Two-step annealing synthesis of MOF-derived Cr-Co-Ru metallic oxides for improving the oxygen evolution reaction in acidic water splitting

Abstract

The development of acid-sensitive OER (Oxygen Evolution Reaction) electrocatalysts based on ruthenium oxides is a crucial step toward achieving large-scale hydrogen production in low-cost Proton Exchange Membrane (PEM) electrolyzers. However, a major challenge in this field is to overcome the tendency of ruthenium-based metal oxide dissolving in acidic environments, which affects long-term stability. In this study, we employed MIL-88B(Cr) as a precursor and used a two-step annealing method to prepare trimetallic metal oxides Cr0.5CoxRu0.5-xO2-δ. Detailed experimental measurements demonstrate that the introduction of Co reduced the volume of individual catalyst crystallites without disrupting the rutile crystal structure and inherent activity of CrO2@RuO2. Simultaneously, Co and Cr doping lowered the oxidation state of Ru within the catalyst system. Lower oxidation states of Ru are more stable during the OER reaction, ensuring the stability of this catalyst to be at least 100 hours. Furthermore, Co incorporation raises the energy required for oxygen vacancy formation, reduced the involvement of lattice oxygen, and enhanced the catalyst's activity. The catalyst Cr0.5Co0.17Ru0.33O2-δ with the best performance exhibited the overpotential of only 224 mV at 10 mA cm-2 in 0.5 M H2SO4. This study offers a viable strategy for developing highly active and stable catalysts in acidic media by controlling the electronic structure of RuO2.