While PEM electrolyser catalyst cost may not be a significant portion of system costs¹ it does represent a bottleneck for the ability to generate TW level of H₂. This is primarily because of the reliance on IrO_x as a stable oxygen evolution catalyst in order to meet future green H₂ needs either replacement or reduction of iridium loading of at least 50 times is needed while maintaining a high level of stability². IrO_x based materials are the only oxygen evolution catalysts combining activity and stability under PEM electrolysis conditions; even so, they are insufficiently stable.

In the current work, we tailored the activity of IrOx catalysts synthesised by a variant of the Adams fusion reaction³ using decomposition of Iridium nitrate and varying temperature of synthesis to generate a series of catalysts with differing crystallinity and surface area. We benchmarked their stability using both accelerated degradation electrochemical measurements (30k cycles 1.2-1.7V_RHE @ 500 mV s^-1) and inductively coupled plasma-mass spectrometry(ICP-MS), both in rotating disk electrode(RDE) measurements and in a single cell PEM electrolyser.

We have compared several different methods for probing electrochemical surface area, including BET, double layer capacitance from cyclic voltammetry, adsorption capacitance using impedance spectroscopy and CO stripping using ultrasensitive on chip electrochemical mass spectrometry.

The results from the RDE measurements are shown in figure 1; they show that while the high surface area amorphous IrO_x catalysts demonstrate higher activity normalised to geometric area, when normalised to specific activity the difference is insignificant. In addition to electrochemical performance losses, the amorphous IrO_x shows an order of magnitude increase in iridium dissolution, determined via ICP-MS. Future studies will look at the ability to overcome the limitations of aqueous model studies for stability testing and utilising testing to select OER catalyst candidates that meet both activity and stability required for long term operation in PEM electrolyser systems.

1 L. Bertuccioli, A. Chan, D. Hart, F. Lehner, B. Madden and E. Standen, Study on development of water electrolysis in the EU, Fuel Cells and hydrogen Joint Undertaking, 2014, vol. 1.

2 P. S. Alexis Grimaud, Jan Rossmeisl, Research nees towards sustainable production of fuels and chemicals, Section 1: Water splitting and sustainable H2 Production, 2019.

3 D. F. Abbott, D. Lebedev, K. Waltar, M. Povia, M. Nachtegaal, E. Fabbri, C. Copéret and T. J. Schmidt, Chem. Mater., 2016, 28, 6591–6604.