Formation of a p-n heterojunction on GaP photocathodes for H-2 production providing an open-circuit voltage of 710 mV

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Abstract

Photocatalytic water splitting for the sustainable production of hydrogen using a two-photon tandem device requires careful optimization of the semiconductors used as photon absorbers. In this work we show how the open-circuit voltage of photocathodes for the hydrogen evolution reaction based on p-GaP was increased considerably by sputtering of different n-type metal oxides on the surface and thereby forming an effective p-n heterojunction. Both n-TiO2 and n-Nb2O5 increased the V-OC of the photocathodes, with the latter giving an ultimate V-OC of 710 mV using Pt as the cocatalyst. This value is unprecedented for a p-GaP-based HER photocathode operating in an acidic electrolyte under simulated 1 Sun illumination. An additional, but highly significant benefit of a TiO2 layer is that it provides a remarkable operational stability of more than 24 h under constant operation. It was found that TiO2 and Nb2O5 overlayers, which were characterized by high donor density, caused a large built-in potential drop that is located almost exclusively in the p-type substrate. The large built-in potential drop in the GaP effectively separates charge carriers driving photogenerated electrons toward the surface of the electrode to perform the HER. According to this result, a further careful choice of materials having specific properties, such as optimal carrier concentration and band positions, could potentially increase V-OC even more, paving the way for the realization of a non-assisted two-photon solar water splitting device.
Original languageEnglish
JournalJournal of Materials Chemistry A
Volume2
Issue number19
Pages (from-to)6847-6853
ISSN2050-7488
DOIs
Publication statusPublished - 2014

Keywords

  • CHEMISTRY,
  • ENERGY
  • MATERIALS
  • DRIVEN HYDROGEN-PRODUCTION
  • ATOMIC LAYER DEPOSITION
  • VISIBLE-LIGHT-DRIVEN
  • PHOTOELECTROCHEMICAL PROPERTIES
  • WATER REDUCTION
  • SURFACTANT-FREE
  • SOLAR-CELLS
  • TIO2
  • EVOLUTION
  • PHOTOCATALYSIS

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