Hydrous Iridium-Metal Oxide Nanoarchitectures for High Activity Oxygen Evolution Electrocatalysts

Abstract

To further the development of proton-exchange membrane (PEM) electrolyzers, oxygen evolution electrocatalysts with high activity, extended durability, and lower costs are needed. Although iridium oxide (IrOx) electrocatalysts have shown high activity and reasonable stability for the oxygen evolution reaction (OER) in acidic conditions, the high costs and limited supply of iridium have motivated our group and other groups to explore approaches that increase the activity and stability of iridium-based catalysts. We have recently demonstrated bimetallic nickel-platinum two-dimensional (2D) nanoframes that function as oxygen reduction electrocatalysts with high specific activity and improved stability.1 Using this approach, we created self-supported metallic Ni-Ir and Co-Ir alloy nanoarchitectures and evaluated their performance as oxygen evolution electrocatalysts. The Ir-M (M=Ni, Co) alloy 2D nanoframes were synthesized by thermal reduction of iridium-decorated metal hydroxide nanosheets followed by chemical leaching. The interaction of iridium with nickel and cobalt was investigated to tune the surface atomic and electronic structure and increase the OER activity. The nanoframes have a self-supported, carbon-free three-dimensional matrix that allows molecular access to the catalytically active surface sites. After electrochemical conditioning within the OER potential range, the surface is predominantly transformed from metallic to a metal oxide/hydroxide, and the metallic alloy phase is retained below the amorphous surface layer. Oxygen evolution activities were determined using rotating disk electrode configuration. The OER mass activities of hydrous iridium-metal oxide nanoarchitectures were significantly higher than those of commercial IrOx. Different temperature treatments were determined to significantly alter the atomic-level structure and influence the electrochemical activity and stability. Additional efforts are aimed at understanding the effect of altering the non-noble transition metal and treatment conditions on the structure and OER activity and stability. The ability to combine highly catalytically active surfaces within a carbon-free 3D nanoarchitecture provides the opportunity to design OER catalysts with improved activity and stability. References Godínez-Salomón, F.; Mendoza-Cruz, R; Arellano-Jimenez, M.J., Jose-Yacaman, M.; Rhodes, C.P; Metallic Two-dimensional Nanoframes: Design of Carbon-free Hierarchical Nickel-Platinum Alloy Electrocatalyst Nanoarchitecture with Enhanced Oxygen Reduction Activity and Stability, ACS Applied Materials & Interfaces, 2017, 9, 18660-18674. DOI: 10.1021/acsami.7b00043