Nanoporous IrO2 catalyst with Ultrahigh Specific Surface Area Synthesized through an Ammoniating Method for Acidic Oxygen Evolution

Abstract

The development of highly active and stable electrocatalysts for OER is urgent due to the slow kinetics and high overpotential of oxygen evolution reaction (OER) [1]. To date, the most promising catalysts for OER are IrO2 based catalysts with ordered porous structures, where a templating method was generally used to ensure the high utilization of the catalysts. However, the synthesis route for such catalysts is generally of high technique complexation, where the templates need to be effectively removed after synthesis [2,3]. Hence, a simple template-free method that leads to the formation of highly porous IrO2 catalysts with high surface area is highly attractive. Herein, a satisfactory template-free ammoniating method was developed in which NH3 ligand was successfully kept until pyrolysis treatment, thus acting as the pore-forming agent to achieve highly porous IrO2. The specific and electrochemical surface areas of as-prepared IrO2 catalysts increased with the increasing quantity of NH3·H2O additive. Specifically, IrO2 (1:100)-450 °C catalyst synthesized with the highest ratio of NH3 ligand exhibited high specific surface area of 363.3 m2 g-1 as metal oxide. Furthermore, IrO2 (1:100)-450 °C showed remarkable electrocatalytic activity for acidic OER in the whole potential window, which can be ascribed to the high catalysts utilization. As shown in Figure 1, the over-potential for the IrO2 (1:100)-450 °C catalysts to attain current at 10 mA cm-2 was only 282 mV, which was shifted negatively by 31 mV and 46 mV in comparison to the home-made IrO2 (without NH3) and commercial IrO2 (CM) catalysts, respectively. Thus, the NH3 mediating method was found a superior method for increasing catalysts utilization, where the IrO2can be conveniently synthesized in large scale. Figure 1. CV curves (Left, the inset shows the specific surface area) and LSV curves (Right, the inset shows the TEM of IrO2 (1:100)-450°C) of IrO2 (1:100)-450°C, IrO2 (1:10)-450°C, IrO2-450°C, and IrO2(CM) catalysts. Acknowledgments This work is supported by National Basic Research Program of China (973 Program, 2012CB932800), National Natural Science Foundation of China (21433003, 21373199), the Science & Technology Research Programs of Jilin Province (20150101066JC, 20160622037JC).