Trans-electrode pressure of gas-diffusion electrodes significantly influencing the electrochemical hydrogen peroxide production.

Hydrogen peroxide (H2O2) synthesis by electrochemical two-electron oxygen reduction has garnered increasing interest as a wide range of potential applications. Gas diffusion electrodes (GDEs) can effectively promote the H2O2 production efficiency by overcoming the oxygen mass transfer limitations but strongly influenced by the electrowetting process along the long-term operation. In this study, the effect of trans-electrode pressure (TEP) of GDE cathode on the electrowetting process was further elucidated. We controlled the TEP values of four types of GDEs: two Ni-based GDEs and two carbon cloth GDEs prepared by hot-pressing or brushing carbon black. SBA-15 was further used to regulate the microstructure of one Ni-based GDE. It was found that an optimal range of TEP occurred for all tested GDEs in terms of the max. concentration, the yield efficiency, the energy consumption, and the stability because TEP may change the triple-phase interface and influence the anti-electrowetting effect. The porosity of hot-pressed Ni GDE can maintain the TEP window and thus enhance the production of H2O2, likely via creating oxygen-containing functional groups and a bimodal pore structure on the electrode, revealed with several characterization techniques including SEM, CA, XPS, Raman spectra, CV and EIS. The porous Ni GDE presented an efficient and stable production of H2O2 for 10 cycles: yielding H2O2 at 4393.2-4602.2 mmol m-2 h-1 with current efficiencies of 94.2-98.7%. The best accumulated H2O2 concentration can reach up to 3.58 ωt% H2O2 at 10 h. The results provide an important reference for the industrial scaleup of electro-production of H2O2 with GDEs.

Integrated electro-Fenton system based on embedded U-tube GDE for efficient degradation of ibuprofen.

Ibuprofen (IBP) is a carcinogenic non-steroidal anti-inflammatory drug (NSAID). It is of certain hazard to aquatic animals and may cause potential harm to human health. As traditional methods cannot effectively remove such a pollutant, many advanced oxidation processes (AOPs) have been developed for its degradation. The electro-Fenton process has the advantages of strong oxidative ability, a synergistic effect of various degradation processes, and a wide application range. This study developed a high-performance gas diffusion electrode (GDE) for electrochemical hydrogen peroxide (H2O2) production. The optimum system performance was found at the current density of 10 mA cm-2, pH of 7.0, and air flow rate at 0.6 L min-1, where the accumulation of H2O2 could reach as high as 769.82 mg L-1. The computational fluid dynamics (CFD) simulation results revealed a fast mass-transfer property in this electro-Fenton system with U-tube GDEs, which resulted in a deep-level degradation (∼100%) of the pollutant (IBP) and a low-concentration degradation of 10 mg L-1 within a 120-min reaction period. The high-performance liquid chromatography-mass spectrometry (LC-MS) studies demonstrated that the hydroxyl radicals were the primary active species in the electro-Fenton system and that the degradation intermediates of IBP were mainly 1-(4-isobutylphenyl) ethanol and 2-hydroxy-2-(4-isobutyl phenyl) propanoic acid through four probable electro-Fenton degradation pathways. This report provides a facile and efficient way to construct a high-performance electro-Fenton reactor, which could be effectively used in advanced oxidation processes (AOPs) to remove emerging contaminants in wastewater and natural water.

Pesticide tailwater deeply treated by tubular porous electrode reactor (TPER): Purpose for discharging and cost saving.

Pesticide tailwater often contains residual and toxic contaminants of triazole fungicides (TFs) due to their poor biodegradability which will do great harm to local aquatic systems. For this case, a novel electrochemical reactor (TPER) equipped a tubular porous RuO2-Sb2O5-SnO2 electrode was assembled and then employed to deeply treat pesticide tailwater. Characterizations of the electrode studied by SEM, EDS and XRD analysis indicated that it owns a porous structure and a compact and crack-free surface. Influence of the porous structure on electrochemical property was examined by cyclic voltammetry and normal pulse voltammetry. The results indicated that porous structure can not only enlarge electrochemical active area but also increase mass transfer efficiency by 5.7-fold in flow-through mode compared with batch mode. Furthermore, the optimal operating conditions of TPER were flow rate of 250 mL min-1 and current density of 4 mA cm-2. After 1.5 h treatment under these conditions, Tz, TC and PPC were removed by 98.9%, 99.0% and 98.4% respectively, while 81.9% of COD was also removed. Additionally, the microbial content was dropped to 0 CFU mL-1 and fecal coliform was lower than 2 MPN (100 mL)-1. All results demonstrated that the treated tailwater has met the Class 1 of National Discharge Standard of China. Especially, operating cost of TPER was only $ 0.33 per ton. The excellent performance together with the low cost indicated that TPER is a promising option for depth treatment of industrial tailwater.