Unleashing the Power of Osmotic Energy: Metal Hydroxide‐Organic Framework Membranes for Efficient Conversion

Abstract Osmotic energy, as a renewable clean energy with huge energy density and stable yield, has received widespread attention over the past decades. Reverse electrodialysis (RED) based on ion‐exchange membranes is an important method of obtaining osmotic energy from salinity gradients. The preparation of ion‐exchange membranes with both high ion selectivity and ion permeability is in constant exploration. In this work, metal hydroxide‐organic framework (MHOF) membranes are successfully prepared onto porous anodic aluminum oxide (AAO) membranes by a facile hydrothermal method to form Ni 2 (OH) 2 @AAO composite membranes, used for osmotic energy conversion. The surface is negatively charged with cation selectivity, and the asymmetric structure and extreme hydrophilicity enhance the ionic flux for effective capture of osmotic energy. The maximum output power density of 5.65 W m −2 at a 50‐fold KCl concentration gradient is achieved, which exceeds the commercial benchmark of 5 W m −2 . Meanwhile, the composite membrane can also show good performance in different electrolyte solutions and acid–base environments. This work provides a new avenue for the construction and application of MHOF membranes in efficient osmotic energy conversion.