title: Amorphous TiO₂ coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation.
abstract: Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel production, these materials are unstable in aqueous media. We show that TiO2 coatings (4 to 143 nanometers thick) grown by atomic layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidation of 1.0 molar aqueous KOH to O2 for more than 100 hours at photocurrent densities of >30 milliamperes per square centimeter and ~100% Faradaic efficiency. TiO2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 milliamperes per square centimeter, respectively, for water oxidation.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA. Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Shu
authors.initials: S
authors.lastname: Hu
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA. Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Shaner
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Beardslee
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA. Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Lichterman
authors.affiliation: Beckman Institute and Molecular Materials Research Center, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Brunschwig
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA. Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, CA 91125, USA. Beckman Institute and Molecular Materials Research Center, California Institute of Technology, Pasadena, CA 91125, USA. Kavli Nanoscience Institute, California Institute of Technology, Pasadena, CA 91125, USA. nslewis@caltech.edu.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Lewis