PHOTOELECTROCHEMICAL CONVERSION OF CARBON DIOXIDE TO METHANOL AND HIGHER ALCOHOLS, A CHEMICAL CARBON SEQUESTRATION STRATEGY

摘要

Concern with rising atmospheric carbon dioxide levels might be addressed by innovative chemical strategies for the conversion of CO2 to chemical species of societal use. One possible scheme is the conversion of carbon dioxide to a fuel such as methanol or another alcohol. Of course, to be of utility with regard to a carbon sequestration scheme, the energy needed to carry out this thermodynamically uphill process must not come from a fossil fuel source. Until the late 1970's, the transformation of aqueous carbon dioxide to methanol was thought to be impossible on a practical scale due to the kinetic difficulties associated with the required six- electron charge transfer. However in 1978 Halmann1 demonstrated the feasibility of this reaction by substituting a copper electrode for the more usual electrode materials (Pt, Au or C). Subsequently, several other non-classical electrode materials including ruthenium, GaP and GaAs were observed to allow the desired conversion. However, in all cases the process was observed to only occur at excessive overpotentials (～1V). Thus, although the conversion could be achieved, the cost was an excessive use of electrical power. If that power were to be derived from standard fossil fuel sources, then more carbon dioxide would be generated in the transformation then was converted to methanol. Thus, from the point of view of carbon mitigation or chemical sequestration, the known electrochemical processes are of little value.