Enhanced Oxygen Evolution Reaction Activity of Iridium Nanostructure Supported on Mesoporous Tantalum Oxide By the SMSI Effect

Abstract

The proton exchange membrane water electrolysis (PEMWE), which transforms the surplus electric energy into a form of transportable hydrogen energy, has been attracting significant attention. PEMWE has the benefits of fast response, high current operation, and gas purity compared to alkaline water electrolysis. Thus PEMWE is more suitable for hydrogen production using fluctuated renewable energies. Since iridium oxide (IrO2) catalysts are stable and fairly active in the water oxidation reaction, researchers have been focusing on increasing the activity and stability of iridium-based catalysts while reducing Ir loading level by developing binary oxide or dispersing on metal oxides [1,2]. To replace carbon support in PEMWE anode, metal oxide supports that are stable to harsh OER conditions such as titanium, neodymium, and tantalum oxides were studied for enhancing electrical conductivity with high surface area [2,3]. In this study, mesoporous Ta2O5 with a high surface area (> 100m2/g) was synthesized through the soft-template method. The Ir nanoparticles were supported on porous Ta2O5 by the formic reduction method. The self-assembling characteristic of the reduction method is attributed to the Ir coated structure of Ta2O5. XPS analysis showed the oxidation states of Ir(0) with Ta(IV) with peak shift owing to strong metal-support interaction (SMSI). The uniform Ir dispersion on the support improved electrical conductivity and electrochemically active surface area (ECSA). The electron transfers from Ta to Ir maintained high Ir3+ composition during the OER. The improved OER activity (288 mV/cm2) and mass activity (898 A/g at 1.55 V) indicates that Ta2O5 support efficiently can reduce the Ir loading levels and it was also demonstrated in MEA performance under PEMWE conditions.