Electrochemical Behavior of Sol‐Gel Produced Ni and Ni‐Co Oxide Films

Abstract

Ni and mixed Ni-Co oxide films were formed at Pt substrates by the sol-gel technique and studied electrochemically in 1 M NaOH solutions. All sol-gel films under study have to be found amorphous. The charge densities of these films are quite high compared to oxides formed by the anodic oxidation of metallic substrates. Mixed Ni-Co oxide films display higher charge densities, broader CV peaks, and negatively shifted equilibrium potentials vs. pure Ni oxide films. At slow sweep rates, all films studied showed kinetically reversible surface electrochemical behavior. At higher sweep rates, the redox reactions became kinetically irreversible, being either surface reactions with no diffusion limitations or controlled by the diffusion rate of species inside the film. The effect of the oxide film formation conditions, i.e., the withdrawal rate of the substrate from the sol solution and the firing temperature, on the electrochemical efficiency of the oxide films was also studied. InfroductionNickel oxide/hydroxide and mixed Ni-Co oxide films have been extensively studied in the past, primarily due to their numerous promising applications. These include their use as battery electrodes,' both in aqueous and nonaqueous media, with much work having been focused on the addition of Co to Ni oxides in order to improve their performance. The electrochromic oxidation/reduction in both cobalt and nickel oxide/hydroxide films, which occurs with the injection and expulsion of mobile ions,2 has facilitated their applications in "smart windows,"3 display panels,4 and rearview mirrors.4 Ni-Co-based alloys also appear to be very promising materials for water electrolysis because of their good electrocatalytic properties and reported stability for the oxygen'' and hydrogen9-" evolution reactions. Cobalt based films are also widely used in recording media.'2The most important electrochemical process for Ni oxide electrodes, which occurs in alkaline solutions, can be described asA similar reaction can be written for cobalt oxide electrodes" and 3Co11 (OH)2 + 2 OH-# Co"111O4 + 4H2O + 2e [21 Co"(OH)2 + OW a Co'1100H + H2O + e Co"OOH + OW # Co"TO, + H2O + e [3] [4]However, it is a well-established fact that these redox reactions are more complex than indicated here''4 and that they involve the intercalation/deintercalation of cations in basic solutions1' in which the oxides are stable, i.e., in simplified form'6Ni" (or Co")oxide + 1.5 OW + 0.5Na s Ni"(or CoIv) oxide (1.5 OH)(0.5 Nat) + e [5] Nickel and cobalt oxide-hydroxide films can be prepared by the anodic oxidation of the metallic substrate," cathodic precipitation,' electron-beam * Electrochemical Society Student Member. * * Electrochemical Society Active Member. electrodeposition,"2 etc. Chemical deposition," electrolytic deposition," spray pyrolysis," etc, are utilized to make mixed nickel-cobalt oxide films, which can also be

Composition, Structure, and Electrochemical Behavior of Sol-Gel Derived Nanoparticulate Pt Thin Films

“…Figure 7 shows an SEM image of the surface, revealing fracturing of the film at certain sites, typical of either hydrated or sol-gel formed thin films composed of small particles. 21 This fracturing has also caused the loss of regions of the film, which may provide an explanation for some of the mass loss ͑Table I͒ seen after rinsing or electrochemistry ͑see the section on Stability and efficiency of use of the nanoparticulate film͒. EDX analysis performed on regions of the film showed crystalline NaCl, perhaps with some Pt or Pt chloride compound trapped from the precipitation process.…”

Electrocatalytic oxidation and determination of insulin at CNT-nickel–cobalt oxide modified electrode

“…A different combination of the two oxides, NiCo 2 O 4 spinel, is also known to be an active and stable bifunctional catalyst for oxygen evolution and reduction in alkaline media, as well as a catalyst in alcohol and amine electro-oxidation [25][26][27]. There are confirmations in the literature that mixing Ni and Co oxides brings beneficial effects on their electrocatalytic activity, but most of the studies were directed toward the electrocatalytic activity investigations of this catalyst of mixed oxides for both oxygen reduction and evolution reactions [24,26,[28][29][30]. There is a challenge for using mixed metal oxide (NiO and CoO) for oxidation of biologic compounds, as insulin.…”

“…Cyclic voltammograms for CNT-NiCoO2/Nafion electrodes (Nafion 1.7%; 3 g NiCoO2/electrode) in 1 M NaOH at different scan rates:10,20,30,40,50, 100, 150 and 200 mV/s.…”

Electrochemical Characterization of Sol-Gel Formed Ir Metal Nanoparticles

“…5 We have gained our experience in the SG deposition of thin films through parallel work with Ni, Co, and mixed Ni-Co oxide films. 6,7 These films have been characterized electrochemically and using various surface analysis techniques. It has been discovered that the mixed Co:Ni oxide films, particularly those of 1:1 composition, have superior charge densities (achieved by optimizing the experimental variables) and redox kinetic properties as compared to similar Ni-Co oxides formed electrochemically or by other conventional deposition methods.…”

“…It is known that, the more rapid the withdrawal rate, the thicker is the surface film. 6,7 The Au substrate surface area varied from ca. 0.1 to 1 cm 2 , with some evidence for a lower coverage of the SG coating at the higher area electrodes.…”