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This is cool science but is it actually likely to be competitive with e-fuel approaches for practical purposes? This suggests in a couple of places it is, in a

This is cool science but is it actually likely to be competitive with e-fuel approaches for practical purposes? This suggests in a couple of places it is, in a vague sort of way, but like almost everything I read in this space it seems to be avoiding a straight out comparison with e-fuels. Like this is a very weak claim: > For example, when compared to e-fuels, the solar thermochemical pathway bypasses the solar electricity generation, the water electrolysis, and the reverse-water gas shift steps, to directly produce solar syngas of desired composition for FT synthesis, i.e., three steps are replaced by one. Reducing the number of steps might lead to some amazing efficiency breakthrough, but if you mention the step reduction and then stop, I'm going to assume it doesn't.

PaulHoule 3y ago
It has the disadvantage that the reactor is only going to run when there is very bright sunlight. Might be more desirable for applications in space where you have sunlight 24 hours. There's also the question of what kind of system it is embedded in. Typically people have made a CO + H2 syngas using pyrolysis of coal or rubber tires or municipal waste or something like that. You could make methane out of that or make gasoline or diesel compatible fuels, not to mention just about any chemical feedstock you need: https://en.wikipedia.org/wiki/C1_chemistry https://en.wikipedia.org/wiki/C1_chemistry The "water shift" and "reverse water shift" reactions are about what to do if your ratio of CO and H2 are wrong for what you are trying to make so you can basically turn CO into H2 or vice versa. That reactor looks like it would make pure CO without any H2 so if you didn't have an H2 source you could use the energy in the CO to split water and make H2 ("water shift") Similarly an e-Fuel factory might primarily have an electrolizer that makes H2 and you would use the reverse water shift to turn some CO2 into CO.
hutzlibu 3y ago
"Reducing the number of steps might lead to some amazing efficiency breakthrough, but if you mention the step reduction and then stop, I'm going to assume it doesn't." It doesn't (yet) and they do mention it: "To date, maximum measured values of efficiency are still in the single digits, namely 5.6% for pure CO2-splitting and 4.1% for co-splitting CO2 and H2O." Not great so far. Also Cerium is a rare earth, even though quite widespread.
- adrian_b 3y ago
  It is by far the cheapest rare-earth metal. It is even much cheaper than it could be expected from its abundance, because it accumulates as a byproduct of producing REEs for which there is a higher demand, e.g. neodymium, and its storage is expensive for the REE producers. They would be almost willing to give it away for free, to get rid of it. In recent years most public information about the current price of metals has disappeared, but 10 years ago the price of pure cerium was around $10/kg, in the same range with the prices of pure copper, pure chromium or pure titanium. Cerium compounds, like the ceria used here, can be significantly cheaper than the metal (because the metal requires a lot of energy for extraction). A Google search indicates that the current price of ceria (i.e. cerium oxide) is around $1.65 per kilogram, so the price of ceria must be a negligible part of the price of such a CO2 splitting device.
  - hutzlibu 3y ago
    Well, under the assumption that this is the great next thing and mass production starts, prices will surely rise, but all in all yes, it likeley will not be a bottleneck, efficency is mainly the problem.
- Animats 3y ago
  Having to run the reaction at 1500°C is a bit much. They had to use a big solar mirror concentrator to get up to that temperature, and they're not producing much product. There are so many of these bad schemes for making "green" burnable fuels by splitting CO2 that there is probably some group subsidizing these articles. Not to the point that the technology actually works, just to the point that it generates PR.

PaulHoule 3y ago

It has the disadvantage that the reactor is only going to run when there is very bright sunlight. Might be more desirable for applications in space where you have sunlight 24 hours. There's also the question of what kind of system it is embedded in. Typically people have made a CO + H2 syngas using pyrolysis of coal or rubber tires or municipal waste or something like that. You could make methane out of that or make gasoline or diesel compatible fuels, not to mention just about any chemical feedstock you need: https://en.wikipedia.org/wiki/C1_chemistry https://en.wikipedia.org/wiki/C1_chemistry The "water shift" and "reverse water shift" reactions are about what to do if your ratio of CO and H2 are wrong for what you are trying to make so you can basically turn CO into H2 or vice versa. That reactor looks like it would make pure CO without any H2 so if you didn't have an H2 source you could use the energy in the CO to split water and make H2 ("water shift") Similarly an e-Fuel factory might primarily have an electrolizer that makes H2 and you would use the reverse water shift to turn some CO2 into CO.

hutzlibu 3y ago

"Reducing the number of steps might lead to some amazing efficiency breakthrough, but if you mention the step reduction and then stop, I'm going to assume it doesn't." It doesn't (yet) and they do mention it: "To date, maximum measured values of efficiency are still in the single digits, namely 5.6% for pure CO2-splitting and 4.1% for co-splitting CO2 and H2O." Not great so far. Also Cerium is a rare earth, even though quite widespread.

adrian_b 3y ago
It is by far the cheapest rare-earth metal. It is even much cheaper than it could be expected from its abundance, because it accumulates as a byproduct of producing REEs for which there is a higher demand, e.g. neodymium, and its storage is expensive for the REE producers. They would be almost willing to give it away for free, to get rid of it. In recent years most public information about the current price of metals has disappeared, but 10 years ago the price of pure cerium was around $10/kg, in the same range with the prices of pure copper, pure chromium or pure titanium. Cerium compounds, like the ceria used here, can be significantly cheaper than the metal (because the metal requires a lot of energy for extraction). A Google search indicates that the current price of ceria (i.e. cerium oxide) is around $1.65 per kilogram, so the price of ceria must be a negligible part of the price of such a CO2 splitting device.
- hutzlibu 3y ago
  Well, under the assumption that this is the great next thing and mass production starts, prices will surely rise, but all in all yes, it likeley will not be a bottleneck, efficency is mainly the problem.
Animats 3y ago
Having to run the reaction at 1500°C is a bit much. They had to use a big solar mirror concentrator to get up to that temperature, and they're not producing much product. There are so many of these bad schemes for making "green" burnable fuels by splitting CO2 that there is probably some group subsidizing these articles. Not to the point that the technology actually works, just to the point that it generates PR.