Nanostructured Manganese Dioxide Thin Films prepared by a Novel Self-Assembly Process

Abstract

We have reported herein a novel self-assembly horizontal submersion process for the deposition of
nanostructured manganese dioxide thin films on metalized plastic supporting substrates at ambient temperature
and pressure. Uniform manganese dioxide thin films were deposited directly onto metallized plastic supporting
substrate via the spontaneous assembly of preformed manganese dioxide nanoparticles in the form of stable
colloidal suspension. This process affords a facile approach for the deposition of manganese dioxide thin films
by simply repeating the submersion process after the prior deposited layer had been air-dried completely. Thinfilm
deposition process initially occurred through the spontaneous adsorption of manganese dioxide
nanoparticles onto specific surface sites of the metalized substrate. Subsequent events of particle growth,
clusters formation, and aggregation or self-organization of particle clusters eventually led to the deposition of
nanostructured thin films which were nanoparticulate and highly porous in nature. The surface morphological
characteristics of deposited thin films were observed to be significantly affected by the duration of submersion
and the post-deposition calcination temperature. By modulating and optimizing these parameters, thin films of
tailored microstructure could therefore be prepared. Optimized manganese dioxide thin films were observed to
exhibit excellent capacitive 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. The
cycling stability and reversibility of these films were evaluated by prolonged charge-discharge cycling and no
substantial deterioration of performance in terms of charge capacity and capacitive behaviors were observed
after 1000 cycles. We speculate that the high capacitance value exhibited by self-assembled manganese dioxide
thin films in mild aqueous electrolyte could be attributed to reversible and homogenous intercalation and
deintercalation of protons during the charge and discharge cycling. The potential utility of self-assembled
manganese dioxide thin films for the fabrication of electrochemical devices, in particular thin-film
electrochemical capacitors is therefore envisaged.