The Electroreduction of Carbon Dioxide in Protic Media Water and Alcohols

The Electroreduction of Carbon Dioxide in Protic Media (Water and Alcohols] 

The stepwise electron reduction of C02, whether direct or indirect, catalyzed, or by direct transfer on an apparently inert conductive surface, has been the object of considerable attention since the first concise reports of formate anion production. Since then, the list of possible derivatives has grown from formates to carbon monoxide, methane, ethylene, and short-chain saturated hydrocarbons. As noted in Section 12.1, this area of research has been expanded in recent years [8, 80, 83], with information relating to increased yields, to the effect of electrode materials on selectivity, as well as further speculations on possible reaction mechanisms, having been obtained on a continuous basis. Yet, the key to these synthetic processes-an understanding of the relationship between the surface of the electrode and the synthetic behavior of the system-seems no closer to being identified. 

The following brief review of recent reports of this subject will focus on the nature of the cathode surface, for which some surprising results have been attained. Attention will also be focused on the hypotheses of applications of the various proposed systems, rather than on the mechanisms or on further electroanalytic 

How the experimental panorama is influenced by parameters still to be defined was demonstrated by Shibata et al. [86]. Here, preliminary results obtained in aqueous media using a specific brand of high-purity commercial copper cathode were positive with regards to hydrocarbons C3+, provided that no electropolishing was performed before the electrochemical process. If electropolishing preceded the C02 reduction, the cathodes behaved similarly to any other copper cathode, leading essentially (besides hydrogen) only to methane end ethylene. A tentative explanation of this behavior was proposed which referred to the polycrystalline matrix of this brand of copper, which made it particularly adaptable to be covered by oxide layers active in the formation of C3+. However, further experimental evidence on the surface structure, composition and modifications with electrolysis time will be required to substantiate this hypothesis. 

Other metals, the performances of which as cathodes in the electroreduction of C02 have already been described in detail, were suggested for the development stage. Thus, Delacourt et al. [87] proposed an electrochemical cell, the design of which was taken from proton exchange membrane fuel cell (PEMFC) technology, 

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