Electrocatalyst coordination number

Metal oxides, 31 78-79, 89, 102, 123, 157-158, 191, 32 199-121 see also Amorphous metal oxides Sulfate-supported metal oxides specific oxides adsorbed oxygen on, 27 196-198 binary, surface acidity, 27 136-138 catalytic etching, 41 390-396 coordination number, 27 136 electrocatalysts, 40 127-128 Fe3(CO)i2 reaction with, 38 311-314 Lewis acid-treated, 37 169-170 multiply-valent metals, electrocatalytic oxidations, 40 154-157 superacids by, 37 201-204 surface acidity, methods for determining, 27 121... 

Kinoshita reported a correlation between the fraction of Pt surface atoms on the (10 0) and (111) crystal faces of the platinum particles of cubo-octahedral structure with varying particle sizes and the specific catalytic activity of platinum electrocatalysts 54). For cubo-octahedral particles, which have both (1 1 1) and (10 0) faces, an optimum in mass activity at a 3.5-nm platinum particle diameter was reported. Under these conditions, the surface fraction of platinum on (1 00) and (111) faces shows a maximum according to calculations of the coordination number with changing average particle size (55). 

Nb-doped Ti02 has also been demonstrated as a possible electrocatalyst support for Pt. Nb is an n-type dopant in Ti02 that is used to increase the number of free electrons in the crystal lattice. Pentavalent n-type donor atoms are incorporated into the titania matrix with a coordination number of 4. This leaves an excess electron whose energy level is much closer to the conduction band of the host material. Thus, the Fermi level is raised, significantly reducing the electron ionization energy, increasing the electronic conductivity of the semiconductor considerably. This effect is illustrated in Fig. 24.18 [158]. 

The element-specific electronic properties, e.g., Pt 5d-band state, of Ptmu electrocatalysts and the local environment, such as bond distance and coordination number of individual component, were obtained using X-ray absorption nearedge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopies, respectively. 

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