Ultrahigh yield of hydrogen peroxide and effective diclofenac degradation on a graphite felt cathode loaded with CNTs and carbon black: an electro-generation mechanism and a degradation pathway

Abstract

A new graphite felt cathode loaded with carbon nanotubes (CNTs) was developed. The resulting electrode showed a very high generation rate of H₂O₂ (10.73 mg h⁻¹ cm⁻²) at a relatively low electric energy consumption (6.90 kW h kg⁻¹). These features improved the in situ production of H₂O₂ by about 20 folds when an optimized ratio of CNTs to carbon black mass (3 : 2) was used. Several manufacturing parameters like the ratio and loads of CNTs were optimized. Also, factors influencing the electro-generated H₂O₂, such as pH and current density, were investigated. Examination of H₂O₂ electro-generation mechanisms indicated that some cathode features would accelerate the oxygen reduction reaction (ORR) activity and enhance the electrochemical behavior during H₂O₂ production. The removal rate of diclofenac by electro-Fenton (EF) using a CNT loaded cathode reached over 99% within 30 min. The total organic carbon (TOC) removal of diclofenac approached 91.71% at 180 min, which was over 4 folds higher than that obtained with the unloaded electrode (19.05%). LC-MS analyses allowed building a possible mechanism and a degradation pathway of diclofenac. In terms of stability, the CNT loaded electrode revealed excellent stability as the removal of TOC was maintained at 87.4% of the original response after ten runs. Such CNT loaded cathodes with efficient and significantly enhanced H₂O₂ production offer efficient and low energy consumption degradation of organic pollutants by EF.