Properties of Ni/NiO films

1. Nanoscale Ni/NiO films for electrode and electrochemical DevicesRelva C. Buchanan (University of Cincinnati), DMR 0407569 • Properties of Ni/NiO films • Ni/NiO thin films have been widely applied and studied for a variety of electrical and electrochemical applications, including sensors[1,2], fuel cells[3], batteries[4] and supercapacitors[3]. • In this study, nanoscale Ni/ NiO thin films were fabricated by MOD(metalo-organic deposition) technique on a variety of substrates, such as silicon and stainless steels. • In this study, film morphology arising from controlled deposition and thermal oxidation processes were correlated to thermo-resistive properties, wetting behavior and corrosion resistance. • The Ni/NiO films exhibit very linear TCR (temperature coefficient of resistance) characteristics (~3500ppm/oC) suitable for compact thermistor and sensor designs. • 3-D nanoscale surface texture with large surface area obtained indicated potential for catalyst support application. • Good wetting properties (~43o) and corrosion rates (Icorr ~46 A/cm2) with controlled oxidation, suggest good potential for PEM bipolar plate fuel cell application. • Overall, surface morphology, phase composition, resistivity and adhesion of the deposited films were shown to be sensitively controlled by processing effects. Electrochemical data show high reversible discharge capacity and good cycling performance, as examined by cyclic voltammetry and dc polarization methods. • [1] S. Doppiu, et al., Ni-NiO Nanocomposites,Chem. Mater. 16 (2004) 5664-5669 • [2] Shin Lin a et. Al., nickel anode electrode,Biosensors and Bioelectronics 20 (2004) 9–14 • [3] M. A. Anderson, et al., J. Electrochem. Soc. 143, 124 (1996); (b) Ullmann’s Encyclopedia of Industrial Chemistry, Vol. A17, 238 (1991). • [4] X.H. Huang et al., NiO–Ni nanocomposite as anode material for lithium ion batteries,J. of Power Sources 161 (2006) 541–544 Fracture cross section and surface morphology of Ni/NiO thin films on silicon substrate showing ,respectively, good density and adhesion and nanoscale texturing of high surface area.

2. Nanoscale Ni/NiO films for electrode and electrochemical DevicesRelva C. Buchanan (University of Cincinnati), DMR 0407569 • Broader Impacts of this Research • Overall, our study shows that Ni/NiO films of controlled morphology and good adhesion can be successfully developed for potential uses as fuel cell bipolar plates, as supercapacitors, and for thermal sensor applications. • Bipolar plates in PEM fuel cells serve to distribute fuel gas and air; conduct electrical current; remove heat from the active area; facilitate water management within the cell; and, prevent leakage of gases and coolant. They require good; interfacial contact resistance, surface wettability, thermal conductivity and good corrosion resistance • The Ni/NiO films film technology can also be applied as supercapacitors elements. These devices store energy in an electrochemical double layer formed at the solid/ electrolyte interface. Applications in the fields of telecommunications and as backup power for batteries in low power applications are envisaged. • The Ni/NiO film technology thus potentially impacts broadly on the field of Emerging Energy Technologies, in energy storage, in fuel power generation and as sensors for a variety of control operations. • The research impacts broadly also on the training of • of undergraduate and graduate students and in helping to promote a interest in science and engineering for high school students exposed to this research. • Wide dissemination of the findings from this research through publications and presentations will also aid in advancing awareness of this emerging energy related area. • Oxidation Kinetics Of NiO Films • For NiO above 800C, film growth typically follows the parabolic oxidation rate law: • (1) • Where kp is the parabolic rate constant (mg2·cm4·s-1), ∆m is the weight gain per unit area (mg cm-2) and t is the oxidation time (s). • Considering the oxide density, Eq. (1) can be rewritten as: • (2) • where d is film thickness and  is the NiO density which is 7.45g cm-3. Below ~500 C, the kinetic mechanism changes to sub-parabolic behavior in which the oxidation rate decreases faster with time. Outward transport of Ni occurs then through short circuit mechanisms––dislocations and grain boundaries. For films (10nm<x<1m, a logarithmic rate law applies, as follows: • (3)