Tailoring morphology to control defect structures in ZnO electrodes for high-performance supercapacitor devices

Zinc oxide (ZnO) nanostructures were synthesized in the form of nanoparticles, nanoflowers and nanourchins. Structural. electronic and optical characterization of the samples were done via standard techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence, Raman and ultraviolet-visible (UV-Vis) spectroscopy. The point defect structures which are specific to each morphology has been investigated in terms of their concetration and location via state of art electron paramagnetic resonance (EPR) spectroscopy. According to core-shell model the samples all revealed core defects however the defects on the surface are smeared out. Finally, all three morphology has been tested as electrode material in a real supercapacitor device and the performance of the device, in particular, the specific capacitance and the storage mechanism has been mediated by the point defects. Morphology dependent defective ZnO electrode enable to monitor the working principle of supercapacitor device from electric double layer capacitor (EDLC) to pseudo-supercapacitor.