Multi-Electron Transfer Reactions

CV is extensively used for the study of multi-electron transfer reactions, adsorbed species on the electrode surface, coupled chemical reactions, catalysis, etc. Figure 18b.9 shows some of the examples. 

Another advantage of SWV over CV can be seen when dealing with a separate multi-electron transfer reaction. The CV current wave of each or each group of electrons always contains the contribution from the previous electron transfer, particularly the diffusion-controlled current. Separating currents from different electron transfers can be tedious, if not impossible. It can be even worse when we have to take into account the capacitive charging current. Since both capacitive and diffusion-controlled currents are absent or at least minimized on the 7net vs E curve of an SW voltammogram, current waves from each electron transfer are much better resolved and more accurate information can be obtained. 

Electrocatalytic Reduction of Dioxygen The electrocatalytic reduction of oxygen is another multi-electron transfer reaction (four electrons are involved) with several steps and intermediate species [16]. A four-electron mechanism, leading to water, is in competition with a two-electron mechanism, giving hydrogen peroxide. The four-electron mechanism on a Pt electrode can be written as follows ... 

The design of such artificial photosynthetic systems suffers from some basic limitations a) The recombination of the photoproducts A and S+ or D+ is a thermodynamically favoured process. These degra-dative pathways prevent effective utilization of the photoproducts in chemical routes, b) The processes outlined in eq. 2-4 are multi electron transfer reactions, while the photochemical reactions are single electron transformations. Thus, the design of catalysts acting as charge relays is crucial for the accomplishment of subsequent chemical fixation processes. 

Research on multi-electron transfer reactions. These are different mechanisms from photovoltaics... 

The intermediate can therefore be considered as a photogenerated surface state. The formation of adsorbed intermediates is a common feature of multi-electron transfer reactions. Other examples are encountered in the photodecomposition of compound semiconductors, for example the pho-toanodic decomposition of n-CdS (cf., equation (8.9)). 

Koper MTM. Thermodynamic theory of multi-electron transfer reactions Implications for electrocatalysis. J Electroanal Chem 2011 660 254-60. 

When metallo-enzymes effect the oxidation or rednction of organic snbstrates or simple molecules such as H2O, N2 or O2, they often function as multielectron donors or acceptors with two or more metals at the active The electronic conpUng between the metals is often accompanied by uniqne spectroscopic features such as electron spin spin coupling. The metal metal electronic coupling may facilitate the multi-electron-transfer reactions with the snbstrates. In simpler molecular systems, two electron-transfer processes most often reqnire snbstrate binding , as in an inner-sphere, gronp (or atom ) transfer process. ... 

Polymetallated porphyrins obtained by attaching [Ru(bipy)2Cl]+ complexes to the peripheral pyridyl residues are able to act as efficient catalysts in multi-electron transfer reactions [60-66] Thus, porphyrins bound to [Ru(bipy)2Cl]+ in cis or trans positions (Fig. 14.19) can also be used for the electrocatalysis of sulfite. 

The frequency of the minimum in the semicircle is equal to the sum of the rate constants for charge transfer and recombination cum/n = k,r + krec- Light modulated microwave measurements therefore provide the sum of the two rate constants, but since it is possible to measure /c,r at high band bending where recombination is negligible, the rate constants can be separated if it is assumed that k,r is independent of potential (this assumption may not be valid for multi-electron transfer reactions as noted in section 4.2). 

---