Unravelling the Role of Synthesis Temperature in δ-MnO2 Nanosphere Formation for High-Performance Supercapacitors

In the present research work, reported a role of controlled temperature for the synthesis of the 2D layered structure of the delta-MnO2 nanospheres, for high capacitance, were synthesized using the simple, facile hydrothermal method. The temperature taken for the synthesis of delta-MnO2 as 140, 160, and 180 degrees C. The highest specific capacitance 525.93 F g-1 in 1 m Na2SO4 electrolyte for 5 mV s-1 scan rate was observed for the sample prepared at a temperature 180 degrees C. The symmetric delta-MnO2 supercapacitor device was fabricated using a liquid-state assembly process, with EIS confirmed low charge transfer resistance and excellent cycling stability. From XRD studies, confirmed that the synthesized material is delta-MnO2 with crystalline size increases from 10 to 16 nm as the temperature increases. FESEM confirmed that the prepared sample is of nanosphere like morphology, and the average grain size decreases from 700 to 300 nm as the temperature increases. EDAX analysis reveals that the prepared sample only contains Mn and O there is no any impurity present. Advantageously, the water contact angle of the prepared electrode is hydrophilic in nature. The Raman and FTIR spectroscopy investigated the chemical structure and functional groups present in delta-MnO2. The oxidation states of Mn and O are analysed using XPS.