Major challenges for effective implementation of the Electro-Fenton (EF) water treatment process are that conventional efficient cathodes are relatively expensive, and H 2 O 2 activation by Fe 2+ may cause secondary pollution. Herein, we propose a low-cost activated carbon/stainless steel mesh (ACSS) composite cathode, where the SS mesh distributes the current and the AC simultaneously supports H 2 O 2 electrogeneration, H 2 O 2 activation, and organic compounds (OCs) adsorption. The oxygen-containing groups on the AC function as oxygen reduction reaction (ORR) sites for H 2 O 2 electrogeneration; while the porous configuration supply sufficient reactive surface area for ORR. 8.9 mg/L H 2 O 2 was obtained with 1.5 g AC at 100 mA under neutral pH without external O 2 supply. The ACSS electrode is also effective for H 2 O 2 activation to generate ‧OH, especially under neutral pH. Adsorption shows limited influence on both H 2 O 2 electrogeneration and activation. The iron-free EF process enabled by the ACSS cathode is effective for reactive blue 19 (RB19) degradation. 61.5% RB19 was removed after 90 min and 74.3% TOC was removed after 720 min. Moreover, long-term stability test proved its relatively stable performance. Thus, the ACSS electrode configuration is promising for practical and cost-effective EF process for transformation of OCs in water.

Efficient H 2 O 2 electrogeneration from 2-electron oxygen reduction reaction (ORR) represents an important challenge for environmental remediation application. H 2 O 2 production is determined by 2-electron ORR as well as H 2 O 2 decomposition. In this work, a novel strategy based on the systematical investigation on H 2 O 2 decomposition pathways was reported, presenting a drastically improved bulk H 2 O 2 concentration. Results showed that bulk phase disproportion, cathodic reduction, and anodic oxidation all contributed to H 2 O 2 depletion. To decrease the extent of H 2 O 2 cathodic reduction, the pulsed current was applied and proved to be highly effective to lower the extent of H 2 O 2 electroreduction. A systematic study of various pulsed current parameters showed that H 2 O 2 concentration was significantly enhanced by 61.6% under pulsed current of "2s ON + 2s OFF" than constant current. A mechanism was proposed that under pulsed current, less H 2 O 2 molecules were electroreduced when they diffused from the porous cathode to the bulk electrolyte. Further results demonstrated that a proper pulse frequency was necessary to achieve a higher H 2 O 2 production. Finally, this strategy was applied to Electro-Fenton (EF) process with ibuprofen as model pollutant. 75.0% and 34.1% ibuprofen were removed under pulsed and constant current at 10 min, respectively. The result was in consistent with the higher H 2 O 2 and •OH production in EF under pulsed current. This work poses a potential approach to drastically enhance H 2 O 2 production for improved EF performance on organic pollutants degradation without making any changes to the system except for power mode.

The performance of cathode on HO electrogeneration is a critical factor that limits the practical application of electro-Fenton (EF) process. Herein, we report a simple but effective electrochemical modification of reticulated vitreous carbon foam (RVC foam) electrode for enhanced HO electrogeneration. Cyclic voltammetry, chronoamperometry, and X-ray photoelectron spectrum were used to characterize the modified electrode. Oxygen-containing groups (72.5-184.0 μmol/g) were introduced to RVC foam surface, thus resulting in a 59.8-258.2% higher HO yield. The modified electrodes showed much higher electrocatalytic activity toward O reduction and good stability. Moreover, aimed at weakening the extent of electroreduction of HO in porous RVC foam, the strategy of pulsed current was proposed. HO concentration was 582.3 and 114.0% higher than the unmodified and modified electrodes, respectively. To test the feasibility of modification, as well as pulsed current, EF process was operated for removal of Reactive Blue 19 (RB19). The fluorescence intensity of hydroxybenzoic acid in EF with modified electrode is 3.2 times higher than EF with unmodified electrode, illustrating more hydroxyl radicals were generated. The removal efficiency of RB 19 in EF with unmodified electrode, modified electrode, and unmodified electrode assisted by pulsed current was 53.9, 68.9, and 81.1%, respectively, demonstrating that the green modification approach, as well as pulsed current, is applicable in EF system for pollutant removal. Graphical abstract ᅟ.

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