Table 2 List of solar fuel systems and their defining technical attributes.

Solar fuels systemState of developmentExample systems
Molecular systemsPersistent charge separation demonstrated;
fuel-producing systems, including efficient, stable
molecular electrocatalysts, must be discovered
Porphyrins linked to quinones either in diads, triads,
or tetrads; Ru-bipyridyl inorganic chromophores linked
to Pt particles or hydrogenases, and linked to
molecular catalysts for water oxidation
Inorganic semiconductor particlesSolar-driven water-splitting devices demonstrated; efficiency,
safety, stability need to be addressed simultaneously
GaN:ZnO w/ RuO2, Cr2O3-coated Rh cocatalysts (123)
Semiconductor photoelectrodesEfficient, safe systems demonstrated; long-term stability,
cost-effectiveness need to be improved
Si/Al0.15Ga0.85As (124), GaAs/GaInP2 (100)
Photovoltaic electrolysisDemoSi PV coupled to electrolyzer (125, 126)