The electrokinetic effect of a charged polymer coating layer on the streaming current generation through microchannels

For mechanical-to-electrical energy conversion, we experimentally and numerically investigate streaming current which arises from charge movement in the electrical double layer (EDL), where electrolyte solution in channels with charged surfaces flows under pressure. We utilize a well-defined tournament-style microchannel for parametric study on the generation of streaming current. Particularly, as the surface charge plays a crucial role in streaming current generation, we coat the microchannel walls with a highly charged polymer, Nafion, to enhance the energy conversion efficiency by increasing the surface charge. With and without Nafion coating, the streaming current of the channel has different trends of with respect to another parameter, the flow rate. In the bare channel, the streaming current exhibits a linear increase with the flow rate, while in the Nafion-coated channel, it shows a non-linear response. Our numerical analysis reveals significant convective currents within the coating layer, explaining the non-linear behavior of streaming current. Therefore, by optimizing the polymer coating to have the minimal convective currents within itself, we aim to develop a streaming current generator with enhanced energy conversion efficiency.