Polyaniline-Cobalt Benzimidazolate Zeolitic Metal-Organic Framework Composite Material for Electrochemical Hydrogen Gas Sensing

The quest for smart sensors with excellent sensitivity, fast response and high reproducibility for hydrogen gas detection has been ongoing for decades. In this work, polyaniline (PANI) was doped with a cobalt-based zeolitic benzimidazolate framework material (CoZIF), to form PANI-CoZIF metal-organic framework (MOF) composite material, which was applied in the electrochemical hydrogen gas sensing. The synthesis of PANI-CoZIF composite was performed by the chemical oxidative polymerization of aniline in the presence of 3.6wt% CoZIF. The structural properties of the synthesized materials (i.e., PANI, CoZIF, and PANI-CoZIF) were studied by ultraviolet-visible (UV-vis), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic analyses, as well as by thermogravimetric analysis (TGA). Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and high-resolution transmission electron microscopy/selected area electron diffraction (HR-TEM/SAED) techniques were used for morphological characterization. Both SEM and TEM analyses revealed the grafting of CoZIF on to the surface of PANI in the PANI-CoZIF composite material. XRD patterns and SAED results indicated that PANI and the composite were amorphous in nature. Spectroscopic analyses by FTIR and Raman techniques revealed the coexistence of CoZIF and PANI in the MOF composite material (PANI-CoZIF), which was also confirmed by the high intensities of the characteristic X-ray peaks of ZIF and the polymer. From Tauc plot analysis, it was found that PANI and PANI-CoZIF had band gap energy (E-g) values of 2.5 and 2.3eV, respectively, indicating that they are both semi-conductors. TGA data confirmed an enhanced thermal stability of PANI-CoZIF compared with pristine PANI. Cyclic voltammetry (CV), chronoamperometry (CA), and Tafel and turn over frequency (TOF) analyses were used to study the electrocatalytic behavior of PANI and PANI-CoZIF in the hydrogen evolution reaction (HER) for gas sensing. There were very significant increases in the TOF value and the magnitude of the catalytic current for PANI-CoZIF compared with pristine PANI as electrocatalysts in the HER. Thus, PANI-CoZIF composite has a greater potential as a suitable electrocatalyst for practical application in the hydrogen fuel technology and hydrogen gas sensing.