Experimental Activity Descriptors for Iridium-Based Catalysts for the Electrochemical Oxygen Evolution Reaction (OER)

Recent\nprogress in the activity improvement of anode catalysts\nfor acidic electrochemical water splitting is largely achieved through\nempirical studies of iridium-based bimetallic oxides. Practical, experimentally\naccessible, yet general predictors of catalytic OER activity have\nremained scarce. This study investigates iridium and iridium–nickel\nthin film model electrocatalysts for the OER and identifies a set\nof general ex situ properties that allow the reliable prediction of\ntheir OER activity. Well-defined Ir-based catalysts of various chemical\nnature and composition were synthesized by magnetron sputtering. Correlation\nof physicochemical and electrocatalytic properties revealed two experimental\nOER activity descriptors that are able to predict trends in the OER\nactivity of unknown Ir-based catalyst systems. More specifically,\nour study demonstrates that the Ir^III+- and OH-surface\nconcentration of the oxide catalyst constitute closely correlated\nand generally applicable OER activity predictors. On the basis of\nthese predictors, an experimental volcano relationship of Ir-based\nOER electrocatalysts is presented and discussed.