Enhanced electrochemical performance of anion-intercalated lanthanum molybdenum oxide pseudocapacitor electrode

The versatile family of molybdenum oxides: synthesis, properties, and recent applications

The family of molybdenum oxides has numerous advantages that make them strong candidates for high-value research and various commercial applications. The variation of their multiple oxidation states allows their existence in a wide range of compositions and morphologies that converts them into highly versatile and tunable materials for incorporation into energy, electronics, optical, and biological systems. In this review, a survey is presented of the most general properties of molybdenum oxides including the crystalline structures and the physical properties, with emphasis on present issues and challenging scientific and technological aspects. A section is devoted to the thermodynamical properties and the most common preparation techniques. Then, recent applications are described, including photodetectors, thermoelectric devices, solar cells, photo-thermal therapies, gas sensors, and energy storage.

Rare Earth-Based Nanomaterials for Supercapacitors: Preparation, Structure Engineering and Application

Supercapacitors (SCs) can effectively alleviate problems such as energy shortage and serious greenhouse effect. The properties of electrode materials directly affect the performance of SCs. Rare earth (RE) is known as "modern industrial vitamins", and their functional materials have been listed as key strategic materials. In the past few years, the number of scientific reports on RE-based nanomaterials for SCs has increased rapidly, confirming that adding RE elements or compounds to the host electrode materials with various nanostructured morphologies can greatly enhance their electrochemical performance. Although RE-based nanomaterials have made rapid progress in SCs, there are very few works providing a comprehensive survey of this field. In view of this, a comprehensive overview of RE-based nanomaterials for SCs is provided here, including the preparation methods, nanostructure engineering, compounds, and composites, along with their capacitance performances. The structure-activity relationships are discussed and highlighted. Meanwhile, the future challenges and perspectives are also pointed out. This Review can not only provide guidance for the further development of SCs but also arouse great interest in RE-based nanomaterials in other research fields such as electrocatalysis, photovoltaic cells, and lithium batteries.

Hetero-Element-Doped Molybdenum Oxide Materials for Energy Storage Systems

In order to meet the growing demand for the electronics market, many new materials have been studied to replace traditional electrode materials for energy storage systems. Molybdenum oxide materials are electrode materials with higher theoretical capacity than graphene, which was originally used as anode electrodes for lithium-ion batteries. In subsequent studies, they have a wider application in the field of energy storage, such as being used as cathodes or anodes for other ion batteries (sodium-ion batteries, potassium-ion batteries, etc.), and electrode materials for supercapacitors. However, molybdenum oxide materials have serious volume expansion concerns and irreversible capacity dropping during the cycles. To solve these problems, doping with different elements has become a suitable option, being an effective method that can change the crystal structure of the materials and improve the performances. Therefore, there are many research studies on metal element doping or non-metal doping molybdenum oxides. This paper summarizes the recent research on the application of hetero-element-doped molybdenum oxides in the field of energy storage, and it also provides some brief analysis and insights.

The Application of a Y-Modified Lanthanum Zirconate Flexible Thin Film for a High-Performance Flexible Supercapacitor

With the rapid development of wearable electronics devices, there is increasing demand for the development of new flexible energy storage devices with high security, and this has become a hot research topic. Although flexible supercapacitors are considered to be high-performance energy-storage equipment because of their fast charging/discharging ability, long cycle life, good reliability, wide operating temperature range, and so on, there are still many drawbacks that need to be overcome. Herein, the La₂ Zr₂ O₇ (LZO) thin film is synthesized as a new energy-storage material by using a facile electrospinning method and calcination at low temperature. In addition, the mechanism of producing the flexibility of this film is determined by TG, IR, and XRD analyses. As previous studies have suggested that the charge storage of the LZO film can be attributed to the mechanism of oxygen intercalation, the Y element is doped into the LZO film to increase the concentration of oxygen vacancies. The changes in structural and electrochemical properties of La₂ Y_x Zr_2-x O₃ (0≤x≤0.5) nanofibers (LNF-x) with increasing Y content are studied carefully to obtain the best doping sample. The LNF-0.1 sample shows the highest areal capacitance of 605.3 mF cm^-2 at 2 mA cm^-2 , so a symmetrical flexible device is fabricated with LNF-0.1 electrodes. This device has a high energy density (76.7 μW h cm^-2 at 2 mW cm^-2 ), good cycling stability, and excellent mechanical flexibility. This study thus provides a new research trend for portable and wearable electronics.

Zero-Dimensional Ordered Sr2CoMoO6-δ Double Perovskite as High-Rate Anion Intercalation Pseudocapacitance

In quest of a stable structure throughout redox reactions, an approach of B-site ordering (0D arrangement) of cations in double perovskites is adopted. Here, we report B-site cation ordering in double perovskite Sr₂CoMoO_6-δ (DP-SCM) that tends to a favorable rock salt structure (0D arrangement). The synergy of Co/Mo having good redox ability further facilitates high oxygen mobility. A high content of oxygen vacancy examined using XPS and EPR facilitates a high oxygen anion diffusion rate (2.03 × 10^-11 cm² s^-1). Moreover, fast kinetics (ΔE_P ≈ 0.013 V@ 1 mV s^-1) of charge storage prohibits any phase transformation reflecting the excellent cycle life (125% retention up to 5000 cycles). Such fast kinetics is majorly furnished from anion intercalation with little involvement from double layer mechanism (C_dl ≈ 42.1 F g^-1). DP-SCM achieves a resultant capacitance of 747 F g^-1@ 1 A g^-1 with a rate capability of 56% up to 10 A g^-1. Motivated by outstanding performance of DP-SCM electrodes, a symmetric cell is assembled with a 1.4 V operating potential that delivers a high energy density of 64 Wh kg^-1@855 W kg^-1. This work on double perovskites suggests that the advance understanding of cation ordering and charge storage mechanism can provide a new direction to fabricate highly capacitive electrode materials.