Engineered Ionic Rectifier with Steep Channel Gradient from Angstrom‐Scale to Mesoscale Based on Ultrathin MXene‐Capped Single Conical Mesochannel: A Promising Platform for Efficient Osmotic Energy Generation

Abstract Ionic rectifier that mimics the directional ion transport in biological ion channels has been shown with potential toward boosting osmotic energy conversion performance. However, the achieved power by existing rectifying devices is still limited, because they are constructed based on tiny nanoscale channels, which experience high resistance. Here, a novel high‐performance ionic rectifier (abbreviated as MXene@MC) with steep channel gradient from angstrom‐scale to mesoscale is reported by capping an ultrathin 2D Ti ₃ C ₂ T _x MXene laminate on an asymmetric conical mesochannel (MC). The device can strongly rectify ionic current (with a high ratio of 7.3‐fold) even in high 0.5 m electrolyte solution, and thus a single channel can achieve an ultra‐large osmotic conductance of 0.596 µS. These features enable MXene@MC as an ultrahigh performance osmotic energy generator, achieving an unprecedented osmotic power of 343 pW under a 1000‐fold salinity gradient at neutral pH. Notably, simulations are also provided to demonstrate the findings of the proposed ionic rectifier and efficient osmotic energy conversion. This study unravels the underlying physics of ion transport induced by the apparent structural asymmetry of ion‐selective channels, thereby providing a promising platform for further development of high‐performance osmotic energy generators.