Various deposition methods, both physical and chemical, were used to functionalize the ZnO NWs with metal or alloy nanoparticles (NPs) for catalytic transformations of important molecules which are relevant to energy and environment. Cu and PdZn NPs were epitaxially grown on ZnO NWs to make them resistant to sintering at elevated temperatures and thus improved the stability of such catalytic systems for methanol steam reforming (MSR) to produce hydrogen. A series of Pd/ZnO catalysts with different Pd loadings were synthesized and tested for MSR reaction. The CO selectivity was found to be strongly dependent on the size of the Pd: Both PdZn alloy and single Pd atoms yield low CO selectivity while Pd clusters give the highest CO selectivity.
By dispersing single Pd atoms onto ZnO NWs, Pd1/ZnO single-atom catalysts (SACs) was synthesized and their catalytic performance was evaluated for selected catalytic reactions. The experimental results show that the Pd1/ZnO SAC is active for CO oxidation and MSR but is not desirable other reactions. We further synthesized ZnO NWs supported noble metal (M1/ZnO; M=Rh, Pd, Pt, Ir) SACs and studied their catalytic performances for CO oxidation. The catalytic test data shows that all the fabricated noble metal SACs are active for CO oxidation but their activity are significantly different. Structure-performance relationships were investigated.
Dealloying under conditions of high TH, (or high intrinsic diffusivity of the more electrochemically reactive component) is considerably more complicated than at low TH. Since solid-state mass transport is available to support this process, a rich set of morphologies, including negative or void dendrites, Kirkendall voids and bi-continuous porous structures, can evolve. In order to study dealloying at high TH we have examined the behavior of Li-Sn and Li-Pb alloys. The intrinsic diffusivities of Li were measured in these alloys using electrochemical titration and time of flight measurements. Morphology evolution was studied with varying alloy composition, host dimension and imposed electrochemical conditions. Owing to diffusive transport, there is no parting limit for dealloying, however, there is a compositional threshold (pPD) as well as a critical potential for the operation of percolation dissolution and the formation of bi-continuous structures. Negative or void dendrite morphologies evolve at compositions below pPD and at large values of the applied electrochemical potential when the rate of dealloying is limited by solid-state mass transport. This process is isomorphic to dendrite formation in electrodeposition. Kirkendall voiding morphologies evolve below the critical potential over the entire range of alloy compositions.
We summarize our results by introducing dealloying morphology diagrams that we use to graphically illustrate the electrochemical conditions resulting in various morphologies that can form under conditions of low and high TH.
This project aimed to understand the effects of composition and phase distribution on the corrosion behavior of magnesium-aluminum (Mg-Al) alloys in an ionic liquid electrolyte. The purpose of studying corrosion in nonaqueous ILs is to determine the anodic dissolution behaviors of the alloy phases without the interference of side reactions that occur in aqueous electrolytes, such as di-oxygen or water reduction. Three commercial Mg-Al alloys were studied: AZ91D (9% Al), AM60 (6% Al), and AZ31B (3% Al). An annealed alloy containing solid-solution α-phase Mg-Al with 5 at% aluminum content (Mg5Al) was also used. The ionic liquid chosen for this project was 1:2 molar ratio choline-chloride:urea (cc-urea), a deep eutectic solvent. After potentiostatic corrosion in cc-urea, the magnesium alloys were found to form a high surface area porous morphology as corrosion duration increased. This morphology consists of aluminum-rich ridges formed by Al nanowires surrounding an aluminum-poor base area, but with an overall increase in surface Al composition, indicating selective dealloying of the Mg in cc-urea and redistribution of the Al on the surface. Further work will focus on the development of hydrophobic coatings using ionic liquids.
In the last several years, there has been interest in the development of flexible batteries as a substitute for traditional Li-ion batteries. Flexible batteries can fold, bend, and twist; studies have shown that mechanical stresses and fatigue may decrease battery performance and cause defects. In this paper, the viability of producing a mechanical fatigue-testing device from 3D printed and other off-the-shelf components was explored. The device was made using a servomotor and LCD screen controlled by a programmed Arduino board, and successfully met the expectations to be cheap, easily reproducible, versatile, and applicable to the testing of battery components. In a proof-of-concept test, the device was used to perform repeated folding tests on lithium cobalt oxide cathodes in different configurations, which were then characterized using a laser microscope. 3D topographical renderings suggested that bending at acute angles induces defects on the surface of the electrode where the electrode is creased. In future work, the device will be used to further explore the effect of mechanical fatigue on Li-ion battery components.