Nonlinear streaming currents: Non-negligible conduction current through a highly charged nanoporous layer

Streaming currents, which convert mechanical energy into electrical current, typically generate minute currents so that various methods for enhancing these currents have been extensively studied. We have applied a highly charged nanoporous coating to the walls of microchannels for this purpose. However, this leads to a nonlinearity between flow rates and resulting currents, largely deviating from the classical theory. We examined that the nonlinearity intensifies with increasing layer thickness or decreasing electrolyte concentration. Further investigations unveiled that the nonlinearity is resulting from the non-negligible conduction current within the nanoporous layer that flows counter to the applied pressure. Finally, a scaling analysis quantifies the layer's physicochemical parameters on this nonlinearity. These insights guide the design of efficient electrokinetic systems utilizing the streaming current, balancing the need for high current throughput with minimal nonlinearity.