Processes occurring at solid-gas, solid-liquid, and solid-solid interfaces are critical to the functionality of most energy storage and conversion devices. However, surfaces and interfaces often exhibit properties that are qualitatively different from their bulk counterparts, preventing straightforward inference of their structural, chemical, and transport characteristics. Moreover, surfaces and interfaces in many operating devices tend to be highly heterogeneous, which introduces additional complexities that must be addressed by diagnostic methods. Predictive modeling based on ab initio simulations offers a unique set of tools for unbiased understanding of interfaces that can operate in tandem with high-fidelity experimental characterization. Indeed, recent advances in hardware, algorithms, and methods have significantly broadened the space of systems accessible to simulations. Nevertheless, accessing the full chemical and structural complexity of interfaces under realistic operating conditions remains a significant challenge for predictive simulations.

In this talk, I will begin by reviewing some of the key difficulties associated with predictive modeling of complex interfaces, with specific reference to solid-liquid and solid-solid interfaces in materials for photoelectrochemical water splitting. Next, I will show how ab initio molecular dynamics can be combined with advanced X-ray spectroscopy (XAS, XES, XPS) and other high-fidelity experimental probes to enable more realistic models of surfaces and interfaces in semiconductor photoelectrodes that go beyond idealized approximations. I will review our recent efforts applying this synergistic approach to study the structural, chemical, and transport properties of III/V semiconductor photoelectrodes under electrochemical and photoelectrochemical operation. I will show how theoretical modeling and experimental characterization operate hand-in-hand in this regard, with experiments aiding the validation and assembly of accurate interface models, and theory aiding the interpretation of complex spectra. The examples will specifically highlight the importance of accounting for structural and chemical changes induced by the presence of the interface under electrochemical conditions, such as surface oxidation and reconstruction, which profoundly alter photoelectrode behavior with consequences for photoelectrochemical durability and efficiency.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.