Theory, Substantiation, and Properties of Novel Reversible Electrocatalysts for Oxygen Electrode Reactions

• Published in: Journal of physical chemistry. C 2015-05, Vol.119 (21), p.11267-11285
• Main Authors: Jaksic, Jelena M, Nan, Feihong, Papakonstantinou, Georgios D, Botton, Gianluigi A, Jaksic, Milan M
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp510234f

Hypo-d–(f)-oxides of transition elements (d ≤ 5) usually feature decisive and highly pronounced effects of spontaneous adsorptive dissociation of water molecules, as the main and initial thermodynamic precondition state for the reversible latent storage and spillover properties of primary oxides (Pt–OH, Au–OH), otherwise indispensable ingredients in electrocatalysis for the oxygen electrode reactions. The higher the altervalent number (or capacity) of the former, and when mostly further advanced for the proper mixed valence hypo-d–(f)-oxide supports, the higher the overall (electro)­catalytic yields primarily for cathodic oxygen reduction (ORR) and its anodic evolution (OER). In fact, cyclic voltammetry revealed the interrelated redox properties of the primary (Pt–OH) and surface (PtO) oxides between the cathodic hydrogen and anodic oxygen evolving limits, though the former has already been for longer known as the intermediate state from hydrogen oxidation in heterogeneous Doeberriner reaction upon Pt catalyst, and as being water molecules self-catalyzed (Ertel). Such interfering interrelated and autocatalytic species substantially define electrocatalytic properties of plain (Pt) or noninteractive supported noble metals (Pt/C), along the potential axis, and within some range even make them highly polarizable. Meanwhile, the latter can be continuously and successfully electrocatalytically depolarized and maintained reactivated. Such spontaneously renewable activation and maintenance of the reversible electrocatalytic state for the oxygen electrode reactions all along such cyclic voltammograms is the main Sir William Grove target challenge of the present study. In such a respect, continuously and spontaneously renewable adsorptive water molecule dissociation effectively means and enables the latent storage and electrocatalytic spillover properties of the primary oxide(s) for the reversible oxygen electrode (ROE) behavior, and these have been identified and substantiated, back and forth, all along the potential axis between hydrogen and oxygen evolving limits. Such advanced electrocatalytic properties imply selective grafting of interactive (SMSI, strong metal–support interaction) nanostructured hyper-d-Pt (Au, RuPt) clusters upon individual and/or preferably composite mixed valence hypo-d–(f)-oxide supports. The latter then feature the extra high stability, pronounced electronic conductivity, and many other d-electronic-based metal properties mostly arising