title: Phosphonic Acid Modification of GaInP2 Photocathodes Toward Unbiased Photoelectrochemical Water Splitting.
abstract: The p-type semiconductor GaInP2 has a nearly ideal bandgap (∼1.83 eV) for hydrogen fuel generation by photoelectrochemical water splitting but is unable to drive this reaction because of misalignment of the semiconductor band edges with the water redox half reactions. Here, we show that attachment of an appropriate conjugated phosphonic acid to the GaInP2 electrode surface improves the band edge alignment, closer to the desired overlap with the water redox potentials. We demonstrate that this surface modification approach is able to adjust the energetic position of the band edges by as much as 0.8 eV, showing that it may be possible to engineer the energetics at the semiconductor/electrolyte interface to allow for unbiased water splitting with a single photoelectrode having a bandgap of less than 2 eV.
authors.forename: Bradley A
authors.initials: BA
authors.lastname: MacLeod
authors.forename: K Xerxes
authors.initials: KX
authors.lastname: Steirer
authors.affiliation: §Department of Materials Science and Engineering, University of Colorado, Boulder, Colorado 80309, United States.
authors.forename: James L
authors.initials: JL
authors.lastname: Young
authors.affiliation: ∥Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States.
authors.forename: Unsal
authors.initials: U
authors.lastname: Koldemir
authors.affiliation: ∥Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States.
authors.forename: Alan
authors.initials: A
authors.lastname: Sellinger
authors.forename: John A
authors.initials: JA
authors.lastname: Turner
authors.forename: Todd G
authors.initials: TG
authors.lastname: Deutsch
authors.forename: Dana C
authors.initials: DC
authors.lastname: Olson
keywords: gallium indium phosphide; phosphonic acid; photoelectrochemical cell; renewable energy; water splitting