[en] The layered oxide Na0.67CoO2 with Na+ occupying trigonal prismatic sites between CoO2 layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O-O separation that favors formation of peroxide ions by O--O- interactions followed by O2 evolution in preference to the conventional route through surface O-OH- species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H+ ions from the surface oxygen to provide surface O- that may either be attacked by solution OH- or react with another O-; a short O-O separation favors the latter route. The role of a strong hybridization of the O-2p and low-spin CoIII/CoIV π-bonding d states is also important; the OER on other CoIII/CoIV oxides is compared with that on Na0.67CoO2 as well as that on IrO2.

[en] Realizing reversible reduction-oxidation (redox) reactions of lattice oxygen in batteries is a promising way to improve the energy and power density. However, conventional oxygen absorption spectroscopy fails to distinguish the critical oxygen chemistry in oxide-based battery electrodes. Therefore, high-efficiency full-range mapping of resonant inelastic X-ray scattering (mRIXS) has been developed as a reliable probe of oxygen redox reactions. Here, based on mRIXS results collected from a series of Li_1.17Ni_0.21Co_0.08Mn_0.54O₂ electrodes at different electrochemical states and its comparison with peroxides, we provide a comprehensive analysis of five components observed in the mRIXS results. While all the five components evolve upon electrochemical cycling, only two of them correspond to the critical states associated with oxygen redox reactions. One is a specific feature at 531.0 eV excitation and 523.7 eV emission energy, the other is a low-energy loss feature. We show that both features evolve with electrochemical cycling of Li_1.17Ni_0.21Co0.08Mn_0.54O₂ electrodes, and could be used for characterizing oxidized oxygen states in the lattice of battery electrodes. This work provides an important benchmark for a complete assignment of all mRIXS features collected from battery materials, which sets a general foundation for future studies in characterization, analysis, and theoretical calculation for probing and understanding oxygen redox reactions.

[en] In this study, we investigated the influence of the pump beam on the electronic and nuclear spin polarization homogeneity in the nuclear magnetic resonance gyroscope (NMRG). An analysis method was proposed based on the three dimensional simulation of the spin polarization spatial distribution. The pump power loss due to the aperture on the structure was considered. The average spin polarization and inertia measurement sensitivity were measured experimentally to demonstrate the simulation results. The results indicate that the nuclear spin polarization retains good homogeneity at different beam diameters, while the homogeneity of the electronic spin polarization highly depends on the beam diameter. It also can be seen that the electronic spin polarization homogeneity is more sensitive to pump power than pump beam diameter, while the nuclear spin polarization homogeneity is more sensitive to pump beam diameter than pump power. Moreover, the optimized beam diameter is obtained to balance the polarization and its homogeneity. The study provides reference for the design of the pump beam diameter and beam shaping structure in NMRG. (paper)

[en] Highlights: • A member of antiperovskite manganese compound Mn₃PdN was successfully synthesized. • A first-order PM to AFM transition occurred at 285​K. • Mn₃PdN exhibits multifunctional properties. A member of antiperovskite manganese compound Mn₃PdN was successfully synthesized. The structural, magnetic, electrical, and thermal transport properties were investigated systematically. The results indicated that Mn₃PdN is a weak correlated system. A first-order paramagnetic (PM) to antiferromagnetic (AFM) transition occurred at 285​K (T_N) combining with an abrupt change in structure. Mn₃PdN exhibits multifunctional properties such as near-zero temperature coefficient of resistivity (TCR) and negative thermal expansion (NTE).

[en] Highlights: • Co₃Fe₇ alloy embedded into nitrogen-doped hollow carbon sphere (CoFe/NHCS) was synthesized for Li-S batteries. • CoFe/NHCS demonstrates an improved adsorptive and electrolytic effect towards polysulfides. • CoFe/NHCS enables Li-S batteries with an excellent rate performance and superior cycling stability. • With a high sulfur loading of 6.7 mg/cm², a high areal capacity of 4.45 mAh/cm² is retained after 100 cycles. • CoFe/NHCS possesses an excellent stability in both physical structures and chemical properties over extended cycles. Lithium-sulfur (Li-S) batteries have attracted extensive attention as a promising next-generation electrochemical energy storage technology, owing to their high energy density and low material cost. However, issues such as severe polarization and poor cycle stability caused by shuttle effect and slow sulfur redox kinetics limit their practical applications. Here, Co₃Fe₇ alloy embedded into nitrogen-doped hollow carbon sphere composite (CoFe/NHCS) was synthesized as an electrocatalyst for Li-S batteries. The Co₃Fe₇ alloy demonstrates a strong chemisorption and superior electrocatalytic conversion towards polysulfides, while the nitrogen-doped carbon hollow spheres promote Li⁺/electron transfer and physically suppress polysulfides shuttling. Their synergistic effect therefore could both accelerate the polysulfides redox conversion and inhibit the polysulfides loss. As a consequence, the Li-S batteries assembled with CoFe/NHCS-modified separators exhibit a superior rate capacity (1029 mAh/g at 2 C) and excellent cycling stability (644 mAh/g at 1 C after 500 cycles). Furthermore, even at a high sulfur loading of 6.7 mg/cm², a high areal capacity of 5.58 mAh/g is achieved, which is retained at 4.45 mAh/cm² after 100 cycles. In addition, the CoFe/NHCS possesses an excellent stability in both physical structures and chemical properties over extended cycles, demonstrating its great potential for high-performance and long-cycle-life Li-S batteries.

[en] Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in $LiN{i}_{1/3}C{o}_{1/3}M{n}_{1/3}{O}_2$. The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries. (© 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

[en] The thermally stable inorganic cesium-based perovskites promise efficient and stable photovoltaics. Unfortunately, the strong ionic bonds lead to uncontrollable rapid crystallization, making it difficult in fabricating large-area black-phase film for photovoltaics. Herein, we developed a facile hydrogen-bonding assisted strategy for modulating the crystallization of CsPbI${}_2$Br to achieve uniform large-area phase-pure films with much-reduced defects. The simple addition of methylamine acetate in precursors not only promotes the formation of intermediate phase via hydrogen bonding to circumvent the direct crystallization of CsPbI${}_2$Br from ionic precursors but also widens the film processing window, thus enabling to fabricate large-area high-quality phase-pure CsPbI${}_2$Br film under benign conditions. Combining with stable dopant-free poly(3-hexylthiophene), the CsPbI${}_2$Br solar cells achieve the record-high efficiencies of 18.14 % and 16.46 % for 0.1 cm${}^2$ and 1 cm${}^2$ active area, respectively. The obtained high efficiency of 38.24 % under 1000 lux illumination suggests its potential in indoor photovoltaics for powering the Internet of Things, etc. (© 2024 Wiley‐VCH GmbH)