Primary electrochemical

Graham, R. W., ed. (1981). Primary Electrochemical Cell Technology Advances Since 1977. Park Ridge, NJ Noyes Data Corporation. 

The "classical" Leclanche cell uses zinc sheet formed into a cylindrical can serving simultaneously as the anode and as the cell container (AB1C1). The cathode is a mixture of Mn02 and graphite wrapped into a piece of separator and contacted by a central carbon rod. The can dissolves slowly when the cell is not in use and faster when the cell delivers electrical energy. The reaction following the primary electrochemical zinc dissolution [Eq. (19)] leads, in the case of an ammonium chloride electrolyte, to a zinc diammine cation ... 

In the past it had been a popular belief that the electrochemical reduction of any inorganic or organic substance involves the primary electrochemical formation of a special, active form of hydrogen in the nascent state (in statu nascendi) and subsequent chemical reaction of this hydrogen with the substrate. However, for many reduction reactions a mechanism of direct electron transfer from the electrode to the substrate could be demonstrated. It is only in individual cases involving electrodes with superior hydrogen adsorption that the mechanism above with an intermediate formation of adsorbed atomic hydrogen is possible. 

These primary electrochemical steps may take place at values of potential below the eqnilibrinm potential of the basic reaction. Thns, in a solntion not yet satnrated with dissolved hydrogen, hydrogen molecnles can form even at potentials more positive than the eqnilibrinm potential of the hydrogen electrode at 1 atm of hydrogen pressnre. Becanse of their energy of chemical interaction with the snbstrate, metal adatoms can be prodnced cathodically even at potentials more positive than the eqnilibrinm potential of a given metal-electrolyte system. This process is called the underpotential deposition of metals. 

Fig. 3. Primary electrochemical mechanism and products formed on oxidation of uric acid at the PGE in 1 M HOAc...

Fig. 10. Mechanism of primary electrochemical oxidation of theobromine (1, R=H) and caffeine (I, R=CH3) at the PGE...

Muller V, Gottschalk G. 1994. The sodium ion cycle in acetogenic and methanogenic bacteria generation and utilization of a primary electrochemical sodium ion gradient. In Drake HL, editor. Acetogenesis. New York Chapman Hall, p 127-56. 

Thus, the free energy change associated with the conversion of formaldehyde, via methylene-H4MPT, to CH3-S-C0M is conserved in a primary electrochemical Na potential (Fig. 6). This conversion represents a second coupling site in methane formation from CO2. 

Fig. 6. Proposed mechanism of the generation of a primary electrochemical sodium potential (AftNa ) coupled to methylene-HaMPT (CH2=H4MPT) conversion to methyl-coenzyme M (CH3-S-C0M) Methyl-H4MPT coenzymeM (H-S-CoM) methyltransferase as a primary Na pump. Numbers in circles (1) methylene-H4MPT reductase (2) CH3-H4MPT H-S-CoM methyltransferase the hatched box indicates membrane-bound methyltransferase n is an unknown stoichiometric factor.

In the following subsections experiments are described which indicate that CO2 reduction to methylene-H4MPT is driven by a primary electrochemical Na potential generated by formaldehyde reduction to CH4. These experiments include (1) studies of the mode of energy transduction of the reverse reaction, the exergonic formaldehyde oxidation to CO2 and 2H2 (2) experiments on the effects of ionophores and inhibitors on CH4 formation from CO2/H2 and CH4 formation from formaldehyde/H2, and the determination of stoichiometries of primary Na" translocation. 

A much-used approach to the study of the primary electrochemical step of aromatic hydrocarbons involves the use of model compounds whose corresponding radical cations (and in some cases dications) are relatively stable. Substituted anthracenes, particularly 9,10-diphenylanthracene (9,10-DP A), have featured largely in such work [12,53-58,135,137,151,163-168]. For instance, on slow-sweep CV in MeCN, purified without... 

In multielectron transfer processes, the reduction of CO2 can yield formic acid, carbon monoxide, formaldehyde, methanol, or methane that is, the primary electrochemical process supplies Ci compounds. These reactions can proceed at reasonable reduction potentials between —0.24 and —0.61 V (NHE) (Equations (6.12-6.16) the reduction potentials, E°, refer to pH 7 in aqueous solutions versus NHE), while the formation of the C02 radical anion is estimated to take place at —2.1 V.104 Reduction of CO (in the presence of H + ) supplies CH2" radicals that may yield methane directly or leads to higher hydrocarbons (e.g., ethene or ethane) by recombination.24,105 Efficient formation of ethene (together... 

Explain the differences between a primary electrochemical cell—one that is not rechargeable—and a storage cell (for example, the lead storage battery), which is rechargeable. 

One or more electrochemical cells connected in series constitute an electrical battery . Primary electrochemical (galvanic) cells are ready to produce current immediately and do not need to be charged in the way secondary cells (described below) do. In disposable cells, the chemical half reactions are not easily reversible, so the cells cannot be reliably recharged. Common disposable cells include the zinc-carbon cells and the alkaline cells. Secondary electrochemical cells contain the active materials in the disclWged state, so they must be charged before use. The oldest form of rechargeable cell is the lead-acid battery. 

The Oxygen Evolution Reaction (OER). The OER is the primary electrochemical reaction in water electrolysis, metal electrowinning, and recharging of metal-air cells. The standard electrode potential for this reaction at 25°C is 1.299 V vs the normal hydrogen electrode (NHE) in acid media and 0.401 V in alkaline media. The pertinent... 

Fig. 11. Primary electrochemical oxidation of bases at the graphite electrodes. A adenine, B guanine.

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