Electrokinetic Energy Conversion by MicroChannel Array: Electrical Analogy, Experiments, and Electrode Polarization

摘要

This paper takes a system-wide perspective of electrokinetic energy conversion devices based on an array of microchannels to help understanding their operation. The approach taken was a combination of developing an electrical analogy and conducting experiments. The electrical analogy included current sources for the convection current, resistors for the conduction current, a capacitor for accumulating the partitioned ions, resistors for ion transport in the reservoirs, diodes and capacitors for the electrochemistry and polarization at the electrodes, and a simple external resistive load. The number of parallel channels profoundly affected the summative resistive and capacitive characteristics of the array, and highlights the differences between a single channel and an array of channels, especially in the transient responses and the role of the electrodes. The electrical analogy was solved by Laplace Transforms to demonstrate a rich and varied response that such a system exhibits to a step change in flow in relation to relative magnitudes of the various resistors and capacitors. Experiments were conducted on a structured glass microchannel array with approximately three million channels (10 μm diameter pore size) with aqueous KCl as the working fluid and tested a variety of electrodes. Besides providing data for in situ resistances and capacitances, in particular for the electrodes, keys aspects of the experimental results were interpreted using the electrical analogy. Results include the potential challenges in interpretation of externally measured potentials and currents as streaming potentials and streaming currents, respectively, measuring the resistances and capacitances of electrodes by novel methodologies, and using the electrical analogy quantitatively to explore maximizing electrokinetic energy conversion in the steady state.