Conducting composite electrodes are versatile devices for biomedical applications
showing good biocompatibility, low cost, ease of construction. They can be bulk
modified with stabilised enzymes to make biosensors and electrodes for biofuel cells.
Low sensitivity to flow conditions arises from the microelectrode array like behaviour
but this is accompanied by high capacitance and bulk resistance which can blur the
voltammetric detail.
We have undertaken a systematic investigation of the effects of composition and
formulation on the voltammetric behaviour and non-faradaic properties. Monodisperse
glassy carbon spherical powders have been used to simplify the modelling and the
relative importance of the patterns of surface conductivity and bulk 3-D connectivity
has been investigated. Three dimensional numerical models based on percolation theory
have been constructed which allow calculation of the distributed resistances in the
composite and which enable qualitative prediction of the voltammetric properties.
Voltammetric results showed a bias of E1/2 (half-wave potential) and an unstable il
(diffusion limiting current) for conducting composite electrodes. A.C. Impedance
showed major changes of Rct (charge transfer resistance) and Cd (double layer
capacitance) as the electrodes’ ratio and thickness are varied. Comparison with carbon
fibre arrays separates the effects of a distributed interface from three dimensional
disparities in the conductance. Key findings are: the distributed resistance in electrodes
results in bias for E1/2 and the overlap of diffusion layers on electrode surface leads to
an uneven il.
Numerical results have shown that the bias of E1/2 and il are in good agreement with
experimental works. Different geometric configuration allows the investigation of
diffusion layer difference caused by electrode array location and different internal
resistance.