Metal-Organic Nanogel with Sulfonated Three-Dimensional Continuous Channels as a Proton Conductor

Developing novel proton conductors is crucial to the electrochemical technology for energy conversion and storage. Metal-organic frameworks (MOFs), with a highly ordered and controllable structure, have been widely explored to prepare high-performance proton conductors. Albeit the prominent merits and great potential of the MOF-based materials such as MOF pellets or composite polymer electrolytes, constructing well-defined proton-transfer channels with much lower grain boundary resistance and more homogeneous distribution deserves extensive explorations. Herein, a kind of nanostructured metal-organic gel (MOG) with a three-dimensional (3D) interconnected proton-conductive network is prepared by a facile sol-gel method using Cr³⁺ and sulfonated terephthalic as the metal source and organic ligand, respectively. During the gelation process, the primary metal-organic nanoparticles are cross-linked through mismatched growth and aggregate into the 3D well-percolated gel network. The resultant MOG features in the tunable hierarchical structure and long-range continuous proton-transfer channels, leading to remarkably reduced energy barrier for proton conduction. Attributed to the sulfonated ligand and well-interconnected proton-conductive pathways, MOG exhibits intrinsic proton conductivity that is about one order of magnitude higher than that of MIL-101-SO₃H pellet (MIL, Matérial Institut Lavoisier). The method in this study can be extended to construct long-range continuous ionic channels for a number of solid electrolytes.