Boosting the Electrocatalytic Activity of Co₃O₄ Nanosheets for a Li‑O₂ Battery through Modulating Inner Oxygen Vacancy and Exterior Co³⁺/Co²⁺ Ratio

Rechargeable Li-O₂ batteries have been considered as the most promising chemical power owing to their ultrahigh specific energy density. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) result in high overpotential (∼1.5 V), poor rate capability, and even a short cycle life, which critically hinder their practical applications. Herein, we propose a synergistic strategy to boost the electrocatalytic activity of Co₃O₄ nanosheets for Li-O₂ batteries by tuning the inner oxygen vacancies and the exterior Co³⁺/Co²⁺ ratios, which have been identified by Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption near edge structure spectroscopy. Operando X-ray diffraction and ex situ scanning electron microscopy are used to probe the evolution of the discharge product. In comparison with bulk Co₃O₄, the cells catalyzed by Co₃O₄ nanosheets show a much higher initial capacity (∼24051.2 mAh g^–1), better rate capability (8683.3 mAh g^–1@400 mA g^–1) and cycling stability (150 cycles@400 mA g^–1), and lower overpotential. The large enhancement in the electrochemical performances can be mainly attributed to the synergistic effect of the architectured 2D nanosheets, the oxygen vacancies, and Co³⁺/Co²⁺ difference between the surface and the interior. Moreover, the addition of LiI to the electrolyte can further reduce the overpotential, making the battery more practical. This study offers some insights into designing high-performance electrocatalysts for Li-O₂ batteries through a combination of the 2D nanosheet architecture, oxygen vacancies, and surface electronic structure regulation

Morphological Evolution of High-Voltage Spinel LiNi_0.5Mn_1.5O₄ Cathode Materials for Lithium-Ion Batteries: The Critical Effects of Surface Orientations and Particle Size

An evolution panorama of morphology and surface orientation of high-voltage spinel LiNi_0.5Mn_1.5O₄ cathode materials synthesized by the combination of the microwave-assisted hydrothermal technique and a postcalcination process is presented. Nanoparticles, octahedral and truncated octahedral particles with different preferential growth of surface orientations are obtained. The structures of different materials are studied by X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption near edge spectroscopy (XANES), and transmission electron microscopy (TEM). The influence of various morphologies (including surface orientations and particle size) on kinetic parameters, such as electronic conductivity and Li⁺ diffusion coefficients, are investigated as well. Moreover, electrochemical measurements indicate that the morphological differences result in divergent rate capabilities and cycling performances. They reveal that appropriate surface-tailoring can satisfy simultaneously the compatibility of power capability and long cycle life. The morphology design for optimizing Li⁺ transport and interfacial stability is very important for high-voltage spinel material. Overall, the crystal chemistry, kinetics and electrochemical performance of the present study on various morphologies of LiNi_0.5Mn_1.5O₄ spinel materials have implications for understanding the complex impacts of electrode interface and electrolyte and rational design of rechargeable electrode materials for lithium-ion batteries. The outstanding performance of our truncated octahedral LiNi_0.5Mn_1.5O₄ materials makes them promising as cathode materials to develop long-life, high energy and high power lithium-ion batteries

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La_6–<i>x</i>WO_{12–<i>y</i>}

Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La_6–<i>x</i>WO_{12–<i>y</i>} (with <i>y</i> = 1.5<i>x</i> + δ and <i>x</i> = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La_6–<i>x</i>WO_{12–<i>y</i>} and for all substituted La_6–<i>x</i>WO_{12–<i>y</i>} compounds was measured in the temperature range of 400–900 °C in wet (2.5% H₂O) and dry mixtures of 4% H₂ in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H₂ at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM