Unifying Concepts in Electro- and Thermocatalysis Towards Hydrogen Peroxide Production

The direct synthesis of H₂O₂ from H₂ and O₂ gas shows many mechanistic similarities to the hydrogen oxidation (HOR) and oxygen reduction reactions (ORR). In each system, water facilitates proton-electron transfer reactions between H*- and O₂*-derived intermediates on metal nanoparticle catalysts. Consequently, these materials should show similar rates and selectivities of H₂O₂ formation if they operate at equivalent electrochemical potentials, determined by the reactant activities, electrode potential, and temperature.

We test this hypothesis by comparing the kinetic parameters measured independently within a fixed-bed reactor and a rotating ring-disk electrode upon twelve mono- and bimetallic nanoparticle catalysts (e.g., Pt, Pd, Au). Under direct synthesis conditions, the balanced rates of the HOR and ORR result in an operating current during H₂O₂ formation, causing the metal to develop a potential. We modeled this system by treating each nanoparticle as a short-circuited electrochemical cell, which sets the rates of the HOR and ORR equal at any given combination of H₂ and O₂ pressures. Thus, Butler-Volmer analysis of electrochemical rate constants and transfer coefficients allows for predictions of the metal's operating potential during direct synthesis reactions. We compared these predictions to empirical measurements of the operating potential measured using a pressurized electrochemical cell held at equivalent H₂ and O₂ pressures used during thermochemical reactor measurements.

Comparisons of the predicted and measured operating potential of the twelve materials show good agreement across a 300 mV, supporting the validity of this model. H₂O₂ selectivities under thermocatalytic and electrocatalytic conditions also correlate across all catalysts at equivalent electrochemical potentials. Overall, this interdisciplinary approach provides quantitative relationships that present opportunities to optimize reaction conditions and design new materials that show significantly improved H₂O₂ formation rates and selectivities.