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

5 years ago

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

Ryan T. Pekarek, Gerard M. Carroll, Nathan R. Neale, Jao van de Lagemaat, Steven T. Christensen, Nicholas C. Anderson

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 TiO₂- 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.

Publisher URL: http://dx.doi.org/10.1021/acs.jpclett.7b01311

DOI: 10.1021/acs.jpclett.7b01311