Electrochemical degradation of methylene blue accompanied with the reduction of CO2 by using carbon nanotubes grown on carbon fiber electrodes

Abstract

AbstractIn this study, the degradation of Methylene Blue (MB) dye accompanied with the reduction of CO2 was performed in an electrochemical (EC) process by using carbon nanotubes grown on carbon fiber (CNTs/CFM) electrodes as the cathode and anode in a two-compartment electrochemical cell. The growth of CNTs on CFM via chemical vapor deposition led to the significant improvement in physicochemical properties of CNTs/CFM which were beneficial for the EC process. The effects of various operating parameters including supporting electrolytes (KHCO3 and H2SO4), initial concentration of MB (5, 10, 15 and 20 mg L− 1) and applied currents (10, 50 and 100 mA) on the degradation of MB were investigated. The results confirmed the vital influence of applied current and initial concentration of MB while the supporting electrolytes played a minor role in MB degradation. On the contrary, the influence of electrolytes in the performance of CO2 reduction was more significant on the production and selectivity of generated products. The optimal electrochemical system included 0.1 M KHCO3 as the electrolyte and an applied current of 50 mA in anodic cell and CO2 saturated solution in cathodic cell; such a system resulted in the EC degradation efficiency of 72% at the MB initial concentration of 10 mg L− 1 in the anodic cell and production of 4.7 mM cm− 2 CO, 67 mM cm− 2 H2, and 11.3 mg L− 1 oxalic acid in the cathodic cell corresponding to the Faradaic efficiencies of 28, 40 and 4%, respectively. The results of reusability test deduced that the stability of CNTs/CFM was still satisfactory after 4 runs. The results of this study demonstrated the good applicability of CNTs/CFM to be simultaneously used the electrodes for the EC oxidation of dye and the EC reduction of CO2 to obtain valuable compounds.