Fenton processes allow to degrade and mineralize toxic organic contaminants, yet classical Fenton processes require continuously adding hydrogen peroxide and ferrous ions, costly solution pH adjustment, and treatment of secondary iron sludge pollution. Heterogeneous electro-Fenton processes deliver oxidizing radicals with only oxygen and electricity consumed. Bifunctional catalysts allow the synthesis and activation of hydrogen peroxide simultaneously, eliminate additional chemical reagents, and yield no metal residues in treated water. Here, we review bifunctional catalysts for heterogeneous electro-Fenton processes. We describe the mechanisms of oxidizing radical generation from oxygen. Then, we compare different types of bifunctional catalysts based on their elemental compositions: (1) metal/carbon composite catalysts, i.e., monometallic iron/carbon composite catalysts, bimetallic/trimetallic carbon composite catalysts, and transition metal single-atom catalysts; (2) metal composite catalysts without carbon; and (3) metal-free carbon catalysts. Then, we present five other approaches beyond electrocatalysts, which have been used to improve the performance of heterogeneous electro-Fenton processes.

Fenton 工艺允许降解和矿化有毒有机污染物，但经典的 Fenton 工艺需要不断添加过氧化氢和亚铁离子、昂贵的溶液 pH 值调整以及二次铁泥污染的处理。多相电-Fenton 过程提供氧化自由基，仅消耗氧气和电力。双功能催化剂允许同时合成和活化过氧化氢，消除额外的化学试剂，并且在处理过的水中不产生金属残留物。在这里，我们回顾了用于多相电芬顿过程的双功能催化剂。我们描述了从氧气中产生氧化自由基的机制。然后，我们根据元素组成比较了不同类型的双功能催化剂：（1）金属/碳复合催化剂，即，单金属铁/碳复合催化剂、双金属/三金属碳​​复合催化剂、过渡金属单原子催化剂；(2) 不含碳的金属复合催化剂；(3) 无金属碳催化剂。然后，我们提出了除电催化剂之外的其他五种方法，这些方法已被用于提高非均相电芬顿过程的性能。