Highly Active and Durable Iridium Nickel Oxide Catalyst for a Proton Exchange Membrane Water Electrolyzer with Low Iridium Loading

Minimizing iridium (Ir) usage is critical for the commercialization of proton exchange membrane water electrolyzer (PEMWE). Herein, layered monoclinic iridium nickel oxide (IrNiO x ) platelets were synthesized via a molten salt method and investigated as oxygen evolution reaction (OER) catalysts in a PEMWE. The IrNiO x hexagonal platelets feature an edge-sharing octahedral framework, in which Ni atoms partially substitute for Ir sites in the crystalline lattice. Layered monoclinic IrNiO x catalyst exhibits high OER activity while effectively suppressing Ni dissolution from the bulk lattice in acidic environments. In a membrane-electrode-assembly (MEA) condition, the unique morphology of these hexagonal platelets enhances interconnectivity within the catalyst layer, thereby promoting efficient electron transfer. Even at a low Ir loading of 0.2 mg Ir cm -2 , the platelets achieved a high performance of 1.70 V at 1 A cm -2 . Furthermore, the PEMWE exhibited stable operation for 150 h with a Ti porous transport layer (PTL) without Pt coating, outperforming commercial Ir oxide and rutile IrO 2 . When Pt-coated Ti PTL was used, the PEMWE was operated stably for 500 h. These results confirm that incorporating earth-abundant transition metals into the Ir oxide lattice is a promising strategy for reducing iridium loading in high performance PEMWEs.