Improved Hydrogen Sensitivity and Selectivity in PdO with Metal-Organic Framework Membrane

Abstract

Metal-organic frameworks (MOFs) are highly designable porous materials and are recognized for their exceptional selectivity as chemical sensors. However, they are not always suitable for incorporation with existing sensing platforms, especially sensing modes that rely on electronic changes in the sensing material (e.g., work-function response or conductometric response). One way that MOFs can be utilized is by growing them as a porous membrane on a sensing layer and using the MOF to affect the electronic structure of the sensing layer. In this paper, a proof-of-concept for electronic modulation with MOFs is demonstrated. A PdO nanoparticle sensing layer on a chemical-sensitive field-effect-transistor is made more sensitive to a reducing gas, hydrogen, and less sensitive to oxidizng molecules, like H2S and NO2, by growing a layer of the MOF “ZIF-8” over the nanoparticles. The proposed mechanism is supported by X-ray photoelectron spectroscopy showing that the ZIF-8 membrane partially reduces the PdO sensing layer.

Application status of zeolitic imidazolate framework in gas sensors

“…It has been demonstrated that even in the absence of metals or metal oxides, unique sensing properties remain on CS-FETs. Gardner et al covered PdO/Pd with ZIF-8 coating not only the response to H 2 but also the response speed was improved [102]. Using XPS to evaluate the electronic structure of the material, compared with PdO, Pd in PdO/ZIF-8 shifts to higher energy, and Zn in ZIF-8 shifts to lower energy, which shows that the electrons in PdO are transferred to Zn in ZIF-8, and the oxidation degree of PdO is higher.…”