From Interfaces to Interphases: Revealing Complexities of Multi-Component Systems by In-Situ Force and Optical Microscopies

The classical textbook perspective of surface science considers changes that arise when an ideal bulk crystal is truncated at some specific plane. Practically relevant interfaces in batteries, electro-, photo- and conventional catalysis, and any realistic chemical conversion, however, are exposed to very complex environments involving typically fluids of multiple components and – often rather strong – external stimuli such as electrical currents, illumination, temperature and concentration gradients. This results in the formation of interfacial boundary layers controlling the performance of the system that can deviate substantially in their chemical composition, transport properties, charge distribution, etc. from the underlying bulk materials.

In this lecture, I will discuss examples of photo- and electrocatalytically active nano-particles as well as mineral surfaces that play a role in geological and  potentially future industrial CO₂ mitigation and mineral carbonation processes. Specifically, I will discuss our AFM-based methods to characterize solid-liquid interfaces from high-resolution imaging at the atomic scale to colloidal scale local charge measurements. In the first application, these techniques will be applied to characterize the local charge distribution and optical response of photocatalytically active faceted nanoparticles of SrTiO₃ and BiVO₄ in ambient electrolytes of variable composition (salt, pH). Subsequently, I will discuss the stability and dissolution of olivine and calcite in aqueous salt solutions and the role of additives and soft interfacial layers in controlling surface reactivity.