Continuum Modeling of Metal-Insulator-Semiconductor Photoelectrodes

Metal-insulator-semiconductor (MIS) photoelectrodes are commonly used in solar-to-chemical energy conversion because of their high catalytic activity and stability. The metal catalyst has lower kinetic overpotentials than the bare semiconductor surface at the same current density. An ultrathin insulator layer helps to protect the semiconductor from electrolyte corrosion and to enhance photovoltage. While previous work has explored the influence of insulator properties on photoelectrochemical (PEC) performance, there is a lack of understanding of how these properties fundamentally impact photovoltage and subsequent fuel-formation rates. Continuum modeling is uniquely suited to elucidate the phenomena leading to enhanced performance and to identify the insulator properties needed for optimal performance.

This talk will present recent continuum modeling efforts to simulate an MIS photoelectrode used for PEC hydrogen evolution. Our simulations have identified how the thickness of the insulator impacts the photovoltage. Specifically, the rise in photovoltage with insulator thickness is a consequence of the reduced electric field at the semiconductor/insulator interface, which increases the electron quasi-Fermi level. Beyond the optimal thickness, the photovoltage decreases due to a large potential drop across the insulator. Sensitivity analyses reveal the optimal band offset between the semiconductor and insulator for high reaction rates. These optimal offsets are then used to identify prospective insulators for next-generation MIS photoelectrodes that exhibit high PEC performance.