Saw the usual so-so article in Guardian but this is a bit better
https://www.newscientist.com/article/2334240-floating-artificial-leaf-converts-energy-from-sunlight-into-fuel

But no one spells it out - where's the carbon coming from, presumably from atmosphere, or maybe from the pond water?!
Seems, at best it's capturing then pretty soon re-emitting carbon already in the cycle, rather than releasing 'new' carbon from fossil sequestration - as well as partially substituting 'harmless' green hydrogen for carbon, in this 'future' fuel mix.

“The crucial point is that we are not decarbonising the economy through techniques like these,” Reisner said. “Carbon is still a key component. What we are doing is to ‘defossilise’ the economy. We will no longer be burning ancient sources of carbon – coal, oil and gas – and adding greenhouse gases to the atmosphere".

What does the team think? What about the embodied energy/carbon, rare elements etc, in making/maintaining the 'machinery' and collecting/distributing the product?

Posted By: Mike1The water - alternative article here:

https://spectrum.ieee.org/artificial-leaf-hydrogen-syngas

No that article says "A new artificial leaf is light enough to float on water, where it can soak up sunlight and carbon dioxide from air". So the answer is the air. There's no carbon in pure water, so it would have to rely on impurities or dissolved gases anyway.

The whole thing will never amount to anything anyway, IMHO.

Yes but the carbon comes from the air. Splitting water (electrolysis) doesn't involve any carbon.