Direct evidence of concentration and potential profiles in the electrolyte diode

Electrolyte diode is an electrochemical microsystem showing complex nonlinear behaviour due to interactions of diffusion, migration and chemical reactions. In our recent works we have developed a mathematical model of the electrolyte diode which predicted steep concentration and potential profiles on a spatial interval of several micrometers in the closed mode. The main aim of this work is the experimental verification of the concentration and potential profiles predicted by the model. In this work two techniques for direct observation of spatial concentration and potential profiles in the electrolyte diode are presented. Two different methods were used: (i) visualization of the acid–base boundary using acid–base indicators and (ii) direct measurements of electric potential profiles using the array of microelectrodes. As the presence of an indicator changes the properties of the system, there is a good agreement between modelling and experimental results only at relatively low values of external potential difference. Results of the other method confirm the model predictions in broad range of external potential difference values.