Engineering Asymmetric Surfaces of Two-Dimensional Single-Layered Polyoxometalate-Layered Double Hydroxide Nanosheets...

Constructing two-dimensional (2D) asymmetric single-layered nanosheets (2D ASNs) with anisotropic microstructures, intrinsic gradient electric field, and unprecedented energy conversion efficiency remains a great challenge. Here, we present an interfacial-assisted out-of-plane assembly method to synthesize a novel type of 2D ASNs composed of layered double hydroxide (LDH), polyoxometalate (POM), and dioctadecyldimethylammonium. The synthesized asymmetric POM-LDH single-layered nanosheets (APLNs) exhibited two distinct surfaces: one with hydrophilic Mg(Al)-OH groups and the other with hydrophobic alkyl chains. Molecular dynamics simulations elucidated that the strong out-of-plane electrostatic forces drive the assembly process and stabilize the asymmetric structures. By varying the size and charges of POMs, we observed a consistent 1: 2 charge ratio between each POM and its corresponding occupied LDH laminate area. This finding was further validated by visualizing the distribution of electron-rich POMs through transmission electron microscopy, inferring that the surface charge distributions on the 2D surfaces could be quantified and visualized. When applied to the electrocatalytic oxygen reduction reaction, the hydrophobic surface of the APLNs demonstrated the H₂O₂ selectivity of ∼90% compared to that of ∼50% for the hydrophilic surface, highlighting the crucial role of the distinct surface properties in modulating the reaction pathway and product selectivity.