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.