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Tue Dec 17, 2019, 12:04 AM

Biochar-Assisted Water Electrolysis

The paper I'll discuss in this brief post is this one: Biochar-Assisted Water Electrolysis (Jun-ichiro Hayashi* et al, Energy & Fuels 2019, 33, 11246−11252)

The paper comes from a journal, Energy and Fuels, from which I have been reading papers for many years; since 2013 I have at least opened, if not actually read, every paper listed in the Table of Contents, and back issues from that time forward are in my personal library. Better than half, and sometimes as much as three quarters of the papers I encounter in this journal are about forms of energy I oppose vehemently, dangerous fossil fuels. There is usually a section, sometimes fair sized, and sometimes not, on biofuels, and usually a few papers on carbon capture, more or less lip service to the rest.

Speaking of lip service, there are a few papers on solar and wind energy, which many people keep saying will save the world, even though the haven't saved the world, aren't saving the world, and won't save the world. And then there's magic hydrogen, which bourgeois moral and intellectual Lilliputians like the Rocky Mountain Institute's Chief (self declared) Scientist, Amory Lovins, thinks might save the world or at least his precious cars, thus assuring he can drive from his luxury "super efficient" "green" 4000 square house in the upscale suburbs of Aspen to the offices of his ignorance factory located in Basalt, Colorado, just outside the upscale ski resort town of Aspen.

Here's a picture of Amory and his monument to boomer excess and contempt for humanity, especially that part of humanity, all 800 million, who go to bed every night wondering if they'll have food the next day:


Here's a picture of the Chief Idiot at RMI with a girlfriend/wife/whatever in front of this moral hell, both wearing insipid grins:


What an ass! OK Boomer?

Anyway, the reason I read Energy and Fuels has nothing to do with uneducated and mindless brats like Amory Lovins who know nothing at all about energy and the environment, and nothing to do a fondness for either hydrogen or wind and solar power, both of which are topics, at least nominally, of the paper I cited at the outset. The reason I read them is to separate, as they say metaphorically, the wheat from the chaff.

As practiced right now, nominally "renewable" biomass is responsible for slightly less than half of the seven million air pollution deaths that take place each year, but biomass has one thing to recommend it: It is self replicating in such a way as it can, without too much input, cover vast surface areas, marine areas, land areas, lacustrine areas, fluvial areas. This allows it to make use of sunlight, even though it is diffuse, and more importantly, to capture dilute gases, notably, of course carbon dioxide.

Although the total amount of carbon dioxide captured by biomass each year is less than an order of magnitude higher than the amount of carbon dioxide dumps each year, it does have the capability to concentrate carbon in such a way as it is recoverable for technological purposes, assuming, probably without justification, that it is done judiciously. As currently practiced, there is nothing judicious about it. Destroying South East Asia's rain forests for "renewable" diesel fuel is not a good idea, nor was destroying the Mississippi River Delta's ecosystem for the gasoline additive ethanol a good idea.

I couldn't care less who wins the Iowa primary. Winning it, as far as I'm concerned, involves a paean to destruction, going back, as much as I hate to say it, to the days of Jimmy Carter. Corn ethanol is not sustainable.

I believe that the only feasible way to make a stab at - success cannot be guaranteed - is via the agency of high temperatures. Biomass utilization can be made safer than the unfortunate and deadly way in which it is practiced now by heating in closed, unvented systems. Two such approaches are reformation, one wet, and one dry. The first utilizes supercritical water, known as SCWO, for supercritcal water oxidation; the water is the oxidant that oxidizes biomass to either carbon monoxide or more generally carbon dioxide and is, in turn reduced to hydrogen. The second is "dry" reforming, where the oxidant is carbon dioxide and the reduced substance is the carbon dioxide which is reduced to carbon monoxide even as the biomass is oxidized to the same thing. If, despite the "dry" designation, water is injected into this system at some point as high temperature steam, the water will be reduced to hydrogen, and the carbon monoxide oxidized back to the dioxide for potential reuse.

A third safer way to recover carbon from biomass is by pyrolysis, which is heating the biomass in the absence of air.

If the heat to drive any of these processes is nuclear heat, the system can be very clean and, depending on the fate of the recovered carbon, carbon negative. In general, pyrolytic products, many of which come under the general rubric of "biooils" have marginal stability. However these oils can be converted via processing to more stable and usable fuels and/or materials.

Any system that produces pure carbon dioxide has the potential to be clean. The process described in the paper can do just that, produce pure carbon dioxide. It is actually a hybrid system; part electrolysis and part carbon "burning," albeit under water.

Hydrogen (H2), as a most promising candidate for an energy carrier as well as a fuel for fuel cell electric vehicles and power generation, is expected to play a key role in the route to a greener future.(1) Although most currently available H2 is produced from fossil fuels, such as natural gas, the introduction of solar/wind power gives hope for the production of H2 renewably and largely through water electrolysis. The voltage-based energy efficiency of alkaline electrolysis cell systems is 62–82%,(2,3) while its further increase is challenging.

Hydrogen is stored energy and not primary energy, irrespective of what morons like Amory Lovins represent with nonsense like "hydrogen hypercars." As I often point out, the second law of thermodynamics - which is not subject to repeal - requires that the storage of energy wastes energy. The introduction of this paper, while evoking the nonsense "expectation" for solar and wind about which we've been hearing for half a century with no meaningful result other than the trashing of pristine wilderness areas, points this out. Via existing electrolysis, between 38% and 18% of energy is lost as entropy, expressed as heat.

Anytime you read that hydrogen is "green" you are reading nonsense.

However, in a world powered by very high temperature processes, electricity could be a side product, particularly in times of low demand, and thus it may be, under these circumstances, to store energy.

Pyrolysis, and to a lesser extent, both wet and dry reformation can produce either biochar, or asphaltenes (tars) that can be converted to biocoke.

The paper suggests that these can work as assists to electrolysis.

The text continues:

The water electrolysis produces H2 and oxygen (O2), following an overall stoichiometry of 2H2O → 2H2 + O2. The presence of solid carbon (C) in water, if it is electrochemically active, alters stoichiometry(4):

(3)This electrolysis system is called “carbon-assisted water electrolysis” (CAWE). A most particular feature of CAWE is integration of electric and chemical energies into that of H2. In theory, CAWE requires a standard potential (°E) as small as 0.21 V, which is about 1/6 of the normal water electrolysis (°E = 1.23 V). In other words, with the introduction of carbon, it is possible to reduce the power consumption for H2 production ideally to 1/6. This means that the chemical energy of H2 from CAWE is theoretically 600% of electricity input, while 500% originates from the chemical energy of carbon. CAWE is also recognized as a type of electrochemical gasification of carbon at an ambient or near-ambient temperature, and it can convert the chemical energy of carbon fully to that of H2.

CAWE was reported for the first time by Coughlin and Farooque.(4−7) They electrolyzed a coal–water slurry with sulfuric acid as a supporting electrolyte and found H2 evolution at a required potential of ∼0.9 V. Later studies showed that Fe2+/Fe3+ species leached from coal had a catalytic role between an anode and coal particles, accelerating CAWE.(8−13) However, the continuous energy conversion from coal to H2 was difficult possibly because of the formation of stable iron-containing solids from those ions.(14−17) Carbon materials other than coal have rarely been used in CAWE. Seehra et al. applied a type of carbon black to CAWE and reported H2 evolution at an interelectrode potential well below 1.0 V.(18) They also applied nanosized carbon and cellulose-derived carbon-rich material to water electrolysis and reported their activities higher than that of carbon black.(19,20)...

...The present authors herein report that biomass-derived char (biochar) is an excellent material for high-performance CAWE. Biochar is a major product from the pyrolysis of lignocellulosic biomass.(21−24) The present authors applied the biochar to CAWE as a result of the following three reasons. First, it is expected that the biomass has not only chemical but also electrochemical reactivity higher than well-carbonized or graphitized carbon materials, such as carbon black as well as graphite. As shown in Table 1, standard potentials for water electrolysis with aromatic hydrocarbons are clearly smaller than that with C as graphite. Biochar is generally rich in aromatic hydrocarbons, and the structure is far from that of graphite.

The authors post a table of putative theoretical "kicks" that aromatic species (those in the table are not really conductive, and most are derived from dangerous fossil fuels):

Biochar, as the authors note, generally is quite porous, and thus has a large surface area relative to its mass. In electrolysis where pure oxygen is produced, the anode introduces inefficiency owing to the fact that the production of oxygen is a 4 electron process. (One can read many papers discussing this point and looking at ways to address the problem, but this another way.

Much of the rest can be approached by looking at the pictures:

The caption:

Figure 1. Conceptual diagram of a system of biomass conversion. This system consists of syngas production by endothermic CO2 gasification that integrates the biomass chemical energy and renewable-power-derived joule heat and H2 production by BAWE that integrates the biochar chemical energy and renewable power. CO2 gasification and BAWE supply biochar with a high specific surface area and CO2 to each other.

Two terms in the captions below are LSV which is "linear sweep voltammetry" and CE, "continuous electrolysis" each referring to a difference in the way the voltage is applied in these systems:

The temperature at which the biochar is formed has an effect on the voltages at which electrolysis (measured as current density) occurs:

The caption:

Figure 2. LSV profiles of BAWE with biochar carbonized at different TC ranging from 550 to 1050 °C and that without biochar (shown as the reference). Electrolyte = 3 mol/L H2SO4 aqueous.

More on surface area:

The caption:

Figure 3. Current density in BAWE (E = 1 V) and specific BET surface area of the corresponding biochar as functions of TC.

The caption:

Figure 4. LSV profiles of water electrolysis with carbon black (CB-A or CB-B) or biochar. Concentration of CB = 20 g/L electrolyte (aqueous solution of 3 mol/L H2SO4 and 0.25 mol/L NaCl).

The addition of sodium chloride unsurprisingly helps drive the reaction:

The caption:

Figure 5. Acceleration of BAWE with 850 °C carbonized biochar by the addition of NaCl to the electrolyte. NaCl concentration = 0.25 mol/L.

After a time, as the biochar is oxidized, it of course induces changes in performance:

The caption:

Figure 6. Time-dependent changes in current and gas evolution in CE mode BAWE. Conditions: TC for biochar used, 850 °C; NaCl concentration in the electrolyte, 0.25 mol/L; and E, 1 V.

The process results in the incorporation of oxygen into the system, and it can be regenerated by heating, presumably releasing the oxygen as CO2.

This table shows the variation in the composition of the biochar after continuous electrolysis at 5000 Coulombs and after regeneration at various temperatures:

Some further exploration of various effects:

The caption:

Figure 7. Change in LSV profiles for six types of biochars with different electrochemical and/or thermal histories: fresh, biochar prepared by carbonization at TC = 850 °C (before CE mode BAWE); CE 1000 C, after the use of fresh biochar for BAWE with a total current of 1000 C; CE 5000 C, after the use of fresh biochar for BAWE with a total current of 5000 C; CE 5000 C biochar after heat treatment at 250 °C; CE 5000 C biochar after heat treatment at 500 °C; and CE 5000 C biochar after heat treatment at 850 °C. The NaCl concentration in the electrolyte was 0.25 mol/L.

The rate of mass loss at various temperatures is recorded with differential thermogravimetry:

The caption:

Figure 8. DTG profiles for heating fresh biochar (TC = 850 °C) and spent chars from CE mode BAWE with 1000 and 5000 C. Heating rate = 5 °C/min.

Comparison of the performance of chars at the differening time points of use:

The caption:

Figure 9. LSV profiles for the fresh biochar (TC = 850 °C) and CO2-gasified biochars (conversion of 25 or 50%). The electrolyte (3 mol/L H2SO4 aqueous) did not contain NaCl.

The paper's conclusion:

The present authors investigated BAWE with the woody-biomass-derived chars and demonstrated the following: (1) BAWE occurs at an interelectrode potential as low as 0.5 V, which is much lower than that of water electrolysis without the biochar, 1.4 V, and also lower than that for CAWE with carbon black. The electrochemical reactivity of the biochar is strongly affected by TC and maximized the carbonization at TC = 850 °C. (2) The addition of NaCl to the electrolyte (3 mol/L H2SO4 aqueous) increases the current in BAWE by a factor of 5. (3) BAWE produces H2 following the well-known stoichiometry, 4H+ + 4e– → 2H2, at the cathode. At the anode, however, the electrochemical oxidation of the biochar carbon to CO2 is minor. Instead, a major portion of oxygen is chemically incorporated into the biochar, forming refractory functional groups. The accumulation of the O-containing functional groups in the biochar results in the loss of its electrochemical reactivity and current decrease. (4) The heat treatment removes O-containing groups that have accumulated in the biochar during the continuous BAWE, fully recuperating it. (5) The CO2 gasification of the biochar activates it to a remarkable extent by developing the porous structure.

Interesting I think. I would expect that in a sustainable world, pyrolysis of biomass would be a somewhat limited pathway compared to supercritical water reformation or dry CO2 reforming. This said, one can imagine that pyrolysis would in fact, take place often, if to a limited extent when compared to the reformation systems.

It's nice to know.

Have a nice day tomorrow.

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Reply Biochar-Assisted Water Electrolysis (Original post)
NNadir Dec 2019 OP
StevieM Dec 2019 #1
NNadir Dec 2019 #2
StevieM Dec 2019 #3
NNadir Dec 2019 #4
TexasTowelie Dec 2019 #5

Response to NNadir (Original post)

Sat Dec 21, 2019, 04:20 PM

1. I thought you might be interested in seeing this article about where the candidates for president

stand on nuclear power.

If you hit "expand answers," and get actual comments from them, I think you have to hit "show former candidates" first in order to have them included in the list of people who you can see expanded comments from.

I am guessing that the candidates you would like the most are Corey Booker, Seth Moulton and Michael Bennet.


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Response to StevieM (Reply #1)

Sun Dec 22, 2019, 12:01 PM

2. Thank you for your suggestion but...

...more important than a primary position is a free and open mind.

The so called "Green New Deal" is more popular nonsense.

The de rigueur opposition to nuclear energy on the left represents our answer to creationism on the far right. It is ignorant and appalling actually since climate change is very real and is a far more critical issue than even we on the left actually understand.

Unfortunately, we, like them, can buy into rote dogma. That is what the Green New Deal is, rote dogma. It has experimentally been shown to be unworkable, and in fact, destructive in places ideas like it have been employed.

A candidate espousing views like mine will not get the nomination. What I am hoping for is that our nominee will show the same flexibility of mind that President Obama showed. I thought his energy policies as stated in the primary season in 2008 were awful, and I supported with caveats, Ms. Rodham Clinton then.

In office, he worked to restart nuclear power plant construction.

Mr. Yang has bought into the thorium cycle, which is just OK with me, but shows he is at least paying attention. My primary vote will not matter, since the nominee will have been decided before the NJ primary takes place.

Any President who practically attempts the Green New Deal will fail to address climate change. That's a fact. Facts matter.

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Response to NNadir (Reply #2)

Sun Dec 22, 2019, 01:42 PM

3. Interesting point about Andrew Yang.

I didn't mention him as a candidate you would like because I know you are not too big on thorium.

You cannot be sure that your primary vote won't matter because we could have a four way race that goes all the way to the end, possibly culminating in a brokered convention.

I do think you should check out the article. It includes actual comments from candidates talking about their thoughts on nuclear energy. Actually, the question that they specifically asked was "do you support building more nuclear power plants?" I appreciated some of their answers and thought that you would too.

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Response to StevieM (Reply #3)

Sun Dec 22, 2019, 05:54 PM

4. Oh, I did look at the article, so thanks again.

It's just that I don't take anything anyone says at this point all that seriously.

From my perspective, the only candidate we have who is probably not intellectually capable of changing his or her mind is the one who is not a Democrat. If however, that person were somehow the Democratic nominee, I would still vote for him because, as detestable as he is to me, he is nowhere near as detestable as the orange racist criminal now in the White House. However, in that case, any hope of saving the world from climate change with the effective participation would be doomed.

That guy carrying on about addressing climate change is rather analogous to Donald Trump talking about addressing racism.

I note that my second choice candidate, Ms. Warren, has expressed views on nuclear power that are extremely dangerous and if practiced, would be fatal to any effort to address climate change. What Ms. Warren has, however, is a record of changing her mind when presented with facts. She was, after all, once a Republican. You know, I despised the guy, but Richard Nixon built a career on opposing communism everywhere and at all times. Thus it may be true that he was the only person who could establish relations with that country that I grew up knowing as "Red" China, a place that was as remote as Mars in the consciousness of children when I was a child.

Let me clarify something about thorium though. I am not opposed to the use of thorium. Thorium is a fine nuclear fuel with much to recommend it, particularly because it can be a breeder fuel in certain kinds of existing reactors, notably heavy water moderated reactors like the CANDU and Indian reactors based on the same technology.

These however, are thermal reactors, and thermal reactors are incapable, under any circumstances, of consuming the world supply of uranium that is already mined and, in fact, already chemically isolated. This is the famous or infamous "depleted uranium." This fuel is available immediately and there is enough of it to provide all of the world's energy needs for centuries without operating a single type of energy mine anywhere on the planet, no coal, no oil, no gas, fracked, unfracked, mined as sands or by mountaintop removal, none of it. In fact, it would be unnecessary to operate uranium mines if this depleted uranium were put to use. We would need less (or potentially no) coal to make steel for wind turbine towers, no furnaces to refine silicon for solar cells, fewer lanthanide mines, no nightmares of rapidly accumulating electronic waste, less copper, less aluminum.

Therefore while I do not object to thorium, I do object to the dubious claim that it is the best nuclear fuel. Thorium does offer certain advantages, particularly, over the long term, for the production of neptunium, for example, although the desired product of neptunium resources, plutonium-238, is accessible from americium-241, albeit not in an isotopically pure form. It is, I think, desirable to have uranium-232 from thorium for the denaturing of purified uranium, although anyone who is really interested in making nuclear weapons can do so with access to seawater; it is impossible to deplete all the world's uranium.

Nevertheless, thorium does not offer the same kinds of neutron fluxes that plutonium can and does. As there is now less and less time to act because we have focused on dreamy reactionary stuff that didn't and isn't and won't work, so called "renewable energy" and because the rate of deterioration of the atmosphere is accelerating, the plutonium uranium cycle can be scaled much, much, much faster.

To fully utilize the world's uranium resources, we need to operate on the fast neutron cycle. The currently developing various "breed and burn" reactors all allow for fast neutron spectra, Terrapower, NuScale, etc, etc. I don't think that these types of designs are fully optimized, and there are many features of them which I find less than ideal, but they are the right idea, to be sure.

I have convinced myself that the world inventory of plutonium in used nuclear fuels offers enough critical masses, along with inventories of americium and neptunium, that in a rational world committed to saving itself, it may be possible to scale nuclear energy at a fast enough pace to actually matter. One can show, that the uranium in American used nuclear fuel alone can power the entire world for decades, and do so, while providing a healthy dollop of neptunium. I am less confident that a thorium cycle can do this.

These things said, thanks for your comments. I certainly appreciate them and your insights.

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Response to NNadir (Original post)

Mon Dec 23, 2019, 03:13 AM

5. K&R! nt

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