Study on the electrocatalytic reduction mechanism of PFOA degradation at gradient sulfur-doped copper sites

Per- and polyfluoroalkyl substance (PFAS) poses significant challenges for environmental remediation owing to poor degradation in terms of its extremely stable C-F bond. Herein, Cu@S/NCNT electrocatalyst was successfully synthesized by precisely regulating Cu sites of gradient Sulfur-doped, suitable for the efficient electrocatalytic reduction of Perfluorooctanoic acid (PFOA). Multimodal characterization revealed that the gradient S doping triggered in situ self-activation of Cu sites, establishing a highly reductive Cu⁰-Cu₂S active interface. It provided an ideal platform for PFOA adsorption-degradation and efficient C-F bond cleavage. Under the Cu@S/NCNT system (-1.8 V vs. Hg/HgO for 12 h), an 85.32% degradation efficiency and 76.96% defluorination efficiency were achieved with a 46.18% TOC reduction. Subsequently, the synergistic degradation mechanism "primary Cu-site-driven direct electron transfer (DET) and adsorbed hydrogen (H_ads) reduction" was elucidated through solvent effect differences in the acetonitrile/water system. LC-MS qualitative analysis was applied to elucidate the stepwise mineralization and defluorination pathway: "PFOA→PFHpA→PFHxA→PFPeA→PFBA→PFPrA→TFA→ … CO₂". This study provides an innovative electrocatalyst design concept for PFOA electrocatalytic reduction, contributing to the control of PFAS pollution discharge in aquatic environments such as concentrated wastewater from chemical industrial parks.