A Versatile Approach to Electrochemical <i>In Situ</i> Ambient-Pressure X-ray Photoelectron Spectroscopy: Application to a Complex Model Catalyst

Abstract

We present a new technique for investigating complex model electrocatalysts by means of electrochemical <i>in situ</i> ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Using a specially designed miniature capillary device, we prepared a three-electrode electrochemical cell in a thin-layer configuration and analyzed the active electrode/electrolyte interface by using "tender" X-ray synchrotron radiation. We demonstrate the potential of this versatile method by investigating a complex model electrocatalyst. Specifically, we monitored the oxidation state of Pd nanoparticles supported on an ordered Co₃O₄(111) film on Ir(100) in an alkaline electrolyte under potential control. We found that the Pd oxide formed in the <i>in situ</i> experiment differs drastically from the one observed in an <i>ex situ</i> emersion experiment at similar potential. We attribute these differences to the decomposition of a labile palladium oxide/hydroxide species after emersion. Our experiment demonstrates the potential of our approach and the importance of electrochemical <i>in situ</i> AP-XPS for studying complex electrocatalytic interfaces.