Effect of Particle Size on the Performance of IrO2 as Electrocatalyst for the Oxygen Evolution Reaction

Hydrogen is expected to play a significant role as one of the most important future energy carriers. A potential method for storing energy from renewable energy sources into hydrogen is water electrolysis producing ultrapure gases, hydrogen and oxygen. In particular, Water Proton Exchange Membrane (PEM) Electrolysers have attracted the global research interest due mainly to their high conversion efficiency compared to the conventional alkaline electrolysers and safety under operation. The main drawback is the relatively high anodic overpotential for the oxygen evolution reaction (OER), which occurs on noble metal electrodes but metal oxides like IrO2, RuO2, etc are generally more active for OER than metal electrodes. However, issues like electrocatalyst stability under continuous operation and cost minimization through reduction of the catalyst loading are of great importance for the research community. In the present study, unsupported IrO2 of various particle sizes were evaluated for the OER and as anode electrodes for PEM water electrolysis [1]. The electrocatalysts were synthesized by the modified Adams fusion method [2, 3]. Physicochemical characterization was conducted using X-ray Diffraction, BET, HighResolution TEM and XPS analyses. For the electrochemical performance of synthesized electrocatalysts in the OER, cyclic voltammetry, ac impedance spectroscopy and linear sweep voltammetry were conducted in a typical 3-cell electrode configuration, using Glassy Carbon as working electrode where the synthesized electrocatalysts were casted on, in 0.5 M H2SO4 solution [3]. The materials as anode PEM water electrolysis electrodes, were further evaluated in a typical electrolytic cell using Nafion ® 115 membrane and Pt/C as cathode electrocatalyst. The results showed that the highest conversion was achieved in the case of IrO2 with particle size close to 5 nm, although the most active for the OER (in terms of starting potential) was the one with smaller particle size, around 2 nm.