REDUCING IRIDIUM CATALYST LOADING IN POLYMER ELECTROLYTE MEMBRANE WATER ELECTROLYSIS (PEMWE)

Rapid developments towards a hydrogen economy driven by renewable energy powered Polymer Electrolyte Membrane Water Electrolysis (PEMWE) are expected to increase demand for iridium, the catalyst used in the oxygen evolution reaction at the anode. As one of the scarcest elements in the world, iridium prices have increased sharply, causing its share in the capital expenditure of PEMWE to also increase as the technology is deployed with greater intensity. Aligned within the broader scope of a project titled “Materials for hydrogen production to lower our dependence on existing ones”, abbreviated as MATHYLDE, this thesis experimentally investigated the feasibility of using thin membranes in facilitating the operation of PEMWEs at high current densities. A commercially available Nafion® 212 membrane, 75 μm thinner than state-of-the-art membranes (i.e. Nafion® 115, 125 µm thick) with an iridium oxide catalyst loading at the anode of 3 mg/cm2, formed the investigated membrane electrode assembly (MEA). Experiments were performed at ambient pressure and operating temperatures of 60 and 80 ℃, reaching current densities up to 4 A/cm2. The overall performance of the electrolytic cell improved with temperature and when compared to the widely used Nafion® 115 membrane, the total ohmic resistance was 2-fold lower with the investigated MEA. This implied that more hydrogen could be produced with the same catalyst loading as the reduction in ohmic overpotential enabled higher current densities to be reached at a lower operating voltage. In addition to the experimentation, this study introduced a parameterised curve-fitting model based on the polarisation curves as well as a qualitative investigation of water transport in the system. Lastly, it was estimated that around 40% less iridium was used to produce 1 kW of hydrogen with Nafion® 212 compared to Nafion® 115 during the start-of-life operation of the electrolyser.