Electrochemically Modeling a Nonelectrochemical System: Hydrogen Peroxide Direct Synthesis on Palladium Catalysts.

Nonelectrochemical hydrogen peroxide direct synthesis (HPDS) under ambient conditions is an environmentally benign and energy-efficient process that produces a green oxidizer, yet the reaction mechanism of HPDS is still controversial. Inspired by the recently suggested heterolytic mechanism that involves electron and proton transfer at Pd catalysts, we propose a new electrochemical density functional theory (DFT) model that combines the Butler-Volmer equation and constant-potential DFT with hybrid explicit-implicit solvent treatment. Application of this model to Pd surfaces showed that the heterolytic mechanism has a lower barrier for the protonation steps for H2O2 production than for the nonelectrochemical hydrogenation steps, leading to advantageous kinetics for H2O2 production over H2O production, while the conventionally accepted Langmuir-Hinshelwood mechanism fails to explain the experimental kinetics. This work resolves the unanswered discrepancies between previous experimental and DFT results, and we expect that these results will readily help the systematic development of improved catalysts for HPDS.