Microdroplet-confined oxygen reduction forms highly active transition metal alloy hydroxides at low overpotentials for oxygen evolution

Abstract

The oxygen evolution reaction plays a key role in many modern energy conversion and storage devices, making the development of catalysts for the reaction of utmost importance. Transition metal hydroxides represent a promising category of oxygen evolution catalysts in alkaline environments, due to the affordability and abundance of material, high activity and good stability. However, precipitation of these catalysts directly on electrode surfaces can be energy intensive, requiring high overpotentials. In this work, we present a new method of electrodeposition using the confined environment of aqueous microdroplets adsorbed on an electrode to produce a high pH through heterogeneous reduction of solvated oxygen, O₂. Using O₂ reduction in this manner requires less cathodic applied potentials compared to other electrodeposition techniques and avoids direct metal reduction. Additionally, this methodology allows for the precipitation of a wide variety of stoichiometrically controlled transition metal hydroxides by only changing the starting metal precursor salts. Through this method, we precipitate a variety of transition metal hydroxides ranging from monometallic to penta-metallic alloys and analyze their morphology, composition and catalytic performance toward oxygen evolution. Overall, this work presents a new, facile method to be used toward electrodepositing a range of highly desirable transition metal hydroxide catalysts.