|
Nanostructured manganese dioxide thin films were deposited on metalized plastic supporting substrates by a horizontal submersion self-assembly process at ambient temperature and pressure. This horizontal submersion process entailed the spontaneous assembly of preformed manganese dioxide nanoparticles in the form of stable colloidal suspension directly onto metallized plastic supporting substrate to form uniform thin films. Films with desired thicknesses were prepared by repeating the submersion process after the prior deposited layer had been air-dried completely. The self-assembly process involved initial adsorption of manganese dioxide nanoparticles onto surface active sites of the metallized supporting substrate, and subsequent particle growth, clusters formation, and aggregation or self-organization of clusters which eventually led to the deposition of nanostructured thin film on the supporting substrate. Scanning electron micrographs had revealed that self-assembled manganese dioxide thin films were nanoparticulate and highly porous in nature with surface morphological characteristics significantly affected by deposition conditions such as pH, temperature, duration of submersion, concentration and ionic strength of suspension, as well as the post-deposition calcination temperature. As such, thin films with tailored microstructure could be prepared through optimizing these parameters. These films were observed to exhibit excellent capacitative behavior as evidenced by the almost perfectly rectangular shape of cyclic voltamograms within the potential range of 0.0 to 1.0 V (versus SCE) in mild aqueous Na2SO4 electrolyte. Besides, these films showed high cycling stability and reversibility upon prolonged cycling of exceeding 2,000 cycles. The high pseudocapacitance of self-assembled manganese dioxide thin films could be attributed to redox reactions involving homogenous intercalation and deintercalation of protons during the charge and discharge cycling. Self-assembled manganese dioxide thin films therefore possess high potential utility for the fabrication of electrochemical devices, in particular thin-film electrochemical capacitors. Key words: Manganese dioxide, nanoparticles, self-assembly, nanostructures, thin films, electrochemical capacitors. |