Controlling ion transport in nanofluidics is fundamental to water purification, bio-sensing, energy storage, energy conversion, and numerous other applications. For any of these, it is essential to design nanofluidic channels that are stable in the liquid phase and enable specific ions to pass. A human neuron is one such system, where electrical signals are transmitted by cation transport for high-speed communication related to neuromorphic computing. Here, we present a concept of neuro-inspired energy harvesting that uses confined van der Waals crystal and demonstrate a method to maximise the ion diffusion flux to generate an electromotive force. The confined nanochannel is robust in liquids as in neuron cells, enabling steady-state ion diffusion for hundred of hours and exhibiting ion selectivity of 95.8%, energy conversion efficiency of 41.4%, and power density of 5.26 W/m2. This fundamental understanding and rational design strategy can enable previously unrealisable applications of passive-type large-scale power generation.