Operando XAS of FexNi100-xOy electrocatalysts for the oxygen evolution reaction reveals dynamic Fe and Ni chemistry

by Acharya, Prashant; Manso, Ryan; Hoffman, Adam S.; Hong, Jiyun; Bare, Simon; Chen, Jingyi; Greenlee, Lauren Fay

FexNi100-xOy electrocatalysts have become a focus for alk. water electrolysis and the oxidative half reaction of oxygen evolution. Under alk. conditions, the oxygen evolution reaction (OER) can be promoted by non-precious metal oxide and hydroxide electrocatalysts. In particular, electrocatalyst compositions from first row late transition metals such as iron, nickel, manganese, and cobalt have emerged as some of the most active catalysts for the OER, and the role of iron has been identified as key within multi-metallic compositions In our research, we have focused specifically on the iron-nickel bimetallic composition and have developed synthesis methods to be able to control the bimetallic composition, surface chem., and three-dimensional morphol. of a suite of FexNi100-xOy nanoparticle electrocatalysts. With this subset of highly-active FexNi100-xOy nanoparticle electrocatalysts, we have recently been focused on ex situ and operando x-ray absorption spectroscopy (XAS) studies to understand how the chem. of the iron and nickel species within these nanocatalysts changes as a result of exposure to the electrochem. environment. This talk will focus on a set of operando data obtained with a quick scan detector at beamline 9-3 at SSRL, where we were able to capture dynamic changes to both nickel and iron chem. as a function of applied voltage in the Faradaic region of the OER. An interpretation of the data will be presented in terms of how the chem. of the nickel and iron species are changing in the electrocatalyst and implications for how we understand the active structure of FexNi100-xOy materials during the OER.