4 ms·

Technically this is about evolving oxygen gas from water more than it is about the hydrogen end of the electrocatalytic reaction. Since this is a cathode (2H+

Technically this is about evolving oxygen gas from water more than it is about the hydrogen end of the electrocatalytic reaction. Since this is a cathode (2H+ + 2e- -> H2 gas) vs. anode process (2H2O -> 4H+ + 4e- + O2) linked up by a wire to close the circuit, you have two chemical processes to manage. The oxygen-evolving one tends to be slower, i.e. rate limiting. For an overview: https://sci-hub.se/10.1039/c9cs00607a https://sci-hub.se/10.1039/c9cs00607a Song, et al. (2020). "A review on fundamentals for designing oxygen evolution electrocatalysts." Chemical Society Reviews. >"Therefore, the OER is the key process that governs the overall efficiency of electrochemical water splitting. To date, IrO2 and RuO2 have been state-of-the-art OER catalysts. However, both of them are made of precious metals and the cost is high. Therefore, it is imperative to seek low-cost alternative materials that can effectively reduce the kinetic limitation of OER and improve the efficiency of water splitting." So, they discovered that the catalyst used at the OER end has some light-activation property, which is pretty interesting, i.e. they discovered a kind of photovoltaic electrocatalyst. Whether it will prove to be industrially useful is anyone's guess. There are similar systems but they're not very practical (i.e. they require high-energy UV): https://physicsworld.com/a/light-activated-catalysts-make-nearly-perfect-water-splitters/ https://physicsworld.com/a/light-activated-catalysts-make-ne... As far as hydrogen-from-water tech, again it has three plausible large-scale cleantech industrial uses: ammonia from atmospheric N2, reduction of iron ore to sponge iron, and methane (and plausibly jet fuel) production from atmospheric CO2.

PaulHoule 4y ago
Hydrogen has numerous uses. Petroleum refineries produce and consume hydrogen in numerous places, if they find they are steam reforming they could use green hydrogen instead, together with storing waste Carbon dioxide to green operations. Even if we quit refining oil from the ground we will still be doing chemistry like petrochemisty with other feedstocks.
- photochemsyn 4y ago
  If you can figure out how to get the carbon feedstock from the atmosphere at scale, why would anyone bother with refining a mixed muck coming out of the ground? What we call 'petrochemistry' today will be called 'aero-hydro-chemistry' tomorrow.
  - PaulHoule 4y ago
    I’ve looked into the chemistry you’d use to turn a carbonaceous asteroid into useful products such as plastic films or material for a biosphere and the old C1 chemistry (manufactured gas and PVC from acetlyene) and the new stuff for utilization of CO2 turns out to be very relevant. For instance you are going to get CO2 as a waste product and you will not throw it away because it is precious so you will add energy to recycle it. You might just get O2 from processing of metals and stones, burn the carbon and feed the CO2 into some system for further processing. The difference with earth is you have 24 hour sunlight and the anility to concentrate it with weightless mirrors.
  - marshray 4y ago
    There really is very, very little carbon in the atmosphere, famously ~410 ppm. (Yes, that little bit is enough to absorb significantly more heat from the sun). So, whatever capture system you use, you'd need to move a lot of air through in order to produce a small amount of something like liquid hydrocarbon fuel. It will require thousands of times more air, by mass. Since the output fuel product is hundreds of times more dense, it would require a crazy large volume of air to extract the carbon necessary to fill a fuel tank. A corn field combined with a methanol fermentation and distillation facility is an example of a machine that does that. Very large.
    - PaulHoule 4y ago
      The advantage of attempting it mechanically is that you might use less water and less fixed nitrogen. Water consumption is directly linked to how plants absorb CO₂ from the atmosphere, see https://ripe.illinois.edu/blog/difference-between-c3-and-c4-plants https://ripe.illinois.edu/blog/difference-between-c3-and-c4-...
    - photochemsyn 4y ago
      Plants pull 100 gigatons of carbon out of the atmosphere every year and convert it to biomass (essentially, oxy-ammonia-hydrocarbons like sugars, proteins, fats, etc.). Humans pull about 6 gigatons of carbon out of the ground each year and pump it into the atmosphere. The reason this cycle doesn't exhaust the atmospheric pool, of course, is that animals and fungi (more the latter) break down biomass into CO2 and release it back into the atmosphere. That's not what I'd call 'very very little carbon'.

PaulHoule 4y ago

Hydrogen has numerous uses. Petroleum refineries produce and consume hydrogen in numerous places, if they find they are steam reforming they could use green hydrogen instead, together with storing waste Carbon dioxide to green operations. Even if we quit refining oil from the ground we will still be doing chemistry like petrochemisty with other feedstocks.

photochemsyn 4y ago
If you can figure out how to get the carbon feedstock from the atmosphere at scale, why would anyone bother with refining a mixed muck coming out of the ground? What we call 'petrochemistry' today will be called 'aero-hydro-chemistry' tomorrow.
- PaulHoule 4y ago
  I’ve looked into the chemistry you’d use to turn a carbonaceous asteroid into useful products such as plastic films or material for a biosphere and the old C1 chemistry (manufactured gas and PVC from acetlyene) and the new stuff for utilization of CO2 turns out to be very relevant. For instance you are going to get CO2 as a waste product and you will not throw it away because it is precious so you will add energy to recycle it. You might just get O2 from processing of metals and stones, burn the carbon and feed the CO2 into some system for further processing. The difference with earth is you have 24 hour sunlight and the anility to concentrate it with weightless mirrors.
- marshray 4y ago
  There really is very, very little carbon in the atmosphere, famously ~410 ppm. (Yes, that little bit is enough to absorb significantly more heat from the sun). So, whatever capture system you use, you'd need to move a lot of air through in order to produce a small amount of something like liquid hydrocarbon fuel. It will require thousands of times more air, by mass. Since the output fuel product is hundreds of times more dense, it would require a crazy large volume of air to extract the carbon necessary to fill a fuel tank. A corn field combined with a methanol fermentation and distillation facility is an example of a machine that does that. Very large.
  - PaulHoule 4y ago
    The advantage of attempting it mechanically is that you might use less water and less fixed nitrogen. Water consumption is directly linked to how plants absorb CO₂ from the atmosphere, see https://ripe.illinois.edu/blog/difference-between-c3-and-c4-plants https://ripe.illinois.edu/blog/difference-between-c3-and-c4-...
  - photochemsyn 4y ago
    Plants pull 100 gigatons of carbon out of the atmosphere every year and convert it to biomass (essentially, oxy-ammonia-hydrocarbons like sugars, proteins, fats, etc.). Humans pull about 6 gigatons of carbon out of the ground each year and pump it into the atmosphere. The reason this cycle doesn't exhaust the atmospheric pool, of course, is that animals and fungi (more the latter) break down biomass into CO2 and release it back into the atmosphere. That's not what I'd call 'very very little carbon'.