Electrocatalytic Carbon Dioxide Reduction in Aqueous Solutions Using Electrodeposited Metalloporphyrin-Graphene Coatings

The sharply rising level of atmospheric CO₂ is one of the largest environmental concerns facing our civilization today. The conversion of CO₂ back to useful compounds is a critical goal that would restore balance to earth’s atmosphere, since CO₂ is the most significant greenhouse gas. CO₂ reduction is possible through chemical catalysis, electrochemistry, photochemistry and biological processes. Chemical catalytic processes generally operate at high temperatures and pressures which lead to high energy cost. The electrochemical method, however, operates at ambient conditions which offer a simple and effective route for CO₂ reduction.

The electrocatalytic capabilities toward CO₂ reduction of some cobalt porphyrins have been reported in the literature, although at considerable overpotentials. The present work deals with the spectroscopic, microscopic and electrochemical examination of the interactions occurring between such porphyrins and graphene derivatives, and their effect on CO₂ reduction. Such self-assembled systems which are formed between 5,10,15,20-Tetrakis(1-methyl-4-pyridinio) porphyrin (CoTMPyP) and graphene oxide (GO) were deposited on electrode surfaces (such as glassy carbon) by means of electrodeposition. TEM images show homogeneously distributed CoTMPyP in the graphene sheets.

The electrodeposited CoTMPyP-GO system showed increased activity for CO₂ reduction vs. water reduction (1.2 and 0.25 mA/cm², respectively, at -1.2V vs. Ag/AgCl), as examined in aqueous 0.1 M Na₂CO₃ solution at pH 11.5.