Single-atom catalysts (SACs) have attracted tremendous research interests in various energy-related fields because of their high activity, selectivity and 100% atom utilization. However, it is still a challenge to enhance the intrinsic and specific activity of SACs. Herein, we present an approach to fabricate a high surface distribution density of iridium (Ir) SAC on nickel-iron sulfide nanosheet arrays substrate (Ir1/NFS), which delivers a high water oxidation activity. The Ir1/NFS catalyst offers a low overpotential of ~170 mV at a current density of 10 mA cm−2 and a high turnover frequency of 9.85 s−1 at an overpotential of 300 mV in 1.0 M KOH solution. At the same time, the Ir1/NFS catalyst exhibits a high stability performance, reaching a lifespan up to 350 hours at a current density of 100 mA cm−2. First-principles calculations reveal that the electronic structures of Ir atoms are significantly regulated by the sulfide substrate, endowing an energetically favorable reaction pathway. This work represents a promising strategy to fabricate high surface distribution density single-atom catalysts with high activity and durability for electrochemical water splitting.

Surface strain engineering is a promising strategy to design various electrocatalysts for sustainable energy storage and conversion. However, achieving the multifunctional activity of the catalyst via the adjustment of strain engineering remains a major challenge. Herein, an excellent trifunctional electrocatalyst (Ru/RuO 2 @NCS) is prepared by anchoring lattice mismatch strained core/shell Ru/RuO 2 nanocrystals on nitrogen-doped carbon nanosheets. Core/shell Ru/RuO 2 nanocrystals with ~5 atomic layers of RuO 2 shells eliminate the ligand effect and produce ~2% of the surface compressive strain, which can boost the trifunctional activity (oxygen evolution reaction [OER], oxygen reduction reaction [ORR], and hydrogen evolution reaction [HER]) of the catalyst. When equipped in rechargeable Zn-air batteries, the Ru/RuO 2 @NCS endows them with high power (137.1 mW cm À2 ) and energy (714.9 Wh kg Zn À1) density and excellent cycle stability.Moreover, the as-fabricated Zn-air batteries can drive a water splitting electrolyzer assembled with Ru/RuO 2 @NCS and achieve a current density of 10 mA cm À2 only requires a low potential ~1.51 V. Density functional theory calculations reveal that the compressive strained RuO 2 could reduce the reaction barrier and improve the binding of rate-determining intermediates (*OH, *O, *OOH, and *H), leading to the enhanced catalytic activity and stability. This work can provide a novel avenue for the rational design of multifunctional catalysts in future clean energy fields.

Main observation and conclusion Perovskites (Ba0.5Sr0.5)1–xCo0.8Fe0.2O3–δ (x = 0.02, 0.05, 0.1 denoted as BSCF‐0.98, BSCF‐0.95, BSCF‐0.9, respectively) with A‐site cation defects are synthesized by simple and efficient sol‐gel method and are proved to have better OER catalytic effect than the well‐known Ba0.5Sr0.5Co0.8Fe0.2O3–δ (BSCF) oxides. BSCF‐0.95 exhibits the best OER catalytic activity in the series perovskite. The current density of BSCF‐0.95 is about 56% higher than that of BSCF oxide at a potential of 1.7 V. The experimental studies have shown that compared with BSCF, BSCF‐0.95 oxide has a larger electrochemical surface area (ECSA), a higher content of O22– species related to surface oxygen vacancies, and faster charge transfer rate, which may be the factors for the enhancement of OER activity. The theoretical calculation results prove that the center positions of the O 2p‐band of perovskite with A‐site cation defects are closer to the Fermi level than BSCF oxide, which agrees with the OER performance trend of the material.

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