Selective interactive grafting of composite bifunctional electrocatalysts for simultaneous anodic hydrogen and CO oxidation - I. Concepts and embodiment of novel-type composite catalysts

The equivalence of interionic hypo-hyper-d-interelectronic interaction (HHDII) in both metallic and any other ionic state and its effect upon electrocatalytic properties for hydrogen electrode reactions has been proved and inferred. Thermal gravimetry (TG) analysis of temperature programmed reduction (TPR) of mixed hypo-hyper-d-electronic oxides of transition elements was broadly employed to prove the interionic bonding effect (the extended Brewer theory) as reflected in dramatically decreased individual temperatures of their mutual reduction into intermetallic phases or alloys. The same interionic (and/or intermetallic) bonding effect has been confirmed both by under potential deposition of hyper-d- upon hypo-d-electronic substrates and vice versa, and by the shift of bonding peaks in X-ray photoelectron spectroscopy analysis. The former affords the basis for new trends in submonolayer hypo-hyper-d-interelectronic electrocatalysis of transition metals. Strong metal support interaction (SMSI) of both individual and composite, prevailingly hyper-d-electronic metallic electrocatalysts upon individual and/or composite, usually hypo-d-electronic oxide substrates have been employed to create and graft (anchor) bifunctional electrocatalysts for simultaneous anodic hydrogen and CO oxidation in low temperature polymer exchange membrane fuel cells. The selective interionic bonding method upon predestined active centers of hypo-d-electronic oxide supports has been adapted to avoid nanostructured colloidal precursors and directly graft (anchor) a priori defined nanosized intermetallic phases and synergetic bifunctional electrocatalysts from decomposition of corresponding stoichiometric mixtures of various individual or intermetallic acetylacetonates. An adapted TG method based on TPR has been properly used to define, control and/or stimulate the homogeneity of the intermetallic crystal bonding and growth of nanostructured composite catalysts, mostly of rather extra strong bonding Brewer intermetallic phases upon proper SMSI oxide supports. Thus, it has been pointed out that the term SMSI has a broader HHDII sense in both the bonding effectiveness and bifunctional catalytic meaning, and in fact stays in the core of such extended Brewer interionic bonding theory. (C) 2003 The Electrochemical Society.