Comprehensive Study of Transient Mass Transport to Platinum Interdigitated Electrode Arrays to Perform Electrochemical pH Adjustment: Experimental and Numerical

Precise pH control is a well-known and necessary process in many biological and chemical applications. Monitoring pH is achieved by adding buffering agents, such as salts of a weak acid and a weak base, to the experimental assays. Local pH adjustment can significantly affect the rate and activity of the electrochemical reactions. It is evident that a comprehensive study of pH change provides in-depth insight into electroanalysis by locally control acidic conditions. In this article, a finite element method has been employed to perform a comprehensive experimental and numerical study of interdigitated electrode arrays to investigate mass transport to the electrode arrays and control the pH change in the buffered and unbuffered solutions. A microfluidic device has been fabricated to visualize the pH change by using a pH indicator to perform image processing and verify the numerical method. Moreover, a 3D numerical model has been developed to couple an electrochemical system with a hydrodynamic flow. Our results revealed that local pH depends highly on the electrode configuration, current density, and buffering capacity in the diffusion-based system, while initial pH has no significant effect on adjusting local pH. By coupling the hydrodynamic flow, convective transport dominates the proton transport along the flow direction. Flow hydrodynamics directly relates to the diffusion process of the protons and pH variation. In such systems, pH control could be enhanced by balancing convective effects and modifying the geometrical parameters, including microchannel height and electrode separation.