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

Currently, hydrogen peroxide (H 2 O 2 ) 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-N 4 -CO, Pd-S 4 -NCO, and Pd-N 2 O 2 -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 (O 2 ) electrochemically reduced to hydrogen peroxide. Interestingly, the Pd-N 4 -CO electrocatalyst shows excellent performance for the electrocatalytic reduction of O 2 to H 2 O 2 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-N 4 -CO > Pd-N 2 O 2 -C > Pd-S 4 -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 H 2 O 2 . According to density functional theory, Pd-N 4 is the active site for selectivity toward H 2 O 2 generation. This work provides an emerging technique for designing high-performance H 2 O 2 electrosynthesis catalysts and the rational integration of several active sites for green and sustainable chemical synthesis via electrochemical processes.