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Title: Covalent surface modification of gallium arsenide photocathodes for water splitting in highly acidic electrolyte

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. Furthermore, 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 -2 within -0.5 V of the reversible hydrogen electrode.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [3] ;  [1] ;  [2] ;  [1] ; ORCiD logo [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States); Colorado School of Mines, Golden, CO (United States)
  3. Colorado School of Mines, Golden, CO (United States)
Publication Date:
Report Number(s):
NREL/JA-5900-67024
Journal ID: ISSN 1864-5631
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
ChemSusChem
Additional Journal Information:
Journal Volume: 10; Journal Issue: 4; Journal ID: ISSN 1864-5631
Publisher:
ChemPubSoc Europe
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Office (EE-3F)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; covalent surface attachment; gallium arsenide; photoelectrochemistry; surface dipole; water splitting
OSTI Identifier:
1352131