Fig. 2

Transmembrane ionic transport. a Schematic of the experimental setup to measure the transmembrane ionic transport. b I–V curves of composite membrane with an ANF weight content of 11% recorded in neutral KCl electrolyte with different concentrations. c Conductance measurement in KCl electrolyte. The ionic conductance deviates from bulk value (red line) at low concentration region, indicating a charge-governed ion transport. Inset: The charged state of MXene and ANF. d I–V curves of composite membrane with an ANF weight content of 11% recorded in 1000-fold KCl concentration gradient under forward and reverse diffusion directions. e The recorded diffusion potential and diffusion current under a series of concentration gradient. The low concentration side is set to 0.1 mM. Error bars represent s.d. f The ion selectivity, defined as transmembrane ion transference number, increases from about 0.6 to 0.8 with increasing concentration gradient