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

Abstract

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 and being established upon the hypo−hyper-d−d−(f)-interelectronic bonding effect, along with and based upon spontaneous dissociative water molecule adsorption upon exposed oxide support surfaces, thereby yielding renewable primary oxide latent storage by simple continuous water vapor supply and imposed characteristic membrane type hydroxide ion surface migration. Migrating hydroxide, as individual species, under imposed polarization transfers its prevailing part of electron to the metallic electrocatalyst, hence resulting as the Pt−OH (Au−OH) dipole, and by the ...

Poetics of Interplay and Interferences of Potentiodynamic Sweeps and Peaks in Electrocatalysis for Oxygen Electrode Reactions

“…[6,7] Since the equimolar ratio of the primary and surface oxide concentrations defines the optimal interfering selfcatalytic spillover reaction step in cathodic oxygen reduction (ORR), [9] or as the overall electrode reaction,…”

“…TiO2, WO3/C), scanned in He stream, ones at negligible moisture content (curve 1) and at 80 °C water vapor saturation (curve 2) (Reprinted with permission from Ref. [7]. Copyright (2014) American Chemical Society).…”

“…Visual presentation of novel spillover latent storage Pt-OH type interactive supported electrocatalyst for oxygen electrode reactions, exampled for Pt/Nb2O5, TiO2/Nb(OH)5,Ti(OH)4 issue (Reprinted with permission from Ref. [7]. Copyright (2014) American Chemical Society).…”

“…In other words, such state of the art enables to perform and even speedup (electro)catalytic processes from very high temperature down at ambient conditions, simply by the impact of adsorptive wetness effect. [6][7][8]12,13,24] The Impact Self-Catalytic Molecular Water or Overall Wetness Effect…”

“…For the catalytic science it was a priori clear that some superior reaction occurs initiated at and provided by the exposed titania surface. [4−8] In other words, the latter is in advance predestined ready and highly susceptible for spontaneous dissociative adsorption of water molecules (TiO2 + 8H2O ⇒ Ti(OH)4 + 4H3O + ), otherwise already being revealed as the subject of latent storage and the Au−OH spillover, [5][6][7][8]12,13] decisive for both heterogeneous catalytic oxidation and reduction reactions, 4 3…”