A Sophisticated Examination of the Electrochemical Reduction of Carbon Dioxide to Give C2 Compounds.

[NNadir]

The paper from the primary scientific literature that I'll discuss in this post was written by scientists in Singapore in colaboration with scientists at UC Berkeley and Yale University. It's this paper: Investigating the Role of Copper Oxide in Electrochemical CO2 Reduction in Real Time (Venkatasan, et al, ACS Appl. Mater. Interfaces, 2018, 10 (10), pp 8574–8584)

It's a very nice paper but before going into it let me say this:

The generation of electricity wastes primary energy and how much energy is wasted depends highly on how it is generated and how it used. The generation of electricity even using clean primary energy - and there is one and only one truly clean form of primary energy, nuclear energy - is a wasteful process. The thermodynamic efficiency of the most common types of nuclear reactors on the planet, light water thermal reactors, is typically on the order of 33% meaning that 67% of the energy is lost. One can certainly conceive of cases where this efficiency might be raised, but it is impossible by the laws of physics to make electricity without losing energy. Further, depending on how the electricity is used, the thermodynamic efficiency can be reduced even further; quite possibly the most wasteful way to use electricity is to charge a battery. Charging a battery with a grotesquely inefficient solar cells - all commercial solar cells have grotesquely low thermal efficiency, although by increasing their toxicity beyond the unacceptable toxicity they already exhibit, it seems to theoretically possible to improve their efficiency to a larger fraction of Carnot (nuclear, coal, petroleum, and non-combined cycle gas plants) efficiency, to as much as roughly 25%.

This said, there are a number of extremely important commodities which are produced using electricity. The most familiar of these commodities is aluminum, which consumes about 3% of the world's electricity in the Hall process. The production of steel requires reduction by coal, and if we were actually serious about phasing out coal - something we're not even remotely serious about doing - to the extent that nuclear electricity was available could reduce the carbon impact of metals by substituting (where possible) aluminum for steel applications, something which has been widely practiced increasingly since the discovery of the Hall process. Another commodity that might replace steel is titanium, which is actually stronger, lighter and has a higher melting point than steel. I used to remark that if the World Trade Center had a titanium frame rather than a steel frame, it might have well survived the September 11, 2001 attacks, attacks which ultimately led, via misplace priorities, to the death of hundreds of thousands Iraqis.

An electrochemical process for the reduction of titanium ore - TiO2, either rutile or anatase - has been developed, and it is known at the FFC_Cambridge_process, which is now undergoing commercialization. One can hope that it will prove as successful as the Hall process proved for aluminum, the metallic form of which was extremely expensive before that process was discovered. (The FFC Cambridge process is not limited to titanium reduction by the way; it is suitable for other metals as well.)

The thermodynamic inefficiency of electricity generation aside, one can make commodities on a large scale.

One commodity which shows up a lot in the literature as potentially sourced by electricity is liquid carbon based fuels and carbon based synthetic precursors, via the electrochemical reduction of carbon dioxide, carbon dioxide being the dangerous fossil fuel waste that is destroying the planet at an ever increasing rate while we all wait, lemming like, for the Godotian grand renewable energy nirvana that never comes.

The synthesis of carbon based fuels from electricity is the topic of the fine paper cited at the outset.

Of course, if the electricity for doing this comes from the combustion of dangerous fossil fuels, which it increasingly does, the attempt to make liquid carbon based fuels from carbon dioxide is nothing more than a Rube Goldbergian perpetual motion machine.

Perpetual motion machines, um, don't work.

However, it has become clear to me in recent years that it is possible to improve the efficiency of nuclear powered devices greatly, one avenue being raising the temperature to a higher level than is found in the currently available light (and for that matter heavy) water reactors. It even seems possible - although more remotely so - to eliminate mechanical intermediates (which waste primary energy) specifically turbines and generators to make solid state and still efficient thermal generation devices. I may discuss in this space in the future recent advances in thermoelectric materials, many of which involve nanostructured materials that are still not commercially available but may be so at some future date. (My son's undergraduate research in Europe this summer suggests several possibilities along these lines that I hope to discuss with him when he comes home in two weeks.)

Thus it is not useless to discuss the electrochemical reduction of carbon dioxide, particularly in situations where continuously generated electricity is not in immediate demand.

Now from the paper's introduction:

Conversion of carbon dioxide (CO2), an important greenhouse gas, into energy-rich chemicals is a viable approach to reducing the global carbon footprint.1 Electrochemical CO2 conversion (CO2R) using renewable electricity is envisaged as a promising technology to achieve this end.2?7 Among the many catalysts studied for CO2R, copper is unique because it is the only metal that reduces CO2 to significant amounts of C2 and higher-order hydrocarbons and alcohols.8,9 Nanostructuring copper into cubes and needles can enhance the selectivity toward C?C coupled products.10?13 Alternatively, copper oxides can be employed as precursors for making high-surface-area structures. 14?22 When operated under CO2R conditions (typically ?0.8 to ?1.1 V vs RHE), the oxides would be reduced to metallic copper (Cu0) in accordance with the Pourbaix diagram, producing nanostructured Cu.23 In the literature, the improved performance of such oxide-derived copper nanostructures toward C2 products has been attributed to a number of factors: (1) a higher local pH at the catalyst surface, favoring the pH independent C?C coupling pathway over the formation of methane,13 (2) a higher density of grain boundaries and defect sites, optimizing the binding energy of reaction intermediates such as CO,14,20 and (3) the presence of oxides and subsurface oxygen alongside the metal, which provides Cu sites with multiple valences to increase catalytic activity.18,19,24

With due respect to the authors, and they certainly deserve respect as they are very fine scientists, their de rigueur remark about so called "renewable energy" - undoubtedly it's grant bait - is meaningless. So called "renewable energy" has not worked; it is not working and it will not work, but it is possible if not widely practiced (enough) to make clean electricity without appeal to wasteful systems with low energy/mass ratios.

The paper is about the known electrochemical catalyst for this reaction, primarily the reduction of carbon dioxide to give the versatile compound ethylene, is nothing more than the common metal copper. (Silver and gold - nanogold - can also catalyze similar reactions, as can several other metals, primarily nickel the platinum group metals (rhodium, ruthenium, palladium, platinum, iridium and osmium). The authors are examining the mechanism of the reaction, i.e. what changes copper goes through before returning to its initial state.

The authors briefly review some scientific history of the investigation of this system:

Studies on copper oxide as a CO2R electrocatalyst showed transient changes in the product distribution attributed to the temporary presence of surface oxide species.21,22 Recently, Li et al. found that thermally oxidized copper showed stable and improved product generation to CO and HCOOH at a lower overpotential compared to that for polycrystalline copper; however, this performance was not attributed to the oxide itself.15 This is reasonable given the Pourbaix diagram for Cu23 and was confirmed in their ex situ X-ray diffraction (XRD) study. Kas et al.17 investigated electrodeposited Cu2O of different orientation and thickness and found that the selectivity depended on the initial oxide thickness and not on the orientation of the starting copper oxide. By performing cyclic voltammetry and employing online electrochemical mass spectrometry, they concluded that CO2R starts only after Cu2O is reduced into Cu. However, this study did not employ an in situ characterization of the catalyst surface. Using in situ Raman spectroscopy, Ren et al. found that in aqueous, CO2- saturated 0.1 M KHCO3 the surface of a Cu2O film reduces within a few minutes to Cu0 at negative potentials.14 Interestingly, in this same study, it was found that when all signals belonging to copper oxide had disappeared, adsorbed CO, the pertinent reaction intermediate in CO2R, is detected. All of these studies suggest that surface Cu0 and not copper oxide is the active catalyst species.

They then discuss the analytical tools available to investigate further:

Herein, we combine Raman spectroscopy with selected-ion flow tube mass spectrometry (SIFT-MS)27?29 to study in real time both the surface and the products generated during electrochemical CO2R. Density functional theory (DFT) calculations were employed to model the system and could rationalize the results very successfully.

SIFT-MS can detect and quantify gaseous products such as methane, ethane, and ethylene as well as higher-order hydrocarbons, like propene, in a time scale of 0.1?10 s (depending on the number of masses scanned). This enables the capture of reaction dynamics. In this way, it overcomes the classic problem faced in much of the literature where the gaseous products of CO2R are analyzed by gas chromatography (GC) with analysis times in the range of minutes. In addition, liquid products, typically detected by high-pressure liquid chromatography (HPLC) or nuclear magnetic resonance spectroscopy (NMR), are only measured once at the end of an experiment by sampling aliquots of the electrolyte.9,20,25,26,30 SIFT-MS allows the simultaneous detection of liquid products with finite vapor pressure (this aspect of the technique will be presented in another paper). SIFT-MS is able to provide this real-time analysis of complex multicomponent mixtures because of its use of gentle chemical ionization reactions. These reactions, such as proton addition, avoid the fragmentation of molecules typical of electron ionization mass spectrometry (MS), which results in an extremely low limit of detection of the parent ion.26 SIFT-MS has been well reviewed in the literature, and we point the reader to these works27?29 for a deeper understanding of the advantages of this technique...

I get marketing blurbs about SIFT-MS several times a week at my job. Some day I'll have to read one before deleting it.

Here, three different forms of Cu2O were synthesized by electrochemical and thermal methods,14,15,31 yielding oxidederived catalysts of different surface structures and different CO2R activities. These catalysts were subsequently evaluated in real time, using an electrochemical cell previously detailed,32 to determine the onset of CO2R after switching on a constant cathodic current. By combining DFT study and in situ Raman spectroscopy with real-time product detection, we show that Cu2O reduction (Cu2OR) typically occurs before CO2R begins because Cu2OR is energetically more favorable.

DFT is "Density Functional Theory" - a widely used computational technique based on the Nobel Prize generating Kohn Sham equations, Kohn being a grown up Jewish boy who narrowly escaped Nazi Germany on the famous Kinder Transport in the late 30's, one of many of the small group of such children who escaped and survived - albeit without their murdered families - and who grew up to display an enormous intellectual impact on humanity in the sciences and the arts.

Children matter.

Anyway...some cute pictures from the paper:



This is a picture of the three types of catalysts.

The caption describing of what the pictures are:

Figure 1. SEM images (scale 1 ?m) of as-prepared copper oxides before CO2R: (a) nanoneedles (NNs), (b) nanocrystals (NCs), and (c) nanoparticles (NPs) and after CO2R: (d) nanoneedles (NNs), (e) nanocrystals (NCs), and (f) nanoparticles (NPs)

.

By X-ray diffraction, one can learn something about the molecular structure of these catalysts:



The caption:

Figure 2. XRD patterns of copper oxide before (black) and after CO2R (red): (a) NNs, (c) NCs, and (e) NPs showing peaks corresponding to Cu2O (black) and underlying Cu substrate (red). Raman spectra of copper oxide before (black) and after CO2R (red): (b) NNs, (d) NCs, and (f) NPs showing peaks corresponding to Cu2O (109, 152, 415, 645), CuO (303, 634), and Cu(OH)2 (490).

Following the reaction products:



The caption:

Figure 3. (a) Comparison of GC (points) and SIFT-MS (lines) data from Cu NNs operated at ?10 mA/cm2 in 0.1 M KHCO3. (b) Semi-log plot of SIFT data for methane (C1), ethylene (C2), and propene (C3).

A comment: Polyethylene and polypropylene, for which ethylene and propene are precursors, are increasingly understood to be environmentally hazardous material, and pollution by them, notably in the oceans is a serious matter. This said, to the extent they might be made from carbon dioxide, they represent economically (if questionably environmental) viable means of carbon sequestration. This is a little different that the vast scale carbon dioxide dumps that people often evoke without any practical effect or realistic practice. Garbage in general is a huge problem and it does not actually seem thermodynamically viable to separate these materials into directly recyclable materials, although some success in this area has been realized, hardly at a sustainable level, but at some level.

An alternative to direct recycling is whole mass recycling under which garbage is reformed using steam at high temperatures. In this case almost all of the carbon in a garbage can, including plastic waste, can be converted into carbon dioxide and hydrogen, or carbon monoxide and hydrogen, said mixtures being known as syn gas, from which pretty much every commercially known carbon commodity can be made.

More pictures:



The caption:

Figure 4. CP (top) and SIFT-MS (bottom) data of Cu2O (a, d) NNs driven at ?10 mA/cm2, (b, e) NCs driven at ?17 mA/cm2, and (c, f) NPs driven at ?15 mA/cm2, all in 0.1 M KHCO3 electrolyte saturated with 1 atm CO2. The SIFT-MS data is corrected for its intrinsic response time (see SI-II, Figure S3).

At low current densities, the product is syn gas:



The caption:

Figure 5. Evolution of CO and H2 at low current density: (a) NC chronopotentiometry, (b) NN chronopotentiometry, (c) NC GC data, and (d) NN GC application of current; GC data show only negligible amount of data evolution of CO and H2 during the first 10?20 min when Cu2OR prevails in the 0.1 M KHCO3 electrolyte saturated with 1 atm CO2.

Some structural and energy level diagrams used in the DFT calculations:



The caption:

Figure 6. DFT-optimized geometries and relative free energies of intermediates of HER (red dash line), CO2R (black dash line), and Cu2OR (green dash line) on Cu (111), Cu2O (111), and Cu2O (200) relative to CO2, H2, and bare surfaces. (a) DFT-optimized surfaces of Cu(111), Cu2O(111), and Cu2O (200) and CO absorption geometries at the fcc site of Cu (111), Cu atop site of Cu2O (111), and bridge site of Cu2O (200). Calculated binding free energies of intermediates on (b) Cu(111), (c) Cu2O(111), and (d) Cu2O(200) surfaces [in eV].

Some concluding remarks from the paper:

In summary, by operando SIFT-MS, computational modeling, and Raman spectroscopy, we show that in three oxide-derived Cu electrocatalysts, with differing surface morphologies and crystal orientations, surface copper oxide reduces prior to CO2R into gaseous products. Even though Cu2O (200) seems to be a possible catalyst for CO2R based on our DFT modeling, CO2R products are not formed as long as Cu2O is present at the surface because Cu2OR is kinetically and energetically more favorable than CO2R. Although we cannot exclude a small percentage of residual oxygen (as has been claimed by Favaro et al.24), it is unlikely that it will be present in the form of Cu2O. Looking forward, the exceptional performance of SIFT-MS for real-time electrochemical CO2R can offer new applications in time-resolved monitoring of reaction intermediates.

A cool paper I think. This type of process I would imagine to be of limited utility, given that thermochemical production of syn gas is probably, even under ideal highly efficient conditions for electrical generation, thermodynamically (and thus environmentally) more favorable. But it's a nice thing to do with systems that continuously generate electricity even in the absence of demand. In particular, nuclear systems operate best when they are operated at high capacity utilization (which in modern times they almost always are).

I wish you a happy and productive Friday.

[Sophia4]

1. More human time and energy needs to be spent on making nuclear energy safe.

Safe from vandals, from the ignorant, from killers, from psychopaths, from terrorists, from time, from all sorts of dangers that are inherent in using nuclear energy.

Then there is the danger of nuclear waste. What do we do with that?

Nuclear energy is not an answer until we solve those very dangerous aspects of its use.

[Eko]

2. NNadir has me blocked.

Supposedly, so they wont see me post this. NNadir will soon accuse you of not giving a shit that 7 million people will die this year from air pollution, that you are anti nuclear and use a strawman fallacy on you. Just watch.

[NNadir]

3. Safer than what?

Right now 7 million people die every year from air pollution, according to the following comprehensive list of all causes of human mortality:

A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010 (Lancet 2012, 380, 2224–60: For air pollution mortality figures see Table 3, page 2238 and the text on page 2240.)

I invite anyone who wants to prattle on about how "dangerous" nuclear energy is to drag their butts to a scientific library, open the paper, and see if they can find the death toll of the allegedly "dangerous" nuclear energy industry.

Today 19,000 human beings died from air pollution. Tomorrow will be the same.

It is appalling, absolutely appalling that we live in a moral universe where 19,000 die every damned day because of the selective attention of a squad of people who insist that nuclear energy, and only nuclear energy needs to be perfect or other forms of energy will be allowed to kill vast numbers of people with no attention paid at all.

Nuclear energy need not be perfect, it need not be risk, to be vastly superior to everything else.

The rhetoric to the contrary is dangerous, immoral and it kills people, because even including the big boogeymen at Fukushima and Chernobyl, nuclear energy saves lives, according to the irrefutable information in one of the most widely read papers in a major scientific journal.

Prevented Mortality and Greenhouse Gas Emissions from Historical and Projected Nuclear Power (Pushker A. Kharecha* and James E. Hansen Environ. Sci. Technol., 2013, 47 (9), pp 4889–4895)

Again, the rote Pavlovian rhetoric about nuclear energy being "dangerous" is a Trumpian scale lie.

Things that routinely kill more people than nuclear energy will ever kill, besides air pollution, are fatty foods, automobile accidents, air craft accidents, railroad accidents, coal mining accidents, oh, and, um, mining cadmium for solar cells.

On moral grounds, I completely and wholly reject this nonsensical claim. I don't get my information from websites in the great circle jerk of anti-nuke ignoramuses quoting one another.

I get my information from the primary scientific literature.

I wish you a pleasant Friday.

[Sophia4]

4. More people than have been acknowledged have been afflicted by cancer from

radiation.

How many died at Chernobyl?

During the accident, steam-blast effects caused two deaths within the facility; one immediately after the explosion, and the other, compounded by a lethal dose of radiation. Over the coming days and weeks, 134 servicemen were hospitalized with acute radiation sickness(ARS), of which 28 firemen and employees died in the days-to-months afterward from the radiation effects.[4] In addition, approximately fourteen radiation induced cancer deaths among this group of 134 hospitalized survivors, were to follow within the next ten years (1996).[5] Among the wider population, an excess of 15 childhood thyroid cancer deaths were documented as of 2011.[1][6] It will take further time and investigation to definitively determine the elevated relative risk of cancer among the surviving employees, those that were initially hospitalized with ARS and the population at large.[7]

The Chernobyl accident is considered the most disastrous nuclear power plant accident in history, both in terms of cost and casualties. It is one of only two nuclear energy accidents classified as a level 7 event (the maximum classification) on the International Nuclear Event Scale, the other being the Fukushima Daiichi nuclear disaster in Japan in 2011.[8] The struggle to safeguard against scenarios which were perceived[3] as having the potential for greater catastrophe, together with later decontamination efforts of the surroundings, ultimately involved over 500,000 workers and cost an estimated 18 billion rubles.[9]

The remains of the No. 4 reactor building were enclosed in a large cover which was named the "Object Shelter", often known as the sarcophagus. The purpose of the structure was to reduce the spread of the remaining radioactive dust and debris from the wreckage and the protection of the wreckage from further weathering. The sarcophagus was finished in December 1986 at a time when what was left of the reactor was entering the cold shut-down phase. The enclosure was not intended as a radiation shield, but was built quickly as occupational safety for the crews of the other undamaged reactors at the power station, with No. 3 continuing to produce electricity up into 2000.

https://en.wikipedia.org/wiki/Chernobyl_disaster

No one has kept track of the cases of cancer that resulted from the atomic and nuclear tests that were performed above ground in the 1940s and 1950s.

Not much nuclear energy is used. That is why the death tolls from nuclear energy are as low as they appear to be.

Where do the statistics you cite on deaths from other forms of energy come from? If they were true, there would hardly be a one of us over the age of 65. They are absurd.

Tobacco and alcohol are greater problems than air pollution when it comes to deaths.

Even sugar is a bigger threat to human life.

And war -- a huge threat.

Where do your numbers on deaths from pollution come from?

[NNadir]

5. I supplied a scientist reference paper authored...

Last edited Fri Jul 20, 2018, 10:07 AM - Edit history (1)

....By an international consortium of academic physicians, epidemiologists and other scientists.

You obviously didn't read it. The source was right there, and you ask "what's the source?"

Your statement that "no one has kept track of cancer..." Is a Trumpian scale bit of misrepresentation. Cancer epidemiology has been a major undertaking of tens of thousands of highly trained PhD level scientists for more than a century. To claim otherwise is to simply display ignorance.

Look I'm a scientist who has literally spent 3 decades studying nuclear energy. I have hundreds of papers on Chernobyl in my files.

I am deeply offended and morally appalled at the Wikipedia based selective attention of poorly educated antinukes and their appeal to selective attention.

Thus kind of rhetoric kills people, including the 19000 people who will die today from air pollution. The suffering of future generations because of this type of ignorance will be huge and it breaks my heart.

I used to argue with people in this class, who live by innuendo, misinformation, and ignorance but they just make me sick. I now just add them to my ignore list.

Welcome to it.