Electroreduction of carbon dioxide on gas-diffusion electrodes modified by metal phthalocyanines

Porous carbon gas-diffusion electrodes modified by 17 kinds of different metal phthalocyanines were used as electrocatalysts for the electrochemical reduction of carbon dioxide. The distribution and current efficiencies of the electrolysis products depend strongly on the nature of the central metal coordinated to the phthalocyanine. In the case of metal phthalocyanines with transition metals of Group VIII, the main electrolysis product was carbon monoxide: A current efficiency of ca. 100% was observed on Co and Ni phthalocyanines. On the other hand, formic acid was formed mainly on metal phthalocyanines with Sn, Pb or In, which belong to Group IIIB or IVB. The highest current efficiency of ca. 70% was observed on Sn phthalocyanine around −1.6 V. In the case of Cu, Ga and Ti phthalocyanines, methane was the main product, the highest current efficiencies being 30–40%.