(Invited) Ambient Pressure X-Ray Photoelectron Spectroscopy of Electrochemical Systems

Abstract

Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) enables investigation of surfaces and interfaces under in-situ and in-operando conditions providing improved fundamental understanding of the physicochemical processes that occur during industrially relevant catalytic reactions and operation of electrochemical devices.1–4 Combining traditional ex situ characterization methods, performance testing, and in-situ diagnostics with AP-XPS studies yields a more comprehensive understanding of both catalyst and electrode properties, and their evolution during operation of electrochemical devices. While many AP-XPS studies of electrocatalytically active materials focus on thin films or other model/well-studied materials,5 it is critical to investigate more complex systems.6 This is particularly important to advance the understanding of surfaces and interfaces in low temperature polymer electrolyte membrane devices, such as electrolyzers and fuel cells. In these systems, multiple interfaces exist between the catalyst, support, ionomer, and other additives, in addition to the presence of gas reactant(s). Studies of such complex systems necessitate holistic approaches to data analysis in conjunction with multi-technique studies. Progress has been made on this front,7 however there are still many additional experimental and analytical considerations. This talk will discuss a variety of challenges in collecting and analyzing AP-XPS data towards the goal of better understanding gas-solid interfaces in electrochemical devices. This includes sample preparation and necessary processing steps prior to XPS measurements, conditions during XPS data acquisition, and approaches to data analysis of these complex systems. Additional considerations for experiments on electrodes/composites, as opposed to just a catalyst material will be discussed. (1) Bluhm, H.; Hävecker, M.; Knop-Gericke, A.; Kiskinova, M.; Schlögl, R.; Salmeron, M. In Situ X-Ray Photoelectron Spectroscopy Studies of Gas-Solid Interfaces at near-Ambient Conditions. MRS Bull. 2007, 32 (12), 1022–1030. (2) Crumlin, E. J.; Bluhm, H.; Liu, Z. In Situ Investigation of Electrochemical Devices Using Ambient Pressure Photoelectron Spectroscopy. J. Electron Spectros. Relat. Phenomena 2013, 190, 84–92. (3) Starr, D. E.; Liu, Z.; Hävecker, M.; Knop-Gericke, A.; Bluhm, H. Investigation of Solid/Vapor Interfaces Using Ambient Pressure X-Ray Photoelectron Spectroscopy. Chem. Soc. Rev. 2013, 42, 5833–5857. (4) Stoerzinger, K. A.; Hong, W. T.; Crumlin, E. J.; Bluhm, H.; Shao-Horn, Y. Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy. Acc. Chem. Res. 2015, 48 (11), 2976–2983. (5) Liu, Q.; Han, Y.; Cai, J.; Crumlin, E. J.; Li, Y.; Liu, Z. CO2 Activation on Cobalt Surface in the Presence of H2O: An Ambient- Pressure X-Ray Photoelectron Spectroscopy Study. Catal. Letters 2018, 148 (6), 1686–1691. (6) Artyushkova, K.; Matanovic, I.; Halevi, B.; Atanassov, P. Oxygen Binding to Active Sites of Fe–N–C ORR Electrocatalysts Observed by Ambient-Pressure XPS. J. Phys. Chem. C 2017, 121, 2836–2843. (7) Dzara, M. J.; Artyushkova, K.; Shulda, S.; Strand, M. B.; Ngo, C.; Crumlin, E. J.; Gennett, T.; Pylypenko, S. Characterization of Complex Interactions at the Gas − Solid Interface with in Situ Spectroscopy : The Case of Nitrogen-Functionalized Carbon. J. Phys. Chem. C 2019, 123 (14), 9074–9086.