Nickel oxide lithiated

Also for cathodic oxygen reduction in low-temperature fuel cells, platinum is indispensible as a catalyst whereas the cathodic electrocatalysts in MCFCs and SOFCs are lithiated nickel oxide and lanthanum-manganese per-ovskite, respectively. Appleby and Foulkes in the Fuel Cell Handbook (101) reviewed the fundamental work as well as the technologically important publications covering electrocatalysis in fuel cells till 1989. 

The cathode today consists of a porous layer of lithiated nickel oxide Li,Nii vO, which, being a p-type semiconductor of high conductivity, provides the necessary electronic conductivity and an internal cathode surface, which is catalytically active for dissociative reduction of 02 species. 

The molten carbonate fuel cells employ LijCOj-f CC (62.38 mol.%) electrolytes, porous Ni alloy, and lithiated nickel oxide as anodes and cathodes at an operating temperature of 723 K. The half-cell reactions of each side are, respectively... 

Gallium-doped nickel oxide contains more metallic nickel than pure or lithiated nickel oxides (Table X). Concentrations of metal deduced from magnetic susceptibility measurements (23) are, moreover, in agreement with the results of chemical analyses (30). The following mechanism of incorporation explains these results (80) ... 

Removal of lattice oxygen from the surface of nickel oxide in vcumo at 250° or incorporation of gallium ions at the same temperature [Eq. (14)] causes the reduction of surface nickel ions into metal atoms. Nucleation of nickel crystallites leaves cationic vacancies in the surface layer of the oxide lattice. The existence of these metal crystallites was demonstrated by magnetic susceptibility measurements (33). Cationic vacancies should thus exist on the surface of all samples prepared in vacuo at 250°. However, since incorporation of lithium ions at 250° creates anionic vacancies, the probability of formation of vacancy pairs (anion and cation) increases and consequently, the number of free cationic vacancies should be low on the surface of lithiated nickel oxides. Carbon monoxide is liable to be adsorbed at room temperature on cationic vacancies and the differences in the chemisorption of this gas are related to the different number of isolated cationic vacancies on the surface of the different samples. 

Material Nickel Lithiated nickel oxide (5 wt%) LiA102... 

The MCFC is a promising power generating source because of its unique characteristics such as high fuel efficiency and ability to use various carbonaceous fuels. Although Ni-10wt% Cr is used in the state-of-the-art MCFC as anode, it needs to be improved in terms of better creep and sintering resistance. In spite of the development in the alternate cathode material research, lithiated nickel oxide has been the choice of cathode material in the kilowatt-level MCFC stacks developed by many companies. Continuous research in the development of stable electrolyte retention matrix, identification of suitable molten carbonate electrolyte composition, and additives to the electrolyte will be a significant milestone. Also, research in the area of current collector/bipolar plate to overcome... 

The MCFC anode is made of porous nickel with 2-10% chromium or aluminium to improve the creep resistance. The state-of-the-art cathode is made of in-situ oxidised and lithiated nickel oxide. Both electrodes are partially filled with carbonate in order to obtain optimal 3-phase contact. The matrix is a porous lithium aluminate tile, which is completely filled with the carbonate mixture. The individual cells are separated by a metallic separator plate. 

Alkaline FCs (AFCs) use KOH as electrolyte and work at 70-90 C they are fully developed and very reliable (they powered on-board instrumentation of the Apollo spacecrafts and they power on-board instrumentation of the space Shuttles). Electrodes are mostly sintered nickel (anode) and sintered, lithiated nickel-oxide (cathode). 

By operating at about 650 °C, the kinetics of the oxygen reduction reaction at the positive electrode are sufficiently accelerated that it is no longer necessary to use platinum-based electrocatalysts. Usually, the positive electrode is fabricated from lithiated nickel oxide (Li Nii 0, where 0.02[Pg.211]

The cathode consists of lithiated nickel oxide. Nickel oxide is a p-type semiconductor, having a rather low conductivity. When doped with lithium oxide, its conductivity increases tens of times, owing to a partial change of Ni + to Ni + ions. The lithiation is accomplished by treating the porous nickel electrode with a lithium hydroxide solution in the presence of air oxygen. The compound produced has a composition given as Lij +Nii j( Nijj +0. This lithiation of nickel oxide was first applied in 1960 by Bacon in his alkaline fuel cell. 

Figure 8.5 Change in transmittance (upper part) and deflection angle variation (lower part) associated with galvanostatic (1= 21 pAcm" ) insertion-deinsertion cycles of a lithiated nickel oxide thin-film electrode. The vertical bar corresponds to a stress variation of 0.5 GPa. Sample thickness 2000A. Counter-electrode Li foil. Electrolyte iM LiC104-PC. From [26] by permission of Elsevier Science Publishers, Amsterdam.

As expected from equation [8.13], the lithiated nickel oxide electrode becomes transparent during the cathodic cycle (Li" insertion) and coloured in the following anodic cycle (Li" extraction). It is interesting to note that the electrochromic efficiency of lithiated nickel oxide is 0.04mCcm" at 633 nm (25), i.e. of the same order as that of tungsten oxide. 

Figure 8.6 Cyclic voltammetry and optical transmittance of a lithiated nickel oxide electrode in a LiC104-PC solution. Light source He-Ne laser (6328A). Scan rate 20 mV s Sample thickness 6(X)A. From [22] by permission of the Electrochemical Society, Inc.

A possible explanation of these phenomena involves the presence in heavily lithiated nickel oxide samples of two different phases or, more simply, of two different intercalation mechanisms for lithium ions. Assuming that pristine nickel oxide films are defective p-type materials due to the presence of trivalent nickel [26], it may be supposed that the electrons initially injected to balance the insertion of the first lithium ions (Qinteract with Ni " in the host matrix. However, and as described for proton intercalation in... 

In conclusion, lithiated nickel oxide is a very convenient electrochromic materal in its optimized concentration range which extends up to l(X)mCcm" pm" while further lithiation may induce an opposite behaviour. However, the optimized range is largely sufficient to assure proper electrochromic behaviour and this places LiyNiO among the most promising anodic ECMs. 

The promising behaviour of lithiated nickel oxide as optically passive counter-electrode in WO3-based EWs has been in fact practically verified [22] by testing windows of the type ... 

Figure 8.12 illustrates the cyclic voltammetry and the transmittance of the window. The feasibility of the electrochromic system is confirmed by the excellent peak definition and low peak separation, as well as by the large transmittance variation upon cycling. One problem associated with the use of lithiated nickel oxide counter-electrodes remains the low diffusion of the Li" ions (calculated to be of the order of 10 cm s [24]), which may lead to long response times. However, this problem may be alleviated by optimizing the morphology of the electrode. 

One of the first examples of these structures is that based on a multilayer combination of a lithiated nickel oxide glass, a film of the (PE0)8LiC104 electrolyte and a tungsten oxide glass [55] ... 

The rest potentials of platinum and other electrodes have also been examined in hydrogen peroxide solutions. On surfaces such as carbon, graphite, and lithiated nickel oxide, the open-current values are the thermodynamically reversible value for the 02-H02 couple in alkaline electrolytes or close to it. On these surfaces, the further reduction of peroxide [reaction (V)] and the overall four-electron reaction are both very inhibited. These surfaces also do not have much catalytic activity for the heterogeneous decomposition of the peroxide. On the other hand, with platinum the overall four-electron reduction is far less inhibited and the platinum surface is a reasonably effective catalyst for peroxide decomposition. Even so, the open-... 

Most of the work on inorganic semiconductor catalysts for O2 reduction has been carried out on metal oxides in alkaline electrolytes. A number of these oxides have moderately high electrocatalytic activity with reasonable stability. These include lithiated nickel oxide/ " perovskites/ and spinel-structured metal cobaltite... 

C. H. Lee and E. Yeager, The Dissolution Kinetics of Lithiated Nickel Oxide in Aqueous Solutions, Tech. Report 5, Office of Naval Research Contract Nonr. 14939(05), Case Western Reserve University Cleveland, Ohio (1969). 

The conventional cathode material is lithiated nickel oxide that is formed by in situ oxidation during cell conditioning. The porosity and thickness are also around 50 % and 1 mm, respectively. The cathode polarization and dissolution/ deposition, which are very important factors of the performance and lifetime, are strongly influenced by the cathode pore structure, electrolyte composition, and operating conditions. The nickel oxide slowly dissolves into the electrolyte as Ni " with an acidic dissolution mechanism as follows ... 

The cathode consists of lithiated nickel oxide. Nickel oxide (NiO) is a p-type semiconductor that has rather low conductivity. When doped with lithium oxide, its conductivity increases tens of times, owing to a partial change of Ni " to Ni3+... 

Lithium/lithiated nickel oxide (Li/Li,NiO,) 2. Polymer electrolyte cells Li Li jNiOj LiAsEe, ME/MA Polypropylene xLi + Lii J fi02 LiNiOj... 

The search for effective electrocatalysts led to investigations of the corrosive resistance and of the reactivity for the O2 reduction of compounds of metals with other elements like boron, carbon, nitrogen, oxygen, etc. The cathode [78] of the Bacon cell represents the classical example. The porous cathodes were made by pressing and sintering mixtures of carbonyl nickel and ammonium bicarbonate. Subsequently, they were coated with a layer of lithiated nickel oxide. 

---