Conversion of interlocked cube-like Mn3O4 into nanoflakes of layered birnessite MnO2 during supercapacitive studies

A facile route based on chemical bath deposition (CBD) from urea containing bath has been developed to deposit the interlocked cubes of hausmannite Mn3O4 electrode for electrochemical supercapacitor application. The as-prepared Mn3O4 electrode showed ideal capacitive behavior during potential cycling within the range of −0.1 to +0.9 V in 1 M Na2SO4 electrolyte. The X-ray diffraction (XRD), scanning electron micrograph (SEM) and Raman scattering (RS) and wettability studies during the supercapacitive stability showed that the interlocked cubes of crystalline Mn3O4 are electrochemically oxidized to nanoflakes of layered birnessite MnO2 due to potential cycling. Due to potential cycling the contact angle of Mn3O4 thin film changed from hydrophilic to superhydrophilic nature. The effect of electrolyte concentration and scan rate on the specific capacitance of so formed MnO2 film has been investigated. Impedance analysis shows that birnessite MnO2 nanoflakes are good conducting than Mn3O4 hence can be used over a wide range of applications. It exhibited highest specific capacitance of 223 F g−1 in 1 M Na2SO4 electrolyte at 5 mV s−1 scan rate and 90% stability after 5000 cycles.