(190d) Unifying Concepts in Electro- and Thermocatalysis Towards Hydrogen Peroxide Production | AIChE

(190d) Unifying Concepts in Electro- and Thermocatalysis Towards Hydrogen Peroxide Production


Adams, J. - Presenter, University of Illinois Urbana-Champaign
Kromer, M., University of Illinois, Urbana-Champaign
Rodríguez-López, J., University of Illinois at Urbana-Champaign
Flaherty, D., University of Illinois At Urbana-Champaign
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.