Cation Segregation of A-Site Deficiency Perovskite La0.85FeO3-δ Nanoparticles toward High-Performance Cathode Catalysts for Rechargeable Li-O2 Battery

Insight of the State for Deliberately Introduced A-Site Defect in Nanofibrous LaFeO3 for Boosting Artificial Photosynthesis of CH3OH

Perovskite-type LaFeO3 is regarded as a potentially efficient visible-light photocatalyst owing to its narrow bandgap energy and unique photovoltaic properties. However, the insufficient active sites and the unsatisfactory utilization of photogenerated carriers severely restrict the realistic application of pure LaFeO3. Herein, we fabricated a series of LaxFeO3-δ nanofibers (x = 1.0, 0.95, 0.9, 0.85, 0.8) with an A-site defect via sol-gel combined with the electrospinning technique. Wherein, the nonstoichiometric La0.9FeO3-δ possessed the highest CH3OH yield of 5.30 μmol·g-1·h-1 with good chemical stability. A series of advanced characterizations were applied to investigate the physicochemical properties and charge-carrier behaviors of the samples. The results illustrated that the one-dimensional (1D) nanostructures combined with the appropriate concentration of vacancy defects on the surface contributed to the radial migration of photogenerated carriers, inhibited the recombination of carriers, and provided more CO2 adsorption-activation sites. Furthermore, density functional theory (DFT) calculations were employed to reveal the influence mechanism of vacancy defects on LaFeO3. This work provides a strategy to enhance the performance of photocatalytic CO2 reduction by modulating the induced oxygen vacancies caused by the A-site defect in perovskite oxides.

Exsolution Modeling and Control to Improve the Catalytic Activity of Nanostructured Electrodes

In situ exsolution for nanoscale electrode design has attracted considerable attention because of its promising activity and high stability. However, fundamental research on the mechanisms underlying particle growth remains insufficient. Herein, cation-diffusion-determined exsolution is presented using an analytical model based on classical nucleation and diffusion. In the designed perovskite system, the exsolution trend for particle growth is consistent with this diffusion model, which strongly depends on the initial cation concentration and reduction conditions. Based on the experimental and theoretical results, a highly Ni-doped anode and an electrochemical switching technique are employed to promote exsolution and overcome growth limitations. The optimal cell exhibits an outstanding maximum power density of 1.7 W cm^-2 at 900 °C and shows no evident degradation when operating at 800 °C for 240 h under wet H₂ . This study provides crucial insights into the developing and tuning of heterogeneous catalysts for energy-conversion applications.

Stepping Up the Kinetics of Li-O2 Batteries by Shrinking Down the Li2O2 Granules through Concertedly Enhanced Catalytic Activity and Photoactivity of Se-Doped LaCoO3

Owing to their structural tunability for furnishing high catalytic activity and photoactivity, perovskite oxides are a class of promising materials for high-performance photocathode catalysts in a photoassisted lithium oxygen battery (LOB), which is still in its infancy. Herein, single-crystalline LaCoO3 (LCO) is successfully synthesized through a microwave-assisted approach and selenylated to simultaneously introduce anionic doping and oxygen vacancies, boosting not only the electrocatalytic activity toward reversible Li2O2 formation/decomposition, but also the photoactivity to further reduce the charge/discharge polarization. As a result, LOBs utilizing Se-doped LCO as the photocathode catalyst demonstrate a superior performance under illumination in all aspects of energy efficiency, specific capacity, and cycling stability, ranking among the best reported in the literature for perovskite oxides. The photoenhanced charge kinetics is found to be correlated with the accelerated Li2O2 nucleation with lowered granule size, which is key to both the improved charge/discharge capacity and reversibility. The results underscore the tailoring of perovskite structure to aggrandize both the catalytic activity and photoactivity for concertedly promoting the kinetics of LOBs.

Defect engineering of oxide perovskites for catalysis and energy storage: synthesis of chemistry and materials science

Oxide perovskites have emerged as an important class of materials with important applications in many technological areas, particularly thermocatalysis, electrocatalysis, photocatalysis, and energy storage. However, their implementation faces numerous challenges that are familiar to the chemist and materials scientist. The present work surveys the state-of-the-art by integrating these two viewpoints, focusing on the critical role that defect engineering plays in the design, fabrication, modification, and application of these materials. An extensive review of experimental and simulation studies of the synthesis and performance of oxide perovskites and devices containing these materials is coupled with exposition of the fundamental and applied aspects of defect equilibria. The aim of this approach is to elucidate how these issues can be integrated in order to shed light on the interpretation of the data and what trajectories are suggested by them. This critical examination has revealed a number of areas in which the review can provide a greater understanding. These include considerations of (1) the nature and formation of solid solutions, (2) site filling and stoichiometry, (3) the rationale for the design of defective oxide perovskites, and (4) the complex mechanisms of charge compensation and charge transfer. The review concludes with some proposed strategies to address the challenges in the future development of oxide perovskites and their applications.

A Facile Surface Preservation Strategy for the Lithium Anode for High-Performance Li-O2 Batteries

Protecting an anode from deterioration during charging/discharging has been seen as one of the key strategies in achieving high-performance lithium (Li)-O₂ batteries and other Li-metal batteries with a high energy density. Here, we describe a facile approach to prevent the Li anode from dendritic growth and chemical corrosion by constructing a SiO₂/GO hybrid thin layer on the surface. The uniform pore-preserving layer can conduct Li ions in the stripping/plating process, leading to an effective alleviation of the dendritic growth of Li by guiding the ion flux through the microstructure. Such a preservation technique significantly enhances the cell performance by enabling the Li-O₂ cell to cycle up to 348 times at 1 A·g^-1 with a capacity of 1000 mA·h·g^-1, which is several times the cycles of cells with pristine Li (58 cycles), Li-GO (166 cycles), and Li-SiO₂ (187 cycles). Moreover, the rate performance is improved, and the ultimate capacity of the cell is dramatically increased from 5400 to 25,200 mA·h·g^-1. This facile technology is robust and conforms to the Li surface, which demonstrates its potential applications in developing future high-performance and long lifespan Li batteries in a cost-effective fashion.

Recent Progress on Catalysts for the Positive Electrode of Aprotic Lithium-Oxygen Batteries †

Rechargeable aprotic lithium-oxygen (Li-O2) batteries have attracted significant interest in recent years owing to their ultrahigh theoretical capacity, low cost, and environmental friendliness. However, the further development of Li-O2 batteries is hindered by some ineluctable issues, such as severe parasitic reactions, low energy efficiency, poor rate capability, short cycling life and potential safety hazards, which mainly stem from the high charging overpotential in the positive electrode side. Thus, it is of great significance to develop high-performance catalysts for the positive electrode in order to address these issues and to boost the commercialization of Li-O2 batteries. In this review, three main categories of catalyst for the positive electrode of Li-O2 batteries, including carbon materials, noble metals and their oxides, and transition metals and their oxides, are systematically summarized and discussed. We not only focus on the electrochemical performance of batteries, but also pay more attention to understanding the catalytic mechanism of these catalysts for the positive electrode. In closing, opportunities for the design of better catalysts for the positive electrode of high-performance Li-O2 batteries are discussed.