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 H₂O₂ 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 H₂O alter the free energy profiles of H₂O₂ decomposition into hydroxyl radicals (˙OH) on Pt(111). Free energy analysis demonstrates that H₂O₂ 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 co-adsorbed H* and H₂O, the water-mediated H₂O₂ decomposition pathway dominates. Our results challenge the current understanding of H₂O₂ decomposition pathways, revealing the critical mechanistic role of surface water and offering new insights for optimizing electrocatalytic Fenton processes.