Accurate numerical electrochemical impedance spectra at channel electrodes are obtained using commercial finite element method software. These agree with experimental measurements on the hexaammineruthenium(II/III) reversible redox couple. The numerical solutions are used as a benchmark to test the validity of some common analytical approximations for the mass-transport impedance.

A microfluidic electrochemical cell with integrated PdH reference electrode for high current experiments. Electrochimica Acta, 225, 69-77. AbstractAn on-chip thin-film palladium hydride reference electrode is described for use with microfluidic electrochemical cells. A Pd electrode fabricated by photolithographic methods is charged with hydrogen in-situ with a simple current step technique. The placement of the reference electrode in a side channel means that it is unaffected by species in the main channel. Placement upstream of the working and sense electrodes is shown to be a significant improvement over cells with the reference electrode placed externally. The adverse effects of solution resistance are investigated quantitatively, and it is shown that the described configuration allows for high current experiments while maintaining accurate potential measurement. A simple formula for calculating the maximum current density for a certain cell geometry and electrolyte resistivity is presented.

A method for measuring downstream concentration effects through electrochemical impedance spectroscopy at double channel electrodes is demonstrated. An ac current perturbation is applied at an upstream working electrode and the resulting ac potential response at a downstream sensing electrode is measured. This generator-detector scheme is implemented with a single potentiostat. Experimental data for a reversible redox couple are presented and good agreement is found with numerical simulations. A qualitative explanation of the features is given which lays the foundation for a more rigorous theoretical treatment. Relationships with flow rate and frequency are found that can scale the data to lie on a universal curve.