Electrochemical Reduction of CO[sub 2] with Transition Metal Phthalocyanine and Porphyrin Complexes Supported on Activated Carbon Fibers

Porphyrin and phthalocyanine transition metal complexes adsorbed on activated carbon fiber nanoporous supports are shown to be effective catalysts for electroreduction in the form of gas diffusion electrodes, yielding carbon monoxide with current efficiencies up to ca. 70%. A comparison of the efficiency of activated carbon supports with a wide pore size distribution, and activated carbon fibers, with slit-shaped pores of ca. 2 nm width, demonstrates that an increase in the catalyst dimensions results in a decrease in the benefit of the so-called nanospace effect. For bulky molecules, e.g., tetra-tert-butyl-substituted phthalocyanines, activated carbon supports are more effective, with a current efficiency as high as 85% for CO production being achieved.