A scanning probe investigation of the role of surface motifs in the behavior of p-WSe2 photocathodes

Jesus M. Velazquez; Jimmy John; Daniel V. Esposito; Adam Pieterick; Ragip Pala; Guofeng Sun; Xinghao Zhou; Zhuangqun Huang; Shane Ardo; Manuel P. Soriaga; Bruce S. Brunschwig; Nathan S. Lewis

doi:10.1039/C5EE02530C

A scanning probe investigation of the role of surface motifs in the behavior of p-WSe₂ photocathodes†

Jesus M. Velazquez,‡^ab Jimmy John,

‡^a Daniel V. Esposito,^cd Adam Pieterick,^be Ragip Pala,^be Guofeng Sun,^b Xinghao Zhou,^be Zhuangqun Huang,^f Shane Ardo,^g Manuel P. Soriaga,^b Bruce S. Brunschwig^bh and Nathan S. Lewis*^abhi

Author affiliations

* Corresponding authors

^a Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA

^b Joint Center for Artificial Photosynthesis, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA

^c Department of Chemical Engineering, Columbia University in the City of New York, 500 W. 120th St., New York, NY 10027, USA

^d National Institute of Standards and Technology, Materials Measurement Laboratory, 100 Bureau Drive, Gaithersburg, MD 20899-1070, USA

^e Division of Engineering and Applied Science, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA

^f Bruker Nano Surfaces, 122 Robin Hill Road, Goleta, CA 93101, USA

^g Department of Chemistry and Department of Chemical Engineering and Materials Science, University of California at Irvine, Irvine, CA 92697, USA

^h Molecular Materials Research Center, Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA

ⁱ Kavli Nanoscience Institute, California Institute of Technology, Pasadena, CA 91125, USA
E-mail: nslewis@caltech.edu

Abstract

The spatial variation in the photoelectrochemical performance for the reduction of an aqueous one-electron redox couple, Ru(NH₃)₆^3+/2+, and for the evolution of H₂(g) from 0.5 M H₂SO₄(aq) at the surface of bare or Pt-decorated p-type WSe₂ photocathodes has been investigated in situ using scanning photocurrent microscopy (SPCM). The measurements revealed significant differences in the charge-collection performance (quantified by the values of external quantum yields, Φ_ext) on various macroscopic terraces. Local spectral response measurements indicated a variation in the local electronic structure among the terraces, which was consistent with a non-uniform spatial distribution of sub-band-gap states within the crystals. The photoconversion efficiencies of Pt-decorated p-WSe₂ photocathodes were greater for the evolution of H₂(g) from 0.5 M H₂SO₄ than for the reduction of Ru(NH₃)₆^3+/2+, and terraces that exhibited relatively low values of Φ_ext for the reduction of Ru(NH₃)₆^3+/2+ could in some cases yield values of Φ_ext for the evolution of H₂(g) comparable to the values of Φ_ext yielded by the highest-performing terraces. Although the spatial resolution of the techniques used in this work frequently did not result in observation of the effect of edge sites on photocurrent efficiency, some edge effects were observed in the measurements; however the observed edge effects differed among edges, and did not appear to determine the performance of the electrodes.

Energy & Environmental Science

A scanning probe investigation of the role of surface motifs in the behavior of p-WSe₂ photocathodes†

Abstract

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A scanning probe investigation of the role of surface motifs in the behavior of p-WSe₂ photocathodes

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