Electrochemical irreversibility

For a totally irreversible electrochemical process, the heterogeneous rate constant ke for electron transfer at the CV peak potential Ep is given by... 

It is difficult to incorporate dehydrogenases that are coupled with NAD(P) into amperometric enzyme sensors owing to the irreversible electrochemical reaction of NAD. We have developed an amperometric dehydrogenase sensor for ethanol in which NAD is electrochemically regenerated within a membrane matrix. 

On one hand, the ionic conductor was unique in creating dynamic junction in LEC. On the other hand, the slow ionic motion and irreversibly electrochemical doping under high biasing field were two of the challenges for polymer LECs to be used in practical applications. More recent works have been focusing on the following directions ... 

A series of complexes of type [Ru(N02)(PR3)2(tpy)] has been prepared starting from RuCl3 xH20. Changing the PR3 ligands causes the CV responses to vary from reversible to irreversible. Electrochemically generated [Ru(N02)(PR3)2(tpy)] is unstable with respect to... 

The Ru " complex [ P(OMe3 2ClRu(//-Se2)(//-Cl)2RuCl P(OMe)3 ] has been prepared and structurally characterized it undergoes irreversible electrochemical reduction. ... 

Electrochemical reduction of mononuclear binary carbonyls on the preparative timescale generally leads to CO loss and the formation of dinuclear dianionic products. For example, M(CO)6 (M = Cr, Mo, or W) undergoes irreversible electrochemical reduction near —2.7 V versus SCE in tetrahydrofuran (THF) containing [NBU4][BP4]. The product of the reductions are the dinuclear dianions [M2(CO)io] [14, 21], although under some conditions... 

M (CO)6 complexes all undergo irreversible electrochemical reduction in nonaqueous electrolytes at peak potentials close to —2.7 V versus SCE in tetrahydrofu-ran (THF) containing [NBu4][Bp4]. The product of the reductions are the din-uclear dianions [M2(CO)io] although under some conditions polynuclear products can also been obtained, Sch. 3 [2]. It was initially proposed that the primary step involved a single-electron transfer with fast CO loss and subsequent dimerization of the 17-electron radical anion [M(C0)5] [34]. A subsequent study showed that a common intermediate detected on the voltammetric timescale was the 18-electron species [M(CO)5] and that the overall one-electron process observed in preparative electrolysis arises by attack of the dianion on the parent material in the bulk solution, Sch. 2 [35]. 

Grygar T (1998) Phonomenological kinetics of irreversible electrochemical dissolution of metal-oxide microparticles. J Solid State Electrochem 2 127-136. 

The cyclic voltammetry of methyltriarylphosphonium tosylates exhibits irreversible electrochemical reduction and oxidations at glassy carbon and platinum electrodes40. 

Irreversible electrochemical oxidation of dimeric 4//-pyrans 163 to monomeric pyrylium ions at about +0.6 V was observed.225,227,228 The anodic oxidation of the dimers in the presence of aromatic hydrocarbons caused electroluminiscence of the latter.228,472 The polarographic oxidation of carbo-ranyl 4//-pyran 174a (R = Ph) at a platinum microelectrode was found to... 

Osmiwn(IV), (V) and (VI). The existence of [0=OsIV(terpy)bipy]2+ has already been mentioned (see above).195 Irreversible electrochemical oxidation of this occurs from pH 1 to 12 at + 1.05 V, and the initial product is thought to be [0=0sv(terpy)bipy]3+ which then loses a bipyridyl ligand and undergoes a further one-electron oxidation to [0s02(terpy)(0H)]+. At pH 13.5 a... 

The irreversible electrochemical oxidation of [Ir(X)(CO)(PR3)2] (X = Cl, Br, I PR3 = PPh3, PPh2Et, PPhEt2, PEt3) on rotating Pt electrodes in Bu4NC104/CH2Cl2 reportedly proceeds at diffusion-controlled rates. In the redox addition process, atom transferability predominates over complex redox properties. Evidence indicates that the insoluble product of the one-electron oxidation of [Ir(X)(CO)(PR3)2] is a dimeric iridium(II) complex with an iridium-iridium bond.96... 

Silver(II) complexes are not technically difficult to make, but they are unstable in aqueous solutions unless stabilized by ligands (typically nitrogenbased). Anumberof different oxidants including SaOg, PbOa, and ozone can be used to oxidize sUver(I) to sUver(II). Electrochemical methods also can oxidize sUver(I) compounds to higher oxidation states. Silver(III) species also can be accessed chemically or electrochemi-cally, but are often unstable in the presence of water or many organic molecules and show irreversible electrochemical reductions (12,13). 

Examples of the interaction between Ir(I) and macro-cyclic ligands include (CO)3lr(/u.-TPP)Ir(CO)3 (H2TPP = tetraphenylporphyrin). The complex undergoes three irreversible electrochemical oxidations leading to [Ir(TPP)]+. ... 

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