Silicon Photoelectrode Thermodynamics and Hydrogen Evolution Kinetics Measured by Intensity-Modulated High-Frequency Resistivity Impedance Spectroscopy

Journal Article · 05 October 2017 · Journal of Physical Chemistry Letters

DOI: https://doi.org/10.1021/acs.jpclett.7b01311 · OSTI ID:1402562

Anderson, Nicholas C. ^[1]; Carroll, Gerard M. ^[1]; Pekarek, Ryan T. ^[2]; Christensen, Steven T. ^[1]; van de Lagemaat, Jao ^[1]; Neale, Nathan R.  ^[1]

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1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
2. National Renewable Energy Lab. (NREL), Golden, CO (United States); The Univ. of Texas at Austin, Austin, TX (United States)

Here, we present an impedance technique based on light intensity-modulated high-frequency resistivity (IMHFR) that provides a new way to elucidate both the thermodynamics and kinetics in complex semiconductor photoelectrodes. We apply IMHFR to probe electrode interfacial energetics on oxide-modified semiconductor surfaces frequently used to improve the stability and efficiency of photoelectrochemical water splitting systems. Combined with current density-voltage measurements, the technique quantifies the overpotential for proton reduction relative to its thermodynamic potential in Si photocathodes coated with three oxides (SiO_x, TiO₂, and Al₂O₃) and a Pt catalyst. In pH 7 electrolyte, the flatband potentials of TiO_2^- and Al₂O₃-coated Si electrodes are negative relative to samples with native SiO_x, indicating that SiO_x is a better protective layer against oxidative electrochemical corrosion than ALD-deposited crystalline TiO₂ or Al₂O₃. Adding a Pt catalyst to SiO_x/Si minimizes proton reduction overpotential losses but at the expense of a reduction in available energy characterized by a more negative flatband potential relative to catalyst-free SiO_x/Si.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1402562
• Report Number(s): NREL/JA-5900-68410
• Journal Information: Journal of Physical Chemistry Letters, Vol. 8, Issue 21; ISSN 1948-7185
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English