Self-Assembled Polyoxometalate Supramolecular Nanosheets for Efficient and Durable Water Oxidation.

Superstructures assembled from nanoscale polyoxometalates (POMs) attract considerable interest due to their well-defined architectures and outstanding physicochemical properties. However, the targeted synthesis of self-assembled POM-based superstructures with high-efficiency electrocatalytic performance remains a significant challenge. Herein, we report the rational design and construction of three POM-based superstructures with ultrathin graphene-like morphologies and well-organized frameworks via a simple self-assembled method, in which transition metals (TMs) bridge POMs into graphene-like planes, while cetyltrimethylammonium bromide (CTAB) serves as an intercalation agent, endowing the structures with high surface area and enhanced electronic conductivity. Among the resulting materials (denote as POM-CTAB-TM, TM═Co, Ni, or Cu), POM-CTAB-Co exhibits the highest catalytic activity toward oxygen evolution reaction (OER), achieving a low overpotential of 292 mV at a current density of 10 mA cm-2. In situ electrochemical spectroscopy and theoretical calculations underscore that the Co atoms within the POM serve as active sites and facilitate the rate-determining step of *OOH formation. Moreover, an anion exchange membrane water electrolyzer employing POM-CTAB-Co as the anode and Pt/C as the cathode demonstrates exceptional performance, delivering a current density of 2 A cm-2 at a cell voltage of 2.247 V, along with remarkable durability exceeding 2000 h at an industrial-grade current density of 500 mA cm-2. This study develops a simple and efficient method for synthesizing supramolecular POM-based nanosheets as OER electrocatalysts.