Challenges and Progress in Membranes, Catalysts, and Meas for PEM Water Electrolysis
ITM Power is at the very heart of the initiatives and programmes to adopt hydrogen technology that will reduce both carbon footprints and energy costs. Using its technology and knowhow, ITM is aiming to be the world leading supplier of both infrastructure for the production of green hydrogen transport fuel, and products for the generation and storage of hydrogen fuel from internittent renewable energy sources.
Despite having a number of electrolyser products on the market, ITM Power have an active PEM electrolyser research and development programme aimed at the next generation of electrolysers. Some of the electrochemical and materials challenges faced by both ITM and the industry will be presented along with recent results, examples given below.
PEM electrolysers have a lifetime of 5-10 years; as such there is difficulty in getting new materials to market. ITM along with the National Physical Laboratory have used a novel in-situ reference electrode to help understand catalyst degradation within the cell. This approach enables separation of the relative contributions of anode and cathode to the overall reaction. During shut down periods it was observed for the first time that the cathode contributes more to changes in the open circuit voltage. This knowledge has been used to show that the majority of the degradation is occurring on the cathode catalyst, which is in contrast to the perceived thought which assumes the anode degrades faster. Changes in the electrochemically active surface area of the platinum cathode as a result of potential cycling were determined in-situ via hydrogen underpotential cyclic voltammetry. Scanning electron microscopy and X-ray tomography were used to correlate changes in catalyst morphology with performance degradation of both carbon-supported and unsupported platinum catalysts. These experiments have led to the development of accelerated stress tests, based on cycling of the electrode potential, for PEM electrolyser catalysts.
In addition ITM have made progress in the development of new membranes for PEM electrolysis. ITM’s approach to membrane development is the UV polymerisation of low cost hydrocarbon monomers. A new highly conductive membrane has been developed and tested to 3 A∙cm-2. This membrane is 125 um thick to minimise hydrogen crossover, has a conductivity of 260 mS∙cm-1 and is extremely low cost. When made into a MEA, this membrane allows a voltage of below 1.6 V at 1 A∙cm-2 at only 55°C. This has been benchmarked against Nafion(R)115.