000 proton electron transfer and we follow a 415 00:15:45,560 --> 00:15:44,820 pathway like this now how does that 416 00:15:49,100 --> 00:15:45,570 manifest 417 00:15:51,230 --> 00:15:49,110 in an experiment well if I apply again 418 00:15:54,139 --> 00:15:51,240 the subbatch a principle the idea that 419 00:15:56,689 --> 00:15:54,149 every every step here needs to be close 420 00:15:59,120 --> 00:15:56,699 to equilibrium in order to have the 421 00:16:00,439 --> 00:15:59,130 optimal rate and if I look at this step 422 00:16:02,840 --> 00:16:00,449 here this is just an acid-base 423 00:16:04,850 --> 00:16:02,850 equilibrium and if I want the acid-base 424 00:16:07,519 --> 00:16:04,860 equilibrium to be close to equilibrium 425 00:16:10,460 --> 00:16:07,529 that basically means that I want the pH 426 00:16:13,400 --> 00:16:10,470 of my solution to be close to the pKa of 427 00:16:15,800 --> 00:16:13,410 this acid-base equilibrium now that 428 00:16:17,480 --> 00:16:15,810 suggests that when you have decoupled 429 00:16:19,730 --> 00:16:17,490 proton electron transfer in your 430 00:16:22,100 --> 00:16:19,740 mechanism there's going to be an optimal 431 00:16:25,910 --> 00:16:22,110 pH at which the reaction likes to take 432 00:16:28,009 --> 00:16:25,920 place and this actually this very simple 433 00:16:30,259 --> 00:16:28,019 idea explains a lot of data in the 434 00:16:32,540 --> 00:16:30,269 electric Atallah C's literature so what 435 00:16:34,400 --> 00:16:32,550 I'm what I'm saying is that once I have 436 00:16:35,689 --> 00:16:34,410 this decoupled proton electron transfer 437 00:16:38,900 --> 00:16:35,699 in my mechanism there's going to be an 438 00:16:41,120 --> 00:16:38,910 optimal pH and so if I look at the rate 439 00:16:43,430 --> 00:16:41,130 at a fixed thermodynamic driving force I 440 00:16:45,499 --> 00:16:43,440 should say that this rate is at the same 441 00:16:46,970 --> 00:16:45,509 thermodynamic driving force for every pH 442 00:16:49,249 --> 00:16:46,980 it's very important to take that into 443 00:16:51,350 --> 00:16:49,259 account then there's going to be an 444 00:16:53,960 --> 00:16:51,360 optimal pH and that optimal pH is going 445 00:16:56,660 --> 00:16:53,970 to be very close to the pKa of the acid 446 00:16:58,790 --> 00:16:56,670 base equilibrium in the mechanism this 447 00:17:00,740 --> 00:16:58,800 explains why many alcohol oxidations 448 00:17:02,960 --> 00:17:00,750 prefer to take place in alkaline media 449 00:17:05,149 --> 00:17:02,970 because alcohols deep protonate an 450 00:17:07,970 --> 00:17:05,159 alkaline media to have a pKa of around 451 00:17:10,399 --> 00:17:07,980 14 or 15 and the deep protonated alcohol 452 00:17:13,730 --> 00:17:10,409 is more easy to oxidize than the 453 00:17:16,549 --> 00:17:13,740 protonated alcohol nitrate reduction 454 00:17:19,970 --> 00:17:16,559 prefers to take place in acid media 455 00:17:22,010 --> 00:17:19,980 nitrate has a pKa of minus 1 and 456 00:17:25,010 --> 00:17:22,020 actually prefers to be protonated before 457 00:17:27,020 --> 00:17:25,020 it reacts further and that's why nitrate 458 00:17:29,720 --> 00:17:27,030 prefers to have very to take place in 459 00:17:32,810 --> 00:17:29,730 very acidic media an intermediate case 460 00:17:35,180 --> 00:17:32,820 is formic acid oxidation formic acid has 461 00:17:36,649 --> 00:17:35,190 a pKa of 4 and we find that if we want 462 00:17:38,870 --> 00:17:36,659 to optimize the rate of formic acid 463 00:17:42,320 --> 00:17:38,880 oxidation for instance in a formic acid 464 00:17:45,530 --> 00:17:42,330 fuel cell the pH of the electrolyte 465 00:17:47,570 --> 00:17:45,540 should be close to 4 that doesn't 466 00:17:49,370 --> 00:17:47,580 necessarily optimize the conductivity of 467 00:17:53,390 --> 00:17:49,380 the electrolyte but it optimizes the 468 00:17:56,630 --> 00:17:53,400 rate of the of the catalytic reaction of 469 00:17:57,830 --> 00:17:56,640 the formic acid oxidation so what I want 470 00:17:59,270 --> 00:17:57,840 to do in the rest of the talk is show 471 00:18:00,890 --> 00:17:59,280 some of these principles in 472 00:18:03,920 --> 00:18:00,900 in relation to the electric analytics 473 00:18:05,540 --> 00:18:03,930 you to reduction if you look in the 474 00:18:07,400 --> 00:18:05,550 literature in purely the 475 00:18:11,690 --> 00:18:07,410 electrochemistry literature of co2 476 00:18:15,530 --> 00:18:11,700 reduction there's basically three major 477 00:18:17,840 --> 00:18:15,540 products that we observe Co formic acid 478 00:18:20,240 --> 00:18:17,850 we've seen them already as the initial 479 00:18:22,520 --> 00:18:20,250 reduction products of co2 and oxalate 480 00:18:25,940 --> 00:18:22,530 oxalate is typically a product in a 481 00:18:27,830 --> 00:18:25,950 protic solvents and all these reactions 482 00:18:29,480 --> 00:18:27,840 are to electron transfer reactions which 483 00:18:33,590 --> 00:18:29,490 I think it's not a coincidence these are 484 00:18:35,180 --> 00:18:33,600 relatively easy to catalyze and and 485 00:18:37,340 --> 00:18:35,190 actually there are catalysts that 486 00:18:39,290 --> 00:18:37,350 catalyze these reactions reversibly I'll 487 00:18:41,450 --> 00:18:39,300 show you an example in the next slide 488 00:18:43,850 --> 00:18:41,460 enzymes there exist enzymes that can 489 00:18:45,170 --> 00:18:43,860 catalyze these reactions reversibly so 490 00:18:48,020 --> 00:18:45,180 they can catalyze them in both 491 00:18:50,660 --> 00:18:48,030 directions with essentially zero zero 492 00:18:52,400 --> 00:18:50,670 over potential if you want to reduce 493 00:18:54,080 --> 00:18:52,410 them further then these are the 494 00:18:56,810 --> 00:18:54,090 intermediate so you can reduce co 495 00:18:58,400 --> 00:18:56,820 further to methane ethylene and other 496 00:18:59,720 --> 00:18:58,410 interesting products will copper 497 00:19:01,850 --> 00:18:59,730 electrodes I'll show you that in a 498 00:19:04,270 --> 00:19:01,860 minute and you can also imagine that you 499 00:19:06,140 --> 00:19:04,280 you oxidize further this carboxylate 500 00:19:10,400 --> 00:19:06,150 functionalities to an aldehyde and 501 00:19:12,500 --> 00:19:10,410 eventually to to an alcohol now just to 502 00:19:14,870 --> 00:19:12,510 show you that you can do this reversibly 503 00:19:17,330 --> 00:19:14,880 so you can reversibly convert co2 into 504 00:19:18,950 --> 00:19:17,340 formic acid in this case and back here's 505 00:19:22,430 --> 00:19:18,960 an example of an experiment from the 506 00:19:24,170 --> 00:19:22,440 group of Judy Hurst in Cambridge where 507 00:19:26,420 --> 00:19:24,180 they immobilize the formate 508 00:19:30,260 --> 00:19:26,430 dehydrogenase on the paralytic graphite 509 00:19:33,410 --> 00:19:30,270 electrode and and they basically they 510 00:19:36,980 --> 00:19:33,420 they change the potential at which the 511 00:19:40,100 --> 00:19:36,990 electrons are transferred to the active 512 00:19:42,860 --> 00:19:40,110 site in in this kind of protein film 513 00:19:45,140 --> 00:19:42,870 voltammetry here's the the redox 514 00:19:47,870 --> 00:19:45,150 potential of the conversion of form a to 515 00:19:50,120 --> 00:19:47,880 co2 if you go negative you see that you 516 00:19:51,830 --> 00:19:50,130 reduce co2 to formate and if you go back 517 00:19:54,020 --> 00:19:51,840 you see that you oxidize formate back 518 00:19:56,300 --> 00:19:54,030 into co2 and note that this happens 519 00:19:59,000 --> 00:19:56,310 essentially reversibly around the 520 00:20:00,680 --> 00:19:59,010 equilibrium potential showing that this 521 00:20:02,600 --> 00:20:00,690 two electron transfer reduction with the 522 00:20:04,700 --> 00:20:02,610 right catalyst these two electron 523 00:20:08,780 --> 00:20:04,710 transfer reaction can be catalyzed 524 00:20:10,880 --> 00:20:08,790 reversibly and and and this inspired me 525 00:20:13,220 --> 00:20:10,890 to see if we can also do this with 526 00:20:15,830 --> 00:20:13,230 something that is not an enzyme 527 00:20:19,279 --> 00:20:15,840 and and this comes the closest to what 528 00:20:21,700 --> 00:20:19,289 we find so far this is the the reduction 529 00:20:23,899 --> 00:20:21,710 of co2 on the platinum palladium 530 00:20:24,980 --> 00:20:23,909 catalyst and basically what we did 531 00:20:26,720 --> 00:20:24,990 there's a lot of literature 532 00:20:29,120 --> 00:20:26,730 electrochemistry literature on formic 533 00:20:31,009 --> 00:20:29,130 acid oxidation and the best catalyst 534 00:20:32,840 --> 00:20:31,019 that people found was a mixture of 535 00:20:35,419 --> 00:20:32,850 palladium and platinum we just took that 536 00:20:37,490 --> 00:20:35,429 catalyst and we ran it in Reverse and we 537 00:20:39,590 --> 00:20:37,500 found that we can reduce u2 to formate 538 00:20:41,629 --> 00:20:39,600 with this catalyst and we can do this 539 00:20:42,799 --> 00:20:41,639 you know almost quasi reversibly and you 540 00:20:44,539 --> 00:20:42,809 can see that very close to the 541 00:20:47,690 --> 00:20:44,549 equilibrium potential you start 542 00:20:50,029 --> 00:20:47,700 generating for me this is not a very 543 00:20:52,190 --> 00:20:50,039 stable catalyst it generates also co and 544 00:20:54,860 --> 00:20:52,200 co will poison the electrode but but 545 00:20:59,690 --> 00:20:54,870 this is just to to illustrate the 546 00:21:01,759 --> 00:20:59,700 principle here's another example when of 547 00:21:04,220 --> 00:21:01,769 a system that we studied this is a 548 00:21:06,259 --> 00:21:04,230 cobalt porphyrin or protoporphyrin that 549 00:21:08,330 --> 00:21:06,269 we immobilized on a graphite electrode 550 00:21:10,460 --> 00:21:08,340 we actually initially we were interested 551 00:21:12,620 --> 00:21:10,470 also in using this this catalyst for 552 00:21:14,389 --> 00:21:12,630 nitrate reduction but at some point we 553 00:21:17,240 --> 00:21:14,399 decided to see if this could be active 554 00:21:19,100 --> 00:21:17,250 for co2 reduction we follow this system 555 00:21:20,870 --> 00:21:19,110 with an online mass spectrometer here 556 00:21:22,789 --> 00:21:20,880 you see the negative current flowing as 557 00:21:25,519 --> 00:21:22,799 we make the potential more negative and 558 00:21:27,139 --> 00:21:25,529 actually I was I was expecting to see Co 559 00:21:29,899 --> 00:21:27,149 because this system had been studied 560 00:21:31,730 --> 00:21:29,909 already and it was found to make Co but 561 00:21:33,860 --> 00:21:31,740 we find actually that this specific 562 00:21:37,789 --> 00:21:33,870 system can make methane so it can do an 563 00:21:40,700 --> 00:21:37,799 8 electron transfer reaction from co2 to 564 00:21:43,399 --> 00:21:40,710 methane the the selectivity however is 565 00:21:46,129 --> 00:21:43,409 not heartwarming this is about 1% and 566 00:21:48,049 --> 00:21:46,139 99% is hydrogen because all this is 567 00:21:51,230 --> 00:21:48,059 taking place in water and water is also 568 00:21:53,629 --> 00:21:51,240 reduced by this catalyst to form 569 00:21:55,639 --> 00:21:53,639 hydrogen but but the interesting thing 570 00:21:59,029 --> 00:21:55,649 here is that this reaction is extremely 571 00:22:02,149 --> 00:21:59,039 sensitive to pH if we shift from pH 1 to 572 00:22:04,340 --> 00:22:02,159 pH 3 we see that we shift the formation 573 00:22:07,009 --> 00:22:04,350 of hydrogen to more negative potentials 574 00:22:09,529 --> 00:22:07,019 but the reduction of co2 still takes 575 00:22:11,450 --> 00:22:09,539 place at the same potential and we 576 00:22:13,279 --> 00:22:11,460 generate here we generate methane and 577 00:22:16,070 --> 00:22:13,289 now we can also see the formation of CO 578 00:22:18,860 --> 00:22:16,080 in our mass spectrometer and now we find 579 00:22:22,250 --> 00:22:18,870 that the formation of of CO at pH 3 can 580 00:22:24,980 --> 00:22:22,260 reach selectivities up to 60% and that 581 00:22:26,630 --> 00:22:24,990 of hydrogen ISM is much lower now 582 00:22:29,990 --> 00:22:26,640 there's different ways of look 583 00:22:33,350 --> 00:22:30,000 this but but the key reason why I think 584 00:22:35,510 --> 00:22:33,360 that this is so sensitive to pH is that 585 00:22:37,190 --> 00:22:35,520 the hydrogen evolution reaction is a 586 00:22:39,350 --> 00:22:37,200 reaction that takes place through 587 00:22:42,620 --> 00:22:39,360 concerted proton electron transfer and 588 00:22:44,900 --> 00:22:42,630 is not very sensitive to pH but the co2 589 00:22:47,390 --> 00:22:44,910 activation is a process that takes place 590 00:22:49,250 --> 00:22:47,400 through an initial electron transfer so 591 00:22:51,440 --> 00:22:49,260 we start from the cobalt porphyrin here 592 00:22:54,350 --> 00:22:51,450 if we reduce that from the 2 plus to the 593 00:22:56,570 --> 00:22:54,360 1 plus state that is when the co2 binds 594 00:22:58,160 --> 00:22:56,580 to the cobalt Center and this is just an 595 00:23:00,350 --> 00:22:58,170 electron transfer and the protons are 596 00:23:02,960 --> 00:23:00,360 only transferred later so here we 597 00:23:04,640 --> 00:23:02,970 decouple proton from electron transfer 598 00:23:06,920 --> 00:23:04,650 and that makes this cycle ph-sensitive 599 00:23:09,830 --> 00:23:06,930 and this cycle not and so now by playing 600 00:23:11,480 --> 00:23:09,840 with pH we can optimize not only 601 00:23:14,150 --> 00:23:11,490 activity but we can also optimize 602 00:23:18,380 --> 00:23:14,160 selectivity and we can tune the pathway 603 00:23:20,270 --> 00:23:18,390 that we want to take place now we've 604 00:23:22,910 --> 00:23:20,280 also studied we can actually calculate 605 00:23:25,040 --> 00:23:22,920 this I don't really want to dwell on 606 00:23:27,080 --> 00:23:25,050 this very much we actually played with 607 00:23:29,420 --> 00:23:27,090 the metal center of these porphyrins to 608 00:23:31,670 --> 00:23:29,430 see if that has an effect on the product 609 00:23:34,340 --> 00:23:31,680 that we make and we find that that 610 00:23:39,170 --> 00:23:34,350 typically our iron and cobalt tend to 611 00:23:41,750 --> 00:23:39,180 make CO and we find that rhodium indium 612 00:23:44,180 --> 00:23:41,760 and tin interestingly make formate they 613 00:23:46,550 --> 00:23:44,190 make a completely different product and 614 00:23:49,070 --> 00:23:46,560 we wanted to understand what property of 615 00:23:52,460 --> 00:23:49,080 the catalyst it is that that that 616 00:23:55,010 --> 00:23:52,470 determines this this selectivity and the 617 00:23:57,440 --> 00:23:55,020 classical theory in this area is that 618 00:23:59,240 --> 00:23:57,450 that has to do with the way you make the 619 00:24:01,910 --> 00:23:59,250 first intermediate and how that first 620 00:24:03,950 --> 00:24:01,920 intermediate binds to the catalyst if 621 00:24:06,380 --> 00:24:03,960 you bind that first intermediate through 622 00:24:08,390 --> 00:24:06,390 the carbon so you have a proton coupled 623 00:24:11,000 --> 00:24:08,400 electron transfer to the co2 and you 624 00:24:13,340 --> 00:24:11,010 make this COOH intermediate that binds 625 00:24:15,200 --> 00:24:13,350 through the carbon that in a next step 626 00:24:18,100 --> 00:24:15,210 you will break a co bond and you will 627 00:24:20,300 --> 00:24:18,110 end up with Co but if you if you 628 00:24:23,210 --> 00:24:20,310 transfer that first proton electron 629 00:24:25,970 --> 00:24:23,220 transfer to the carbon here and you bind 630 00:24:27,620 --> 00:24:25,980 through the oxygen then you make a kind 631 00:24:29,690 --> 00:24:27,630 of formate intermediate and this will 632 00:24:31,910 --> 00:24:29,700 dissociate from the catalyst and your 633 00:24:34,310 --> 00:24:31,920 product will be formic acid and all this 634 00:24:36,800 --> 00:24:34,320 is always in competition with hydrogen 635 00:24:38,990 --> 00:24:36,810 evolution and this is something again 636 00:24:40,280 --> 00:24:39,000 that you can calculate you can do DFT 637 00:24:41,570 --> 00:24:40,290 calculations for all your 638 00:24:43,820 --> 00:24:41,580 catalyst and you can see which 639 00:24:47,150 --> 00:24:43,830 intermediate binds the strongest or is 640 00:24:48,860 --> 00:24:47,160 binding the most favorable to the 641 00:24:51,530 --> 00:24:48,870 catalyst and in that way you can predict 642 00:24:54,080 --> 00:24:51,540 what kind of product you will you will 643 00:24:57,800 --> 00:24:54,090 make using using quantum chemical 644 00:25:01,190 --> 00:24:57,810 calculation now this did not allow us to 645 00:25:02,720 --> 00:25:01,200 explain our data on the on the different 646 00:25:05,240 --> 00:25:02,730 porphyrins and so we came up with a 647 00:25:09,050 --> 00:25:05,250 different mechanism we actually found 648 00:25:11,000 --> 00:25:09,060 that if we do this on indium or tin co2 649 00:25:13,940 --> 00:25:11,010 does not want to bind to the metal 650 00:25:16,460 --> 00:25:13,950 center and we also find that we do not 651 00:25:21,410 --> 00:25:16,470 reduce the metal center of indium and 652 00:25:24,020 --> 00:25:21,420 tin porphyrins what we reduce is the the 653 00:25:26,810 --> 00:25:24,030 ligand and we generate a hydrogen or 654 00:25:29,420 --> 00:25:26,820 actually we generate a hydride on the 655 00:25:34,640 --> 00:25:29,430 ligand we generate an h- on the ligand 656 00:25:38,750 --> 00:25:34,650 and this h- attacks the carbon of the co 657 00:25:41,120 --> 00:25:38,760 2 and this generates the formate and we 658 00:25:43,730 --> 00:25:41,130 find that we can generate that h- that 659 00:25:47,410 --> 00:25:43,740 hydride intermediate not only on the 660 00:25:50,090 --> 00:25:47,420 ligand we find it on indium and and tin 661 00:25:52,430 --> 00:25:50,100 protoporphyrin s-- we make it on the 662 00:25:55,730 --> 00:25:52,440 ligand on rhodium actually find we can 663 00:25:58,370 --> 00:25:55,740 make it on the metal center and serve 664 00:26:00,320 --> 00:25:58,380 rhodium is activated not by binding co2 665 00:26:02,420 --> 00:26:00,330 but rhodium is activated by binding a 666 00:26:05,570 --> 00:26:02,430 hydride and this hydride attacks than 667 00:26:10,300 --> 00:26:05,580 the co2 and that is the way in which you 668 00:26:12,890 --> 00:26:10,310 make formate so our idea of how how the 669 00:26:14,300 --> 00:26:12,900 selectivity of this reaction is is is 670 00:26:16,370 --> 00:26:14,310 determined is a little bit different 671 00:26:18,650 --> 00:26:16,380 from the some of the ideas that exist in 672 00:26:20,030 --> 00:26:18,660 the literature and we think it is it is 673 00:26:22,430 --> 00:26:20,040 really the nature of this nucleophilic 674 00:26:24,320 --> 00:26:22,440 attack that you have after you've 675 00:26:26,870 --> 00:26:24,330 reduced the catalyst that determines the 676 00:26:28,820 --> 00:26:26,880 product that you make if the if the 677 00:26:30,380 --> 00:26:28,830 electron density is located on the metal 678 00:26:32,540 --> 00:26:30,390 center you will bind through the carbon 679 00:26:35,090 --> 00:26:32,550 and you will make co if the electron 680 00:26:37,130 --> 00:26:35,100 density generates a hydride intermediate 681 00:26:41,870 --> 00:26:37,140 that hydride will attack the carbon and 682 00:26:43,670 --> 00:26:41,880 you will make you will make formate now 683 00:26:45,680 --> 00:26:43,680 we can reduce these products further and 684 00:26:47,900 --> 00:26:45,690 one metal that is very good in that is 685 00:26:50,150 --> 00:26:47,910 is copper and this was actually this was 686 00:26:52,640 --> 00:26:50,160 discovered in Japan or so far from here 687 00:26:53,850 --> 00:26:52,650 in the university of chiba by Yoshio 688 00:26:56,400 --> 00:26:53,860 hoary about 30 689 00:26:58,260 --> 00:26:56,410 years ago and he discovered that copper 690 00:27:03,120 --> 00:26:58,270 electrodes room-temperature aqueous 691 00:27:05,280 --> 00:27:03,130 media are able to reduce co2 and co2 now 692 00:27:07,080 --> 00:27:05,290 what I would call a non-trivial products 693 00:27:09,299 --> 00:27:07,090 like methane and especially ethylene 694 00:27:11,240 --> 00:27:09,309 here and also ethanol is interesting so 695 00:27:13,770 --> 00:27:11,250 we make a carbon-carbon bond 696 00:27:16,590 --> 00:27:13,780 electrochemically on copper electrodes 697 00:27:18,720 --> 00:27:16,600 and we studied this again with an online 698 00:27:20,549 --> 00:27:18,730 mass spectrometry system so here we can 699 00:27:22,919 --> 00:27:20,559 follow the formation of the gaseous 700 00:27:24,930 --> 00:27:22,929 product have we changed the potential so 701 00:27:27,750 --> 00:27:24,940 again here we start from zero volt we go 702 00:27:29,669 --> 00:27:27,760 more negative so we make the the 703 00:27:31,380 --> 00:27:29,679 environment more reductive and you see 704 00:27:33,900 --> 00:27:31,390 the current flowing year this is by the 705 00:27:36,030 --> 00:27:33,910 way mainly hydrogen formation as you can 706 00:27:38,460 --> 00:27:36,040 see here you see that as we go more 707 00:27:40,230 --> 00:27:38,470 negative from co2 we make some formic 708 00:27:42,780 --> 00:27:40,240 acid but formic acid is not reduced 709 00:27:46,260 --> 00:27:42,790 further on copper but what you can also 710 00:27:48,620 --> 00:27:46,270 see is that both from CO 2 and co we 711 00:27:50,880 --> 00:27:48,630 make methane and we make ethylene and 712 00:27:53,340 --> 00:27:50,890 you can see that these look very very 713 00:27:55,799 --> 00:27:53,350 similar these profiles that we measure 714 00:27:58,380 --> 00:27:55,809 in the mass spectrometer suggesting that 715 00:28:00,960 --> 00:27:58,390 CEO is an intermediate in the co2 716 00:28:03,570 --> 00:28:00,970 reduction so we go from co2 to CO and 717 00:28:06,780 --> 00:28:03,580 then we reduce a co further to methane 718 00:28:09,000 --> 00:28:06,790 and ethylene and especially the 719 00:28:10,980 --> 00:28:09,010 formation of ethylene is intriguing so 720 00:28:13,110 --> 00:28:10,990 how is this carbon-carbon bond made and 721 00:28:14,760 --> 00:28:13,120 we studied this on this the same 722 00:28:17,039 --> 00:28:14,770 reaction on single crystal so now we 723 00:28:19,560 --> 00:28:17,049 play with the structure of the copper 724 00:28:22,140 --> 00:28:19,570 catalyst here we start from Co because 725 00:28:24,060 --> 00:28:22,150 that allows us to to start playing with 726 00:28:26,700 --> 00:28:24,070 pH a little bit more than when we would 727 00:28:28,440 --> 00:28:26,710 we would use co2 because co2 itself is 728 00:28:31,919 --> 00:28:28,450 is involved in all kinds of pH dependent 729 00:28:34,110 --> 00:28:31,929 equilibria if we do this reaction of 730 00:28:36,090 --> 00:28:34,120 copper 1 1 1 so where the surface atoms 731 00:28:38,280 --> 00:28:36,100 are arranged in this exact '''l fashion 732 00:28:39,539 --> 00:28:38,290 you can see that we make methane and we 733 00:28:41,159 --> 00:28:39,549 make ethylene or you can see the 734 00:28:42,380 --> 00:28:41,169 profiles in the mass spectrum are very 735 00:28:44,669 --> 00:28:42,390 very similar 736 00:28:47,640 --> 00:28:44,679 suggesting that they they are made in 737 00:28:49,890 --> 00:28:47,650 the same pathway if we do the same 738 00:28:51,330 --> 00:28:49,900 reaction but now on copper 100 you know 739 00:28:52,530 --> 00:28:51,340 the atoms are arranged in a square 740 00:28:55,020 --> 00:28:52,540 fashion you see that you have a 741 00:28:58,010 --> 00:28:55,030 potential window where we only make 742 00:29:00,690 --> 00:28:58,020 ethylene but we make no methane 743 00:29:02,299 --> 00:29:00,700 apparently here the carbon-carbon bond 744 00:29:04,950 --> 00:29:02,309 formation happens first 745 00:29:08,399 --> 00:29:04,960 even though thermodynamically speaking 746 00:29:10,419 --> 00:29:08,409 the most favorable product is methane 747 00:29:12,820 --> 00:29:10,429 apparently this carbon-carbon bond 748 00:29:14,739 --> 00:29:12,830 formation is extremely sensitive to the 749 00:29:17,139 --> 00:29:14,749 structure of the surface it is also 750 00:29:21,009 --> 00:29:17,149 extremely sensitive to pH note that here 751 00:29:22,899 --> 00:29:21,019 I compare pH 7 and pH 13 if I go from pH 752 00:29:24,460 --> 00:29:22,909 7 to 13 note that the formation of 753 00:29:27,009 --> 00:29:24,470 ethylene shifts to less negative 754 00:29:28,629 --> 00:29:27,019 potential so it happens earlier whereas 755 00:29:30,789 --> 00:29:28,639 the formation of hydrogen still happens 756 00:29:32,979 --> 00:29:30,799 at the same potential so parently by 757 00:29:35,430 --> 00:29:32,989 playing with pH again I can play with 758 00:29:37,749 --> 00:29:35,440 the selectivity of the reaction and 759 00:29:39,789 --> 00:29:37,759 again I think this is because the 760 00:29:42,310 --> 00:29:39,799 formation of ethylene happens through a 761 00:29:44,409 --> 00:29:42,320 decoupled proton electron transfer that 762 00:29:46,869 --> 00:29:44,419 favors this reaction in very alkaline 763 00:29:48,789 --> 00:29:46,879 media the more alkaline the better and 764 00:29:52,389 --> 00:29:48,799 the higher the selectivity towards 765 00:29:53,979 --> 00:29:52,399 towards ethylene but to quickly take you 766 00:29:56,379 --> 00:29:53,989 through the mechanism that we think is 767 00:29:59,229 --> 00:29:56,389 happening so we start from co2 we make 768 00:30:02,139 --> 00:29:59,239 formic acid but that is not reduced any 769 00:30:03,849 --> 00:30:02,149 further we make co that binds to the 770 00:30:05,200 --> 00:30:03,859 catalyst and the reason why copper is 771 00:30:08,139 --> 00:30:05,210 such a good catalyst under these 772 00:30:11,229 --> 00:30:08,149 conditions for co2 reduction is that it 773 00:30:13,690 --> 00:30:11,239 is the only metal that binds co with an 774 00:30:15,820 --> 00:30:13,700 intermediate binding strength all other 775 00:30:17,859 --> 00:30:15,830 matters metals either bind it to weakly 776 00:30:20,440 --> 00:30:17,869 or bind it so strongly that they become 777 00:30:23,560 --> 00:30:20,450 poisoned for instance platinum can 778 00:30:25,029 --> 00:30:23,570 reduce co2 to co but co binds so 779 00:30:28,119 --> 00:30:25,039 strongly to platinum that it cannot 780 00:30:29,830 --> 00:30:28,129 reduce it any further this co can be 781 00:30:31,869 --> 00:30:29,840 further hydrogenated you make these type 782 00:30:33,339 --> 00:30:31,879 of intermediates the co bond will break 783 00:30:35,440 --> 00:30:33,349 at some point you will end up with 784 00:30:38,469 --> 00:30:35,450 methane some of these intermediates may 785 00:30:40,659 --> 00:30:38,479 dimerize and form ethylene and this is 786 00:30:42,580 --> 00:30:40,669 the pathway that happens on on copper 787 00:30:44,019 --> 00:30:42,590 one one one and and the rate determining 788 00:30:46,029 --> 00:30:44,029 step here is a conservative proton 789 00:30:49,269 --> 00:30:46,039 electron transfer but a couple 100 790 00:30:51,519 --> 00:30:49,279 something else happens remember that 791 00:30:54,249 --> 00:30:51,529 there we make only c2 and we don't make 792 00:30:56,769 --> 00:30:54,259 any c1 products at least in a certain 793 00:30:57,879 --> 00:30:56,779 potential window and the way we explain 794 00:31:00,129 --> 00:30:57,889 this is through this dimerization 795 00:31:02,229 --> 00:31:00,139 mechanism so we make a negatively 796 00:31:05,440 --> 00:31:02,239 charged dimer that binds to the surface 797 00:31:07,269 --> 00:31:05,450 and this negatively charged dimer is the 798 00:31:10,769 --> 00:31:07,279 key intermediate and that isn't further 799 00:31:13,570 --> 00:31:10,779 hydrogenated and this is made through a 800 00:31:16,509 --> 00:31:13,580 electron transfer step that is decoupled 801 00:31:19,570 --> 00:31:16,519 from proton transfer and this eventually 802 00:31:20,820 --> 00:31:19,580 ends up in ethylene but it can also 803 00:31:23,159 --> 00:31:20,830 generate as 804 00:31:25,769 --> 00:31:23,169 in a bifurcation that happened somewhere 805 00:31:27,860 --> 00:31:25,779 here later on in the pathway so what we 806 00:31:30,720 --> 00:31:27,870 happened what happens here is a kind of 807 00:31:33,269 --> 00:31:30,730 reductive dimerization or reductive Co 808 00:31:35,130 --> 00:31:33,279 coupling my organic chemistry colleagues 809 00:31:38,820 --> 00:31:35,140 tell me this is very similar to McMurray 810 00:31:40,440 --> 00:31:38,830 coupling there's various arguments that 811 00:31:42,360 --> 00:31:40,450 I can give why I think this is a 812 00:31:44,639 --> 00:31:42,370 reasonable pathway one of them is that 813 00:31:46,380 --> 00:31:44,649 we've calculated this by dou Y of T 814 00:31:49,440 --> 00:31:46,390 calculations and we find that actually 815 00:31:51,419 --> 00:31:49,450 the in the absence of solvent I should 816 00:31:53,940 --> 00:31:51,429 say the most stable configuration of the 817 00:31:55,379 --> 00:31:53,950 dimer is like this and we indeed find 818 00:31:57,659 --> 00:31:55,389 that it's negatively charged so if you 819 00:31:58,980 --> 00:31:57,669 put this kind of dimer on a couple 100 820 00:32:00,360 --> 00:31:58,990 surface in a quantum chemical 821 00:32:02,430 --> 00:32:00,370 calculation you will find that there's 822 00:32:04,980 --> 00:32:02,440 an electron transfer flowing from the 823 00:32:07,379 --> 00:32:04,990 copper into the dimer and if you 824 00:32:08,700 --> 00:32:07,389 actually view ad solvent the structure 825 00:32:10,409 --> 00:32:08,710 looks a little bit different but it's 826 00:32:12,299 --> 00:32:10,419 still negatively charged and it actually 827 00:32:13,950 --> 00:32:12,309 stabilizes because it is negatively 828 00:32:17,310 --> 00:32:13,960 charged the solvent actually helps 829 00:32:18,870 --> 00:32:17,320 stabilizing discharged intermediate and 830 00:32:20,129 --> 00:32:18,880 and through that we come to the 831 00:32:22,409 --> 00:32:20,139 conclusion that this is a very 832 00:32:24,240 --> 00:32:22,419 reasonable pathway interesting leaders 833 00:32:26,490 --> 00:32:24,250 can also explain why it is so sensitive 834 00:32:28,259 --> 00:32:26,500 to the structure because to bind this 835 00:32:31,139 --> 00:32:28,269 intermediate to the structure we find 836 00:32:33,480 --> 00:32:31,149 that we need these kind of sites on the 837 00:32:35,700 --> 00:32:33,490 surface this dimer really likes to sit 838 00:32:37,680 --> 00:32:35,710 on these kinds of square sites it 839 00:32:39,210 --> 00:32:37,690 doesn't like it doesn't like to sit on 840 00:32:41,519 --> 00:32:39,220 the surface where we do not have these 841 00:32:43,470 --> 00:32:41,529 square sites and that explains why it is 842 00:32:48,799 --> 00:32:43,480 so sensitive to the structure of the 843 00:32:53,070 --> 00:32:51,450 many people when I show there's always 844 00:32:55,019 --> 00:32:53,080 ask me do you have any evidence for this 845 00:32:56,909 --> 00:32:55,029 intermediate because this is just in DFT 846 00:32:59,759 --> 00:32:56,919 calculations can you see it using 847 00:33:01,529 --> 00:32:59,769 spectroscopy maybe well maybe we do and 848 00:33:04,669 --> 00:33:01,539 these are some data that we generated 849 00:33:07,799 --> 00:33:04,679 using in situ infrared spectroscopy 850 00:33:10,649 --> 00:33:07,809 where we find that very close to the 851 00:33:13,919 --> 00:33:10,659 onset of ethylene formation on copper 852 00:33:15,960 --> 00:33:13,929 100 we we measured these infrared 853 00:33:18,180 --> 00:33:15,970 spectra and we see two Co bands one 854 00:33:20,580 --> 00:33:18,190 seems to be a single Co bond the other 855 00:33:22,350 --> 00:33:20,590 seems to be a double Co bond we only see 856 00:33:24,509 --> 00:33:22,360 this on couple 100 we never see this on 857 00:33:26,940 --> 00:33:24,519 couple one on one and when we try to 858 00:33:28,710 --> 00:33:26,950 assign these bands we find that it 859 00:33:31,320 --> 00:33:28,720 doesn't correspond to anything that we 860 00:33:34,350 --> 00:33:31,330 can measure and the only thing it seems 861 00:33:36,810 --> 00:33:34,360 to correspond to when we do DFT 862 00:33:39,480 --> 00:33:36,820 patience is this type of hydrogenated 863 00:33:41,850 --> 00:33:39,490 dimer here that has Co frequencies that 864 00:33:43,710 --> 00:33:41,860 are relatively close to what we measure 865 00:33:45,660 --> 00:33:43,720 experimentally so this may be considered 866 00:33:48,360 --> 00:33:45,670 as at least some kind of evidence for 867 00:33:52,100 --> 00:33:48,370 the formation of a key intermediate in 868 00:33:56,220 --> 00:33:52,110 the in the CC coupling on copper 100 869 00:33:58,350 --> 00:33:56,230 that this this seems a bit of like an 870 00:34:02,280 --> 00:33:58,360 odd mechanism is this this seal 871 00:34:03,930 --> 00:34:02,290 dimerization but interestingly nature 872 00:34:08,250 --> 00:34:03,940 there's something very very similar not 873 00:34:10,860 --> 00:34:08,260 with Co but with n o nitric oxide 874 00:34:15,900 --> 00:34:10,870 reductase is an enzyme that catalyzes 875 00:34:18,120 --> 00:34:15,910 the reduction of no.2 nitrous oxide and 876 00:34:20,280 --> 00:34:18,130 there are various mechanisms for this I 877 00:34:22,380 --> 00:34:20,290 am NOT up to date about the mechanism as 878 00:34:24,620 --> 00:34:22,390 you can see this is a very old paper but 879 00:34:27,930 --> 00:34:24,630 one of the suggestions in this paper is 880 00:34:30,240 --> 00:34:27,940 that this enzyme catalyzes the reduction 881 00:34:33,930 --> 00:34:30,250 of NL by the formation of this NL dimer 882 00:34:36,090 --> 00:34:33,940 and only after the formation of the a no 883 00:34:40,350 --> 00:34:36,100 dimer you break the NL bond and you end 884 00:34:42,060 --> 00:34:40,360 up with n 2o so again here Ana Rita 885 00:34:44,310 --> 00:34:42,070 taste seems to have developed a 886 00:34:46,410 --> 00:34:44,320 reductive dimerization pathway at these 887 00:34:48,030 --> 00:34:46,420 low temperatures to make NN bombs and 888 00:34:50,220 --> 00:34:48,040 what I'm suggesting is that for Co you 889 00:34:51,570 --> 00:34:50,230 can have something similar and the 890 00:34:53,340 --> 00:34:51,580 interesting experiment that we're trying 891 00:34:55,950 --> 00:34:53,350 to do now in my lab is to see if we use 892 00:34:59,190 --> 00:34:55,960 mixtures of CO and I know if we can make 893 00:35:00,900 --> 00:34:59,200 C as C n bones in this way so far the 894 00:35:03,450 --> 00:35:00,910 results have not been positive but we 895 00:35:07,860 --> 00:35:03,460 may have to tweak we have to tweak the 896 00:35:09,740 --> 00:35:07,870 the conditions a little bit a final 897 00:35:13,110 --> 00:35:09,750 thing that I wanted to show is that 898 00:35:14,700 --> 00:35:13,120 actually because these intermediates in 899 00:35:16,800 --> 00:35:14,710 these catalytic pathways are in this 900 00:35:18,840 --> 00:35:16,810 case negatively charged they are 901 00:35:21,390 --> 00:35:18,850 extremely sensitive to the nature of the 902 00:35:24,150 --> 00:35:21,400 electrolyte not only to the pH but also 903 00:35:26,100 --> 00:35:24,160 to the the cations that exists in the 904 00:35:28,440 --> 00:35:26,110 electrolyte and this was actually 905 00:35:32,280 --> 00:35:28,450 already observed by by by jaurim 906 00:35:34,770 --> 00:35:32,290 many years ago that the the selectivity 907 00:35:36,870 --> 00:35:34,780 to ethylene is very very sensitive to 908 00:35:38,660 --> 00:35:36,880 the nature of the cation in the 909 00:35:41,130 --> 00:35:38,670 electrolyte and we find that we see in 910 00:35:43,230 --> 00:35:41,140 an enhancement in the formation of 911 00:35:45,090 --> 00:35:43,240 ethylene when we do this in cesium 912 00:35:47,370 --> 00:35:45,100 hydroxide whereas in lithium hydroxide 913 00:35:50,190 --> 00:35:47,380 we see much less ethylene form 914 00:35:53,760 --> 00:35:50,200 and interestingly in cesium hydroxide we 915 00:35:55,800 --> 00:35:53,770 also start seeing c3 products again 916 00:35:58,560 --> 00:35:55,810 they're actually there's a bit of a 917 00:36:00,990 --> 00:35:58,570 debate in in the community right now how 918 00:36:02,790 --> 00:36:01,000 to explain this we have done some DFT 919 00:36:05,250 --> 00:36:02,800 calculations that suggest that the 920 00:36:07,470 --> 00:36:05,260 presence of cesium seems to have a 921 00:36:08,910 --> 00:36:07,480 positive effect on the stability of some 922 00:36:10,890 --> 00:36:08,920 of the intermediate so it acts like a 923 00:36:13,560 --> 00:36:10,900 kind of promoter it put a sort of 924 00:36:14,760 --> 00:36:13,570 flattens out the catalytic landscape but 925 00:36:17,910 --> 00:36:14,770 there are other other theories that 926 00:36:21,090 --> 00:36:17,920 suggest that that this has an effect on 927 00:36:25,110 --> 00:36:21,100 the local pH and that may have been an 928 00:36:27,270 --> 00:36:25,120 effect only on the final selectivity the 929 00:36:29,460 --> 00:36:27,280 formation of c3 is something that that 930 00:36:31,920 --> 00:36:29,470 is also interesting I think this happens 931 00:36:34,170 --> 00:36:31,930 through a kind of Co insertion mechanism 932 00:36:37,290 --> 00:36:34,180 it has been found that if you mix 933 00:36:38,820 --> 00:36:37,300 ethylene and co electrochemically and 934 00:36:41,160 --> 00:36:38,830 you reduce that electro chemically you 935 00:36:45,990 --> 00:36:41,170 you can make propionaldehyde and that 936 00:36:47,880 --> 00:36:46,000 can be reduced further to 2-propanol it 937 00:36:49,920 --> 00:36:47,890 looks like under these conditions again 938 00:36:52,590 --> 00:36:49,930 electrochemical conditions aqueous 939 00:36:54,480 --> 00:36:52,600 solutions we have some kind of electro 940 00:36:56,970 --> 00:36:54,490 hydroformylation reactions that can take 941 00:37:00,240 --> 00:36:56,980 place that allow us to grow these carbon 942 00:37:02,460 --> 00:37:00,250 chains the final thing is that when this 943 00:37:03,990 --> 00:37:02,470 takes place this always happens 944 00:37:06,360 --> 00:37:04,000 simultaneously with hydrogen evolution 945 00:37:08,640 --> 00:37:06,370 that means that locally the pH is 946 00:37:12,020 --> 00:37:08,650 increasing so any formaldehyde or 947 00:37:14,340 --> 00:37:12,030 aldehydes that we make will take part in 948 00:37:17,280 --> 00:37:14,350 disproportion asian reactions and we 949 00:37:20,130 --> 00:37:17,290 typically see that when we see alcohols 950 00:37:22,290 --> 00:37:20,140 we also see carboxylic acids so when we 951 00:37:24,240 --> 00:37:22,300 see ethanol we almost always also see 952 00:37:26,340 --> 00:37:24,250 acetate which suggests that actually 953 00:37:28,680 --> 00:37:26,350 what we make is a seed aldehyde that is 954 00:37:31,800 --> 00:37:28,690 disproportionate that disproportionate 955 00:37:35,430 --> 00:37:31,810 due to the low Heikal to do the high a 956 00:37:36,890 --> 00:37:35,440 local pH into the into the alcohol and 957 00:37:38,090 --> 00:37:36,900 the carboxylic acid or at or 958 00:37:40,470 --> 00:37:38,100 carboxylated 959 00:37:42,180 --> 00:37:40,480 okay that brings me to the final slide I 960 00:37:43,830 --> 00:37:42,190 showed you that it's possible to reduce 961 00:37:45,810 --> 00:37:43,840 you to close to the somewhat and I'm a 962 00:37:47,400 --> 00:37:45,820 potential but you should restrict 963 00:37:48,480 --> 00:37:47,410 yourself to two electron transfer and 964 00:37:50,250 --> 00:37:48,490 then you can find the optimal 965 00:37:52,550 --> 00:37:50,260 intermediate if you have the right 966 00:37:55,560 --> 00:37:52,560 catalyst we try to argue that the 967 00:37:57,150 --> 00:37:55,570 activation 2co of formic acid follows 968 00:38:00,120 --> 00:37:57,160 different pathways depending on the 969 00:38:01,230 --> 00:38:00,130 nature of the nucleophilic attack that 970 00:38:03,740 --> 00:38:01,240 under electrochemical 971 00:38:06,000 --> 00:38:03,750 we make these charged intermediates and 972 00:38:07,770 --> 00:38:06,010 that means that these reactions are very 973 00:38:09,000 --> 00:38:07,780 very sensitive to pH and they're 974 00:38:11,820 --> 00:38:09,010 sensitive to the nature of the 975 00:38:13,500 --> 00:38:11,830 electrolyte and specifically the kind of 976 00:38:15,390 --> 00:38:13,510 cations that you have in solution and 977 00:38:17,280 --> 00:38:15,400 that you have somewhat unusual 978 00:38:19,800 --> 00:38:17,290 carbon-carbon bond formation pathways 979 00:38:21,270 --> 00:38:19,810 like reductive dimerization and maybe 980 00:38:23,100 --> 00:38:21,280 electrolyte a formulation is not so 981 00:38:25,620 --> 00:38:23,110 unusual but it's not always considered 982 00:38:28,380 --> 00:38:25,630 in the mechanisms that people have 983 00:38:30,060 --> 00:38:28,390 suggested final slide these are the PhD 984 00:38:32,700 --> 00:38:30,070 students postdocs that were involved in 985 00:38:33,690 --> 00:38:32,710 this work and the funding agencies and I 986 00:38:45,660 --> 00:38:33,700 would like to thank you for your 987 00:38:48,480 --> 00:38:45,670 attention okay questions I don't know if 988 00:38:54,600 --> 00:38:48,490 I should throw it that far might bonk 989 00:38:59,760 --> 00:38:54,610 somebody in the head sorry just to ask 990 00:39:01,410 --> 00:38:59,770 the obvious question you made us aware 991 00:39:03,510 --> 00:39:01,420 that this is not your field but I would 992 00:39:06,300 --> 00:39:03,520 like to know what you think about the 993 00:39:07,830 --> 00:39:06,310 situation four billion years ago 4.2 994 00:39:09,990 --> 00:39:07,840 billion years ago when life was starting 995 00:39:12,270 --> 00:39:10,000 how do you see this happening so many of 996 00:39:14,310 --> 00:39:12,280 us would like to see co2 being fixed 997 00:39:16,860 --> 00:39:14,320 some people don't like it some people 998 00:39:18,420 --> 00:39:16,870 say molecules came from space and people 999 00:39:21,780 --> 00:39:18,430 say they did come from here but not from 1000 00:39:24,570 --> 00:39:21,790 co2 how do you see it so what would be 1001 00:39:26,400 --> 00:39:24,580 your point is for us in the those of us 1002 00:39:29,690 --> 00:39:26,410 trying to make molecules from zero from 1003 00:39:35,760 --> 00:39:34,050 Wow that's it I think this should be 1004 00:39:38,040 --> 00:39:35,770 considered that that's all I can say I 1005 00:39:42,350 --> 00:39:38,050 mean it's very difficult to to answer 1006 00:39:44,220 --> 00:39:42,360 that question I'm just pointing out that 1007 00:39:45,390 --> 00:39:44,230 there are many different types of 1008 00:39:47,130 --> 00:39:45,400 catalysts one of the things I was 1009 00:39:49,740 --> 00:39:47,140 thinking about this morning what if you 1010 00:39:51,330 --> 00:39:49,750 have small metal nanoparticles I mean 1011 00:39:54,570 --> 00:39:51,340 that could act as catalysts as wellness 1012 00:39:56,310 --> 00:39:54,580 is not just ions there are many 1013 00:39:58,830 --> 00:39:56,320 different pathways out there that that's 1014 00:40:00,480 --> 00:39:58,840 it I think my main idea and it's very 1015 00:40:01,980 --> 00:40:00,490 difficult to choose which ones would 1016 00:40:04,740 --> 00:40:01,990 have played a role maybe they've all 1017 00:40:06,360 --> 00:40:04,750 played a role somehow I think the key 1018 00:40:10,470 --> 00:40:06,370 really is how or how did all this 1019 00:40:16,599 --> 00:40:10,480 organize into something like a cell that 1020 00:40:22,220 --> 00:40:19,220 thank you very much great talk so I 1021 00:40:24,740 --> 00:40:22,230 think emergence of selectivity of 1022 00:40:26,750 --> 00:40:24,750 catalyst is a one of the key topics of 1023 00:40:29,620 --> 00:40:26,760 play by the chemistry and you clearly 1024 00:40:31,520 --> 00:40:29,630 demonstrated if we can control 1025 00:40:34,130 --> 00:40:31,530 decoupling and a coupling rhythm 1026 00:40:36,770 --> 00:40:34,140 transfer just change the pH we can 1027 00:40:39,320 --> 00:40:36,780 control selectivity at the point you 1028 00:40:41,450 --> 00:40:39,330 talk right in the first topics and my 1029 00:40:43,010 --> 00:40:41,460 question is I think selectivity depends 1030 00:40:44,570 --> 00:40:43,020 on many things it depends on having the 1031 00:40:46,970 --> 00:40:44,580 right catalyst but also having the right 1032 00:40:49,070 --> 00:40:46,980 catalytic conditions like pH but also 1033 00:40:50,570 --> 00:40:49,080 electrolyte what I'm trying to say I 1034 00:40:52,520 --> 00:40:50,580 guess is that the the issue of 1035 00:40:54,380 --> 00:40:52,530 selectivity is a very complex one and is 1036 00:40:56,420 --> 00:40:54,390 one that you can tune in many different 1037 00:40:58,400 --> 00:40:56,430 ways and we're not always considering 1038 00:41:01,430 --> 00:40:58,410 all these different ways okay so 1039 00:41:02,870 --> 00:41:01,440 question can you rationally predict so 1040 00:41:05,630 --> 00:41:02,880 it's about you have this kind of 1041 00:41:07,310 --> 00:41:05,640 material with that experiment can you 1042 00:41:11,210 --> 00:41:07,320 predict all this material have a 1043 00:41:13,280 --> 00:41:11,220 function to D capo or capo yes you can 1044 00:41:15,020 --> 00:41:13,290 predict if you if you know the pka's of 1045 00:41:16,670 --> 00:41:15,030 of the different intermediates involved 1046 00:41:19,310 --> 00:41:16,680 and then you can say which which one 1047 00:41:21,650 --> 00:41:19,320 should you should take place it's a 1048 00:41:26,900 --> 00:41:21,660 neutral pH conditions and which ones are 1049 00:41:29,480 --> 00:41:26,910 less likely as pathway hey thanks for 1050 00:41:31,460 --> 00:41:29,490 that some point you mentioned the 1051 00:41:33,140 --> 00:41:31,470 hydrogen evolution reaction and how it 1052 00:41:35,660 --> 00:41:33,150 generates pH gradients that create 1053 00:41:37,970 --> 00:41:35,670 localized alkaline environments one of 1054 00:41:39,620 --> 00:41:37,980 the key types of mechanisms in 1055 00:41:41,090 --> 00:41:39,630 biochemistry is the formation of an 1056 00:41:42,620 --> 00:41:41,100 enolate which then goes on to 1057 00:41:47,030 --> 00:41:42,630 carboxylate something which can form a 1058 00:41:48,770 --> 00:41:47,040 CC bond that way I'm wondering is it how 1059 00:41:50,960 --> 00:41:48,780 powerful is that or how fast is that 1060 00:41:52,940 --> 00:41:50,970 hydrogen release reaction have to be so 1061 00:41:55,599 --> 00:41:52,950 that you could build up a localized 1062 00:41:57,890 --> 00:41:55,609 alkaline environment strong enough to 1063 00:41:59,720 --> 00:41:57,900 form an enolate from a ketone for 1064 00:42:01,550 --> 00:41:59,730 instance is that feasible or is 1065 00:42:02,950 --> 00:42:01,560 diffusion so fast that you can never 1066 00:42:07,099 --> 00:42:02,960 form such a strongly alkaline 1067 00:42:08,300 --> 00:42:07,109 environment how can I answer that if I 1068 00:42:12,140 --> 00:42:08,310 don't know if you don't have a question 1069 00:42:13,880 --> 00:42:12,150 I would need to know the local current 1070 00:42:16,790 --> 00:42:13,890 density which is something that's not so 1071 00:42:18,500 --> 00:42:16,800 yeah but it really depends on the rate 1072 00:42:21,190 --> 00:42:18,510 with which we generate hydrogen and the 1073 00:42:23,930 --> 00:42:21,200 rate with which you can replenish the 1074 00:42:26,300 --> 00:42:23,940 proton donor and if those are 1075 00:42:27,410 --> 00:42:26,310 sufficiently different you will have pH 1076 00:42:32,509 --> 00:42:27,420 gradients 1077 00:42:34,430 --> 00:42:32,519 buffer capacity if the local buffer 1078 00:42:37,759 --> 00:42:34,440 capacity is poor then the pH gradient 1079 00:42:39,140 --> 00:42:37,769 will be will be bigger as well that's 1080 00:42:41,180 --> 00:42:39,150 another parameter actually buffer 1081 00:42:43,069 --> 00:42:41,190 capacity can have a huge influence here 1082 00:42:44,809 --> 00:42:43,079 on the selectivity of the reaction 1083 00:42:48,140 --> 00:42:44,819 simply by it by the fact that it 1084 00:42:50,509 --> 00:42:48,150 generates different pH gradients okay 1085 00:42:55,759 --> 00:42:50,519 one last question while relay get set up 1086 00:42:57,349 --> 00:42:55,769 for the next time mark let me say I 1087 00:42:59,180 --> 00:42:57,359 think there was the most rational talk 1088 00:43:00,920 --> 00:42:59,190 I've ever heard on this subject and it 1089 00:43:03,259 --> 00:43:00,930 is fantastic 1090 00:43:05,359 --> 00:43:03,269 what happens if you use let's say liquid 1091 00:43:07,700 --> 00:43:05,369 ammonia where you can actually inject an 1092 00:43:11,839 --> 00:43:07,710 electron and have it sit in the solution 1093 00:43:13,549 --> 00:43:11,849 or HM PA what do you see then actually 1094 00:43:16,370 --> 00:43:13,559 if you reduce the oh and liquid ammonia 1095 00:43:18,049 --> 00:43:16,380 you make a seal dimer that that is that 1096 00:43:20,390 --> 00:43:18,059 is one of the reasons why why I think 1097 00:43:23,059 --> 00:43:20,400 the seal dimer is or is a reasonable 1098 00:43:25,309 --> 00:43:23,069 intermediate what about you you avoid 1099 00:43:27,200 --> 00:43:25,319 you avoid a protonation reaction because 1100 00:43:30,309 --> 00:43:27,210 what about co2 can you make oxalate 1101 00:43:32,210 --> 00:43:30,319 dianna oxalate will be the product I 1102 00:43:34,309 --> 00:43:32,220 should have had your chat with a 1103 00:43:36,410 --> 00:43:34,319 graduate student who spent six months 1104 00:43:42,049 --> 00:43:36,420 spraying ammonia all over everything 1105 00:43:45,009 --> 00:43:42,059 trying that would solve the ammonia 1106 00:43:47,539 --> 00:43:45,019 problem though wouldn't it very good 1107 00:43:50,420 --> 00:43:47,549 okay so let's move on to the next talk 1108 00:43:52,160 --> 00:43:50,430 which will be given by actually let's 1109 00:43:55,400 --> 00:43:52,170 take mark again 1110 00:44:46,710 --> 00:43:55,410 [Applause]