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NNadir

(33,368 posts)
Mon Feb 5, 2018, 08:54 PM Feb 2018

Electrolytic reduction of carbon dioxide to formate using low over-voltages.

Here's a fun paper: Highly Selective Reduction of CO2 to Formate at Low Overpotentials Achieved by a Mesoporous Tin Oxide Electrocatalyst (Rahman Daiyan, Xunyu Lu*, Wibawa Hendra Saputera, Yun Hau Ng , and Rose Amal* ACS Sustainable Chem. Eng., 2018, 6 (2), pp 1670–1679)

Let me tell you something: Anyone with a name like Wibawa Hendra Saputera is definitely cooler than I will ever be, probably cooler than you'll ever be too.

Here's the introduction to the paper, what it's about:

Rising level of CO2 accumulation in the atmosphere has attracted considerable research interest in technologies capable of CO2 capture, storage, and conversion.(1-3) The electrochemical reduction of CO2 into high-value liquid organic products could be of vital importance to mitigate this issue.(4, 5) The direct conversion of CO2 to liquid fuel using renewable energy, which can readily be integrated with the current infrastructure, will help realize the creation of a sustainable cycle of carbon-based fuel that will promote zero net CO2 emissions.(6-10) Despite initial promising findings, significant progress is required in improving the production rate, efficiency, stability, and cost to make this technology realistic for large-scale utilization.(7, 11)

The current benchmarking electrocatalysts for CO2RR to formate (HCOO–) are sp group metals, notably, Pb, In, and Sn.(12-19) Among the high-performing materials, Sn-based catalysts are especially favored due to their relative low cost, abundance, and nontoxic properties, compared to Pb and In catalysts.(20) Sn catalysts however exhibit certain characteristics, for instance, the local chemical structure of Sn is shown to play a major role in CO2RR, as the bulk Sn foils are reported to have inconsistent formate Faradaic efficiency (FEHCOO–) at a wide range of potentials.(16, 21) To address such discrepancy in catalytic performances, numerous studies on the effect of electrolyte, pH, morphology, and catalyst deactivation for CO2RR with Sn-foil-based catalysts have been undertaken.(22-25) In spite of the insights and understanding into the mechanisms obtained by such studies, Sn-foil-based catalysts still require large overpotentials to attain high values of FEHCOO–. For example, three-dimensional Sn foam grown on Sn foil catalysts require a large applied potential of ?1.3 V (vs RHE, applies for all potentials mentioned in this study) to achieve a FEHCOO– of 90%.(26) Similarly, the heat-treated Sn dendrite electrodeposited on Sn foil is also reported to convert CO2 to formate with a moderate FEHCOO– of 71% but this is also done at a large negative applied potential of ?1.35 V.(22)


With all due deference to Wibara, this statement is a little off:

The direct conversion of CO2 to liquid fuel using renewable energy, which can readily be integrated with the current infrastructure, will help realize...


The current infrastructure contains very little so called "renewable energy;" overall the fraction of fossil fuels representing world energy portfolios is rising, not falling. In 2000, 80% of world energy came from dangerous fossil fuels. In 2016 (the latest data available) 81% of world energy came from dangerous fossil fuels.

Capturing carbon dioxide using electrical infrastructure that is almost entirely fossil fuel based is simply a perpetual motion machine.

But in theory, if not in practice, clean electricity is potentially available, albeit not from so called "renewable energy.'

No matter.

Some cool pictures of how they make their tin oxide mesoporous catalyst:



The caption:

Scheme 1. Fabrication of m-SnO2 Catalyst


A description of what's going on:

Mesoporous SnO2 was prepared by nanocasting method using KIT-6 as the hard template. KIT-6 was fabricated using an established method.(46) Briefly, 2 g of P123 (Pluronic P-123, Sigma-Aldrich, 99%) was dissolved in 72 mL of deionized water, followed by the addition of 2.5 mL of HCl. Then 2.47 mL of butanol was added dropwise and the mixture was stirred for a duration of 1 h at 35 °C. The solution was then transferred to a hydrothermal reactor and heated to 100 °C for 24 h. The solid product formed was then filtered and calcined at 600 °C for 5 h. To prepare mesoporous SnO2, 1.75 g of tin(IV) tetrachloride pentahydrate (SnCl4·5H2O, Sigma-Aldrich, 99%) was dissolved in 30 mL of ethanol. Then 0.6 g of KIT-6 was added and the mixture heated to 70 °C to evaporate ethanol. The sample was then calcined at 600 °C for 3 h. The impregnation and the calcination process were repeated again with two thirds of the Sn precursor used in the first step to complete the nanocasting process. The KIT-6 templates were then removed by washing the calcined powder twice in a hot 2 M NaOH solution. The resulting samples were collected by repeated centrifugation and washing with deionized water.


KIT-6 is mesoporous silica. I don't know how it's made, but I could look it up, but I'm short on time.

Here's some micrographs of the product anyway:



One of the interesting things about this paper is that the species being reduced is not carbon dioxide but rather the potassium bicarbonate salt. Electrolytic reduction of carbon dioxide is always limited by the low solubility of the gas in water, however the bicarbonate salt (which is made by the absorption of carbon dioxide into basic solutions) is very soluble.

The conclusion:

In summary, mesoporous SnO2 catalyst prepared by a simple and facile nanocasting method using a hard template was successfully employed as a novel electrocatalyst for the selective conversion of CO2 to HCOO–. The as-synthesized catalyst was capable of reducing CO2 to HCOO– with high efficiency and current density at low overpotentials and demonstrated a maximum Faradaic efficiency of 75% and a large current density of 10.8 mA cm–2 at an applied potential of ?1.15 V. The results presented herein also demonstrated the high stability of the m-SnO2 electrode toward CO2RR, displaying a stable current density and Faradaic efficiency with no observable decay over 16 h of operation. The improved catalytic activity of the m-SnO2 electrode was ascribed to (i) preferential exposure of crystalline facets that provides sufficient active sites for CO2RR, (ii) significant presence of oxygen vacancy defects, and (iii) enhancement of CO2RR reaction kinetics due to reduced impedance and greater transport of reactants and facile dissipation of products through the large mesopores and well-dispersed catalyst.


Because we have been disinterested in their fate, future generations will need to clean up our carbon dioxide mess, and will need to do so with diminished resources, basically the trash we leave them.

In this regard, this is an interesting paper, since things like this may give them something to work with.

Have a nice evening.



4 replies = new reply since forum marked as read
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Electrolytic reduction of carbon dioxide to formate using low over-voltages. (Original Post) NNadir Feb 2018 OP
I do appreciate your posts, NNadir. byronius Feb 2018 #1
I wouldn't call it an "occasional insertion." It's pretty much all the time. But thank you... NNadir Feb 2018 #2
An ability to cleanly remove greenhouse gases from the atmosphere Ghost Dog Feb 2018 #3
It will not make sense to capture CO2 merely... NNadir Feb 2018 #4

byronius

(7,369 posts)
1. I do appreciate your posts, NNadir.
Mon Feb 5, 2018, 10:53 PM
Feb 2018

And I don't resent your occasional insertion of your support for nuclear power, although I can't quite get there because of my general distrust of the private sector (of which I am a long-time member) as well as my absolute mistrust of Rick Perry. Well, none of us saw that one coming. Hoo boy. No science is safe with this crew, not even the science that keeps us alive.

BTW -- my son the Hopkins researcher agrees with you somewhat vociferously, and he and I have had long conversations about those issues.

Anyway, I just wanted you to know I appreciate your posts.

NNadir

(33,368 posts)
2. I wouldn't call it an "occasional insertion." It's pretty much all the time. But thank you...
Mon Feb 5, 2018, 11:15 PM
Feb 2018

The relative safety of nuclear power vis a vis fossil fuels is quite the same whether the Secretary of Energy is Rick Perry or whether it is Nobel Laureate Steven Chu, who, by the way, also agreed with me on nuclear issues.

If you do not trust Rick Perry with nuclear power, then you will be trusting him with dangerous fossil fuels.

No matter who's been in charge over the last half a century, the fact is that all nuclear events for all time since the commercialization of nuclear power don't match two days of dangerous fossil fuel deaths.

I am pleased that your son agrees with me, and doubly pleased that he's vociferous.

My sons both talk the nuclear talk as they were raised to do. They tell me that they are seldom met with resistance among their peers.

Their generation is up against the wall because of our irresponsibility. They must think clearly if they are to survive what we have done to them. I'm very impressed with them overall, these sometimes maligned millennials. Both of my sons are way smarter, vastly smarter, than I was at their age, and I would say the same for the people they know and with whom they hang out.

I think my generation - the dumb generation - grew up with fear of nuclear war. We became idiots as a result, living in fear and thriving on ignorance. I certainly went to school many times thinking I'd be vaporized in the afternoon. I can't say that fear made me think more clearly. The two, nuclear war and nuclear power, are easily conflated, although if you actually know something about nuclear power - and the vast majority of people in my generation are completely ignorant of the subject - you can easily see that the only way to achieve nuclear disarmament and to reduce the probability of nuclear war is through the denaturing of both plutonium and uranium. This is only possible with nuclear reactors.

As I argued elsewhere, nuclear war has never been impossible, and never will be impossible, since it is impossible to consume the world's uranium.

The only way to address some very intractable chemical wastes is to use high energy radiation, available from fission products, often incorrectly described as "nuclear waste."

Thank you again, for your kind words though. It means a lot to me that someone enjoys this stuff.

All the best,

NNadir.



 

Ghost Dog

(16,881 posts)
3. An ability to cleanly remove greenhouse gases from the atmosphere
Tue Feb 6, 2018, 06:40 AM
Feb 2018

would be very useful if they can also be 'sequestered'. Being able to reduce and stop further emissions would also be very useful.

Does it not sound as if these researchers might have the interests of fossil-fuel producers at heart when the state their aim as:

The direct conversion of CO2 to liquid fuel using renewable energy, which can readily be integrated with the current infrastructure, will help realize the creation of a sustainable cycle of carbon-based fuel that will promote zero net CO2 emissions.


in the sense that the availability of such technology could be used, as stated here, to justify continuing to run a carbon-based, fossil-fuel economy?

NNadir

(33,368 posts)
4. It will not make sense to capture CO2 merely...
Tue Feb 6, 2018, 10:12 AM
Feb 2018

...to put in a CO2 dump. Such a dump will likely be temporary and extremely dangerous - as we found out in the Lake Nyos event.

There would also be no economic advantage.

This scheme should it be industrialized, is effectively a CO2 splitting scheme. Formic acid is the hydrate of carbon monoxide.

In general I'm not fond of electrolytic schemes except in metal processing. Thermochemical carbon dioxide splitting is likely to be far more efficient.

I posted this as a point of general interest but view it at best as a scheme for perhaps putting spinning reserve to use while it runs in support of the grid.

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