Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 33: Solid-Liquid Interfaces III

O 33.6: Vortrag

Dienstag, 2. April 2019, 15:15–15:30, H10

Charge transfer across the GaP(100) photoanode/electrolyte interface during direct, Au-catalysed photoelectrochemical water splitting — •waqas saddique, gerhard lilienkamp, and winfried daum — IEPT, Technical University Clausthal, Clausthal-Zellerfeld, Germany

We have developed a procedure to stabilize n-GaP(100) for operation as a photoanode in hydrochloric acid electrolytes by a thin and dense surface layer of gallium oxide. Here, we report on direct photoelectrochemical water splitting achieved with stabilized photoanodes that, in addition, were functionalized with Au nanoparticles (NPs) as catalysts for water oxidation. The pronounced peaking of the photocurrent at a potential around 0 V vs RHE points to an indirect charge transfer of holes across the semiconductor/electrolyte interface, presumably via defect or interface states with energies in the band gap of GaP. To investigate the charge transfer processes at GaP photoanodes, Nyquist plots were measured for different applied potentials by electrochemical impedance spectroscopy, and reproduced by simulations with an appropriate equivalent electrical circuit. The plots reveal minimum impedance at a potential of -0.05 V vs RHE, which coincides with the exact potential of maximum photocurrent in cyclic voltammetry. The Nyquist plots are composed of 6 (!) semi-circles, and their specific potential dependence reveals unprecedented details of a 6-step charge transfer process that includes all four steps of the water oxidation reaction. Our results highlight the favourable electrocatalytic properties of Au-NPs for all intermediate steps of the water oxidation reaction.