Comparative Study\nof Ru-Transition Metal Alloys and\nOxides as Oxygen Evolution Reaction Electrocatalysts in Alkaline Media

Abstract

The oxygen evolution reaction (OER), as the anodic reaction\nin\nwater electrolyzers, generally exhibits much higher overpotentials\nthan the hydrogen evolution reaction (HER) and thus requires the development\nof more active, robust, and stable electrocatalysts. In this work,\na series of carbon-supported Ru–M alloy nanoparticles (M =\nIr, Co, Ni, and Fe), transition metal (TM)-doped RuO₂ nanoparticles\nsuch as Ru_1–<i>x</i>Mn<i>_x</i>O₂, Ru_1–<i>x</i>Co<i>_x</i>O₂, Ru_{1–<i>x</i>–<i>y</i>}Mn<i>_x</i>Co<i>_y</i>O₂, Ru_1–<i>x</i>Fe<i>_x</i>O₂, Ru_1–<i>x</i>Ni<i>_x</i>O₂, and\nRu_1–<i>x</i>V<i>_x</i>O₂/C, as well as RuO₂, MnO₂, Co₃O₄, and Co_3–<i>x</i>Mn<i>_x</i>O₄ nanoparticles have been\nsynthesized with comparable nanoparticle sizes and compared for their\nOER intrinsic activities in alkaline media. All studied Ru–M\nalloy nanoparticles exhibited higher OER activity than pure Ru nanoparticles,\nand among them, Ru_1–<i>x</i>Ir<i>_x</i>/C (<i>x</i> = 0.3–1) catalysts\nwere found to be the most active. All studied Ru–TM oxide nanoparticles\nexhibited higher OER activity than the corresponding Ru–TM\nalloy nanoparticles with 30–50 atom % Co-doped RuO₂/C catalysts being the most active. The OER enhancement on Ru–TM\noxides is ascribed to the weaker O adsorption to their surfaces relative\nto the respective Ru–TM alloys. Small amounts of Mn (≤0.15\natom %)-doped RuO₂ nanoparticles also slightly enhanced\nthe OER kinetics. In contrast to Co and Mn, Ni-, Fe-, and V-doped\nRuO₂ nanoparticles inhibited the OER. Among Ru–TM\noxide nanoparticles, Ru_0.7Co_0.3O₂/C and Ru_0.85Mn_0.15O₂/C represent\npromising bifunctional catalysts for both the OER and oxygen reduction\nreaction (ORR).