Potential reaction layer approach

The disadvantage of the rigorous approach to this type of problem is that the mathematics are very difficult for any case except the most simple e.g., this first order reaction). Instead, it is common to consider the somewhat vague concept of the reaction layer . This is an approach which gives a physical idea of the processes involved as well as allowing rate coefficients to be derived for more complicated kinetic mechanisms. The reaction layer is a hypothetical layer surrounding the electrode within which all the HA molecules produced by reaction (9) reach the electrode and are reduced. Its thickness p depends on the reverse rate coefficient, ky, (p = Suppose the applied potential is only sufficient to discharge... 

Advances in nanostructured conducting materials for DET have resulted in impressive current densities for the ORR, and application of these three-dimensional materials to DET from MCOs other than CueO may provide biocathodes with the characteristics suitable for an implantable EFC. While a DET approach using MCOs can provide for ORR at potentials approaching the thermodynamic reduction potential for oxygen, the current density achievable in this approach still relies upon intimate contact, and correct orientation, ofthe MCO to a conducting surface. Use of a mediator, capable of close interaction with the TI site of the MCOs, and with a redox potential tailored to permit rapid electron transfer to the TI site, can eliminate the requirement for direct contact in the correct orientation between MCO and electrode, and offer the possibility of a three-dimensional biocatalytic reaction layer on electrodes for higher ORR current densities. 

Macroscopic experiments allow determination of the capacitances, potentials, and binding constants by fitting titration data to a particular model of the surface complexation reaction [105,106,110-121] however, this approach does not allow direct microscopic determination of the inter-layer spacing or the dielectric constant in the inter-layer region. While discrimination between inner-sphere and outer-sphere sorption complexes may be presumed from macroscopic experiments [122,123], direct determination of the structure and nature of surface complexes and the structure of the diffuse layer is not possible by these methods alone [40,124]. Nor is it clear that ideas from the chemistry of isolated species in solution (e.g., outer-vs. inner-sphere complexes) are directly transferable to the surface layer or if additional short- to mid-range structural ordering is important. Instead, in situ (in the presence of bulk water) molecular-scale probes such as X-ray absorption fine structure spectroscopy (XAFS) and X-ray standing wave (XSW) methods are needed to provide this information (see Section 3.4). To date, however, there have been very few molecular-scale experimental studies of the EDL at the metal oxide-aqueous solution interface (see, e.g., [125,126]). 

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