Overcoming the Selectivity-Sensitivity Trade-Off in Electroactive Gas Sensing Using Hybrid Glass Composites

Abstract

Hybrid glasses derived from meltable metal-organic frameworks (MOFs) have emerged as a new class of amorphous materials. Combining the porosity of MOFs with the processing ability of glasses, they are thought to enable a wholly new range of functional compounds. By way of example, it is demonstrated here how the intrinsic porosity of glasses obtained from zeolitic imidazolates (ZIFs) can be used to overcome the selectivity-sensitivity trade-off in electroactive gas sensing. For this, composites are fabricated in which metallophthalocyanines are embedded within a ZIF-62 MOF glass matrix. Such a material enables the detection of gas species (or their absence) utilizing the pronounced electrochemical sensitivity of phthalocyanines. Thereby, the solid glass does not only stabilize and protect the active component, but also – through its retained, highly tunable porosity – ensures sensor selectivity by molecular sieving and targeted size exclusion of larger molecules. In addition, the hydrophobicity of the ZIF pore interior protects the active component from degradation caused by ambient humidity. Investigations of the structural, optical and electronic properties of the composite indicate that compoundation is purely physical, that is, chemical interactions between the compound partners are avoided and the individual properties of the hybrid glass matrix and the electroactive metallophthalocyanine are retained. Atmosphere-controlled high-temperature electrical impedance measurements reveal significant shifts in resistance in CO₂ and Ar atmosphere as compared to airflow. These results provide a proof of concept for sensitive and selective gas sensors based on such composites.