Researchers at the University of Delaware have developed an inexpensive bismuth−carbon monoxide evolving catalyst (Bi-CMEC) that can be used in conjunction with ionic liquids to convert CO2 to carbon monoxide (CO) using electricity. CO can then be reacted with H2O via the water−gas shift to generate H2, and this CO/H2 mixture (syngas) can be used to generate synthetic petroleum and liquid fuels using Fischer−Tropsch methods.
The combination, suggests the team in paper published in the Journal of the American Chemical Society, could integrate into energy storage and distribution networks to provide a means for renewable energy storage.
Storage of solar and other sources of renewable electricity may be enabled by the catalytic production of fuels such as H2 or reduced carbon-containing compounds via the electro-chemical reduction of H2O or CO2, respectively. The renewable production of reduced carbon compounds is especially attractive, as liquid fuels can directly address energy needs associated with transportation, which account for nearly 30% of the US energy demand. An attractive strategy for the synthesis of carbon-based fuels is the marriage of a robust electrocatalyst for CO2 reduction with a photoelectrochemical device or a conventional electrolyzer powered by a renewable source of electrical current.
...Bismuth is an attractive material for development of heterogeneous CO2 reduction catalysts, as this metal is nontoxic and has a very small environmental impact. Moreover, Bi is a byproduct of Pb, Cu, and Sn refining, and has few significant commercial applications, resulting in the price of Bi being low and stable. Despite these attractive qualities, there has been only one report of electrocatalytic CO2 reduction using Bi, and the ability of this metal to drive CO production has not been demonstrated. As such, development of Bi-based cathodes for conversion of CO2 to CO would represent an important development for the fields of CO2 electrocatalysis and renewable energy conversion.—DiMeglio and Joel Rosenthal
The researchers electro-deposited a material containing Bi0 and Bi3+onto an inert electrode substrate to produce the Bi-CMEC catalyst. Used in conjunction with ionic liquids, it effected the electrocatalytic conversion of CO2 to CO with appreciable current density at overpotentials below 0.2 V.
Under these conditions, Bi-CMEC is selective for production of CO, operating with a Faradaic efficiency (FE) of approximately 95%. When taken together, these correspond to a high-energy efficiency for CO production, on par with that which has historically only been observed using expensive silver and gold cathodes.
...this Bi0/Bi3+ assembly catalyzes the conversion of CO2 to CO with high selectivity and FE. At present, the importance of the Bi3+ ions to the efficacy of Bi-CMEC is unclear. It is possible that the interface between Bi0 and Bi3+ sites serves to stabilize CO2•− intermediates at the electrode surface in a fashion similar to that proposed for metal oxides on etched electrodes.
Alternatively, the exceptional activity of Bi-CMEC may be derived from in situ reduction of the Bi0/Bi3+ material to generate metastable surfaces with enhanced catalytic properties. The use of imidazolium ILs may be especially critical in this regard, as recent work has demonstrated that interplay between adsorbed imidazolium cations and CO2 at bulk platinum electrodes can significantly enhance electrocatalytic CO2 reduction. Future efforts to uncover the atomic-level structure of Bi-CMEC will be critical to understanding the mechanism by which this system activates CO2 and, more generally, may provide a rational route for the development of additional inexpensive electrode materials for CO evolution.—DiMeglio and Joel Rosenthal
John L. DiMeglio and Joel Rosenthal (2013) Selective Conversion of CO2 to CO with High Efficiency Using an Inexpensive Bismuth-Based Electrocatalyst. Journal of the American Chemical Society 2013 135 (24), 8798-8801doi: 10.1021/ja4033549