(619e) Continuum Modeling of Metal-Insulator-Semiconductor (MIS) Photoelectrodes

Photoelectrochemical (PEC) cells have attracted considerable attention for their potential to convert solar energy into chemical bonds, thereby enabling the storage of solar energy in forms that can be transported and used on demand. A critical challenge for PEC systems is the design and fabrication of stable and active photoelectrodes that absorb light and catalyze the reaction. A promising photoelectrode architecture to meet these criteria are metal-insulator-semiconductor (MIS) systems. The ultrathin insulator layer has been shown to protect the semiconductor from corrosion by aqueous electrolytes, enabling the use of conventional, high-performing materials. Moreover, using active metal catalysts, instead of the semiconductor surface, to drive the electrochemical reactions offers lower kinetic overpotentials. While there has been work exploring the influence of MIS properties on PEC performance, there is a lack in understanding of how these properties fundamentally impact photovoltage and fuel formation rates. Continuum modeling is uniquely suited to elucidate the phenomena governing enhanced MIS performances and approaches that leverage this phenomenon for improved fuel production.

This talk will present a framework for accurately modeling MIS photoelectrodes, which is used for PEC water splitting but could be extended to any PEC reaction. Furthermore, our modeling efforts have identified that the surface quasi-fermi level of electrons drives the hydrogen evolution reaction for photocathodes. At the semiconductor surface, the quasi-fermi level of electrons bends downward because of the strong electric field and carrier concentration gradients near the MIS interface, which ultimately reduces the reaction driving force. Our work is the first to identify the mechanisms governing this bending near the MIS interface and how tuning the interfacial properties of the MIS photoelectrode can mitigate the electron quasi-fermi level bending and improve performance. Through modeling, we can understand the property-performance relationships of MIS photoelectrodes and provide guidelines to enhance PEC fuel forming rates.