Photodriven Two‐Dimensional Optoelectronic Heterojunction Membranes for Highly Efficient Lithium Separation

ABSTRACT Efficient and selective lithium (Li + ) extraction from salt Lake brines, particularly in the presence of high concentrations of magnesium (Mg 2+ ), remains a critical challenge due to low separation efficiency and high‐energy consumption. Here, we report a two‐dimensional (2D) photoelectronic heterojunction membrane (PEM) constructed from graphene oxide (GO) and in situ grown CsPbBr 3 nanosheets. Confined within the interlayer nanochannels, CsPbBr 3 exhibits enhanced water stability, while under solar illumination, it captures photogenerated holes in GO and efficiently transfers electrons, generating a built‐in photogenerated microelectric field that enhances charge separation and transport while providing additional driving force, which facilitates rapid Li + migration while suppressing Mg 2+ transport. The membranes achieve a Li + /Mg 2+ selectivity of up to 97 under sunlight. Even after 264 h of cycling at room temperature, PEM membranes maintained high separation efficiency, highlighting GO's role in enhancing water stability and its industrial potential. Molecular dynamics simulations reveal that the microelectric field intensifies the diffusion of Li + , whereas the stronger electrostatic interaction between Mg 2+ and the heterojunction limits its mobility and further improves separation efficiency. This work establishes a new paradigm for light‐driven ion separation, offering an energy‐efficient and sustainable strategy for lithium extraction from complex brine systems.