Questioning the Role of Adsorbed H in H₂O₂ Decomposition on Pt(111) for the Electrocatalytic Green Fenton Process

Abstract

To overcome the limitations of traditional Fenton processes (such as narrow operating pH range and iron precipitation), an electrocatalytic green Fenton process mediated by adsorbed hydrogen (H*) was proposed. However, the role of H* in H 2 O 2 decomposition remains debated, and the solvent effects have been overlooked in previous studies. To address these gaps, we employed density functional theory (DFT) calculations combined with the blue moon ensemble (BME) method to examine how H* and H 2 O alter the free energy profiles of H 2 O 2 decomposition into hydroxyl radicals ( • OH) on Pt(111). Free energy analysis demonstrates that H 2 O 2 decomposition is exothermic in systems containing either H* or surface water, with the latter scenario being more favorable. In contrast, H* kinetically hinders the decomposition by raising the activation barrier to 0.356 eV (vs. 0.165 eV on pristine Pt( 111)), whereas the process becomes almost barrierless (0.029 eV) when water molecules are present. DFT based molecular dynamics simulations further demonstrate that in systems with coadsorbed H* and H 2 O, the water-mediated H 2 O 2 decomposition pathway dominates. Our results challenge the current understanding of H 2 O 2 decomposition pathways, revealing the critical mechanistic role of surface water and offering new insights for optimizing electrocatalytic Fenton processes.