[Robotbeat]

It’s kind of annoying that this is always brought up as a gotcha. Direct air CO2 capture is not a massive contributor to the total energy usage. It’s still dominated by electrolysis itself. The numbers aren’t that hard to find, either. A kilogram of propane has a specific energy of 50MJ and emits 3kg of CO2. Assuming this electrolysis is 50% efficient, that requires 100MJ to make. CO2 direct air capture is about 4.3MJ/kgCO2, or about 13MJ/kgPropane compared to the 100MJ/kgpropane of electrolysis. So it’s still a pretty small fraction of the total energy costs.

EDIT: note that burning that propane in a cheap generator is only gonna net you 10MJ/kg of electricity, maybe 17MJ/kg in a large expensive generator. So the roundtrip efficiency is just 9-15% efficient. But it potentially saves you a LOT in storage costs if you’re only cycling this storage once or twice a year.

(Note that propane is a great way to store hydrocarbons as the pressure is low but it’s self pressurizing and thus it doesn’t get water ingress or have any of the storage difficulties of gasoline and diesel, which last only 3-6 months or 6-12 months respectively. It’s also very clean burning compared to those two.)

[walnutclosefarm]

I wasn't looking for a "gotcha." Just saying that you need to consider all the input costs to know how this pencils out.

50% is almost exactly the paper's claimed efficiency for the lab cell, so it's a reasonable number.

Overall, I'm very enthusiastic electrocatalytic methods for producing hydrocarbons as a combustion fuel source for applications where direct electric technologies are not feasible. I'd much rather seen money and energy going into making something like this work, than all the effort on hydrogen. Propane, or any hydrocarbon in the 3C-8C range, is a way better fuel for any fossil fuel replacement energy system than hydrogen.