Surface termination engineering of MXene nanofluidic membranes for efficient osmotic energy harvesting

Abstract

The surface chemistry of two-dimensional (2D) materials plays a pivotal role in regulating ion transport and boosting osmotic energy conversion. Nevertheless, a systematic and comprehensive understanding of the correlation between surface termination and ionic behavior remains insufficient. In this study, we establish, for the first time, a direct relationship between ionic transport properties and specific surface terminal atoms. As a proof of concept, we successfully engineered Ti₃C₂T_x MXenes with precisely tailored surface terminations. These 2D nanofluidic membranes exhibit well-defined surface-charge-dependent ion transport and exceptional cation selectivity. Leveraging synergistic chlorine–chlorine interactions, the Ti₃C₂Cl₂ nanofluidic membrane achieved an outstanding osmotic power output of up to 17.84 W m⁻² under a 500-fold salinity gradient, surpassing most reported MXene-based energy generators. Theoretical insights further reveal that Cl–Cl interactions promote a chlorine-rich surface environment, enhancing negative surface charge density and facilitating cationic adsorption and selective passage. This work highlights surface termination engineering as a powerful strategy for tuning nanofluidic ion transport and osmotic energy conversion, providing deep insights into the atomistic-level governance of ionic selectivity in 2D nanofluids.