Trace hydrogen sensing with ultra-high selectivity utilizing hierarchical Ni-BTC@ZIF-8 MOF-on-MOF heterojunctions

Large-scale utilization of hydrogen for fuel cells and chemical manufacturing imposes urgent demands on hydrogen sensing materials with superior sensitivity and selectivity. Herein, we successfully fabricated a Ni-BTC@ZIF-8 MOF-on-MOF heterostructure using polyvinylpyrrolidone (PVP) as a stabilizer and bridging agent. The hierarchical porous architecture enables size-selective microporous sieving in the outer ZIF-8 layer, facilitating H 2 permeation while blocking larger interfering molecules. This selective mass transfer optimizes H 2 accessibility at the sensing interface. Owing to the favorable mass-transport behaviour, the Ni-BTC@ZIF-8 sensor delivers an ultrahigh selectivity with a response value of 6.0 toward 20 ppm H 2 at 200 ℃, alongside an exceptionally fast recovery speed (∼6 s). Moreover, the device demonstrates excellent cycling stability and long-term reliability. This work further probes the underlying mechanism responsible for the improved H 2 -sensing performance of the MOF-on-MOF heterostructure, which arises from interfacial synergistic effects. Specifically, the intimate ZIF-8/Ni-BTC contact affords selective gas-transport channels from ZIF-8 and efficient electron-conduction pathways, with Ni-BTC serving as the active sensing layer for signal transduction. Such a synergistic interplay optimizes the coupling between molecular-sieving and sensing response. These findings provide a feasible and scalable paradigm for constructing novel high-performance hydrogen gas sensors.