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Na 0.44 MnO 2 nanowires were acid leached in nitric acid, and dehydrated by heat treatment to induce controllable defect formation as monitored by high resolution TEM studies. The charge-discharge tests using these materials as catalysts (or ''promoters'') in rechargeable lithium-oxygen batteries (in noncarbonate electrolytes) showed that a high defect concentration results in a doubling of the reversible energy storage capacity up to 11 000 mA h g À1 , and lowered overpotentials for oxygen evolution. The role of the defects/vacancies in determining oxygen reduction behavior is highlighted.

Surface in and ex situ analysis have shown that in the course of cathodic oxygen reduction (ORR), all along the reversible potential range (the low slope Tafel plots, about 30 mVs/dec), nanostructured Pt electrocatalyst is covered by the interfering primary (Pt−OH) and surface (PtO) oxide mixture, while the higher polarization (120 mVs/dec) characterizes electrocatalytic surface deprived from these oxides and, consequently, the reaction mechanism of direct electron exchange on clean electrode surface. The substantial difference between the standard RHE (reversible hydrogen electrode) and ROE (reversible oxygen electrode), is that the former implies spontaneous hydrogen adsorption, fast H-adatoms (Pt−H) effusion and reversible electrode behavior (Pt(H 2 )/Pt−H/H 3 O + ), while the latter features the strong irreversible PtO adsorptive strength, and which is more significant, missing the Pt−OH spillover within the critical potential range between the primary oxide adsorption/desorption peaks position and oxygen evolving limits in both potentiodynamic scan directions (or the imposed polarization energy barrier of about 600 mVs). Since the Pt−OH presence and spillover are unavoidable decisive and indispensable for establishing the ROE properties, and thermodynamic electrode equilibrium (Pt(O 2 )/Pt−OH/PtO/OH − ), within the pronounced high polarization broad potential range, such spillover species has the same meaning and significance for the ROE as Pt−H plays for the RHE. Thence, to fill such a high polarization gap, the guiding concept implies homogeneous nanostructured distribution and selective grafting while interactive hypo-hyper-d-d-interelectronic bonding of Pt nanoclusters upon various mixed valence hypo-d-oxide supports, primarily Nb 2 O 5 ,TiO 2 (or Ta 2 O 5 ,TiO 2 ), because of their much thermally advanced electronic conductivity and extra high stability. In such a constellation, nanoparticles of Pt and solid oxides establish the so-called SMSIs (strong metal−support interactions), the strongest ones in all of chemistry, together with advanced electron conductive transfer, while the exposed surface of the latter undergoes spontaneous dissociative adsorption of water molecules (Nb 2 O 5 → 2 Nb(OH) 5 ), and thereby becomes, along with continuous further water vapor supply, the undisturbed and almost unlimited, (alike electrons in metals) renewable latent storage and spillover source of the Pt−OH all along the potential axis between oxygen and hydrogen evolving limits, with inexhaustible abilities of further optimizations. The reversible alterpolar changes instantaneously result by the spillover of H-adatoms with corresponding bronze type (Pt/H x NbO 5 , x ≈ 0.3) electrocatalysts under cathodic, and/or its hydrated state (Pt/Nb(OH) 5 ), responsible for Pt−OH effusion, under anodic polarization. This way there establishes the reversibly revertible alterpolar bronze features (Pt/H x NbO 5 ↔ Pt/Nb(OH) 5 ), as the thermodynamic equilibrium, and thereby substantially advanced electrocatalytic properties of th...

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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 ...