Fine-tuned ion transport across nanoscale pores is key to many biological processes, including neurotransmission. Recent advances have enabled the confinement of water and ions to two dimensions, unveiling transport properties inaccessible at larger scales and triggering hopes of reproducing the ionic machinery of biological systems. Here we report experiments demonstrating the emergence of memory in the transport of aqueous electrolytes across (sub)nanoscale channels. We unveil two types of nanofluidic memristors depending on channel material and confinement, with memory ranging from minutes to hours. We explain how large time scales could emerge from interfacial processes such as ionic self-assembly or surface adsorption. Such behavior allowed us to implement Hebbian learning with nanofluidic systems. This result lays the foundation for biomimetic computations on aqueous electrolytic chips.

Carbon emerged as a unique material in nanofluidics, with reports of fast water transport, molecular ion separation, efficient osmotic energy conversion. Many of these phenomena still await proper rationalization due to lack of fundamental understanding of nanoscale ionic transport, which can only be achieved in controlled environments. Here, we develop fabrication of 'activated' two dimensional carbon nanochannels. Comparing to nanoconduits with 'pristine' graphite walls, this enables investigation of nanoscale ionic transport with unprecedented details. We show that 'activated' carbon nanochannels outperforms pristine channels by orders of magnitude in terms of surface electrification, ionic conductance, streaming current, (epi-)osmotic currents. A detailed theoretical framework allows us to attribute the enhanced ionic transport across activated carbon nanochannels to an optimal combination of high surface charge and low friction. Further, this demonstrates the unique potential of activated carbon for energy harvesting from salinity gradients with single-pore power density across activated carbon nanochannels reaching hundreds of kW/m 2 , surpassing alternative nanomaterials.