Ternary Alloy Cu–Ru–Ir Nanocages for Acidic Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a key process for renewable energy technologies, but the design of economical electrocatalysts that are robust in acidic media over long lifecycles is an unsolved issue. Here, we report an example of trimetallic (i.e., ternary) Cu_xRu_yIr_z alloys with tunable compositions, prepared as nanocages (NCs) with 10-11.5 nm diameters. The Cu_xRu_yIr_z NCs were prepared using 10.3 ± 1.5 nm Cu cuboctahedral nanoparticles (NPs) as sacrificial cores for the subsequent overgrowth of Ru-Ir alloy shells, with average thicknesses of 4-5 atomic overlayers. Cu@Ru_yIr_z core-shell NPs were then subjected to chemical etching in 3.0 M HCl at 60 °C, which completely removed the Cu cores, leaving behind hollow NC structures with high surface area-to-volume ratios. Importantly, the Cu etching process resulted in the inclusion of Cu atoms into the Ru-Ir shells, directly forming ternary Cu-Ru-Ir alloys in which the Cu:Ru/Ir ratio was controllable by etching time. Composition tunability was explored across a wide range of Cu, Ru, and Ir ratios. Electrochemical measurements of various Cu_xRu_yIr_z NCs in 0.1 M HClO₄ revealed that the OER activity is highly sensitive to the amount of Cu in the ternary alloys. Cu₁₀Ru₁₉Ir₇₁ NCs were the most active OER catalysts, requiring a low overpotential of 255 mV to achieve a current density of 10 mA cm^-2. The NC structures were unchanged postcatalysis. Compared to that of conventional Ru-Ir binary alloys, the enhancement of the OER activity in Cu_xRu_yIr_z NCs underlines the important role played by Cu in modifying the electronic properties of the ternary alloy.