Synthesis and OER catalytic activity of quasi zeolitic imidazolate Framework-67 having two and three dimensional morphology

Zeolitic imidazolate framework-67 (ZIF-67), in two and three dimensional (2D/3D) morphologies have been synthesized at room temperature using different solvent media, and annealed at 350 and 920 °C to derive the modified ZIF-67 based catalysts. All the ZIF-67 based catalysts were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, Thermogravimetric analysis, N2 gas adsorption method, and Positron annihilation lifetime spectroscopy. It has been observed that catalytic activity of the ZIF-67 based catalysts towards oxygen evolution reaction (OER) depends on the morphology and annealing-induced modifications in active sites. Among different morphologies of as-synthesized ZIF-67, 2D ZIF-67 (nanosheet and disc like morphology) exhibits the best electrocatalytic activity in as-synthesized as well as in the annealed form in comparison to 3D ZIF-67 (rhombic dodecahedron) owing to their better electronic properties. All the types of ZIF-67 annealed at 920 °C show the lower Tafel slopes suggesting higher OER rate.