Hydrogen Evolution at the Buried Interface between Pt Thin Films and Silicon Oxide Nanomembranes

This paper reports the performance of hydrogen evolution reaction (HER) electrocatalysts based on Pt thin film electrodes that are encapsulated by silicon oxide (SiO_x) nanomembranes. This membrane-coated electrocatalyst (MCEC) architecture offers a promising approach to enhancing electrocatalyst stability while incorporating advanced catalytic functionalities such as poison resistance and tunable reaction selectivity. Herein, a room-temperature ultraviolet (UV) ozone synthesis process was used to systematically control the thickness of SiO_x overlayers with nanoscale precision and evaluate their influence on the electrochemically active surface area (ECSA) and HER performance of the underlying Pt thin films. Through detailed characterization of the physical and electrochemical properties of the SiO_x-encapsulated electrodes, it is shown that proton and H₂ transport occur primarily through the SiO_x coating such that the HER takes place at the buried Pt|SiO_x interface. Increasing the thickness of the SiO_x overlayers results in monotonic increases in the overpotential losses of the MCEC electrodes. These overpotential losses were fit using a one-dimensional diffusion model, from which the H⁺ and H₂ permeabilities through SiO_x were obtained. Importantly, the SiO_x nanomembranes were found to exhibit high selectivity for proton and H₂ transport in comparison to Cu²⁺, a model HER poison. Leveraging this property, we show that SiO_x encapsulation can enable copper-resistant operation of Pt HER electrocatalysts. It is expected that a more complete understanding of the structure-property-performance relationships of the SiO_x overlayers will enable the design of stable MCECs capable of multifunctional catalysis with minimal loss in efficiency from concentration overpotential losses associated with mass transport through SiO_x.