In order to enable the scale-up of the proton exchange membrane (PEM) electrolyser technology to the terawatt level, improvements in anode catalyst utilisation are necessary. State of the art PEM electrolysers typically use IrO_x to catalyse the oxygen evolution at the anode; however, further improvements in iridium utilisation need to be made without compromising performance or device lifetime. The research community has only recently started to attempt systematic benchmarking of catalyst stability. Short term electrochemical methods alone are insufficient to predict catalyst degradation; they can both underestimate and overestimate catalyst durability.

In this work, detailed methods to track trends in catalyst stability using conventional techniques such as rotating disk electrode studies are conducted and supported by complementary techniques. These complementary techniques include inductively coupled plasma – mass spectrometry to track performance and stability during accelerated stress testing. These methods were then assessed by testing a series of IrO_x nanoparticles both commercially obtained and synthesized via a variant of the Adams Fusion method[1],[2]. Catalysts synthesized via Adams Fusion method demonstrated significant increases in stability with approximately an order of magnitude difference in dissolved Ir observed between those synthesized at 400 ^oC and 500 ^oC. This correlates with change between amorphous (400 ^oC) and crystalline (500 ^oC, 600 ^oC) structure with less significant improvements in stability being seen between 500 ^oC and 600 ^oC. Increasing annealing temperature also correlated with reduced surface area and reduced activity. The comparison of different lower potential limits during stability testing also demonstrated increased dissolution upon decreasing lower potential limit. Therefore, the observations indicate that electrochemical reduction plays a large role in the heightened dissolution observed from potential cycling.

From this work, it is clear that protecting the anode catalyst from reductive conditions, that can occur during OCV, or selecting catalysts that demonstrate increased resistance to reductive cycling is key to maintaining PEM electrolyser device lifetime. Understanding further how these effects manifest in real systems is crucial for the future development of PEMWE technology. This applies both, for designing CCM level accelerated stress testing protocols and for the development of catalysts and layers that increase Ir utilisation; removing this bottleneck will bring us one step closer to terra-watt H₂ scale deployment of PEMWE technology.