Crystal orientation control in angstrom-scale channel membranes for significantly enhanced blue energy harvesting

Abstract

Achieving high-performance blue energy harvesting from the interface between seawater and river water remains challenging, because the current ion-selective membrane suffers from a trade-off between ion permeability and selectivity. Here, we tackle this issue by manipulating the crystal orientations within metal–organic framework (MOF) MIL-178 membranes, including one with the a-axis perpendicular to the substrate, and the other with the b-axis similarly configured. We show that the MIL-178-a-oriented membrane exhibited over one order of magnitude faster ion transport than the MIL-178-b-oriented membrane, and one-dimensional angstrom-scale (∼3.2 Å) channels endow the former with ultrahigh ion selectivity. Consequently, the MIL-178-a-oriented membrane achieves an ultrahigh power density of ∼9.64 W/m2, with an unprecedented energy conversion efficiency of ∼38.5 % approaching the theoretical upper limit of 50 %, when simulated seawater and river water are mixed, surpassing all the reported non-oriented MOF-based membranes. This study presents a method for finely tuning preferred orientations within polycrystalline MOF membranes, enabling precise engineering of ultrahigh-performance osmotic energy conversion.