Theoretical insights into the hydrogen peroxide oxidation and reduction reactions on low-index Pt surfaces

Hydrogen peroxide (H2O2) oxidation and reduction reactions (HPOR/HPRR) are pivotal in various innovative electrochemical energy conversion devices. A comprehensive understanding of these mechanisms is critical for catalyst design and performance improvement in these applications. In this work, we systematically investigate the HPOR/HPRR mechanisms on low-index Pt surfaces, specifically Pt(111), Pt(100) and Pt(110), through density functional theory (DFT) calculations combined with the computational hydrogen electrode (CHE) model. For HPOR, all the low-index Pt surfaces exhibit a unified potential-determining step (PDS) involving the electrochemical oxidation of hydroperoxyl intermediates (HOO*). The binding free energy of HOO* (ΔGHOO*) emerges as an activity descriptor, with Pt(110) exhibiting the highest HPOR activity. The HPRR mechanism follows a chem-electrochemical (C-EC) pathway. The rate-determining step (RDS) of HPRR is either the cleavage of the HO–OH bond (chemical) or the reduction of HO (electrochemical), depending on their respective activation energies. These activation energies are functions of the HO* binding free energy, ΔGHO*, establishing ΔGHO* as the descriptor for HPRR activity prediction. Pt(111) and Pt(100) are identified as the most active HPRR catalysts among the studied metal surfaces, although they still experience a significant overpotential. The scaling relationship between ΔGHOO* and ΔGHO* reveals a thermodynamic coupling of HPOR and HPRR, explaining their occurrence on Pt surfaces. These findings provide important insights and activity descriptors for both HPOR and HPRR, providing valuable guidance for the design of electrocatalysts in H2O2-related energy applications and fuel cells.