Enhancement of Cr(VI) reduction by polyaniline nanorod-modified cathode in flow-through electrode system

Cr(VI) reduction to Cr(III) has been demonstrated to be an effective method for Cr(VI) detoxification. Herein, we fabricated polyaniline (PANI) nanorod forests-modified Carbon fiber felt (CFF) as CFF-PANI cathode in a Flow-through electrode system (FES) with the counter CFF anode for enhancing Cr(VI) reduction. The CFF-PANI was synthetized via in-situ polymerization under different aniline concentration to investigate the effect of PANI nano-structures on Cr(VI) reduction. It was revealed that BET and electrochemical surface area of PANI nanorods significantly affected the Cr(VI) reduction, and CFF-PANI cathode with the largest BET and electrochemical surface area exhibited ∼ 45% higher Cr(VI) removal and ∼ 35% lower specific energy consumption than the CFF cathode. A decrease-then-stable Cr(VI) removal was observed within 120 min operation time, which was attributed to the electro-adsorption of Cr(VI) species on CFF anode. In-situ sampling experiments revealed that the electrochemical oxidation on CFF anode inhibited the Cr(VI) electro-adsorption, and at applied voltage above 0.7 V, the Cr(VI) reduction on cathode was the main mechanism for Cr(VI) removal. The operation of FES at 0.8 V had the lowest specific energy consumption (48.5 Wh/mol) and maintained ∼ 95% energy efficiency for Cr(VI) reduction with minor competitive reduction of H2O or O2 species. The results suggested that CFF-PANI can be a promising cathode for Cr(VI) reduction from aqueous solutions.