Electrocatalytic reduction cycle

An Electrocatalytic Reduction Cycle using Low-valent Tungsten... 

Figure 13. Postulated mechanistic cycle for the electrocatalytic reduction of CO2 into CO by Nicyclam in water. Reprinted with permission from Ref. 184, Copyright (1986) American Chemical Society.

Electrode processes in experiments with redox indicators involved one or a few electrons and were, therefore, inherently low-yield reactions. Recently catalytic processes have been used to collect as many electrons as possible ([327, 454, 455] E. Palecek, M. Fojta, and L. Havran, unpublished). Thorp [327] used a soluble mediator that moved close to G residues present only in target DNA (but absent in the probe) and shuttled electrons to the polymer-modified ITO electrode. The reduced form of the mediator [Ru(bipy)3] + was oxidized by holding the electrode at a sufficiently positive potential. The oxidized form of the mediator removed electrons from G residues, generating reduced [Ru(bipy)3] + and completing a catalytic cycle. About 100 electrons per hybridized G could be collected under favorable conditions. Horseradish peroxidase coupled to target DNA was applied to detect the hybridization by electrocatalytic reduction of hydrogen peroxide... 

Electrocatalytic Reduction of Oxygen. Oxygen reduction reaction (ORR) occurs on the cathode side of low temperature fuel cells and heavily loaded Pt/C is the most common electrocatalyst. Replacement of ORR catalysts with less expensive materials would have higher technical impact than for anode catalysts. Transition metals loaded carbides and carbide-metal codeposited carbon have been investigated for ORR application. For example, 40 wt% Pt/WC electrocatalyst prepared with RDE electrode showed a cathodic current (-5 x 10 A) similar to that of 40 wt% Pt/C with 0.5 M H2SO4, 100 mv/s and 2000 rpm (160). Also, 40 wt% Pt/WC exhibited electrochemical stability after 100 cycles of cyclic voltammetry from 0 to 1.4 V (vs RHE), whereas the cathodic current of 40 wt% Pt/C disappeared after 100 cycles. 

Figure 5.18. Proposed redox cycle for the electrocatalytic reduction of oxygen to hydrogen peroxide on Co(II) hydroxide [99]. (Reprinted from Journal of Electroanalytical Chemistry, 599(2), Wass Tobias Johnsson JR, Panas I, Asbjomsson J, Ahlberg E. Quantum chemical modelling of oxygen reduction on cobalt hydroxide and oxyhydroxide, 295-312, 2007 with permission from Elsevier.)...

Scheme 5.6. Catalytic cycle for cooper phthalocyanine. Reprinted from Scheme 1 T.V. Magdesieva, I.V. Zhukov, D.N. Kravchuk, O.A. Semenikhin, L.G. Tomilova, and K.P. Butina, Electrocatalytic CO2 reduction in methanol catalyzed by mono-, di- and elec-tropolymerized phthalocyanine complexes, Russian Chemical Bulletin 41 (2002) 805-812. With permission of Springer, Kluwer Academic/Plenum Publishers.

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