In-situ grown MIL-101(Fe) in PBI membranes enables acid-state regulation for efficient proton conduction and durable high-temperature operation

High-temperature proton exchange membranes had attracted considerable interest for electrochemical devices such as fuel cells. However, it remained challenging to simultaneously achieve high proton conductivity, effective acid retention, and robust dimensional stability. To address the limitations of conventional filler incorporation, which was insufficient to realize both efficient acid utilization and the construction of continuous proton-conduction networks, we developed a PBI-based mixed-matrix membrane (MMMs) via the in-situ growth of MIL-101(Fe). The in-situ introduced MIL-101(Fe) not only formed a well-dispersed MOFs framework with excellent interfacial compatibility, but also reconfigured the spatial distribution and physicochemical state of phosphoric acid within the membrane, transforming it from disordered accumulation into a continuous hydrogen-bonded pathway for cooperative proton transport. As the extent of MIL-101(Fe) in-situ growth increased, the acid distribution became more uniform, the proton-conduction pathways became more interconnected, the transport resistance was significantly reduced, and the conductivity was markedly enhanced. Meanwhile, the confinement effect of the MOFs channels and their interfacial nanodomains on phosphoric acid effectively suppressed acid loss and substantially improved the dimensional stability of the membrane. This study demonstrated that in-situ grown MIL-101(Fe) not only increased acid accommodation, but more importantly enabled microenvironment regulation and reconstruction of the proton-transport network, thereby providing new insight into the design of high-performance and durable high-temperature proton exchange membranes.