Janus Nanoporous Metal–Phenolic Nanosheet Membranes for Highly Efficient Osmotic Energy Harvesting

ABSTRACT Osmotic energy, harvested by reverse electrodialysis, is a huge and promising renewable power source. However, the implementation still remains a longstanding bottleneck due to the lack of high‐efficiency membranes with both remarkable ionic conductivity and high permselectivity. Here, we report a new membrane constructed by Janus nanoporous metal–phenolic nanosheets (Janus MPNs), which overcomes the intrinsic trade‐off between ion permeability and selectivity. The Janus MPNs prepared via a facile interface‐induced coordination assembly strategy feature an asymmetric bilayer architecture comprising a microporous domain containing ∼0.96 nm pores and a mesoporous domain containing ∼9.4 nm pores, with each domain approximately 10 nm thick. The assembled Janus MPNs membrane integrates interlayer 2D nanofluidic pathways with ordered intralayer 1D nanochannels, enabling ultrafast ion transport rates approximately 21 times those of membranes relying solely on interlamellar transport. More importantly, the intrinsic sub‐nanometer pores and abundant negative surface charges within the metal–phenolic framework enable high cation selectivity, yielding a cation transference number ( t + ) of ∼0.936. When applied in reverse electrodialysis, the Janus MPNs membrane delivers a power density of 22.1 W m −2 under a simulated sea/river salinity gradient, outperforming state‐of‐the‐art two dimensional (2D)‐material‐based membranes. This work establishes new scaffolds for membrane technology and osmotic energy harvesting.