Instead, this paper introduces a materials engineering advance in a prototype UV-absorbing catalyst, that pushes EQE values to maximum, and suggests similar can be done to an existing visible-absorbing catalyst, to give an STH of 10%, which is very high for these durable, cheap catalysts. I got this from a quick reading of this paper and related papers.
Relevant section:
Recently, Ta3N5 and Y2Ti2O5S2 have been reported to split water into hydrogen and oxygen under visible light. These materials absorb visible light with wavelengths of up to 600 nm and 640 nm, respectively, and the STH efficiency can reach 10% once the EQE is improved to a level similar to that of SrTiO3:Al. The suitable photocatalyst design presented here should provide impetus to the development of particulate semiconductor photocatalysts for practical solar hydrogen production from water.
It's not one H20. I read the graphic as:
110 H30+ + 100 OH- -- 350-360nm UV light + Al-doped SrTiO3 selectively coloaded with Rh/Cr2O3 + CoOOH --> 210 H20 + 5 H2
That looks like if it were paired with a cathode, you could take water and produce H2 more efficiently, but you'd need to keep the H+ sufficiently high or continue to supply it with more water, otherwise you develop higher OH- and H2O2 elsewhere in the solution from the H+ depletion, and that'll probably create some O2, but not at the rate you would with electrolysis, because the catalyzed reaction above would itself create a higher H+ environment, which feeds into itself from the H3O, but the H2 gas is escaping, depleting the H2 from the solution whereas the O2 is not gathering and escaping like that as much.
So, you could efficiently turn H2O into H2 source for a fuel cell.
But, you could also use this to make water more basic.
More detail:
Water is naturally a solution of H2, O2, H+, OH-, O--, H20, and H3O+, H2O2--. Except for H+ and O--, those are splitting and recombining most of the time while in liquid state, because the various ions in water and larger structures, etc. act as catalysts to the various reactions.
With light and the catalysts, the reaction above would seem to continue for quite a while, since the reaction produces H+ which will combine with surrounding H2O to product H3O.
Eventually, you're left with a greater concentration of OH- elsewhere in the solution (though surface of the catalyst near the reaction and the area above it that the H2 flows through would be more acidic). The reaction could stop if the availability of H3O and H2O would become too low, and at that point, the water would be more basic, because you wouldn't have sufficient free H+.
The quantum efficiency is therefore likely a meaningless number in practice. Though it’s handy from a scientific perspective.
>Overall water splitting, evolving hydrogen and oxygen in a 2:1 stoichiometric ratio, using particulate photocatalysts is a potential means of achieving scalable and economically viable solar hydrogen production. To obtain high solar energy conversion efficiency, the quantum efficiency of the photocatalytic reaction must be increased over a wide range of wavelengths and semiconductors with narrow bandgaps need to be designed. However, the quantum efficiency associated with overall water splitting using existing photocatalysts is typically lower than ten per cent1,2. Thus, whether a particulate photocatalyst can enable a quantum efficiency of 100 per cent for the greatly endergonic water-splitting reaction remains an open question. Here we demonstrate overall water splitting at an external quantum efficiency of up to 96 per cent at wavelengths between 350 and 360 nanometres, which is equivalent to an internal quantum efficiency of almost unity, using a modified aluminium-doped strontium titanate (SrTiO3:Al) photocatalyst3,4. By selectively photodepositing the cocatalysts Rh/Cr2O3 (ref. 5) and CoOOH (refs. 3,6) for the hydrogen and oxygen evolution reactions, respectively, on different crystal facets of the semiconductor particles using anisotropic charge transport, the hydrogen and oxygen evolution reactions could be promoted separately. This enabled multiple consecutive forward charge transfers without backward charge transfer, reaching the upper limit of quantum efficiency for overall water splitting. Our work demonstrates the feasibility of overall water splitting free from charge recombination losses and introduces an ideal cocatalyst/photocatalyst structure for efficient water splitting.
Not so sure about the fuelcellsworks article clickbaiting up the 'quantum' bit when all it means is one photon splitting one H2O.