CO2 Hydration Conditions during Hydrogen Evolution and Carbon Dioxide Reduction Gas Diffusion Electrode Reactions

The paper to which I'll refer is this one: Is Hydroxide Just Hydroxide? Unidentical CO2 Hydration Conditions during Hydrogen Evolution and Carbon Dioxide Reduction in Zero-Gap Gas Diffusion Electrode Reactors Henrik Haspel and Jorge Gascon ACS Applied Energy Materials 2021 4 (8), 8506-8516.

As I often note, electricity is a thermodynamically degraded form of energy, and, as such, despite the common public misapprehension that it is "green," perhaps driven by familiarity and a large dollop of wishful thinking, it is dirty. The relationship between thermodynamics and environmental cost is more or less direct; any system with poor thermodynamics will require the generation of more energy than necessary. The generation of electricity wastes energy, even without further waste by the storage of electricity in batteries, or worse, hydrogen.

Electricity production on this planet, as is the case with all forms of energy, remains increasingly dependent on combustion, overwhelmingly the combustion of dangerous fossil fuels.

It follows that the electrochemical reduction of CO₂ using electricity, just like the electrochemical reduction of water to make hydrogen will be intrinsically involved with exergy destruction, that is, poor thermodynamics.

There is an important caveat to the above statement; electricity can represent a thermodynamically improvement where it is a side product which recovers exergy by the transformation of waste heat.

Consider the Sulfur Iodine Cycle, a process for the thermochemical decomposition of water into hydrogen and oxygen without the use of thermodynamically degraded electricity. In this process, H₂SO₄, sulfuric acid is decomposed into SO₂ gas and O₂ gas and steam H₂O at high temperatures, on the order of 1000°C. Some of this heat can be recovered for another reaction in the cycle, the decomposition of hydrogen iodide (HI) gas into H₂ and I₂ gases, but this step takes place at a much lower temperature than the decomposition of hydrogen iodide gas. In addition, at high temperatures, the products of sulfuric acid decomposition can recombine to result in the reverse reaction, the formation of sulfuric acid, to take place.

Thus it is useful to consider cooling the mixture SO₂ gas and O₂ gas and steam H₂O rapidly to a temperature at which SO₂ gas. The critical temperature, the highest temperature at which a gas can be liquified, of SO₂, T_c gas is 430.3K, or 147.1°C, well above the boiling point of water, suggesting one could recover exergy by placing a steam engine in the stream. This case is a simplification, and for various reasons there are better approaches for exergy recovery from the sulfur iodine cycle, but it is illustrative. The point is that in producing chemical energy, that represented by hydrogen, which can be used for the synthesis of portable fuels, one can recover electricity as a side product, rather than rejecting the heat to the atmosphere.

I do not expect energy sanity to emerge in the future, since popular thinking is either reactionary or conservative but I do concede that energy sanity is feasible, if not likely.

The paper referenced at the outset of this post is about the electrochemical reduction of carbon dioxide, a much studied concept. The issue of carbon dioxide utilization can often be subject to appeal by people trying to greenwash fossil fuels, as is the case with people trying to rebrand fossil fuels as hydrogen, here at DU and elsewhere. Nonetheless, although the thermodynamics of the reduction of carbon dioxide requires that we not only produce all of the energy that put it there, the enthalpy, we must also produce additional energy to overcome the entropy of mixing. I make this point repeatedly. Often, as is the case with people selling fossil fuels by attempting to rebrand them as "hydrogen" this sort of thing, similar to the nonviable and unpracticed scam of carbon dioxide sequestration, appeal to these ideas is to greenwash fossil fuels. Nevertheless, so far as direct air capture, or better, capture via the intermediate of seawater, is concerned, I think it is important, to use the cliche, "not to throw the baby out with with the bathwater."

The question to my mind with respect to direct air (or seawater) capture and reduction (utilization) is "Do we have any choice but to do otherwise?"

For direct air capture, I often consider strong bases, among the strongest being the aqueous hydroxides of rubidium and cesium, both of which are fission products, with cesium having the additional benefit of being highly radioactive, and thus capable of mineralizing extremely difficult to destroy pollutants, notably those having carbon fluorine bonds.

Thus, considering the feasibility of the case - not likely, but feasible - where electricity is a side product rather than the main product of the production of heat, the paper caught my eye, as I was poking around for the kinetics of the hydration of carbon dioxide.

From the introduction: