Making cathode composites more efficient for electro-fenton and bio-electro-fenton systems: A review

Electro-Fenton (E-Fenton) and Bio-Electro-Fenton (BEF) technologies have been proved to be efficient in undegradable pollutants purification. However, various limitations, such as stringent pH control, excessive iron-producing sludge, and poor stabilities, are always the key issues that prevent E-Fenton and BEF systems from being widely deployed in environmental remediation. As a result, various studies have been done to solve these drawbacks and this review focuses on the critical issue of cathode composites. First, the hotspots and research fronts of E-Fenton and BEF technologies were revealed by the keyword clusters obtained by CiteSpace software, and then the main influencing parameters shared by E-Fenton and BEF systems were analyzed. In view of the above results, the composite composition was divided into two parts: substrate materials and heterogeneous Fenton/Fenton-like catalysts. Following that, the mechanisms and improved methods of oxygen reduction electrocatalysis materials (e.g., surface functional groups, heteroatom doping) as well as advances in heterogeneous Fenton/Fenton-like in E-Fenton and BEF systems are summarized, with a view to developing effective cathode composites. Finally, the state development status and prospects of cathode composites are investigated in the hope that they will be useful in the future development of E-Fenton and BEF processes.