Bonding and Structures of Transition Metals

Abstract

Bre'vlc"(" ,L , The creat variety of structures and combining ratios in intermetallic compound:; offers a challenge to bonding theories. Can the compositions and structures of these in:termetallics be correlated and explained in terms of the same principles used for chemical substances generally? For all substances it is the'electrons through their interactions with the nuclei which constitute the glue that binds atoms together and any explanation of the structures, compositions and stabilities of intermetallic' compounds must be based upon the same principies of electronic interactions that apply to all mat.erials. Valence-Bonds and Molecular-Orbitals The common app~oaches to the description of electronic bondinG are termed the molecular-orbital and valence-bond methods. 1 The molecularorbital method starts with the atoms already assembled in the molecule or solid and then the electrons are added to molecular orbitals in an aufb~l.u or building-up process patterned after the aufbau process for free atoms. The valence-bond approach starts with the eiectrons on the separated atoms, either in the ground electronic states or in low lying exci 1;ed electronic states, and the bonding is described generally in terms~6f electron-pair bonds between the nuclei of the approaching atoms. _ 2. lt has been shown that the methods become equivalent if used in full complexity. However, at a practical level of approximation, each method has serious deficiencies. The simple molecular-orbital method underestjmates and the simple valence-bond method overestimates electroncorrelation due to the coulombic repulsion of the electrons in an electron-pair bond. The molecular-orbital method has the haridicap of

Improvement of performances of complex non-platinum electrode materials for hydrogen evolution

“…The small peak on position of 854.2 eV indicates a presence of small amount of NiO with the same table value as the measured one, while the peak on position 853.1 eV corresponds to presence of NiTi phase (table value of 853.15 eV). This is in accordance with the previous spectra of TiO 2 phase as well as the IR spectra. The peak on position 852.4 eV for the catalyst modified with adding of Co (sample 5) implies a presence of small amount of NiCo (table value 852.7 eV).…”

“…4a) The peak of Ni2p 3/2 spectra on position of binding energy of 856.6 eV and satellite peak Ni2p 3/2(sat) on 862 eV suggest an existence of Ni(OH) 2 phase. This means that the main amount of Ni on the surface layer up to depth of severalÅ exists as Ni(OH) 2 . The small peak on position of 854.2 eV indicates a presence of small amount of NiO with the same table value as the measured one, while the peak on position 853.1 eV corresponds to presence of NiTi phase (table value of 853.15 eV).…”

“…Analyzing the values of binding energy of Ti-spectra (Fig. 4a) The peak of Ni2p 3/2 spectra on position of binding energy of 856.6 eV and satellite peak Ni2p 3/2(sat) on 862 eV suggest an existence of Ni(OH) 2 phase. This means that the main amount of Ni on the surface layer up to depth of severalÅ exists as Ni(OH) 2 .…”

“…It started with combining the most active precious metals, as Pt-Pd or Ir-Re [1], but the resulting synergetic effect did not satisfy the expectations. Latter on, based on theoretical analysis given by Brewer [2], Jakšić et al [3], the efforts were oriented towards combining nonprecious met- * Corresponding author. Tel.…”

Study of structural and electrochemical characteristics of Co-based hypo–hyper d-electrocatalysts for hydrogen evolution

“…with Ti 1−x Ni x , Zr-Ni, Ni-Co-Mo, Ni-W-S, Ni-W-P, etc., [4][5][6][7]. The basic aspects of combining d-metals and prediction of structural and electrocatalytic characteristics of the compsite catalysts were given by Jakšić's interpretation [8][9][10]] of Brewer's theory of bonding in transition metals and intermetallic phases [11]. So, significant synergetic effect can be achieved by combining transition metals with dissimilar electronic character, i.e.…”