Heteroatom-Coordinated Palladium Molecular Catalysts for Sustainable Electrochemical Production of Hydrogen Peroxide

Abstract

Currently, hydrogen peroxide (H₂O₂) manufacturing involves an energy-intensive anthraquinone technique that demands expensive solvent extraction and a multistep process with substantial energy consumption. In this work, we synthesized Pd-N₄-CO, Pd-S₄-NCO, and Pd-N₂O₂-C single-atom catalysts via an in situ synthesis approach involving heteroatom-rich ligands and activated carbon under mild reaction conditions. It reveals that palladium atoms interact strongly with heteroatom-rich ligands, which provide well-defined and uniform active sites for oxygen (O₂) electrochemically reduced to hydrogen peroxide. Interestingly, the Pd-N₄-CO electrocatalyst shows excellent performance for the electrocatalytic reduction of O₂ to H₂O₂ via a two-electron transfer process in a base electrolyte, exhibiting a negligible amount of onset overpotential and >95% selectivity within a wide range of applied potentials. The electrocatalysts based on the activity and selectivity toward 2e^- ORR follow the order Pd-N₄-CO > Pd-N₂O₂-C > Pd-S₄-NCO in agreement with the pull-push mechanism, which is the Pd center strongly coordinated with high electronegativity donor atoms (N and O atoms) and weakly coordinated with the intermediate *OOH to excellent selectivity and sustainable production of H₂O₂. According to density functional theory, Pd-N₄ is the active site for selectivity toward H₂O₂ generation. This work provides an emerging technique for designing high-performance H₂O₂ electrosynthesis catalysts and the rational integration of several active sites for green and sustainable chemical synthesis via electrochemical processes.