Fabrication by Reactive Spray Deposition Technology (RSDT) and Characterization of Advanced Materials for Electrochemical Applications

Human activities such as electricity generation, industry, and transportation produce significant amounts of air pollution, which has wide-ranging effects on society and the environment. Many electrochemical technologies have recently received increased attention for lessening anthropogenic emissions. This dissertation focuses specifically on vanadium redox flow batteries (VRFBs) for the storage of renewably sourced electricity and chemiresistive ammonia sensors for monitoring ammonia emissions from selective catalytic reduction systems in vehicles.
Novel separator membranes were developed for VRFBs to improve the energy efficiency of the batteries, and their efficacy was demonstrated in 25 cm2 cells. These membranes consist of commercial Nafion membranes coated with a Nafion-based composite layer (“barrier layer”), the thickness of which is on the order of microns. Materials characterization was performed on the barrier layers, which showed that the layers consist of Nafion polymer impregnated with nanoparticles of carbon and/or silica. Based on the materials characterization and the cell performance, it has been hypothesized that the additives in the barrier layer favorably alter the pore structure of the Nafion polymer in the barrier layer, thereby improving the efficiency of the cell.
In the context of ammonia sensors, α-MoO3 sensing films of different morphologies were fabricated on interdigitated electrodes. Sensors with sensing films of an optimized morphology exhibited repeatable and reproducible sensing responses to ammonia concentrations between 0.1 and 5 ppm at 673 K in dry air. The sensing results were consistent with the well-established charge-depletion layer model up to 3 ppm; at 5 ppm the sensing response repeatedly departed from the expected trend. In light of these sensing results, additional electrochemical contributions to the sensing response have been hypothesized, and additional experimental work has been proposed.
The barrier layers and ammonia sensing films were fabricated directly onto their respective substrates using Reactive Spray Deposition Technology (RSDT). RSDT is a unique flame-based process developed by Dr. Maric and is well established for the synthesis of catalysts for fuel cells and electrolyzers. In this dissertation, the optimization of the RSDT for the fabrication of the barrier layers and sensing films is discussed in the context of fundamental mechanisms.