Mesoporous Metal Electrocatalysts for the Oxygen Evolution Reaction

Abstract

Introduction Development of anode electrocatalys for the PEM type water electrolyzer is challenging since carbon supports cannot be used in order to disperse small catalyst particles under the high potential condition over 1.5 V. Without carbon supports, electrocatalysts result in relatively low active surface area and low activity. Our group has been working on mesoporous materials for PEFC and has found that mesoporous materials can keep their porous structure even after being built into the device. Based on the similar idea used in our PEFC studies, we propose development of carbon-free mesoporous metal electrocatalysts with high active surface area to increase the efficiency of water electrolyzer cells. In this study, mesoporous platinum and iridium materials were particularly developed, and their oxygen evolution reaction (OER) activity was evaluated. Experimental method Mesoporous platinum and mesoporous iridium materials were synthesized using Pt(acac)2 or Ir(acac)3 as a metal precursor and Pluronic F127 as a surfactant. After mixing the surfactant and metal precursor, the resulting mixture was heated up under N2 or Air atmosphere to decompose Pluronic F127 and make the mesoporous structure. Their electrochemical measurements were performed using a common half-cell setup in the solution, in order to evaluate OER activity. The durability against high potential like 1.8 V was also analyzed. Results and discussion The resulting platinum and iridium materials were confirmed to have the randomly oriented porous structure constructed by aggregation of Pt and Ir/IrOx nanoparticles, respectively. The pore diameter was found mostly smaller than 100 nm. With these porous metal materials, OER activity was evaluated. Regarding platinum based materials, the initial activity resulted in the same as a standard Pt/KB electrocatalyst, TEC10E50E, even though ECSA was six times higher for Pt/KB. However, for their durability, as expected, Pt/KB lost most of OER activity owing to carbon corrosion. Consequently, carbon-free porous Pt electrocatalyst with high activity and durability was successfully prepared. Similarly, a porous iridium electrocatalyst has been prepared, and its OER activity will be discussed.