Better Durability with Less Iridium: Control of the Crystal Phase of Iridium–Ruthenium–Manganese Electrocatalysts for Oxygen Evolution Reaction Performance

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This paper presents a study of designing phase-specific and -mixed Ir–Ru–Mn trimetallic electrocatalysts with enhanced performance. By changing the content of Ru, the alloy electrocatalyst evolved from a face-centered tetragonal (fct) phase to a mixture of fct and hexagonal close-packed (hcp) phases and finally to the hcp phase. Among these trimetallic systems, the hcp-phase Ir 0.23 Ru 0.20 Mn 0.57 electrocatalyst (Ru/Ir = 0.47:0.53) delivered the best performance toward the oxygen evolution reaction (OER), achieving an overpotential of 226 mV at 10 mA cm –2 and a Tafel slope of ∼46.8 mV dec –1 . Interestingly, this low-Ir hcp-phase catalyst maintained stable operation for >57 h at a current density of 100 mA cm –2 in 0.1 M HClO 4, whereas the Ir-rich fct-phase counterpart (Ir 0.35 Ru 0.07 Mn 0.58 ) degraded within 22 h under identical conditions. Potentiodynamic polarization curve study indicated that oxidative dissolution is the dominant degradation pathway, and the structural characterizations indicated that the hcp-phase alloy remained intact, while rutile-type IrRuMnO x oxide was formed for the fct-phase alloy electrocatalyst. These results underscore the effect of the crystal phase on OER durability of the electrocatalyst and point to a design strategy for improving the durability of OER electrocatalysts without increasing the Ir content.