More efficient electrochemical energy conversion through near-wall flow control

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The demand for energy is growing continuously due to the rising world population and the industrialization of emerging economies. An increasing part of this demand has to be produced using regenerative energy sources. Some of these sources, such as wind power and sunlight are not continuously available. Thus, the efficient energy storage is of great importance. Especially the electro chemical energy conversion in fuel cells or cells for electrolysis plays an important role. Since the reaction in these devices takes place at the electrodes surface, microfluidic solutions seem to be favourable. The surface can be largely increased by keeping the necessary volume small. The connection in series of plenty such microfluidic fuel cells can be used to establish the necessary power. The aim of the proposed project is to increase the efficiency of the electro chemical energy conversion by the application of near wall flow control and to understand the underlying physical phenomena in order to improve the design of future devices. Therefore measurements of the velocity field and scalar distributions of temperature, pH-value and pressure with high spatial and temporal resolution will be applied in single and multiphase micro flows. The proposed project focusses on the control of the near wall convection by the application of electromagnetic volume forces in multiphase systems and the flow control via passive secondary flows for single phase systems.One goal is the development of a microfluidic fuels cell in which the fuel and the oxidant flow next to each other without convective mixing. Therefore the expensive membrane of conventional fuel cell is not necessary. The efficiency of such a microfluidic fuel cell shall be enhanced using convection due to secondary flows which removes the depletion layer from the electrodes and refreshes the solution. Another goal is the investigation of the flow around single hydrogen bubbles produced on a macroscopic electrode mimicking a real electrolyser. Therefore highly resolved measurements of the velocity and the temperature will be performed with and without the application of Lorentz forces. Furthermore, a Marangoni convection was seen for the first time during water electrolysis on microelectrodes and further measurements on macroscopic electrodes on single hydrogen bubbles shall help to investigate if the origin of this phenomenon is related to temperature or concentration gradients.