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Downsizing the materials into isolated atoms is beneficial for reducing the amount of bulk metal, which can greatly maximize the atom-utilization efficiency, leading to remarkable catalytic mass activity 30, 31, 32. Recently, the strategy of constructing highly dispersed single-sites catalysts has attracted significantly attentions for a range of electrocatalytic reactions 29. Notwithstanding these efforts to modify Co-based nanomaterials as alternative OER catalysts, it remains difficult to tip the balance between low cost and high performance. developed a catalyst with single Co atoms doped on RuO 2 sphere, yielding remarkable catalytic performances for water splitting 28. Pi and co-workers also demonstrated that IrCo bimetallic nanoclusters can be employed as efficient OER electrocatalysts 27. reported that the Sr 2CoIrO 6-δ, which benefits from a synergy between Co and Ir active sites, exhibits a low overpotential toward OER 26. One available method that has been frequently used is incorporating bulk amounts of noble metals with Co or its derivatives to obtain hybrid 3 d/4 d or 3 d/5 d nanomaterials as OER electrocatalysts 23, 24, 25. It is well known that the 4 d/5 d noble elements possess a large d-electronic wave-function spatial extent, generating versatile electronic structures via the interaction between 3 d and 4 d/5 d orbitals, which is beneficial for enhancing OER activity. Moreover, Co 3O 4 is unstable under the harsh OER conditions at the high oxidizing potential in corrosive media such as an acidic electrolyte 20, 21, 22.
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Nevertheless, Co 3O 4 still suffers from an overpotential of more than 400 mV for the OER at a current density of 10 mA cm −2, which is far from meeting the requirements for practical applications. Among all 3 d transition metal oxides, cobalt-based oxides such as spinel Co 3O 4 have been widely used to activate OER activity, as demonstrated by both experimental data and theoretical calculations 16, 17, 18, 19. As a result, the first row 3 d transition metal oxides and their derivatives, with merits of high abundance and low cost have received much attention as alternative OER candidates 11, 12, 13, 14, 15. However, their widespread applications are limited by the cost and scarcity of Ir and Ru 7, 8, 9, 10. Over the past few decades, the noble metal oxides based on iridium (Ir) and ruthenium (Ru) are considered the state-of-the-art OER electrocatalysts. Therefore, tremendous effort has been devoted to the rational design of robust electrocatalysts which improve the OER activity and energy conversion efficiency. Nevertheless, due to the sluggish kinetics of the complex four-electron transfer process, the oxygen evolution reaction (OER) at the anode side of the water electrolyzer demonstrates high overpotentials, which severely limit the overall operation efficiency and impede the large commercialization of water electrolyzers 3, 4, 5, 6. Among many H 2 production methods, water electrolysis has received much attention as a feasible technology for practical applications. Hydrogen (H 2) is considered a promising alternative energy carrier of the future owing to its high energy density and potential for carbon-free emission 2. Similar content being viewed by othersĬenturies of industrialization and human activities have consumed enormous amounts of fossil fuels, which has inevitably led to the current energy crisis and global warming 1. The present approach highlights the concept of constructing single noble metal atoms incorporated cost-effective metal oxides catalysts for practical applications. Moreover, the catalyst preparation can be easily scaled up to gram-level per batch. As a result, Ir-Co 3O 4 exhibits significantly higher mass activity and turnover frequency than those of benchmark IrO 2 in acidic conditions. Theoretical calculations further disclose the isolated Ir atoms can effectively boost the electronic conductivity and optimize the energy barrier. Operando X-ray absorption spectroscopy reveals that Ir atoms are partially oxidized to active Ir >4+ during the reaction, meanwhile Ir and Co atoms with their bridged electrophilic O ligands acting as active sites, are jointly responsible for the enhanced performance. Herein, we report on a cobalt oxide incorporated with iridium single atoms (Ir-Co 3O 4), prepared by a mechanochemical approach. Designing active and stable electrocatalysts with economic efficiency for acidic oxygen evolution reaction is essential for developing proton exchange membrane water electrolyzers.