Electrocatalysis carbon dioxide

Electrocatalysis at metal electrodes in aqueous (1.2) and non-aqueous ( ) solvents, phthalocyanine ( ) and ruthenium ( ) coated carbon, n-type semiconductors (6.7.8),and photocathodes (9,10) have been explored in an effort to develop effective catalysts for the synthesis of reduced products from carbon dioxide. The electrocatalytic and photocatalytic approaches have high faradaic efficiency of carbon dioxide reduction (1,6). but very low current densities. Hence the rate of product formation is low. Increasing current densities to provide meaningful amounts of product, substantially reduces carbon dioxide reduction in favor of hydrogen evolution. This reduction in current efficiency is a difficult problem to surmount in light of the probable electrostatic repulsion of carbon dioxide, or the aqueous bicarbonate ion, from a negatively charged cathode (11,12). 

Investigation of carbon dioxide catalytic activation is explored by a variety of subdisciplines (homogeneous catalysis, heterogeneous catalysis, electrocatalysis/photoelectrocatalysis), often with little cross-citation of work. This situation created a need to bring together the leading researchers to provide an overview of methods and accomplishments to date. 

One has also to keep the same temperatures in comparing electrocatalysis and although this is obvious, it sometimes turns out that a desired reaction is only viable at a lower rather than at room temperature. An example would be the work of Hori on the reduction of carbon dioxide. He found... 

The electrochemical oxidation of methanol has been extensively studied on pc platinum [33,34] and platinum single crystal surfaces [35,36] in acid media at room temperature. Methanol electrooxidation occurs either as a direct six-electron pathway to carbon dioxide or by several adsorption steps, some of them leading to poisoning species prior to the formation of carbon dioxide as the final product. The most convincing evidence of carbon monoxide as a catalytic poison arises from in situ IR fast Fourier spectroscopy. An understanding of methanol adsorption and oxidation processes on modified platinum electrodes can lead to a deeper insight into the relation between the surface structure and reactivity in electrocatalysis. It is well known that the main impediment in the operation of a methanol fuel cell is the fast depolarization of the anode in the presence of traces of adsorbed carbon monoxide. 

Schwartz, M., R.L. Cook, V.M. Kehoe, R.C. MacDuff, J. Patel, and A.F. Sammels (1993). Carbon dioxide rednction to alcohols using Perouskite-type electrocatalysis. 

Kondelka, M., A. Monnier, and J. Augustyniski (1984). Electrocatalysis of the cathodic rednction of carbon dioxide on platinized titanium dioxide film electrode. 

Tanabe, H. and K. Ohno (1987). Electrocatalysis of metal phthalocyanine thin film prepared by the plasma-assisted deposition on a glassy carbon in the reduction of carbon dioxide. Electrochim. Acta, 32(7), 1121-1124. 

Meshituka, S., M. Ichikawa, and K. Tamaru (1974). Electrocatalysis by metal phthalocyanines in the reduction of carbon dioxide. J. Chem. Soc. Chem. Commun. 5, 158-159. 

For a given electrochemical system, the increase of the voltage efficiency is directly related to the decrease of the overpotentials of the oxygen reduction reaction, t]c, and alcohol oxidation reaction, T]a, which needs to enhance the activity of the catalysts at low potentials and low temperature, whereas the increase of the faradic efficiency is related to the ability of the catalyst to oxidize completely or not the fuel into carbon dioxide, i.e. it is related to the selectivity of the catalyst. Indeed, in the case of ethanol, taken as an example, acetic acid and acetaldehyde are formed at the anode [10], which corresponds to a number of electrons involved of 4 and 2, respectively, against 12 for the complete oxidation of ethanol to carbon dioxide. The enhancement of both these efficiencies is a challenge in electrocatalysis. 

Sammels AE, Cook RL (1993) Electrocatalysis and Novel Electrodes for High Rate CO2 reduction under Ambient Conditions. In Sullivan BP, Krist K, Guard HE (eds) Electrochemical and electrocatalytic reduction of carbon dioxide. Elsevier, Amsterdam, p 247... 

Research in electrocatalysis was strongly stimulated in the early 1960s by efforts toward the development of various types of fuel cells. Studies were initiated on the various factors influencing the rates not only of hydrogen evolution but also of other reactions, particularly cathodic oxygen reduction and the complete oxidation of simple organic substances ( fuels ) to carbon dioxide. The... 

Christophe J, Doneux T, Buess-Herman C (2012) Electroreduction of carbon dioxide on copper-based electrodes activity of copper single crystals and copper-alloys. Electrocatalysis 3 139-146... 

Electrocatalysis by transition metal complexes is elegantly illustrated by the work of DuBois and colleagues.2 In the absence of CO2, the palladium (II) complex undergoes two-electron reduction, but when CO2 is present, the one-electron reduction product binds CO2 (DMF as solvent) (Figure 5.9). With added acid, carbon monoxide is produced catalytically from carbon dioxide. This chemistry likely involves the protonated carbon dioxide adduct (hydroxycarbonyl complex) shown in Figures 5.9 and 5.10. Catalytic turnover numbers greater than 100 have been reported for this and related compounds. Some hydrogen is produced in parallel, evidently via a hydride complex. 

Y. Kwon and J. Lee, Eormic acid from carbon dioxide on nanolayered catalyst. Electrocatalysis 1,2010,108-115. 

---