High Proton‐Conductivity in Covalently Linked Polyoxometalate‐Organoboronic Acid‐Polymers

The controlled bottom‐up design of polymers with metal oxide backbones is a grand challenge in materials design, as it could give unique control over the resulting chemical properties. Herein, we report a 1D‐organo‐functionalized polyoxometalate polymer featuring a purely inorganic backbone. The polymer is self‐assembled from two types of monomers, inorganic Wells–Dawson‐type polyoxometalates, and aromatic organo‐boronates. Their covalent linkage results in 1D polymer strands, which combine an inorganic oxide backbone (based on B−O and Nb−O linkages) with functional organic side‐chains. The polymer shows high bulk proton conductivity of up to 1.59×10−1 S cm−1 at 90 °C and 98 % relative humidity. This synthetic approach could lead to a new class of organic–inorganic polymers where function can be designed by controlled tuning of the monomer units. Polyoxometalate polymers with high proton conductivity are accessed for the first time by controlled covalent polymerization of Wells–Dawson‐type niobotungstate and organoboronic acid monomers. The resulting polymer features a purely inorganic backbone, organic sidechains, and acts as a solid‐state proton conductor.