Tuesday, October 22, 2019

"Artificial leaf"

Powered by Sunlight, ‘Artificial Leaf’ Successfully Produces Clean Gas From CO2 and Water says
A widely-used gas that is currently produced from fossil fuels can instead be made by an ‘artificial leaf’ that uses only sunlight, carbon dioxide, and water, and which could eventually be used to develop a sustainable liquid fuel alternative to petrol.


Syngas is currently made from a mixture of hydrogen and carbon monoxide, and is used to produce a range of commodities, such as fuels, pharmaceuticals, plastics and fertilizers.

OK, sounds interesting. I've been wondering what we're going to make plastics out of when we run out of oil...

The article in Nature says:

The perovskite photocathodes maintain selective aqueous CO2 reduction for one day at light intensities as low as 0.1 sun, which provides pathways to maximize daylight utilization by operating even under low solar irradiance. Under 1 sun irradiation, the perovskite–BiVO4 PEC tandems sustain bias-free syngas production coupled to water oxidation for three days. The devices present solar-to-H2 and solar-to-CO conversion efficiencies of 0.06 and 0.02%, respectively, and are able to operate as standalone artificial leaves in neutral pH solution.

It seems the perovskite cathodes can be sensitive to moisture, and have to be protected. Very much not quite ready, but interesting. The process does not produce CO2, which I gather is why the headline writer though it was "Clean Gas." Whether this is because CO2 is evil, or because the result is supposedly entirely syngas (betcha there's a lot of water vapor in there too..) I can't say. FWIW, the energy efficiency of photosynthesis is of order less than 1%, though that isn't usually achieved because plants aren't interested in overproducing. (Sugar cane is 3.5%) I'm not sure if that's the same efficiency as quoted in the abstract.

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