Searching for Order in Complex Electrochemical Systems: From Epitaxial Semiconductor-Electrolyte Interfaces to Liquid-Metal Electrodes

Electrochemical interfaces of semiconductors are often poorly understood on an atomistic level as their (electronic) structure can vary significantly within the accessible electrochemical parameter space. Initial corrosion of single-crystalline systems typically introduces amorphous interfaces and -phases, creating significant challenges for the correlation between experiment and electronic structure modelling based on small supercells. Quantitative access to the structure of the very solid-liquid interface in a time-resolved manner constitutes a major hurdle for the identification of hypervolumes in the experimental parameter space, where highly ordered interfaces exist. By a combination of experimental and computational reflection anisotropy spectroscopy we can gain such an access under operating conditions. Hereby, we are able to identify such high degrees of ordering at single-crystalline InP as well as epitaxial multi-junction photoelectrodes. We can then for instance identify the potentials, where surface states develop, testing the accuracy of our electronic structure models. We have also shown that this approach works for the case of battery systems, but with their more complex interphases, deriving an atomistic understanding becomes more challenging. I will conclude with an outlook on the class of liquid-metal electrocatalysts, where we are just at the beginning of our search, as even the interface stoichiometry is a (reversible) function of the applied potential.