Shaping low-iridium IrRuOx electrocatalysts with structural and electronic modulation for proton exchange membrane electrolyzers

Abstract

Reducing iridium (Ir) loading without compromising the stability of the oxygen evolution reaction (OER) activity is essential for the sustainable deployment of proton exchange membrane (PEM) electrolyzers. One promising approach is the development of Ir-based mixed oxides, such as Ir–Ru systems, which harness synergistic effects to enhance activity and durability beyond that of IrO_x benchmarks. Here, we report a unique high-performance IrRuO_x catalyst synthesized via a straightforward solid-state molten-salt method. Structural characterization employing both synchrotron and in-house XRD revealed lattice contraction in IrRuO_x relative to IrO_x, which hinted a solid-solution formation. X-ray photoelectron spectroscopy confirmed higher oxidation states of Ru in Ir_0.25Ru_0.75O_x compared to RuO_x, which is correlated with its enhanced electrochemical performance. Electron microscopy studies showed the formation of 2D nanosheets rich in grain boundaries (GBs), which facilitate charge transport and stabilize active sites. Pair distribution function (PDF) analysis revealed the coexistence of rutile and hollandite phases, with hollandite content decreasing at higher synthesis temperatures and with increasing Ru content. As an anode in a proton exchange membrane electrolyzer, Ir_0.25Ru_0.75O_x demonstrated superior performance and delivered 1 A cm⁻² at 1.69 V with only ∼0.3 mg_Ir cm⁻²—outperforming commercial IrO₂ (1.75 V) and IrRuO_x (1.77 V) under similar conditions.