Surface films charge transfer through

The ohmic loss is relatively easy to understand because the electrical resistance of the cell components behaves as a cause of voltage loss. However, determination of overpotential from the electrochemical reaction resistance at the electrodes has been an interesting research topic. The fuel cell electrodes require a large surface area to increase the reaction rate, and thus porous materials are employed. In addition, the electrode surface is covered by thin electrolyte film to provide the three-phase boundary of gas-liquid-solid where the electrochemical reaction occurs. Thus, the electrochemical resistance in MCFC is comprised of charge-transfer resistance on the electrode surface and mass transfer through the liquid film and gas channel as shown in Fig. 8.2. 

Electrochemical impedance spectroscopy, on the other hand, is typically used for affinity biosensing, in which antibodies or nucleic acids bioreceptors are attached to the working electrode surface. The charge transfer resistance experienced by those electroactive reporters diffused through the film of bioreceptors is a measure of the amount of bound analyte. However, this technique is highly sensitive to nonspecific adsorption (Rackus et al., 2015). 

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