Nucleation/Growth Mechanisms and Morphological Evolution of Porous MnO(2) Coating Deposited on Graphite for Supercapacitor

The nucleation and growth mechanisms of porous MnO(2) coating deposited on graphite in MnSO(4) solution were investigated in detail by cyclic voltammetry, chronoamperometry and scanning electron microscopy. The electrochemical properties of honeycomb-like MnO(2) were evaluated by cycle voltammetry and galvanostatic charge-discharge. Results indicated that MnO(2) was synthesized by the following steps: [Formula: see text] , [Formula: see text] , and [Formula: see text]. The deposition of MnO(2) was divided into four stages. A short incubation period (approximately 1.5 s) was observed, prior to nucleation. The decreasing trend of the current slowed as time increased due to nucleation and MnO(2) growth in the second stage. A huge number of nuclei were formed by instantaneous nucleation, and these nuclei grew and connected with one another at an exceedingly short time (0.5 s). In the third stage, the gaps in-between initial graphite flakes were filled with MnO(2) until the morphology of the flakes gradually became similar to that of the MnO(2)-deposited layer. In the fourth stage, the graphite electrode was covered completely with a thick and dense layer of MnO(2) deposits. All MnO(2) electrodes at different deposition times obtained nearly the same specific capacitance of approximately 186 F/g, thus indicating that the specific capacitance of the electrodes is not related with deposition time.