Potential and pH Dependence of the Buried Interface of Membrane-Coated Electrocatalysts

Semipermeable silica membranes are attractive as protective coatings for metal electrocatalysts such as platinum, but their impact on the catalytic properties has not been fully understood. Here, we develop a first-principles formalism to investigate how silica membranes interact with the surface of platinum metal electrocatalysts to develop a better understanding of the membrane–metal interplay. By generalizing the concept of Pourbaix diagrams to electrochemical solid–solid interfaces, we establish which bonds are formed between the SiO2 membrane and Pt(111) surface in aqueous electrolytes for different pH values and potential biases. We find that the membrane termination changes as a function of the pH and potential, which affects the adhesion strength and the energy requirements for partial membrane detachment, controlling the Pt surface area that is accessible for reactant species. The charge transfer between the Pt surface and SiO2 membrane is also pH- and potential-dependent and results in changes of the Pt surface d-band states, which are known to correlate with catalytic activity. Our analysis reveals the complex response of a buried interface to the electrochemical environment and identifies trends that are expected to apply also to other membrane-coated electrocatalysts.