Simultaneous utilization of electro-generated O₂ and H₂ for H₂O₂ production: An upgrade of the Pd-catalytic electro-Fenton process for pollutants degradation

The Electro-Fenton (EF) process is one of the promising advanced oxidation processes (AOPs) for environmental remediation. The H₂O₂ yield of EF process largely determines its performance on organic pollutants degradation. Conventional Pd-catalytic EF process generates H₂O₂ via the combination reaction of anodic O₂ and cathodic H₂. However, the relatively expensive catalyst limits its application. Herein, a hybrid Pd/activated carbon (Pd/AC)-stainless steel mesh (SS) cathode (PACSS) was proposed, which enables more efficient H₂O₂ generation. It utilizes AC, the support of Pd catalyst, as part of cathode for H₂O₂ generation via 2-electron anodic O₂ reduction, and SS serve as a current distributor. Moreover, H₂O₂ could be catalytically decomposed upon AC to generate highly reactive ^[rad]OH, which avoids the use of Fe²⁺. Compared with conventional Pd catalyst, H₂O₂ concentration obtained by PACSS cathode is 248.2% higher, the O₂ utilization efficiency was also increased from 3.2% to 10.8%. Within 50 min, 26.3%, 72.5%, and 94.0% H₂O₂ was decomposed by Pd, AC, and Pd/AC. Fluorescence detection results implied that Pd/AC is effective upon H₂O₂ activation for ^[rad]OH generation. Finally, iron-free EF process enabled by PACSS cathode was examined to be effective for reactive blue 19 (RB19) degradation. After continuous running for 10 cycles (500 min), the PACSS cathode was still stable for H₂O₂ generation, H₂O₂ activation, and RB19 degradation, showing its potential application for organic pollutants degradation without increase in the running cost.