Tubular and bio-based carbons as binder-free gas diffusion electrodes for heterogeneous electro-Fenton to remove micropollutants

Abstract

Heterogeneous electro-Fenton (HEF) coupled with anodic oxidation offers a plug-and-treat and chemical-free process over a wide range of pH values for removing recalcitrant micropollutants (MPs). This work introduces a self-standing and Fe-containing tubular carbon as a gas diffusion electrode (GDE) for HEF. Unlike planar Fe-containing carbon electrodes, as-synthesized carbons contain no fluorinated polymer as a subgroup of perfluoroalkyl and polyfluoroalkyl substances (PFAS), omitting the risk of secondary pollution due to undesired PFAS release during electrolysis. The implementation of GDE enables the increase of current densities up to 25mAcm−2, approaching relevant conditions for real-life applications. The altering pore structure on the gas channel side illustrates the possibility of minimizing GDE flooding without using hydrophobic and fluorinated polymers. GDEs without catalyst shows a specific H2O2 production rate of 3.6mgcm−2h−1 with a current efficiency of 56% at an applied current density of 8.5mAcm−2. Additionally, the Fe-containing GDE removes sulfamethoxazole (SMX) and carbamazepine (CBZ), revealing a declined degradation rate in a mixture, especially for a more recalcitrant pollutant such as CBZ. This work reveals the potential of as-synthesized self-standing tubular GDEs as PFAS-free electrodes for a decentralized and modular water treatment unit.