|
Abstract:
|
The design of nanoparticles in mesoporous supports is explored through synthetic strategies of electrophoretic deposition and electroless deposition with application towards energy storage . Electrophoretic deposition of nanoparticles into a mesoporous thin film is examined using charged nanocrystals in a low -permittivity solvent . To provide a basis for the deposition , the mechanism of particle charging in a low -permittivity solvent was studied . Dispersions of carbon black particles in toluene with an anionic surfactant were characterized using differential -phase optical coherence tomography with close electrode spacing to measure the electrophoretic mobility . The particle charge in concentrated dispersions was found to decrease as a function of increasing surfactant concentration . Partitioning of cations between the surfactant -laden particle surface and micelle cores in the double -layer was found to govern the dynamics of particle charging . Subsequently , charged Au nanocrystals were deposited by electrophoresis within perpendicular mesochannels of a TiO2 support . High loadings of 21 wt % Au with good dispersion were achieved within the mesoporous TiO2 support using electrophoretic deposition , which would otherwise be inhibited by the weak nanocrystal -support interaction . According to a modified Fokker -Planck equation , the mean penetration depth of a single nanocrystal inside of the perpendicular pores was found to be dependent on the electric field strength , electrophoretic mobility , pore diameter , nanocrystal size , and local deposition rate constant .
Nanocomposites for electrochemical capacitors were designed via electroless deposition of redox -active MnO2 in a high surface area mesoporous carbon support . Disordered mesoporous carbon supports with a pore size of ~8 nm were used both in amorphous (AMC ) and graphitic (GMC ) form , with a ~1000 -fold larger conductivity for GMC . High loadings of 30 wt % MnO2 were achieved in the AMC in the form of ~1 nm thick domains , which were highly dispersed throughout the support . Oxidation of the GMC was necessary to facilitate wetting and deposition of the MnO2 precursor in order to achieve high loadings of 35 wt % MnO2 with ~1 nm thickness . High gravimetric MnO2 pseudocapacitances of >500 F /gMnO2 were achieved at low loadings and low scan rate of 2 mV /s for both carbon supports . However , at high scan rates ≥100 mV /s , the MnO2 pseudocapacitance is twofold larger for MnO2 /GMC , relative to MnO2 /AMC . Sodium ion diffusion throughout both MnO2 /AMC and MnO2 /GMC was shown to be facile . For the GMC versus AMC support , the higher MnO2 pseudocapacitance is attributed to the higher electronic conductivity , which facilitates electron transport to the MnO2 domains . |