Oxygen transition metal chalcogenides

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

Binary systems of ruthenium sulfide or selenide nanoparticles (RujcSy, RujcSey) are considered as the state-of-the-art ORR electrocatalysts in the class of non-Chevrel amorphous transition metal chalcogenides. Notably, in contrast to pyrite-type MS2 varieties (typically RUS2) utilized in industrial catalysis as effective cathodes for the molecular oxygen reduction in acid medium, these Ru-based cluster materials exhibit a fairly robust activity even in high methanol content environments of fuel cells. 

With respect to non-noble and non-Ru catalysts, transition metal chalcogenides with spinel and pyrite structures have been investigated and shown that these can also be active to oxygen reduction processes. The motivation in the present case is that chalcogen addition might enhance the stability and activity toward the ORR... 

Solorza-Eeria O, EUmer K, Giersig M, Alonso-Vante N (1994) Novel low-temperature synthesis of semiconducting transition metal chalcogenide electrocatalyst for multielectron charge transfer Molecular oxygen reduction. Electrochim Acta 39 1647-1653... 

Alonso-Vante N, Tributsch H, Solorza-Eeria O (1995) Kinetics studies of oxygen reduction in acid medium on novel semiconducting transition metal chalcogenides. Electrochim Acta 40 567-576... 

In a transition metal chalcogenide or oxide, positive guests like Li occupy sites surrounded by negative chalcogen or oxygen ions, and distance themselves as far as possible from the positive transition metal ions. Since Li has a filled outer core of electrons (unlike the transition metal ions in many of the hosts), the geometry of the site is not important as long as the anions are distributed evenly around the site. Thus y" surrounded by four anions would prefer the anions to form a tetrahedron rather than a square. 

N. Alonso-Vante, M. Fieber-Erdmann, H. Rossner, E. Holub-Krappe, C. Giorgetti, A. Tadjeddine, E. Dartyge, A. Fontaine, R. Frahm, The catalytic centre of transition metal chalcogenides vis-a-vis the oxygen reduction reaction An in situ electrochemical EXAFS study. J. de Physique IV France 1997, 7, C2-887-C2-889. 

Tiitsaiis GA, Greeley J, Rossmeisl J, Norskov JK (2011) Trends in oxygen reduction and methanol activation on transition metal chalcogenides. Electrochim Acta 56 9783-9788... 

Structure and Reactivity of Transition Metal Chalcogenides toward the Molecular Oxygen Reduction Reaction... 

It is believed that the catalytic activity on transition metal chalcogenides takes place through the interaction of the molecular oxygen with the transition metal d-states. The bands are filled with valence electrons of the atoms up to the Fermi level as shown for Mo4Ru2Seg cluster compounds (Fig. 14.2) [21]. 

Alonso-Vante N (2011) Stmcture and reactivity of transition metal chalcogenides toward the molecular oxygen reduction reaction. In Vayenas CG (ed) Interfacial phenomena in electrocatalysis, vol 51, Modem aspects of electrochemistry. Springer, New York, pp 255-300... 

Baresel D, Sarholz W, SchamerP, Schmitz J (1974) Transition metal chalcogenides as oxygen catalysts for fuel cells. Ber Bunsen-Ges 78(6) 608-611... 

Alonso-Vante N, Fieber-Erdmann M, Rossner H, Holub-Krappe E, Giorgetti C, Tadjeddine A, Dartyge E, Fontaine A, Frahm R (1997) The catalytic centre of transition metal chalcogenides vis-4-vis the oxygen reduction reaction an in situ electrochemical EXAFS study. J Phys IV 7(2 Part 2) 887-889... 

Figure 15.11. Interaction of molecular oxygen in acid medium at the Chevrel phase cluster-electrolyte interface [6]. (Reprinted from Journal de Physique, vol. 7, C2, The Catalytic Centre of Transition Metal Chalcogenides vis- -vis the Oxygen Reduction Reaction An In situ Electrochemical EXAFS Study, Alonso-Vante, N. et al. 31997, with permission from EDP Sciences.)...

Table 15.2. Catalytic activity of various transition metal chalcogenides for ORR in 4N H2SO4 at 70 °C [104]. (Reprinted from Baresel VD, Sarholz W, Schamer P, Schmitz. Transition metal chalcogenides as oxygen catalysts for fuel cells. Berichte Der Bunsen-Gesellschaft 1974 78 608-11, with kind permission of Deutsche Bunsen-Gesellschaft fur Physikahsche Chemie.)...

---