Modulated Nickel Single-Atom Sites as Highly Active Catalysts for the Synthesis of Neutral H2O2 at Ampere-Level Current Densities

The versatile neutral hydrogen peroxide (H₂O₂), synthesized via electrocatalytic oxygen reduction reaction (ORR), holds significant promise for various applications. However, there have been limited reports on catalysts that operate at ampere-level current densities. The insufficient research on catalysts has hindered advancements in the 2e^- ORR. Understanding how the coordination environment of single-atom catalysts influences 2e^- ORR performance is crucial. In this study, we adjusted the adsorption energy of the reaction intermediates on nickel single-atom sites by utilizing oxygen functional groups present on carbon supports. Through a combination of comparative experiments and theoretical calculations, we demonstrated that Ni sites regulated by hydroxyl groups through direct interactions serve as excellent 2e^- ORR sites. The resulting nickel single-atom catalyst (NiTPP@CNT-ox) exhibited an impressive H₂O₂ selectivity of up to 97.0% during rotating ring-disk electrode tests conducted in a 0.1 M K₂SO₄ solution at 0.4 V (vs RHE). In a two-electrode flow cell equipped with the NiTPP@CNT-ox-loaded gas diffusion electrode, a Faradaic efficiency exceeding 92.1% was achieved at current densities ranging from 0.2 to 1 A cm^-2. Furthermore, the current density reached an unprecedented level of 1.6 A cm^-2 while maintaining a Faradaic efficiency of 86.2%. Through cyclic operation, a H₂O₂ concentration of 10.0 wt % was attained. When scaling up the electrode area to 40 cm², it is possible to obtain H₂O₂ at a concentration of 3.62 wt % directly without necessitating electrolyte recycling, thereby satisfying the concentration requirements for medical applications.