Ambient Pressure XPS Study of a Ni Fe Electrocatalyst for the Oxygen Evolution Reaction
Chemical analysis of solid liquid interfaces under electrochemical conditions has recently become feasible due to the development of new synchrotron radiation techniques. Here we report the use of "tender" X ray ambient pressure X ray photoelectron spectroscopy (APXPS) to characterize a thin film of Ni Fe oxyhydroxide electrodeposited on Au as the working electrode at different applied potentials in 0.1 M KOH as the electrolyte. Our results show that the as prepared 7 nm thick Ni Fe (50% Fe) film contains Fe and Ni in both their metallic as well as oxidized states, and undergoes further oxidation when the sample is subjected to electrochemical oxidation reduction cycles. Metallic Fe is oxidized to Fe3+ and metallic Ni to Ni2+/3+ This work shows that it is possible to monitor the chemical nature of the Ni Fe catalyst as a function of potential when the corresponding current densities are small. This allows for operando measurements just above the onset of OER; however, current densities as they are desire.