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