Copper (II) hydroxide nanorods grown on copper and nickel plated nanofibres for pseudocapacitor electrodes in regenerative braking

The threat of climate change has created a demand for superior energy storage devices. One application for them is regenerative braking in hybrid vehicles to reduce fuel consumption and greenhouse gas emissions. Instead of using brakes, the friction generated from turning electric motors charges batteries stops the vehicle. In turn, the batteries are used to accelerate the vehicle. Since braking time is short, batteries are imperfect for this application due to low rate of energy transfer (power). Supercapacitors are superior for power, but cost and amount of energy stored needs to be improved. In this study, Cu(OH)₂ nanorods grown on copper-nickel plated nanofibres (Cu(OH)₂ NGCuNiPN) were fabricated as electrodes for the pseudocapacitor application. The aim is to use nanofibres as a light weight support, the high conductivity of nickel for power and as a current collector, and Cu(OH)₂ nanorods for pseudocapacitance energy storage. Cu(OH)₂ NGCuNiPN electrodes were fabricated by electrospinning, electroless plating, and wet-chemical Cu(OH)₂ nanorod growth. Polyacrylonitrile-co-methyl-acrylate/Pd(C₅H₇O₂)₂ nanofibre sheets were fabricated with electrospinning. A heat treatment process converted Pd(C₅H₇O₂)₂ to Pd catalyst, which was necessary for electroless plating. Nickel was plated on the surface and through the thickness of the nanofibre sheet. Cu was plated on top of the Ni and converted to Cu(OH)₂ nanorods. X-ray photoelectron spectroscopy determined the wet-chemical method converted some nickel to nickel compounds (NiO, Ni(OH)₂, NiOOH) in addition to Cu(OH)₂ nanorod growth. Electrochemical analysis determined Cu(OH)₂ nanorods reduced power density and did not affect energy density, but the nickel compounds improved energy density. Galvanic charge-discharge determined the specific energy and specific power densities of nickel plated nanofibres submerged in 3.75 M NaOH-0.3 M ammonium persulfate for 180 min were 13.2 Wh kg-¹ and 7892 W kg-¹ respectively at a current density of 28.8 A g-¹. Only 20% of capacitance was loss when current density was increased from 3.6 g-¹ to 28.8 A g-¹. Cyclic testing showed specific capacitance increased by 44% (330 F g-¹ to 476 F g-¹) after 1000 cycles. The increase in capacitance is likely due to the formation of additional nickel compounds under alkali conditions.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat