Mesoporous IrO2 Films Templated by PEO-PB-PEO Block-Copolymers: Self-Assembly, Crystallization Behavior, and Electrocatalytic Performance

Synthesis of mesoporous iridium oxide films via soft templating and evaporation-induced self-assembly is demonstrated employing an amphiphilic triblock-copolymer PEO-PB-PEO. Films possess nanocrystalline walls and feature locally ordered pores of about 16 rim diameter. Analysis of the film properties by SEM, TEM, EDX, XPS, SAXS, XRD, and BET along the thermal treatment that succeeds dipcoating shows that the polymer template is removed by calcination between 200 and 300 degrees C, accompanied by uniaxial shrinkage of film and pore system perpendicular to the substrate. Treating the film in excess of 450 degrees C leads to further growth of crystallite size and loss of surface area progressing gradually with increasing calcination temperature. Templated IrO2 films conditioned at 450 degrees C show substantially reduced electrocatalytic overpotentials (efficiency increases) for the oxygen evolution reaction (OER) compared to those of untemplated coatings. Pore templating thus enables direct control over surface catalytic properties of iridium oxide.