Electrocatalysts nickel

Helm ML, Stewart MP, Bullock RM, Rakowski DuBois M, DuBois DL. A synthetic nickel electrocatalyst with a turnover frequency above 100,000 S 1 for H2 production. Science. 2011 333(6044) 863 6. 

Raney nickel electrocatalysts have also found useful applications as active electrodes for the HER (179, 180). The activity of Raney Ni catalysts is established after leaching out the base metal, Al or Zn. Choquette et al. (181) have examined the changes in morphology and composition of Raney-Ni composite catalytic electrodes accompanying dissolution of the base metal in concentrated NaOH. The depletion of Al from the Raney particles is, of course, accompanied by a major increase in real area with time of leaching and also, interestingly, with possible phase transformations (181). The electro-catalytic activity is, however, surprisingly, practically independent of time. 

Gunnar RD and Langer SH. Comparisons of Ebonex and graphite supports for platinum and nickel electrocatalysts. Electrochim Acta 1998 44 437 44. 

Hoffert WA, Roberts JAS, Bullock RM, Helm ML (2013) Production of H2 at fast rates using a nickel electrocatalyst in water—acetonitrile solutions. Chem Crnmnun 49(71) 7767—7769. 

Liu et al. (2003) studied the oxidation of BH2 on nickel electrocatalyst and reported that the reaction proceeds by the four-electron rather than eight-electron pathways. Normally, Na" " or K" cations in the solution do not influence the four-electron reaction pathways. The four-electron reaction pathways and hydrolysis reaction leads to a decrease in efficiency of oxidation. A suitable catalyst should be identified such that the eight electron mechanism of electro-oxidation of NaBH4 is followed. Otherwise, hydrogen gas generated from four-electron mechanism of electro-oxidation should be utilized to maintain higher efficiency. 

In addition to these different types of alloys, some studies were also devoted to alternatives to platinum as electrocatalysts. Unfortunately, it is clear that even if some catalytic activities were observed, they are far from those obtained with platinum. Nickel tungsten carbides were investigated, but the electrocatalytic activity recorded for methanol oxidation was very low. Tungsten carbide was also considered as a possible alternative owing to its ability to catalyze the electrooxidation of hydrogen. However, it had no activity for the oxidation of methanol and recently some groups showed that a codeposit of Pt and WO3 led to an enhancement of the activity of platinum. ... 

Nickel oxide anodes are another example for a relatively simple oxide electrocatalyst used rather widely in the oxidation of organic substances (alcohols, amines, etc.) in alkaline solutions at relatively low anodic potentials (about +0.6 V RHE). These processes, which occur at an oxidized nickel surface, are rather highly selective. As an example, we mention the industrial oxidation of diacetone-L-sorbose to the corresponding acid in vitamin C synthesis. This reaction occurs at nickel oxide electrodes with chemical yields close to 100%. 

Low-valent nickel complexes of bpy are also efficient electrocatalysts in the reductive coupling reaction of aromatic halides.207 Detailed investigations are in agreement with a reaction mechanism involving the oxidative addition (Equation (40)) of the organic halide to a zero valent complex.208-210 Starting from [Nin(bpy)2(X)2]0 with excess bpy, or from [Nin(bpy)3]2 +, results in the [Ni°(bpy)2]° complex (Equations (37) and (38)). However, the reactive complex is the... 

The transfer of redox equivalents can be achieved by an electrocatalyst (mediator) or a modified electrode. Indirect electrolysis can lead to a better selectivity due to the specific interaction of the mediator with the substrate. However, low turnovers and the need to separate the mediator from the product are possible disadvantages, as mentioned above. The nickel hydroxide electrode [195,196] is fairly free from these disadvantages. The following mechanism for the oxidation at the nickel hydroxide electrode has been proposed in the literature [195]. 

Molten Carbonate Fuel Cell The electrolyte in the MCFC is a mixture of lithium/potassium or lithium/sodium carbonates, retained in a ceramic matrix of lithium aluminate. The carbonate salts melt at about 773 K (932°F), allowing the cell to be operated in the 873 to 973 K (1112 to 1292°F) range. Platinum is no longer needed as an electrocatalyst because the reactions are fast at these temperatures. The anode in MCFCs is porous nickel metal with a few percent of chromium or aluminum to improve the mechanical properties. The cathode material is hthium-doped nickel oxide. 

In the case of ethanol, Pd-based electrocatalysts seem to be slightly superior to Pt-based catalysts for electro-oxidation in alkaline medium [87], whereas methanol oxidation is less activated. Shen and Xu studied the activity of Pd/C promoted with nanocrystalline oxide electrocatalysts (Ce02, C03O4, Mn304 and nickel oxides) in the electro-oxidation of methanol, ethanol, glycerol and EG in alkaline media [88]. They found that such electrocatalysts were superior to Pt-based electrocatalysts in terms of activity and poison tolerance, particularly a Pd-NiO/C electrocatalyst, which led to a negative shift of the onset potential ofthe oxidation of ethanol by ca 300 mV compared... 

This is the mechanism of an indirect electrolysis, where the nickel oxide hydroxide acts as an electrocatalyst that is continuously renewed. Some observations, however, are not consistent with this mechanism. The addition of an oxidizable alcohol should lead to an increase of the current for the nickel hydroxide oxidation and a decrease for its reduction This is not the case. The currents for nickel hydroxide and nickel oxide hydroxide remain unchanged, whilst at more anodic potential a new peak for the alcohol oxidation appears. This problem has also been addressed by Vertes... 

Due to their relatively low cost, the most frequently applied electrocatalysts are nickel sulfide and Raney nickel for alkaline conditions. 

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. 

Nickel boride (Ni2B) has been quoted sometimes as an excellent electrocatalyst in alkaline solution [3, 10, 400]. However, there exists only one paper describing a practical stability test [107]. A patent filed in 1974 describes the electroless formation... 

In the most important series of polymers of this type, the metallotetraphenylporphyrins, a metalloporphyrin ring bears four substituted phenylene groups X, as is shown in 7.19. The metals M in the structure are typically iron, cobalt, or nickel cations, and the substituents on the phenylene groups include -NH2, -NR2, and -OH. These polymers are generally insoluble. Some have been prepared by electro-oxidative polymerizations in the form of electroactive films on electrode surfaces.79 The cobalt-metallated polymer is of particular interest since it is an electrocatalyst for the reduction of dioxygen. Films of poly(trisbipyridine)-metal complexes also have interesting electrochemical properties, in particular electrochromism and electrical conductivity.78 The closely related polymer, poly(2-vinylpyridine), also forms metal complexes, for example with copper(II) chloride.80... 

---