OER Activity of Iridium Nanoparticle Catalysts By RDE and Comparison with MEAs

Abstract

To accelerate the deployment of green hydrogen, lowering the cost of water electrolyzer is one of the important issues. Iridium anode catalyst is a key material for highly efficient and stable operation of proton exchange membrane (PEM) water electrolyzer, however, limited resources of iridium lead to higher cost and the limited availability. Therefore, there is a strong need to develop novel catalysts that can reduce iridium usage without compromising on activity. Rotating electrode half-cell is a useful technique for OER activity measurement of anode catalysts [1], however broader consensus about the activity measurement protocol is still missing. In addition, it is also unclear whether the measured activity values from the RDE are consistent with those of the MEA. The RDE activity is influenced by various measurement parameters; catalyst loading on the disk electrode, ionomer content, electrolyte conductivity, potential range etc. Here, we demonstrate the impact of these RDE parameters on the measured OER activity using various iridium catalysts [2]. The OER activity was evaluated by linear sweep voltammogram at a scan rate of 1 mV sec-1 and a disk rotation rate of 3,600 rpm to minimize the contribution of capacitive current and mass transfer loss due to O2 bubbles. Too much catalyst loading on the disk electrode leads to a decrease in apparent OER activity, so that catalyst loading should be in the range where the catalyst activity is independent of the loading amount. Electrolyte solution was also found to have a significant effect on OER activity; comparing to the activity in perchloric acid solution (0.1 M HClO4), sulfuric acid solution (0.05 M H2SO4) and phosphoric acid (0.1 M H3PO4) showed 60% and 40% activity, respectively. To verify the obtained values of OER activity by RDE at the optimized condition, the OER activities were also determined by MEAs at corresponding conditions. The OER activities of MEA and RDE were found to be approximately the same regardless of catalyst species. Detailed measurement conditions and results will be discussed at the Meeting. References S. M. Alia, G. C. Anderson, J. Electrochem. Soc., 166 (2019) F282. T. Ioroi, T. Nagai, Z. Siroma, K. Yasuda, Int. J. Hydrogen Energy, 47 (2022) 38506.