Electrochemical CO2 Reduction on Metal Electrodes

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Carbon dioxide is a potential carbon resource abundant on earth. It is also a green house gas with a rapidly increasing atmospheric concentration during the last two centuries. Chemical fixation of CO2 is an attractive technique for utilization of carbon resources, as well as for the reduction of the atmospheric concentration of CO2. Nevertheless, CO2 is the stablest among carbon based substances under the environmental conditions. It has not been incorporated as a major industrial material.

Carbon dioxide can be electrochemically reduced to useful products under mild conditions. However, the energy conversion efficiency, defined as the ratio of the free energy of the products obtained in electrochemical CO2 reduction and that consumed in the reduction, would be roughly 30 to 40%. Such a low efficiency may discourage practical application of CO2 reduction in the very near future. However, the significance of the CO2 reduc- tion will be reevaluated in various aspects of science in future, since many interesting facts in basic electrochemistry have been revealed by recent studies. At the moment, electrochemical reduction of CO2 is an interesting as well as an important topic in chemistry.

Fundamental studies of the electrochemical reduction of CO2 started as early as the 19th century, and have been further promoted by many workers in recent years. Numerous reports have been published in the last two decades. At the same time, confusions and contradictions are found in this field.

This article attempts to provide a review of CO2 reduction at metal electrodes. Several review papers have already appeared, which contain the history and classical works of CO2 reduction. Thus this paper will not repeat the historical aspects of CO2 reduction. This chapter will review recent progress, putting emphasis on basic problems and particularly on electrocatalytic aspects.