First-Principles Study of Oxygen Evolution Reaction on Ir with Different Coordination Numbers Anchoring at Specific Sites of Co 3 O 4 (111) Surface

Anchoring noble metals to non-noble metals oxide to create single-atom catalysts (SACs) was an appealing approach to improve atomic efficiency and catalyst activity with simultaneous reduction of cost. However, knowledge of how single-atom anchors at unique loading positions and varying numbers of coordination atoms behavior in oxygen evolution reaction (OER) was still inadequate. Herein, the Ir was chosen to anchor at three-fold face center cubic (FCC) hollow sites, three-fold hexagonal close packed (HCP) hollow sites, and Oxygen Vacancy (OV) sites on Co 3 O 4 (111) surface with different coordination environments by first-principles study of OER. The results displayed that the overpotential ( η ) of threefold FCC hollow sites with four coordination oxygens (FCC-4O) was 0.35 V, which was the lowest overpotential among our catalysts. The d-band center and Bader charge results demonstrated the coordination oxygen could change Ir electron structure, specifically FCC-4O, making the adsorption between the carrier and the intermediate more moderate for reducing the energy barrier of the potential-determining step. When Ir possesses five coordination oxygens, the HCP sites spontaneously transformed into the FCC sites, showing it was an unstable state. In addition, band gap studies indicated that the OV sites catalysts had a reduced band gap and stronger electron transport ability, notably for the Ir with four-coordination hydroxyl group (OV-4OH), which led to high OER performance ( η = 0.46 V). Finally, the solvation effect and kinetic stability were tested, it could be found that both FCC-4O and OV-4OH showed good OER performance, especially FCC has good stability and may be more possible in experimental conditions. Graphical Abstract The figure described volcano diagram of our catalysts and the illustration of FCC sites, HCP sites, and OV sites. FCC-4O had the best OER performance among our catalysts with η = 0.35 V.