Enhancement of oxygen reduction on a newly fabricated cathode and its application in the electro-Fenton process

Abstract High catalytic activity, energy-saving cathodes are desirable for improving the efficiency of the electro-Fenton system. Herein, carbon felt (CF) modified with graphene oxide (GO) and anthraquinone sulfonate (AQS) as a cathode was fabricated. The CF/GO/AQS cathode with excellent catalytic performance for oxygen reduction was further applied in the electro-Fenton process. Surface morphology and structural characteristics of CF/GO/AQS cathode were characterized by scanning electron microscopy (SEM), X-ray spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Rhodamine B (RhB) was applied as the target pollutant, and the decolorization rate could reach 95% within 1 h using the CF/GO/AQS cathode, which was 2.3 times higher than that of the unmodified cathode. It was attributed to the prominent capacity to accelerate oxygen reduction reaction (ORR) of CF/GO/AQS cathode. The response current of CF/GO/AQS reached −2.48 mA cm−2, which was about six times higher than that of the bare CF cathode. Electron transfer number determined by linear sweep curves on a rotating disk electrode was calculated to be 1.9–2.2, which indicated the catalytic reduction of molecular oxygen by CF/GO/AQS cathode was dominated by a two-electron reaction pathway. Quinones can catalyze the reduction of molecular oxygen to superoxide radicals. Then the formed superoxide radicals combine with protons to produce hydrogen peroxide (H2O2), which provides a new way of H2O2 generation applied in the electro-Fenton system. The TOC removal rate arrived at 89.9%, and corresponding energy consumption was 4.23 kWh kg−1. The catalytic performance of the CF/GO/AQS cathode kept almost stable after six cycles of a repeated experiment. This new CF/GO/AQS cathode can be a promising material applied in the electro-Fenton process for organic pollutant removal.