Here is the basic construction of the device from TFA:
"The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 square centimeters to harvest light; the tungsten diselenide and ionic liquid co-catalyst system on the cathode side; and cobalt oxide in potassium phosphate electrolyte on the anode side."
So, the cathode is immersed in a combination of water and ethyl-methyl-imidazolium tetrafluoroborate (from TFA).
The anode is immersed also in an electrolyte.
The result is that "hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode." (From TFA)
There's a big piece missing here: how does the CO2 from the atmosphere get to the cathode to be catalyzed, as it is immersed in this ionic fluid? Where does the Hydrogen come from - the electrolyte? It must, because there is no other place for it to come from. This means that the electrolyte is consumed unless it reclaims the Hydrogen, which we've been told is not the point.
So, the questions I have are:
1) How does CO2 get from the atmosphere to the cathode?
2) If the electrolyte is consumed in the process, does the H come from the water in the mix or from the ethyl-methyl-imidazolium tetrafluoroborate? (Slightly less bad if all we have to do is add water, but the fact they don't answer this question leads me to believe the H comes from the ethyl-methyl-imidazolium tetrafluoroborate)
3) Since we're releasing H and CO from the electrolyte in which the cathode is immersed, then we must also necessarily release Oxygen, both from the CO2, and from the electrolyte if it is the water being electrolyzed. Why do they not mention Oxygen bubbling up from the cathode, as it must?