title: Covalent Surface Modification of Gallium Arsenide Photocathodes for Water Splitting in Highly Acidic Electrolyte.
abstract: Efficient water splitting using light as the only energy input requires stable semiconductor electrodes with favorable energetics for the water-oxidation and proton-reduction reactions. Strategies to tune electrode potentials using molecular dipoles adsorbed to the semiconductor surface have been pursued for decades but are often based on weak interactions and quickly react to desorb the molecule under conditions relevant to sustained photoelectrolysis. Here, we show that covalent attachment of fluorinated, aromatic molecules to p-GaAs(1 0 0) surfaces can be employed to tune the photocurrent onset potentials of p-GaAs(1 0 0) photocathodes and reduce the external energy required for water splitting. Results indicate that initial photocurrent onset potentials can be shifted by nearly 150 mV in pH -0.5 electrolyte under 1 Sun (1000 W m-2) illumination resulting from the covalently bound surface dipole. Though X-ray photoelectron spectroscopy analysis reveals that the covalent molecular dipole attachment is not robust under extended 50 h photoelectrolysis, the modified surface delays arsenic oxide formation that results in a p-GaAs(1 0 0) photoelectrode operating at a sustained photocurrent density of -20.5 mA cm-2within -0.5 V of the reversible hydrogen electrode.
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: Logan E
authors.initials: LE
authors.lastname: Garner
authors.affiliation: Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado, CO 80401, United States.|Current address: Department of Physics, Colorado School of Mines, Golden, Colorado, CO 80401, United States.
authors.forename: K Xerxes
authors.initials: KX
authors.lastname: Steirer
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: James L
authors.initials: JL
authors.lastname: Young
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Anderson
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: Elisa M
authors.initials: EM
authors.lastname: Miller
authors.affiliation: Department of Chemistry and Materials Science Program, Colorado School of Mines, Golden, Colorado, 80401, United States.
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Tinkham
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: Todd G
authors.initials: TG
authors.lastname: Deutsch
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.|Department of Chemistry and Materials Science Program, Colorado School of Mines, Golden, Colorado, 80401, United States.
authors.forename: Alan
authors.initials: A
authors.lastname: Sellinger
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: John A
authors.initials: JA
authors.lastname: Turner
authors.affiliation: Chemistry & Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado, 80401, United States.
authors.forename: Nathan R
authors.identifier: 0000-0001-5654-1664
authors.initials: NR
authors.lastname: Neale
mesh_terms: D000143:Acids; D001017:Aortic Coarctation; D001152:Arsenicals / Q000737:chemistry*; D055664:Electrochemical Techniques / Q000379:methods*; D004566:Electrodes; D004572:Electrolysis / Q000379:methods*; D004573:Electrolytes; D005124:Eye Abnormalities; D005708:Gallium / Q000737:chemistry*; D020752:Neurocutaneous Syndromes; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D000143:Acids; D001152:Arsenicals; D004573:Electrolytes; D014867:Water; C043055:gallium arsenide; D005708:Gallium
keywords: covalent surface attachment; gallium arsenide; photoelectrochemistry; surface dipole; water splitting