Electrochemical reduction, intercalation

Staging phenomena as well as the degree of intercalation can be easily observed during the electrochemical reduction of carbons in Li+-containing electrolytes. Figure 6 (left) shows a schematic poten-tial/composition curve for the galvanostatic... 

Electrochemical studies have been performed with the alkylammonium intercalated VOx nanotubes139 as well as Mn intercalated VO nanotubes87 Cyclic voltammetry studies of alkylammonium-VO nanotubes showed a single reduction peak, which broadened on replacing she amine with Na wish an additional peak. Li ion reactivity has also been tested with Mn-VO nanotubes by reacting with rt-butyllithium, and found that -2 lithiums per V ion are consumed. Electrochemical Li intercalation of Mn-VO nanotubes show that 0.5 Li ions per V atom were intercalated above 2 V.87 This observation may be relevant to battery applications. 

It has been shown that electroactive polymer films on electrodes can mediate electron transfer for metal deposition (9-11). Haushalter and Krause (5) have described the treatment of PMDA-ODA films with highly reactive Zintl complexes (e.g., Sn9 4, SnTe4 4) to yield an intercalated material able to reduce ions of platinum, palladium and silver at the film surface. Mazur et al., (12) reported the deposition of conductive Ag, Cu, and Au metal interlayers within a PMDA-ODA film by electrochemical reduction. 

Reduction of ketones. Saturated and conjugated ketones can be reduced by the reagent to alcohols, probably by a mechanism similar to electrochemical reduction (as illustrated for acetophenone in scheme I). In some cases, ptnacols are formed as well. Thus acetophenone is reduced to the alcohol (45 % yield) and the pinacol (45% yield). Generally the alcohol is the predominant product. For example, benzophenonc is reduced to benzhydrol in 98 % yield. a,)3-Unsaturated ketones are reduced to saturated alcohols. Reduction of camphor gives predominantly the exo-alcohol note that reduction with sodium in alcohol or with potassium, in the presence of graphite (not intercalated), gives predominantly the endo-alcohol. 

The electrochemical reduction of Ti02 is known to be accompanied by the intercalation of small cations. This finding has been explored in sensitizing anatase films for battery applications [149]. Cation coordination to titanium alkoxide sol-gel precursors is also well known [150]. Lyon and Hupp used quartz crystal microbalance techniques to determine the mass of intercalating cations as the TiOa film is reduced [151]. Hagfeldt and co-workers have studied Li+ and Na intercalation into anatase Ti02 both theoretically and experimentally [152, 153). They found that the diffusion constants for Li and Na+ are temperature dependent with an activation barrier of 0.4 eV for insertion and 0.5 eV for extraction. The Li+ diffusion coefficient at 25 °C into the nanoporous structure was approximately 2 X 10 cm s for insertion and 4 x 10 cm s for extraction. 

Solid isopoly- and heteropolymetalate compounds have been synthesized. Within this group of materials, one can include the so-called metal oxide bronzes (typically tungsten bronzes). Starting from WO, electrochemical reduction processes yield intercalation materials with electrochromic properties (Grandqvist, 1999). 

Cation- and anion-graphite intercalation compounds can be prepared by electrochemical reduction or oxidation of graphite in appropriate electrolytes. Such electrochemical solid-state reactions require mixed conductivity of the solid, i.e., existence of electronic and ionic conductivity. 

Figure 6 The presence of a CA mismatch between electrode and intercalator prohibits the electrochemical reduction of crosslinked DM (Ref. 24.)...

Figure 5 Efectrochemical cation radical formation in the polyion complex films of the viologen polymers 17 and anionic amphiphile 4 cast on ITO electrodes (a) spectral changes of even and odd polymers during electrochemical reduction (h) schematic illustrations of the organization of the polymer chain intercalated into the amphiphile bilayers. Upper figure describes in-plane view of the polymer layer.

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