High Surface Area Nickel Research Articles

High Specific Surface Area Nickel Mixed Oxide Powders LaNiO3 (Perovskite) and NiCo2O4 (Spinel) via Sol-Gel Type Routes for Oxygen Electrocatalysis in Alkaline Media

A novel sol-gel process of preparation of oxide electrocatalysts is investigated to prepare Ni-containing mixed oxides LaNiO3 and NiCo2O4 at moderate temperatures. High surface area (20-55 m2 g-1) powders and high roughness electrodes (30-1500) were obtained. Apparent and real electrocatalytical activity are compared and discussed.

Electrooxidation of benzyl alcohol at high surface area nickel (NiS x ) electrodes in alkaline solution

The heterogeneous catalytic redox behaviour of NiSx deposited electrodes was investigated with and without benzyl alcohol in KOH solution using cyclic voltammetry and linear sweep voltammetry. The limiting current density for benzyl alcohol oxidation on a NiSx electrode was 22 times larger than that on a polished nickel electrode. The experimental results in galvanostatic electrolysis using fractional factorial design showed that the main and interaction effects of benzyl alcohol concentration, temperature, and OH− concentration are the key variables influencing the selectivity of benzaldehyde formation during electrolysis.

High surface area nickel cathodes from electrocomposites

Abstract Raney-nickel cathodes prepared by different methods are increasingly applied in the two most important electrochemical technologies, i.e. chloralkali and water electrolysis. The effectiveness in enhancing the catalytic activity of nickel electrodes by employing three types of particulate materials, namely Raney-nickel, aluminium and alumina powders during the cathodic codeposition of nickel has been investigated. The amount of codeposited precursor depended on its specific gravity and the geometrical arrangement of the substrate (cathode). Composites produced by keeping the substrate horizontal during the deposition exhibited higher catalytic activity. The Tafel parameters for hydrogen evolution have been compared for the above three types of electrodes with those of mild steel and nickel. Cyclic voltammograms indicated high tolerance to current reversals with electrodes prepared using an aluminium precursor. The catalytic activity was in the order of cathodes from NiAl > NiAl2O3 > NiRaneyNi composites.

The influence of conditions on the electrocatalytic hydrogenation of organic molecules

The electrocatalytic hydrogenation of several functional groups has been studied at high surface area nickel, palladium, platinum and rhodium cathodes in methanol as a function of pH and current density. It is demonstrated that syntheses may be designed where good current efficiency and selectivity are possible at reasonable current densities and that the product can depend both on the choice of cathode metal and the solution conditions.

Neutron spectroscopic studies of the adsorption and decomposition of C 2H 2 and C 2H 4 on raney nickel

Incoherent neutron inelastic scattering has been applied to the study of the chemisorption of C 2H 2 and C 2H 4 on Raney nickel (a high surface area nickel powder) as a function of temperature. Surface vibrational spectra of the adsorbed layer obtained through neutron scattering demonstrate that at 150 K C 2H 2 adsorbs molecularly on the nickel surface. Ethylene, however, is more reactive. Even at 120 K there is some C 2H 4 decomposition. In addition, perdeuteroethylene coadsorbed with atomic hydrogen undergoes isotopic exchange at 120 K. As the temperature is raised to 275 K both hydrocarbons decompose. The vibrational spectra of the molecularly adsorbed species are similar to those observed on flat Ni(111) single crystal surfaces with EELS. However, the decomposition process at higher temperature is not simply related to results reported on either flat or stepped Ni(111) surfaces. We conclude that the dominant influence of steps (or other defect structures) on high surface area nickel powders is to lower the activation energy for dissociation.

Derivatized, high surface area, supported nickel catalysts

A new and general procedure for preparing high surface area, supported intermetallic compound and alloy catalysts is described. In this technique, the volatile Group IIIA and IVA organometallic compounds SiH 4, Me 6Si 2, Me 6Ge 2, BH 3 · Et 3N, and Et 3Al are decomposed thermally on high surface area nickel, supported on either SiO 2 or Al 2O 3, to yield, directly, mixed metal catalysts of varied composition and structure. Using the competitive dehydrogenation and hydrogenolysis of cyclohexane as model reactions, the effects of intermetallic compound formation on catalytic activity are described.

Hydrogen production by high temperature, high pressure water electrolysis, results of test plant operation

A high temperature, high pressure water electrolyzer has been developed. A test plant was built with a hydrogen production capacity of 4 m 3 h −1, operating at 120°C and 20 kg cm −2 G. The development of the test plant was reported previously. The test plant was operated for 22 months under various operating conditions and with various combinations of electrodes. Of the electrodes, a high surface area nickel electrode showed the best results, its cell voltage being 1.64 V at 102°C and 400 mA cm −2. PTFE impregnated with a Ti compound was used as the diaphragm material. The operating pressure did not show much effect on cell voltage.

Plasma-sprayed nickel cathode coatings for hydrogen evolution in alkaline electrolytes

Hydrogen evolution cathodes with plasma-sprayed nickel coatings were much more efficient in alkaline electrolytes than either uncoated cathodes or cathodes with porous sintered nickel coatings. This efficiency improvement could not be attributed to either superior coating morphology or increased surface area. The degree of coating oxidation appeared to be the main factor influencing the hydrogen evolution overpotentials at either the plasma-sprayed or sintered nickel cathode coatings studied. Highly-oxidized nickel surfaces produced much lower Tafel slopes than similar unoxidized surfaces. Plasma-sprayed nickel cathode coatings made with fine, high surface area nickel powder produced hydrogen evolution overpotentials in the range 0.10–0.14 V.

Neutron vibrational spectroscopy of hydrogen and deuterium on Raney nickel

Incoherent neutron inelastic scattering has been applied to the study of the chemisorption of hydrogen and deuterium on Raney nickel (a high surface area nickel powder). The binding sites have been identified by comparing the vibrational frequencies and intensities provided by the inelastic scattering with calculations for model structures of different geometries, force constants, and symmetries. We conclude that, on Raney nickel above 150 K, hydrogen chemisorbs predominantly in sites of threefold symmetry. The ’’best fit’’ corresponds to a Ni–H bond distance of 1.88±0.03 Å and a force constant of 0.58±0.03 mdyn/Å. In addition, we have observed lateral adsorbate interactions, deuterium isotope shifts, and temperature dependent binding sites.

Single crystals as model catalysts

Recent work has demonstrated the special advantages of meshing in a single apparatus kinetic measurements at process‐like conditions with modern surface analytical techniques for fundamental catalytic studies. These data have shown that low surface area monolithic materials can be used successfully to model certain catalytic systems. Virtually identical kinetic parameters have been found for the methanation reaction over single crystals of nickel and ruthenium as have been measured for high surface area nickel and ruthenium process catalysts. Surface probes have allowed the methanation reaction to be mechanistically dissected, in that the kinetics associated with the two major reaction steps have been individually measured. Using surface probes to monitor quantity and ordering of the impurity atoms, a correlation has been found between the electronegativity of the impurity atom and its catalytic poisoning ability. Electronic effects, as opposed to site blocking, are shown to dominate.

The preparation of high surface area nickel oxide electrodes for synthesis

A study of the electrodeposition of nickel onto copper and graphite is described; the objective was to prepare high surface area, i.e. microrough, but stable deposits which could be used as nickel oxide anodes in aqueous base. It is shown that such electrodes may be prepared by electrodeposition at a high current density (200 mA cm−2) from a Watts bath and that they give useful apparent current densities for a model synthetic reaction, the oxidation of ethanol to acetic acid.

Adsorption species of oxygen on the surfaces of transition metal oxides

Abstract A method for the determination of the mean number of elementary electric charges acquired by one oxygen atom adsorbed on the surface of such oxides as NiO, CoO, MnO is proposed. It consists of the determination of the volume of oxygen gas adsorbed on a high surface area sample of strictly stoichiometric oxide and the subsequent analytical determination of the number of metal ions promoted to a higher oxidation state as the result of electron transfer from the adsorbent to the adsorbate. Using this method it has been shown that, in the case of high surface area nickel oxide, oxygen is chemisorbed at room temperature predominantly in the form of O− ions (irreversible adsorption). The percentage of reversibly adsorbed oxygen decreases with the time of contact. At 150 °C only the O− form was observed after a short period of adsorption. Slow formation of O2− could be subsequently observed. The velocity of this latter process increases with an increase in temperature. In the case of high surface area cobalt oxide, the O2− form predominates even at room temperature.

The effect of chemisorbed species upon the physical adsorption of argon on nickel oxide

At room temperature, high surface area nickel oxide, prepared by decomposition of nickel hydroxide, chemisorbs oxygen, carbon monoxide, and carbon dioxide. The surface coverage by these species does not exceed 20%. The chemisorption of these gases reduces the physical adsorption of argon by an amount approximately proportional to the coverage by the chemisorbed species. The application of the t-plot shows that the nickel oxide is a microporous material and that the blocking of the micropores by chemisorbed species is responsible for the decrease in the physical adsorption of argon. Considerations on the correct application of the t-plot are developed.

Inhibition of sintering in molten carbonate fuel cell anodes

Molten carbonate fuel cells operate at 600–700°C. At these high temperatures, high surface area nickel anodes lose their activity rapidly due to sintering. A study of the sintering kinetics of Ni, Ni-Ag and Ag powder revealed that when Ni and Ag particles are present in similar numbers, sintering is significantly inhibited. This is achieved by minimizing volume diffusion between adjacent particles — Ni and Ag have virtually no solid solubility at any temperature. Paste electrolyte cells using such electrodes gave 114 mA/cm2 at 0.65 V on 80% H2/20% CO2 fuel, compared to 80 mA/cm2 at 0.65 V for a cell using sintered nickel anodes.