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 IrOx 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 IrOx nanoparticles both commercially obtained and synthesized via a variant of the Adams Fusion method. 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.
Several operando techniques are also demonstrated for investigation of the fundamental understanding of activity and stability of IrOx nanoparticle catalysts using electrochemistry mass spectrometry and optical absorption spectroscopy to probe gas phase products and reaction intermediates. The results of these studies show an optically observable species on the nanoparticle catalysts that begins to occur approximately 100 mV less positive than oxygen onset, defined as the initial potential at which evolved oxygen can be directly observed either electrochemically or via the use of in-situ techniques, and tracks into the oxygen evolving region. Additionally, the differences observed between oxygen onset observed from mass spectrometry between amorphous and crystalline catalysts track with results observed from optical signals.