Interlayer Confinement Strategy in Two-Dimensional Polyoxometalate-Based Metal–Organic Frameworks for Enhancing Proton Conduction

Proton exchange membranes are crucial components in electrochemical energy devices. Nevertheless, the development of high-performance proton-conducting materials remains a considerable challenge, primarily due to the inherent difficulty in constructing dense and continuous hydrogen-bonding networks under ambient conditions. To overcome this limitation, the intentional incorporation of short hydrogen bonds has been applied as a critical design strategy and plays a critical role in enabling efficient proton transport. In this work, we adopt an interlayer confinement strategy to enhance proton conductivity by introducing chitosan into a newly developed two-dimensional (2D) layered polyoxometalate-based metal-organic framework (POMOF), {[Cu₂(4-abpt)₂][Cr(OH)₆Mo₆O₁₈]} (CUST-877). The introduction of chitosan promotes the formation of continuous hydrogen-bonding networks and facilitates efficient proton transfer pathways within the layered structure. By regulating the interlayer spacing of the POMOF structure, the CS/CUST-877-10 composite exhibits a proton conductivity of 4.52 × 10^-3 S cm^-1 at 98% RH and 80 °C, which is 2 orders of magnitude higher than that of the pristine CUST-877. This work offers a new design concept for the development of POM-based proton conductors and highlights the potential of polymer-modified 2D-MOF systems for energy conversion technologies.