The elusive photocatalytic water splitting reaction using sunlight on suspended nanoparticles: is there a way forward?

For many decades hydrogen production by photocatalytic methods has been pursued over a variety of semiconductors with probably over a thousand formulations of powder catalysts in many structures and compositions. Yet, with the exception of a few reports, water splitting to molecular hydrogen and oxygen has remained elusive. The only reproducible results are those involving other additives to water: electron donors or acceptors yielding either hydrogen or oxygen, but not both. The consequence of this is a system unrelated to water splitting but simply driven by the organic or inorganic redox potential. One may argue that thermodynamic limitations indicate that an inorganic semiconductor with a band gap within the spectrum of sunlight, and that is stable in water, cannot split water. Otherwise, it would not have existed on earth. For many decades hydrogen production from water by photocatalytic methods has been pursued over a variety of semiconductor powder catalysts featuring many structures and compositions. The stoichiometric formation of molecular hydrogen and oxygen has stayed largely elusive.