Hydrogen peroxide electrocatalytic reduction

Armstrong FA, Bond AM, Buchi FN, Hanmett A, Hill HAO, Lannon AM, Lettington OC, Zoski CG. 1993. Electrocatalytic reduction of hydrogen-peroxide at a stationary pyrol3ftic-graphite electrode surface in the presence of cytochrome-c peroxidase— A description based on a microelectrode array model for adsorbed enzyme molecules. Analyst 118 973-978. 

A.A. Karyakin, E.E. Karyakina, and L. Gorton, The electrocatalytic activity of Prussian blue in hydrogen peroxide reduction studied using a wall-jet electrode with continuous flow. J. Electroanal. Chem. 456, 97-104 (1998). 

Clays are usually cation-exchangeable aluminosilicates, and exfoliated clay particles have a platelet shape with nanoscopic size. Cast protein-clay films on electrodes have been used to immobilize proteins. The Clay/Mb electrode has good electrocatalytic properties for the reduction of oxygen and hydrogen peroxide [236] and the biosensors can also be made based on these properties. 

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 ... 

SCHEME 5. Mechanism of electrocatalytic reduction of hydrogen peroxide with a biosensor. Top Direct reduction with enzyme-modified CPE. Bottom Accelerated reduction with enzyme-modified CPE, incorporating a mediator M (e.g. 150). The potential is relative to SCSE... 

Table 13 gathers the main electrocatalytic processes triggered by POMs dissolved in solution. The electrocatalytic reductions of dioxygen, hydrogen peroxide and of several NOx including nitrite, nitric oxide, and nitrate are selected for a more detailed description. 

Electrocatalytic Reduction of Dioxygen and Hydrogen Peroxide These two processes must be emphasized because reduction of dioxygen, and eventually hydrogen peroxide, features the usually claimed pathway for reoxidation of reduced POMs after the participation of the latter in oxidation processes. As a consequence, electrocatalysis of dioxygen and hydrogen peroxide reduction is a valuable catalytic test with most new POMs [154, 156,161]. 

Examination of the dioxygen and hydrogen peroxide electrocatalytic processes discussed here may also shed some light on possible reaction pathways. Dioxygen does not coordinate to Fe(III) butitdoesco-ordinate to Fe(II). Then, the presence of another reduced Fe center could drive the catalytic process to completion by carrying out immediate further reduction of the Fe-02 adduct. In-line with these observations, the... 

Although 2e reduction with fast, chemically catalyzed H202 disproportionation, seems to be the mechanism of highest importance, it had been shown that hydrogen peroxide also can be electrocatalytically reduced to water according to... 

The use of a PPy film as a convenient matrix for dispersing an oxygen reduction electrocatalyst is questionable since the PPy matrix can react itself with O2, leading to H2O2 by a two-electron transfer reaction [13,15]. Hydrogen peroxide can then oxidize the PPy film, leading to degradation of the polymer and to a decrease of the electrocatalytic activity with time. 

Apart from poisoning by adsorbing impurities, the working electrode potential can also contribute to suppress electrocatalytic activity. Platinum metals, for instance, passivate or form surface oxygen and oxide layers above 1 V (Section IV,D), which inhibit Oj reduction (779,257,252) and oxidation of carbonaceous reactants (7, 78, 253, 254) however, decomposition of hydrogen peroxide on platinum is accelerated by oxygen layers (255). Some electrocatalysts may corrode or dissolve, especially in acidic electrolytes, while reactants may contribute to dissolution. Thus, ethylene oxidation on palladium to acetaldehyde proceeds via a Pd-ethylene complex, which releases colloidal palladium in solution (28, 29). Equivalent to this is the surface roughening and the loss of Pt in gas phase ammonia oxidation (256, 257). 

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