Oxidation states nickel

Electrodes. A number of different types of nickel oxide electrodes have been used. The term nickel oxide is common usage for the active materials that are actually hydrated hydroxides at nickel oxidation state 2+, in the discharged condition, and nickel oxide hydroxide [12026-04-9] NiO OH, nickel oxidation state 3+, in the charged condition. Nickelous hydroxide [12034-48-7J, Ni(OH)2, can be precipitated from acidic solutions of bivalent nickel... 

The terminology partially reduced and partially oxidized dithiolenes used in this physics-dominated field may be confusing, and a few words to clarify this situation may be needed, (i) The Ni atom in an Ni(mnt)2 complex, in which n — 0, 1, 2 or 3, will have a formal oxidation state of 4 +, 3 +, 2+ or 1 +, respectively, (ii) An Ni(mnt)2- complex with a nonintegral nickel oxidation state, for example 3.5 + in a complex with n - 0.5, can be formally and experimentally derived either from Ni(mnt) by partial reduction or from Ni(nmt)2" by partial oxidation, (iii) A look at the formula of the product will convince the confused reader that the terms partially oxidized and partially reduced are used interchangeably and that they may indeed describe the same complex. 

In order to confirm the nickel oxidation state in the active entity and to study the influence of the composition of its coordination sphere [coordination number, nature of the trialkylphosphine (TAP) ligands] on the catalytic performances, we have used a set of silica-supported unsaturated Ni complexes [58] with a given number of TAP ligands of different electronic and steric properties [59,60],... 

Holm and coworkers found that thiolates, amidates and oximates were most effective at making higher nickel oxidation states accessible (25), However, the studies noted in the previous section showed that in O2 reactions of their Ni(II) complexes, amidates and thiolates were themselves readily oxidized in a manner that precludes catalysis. Oximates have been shown to support stable nickel complexes in both the Ni(III) and Ni(IV) oxidation states (26-28), They also lack the a- and P-hydrogen atoms that are most prone to oxidative abstraction by high valent metals, thereby additionally satisfying the second design criterion. 

One of the major problems with the MCFC is that the nickel oxide state-of-the-art cathode material has a small, but significant, solubility in molten carbonates. Through dissolution, some nickel ions are formed in the electrolyte. These then tend to diffuse into the electrolyte towards the anode. As the nickel ions move towards the chemically reducing conditions at the anode (hydrogen is present from the fuel gas), metallic nickel can precipitate out in the electrolyte. This precipitation of nickel can cause internal short-circuits of the fuel cell with subsequent loss of power. Furthermore, the precipitated nickel can act as a sink for nickel ions, which promotes the further dissolution of nickel from the cathode. The phenomenon of nickel dissolution becomes worse at high CO2 partial pressures because of the reaction... 

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