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

Minimizing the use of iridium (Ir)
in proton exchange membrane
water electrolyzers (PEMWEs) is essential for hydrogen production
without carbon emission. Herein, layered monoclinic iridium nickel
oxide (IrNiOx) platelets were synthesized
using the molten salt method and used for the oxygen evolution reaction
(OER) in a PEMWE. The IrNiOx hexagonal
platelets consist of the edge-sharing octahedral framework, in which
Ni atoms replace Ir sites in the crystalline lattice. Thin IrNiOx platelets exhibited high OER activity with
suppressed Ni dissolution from the bulk lattice in acidic media. When
the platelets were applied in a membrane electrode assembly (MEA),
they presented improved interconnectivity in the catalyst layer, facilitating
electron transfer. Even at a low Ir loading of 0.2 mgIr cm–2, the platelets presented good performance
with an initial cell voltage of 1.70 V at a current density of 1 A
cm–2. Despite the use of a Ti porous transport layer
(PTL) without Pt coating, the PEMWE operated stably for 150 h, exceeding
the performance achievable by commercial Ir oxide and rutile IrO2. When a Pt-coated Ti PTL was used, the PEMWE could be operated
stably for 500 h. Incorporating earth-abundant transition metals into
the Ir oxide lattice can be an effective way to minimize the use of
Ir in PEMWEs.