Efficient Formaldehyde Degradation in Electro-Fenton Systems: Modulating HER/ORR Competition on Carbon Cathodes via Hydrophobic Modification

Electro-Fenton (EF) has been proven to be an efficient method for formaldehyde degradation. Notably, the cathode in the EF system inevitably undergoes the hydrogen evolution reaction (HER) during operation. The excessive accumulation of H₂ not only creates safety hazards but also, during its generation process, occupies oxygen reduction reaction (ORR) active sites and competes with ORR for electrons, thereby severely restricting both H₂O₂ synthesis efficiency and formaldehyde degradation performance. This study fabricated a hydrophobic carbon-based cathode via a poly(tetrafluoroethylene) (PTFE) coating method, which effectively modulates the competitive reaction pathways between the HER and ORR. The cathode decreased HER dynamics by preventing H₂O attachment to the active site, opening up more sites for O₂ adsorption and ORR. Meanwhile, the suppression of HER facilitated electron transfer toward the 2e^-ORR pathway. The ideal ratio of 10% PTFE/activated-carbon was discovered by combining experimental and simulations. The optimized system was demonstrated to achieve a 50.54% reduction in H₂ accumulation, a 3.27-fold increase in the H₂O₂ production yield, and a 16.56% enhancement in formaldehyde decomposition efficiency. The process safety and catalytic selectivity were synergistically improved, resulting in a dependable solution for the safe and efficient degradation of organic contaminants.