The effect of pore boundary shape on the performance of catalytic self-pumping membranes and channels

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Many technologies demand highly controllable membranes, including lab-on-a-chip systems, microfluidic sensors, and electrochemical cells. The pumps for these systems can be scaled down by many orders of magnitude with electrochemical pumps, and more still with recently invented membrane pumps. Such pumps have been demonstrated to independently pump fluid via catalytic reactions that create and consume H+ cations on opposite sides of the membrane. Our prior work showed that the mechanism behind this phenomenon was a self-generated electric field driving the fluid flow caused by the space charge polarization due to the electrochemical reactions. However, that work assumed that the pores inside a membrane were perfectly cylindrical, which is not always true. This work investigates more complicated and realistic structures that deviate from a perfectly cylindrical shape, as is typical of actual track-etched or polymeric membranes. The pore structures were studied using a 2D model, which solved the Poisson-Nernst-Planck-Stokes equations in COMSOL 5.5. Based on our previously validated model, we examine the impact of different parameters on self-pumping flow rates, including pore width, contracting/expanding variation, pore length, and pore inclination angle. According to the results, the self-pumping flow rate is more sensitive to pore width than pore length. Regarding the effects of pore defects, membranes with complicated shapes of contracting/expanding pores and cross-linked connecting pores should follow the same pattern as those membranes with straight pores and similar pore size; likewise, pore inclination does not significantly influence self-pumping flow. Therefore, the conclusions we obtained for cylindrical straight pores are still applicable. The results highlight the potential of utilizing catalytic reactions to manipulate liquid via actual track-etched membranes.