Fabrication and characterization of high surface area nickel-deposited graphite substrates

Abstract

In certain electrochemical battery cells, inefficiencies arise due to the formation of hydrogen from corrosion reactions at the anode. One way to reduce these inefficiencies is to operate the cell at high current densities, which is obtainable given a high cathode to anode surface area ratio; however, commercially available metal foams often do not provide sufficient surface area density (cm 2/g). Coating high-surface area materials in the appropriate metal is a premier alternative, but while methods to effectively coat two-dimensional substrates in metal through electrodeposition has been well documented, attempts to scale electrodeposition to three-dimensional coating to achieve high-surface area catalysts has encountered certain challenges. The formation of a pure metal crust on the outer surface area of the catalyst prevents the penetration of metal ions into the inner fibers of the material, resulting in a lower surface area density. This thesis describes simple, repeatable electrodeposition methods to increase the homogeneity of the nickel coating throughout highly porous graphite catalysts and prevent the formation of a metal crust. Parameters such as direct/pulsating current, ultrasonic vibration pretreatment, and varying electrodeposition solution concentrations were tested in order to optimize the electrodeposition procedure. Three techniques were used to characterize the post-synthesis surface condition including scanning electron microscopy, electron dispersive spectroscopy and cyclic voltammetry. The improved electrodeposition method led to nickel-coated graphite felt with a specific surface area of 620 cm2/cm 3 and a surface area density of 7500 cm2/g, achieving a 890% higher surface area and 4650% higher surface area density than commercially available nickel foams. The proposed electrodeposition method provides high-surface area, full-volume coating of highly porous catalysts, applicable not only to electrochemical batteries but to any battery chemistry with an electrolyte that contains fuels, particularly flow batteries. The proposed methods to obtain effective full-coated, high-surface area catalysts have the potential to optimize outputted battery power and thereby revolutionize battery electrode fabrication.