Over 18% solar energy conversion to generation of hydrogen fuel; theory and experiment for efficient solar water splitting

Contemporary models are shown to significantly underestimate the attainable efficiency of solar energy conversion to water splitting, and experimentally a cell containing illuminated AlGaAs/Si RuO2/Ptblack is demonstrated to evolve H2 and O2 at record solar-driven water electrolysis efficiency. Under illumination, bipolar configured Al0.15Ga0.85As (Eg=1.6 eV) and Si (Eg=1.1 eV) semiconductors generate open circuit and maximum power photopotentials of 1.57 and 1.30 V, well suited to the water electrolysis thermodynamic potential:H2O→H2+1/2O2; EH2O°=EO2−EH2; EH2O°(25°C)=1.229 V.The EH2O°/photopotential matched semiconductors are combined with effective water electrolysis O2 or H2 electrocatalysts, RuO2 or Ptblack. The resultant solar photoelectrolysis cell drives sustained water splitting at 18.3% conversion efficiencies. Alternate dual bandgap systems are calculated to be capable of attaining over 30% solar photoelectrolysis conversion efficiency.