A zero-gap proton exchange membrane electrolyzer cell using Nafion®117 membrane-containing copper porphyrin cathode electrocatalyst in CO₂ saturated 0.1 M aqueous NaOH catholyte produces C₂H₄, CO, and CH₄ as products.

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.