Over 18% solar energy conversion to generation of hydrogen fuel; theory and experiment for efficient solar water splitting (Reprinted from J. Phys. Chem. B, vol 104, pg 8920-8924, 2000)

Contemporary models are shown to significantly underestimate the attainable efficiency of solar energy conversion to water splitting, and experimental ly a cell containing illuminated AlGaAs/Si RuO2/Pt-black is demonstrated to evolve H-2 and O-2 at record solar-driven water electrolysis efficiency. U nder illumination, bipolar configured Al0.15Ga0.85As (E-g = 1.6 eV) and Si (E-g = 1.1 eV) semiconductors generate open circuit and maximum power photo potentials of 1.57 and 1.30 V, well suited to the water electrolysis thermo dynamic potential: H2O --> H-2 + 1/2O(2); E-H2O(degrees) = E-O2 - E-H2; E-H2O(degrees)(25 degr eesC) = 1.229 V. The E-H2O(degrees)/photopotential matched semiconductors are combined with effective water electrolysis O-2 or H-2 electrocatalysts, RuO2 or Pt-black The resultant solar photoelectrolysis cell drives sustained water splitting at 18.3% conversion efficiencies. Alternate dual bandgap systems are calcu lated to be capable of attaining over 30% solar photoelectrolysis conversio n efficiency. (C) 2001 International Association for Hydrogen Energy. Publi shed by Elsevier Science Ltd. All rights reserved.