Structure–property relationships describing the buried interface between silicon oxide overlayers and electrocatalytic platinum thin films

Abstract

Encapsulation of an active electrocatalyst with a permeable overlayer is an attractive approach to simultaneously enhance its stability, activity, and selectivity. However, the structure–property relationships that govern the performance of encapsulated electrocatalysts are poorly understood, especially those describing the electrocatalytic behavior of the buried interface between the overlayer and active electrocatalyst. Using planar silicon oxide (SiO_x)-encapsulated platinum (Pt)/titanium (Ti) bilayer thin films as model electrodes, the present study investigates the physical and electrochemical properties of the SiO_x|Pt buried interface. Through a combination of X-ray photoelectron spectroscopy and electroanalytical measurements, it is revealed that a platinum oxide (PtO_x) interlayer can exist between the SiO_x overlayer and Pt thin film. The thickness and properties of the PtO_x interlayer can be altered by modifying (i) the thickness of the SiO_x overlayer or (ii) the thickness of the Pt layer, which may expose the buried interface to oxophilic Ti. Importantly, SiO_x|Pt electrodes based on ultrathin Pt/Ti bilayers possess thinner PtO_x interlayers while exhibiting reduced permeabilities for Cu²⁺ and H⁺ and enhanced stability during cycling in 0.5 M H₂SO₄. These findings highlight the tunability of buried interfaces while providing new insights that are needed to guide the design of complex electrocatalysts that contain them.