The oxygen evolution reaction that occurs during water oxidation is of considerable importance as an essential energy conversion reaction for rechargeable metal–air batteries and direct solar water splitting. Cost-efficient ABO3 perovskites have been studied extensively because of their high activity for the oxygen evolution reaction; however, they lack stability, and an effective solution to this problem has not yet been demonstrated. Here we report that the Fe4+-based quadruple perovskite CaCu3Fe4O12 has high activity, which is comparable to or exceeding those of state-of-the-art catalysts such as Ba0.5Sr0.5Co0.8Fe0.2O3−δ and the gold standard RuO2. The covalent bonding network incorporating multiple Cu2+ and Fe4+ transition metal ions significantly enhances the structural stability of CaCu3Fe4O12, which is key to achieving highly active long-life catalysts.

polyhedra are associated, have been reported. [2f,g,5] Such vacancydriven catalysis has also been investigated in other OER/ORR catalysts, such as MnCo 2 O 4 spinel and La 1−x Sr x CoO 3−δ perovskite, [6] to propose an efficient way to improve catalytic activity.The quadruple perovskite CaCu 3 Fe 4 O 12 , in which three quarters of A-site (=A′-sites) are occupied by Cu ions, [7] allows for more active and stable catalysis for the OER than the simple perovskite CaFeO 3 (see crystal structures of simple ABO 3 and AA′ 3 B 4 O 12 perovskites in Figure 1a,b, drawn by using the VESTA-3 program [8] ). [9] The authors proposed that several features of CaCu 3 Fe 4 O 12 are probably associated with its activity and stability. These include a widespread covalent network, heavily bent FeOFe bonds to shorten distances between the neighboring adsorbates, the contribution of the A′-site Cu ions, and a possible OER mechanism on two active sites. However, in-depth studies are needed to unveil the structureactivity relationship in this system. In quadruple perovskites AMn 7 O 12 (A = Ca, La), both A′-and B-sites are solely occupied by Mn atoms. This allows investigations on pure structural features concerning catalysis (including comparison with their corresponding simple perovskite AMnO 3 ), leading to the discovery of novel structure-activity relationships. In this paper, we describe the OER/ORR catalytic activities for simple and quadruple manganese perovskites. The quadruple perovskites AMn 7 O 12 (A = Ca, La) display bifunctional catalysis for OER and ORR. On the other hand, the simple perovskites AMnO 3 (A = Ca, La) only display catalysis for the ORR. The enhancement of OER activity for AMn 7 O 12 is probably driven by the structural features of the quadruple perovskite. This finding suggests that AMn 7 O 12 perovskites are promising candidates as bifunctional catalysts.Manganese perovskite catalysts, AMnO 3 and AMn 7 O 12 (A = Ca, La), were synthesized from solid-state reactions using precursors prepared by polymerized method [10] (Supporting Information). CaMnO 3 , LaMnO 3 , and CaMn 7 O 12 were synthesized under ambient pressure, whereas LaMn 7 O 12 could be obtained by high-pressure synthesis method. All synthesized samples were almost single-phase ( Figure S1, Supporting Information). Their crystal structures, determined by the Rietveld refinement using the [11] were identical with those reported previously (Table S1, Supporting Information). [12] Based on the Rietveld refinement results, we confirmed that all the manganese perovskite samples did not contain any substantial amount of oxygen vacancies. Thus, their valence states are Ca 2+ Mn 4+ O 3 , La 3+ Mn 3+ O 3 , Ca 2+ Mn 3+ 3 (Mn 3+ 3 Mn 4+ 1 )O 12 , and La 3+ Mn 3+ 3 Mn 3+ 4 O 12 , [12b] where the Mn ions at A′-sites (squareplanar coordination) are trivalent due to the strong Jahn-Teller property of Mn 3+ (d 4 ) ions. The scanning electron microscopy

In general, the ionic conductivity of sulfide glasses decreases with their crystallization, although it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li7P3S11: 70Li2S-30P2S5). We found that the ionic conductivity of 75Li2S-25P2S5 sulfide glass, which consists of glassy and crystalline phases, is improved by optimizing the conditions of the heat treatment, i.e., annealing. A different mechanism of high ionic conductivity from the conventional mechanism is expected in the glassy phase. Here, we report the glassy structure of 75Li2S-25P2S5 immediately before the crystallization by using the differential pair distribution function (d-PDF) analysis of high-energy X-ray diffraction. Even though the ionic conductivity increases during the optimum annealing, the d-PDF analysis indicated that the glassy structure undergoes no structural change in the sulfide glass-ceramic electrolyte at a crystallinity of 33.1%. We observed the formation of a nanocrystalline phase in the X-ray and electron diffraction patterns before the crystallization, which means that Bragg peaks were deformed. Thus, the ionic conductivity in the mixture of glassy and crystalline phases is improved by the coexistence of the nanocrystalline phase.

Transition metal oxides have been extensively investigated as novel catalysts for oxygen evolution reaction (OER). Partial elemental substitutions are effective ways to increase catalytic performance and such electronic interactions between multiple elements are known as synergistic effects. However, serious issues such as random atomic arrangement and ambiguous roles of constituent elements humper theoretical investigations for rational materials design. Herein, we describe systematic study on OER activity of AA′ 3 B 4 O 12 -type quadruple perovskite oxides, in which multiple transition metal ions are located at distinct crystallographic sites. Electrochemical measurements demonstrate that OER catalytic activities of quadruple perovskite oxide series, CaCu 3 B 4 O 12 (B = Ti, V, Cr, Mn, Fe, and Co), are all superior to those of simple perovskite counterparts CaBO 3 . The order of activity of B-site transition metal ions for CaBO 3 (Fe 4+ > Co 4+ ≫ Ti 4+ , V 4+ , Cr 4+ , Mn 4+ ) is retained in CaCu 3 B 4 O 12 , indicating that B-site ions play a primary role whereas A′-site Cu ions secondarily contribute to OER activity for CaCu 3 B 4 O 12 . Charge-transfer energies, energy differences between oxygen 2p band center and unoccupied 3d band center of B-site transition metal obtained from first-principles electronic-state calculations, illustrate that OER overpotentials of quadruple perovskite oxides are lower than simple perovskite oxides by ∼150 mV. These findings propose a simple avenue to realize enhanced OER activity for multiple transition-metal ions.

There are two types of solid electrolytes which has been recently expected to be applied to all-solid-state batteries. One is the glasses characterized by an amorphous state. The other is the glass ceramics containing crystalline in an amorphous matrix. However, the non-crystalline state of glasses and glass ceramics is still an open question. It has been anticipated that sea-island and core-shell structures including crystalline nanoparticles have been proposed as candidate models for glass ceramics. Nevertheless, no direct observation has been conducted so far. Here we report the non-crystalline state of Li2S–P2S5 glasses and glass ceramics, and the crystallization behavior of the glasses during heating via direct transmission electron microscopy (TEM) observation. High resolution TEM images clearly revealed the presence of crystalline nanoparticles in an amorphous region. Eventually we suggest that the precipitation and connection of crystalline nanoparticles in an amorphous matrix are key to achieving high ionic conductivity.