A microfluidic electrochemical cell with integrated PdH reference electrode for high current experiments

Abstract

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.

Design of Electrochemical Microfluidic Detectors: A Review

“…Many such systems exist, for example standard or reversible hydrogen electrodes (SHE or RHE), the silver-silver chloride system (Ag|AgCl), mercury-mercury sulfate electrodes, and standard calomel electrodes (SCE). For integration in microfluidic systems, two strategies can generally be used, firstly to have an external reference electrode that is connected through the electrolyte or a salt bridge to the working electrode, often in the outlet reservoir, [57][58][59] see Figure 2a, or to have an internal reference electrode embedded in the microfluidic cell, [60] see Figure 2b. The first approach is more flexible in terms of the choice of reference electrode system and can generally be used for all types of reference electrodes, also involving gases such as the SHE and RHE systems.…”

“…Palladium hydride (PdH) has also been used and shown stability for several hours. [60] Due to the influence of the electrolyte, the reference electrode is often placed in a side channel separate from the flow and with an undisturbed electrolyte or separate electrolyte supply, see example in Figure 2b. Pseudo-reference electrodes can also be used, where the potential is not as wellknown or as stable as standard reference systems.…”

“…On the other hand, the top-bottom configuration in the right of Figure 2d gives straight current lines (black lines), which is both ideal for even current distribution on the electrodes and establishes a well-defined potential distribution in the electrolyte. This alleviates problems with potential distribution in the channel, for example, in a recent work by Fanavoll et al [60] , it was argued that the measurement of the potential at the working electrode was not feasible when the counter electrode was downstream of the working electrode and the reference electrode was placed in the outlet chamber. As such, they implemented an internal Pd-H reference electrode that was placed upstream of the working electrode to alleviate this problem.…”

“…Reproduced with permission. [60] Copyright 2016, Elsevier Ltd. c) Electrode positions: bottom wall, side wall, bottom and top walls, side, top, and bottom walls. d) Potential and electric field lines modeled using COMSOL Multiphysics 4.3b for a 100 × 100 μm cross-section of a microchannel where (left) represents electrode pads (5 × 20 μm), (middle) represents wire electrodes (radius 10 μm), and (right) represents an ideal, conformally coated electrode on the side walls of the channel.…”

Microfluidic bioanalytical flow cells for biofilm studies: a review

“…Electrode integration remains at the heart of the movement towards highly integrated, system-level microfluidic platforms, with examples in biosensing, point-of-care diagnostics, sample manipulation, high current applications, imaging, and other areas. [108][109][110][111][112] These technical successes are attributed to the diverse backgrounds of microfluidic community researchers, and a wide range of suitable materials and microfabrication techniques for creation and integration of miniaturised electrodes. [113][114][115] Therefore, the stage has been set for innovative electrochemical studies of biofilms in microchannels.…”