Square-Wave Alternating Voltage for Enhancing Cr(VI) Reduction in a Carbon Fiber-Based Flow-Through Electrode System

Abstract

Electrochemical reduction with a flow-through electrode system (FES) has been regarded as an effective method for water decontamination. However, under a direct voltage (DV) power supply, the reduction efficiencies were strongly limited by the gas bubbles generated in porous electrodes and the electrostatic repulsion between the negatively charged pollutants and cathode. Herein, square-wave alternating voltages (SWAV) were applied to regulate the anodic−cathodic polarities of electrodes for eliminating the gas accumulation in porous electrodes and enhancing the mass transfer efficiency. Under the optimized SWAV parameters, the Cr(VI) reduction and energy efficiency were increased obviously to ∼86 and 84% as compared with the 20%−30% Cr(VI) reduction and 30%−50% energy efficiency under the DV power supply. With periodically altering the anode to cathode, localized H + and Cr(VI) species were formed on the anodic interface via H 2 O oxidation and Cr(VI) adsorption, which were further in situ reduced for enhancing the Cr(VI) mass transfer and reduction efficiencies. In addition, O 2 species generated via H 2 O oxidation was also in situ reduced to H 2 O 2 species, hence promoting the Cr(VI) reduction and operation stability for most Cr(VI) reduction with a stable energy efficiency (∼82%) over a 10 day operation (8 mg/L Cr(VI) and 500 L/m 2 /h flux). The successful application of SWAV may derive similar decontamination strategies, especially for electrically charged pollutants with the H + or OH − ions as reactants.

Pulsed-waveform electrocatalytic detoxification of hexavalent chromium promoted by pseudocapacitive effects

“…A recent study also demonstrated that the Cr( vi ) reduction efficiency increased to 86% at square-wave alternating voltages as compared with 20–30% at the direct voltage, using a flow-through electrode system with the double carbon fiber felt. 50 These results demonstrate that the combination of the pulsed voltage with the pseudocapacitive electrode ( e.g. PANI) was suitable for continuous operation to achieve a high Cr( vi ) reduction efficiency.…”

Composite modification of carbon fiber cathode with tree-like branched polypyrrole-microwires and polyaniline-nanorods for enhancing hexavalent chromium reduction

“…Titanium rods were used to connect the anode and cathode with an adjustable DC power supply (DG1718E-5), and a piece of quantitative filter paper was put between the electrodes to avoid short circuit problems. Based on our previous work, 21 the synthetic Cr( vi ) solution was first oxidized by the CFF anode, then Cr( vi ) was reduced to Cr( iii ) by the cathodes, and finally discharged from the water collector using a peristaltic pump.…”