Enhanced activity and durability of Ir single-atom catalysts for the electrocatalytic oxygen evolution reactions through synergistic electronic coupling with Co3O4 matrix

Abstract

Single-atom catalysts (SACs), owing to their high activity, selectivity, and 100% atom economy, show great potential for heterogeneous catalysis. However, their synthesis is still a challenge because of their poor stability and low tendency to aggregate. In this regard, we propose an approach for synthesizing a stable Ir single-atom catalyst on a Co₃O₄ substrate using a hydrothermal technique followed by calcination. The XAS and XPS analyses revealed the strong electronic coupling between the Ir SAC and the support matrix, which stabilized the single atoms via the formation of Ir–O and Ir–Co bond pairs. The strong electronic interaction resulted in an enhanced density of unoccupied d-orbitals of Ir single atoms and a higher valence state of Co atoms, both of which synergistically improved the electrocatalytic activity. HAADF-STEM images confirmed the isolated homogeneous distribution of Ir single atoms on the Co₃O₄ matrix. The synthesized catalyst, Ir_SAC–Co₃O₄, showed improved activity for the electrocatalytic oxygen evolution reaction (OER) in 1 M KOH, with an overpotential of 270 mV and a Tafel slope value of 76 mV dec⁻¹. The Ir_SAC–Co₃O₄ catalyst exhibited a high electrocatalytic durability up to 96 hours at an elevated current density of 130 mA cm⁻², demonstrating the robust electronic interaction of single atoms with the support matrix, which prevented the aggregation of single atoms. Post-electrocatalytic XPS analysis revealed no substantial change in the valence state, which can be further accredited to the electronic coupling between the support and the single atom. DFT findings demonstrated that the presence of the Ir single atom promoted the OER kinetics by stabilizing the key reaction intermediates and lowering the overpotential of the rate-determining step.