Enhanced Activity and Durability of Ir Single Atom Catalyst for Electrocatalytic Oxygen Evolution Reaction Through Synergistic Electronic Coupling with Co3O4 Matrix

Abstract

Single atom catalysts (SACs), owing to their high activity, selectivity, and 100 % atom utilization properties, show a great potential for heterogeneous catalysis. However, it is still a challenge to synthesize SACs because of their poor stability and tendency to aggregate. In this regard, we propose an approach to synthesize a stable Ir single atom catalyst on Co3O4 substrate using hydrothermal technique followed by calcination. The XAS and XPS analysis reveals the strong electronic coupling between the Ir SAC and support matrix, that stabilizes the single atoms via formation of Ir-O and Ir-Co bond pairs. The strong electronic interaction results into enhanced density of unoccupied d-orbitals of Ir single atoms, and higher valance state of Co atoms, both synergistically improved the electrocatalytic activity. HAADF-STEM images confirm the isolated homogenous distribution of Ir single atoms on the Co3O4 matrix. The synthesized catalyst, IrSAC-Co3O4 shows improved activity for electrocatalytic oxygen evolution reaction (OER) in 1 M KOH, with an overpotential of 270 mV, and a Tafel slope value of 76 mV/dec. IrSAC-Co3O4 catalyst exhibits high electrocatalytic durability up to 96 hours at an elevated current density of 130 mA/cm2, demonstrates robust electronic interaction of single atoms with the support matrix, that prevents the aggregation of single atom. Post-electrocatalytic XPS analysis reveals no substantial change in the valence state, which can be further accredited to the electronic coupling between the support and single atom. DFT finding demonstrates that the presence of Ir single atom promotes the OER kinetics by stabilizing the key reaction intermediates and lowering the overpotential of rate determining step.