Ultrathin Polypyrrole Layers Boosting MoO3 as Both Cathode and Anode Materials for a 2.0 V High-Voltage Aqueous Supercapacitor

Pulsed Laser Ablation of Oxygen deficiency Enriched Superlattice Vanadium Pentoxide (V2O5) Ultrathin Nextrode aiming for Flexible Binder-less Tandem Energy Harvesting Devices

For the initial instance, oxygen deficiency-enriched vanadium pentoxide (O─V2O5@500) thin film electrodes are tuned by the Pulsed Laser Ablation technique. The O─V2O5@500 thin film electrode shows remarkable electrochemical performances confirming the greater potential window of -0.4 to 0.9 V versus Hg/HgO in an alkaline electrolyte; also, the O─V2O5@ 500 thin film electrode exhibits a noteworthy volumetric capacity of 167.7 mAh cm-3 (areal capacity of 73.3 µAh cm-2). Additionally, Density Functional Theory (DFT) theory calculations are carried out for oxygen-deficient V2O5. From the partial density of states (pDOS) and partial charge density analysis, it is clear that oxygen vacancy improves the electrical conductivity due to the higher degree of electron delocalization of V─O─V near the vacancy and enhances the redox properties due to the formation of in-gap states. Further, it is reported that a O─V2O5@ 500 ||PVA-KOH|| Bi2O3 A-650 thin film supercapbattery (TFSCB) device attains an exceptional discharge volumetric capacitance of 182.85 F cm-3 (equal volumetric capacity of 124.5 mAh cm-3). Furthermore, the TFSCB device exhibits an extraordinary maximum volumetric energy (power) density of 14.28 mWh cm-3 (1.66 W cm-3); TFSCB succeeds in supreme capacity retention of 86% with outstanding coulombic efficiency of 94.4% after 21 000 cycles.

Heterostructured MoO3@CoWO4 nanobelts towards high electrochemical performances via oxygen vacancies generation

Heterostructured nanomaterials tend to have a high proportion of oxygen vacancies (VO) due to the presence of heterogeneous interfaces. Herein, a new kind of heterostructured MoO3@CoWO4 nanobelts was successfully evaluated as fascinating cathode material. SEM and TEM analysis indicated that the MoO3 nanobelts were fully blanketed with CoWO4 nanodots. The generation of Vo species was confirmed by XPS and EPR data. By profiting both synergistic and Vo generation effects, MoO3@CoWO4 electrode displayed an excellent capacitance of 246 mAh·g-1 (1966 F·g-1at 0.5 A·g-1) with high-rate capability of 174 mAh·g-1 (1394 F·g-1 at 30 A·g-1) as well as superb stability of 94 % (over 15,000 cycles). Notably, all-solid-state device delivered a good energy value of 63.1 Wh·kg-1 at 375 W·kg-1. Interestingly, the supercapacitor device showed super-low self-discharge comportment of only 12.1 % during 24 h. Importantly, the generation of the VO defects could control the ions diffusion process and lead a sharp decrease in the self-discharge process.

Controlling crystallites orientation and facet exposure for enhanced electrochemical properties of polycrystalline MoO3 films

This study focuses on the development and optimization of MoO3 films on commercially available FTO substrates using the pulsed laser deposition (PLD) technique. By carefully selecting deposition conditions and implementing post-treatment procedures, precise control over crystallite orientation relative to the substrate is achieved. Deposition at 450 °C in O2 atmosphere results in random crystallite arrangement, while introducing argon instead of oxygen to the PLD chamber during the initial stage of sputtering exposes the (102) and (011) facets. On the other hand, room temperature deposition leads to the formation of amorphous film, but after appropriate post-annealing treatment, the (00k) facets were exposed. The deposited films are studied using SEM and XRD techniques. Moreover, electrochemical properties of FTO/MoO3 electrodes immersed in 1 M AlCl3 aqueous solution are evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. The results demonstrate that different electrochemical processes are promoted based on the orientation of crystallites. When the (102) and (011) facets are exposed, the Al3+ ions intercalation induced by polarization is facilitated, while the (00k) planes exposure leads to the diminished hydrogen evolution reaction overpotential.

Boosting the capacity and stability of a MoO3 cathode via valence regulation and polypyrrole coating for a rechargeable Zn ion battery

Molybdenum trioxide (MoO₃) is emerging as a hugely competitive cathode material for aqueous zinc ion batteries (ZIBs) for its high theoretical capacity and electrochemical activity. Nevertheless, owing to its undesirable electronic transport capability and poor structural stability, the practical capacity and cycling performance of MoO₃ are yet unsatisfactory, which greatly blocks its commercial use. In this work, we report an effective approach to first synthesise nanosized MoO_3-x materials to provide more active specific surface areas, while improving the capacity and cycle life of MoO₃ by introducing low valence Mo and coated polypyrrole (PPy). MoO₃ nanoparticles with low-valence-state Mo and PPy coating (denoted as MoO_3-x@PPy) are synthesized via a solvothermal method and subsequent electrodeposition process. The as-prepared MoO_3-x@PPy cathode delivers a high reversible capacity of 212.4 mA h g^-1 at 1 A g^-1 with good cycling life (more than 75% capacity retention after 500 cycles). In contrast, the original commercial MoO₃ sample only obtains a capacity of 99.3 mA h g^-1 at 1 A g^-1, and a cycling stability of 10% capacity retention over 500 cycles. Additionally, the fabricated Zn//MoO_3-x@PPy battery obtains a maximum energy density of 233.6 W h kg^-1 and a power density of 11.2 kW kg^-1. Our results provide an efficient and practical approach to enhance commercial MoO₃ materials as high-performance cathodes for AZIBs.

Supercapacitive performance of C-axis preferentially oriented TiO2 nanotube arrays decorated with MoO3 nanoparticles

The highest specific capacitance of the MoO3-p-CTNTA electrode achieved is 194 F g−1 at a current density of f 1 A g−1.

Self-Assembly Vertical Graphene-Based MoO3 Nanosheets for High Performance Supercapacitors

Supercapacitors have been extensively studied due to their advantages of fast-charging and discharging, high-power density, long-cycling life, low cost, etc. Exploring novel nanomaterial schemes for high-performance electrode materials is of great significance. Herein, a strategy to combine vertical graphene (VG) with MoO₃ nanosheets to form a composite VG/MoO₃ nanostructure is proposed. VGs as transition layers supply rich active sites for the growth of MoO₃ nanosheets with increasing specific surface areas. The VG transition layer further improves the electric contact and adhesion of the MoO₃ electrode, simultaneously stabilizing its volume and crystal structure during repeated redox reactions. Thus, the prepared VG/MoO₃ nanosheets have been demonstrated to exhibit excellent electrochemical properties, such as high reversible capacitance, better cycling performance, and high-rate capability.

1D-on-1D core-shell cobalt iron selenide @ cobalt nickel carbonate hydroxide hybrid nanowire arrays as advanced battery-type supercapacitor electrode

Sluggish kinetics and poor structural stability are two main obstacles hampering the exploration of transition metal selenides (TMSs) for supercapacitor. Developing a reasonable core-shell heterostructure with unique morphology is an effective approach to resolve these issues. Herein, a core-shell cobalt iron selenide (CoFe₂Se₄) @ cobalt nickel carbonate hydroxide (CoNi-CH) heterostructure is directly fabricated on carbon cloth via an electrodeposition method followed by a hydrothermal reaction. In this well-defined heterostructure, one-dimensional (1D) CoFe₂Se₄ nanowires function as the cores and CoNi-CH nanowires as the shells, which combines the merits of highly conductive CoFe₂Se₄ for rapid electron transfer and highly electroactive CoNi-CH for multiple redox reactions. Further, the intimate interaction between CoNi-CH and CoFe₂Se₄ realizes large surface area with hierarchical network and generates rich heterointerfaces with modified the electronic structure. By virtue of its facile 1D-on-1D nanoarchitecture and synergistic effect, the CoFe₂Se₄@CoNi-CH electrode delivers a increased specific capacity of 218.6 mAh g^-1 at 1 A^-1 and enhanced rate capability (65.5% at 20 A g^-1) compared with pure CoFe₂Se₄ and CoNi-CH. Besides, a hybrid supercapacitor is established by coupling CoFe₂Se₄@CoNi-CH cathode and porous carbon anode, which enjoys a maximum energy density of 67.3 Wh kg^-1 at 765.9 W kg^-1 and prominent durability with 85.4% of capacity retention over 20,000 cycles.

Synchronous Defect and Interface Engineering of NiMoO4 Nanowire Arrays for High-Performance Supercapacitors

Developing high-performance electrode materials is in high demand for the development of supercapacitors. Herein, defect and interface engineering has been simultaneously realized in NiMoO4 nanowire arrays (NWAs) using a simple sucrose coating followed by an annealing process. The resultant hierarchical oxygen-deficient NiMoO4@C NWAs (denoted as "NiMoO4-x@C") are grown directly on conductive ferronickel foam substrates. This composite affords direct electrical contact with the substrates and directional electron transport, as well as short ionic diffusion pathways. Furthermore, the coating of the amorphous carbon shell and the introduction of oxygen vacancies effectively enhance the electrical conductivity of NiMoO4. In addition, the coated carbon layer improves the structural stability of the NiMoO4 in the whole charging and discharging process, significantly enhancing the cycling stability of the electrode. Consequently, the NiMoO4-x@C electrode delivers a high areal capacitance of 2.24 F cm-2 (1720 F g-1) at a current density of 1 mA cm-2 and superior cycling stability of 84.5% retention after 6000 cycles at 20 mA cm-2. Furthermore, an asymmetric super-capacitor device (ASC) has been constructed with NiMoO4-x@C as the positive electrode and activated carbon (AC) as the negative electrode. The as-assembled ASC device shows excellent electrochemical performance with a high energy density of 51.6 W h kg-1 at a power density of 203.95 W kg-1. Moreover, the NiMoO4//AC ASC device manifests remarkable cyclability with 84.5% of capacitance retention over 6000 cycles. The results demonstrate that the NiMoO4-x@C composite is a promising material for electrochemical energy storage. This work can give new insights on the design and development of novel functional electrode materials via defect and interface engineering through simple yet effective chemical routes.