Perspectives on current and future iridium demand and iridium oxide catalysts for PEM water electrolysis

Abstract

Proton exchange membrane water electrolysis (PEMWE) is projected to become a key technology to enable the decarbonisation of ‘hard to abate’ sectors of the economy. However, the technology’s reliance on iridium, one of the scarcest elements on Earth, as an oxygen evolution reaction catalyst, has led to uncertainty over whether a large-scale PEMWE industry can be realised. This work investigates the future iridium demand of the global PEMWE sector and examines how different catalyst strategies can improve iridium utilisation in the anode catalyst. Iridium utilisation targets necessary to avoid a situation where the PEMWE sector becomes limited by iridium supply are reviewed. Modelling the iridium demand of the PEMWE sector shows that iridium utilisation needs to improve by an order of magnitude by 2050 to avoid iridium supply limiting the capacity expansion. Furthermore, implementing closed-loop iridium recycling by 2035 would increase the installed capacity in 2050 by ∼2.7x compared to a scenario with no iridium recycling. If these two conditions are met, global PEMWE capacity could reach 1.3 TW by 2050 using only 20% of annual global primary iridium supply, which we consider to be realistic given future demand projections. Different types of iridium-based anode catalysts are compared in terms of iridium utilisation using membrane electrode assembly (MEA) testing data from the literature, with the order found to be supported nanoparticles ≈ extended surface structures > mixed oxides > nanoparticles. The need to place greater research focus on catalyst stability and the ability to make homogeneous catalyst layers at low iridium loadings is discussed. As a main result, it is found that a terrawatt-scale PEMWE industry can avoid being constrained by iridium supply if technological development of a similar level to that seen in PEM fuel cells and high iridium recycling rates are realised.