Biomimetic Dual Asymmetric MXene-Based Nanofluidics for Advancing Osmotic Power Generation

Nanofluidics-based reverse electrodialysis offers a promising approach for harnessing the osmotic energy that exists between saline and fresh water, thereby providing a sustainable source of power. Nevertheless, the key obstacle to realizing a commercially viable power output stems from inadequate ion permselectivity in nanofluidics. Here, we engineer dual asymmetric MXene-based composite nanofluidics (DA-MXCNs) composed of a negatively charged, porous MXene layer and a positively charged, confined MXene layer, which strategically incorporates asymmetric channel dimensions and opposing charge distributions. This design simultaneously reduces ion diffusion paths and amplifies ion potential differences, thereby optimizing the ion permeability and selectivity. The DA-MXCNs exhibit a 3.4-fold increase in ion flux (7.71 mmol m^-2 h^-1) over the unmodified nanofluidics, and thus a high Na⁺ selectivity coefficient of 0.985 and a Na⁺/Cl^- selectivity ratio of approximately 65.7, indicative of superior preferential cation transport. Experimental and theoretical evidence supports that the dual asymmetric manipulations not only enable unidirectional and rapid cation transport but also create a high energy barrier for anions and a low one for cations, thereby achieving ultrahigh ion selectivity. Utilizing the DA-MXCNs, the osmotic energy conversion system achieves an impressive power density of up to 126.0 W m^-2, which surpasses the performance of existing MXene-based nanofluidics and shows the capacity for powering a variety of electrical devices. This strategy, grounded in optimized permselective nanofluidics, lays the foundation for advancements in ion batteries and ion separation technologies.