Modification of palladium surfaces by electrochemical atomic layer deposition (E-ALD) and atomic layer electroless deposition (ALED) for enhanced hydrogen transport kinetics
Benson, David Michael
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Applications that rely on hydrogen storage and exchange, such as sensors, catalysis, and energy storage, can be improved by increasing the rate at which hydrogen can be both stored and accessed. Pd is a well-known candidate for hydrogen storage and exchange purposes. In this lab, surface modification of Pd films by Rh deposition using electrochemical atomic layer deposition (E-ALD), a condensed-phase equivalent of atomic layer deposition (ALD), has been shown to enhance the rates of hydrogen sorption and desorption into and out of the Pd film. Using a new columnar flow cell design, this deposition technique has been applied to Pd powder. Modified powders were studied using cyclic voltammetry, scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS), and X-ray photoelectron spectroscopy (XPS). An analogous electroless deposition technique, atomic layer electroless deposition (ALED), uses hydrogen rather than a metal as the sacrificial element and has also been adapted to the flow cell system. Deposits of Pd and Rh on a Pd substrate were created. Films grown in the flow cell by E-ALD and ALED were compared by cyclic voltammetry and by voltammetric stepping. Another electroless deposition technique, electroless atomic layer deposition (EL-ALD) is presented. EL-ALD uses redox couples in solution to poise the potential at a desired voltage to promote underpotential deposition (UPD) of a metal which then acts as a sacrificial layer to deposit another desired metal. Results and future directions are presented.