Postma, J.I.; Deiters, G., Haverkort, J.W
Delft University of Technology, Process & Energy, Leeghwaterstraat 39, 2628 CB Delft, Netherlands.
* Corresponding author: j.i.postma-1@tudelft.nl
Abstract In alkaline water electrolysis a membrane or diaphragm is typically used to reduce gas cross-over. While this leads to additional resistive energy losses, it does not fully mitigate product impurity and safety concerns [1,2]. Membraneless flow-through electrolyzers have several advantages over conventional or zero gap membrane-based designs [3], including lower ohmic dissipation, lower cost, and lower gas cross-over and improved mass transfer. The main design principle of flow-through electrolyzers is to flow the electrolyte across the porous electrodes, in opposing directions, to prevent gas cross-over. One of the problems of this design is the inhomogeneity of the cross flow along the electrodes, since it reduces its techno-economic performance. Here, we propose a new design in which the discharge channel width is varied to give a uniform flow distribution (Figure 1). An analytical expression is used to determine the optimal discharge channel geometry. The effectiveness of this analytically obtained shape was confirmed with simulations in COMSOL (Figure 2). This geometry aids in maintaining a small pressure drop across the porous electrode. Consequently, the inlet velocity can be increased to keep the majority of the produced gases dissolved in the electrolyte. A prototype has been designed and the initial experimental results will be shared.
Figure 1: Velocity profile for the novel discharge channel geometry. The variable channel width ensures uniform flow through the electrodes.
Figure 2: Flow velocity through electrode for the straight in blue and novel discharge channel geometry in red from COMSOL simulations. The variable discharge channel width results in a more uniform flow through the electrode.
Key words Flow Through Electrolyzer, Microfluidic Flow Cells, Analytical Optimization, Membraneless Laminar Flow
Bibliography
[1] HAUG Philipp, KOJ Matthias, TUREK Thomas; Int. J. Hydrogen Energy; 10.1016/j.ijhydene.2016.12.111
[2] RAJAEI Hadi, RAJORA Aviral, HAVERKORT J.W. (Willem); J. Power Sources; 10.1016/j.jpowsour.2020.229364
[3] HAMPSON N.A., MCNEIL A.J.S.; SPR Electrochemistry; 10.1039/9781847559944-00001