Potential and pH dependence of the buried interface of membrane-coated electrocatalysts

TL;DR

This study develops a first principles formalism to understand how silica membranes interact with platinum electrocatalysts under different pH and potential conditions, revealing how the buried interface influences catalytic activity.

Contribution

It introduces a generalized Pourbaix diagram approach for electrochemical solid-solid interfaces, elucidating membrane-metal interactions and their dependence on electrochemical environment.

Findings

Membrane termination varies with pH and potential.

Adhesion strength and membrane detachment energy depend on electrochemical conditions.

Charge transfer affects Pt surface d-band states and catalytic activity.

Abstract

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 SiO$_2$ membrane and the 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 the 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 the SiO$_2$ 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.