(Invited) Using Ambient Pressure XPS to Probe the Solid/Gas and Solid/Liquid Interface Under in Situ and Operando Conditions

Abstract

Interfaces play an essential role in nearly all aspects of life and are critical for electrochemistry. Prof. Robert Savinell has played a pivotal interface to me in the role of mentorship in both life and electrochemistry, and I look to honor his contributions to both through this talk. Electrochemical systems ranging from high-temperature solid oxide fuel cells (SOFC) to batteries to capacitors have a wide range of important interfaces between solids, liquids, and gases, which play a pivotal role in how energy is stored, transferred, and converted. I will share the use of ambient pressure XPS (APXPS) to directly probe the solid/gas and solid/liquid electrochemical interface. APXPS is a photon-in/electron-out process that can provide both atomic concentration and chemical-specific information at pressures greater than 20 Torr. Using synchrotron X-rays at Lawrence Berkeley Nation Laboratory, the Advanced Light Source has several beamlines dedicated to APXPS endstations that are outfitted with various in situ/operando features such as heating to temperatures > 500 °C, pressures greater than 20 Torr to support solid/liquid experiments and electrical leads to support applying electrical potentials support the ability to collect XPS data of actual electrochemical devices while it's operating in near ambient pressures. This talk will introduce APXPS and provide several interface electrochemistry examples using in situ and operando APXPS, including the probing of Sr segregation on a SOFC electrode to a Pt metal electrode undergoing a water-splitting reaction to generate oxygen, the ability to measure the electrochemical double layer (EDL) to our most recent efforts to directly probe an ion exchange membranes Donnan potential. Gaining new insight to guide the design and control of future electrochemical interfaces and how Bob, electrochemistry, and I have interfaced over the years.