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A Theoretical and Experimental Study of Electrochemical pH Control at Gold Interdigitated Microband Arrays

In electroanalysis, solution pH is a critical parameter that often needs
to be adjusted and controlled for the detection of particular analytes. This is
most commonly performed by the addition of chemicals, such as strong acids or
bases. Electrochemical in-situ pH control offers the possibility for the local adjustment
of pH at the point of detection, without additional reagents. FEA simulations
have been performed to guide experimental design for both electroanalysis and in-situ
control of solution pH. No previous model exists that describes the generation
of protons at an interdigitated electrode array in buffered solution with one
comb acting as a protonator, and the other as the sensor. In this work, FEA
models are developed to provide insight into the optimum conditions necessary
for electrochemical pH control. The magnitude of applied galvanostatic current
has a direct relation to the flux of protons generated and subsequent change in
pH. Increasing the separation between the electrodes increases the time taken
for protons to diffuse across the gap. The final pH achieved at both,
protonators and sensor electrodes, after 1 second, was shown to be largely
uninfluenced by the initial pH of the solution. The impact of buffer concentration
was modelled and investigated. In practice, the pH at the electrode surface was
probed by means of cyclic voltammetry, i.e., by cycling a gold electrode in
solution and identifying the potential of the gold oxide reduction peak. A pH indicator, methyl red, was used to
visualise the solution pH change at the electrodes, comparing well with the
model’s prediction