Concurrent electrochemical CO2 reduction to HCOOH and methylene blue removal on metal electrodes

Abstract

Experimental studies were done for simultaneous CO₂ reduction and methylene blue (MB) dye removal using Sn and Zn as cathode and Co₃O₄ as anode electrocatalysts. The extent of CO₂ reduction and dye removal were observed in NaHCO₃ and KHCO₃ electrolytes separately. The electrodes (cathode and anode) were prepared by coating the respective electrocatalyst on the graphite plate surface. A mixture of 0.5 M salt and 10 mg l⁻¹ of MB was considered as a base solution to conduct the reduction and dye removal studies at different applied voltages of 2 to 3.8 V. The reacted samples were collected for different time intervals of 5, 10, 15, 20 and 25 min to obtain the product formation using ultra-fast liquid chromatography (UFLC) and dye analysis by an UV visible spectrophotometer. The results confirm the formation of HCOOH for both cases with simultaneous CO₂ and MB removal. A maximum faradaic efficiency of 57.9% (KHCO₃) was observed using Sn as an electrocatalyst for a reaction time of 15 min and 31.7% (KHCO₃) in 5 min using Zn as an electrocatalyst. With increasing applied voltages the faradaic efficiencies were gradually decreased whereas dye removal is increased. However, the present studies were able to give a new topic for both simultaneous dye removal and CO₂ reduction in order to reduce atmospheric CO₂ concentrations and water purification. The selected electrocatalyst combinations were able to be used effectively for reduction studies which gives a new application for both CO₂ reduction and dye removal.