Nano-Engineered Materials for Energy Conversion and Storage Applications: Synthesis, Characterization, and Mathematical Modeling

Tuesday, 30 May 2017: 08:40
Marlborough B (Hilton New Orleans Riverside)
S. Karimi (University of Toronto)
Pulsed current electrodeposition (PCE) was employed to deposit a number of metals on different substrates for various applications. Influence of key PCE parameters, including duty cycle, peak deposition current density, pulse on-time-on and off-time and type of pulse waveform, on the morphology, size, distribution and catalytic activity of the electrodeposited layers were investigated. Platinum and palladium were electrodeposited on carbon substrates for fuel cell applications and nickel, copper, cobalt and platinum were electrodeposited on highly ordered titania nanotubes (TNTs) for solar hydrogen generation and wastewater treatment processes. The presence of nanocrystalline platinum and palladium, ranging from 2-10 nm in diameter, on carbon paper and cloth were confirmed by scanning electron microscopy and x-ray diffractometry. Their catalytic activity also was examined by fabricating membrane-electrode assemblies and testing them in single-cell proton exchange membrane and direct methanol fuel cells. Doped TNTs also were characterized by microscopy, x-ray diffractometry and UV-Vis spectroscopy. Structural investigation of the prepared TNTs via a simple anodization technique followed by metal doping, utilizing the aforementioned PCE method, confirmed the presence of anatase nanocrystalline TNTs after annealing in air and vacuum at elevated temperatures. The presence of nickel and copper nanoparticles 10-50 nm in diameter also was observed and, subsequently, confirmed. The efficiency of the photoanodes was found to increase as the amount of dopant increased to 3%. Further increase in metal dopants, however, resulted in a decrease in efficiency.

A comprehensive mathematical model based on progressive nucleation was developed to accurately predict the influence of the aforementioned electroplating parameters on the resulting layers and films with the aim of process optimization for a particular plating system. The model takes into account contributions from both nucleation and growth currents and assumes a dynamic; i.e., changing, diffusion coefficient during electrodeposition. According to this model, high peak deposition current densities, low duty cycles, pulses delivered in microsecond range and employing a ramp-down waveform yielded the highest nucleation rates, leading to the smallest average grain size of the deposited nanoparticles, and confirming the experimental findings.