Unveiling the synergistic effect of Cl− doping to promote formaldehyde oxidation performance of Ag for anodic hydrogen production

Abstract

Formaldehyde oxidation reaction (FOR) at low potential (−0.22 V vs. RHE) offers a promising alternative, simultaneously producing valuable formate and H₂. However, Ag-based catalysts exhibit limited FOR activity, and the low-potential pathway typically follows a kinetically constrained 1 e⁻ transfer mechanism with inherent selectivity challenges. This study introduces chloride anion-doped Ag catalysts (Cl⁻/Ag) as a novel electrocatalytic system that substantially enhances low-potential FOR performance while actively modulating the oxidation pathway. Innovatively, Cl⁻ doping achieves triple synergistic effects: (i) reducing the activation energy barrier for C–H bond cleavage to accelerate FOR kinetics, (ii) optimizing Ag's electronic structure through electron withdrawal to facilitate intermediate adsorption, and (iii) strengthening adsorbed hydrogen (*H) binding to promote the Volmer oxidation step, thereby shifting the reaction pathway. Crucially, this anion-mediated structural control demonstrates that low-potential HCHO oxidation is not restricted to the 1 e⁻ route. The Cl⁻/Ag catalyst design represents a simple yet effective strategy to overcome activity limitations in Ag-based systems and provides new mechanistic insights for engineering energy-efficient electrocatalysts that couple selective chemical synthesis with sustainable H₂ production.