![]() When evaluated in the three-phase-flow cell, a H 2O 2 production rate of 9.68 mol g −1 h −1 is achieved at the current density of 100 mA cm −2. ![]() The partial current density for H 2O 2 production (iH 2O 2), a criterion for evaluating the H 2O 2 productivity, is as high as 1.92 mA cm −2 at 0.65 V for the CoIn-N-C DAC. Electrochemical kinetics analysis demonstrates that the rate constant of ORR via 2e pathway is a magnitude higher than that via 4e pathway on CoIn-N-C, leading to a H 2O 2 yield of >90% in a wide potential range. This moderate adsorption of OOH grants CoIn-N-C the favorable 2e-ORR kinetics, reaching the apex of the volcano-type plot between predicted activity and OOH adsorption energy. The density function theory (DFT) calculations reveal that the valance electron number, as well as the d-band center of Co 3d orbital, can be regulated by OH-blocked In, which optimizes the bonding of key OOH intermediate on Co. Herein, a CoIn-N-C dual-atom catalyst (DAC) is proposed as an effective 2e-ORR catalyst for H 2O 2 production in acid media. In comparison with SACs, the neighboring metal pairs within a short range in dual-atom catalysts (DACs) enable more possibilities of tuning the adsorption properties of reaction intermediates 23, 24, 25, and might provide an effective method of boosting the 2e-ORR activity and selectivity. Moreover, the acidic ORR on SACs often follows the four-electron pathway 19, 20, 21, 22. Unfortunately, the acidic 2e-ORR kinetics on SACs is far slower than that in alkaline solution, despite the optimization of various metal coordination configurations 11, 18. ![]() Inspired by these studies, a few attempts have thus been made to catalyze the 2e-ORR using SACs in acid media. Recently, single-atom catalysts (SACs) have shown excellent 2e-ORR activity and selectivity in alkaline media, mainly due to their atomically dispersed metal centers such as Ni, Co, Pt, Pd, and Mo 11, 12, 13, 14, 15, 16, 17. Moreover, increasing polarization of the cathode catalysts even worsens their selectivity to H 2O 2, further lowering the overall energy conversion efficiency of H 2O 2 electrolyzers 5. However, the present developed catalysts, including the precious metal catalysts such as PtHg/PtAu alloys and the non-precious metal carbon-based catalysts, cannot achieve satisfying activity and selectivity for the acidic 2e-ORR 8, 9, 10. The catalysts with high activity and H 2O 2 selectivity enable a large H 2O 2 production rate at a minimum overpotential, which is critical to the practical application of acidic H 2O 2 electrolyzers 6, 7, 8. The energy conversion efficiency of acidic H 2O 2 electrolyzers is mainly determined by the cathodic 2e-ORR catalysts. In particular, the electrochemical H 2O 2 production in acid media is the most desirable because H 2O 2 is stable and more oxidative in the low pH region 5. The electrochemical two-electron oxygen reduction reaction (2e-ORR) marks a promising route for clean H 2O 2 production, due to its mild aqueous condition and capability of being powered by green electricity, which is completely compatible with the sustainable economy. Nevertheless, the traditional anthraquinone-based methods for H 2O 2 production are energy intensive, and are not environmental-friendly as a large amount of toxic organic solvents are required 4, 5. Hydrogen peroxide (H 2O 2) is an important green oxidant with wide range applications in both industries and household scenarios, including pulp/textile bleaching, waste-water treatment, chemical synthesis and disinfection 1, 2, 3. This work provides inspiring insights into the rational design of active catalysts for H 2O 2 production and other catalytic systems. Additionally, the CoIn-N-C presents excellent stability during the long-term operation, verifying the practicability of the CoIn-N-C catalyst. The H 2O 2 partial current density reaches 1.92 mA cm −2 at 0.65 V in the rotating ring-disk electrode test, while the H 2O 2 production rate is as high as 9.68 mol g −1 h −1 in the three-phase flow cell. As a result, the oxygen reduction on Co atoms shifts to two-electron pathway for efficient H 2O 2 production in acid. Herein, both density function theory calculation and in-situ characterization demonstrate that in dual-atom CoIn catalyst, O-affinitive In atom triggers the favorable and stable adsorption of hydroxyl, which effectively optimizes the adsorption of OOH on neighboring Co. The two-electron oxygen reduction reaction in acid is highly attractive to produce H 2O 2, a commodity chemical vital in various industry and household scenarios, which is still hindered by the sluggish reaction kinetics.
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