Copper electrocatalysts

Similarly, Pd, Ag, and Pd-Ag nanoclusters on alumina have been prepared by the polyol method [230]. Dend-rimer encapsulated metal nanoclusters can be obtained by the thermal degradation of the organic dendrimers [368]. If salts of different metals are reduced one after the other in the presence of a support, core-shell type metallic particles are produced. In this case the presence of the support is vital for the success of the preparation. For example, the stepwise reduction of Cu and Pt salts in the presence of a conductive carbon support (Vulcan XC 72) generates copper nanoparticles (6-8 nm) that are coated with smaller particles of Pt (1-2 nm). This system has been found to be a powerful electrocatalyst which exhibits improved CO tolerance combined with high electrocatalytic efficiency. For details see Section 3.7 [53,369]. 

But think what happens when a piece of copper is immersed in a silver nitrate solution (Fig. 7.118) and then made an electron-source electrode. The electronation of Ag+ ions to silver metal takes place on the copper, and the reddish copper surface becomes coated with a silvery color. A cross section of the electrode shows that the electrode surface has advanced toward the solution (Fig. 7.119). Silver has electro-crystallized on the copper. Thus, the copper electrode has not behaved as an electrocatalyst ithasbeen altered by electrociystallization. It is not simply an electron source. 

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... 

There are a number of different ways to prepare metal overlayers in practical nanoscale fuel cell electrocatalysts. One approach is schematically shown in Figure 3.3.13A, where a spherical alloy nanoparticle consisting of a noble metal (grey), platinum, and a nonnoble metal (red), such as copper, is subject to a corrosive electrochemical... 

T. Ito, S. Matsuzawa, K. Kato (Pt-Cu) USP 4,716,087, Platinum-Copper Alloy Electrocatalyst and Acid-Electrolyte Fuel Cell Electrode Using the Same, File date 10 Dec 1986, Issue date 29 Dec 1987. 

The selective oxidation or preferential oxidation of CO in hydrogen-rich stream is another important object for ceria based catalysts. The gas mixture from steam reforming/partial oxidation of alcohols or hydrocarbons, followed by the WGS reaction contains mainly FI2, CO2 and a small portion of CO, H2O, and N2. When such gaseous stream would be taken as input for hydrogen fuel cells, the CO has to be removed to avoid poisoning of the anode electrocatalysts. Ceria based nanomaterials, such as ceria/gold, ceria/copper oxide catalysts exhibit suitable catalytic activities and selectivities for CO PROX process. 

Copper complexes adsorbed (167-169) and covalently (170) bound to electrode siufaces were shown to be good electrocatalysts for the four-electron reduction of dioxygen. The results indicate that a CU2O2L2 (L = phenantroline) intermediate is formed dining the reduction. 

Fig. 2.24 TEM of homogeneously alloyed Cu/Pt nanoparticles on carbon (a) and the onion-type Pt Cu electrocatalyst (b). The inset on micrograph (b) shows small Pt nanoparticles (1-2 nm) decorating larger copper nanoparticles (6-8nm).

M. nieva, V. Tsakova, and W. Erfurth, Electrochemical formation of bi-metal (copper-palladium) electrocatalyst supported on poly-3,4-ethyelenedioxythiophene, Electrochim. Acta, 52, 816-824 (2006). 

Weng YC, Fan FR, Bard AJ (2005) Combinatorial biomimetics. Optimization of a composition of copper(II) poly-L-histidine complex as an electrocatalyst for O2 reduction by scanning electrochemical microscopy. J Am Chem Soc 127(50) 17576-17577... 

Green CL, Kucemak A (2002) Determination of the platinum and ruthenium surface areas in platinum-ruthenium alloy electrocatalysts by underpotential deposition of copper. 1. Unsupported catalysts. J Phys Chem B 106 1036-1047... 

Xi YT, Wei PJ, Wang RC, Liu JG (2015) Bio-inspired multinuclear copper complexes covalently immobilized on reduced graphene oxide as efficient electrocatalysts for the oxygen reduction reaction. Chem Commun 51 7455-7458... 

Barnett SM, Goldberg KI, Mayer JM. A soluble copper-bipyridine water-oxidation electrocatalyst. Nat Chem. 2012 4 498-502. 

Recently, Peterson and Norskov [47] compared trends in binding energies for the intermediates identified in CO2 electrochemical reduction, and presented a Volcano-based activity of the experimentally observed variations in transition metal catalysts. They confirmed that copper is the best-known metal electrocatalyst. The authors proposed new strategies to be adopted towards the discovery of potent catalysts that can operate with a reduced overpotential. 

---