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Hydrogen is one of the world's most important chemicals, with global production of about 50 billion kg/yr. Currently, hydrogen is mainly produced from fossil fuels such as natural gas and coal, producing CO 2. Water electrolysis is a promising technology for fossilfree, CO 2-free hydrogen production. Proton exchange membrane (PEM)-based water electrolysis also eliminates the need for caustic electrolyte, and has been proven at megawatt scale. However, a major cost driver is the electrode, specifically the cost of electrocatalysts used to improve the reaction efficiency, which are applied at high loadings (>3 mg/cm 2 total platinum group metal (PGM) content). Core shell catalysts have shown improved activity for hydrogen production, enabling reduced catalyst loadings, while reactive spray deposition techniques (RSDT) have been demonstrated to enable manufacture of catalyst layers more uniformly and with higher repeatability than existing techniques. Core shell catalysts have also been fabricated with RSDT for fuel cell electrodes with good performance. Manufacturing and materials need to go hand in hand in order to successfully fabricate electrodes with ultra-low catalyst loadings (<0.5 mg/cm 2 total PGM content) without significant variation in performance. This paper describes the potential for these two technologies to work together to enable low cost PEM electrolysis systems.

No abstract

Iridium oxide is one of the most common anode catalysts in commercial proton exchange membrane (PEM) electrolyzers because of its strong mix of high activity and stability under oxygen evolution reaction (OER) conditions. Unfortunately, benchmarking iridium oxide OER catalysts has proven difficult since IrO 2 cannot undergo proton underpotential deposition like platinum and other transition metal eletrocatalysts, making it difficult to estimate the electrochemically active surface area (ECSA), as well as OER specific and mass activity. In this work, we propose a method to calculate the ECSA of iridium oxide in an operating PEM electrolyzer. A universal constant, 596 (± 21) μC/cm 2 , was obtained from the correlation of pseudocapacitive charge and ECSA of iridium oxide. In the membrane electrode assembly (MEA), the calculated ECSA (1.81 (±0.065) m 2 over a 25-cm 2 geometric area) showed an iridium oxide catalyst utilization of ∼93%. Additionally, the IrO 2 OER specific and mass activities at 80 • C, 1.6 V in an operating PEM electrolyzer were 0.401 (±0.014) mA/cm 2 and 132 mA/mg, respectively.