Electrochemical reduction of carbon monoxide

Mechanistic Aspects of the Electrochemical Reduction of Carbon Monoxide and Methanol to Methane at Ruthenium and Copper Electrodes... 

The electrochemical reduction of carbon monoxide also offers a route for the production of fuels from inorganic sources. For example, carbon monoxide is formed from coal in gasification... 

The electrochemical reductions of carbon monoxide and methanol to methane (Equations 1 and 2) have potentials, under standard conditions, of +0.019 and +0.390 V vs SCE respectively (or a... 

Electrochemical reduction of carbon monoxide in dry nonaqueous media at moderate to low pressures leads to the formation of the 1,3-cyclobutanedione dianion (squarate) at current efficiencies, up to about 45% depending on the cathode material [1,2]. In aqueous solution, electroreduction can lead to the formation of methane and other hydrocarbon products. The role of the metal/adatom in determining the extent of CO and hence hydrocarbon formation during the reduction of carbon dioxide is related to the ability of the electrode material to favor CO formation (Cu, Au, Ag, Zn, Pd, Ga, Ni, and Pt) and stabilize HCCO [3, 4]. 

Y. Hori, A. Murata, R. Takahashi and S. Suzuki, Electrochemical reduction of carbon monoxide to hydrocarbons at various metal-electrodes in aqueous solution, Chem. Lett. 8,1987,1665-1668. 

Ammonium ions have been shown to act as a catalyst for the photo-electrochemical reduction of carbon dioxide to carbon monoxide (36). 

Hawecker J, Lehn J-M, Ziessel R (1986) Photochemical and electrochemical reduction of carbon dioxide to carbon monoxide mediated by (2,2 -bipyridine)tricarbonylchlororhenium (I) and related complexes as homogeneous catalysts. Helv Chim Acta 69(8) 1990-2012. doi 10.1002/hlca. 19860690824... 

Another aspect of the problem of producing new energy carriers is synthesis of methanol-like substances by cathodic reduction of carbon monoxide. This is a comparatively new type of electrochemical reaction. 

Cyclic voltammetry of the Mo dibromide under molecular nitrogen (1 atmosphere) shows that reduction gives some dinitrogen complex but other species, also observed under argon, are co -produced. In contrast, electrochemical reduction under carbon monoxide is a relatively clean process. Scheme N. 

Hori Y, Murata A, Takahashi R, Suzuki S (1987) Electrochemical reduction of carbon dioxide to carbon monoxide at a gold electrode in aqueous potassium hydrogen carbonate. Chem Commun 10 728-729... 

The presence of defects opens new pathways which significantly decrease the thermal stability of the reconstructed Rh(llO) surfaces [39]. Although the activity of electrochemical oxidation of carbon monoxide and methanol electro-oxidation can be increased by increasing surface steps on Pt nanoparticles, the oxygen reduction reaction activity of the 2-nm-sized Pt nanoparticle has been found insensitive to the step area, as shown in Fig. 20.3 [40], in contrast to the methanol oxidation reaction activity. 

S. Dceda, T. Tagaki and K. Ito, Selective formation of formic acid, oxalic acid, and carbon monoxide by electrochemical reduction of carbon dioxide, B. Chem. Soc. Japan 60,1987,2517-2522. 

The reduction of carbon dioxide is another of the basic electrochemical reactions that has been studied at modified electrodes. The reduction at Co or Ni phthalocyanine in acidic solution yields formic acid or carbon monoxide A very high selectiv-... 

Ito et al.40 examined the electrochemical reduction of C02 in dimethylsulfoxide (DMSO) with tetraalkylammonium salts at Pb, In, Zn, and Sn under high C02 pressures. At a Pb electrode, the main product was oxalic acid with additional products such as tartaric, malonic, glycolic, propionic, and n-butyric acids, while at In, Zn, and Sn electrodes, the yields of these products were very low (Table 3), and carbon monoxide was verified to be the main product even at a Pt electrode, CO was mainly produced in nonaqueous solvents such as acetonitrile and DMF.41 Also, the products in propylene carbonate42 were oxalic acid at Pb, CO at Sn and In, and substantial amounts of oxalic acid, glyoxylic acid, and CO at Zn, indicating again that the reduction products of C02 depend on the electrode materials used. 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

In aprotic solvents, direct electrochemical reduction of C02 (—2.23 V vs. SCE) yields carbon monoxide and carbonate ion.29 The (porT)Fe dianion also reduces C02 to CO, but at a less negative potential (-1.70 V).30 Hence, the estimated iron-carbon bond energy (—AGbF) for the (porT)Fera—C(0)0 dianion is at least 50 kJ mol-1 [—AGBF > 96.5(—1.70 + 2.23)]. 

We here report the first example of an electrochemical polymerization process which leads to formation of a modified electrode having the generic formula [Ru (bpy)(CO)2Cl]n, and which displays outstanding electrochemical activity towards reduction of carbon dioxide to either carbon monoxide or formate. A crucial stereochemical effect of the leaving groups on the feasibility of polymerization is demonstrated. Formation of the polymer occurs stepwise, through the formation of a dimeric or a tetrameric intermediate. 

These modified electrode having the generic formula [Ru (bpyRR)(CO)2Cl] , display outstanding electrochemical activity towards the reduction of carbon dioxide to either (i) carbon monoxide, 100 % faradic yield in water at -1.2 V vs SCE, bpy = 2,2 -bipyridine, R = H (ii) or formate, 95 % faradic yield in aqueous electrolyte at -1.2 V vs Ag/Ag, R = isopropyl esters groups. 

Studies are in progress to identify and quantify the products formed by the electrochemical reduction of CO2 on precious metal electrodes as well as on other electrodes such as Mo when nearly neutral electrolytes are used that minimize proton donor or acceptor reactions. A review of CO2 reduction on metal electrodes shows that CHi+ is produced on Ru and Cu (8, 9), CH3OH is a major product on Ru and Mo (6-8), carbon monoxide is formed on Ru, Pd, Pt, Co, Fe, Au, and Ag (7-9), HCOO is the main product on Cd, In, Sn, and Pb (, ), and a product more complex than formic acid is reported for Pt... 

The first concept is the closed-loop-controlled three-way catalyst. In this, one type of catalyst, which is placed in the exhaust gas stream, is able to promote all the main reactions that lead to the simultaneous removal of carbon monoxide, hydrocarbons and nitrogen oxides. To balance the extent of the oxidation and the reduction reactions, the composition of the engine-out exhaust gas is maintained at or around stoichiometry. This is achieved by a closed-loop engine operation control, in which the oxygen content of the engine-out exhaust gas is measured up-stream of the catalyst with an electrochemical oxygen sensor, also called lambda sensor. 

Iron(O) tetraphenylporphyrin is also a catalyst of the electrochemical carbon dioxide reduction to carbon monoxide in DMF electrolytes [29-31]. Under CO, the catalyst is, however, rapidly destroyed by either carboxylation or hydrogenation of the porphyrin ring. The mechanism proceeds through coordination of CO2 to Fe(0). At low temperature (-40°C), a second CO2 molecule adds to the first-coordinated one in an acid-base reaction fashion. This is followed by the cleavage of a C—O bond of the first-coordinated CO2 molecule and concomitant formation of the Fe(II)CO complex and a carbonate anion. After reduction of the Fe(ll)CO complex by the Fe(0) complex, CO is... 

Ni3(/i3-I)(/i2-dppm)3(/X3-CN-spacer-/i3-NC)Ni3(/i3-I)(/i2-dppm)3], formed from diisocyanides with />-phenyl and 1,6-hexyl group spacers. The isocyanide-capped clusters 30 show a reversible single-electron reduction from a 48-electron to a 49-electron electronic configuration at ca. —1.20 V versus SCE. A study of the electrocatalytic activity of clusters 30 toward the reduction of carbon dioxide has appeared. Electrochemical kinetics indicate that the rates of reaction with CO2 are first order on [cluster] and first order on [GO2]. The observed products are carbon monoxide and carbonate, corresponding to the reductive disproportionation of GO2. 

---