Electron transfer diamond electrodes

The suitability of boron-doped diamond as anode material for the generation of aggressive reagents, such as bromine, has been investigated. Vinokur et al. reported that the electron transfer at boron-doped diamond electrodes is strongly affected by the nature of the electrode process. Irmer-sphere processes such as the bromine evolution from bromide seem to be Id-netically slow, [73,120] in particular, when occurring positive of a potential of approximately —0.05 V vs. SCE. This is currently limiting possible wider applications of boron-doped diamond electrode materials. 

Diamond surfaces after anodic oxidation treatment involve oxygen-containing surface functional groups. The electron-transfer kinetics for ions and polar molecules are expected to be quite different. Fe(CN)l /4 was highly sensitive to the surface termination of diamond. For an anionic reactant, there was an inhibition of the electron transfer for the oxygen-terminated diamond electrodes compared with the hydrogen-terminated diamond electrodes, and there was also an acceleration of the electron transfer for oxygen-terminated diamond for some cationic reactants such as Ru(NH3) +/3+ and Fe2+/3+. These results can be explained by electrostatic effects, which interact between the ionic... 

Duo, I. (2003) Control of electron transfer kinetics at boron-doped diamond electrodes by surface modification, PhD Thesis, Ecole Polytechnique Federale Lausanne. 

Refs. [i] HollemanAF, WibergN(1995) Inorganic chemistry. Academic Press, London [ii] Pierson HO (1993) Handbook of carbon, graphite, diamond andfullerenes. Noyes Publications, New Jersey [iii] McCreery RL (1991) Carbon electrodes structural effects on electron transfer kinetics. In Bard AJ (ed) Electroanalytical chemistry, vol. 17. Marcel Dekker, New York [iv] Banks CE, Compton RG (2005) Anal Sci 21 1263 [v] Conrad LS, HiUHAO, HuntNI, Ulstrup J (1994) JElectroanal Chem 364 17... 

Apart from a doping of the bulk phase, the electronic band structure may also be infiuenced by processes on the phase boundary between the diamond film and its environment For example, solutes like, for example, O2, CO2, or H2 contained in the water film adsorbed on the diamond surface may cause an electron transfer from or into the diamond electrode according to their chemical potential. With the latter being situated below the Fermi level of the electrode, electrons will be transferred to the adsorbed film until the same level is attained for both the diamond s Fermi level and the potential of the surface film (Figure 6.31). In doing so a p-doped space-charge zone arises directly in the diamond surface. At opposite conditions the electron transfer takes its course into the electrode and an n-doped zone is formed. 

M. E., Macpherson, J.V., and Unwin, P.R. (2012) Electrochemical mapping reveals direct correlation between heterogeneous electron-transfer kinetics and local density of states in diamond electrodes. Angew. Chem. Int. Ed., 51(28), 7002 - 7006. 

The past two decades have seen the establishment of a very extensive literature on the application of boron-doped diamond electrodes for the decoloration and the removal of COD and TOC from effluents, the disinfection and quality improvement of water, and the complete oxidation of particular organic molecules [26, 38, 39, 71-75]. There can be no doubt that boron-doped diamond anodes allow the effective killing of microorganisms and the complete oxidation of a wide range of organic compounds to carbon dioxide (and other inorganic fragments). Both direct and indirect mechanisms have been invoked. The direct mechanisms involve electron transfer and oxidation via weakly adsorbed OH radicals, while the indirect mechanisms have seen a role for solution-free OH radicals, ozone, sulfate radicals, or chlorine compounds if suitable anions are present or added. Indirect routes via ozone [20, 21] and sulfate radicals [40, 74, 76-78] can, of course, become dominant with appropriate selection of the conditions. This literature has been extensively reviewed and the interested reader is referred to these reviews [26, 38, 39, 71-75]. 

Lee, J, Einaga, Y., Fujishima, A, and Park, S.-M. (2004) Electrochemical oxidation of Mn " " on boron-doped diamond electrodes with Bi used as an electron transfer mediator. /. ElectrmJrem. Sm ., 151, E265—E270. 

Some oxidation systems have been reported to decompose perfluorocarboxylic acids (PFA) and the corresponding sulfonic acids (PFS) at bench scale. The primary products are PFAs with shorter chain length, CO2 and fluoride. The reaction is often proposed to be initiated by electron transfer from the ionic head group to an appropriate electron acceptor. In that regard, especially sulfate radical anions and electrolysis using boron-doped diamond electrodes have been reported to degrade PFA respectively PFS. 

Cyclic Voltammetric and Heterogeneous Electron Transfer Rate Constant Data for Four Aqueous-Based Redox Systems at Boron-Doped Microcrystalline Diamond Thin-Film Electrodes... 

VI. FACTORS AFFECTING ELECTRON TRANSFER AT DIAMOND ELECTRODES... 

A subsequent one-electron transfer occurs at more positive potentials, 0.9 V, to form the dication, CPZ", which is quickly hydrolyzed [179]. The electrode reaction kinetics for this redox system (CPZ/CPZ ) at diamond are mainly influenced by the density of electronic states at the formal potential [22,30]. Rapid electrode-reaction kinetics have been observed for boron-doped diamond electrodes, with no evidence of any molecular adsorption [22,30]. The QS jQp ratio for the CPZ/CPZ redox reaction is ca. 1. The ip and ip values varied linearly with the scan rate, while Qp and Qp were independent of scan rate. These trends are predicted for thin-layer voltammetric behavior. 

Diamond OTEs are also useful for studying the electrochemical and optical properties of important biomolecules, like cytochrome c. We recently reported that boron-doped microcrystalline diamond thin film electrodes are quite responsive for horse heart cytochrome c, exhibiting a very active and stable cyclic voltammetric response without any pretreatment or surface modification [119,124]. Heterogeneous electron-transfer... 

Nitrate electroreduction has been extensively studied over the last few decades. This reactitMi is a multi-electron transfer process showing different mechanisms as a function of pH, nitrate and supporting electrolyte concentration, chemical composition and structure of the catalyst. In recent years, nitrate electroreduction has been widely studied over diamond and many monometallic electrodes such as Pb, Ni, Zn or Rh, Ru, Ir, Pd, Cu, Ag and Au. Because none of the common pure metals is able to provide high selectivities for nitrogen, bimetallic alloys or monometals modified with foreign metal adatoms were prepared and evaluated for the reduction of nitrate. More recently, an electrochemical process in which nitrate ions are reduced to ammonia at the cathode, and where the produced ammonia is oxidized at the anode to nitrogen with the contribution of hypochlorite ions, has been evaluated. 

Boron as a dopant allows silicon and carbon materials to significantly change their conductivity and thereby open up applications in particular with boron-doped diamond (sp -carbon) as mechanically and chemically robust electrode material. The range of beneficial effects of boron in boron-doped diamond as electrode materiaP has been reported. Bio-electrochemical processes like the oxidation of NADH are possible with diamond dominating the interfacial chemistry. The sp nature of the diamond allows adsorption processes to be modified, and electrode erosion to be minimised, with electroanalytical application even under extreme conditions, for example in the presence of ultrasound and for pharmaceutical components. Boron surface functional groups have been reported to be crucial for electron transfer, for example, during glucose oxidation. ... 

Electrically conducting diamond is a new type of carlxm electrode material that is beginning to find widespread use in electroanalysis (86-88). The material possesses properties superior to other forms of carbon that include (i) low and stable background current over a wide potential range, (ii) wide working potential window in aqueous media, (iii) relatively rapid electron-transfer kinetics for several redox systems without conventional pretreatment, (iv) weak molecular adsorption, (v) dimensional stability and corrosion resistance, and (vi) optical transparency. The material is now available from several commercial sources and is not overly expensive, as commonly perceived (89). 

Diamond electrodes tend to be quite active for electron transfer without pretreatment, at least for some outer-sphere redox systems. Exposure to the laboratory atmosphere does not deactivate this electrode like it does other sp carbons (39). As deposited diamond... 

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