Template synthesis of 3-DOM IrO2 powder catalysts: temperature-dependent pore structure and electrocatalytic performance

Over the past decades, a tremendous effort has been put into developing cost-effective and highly active electrocatalysts toward oxygen evolution reaction (OER) for proton exchange membrane water electrolyzer. This report explores a hard-template-assisted pyrolysis method to fabricate IrO2 electrocatalyst powders with hierarchically ordered porous structure. The effect of the calcination temperature on the pore structure and electrocatalytic property of periodically ordered macroporous IrO2 material is studied. XRD, BET, and SEM characterizations show that the templated IrO2 powders at 450 °C exhibit the honeycomb array of macropores with cross-linking mesopores on the pore walls. The calcination temperature above 450 °C will further lead to a growth of crystallite size and a loss of surface area. Once the calcination temperature exceeds 700 °C that is higher than the glass-transition temperature of the SiO2 template, the ordered porous structures of IrO2 material are prohibited from the formation. The templated IrO2 at 450 °C shows substantially reduced electrocatalytic overpotentials for the OER, i.e., the efficiency increases as compared with other samples treated at higher calcination temperatures. As compared with the untemplated IrO2 prepared by a simple pyrolysis method at 450 °C, the 3-DOM IrO2 (450 °C) exhibited more than 2 times enhancement in BET area, voltammetric charges, and OER activity. It clearly reveals the control effect of the pore structure on the surface catalytic properties of iridium oxide. The present method is effective in improving the utilization of precious metals.