Intrinsic oxygen evolution reaction activity and stability enhancement of IrO_x electrocatalysts by microwave irradiation

A surfactant free hydrolysis approach was used to synthesize colloidal IrO_x nanoparticles, which were loaded on a high surface area carbon support to obtain IrO_x (IrO_x/C), having a mass specific oxygen evolution reaction (OER) activity ∼ 5 times higher than that of unsupported IrO₂, a benchmark commercial OER electrocatalyst. The synthesized IrO_x/C and the unsupported IrO₂ were then treated under microwave (MW) irradiation and their electrocatalytic activity and stability towards OER in acidic media was investigated. For both electrocatalysts, the microwave treatment improved the mass specific OER activity and enhanced the durability, with no apparent increase in the IrO_x nanoparticle size, demonstrated in a potentiodynamic accelerated stress test (AST). Surface chemical state studies of the as-synthesized and MW-treated IrO_x/C samples suggest increased Ir-O-Ir bonding on expense of the Ir-OH bonding through MWI. Further, using X-ray pair distribution function (PDF) analysis it was suggested that the MW treated IrO_x/C leads to a gradual change in the local coordination from a rutile-like structure to a highly OER active hollandite-like structure. The presented OER catalyst synthesis route and microwave irradiation approach may be put to use as a scalable method for the stability enhancement of the IrO_x electrocatalysts for acidic water electrolysis.