The dependence of CO2 hydrogenation to methanol on the surface coordination of copper catalysts.

[NNadir]

2. Thank you. I'm aware of the so called "hydrogen rainbow" and am somewhat annoyed by it.

Here's one evocative chart of it:



Source: Energy Analysis of Low Carbon Hydrogen from Methane and End Use Implications Christine A. Ehlig-Economides and Dimitrios G. Hatzignatiou Energy & Fuels 2022 36 (16), 8886-8899.

The existence of all of these "colors" generally implies that each of them is a "thing," but with the exception of two cases, they are all Potemkin greenwashing of the unfortunate reality of hydrogen, which is that it is an extremely dirty fuel, which is why it is only rarely used as a fuel while being nonetheless an important chemical intermediate on which the world's food supply depends.

Better than 98% of the hydrogen produced on this planet, are either what the chart calls "grey" and "black."

All hydrogen, no matter what the source, represents destroyed exergy except of course, so called "white hydrogen" which is trivial and useless, probably a side product of reformation at the crust/mantle interface of reformation.

I analyzed this situation here:

A Giant Climate Lie: When they're selling hydrogen, what they're really selling is fossil fuels.

As for nuclear energy, what is called alternatively "pink hydrogen," "red hydrogen" and "purple hydrogen" the proposed pathway is electrolysis, which is obscene because all electricity is thermodynamically degraded.

There is a pathway, which I've discussed in various places here and elsewhere where hydrogen production for captive use as a synthetic starting material, is accomplished thermochemically using nuclear energy. In this case the point would be to raise efficiency via process intensification, which is not a requirement for new energy, but rather a wiser use of existent energy, essentially exergy capture. The laws of thermodynamics do not allow for 100% efficiency, but most nuclear plants are Rankine type devices with low thermodynamic efficiency, usually around 33% to 34%. If we add to that the thermal efficiency (as opposed to Faradaic efficiency) of electrolysis is well below 70%, we're talking overall efficiency of less than 25%, as miserable as solar cells, and unacceptable.

It seems to me that with process intensification, given the high temperatures of nuclear fuels in operation, thermodynamic efficiencies even higher than combined cycle gas plants should be possible, efficiencies of around 80% seem approachable for nuclear facilities, with some of the recovered energy in the form of chemical fuels or materials.