Electrochemical Reduction of CO₂ in a Zero-Gap Electrolyzer Cell on a Metal Molecular Electrocatalyst

Electrochemical reduction of CO₂ (ECR) on transition metal-containing porphyrin systems often leads to carbon monoxide. Herein, a modified zero-gap polymer electrolyte membrane water electrolyzer is used with 5,10,15,20-tetraphenyl-21H,23H-porphine copper (II) as a cathodic electrocatalyst for ECR in 0.1 M NaOH as an aqueous catholyte. The setup yields CO, CH₄, and C₂H₄ along with hydrogen evolution, with selectivity toward C₂H₄ formation as indicated by gas chromatographic analysis. Although hydrogen formation is predominant, the system yields a high average current density of 146.94 mA cm^-2 and a Tafel slope of ≈226 mV dec^-1 in concurrence. The cyclic voltammetric experiments show the stepwise formation of Cu (II) → Cu (I) → Cu (0) based on the potentials referenced against the reversible hydrogen electrode, which could have been the driving factor for the ECR.