Operando X-Ray Photoelectron Spectroscopy Studies of Aqueous Electrocatalytic Systems

Development of efficient fuel cell and electrochemical cell devices to retrieve energy in a renewable manner lies in the molecular level understanding of the conversion processes taking place at surfaces and interfaces. These processes involve complicated bond breaking and formation at the surfaces as well as charge transfer through interfaces which are challenging to track under operational conditions. We address the nature of these interfacial processes using ambient pressure X-ray photoelectron spectroscopy by leveraging both its chemical and surface sensitivity. Herein, we give several examples of fuel cell and electrolysis reactions to demonstrate the importance of probing the surface under operating conditions. Oxygen reduction reaction taking place on the platinum cathode in proton exchange membrane fuel cells, water splitting reactions including oxygen evolution reaction over IrO2 and hydrogen evolution reaction over MoSx reveal that different species dominate on the surface under different operational conditions and surface activities are directly related to the stabilities of those intermediate species and possible structural rearrangements of the catalyst material.