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Sluggish transport kinetics and unstable host structure are major obstacles that impede the development of advanced cathode materials for high-performance aqueous Zn-ion batteries (AZIBs). In this work, we report the rational design of holey carbon-encapsulated vanadium dioxide nanobelts (denoted as holey C@VO2) via a unique dual-engineering strategy combining the morphology and interface. As the cathode material for AZIBs, it can deliver a specific capacity of 386.9 mA h g−1 at 0.2 A g−1, as well as an excellent high-rate performance of 332 mA h g−1 at 5 A g−1 with capacity retention of 84.3% after 600 cycles. The reaction mechanism of the holey C@VO2 electrode was systematically studied by combining in situ and ex situ technologies, which reveals the synergistic intercalation/de-intercalation behavior of H+/Zn2+, accompanied by the reversible formation/decomposition of a sheet-like by-product. Moreover, the study of in situ electrochemical impedance spectra also confirms the stable electronic transport process that occurs in the holey C@VO2 electrode upon cycling. Therefore, the superior electrochemical performance of such an electrode should be mainly benefited from the efficient transport kinetics and abundant reaction sites. Such a unique strategy proposed in this work, as well as the systematic studies of the reaction mechanism is expected to not only provide scientific guidance for designing other advanced cathodes, but also pave the way to a deep understanding of the fundamentals of AZIBs. [ABSTRACT FROM AUTHOR]

The yolk–shell structure, realized by various synthesis methods, exhibits unique morphology and structural properties, which is currently undergoing a transition from material production technology to energy storage applications. To design an anode for lithium ion batteries (LIBs), a buffer space is designedly built between the Sb2Se3 nanorod yolk and the mesoporous carbon shell to obtain a novel yolk–shell structure (i.e., Sb2Se3@void@C). The confined void space is created by using a sacrificial template (such as silica) and the mesoporous carbon shell is obtained from the pyrolysis of phenolic resin, which effectively improves the electrical conductivity and structural stability of Sb2Se3 anode materials for LIB. Both the void space in the yolk–shell structure and the mesoporous carbon shell can efficiently buffer the volume expansion during the repeated discharge–charge processes, and further maintain the structural integrity. Besides, the permeable mesoporous carbon shell facilitates the electrolyte infiltration into the void space to ensure enough contact area between the Sb2Se3 and electrolyte, which benefits the shortening of the diffusion paths of Li+ ions. As a result, the Sb2Se3@void@C anode exhibits a high reversible specific capacity of 404.8 mA h g−1 at a rate of 1.0 A g−1 for at least 200 cycles, and maintains an average capacity of 594.7 at a rate of 3.0 A g−1. To further establish the detailed lithium storage behavior, in situ XRD is conducted to reveal the conversion reaction and alloying/dealloying reaction mechanisms. This research sheds light on yolk–shell structure designs with various morphologies to improve the electrochemical performance of energy storage materials. [ABSTRACT FROM AUTHOR]

Herein, a uniformly distributed SnS2/Co3S4 heterostructure nanosheet array was grown on carbon cloth (CC) fibers by a simple solvothermal method and an oil bath method. When the hierarchical SnS2/Co3S4@CC nanoarray composite is used as a binder-free anode for sodium-ion batteries, its charge and discharge capacity is stabilized at 910.1 mA h g−1 at a current density of 0.5 A g−1 after 100 cycles. Even under a high current density of 2 A g−1, after 760 long-term cycles, the reversible capacity is stable at 637.2 mA h g−1, and still has excellent cycle stability with capacity retention of 87.3%. This excellent performance can be attributed to the reasonable design of the arrayed-electrode structure and the in situ growth of Co3S4 nanoparticles on the heterointerface of matrix SnS2 nanosheets: the well-defined array structure can shorten the diffusion path of Na+ ions and effectively alleviates volume expansion under long-cycle performance; the hierarchical heterostructure of SnS2/Co3S4 nanosheets can expand the interface contact area, provide more active sites and effectively enhance the electrochemical kinetics for sodium storage. The excellent electrochemical performance brought by the rational design of the heterogeneous nanostructure arrays provides new possibilities for the practical application of energy storage in the future. [ABSTRACT FROM AUTHOR]

The sluggish kinetics and large volume expansion arising from the large ionic radius of Na+ remain elusive weaknesses of sodium ion batteries (SIBs). Here, we report a transition from bulk diffusion to surface-dominant pseudocapacitive charge storage by nanoscaling and heterostructuring, which enables fast and stable charge storage kinetics for SIBs. An electronic attraction induced self-assembly strategy was developed for the synthesis of the 1T/2H MoS2@SnO2 heterostructure. Ultrasmall SnO2 nanoparticles with a low crystallinity were uniformly distributed on the basal plane of MoS2. The intercalated SnO2 serves as an interfacial pillar to restrict the restacking of MoS2 nanosheets, whereas dual-phase 1T/2H MoS2 provides a continuous network for efficient charge transfer and restrains the aggregation of NaxSn. As a result, the 1T/2H MoS2@SnO2 heterostructure exhibits a higher specific capacity (626 mA h g−1 at 0.1 A g−1), and superior cycling and rate capabilities (262 mA h g−1 at 2 A g−1 for 500 cycles) compared to the raw MoS2 and 2H MoS2@SnO2 counterparts. Electrochemical kinetics analyses reveal that the charge transfer kinetics are boosted by the synergistic effect between the 1T/2H MoS2 and SnO2 nanoparticles. Quantitative examination into the origin demonstrated that the Na+ storage is dominated by the fast surface redox reaction, which endows the heterostructure with a durable high rate capability. [ABSTRACT FROM AUTHOR]

Solid-state polymer electrolytes are regarded as promising candidates to suppress the growth of lithium dendrite and settle the inflammable issues of organic-liquid electrolytes. However, solid-state polymer electrolytes still cannot meet the requirements of high mechanical strength, satisfactory ionic conductivity and extended electrochemical window at room temperature. To solve these issues, a novel ionic liquid composite polymer electrolyte (ILCPE) was synthesized via solvent tape-casting technique, consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based composite polymer electrolytes, filled with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Al2O3 particles and [BMIM]BF4. With good fire resistance and excellent mechanical performances, the ILCPE exhibits an improved electrochemical stability window of 5.6 V versus Li/Li+ potential, as well as a high ionic conductivity of 5.26 × 10−3 S cm−1 at 25 °C. The Li‖ILCPE‖Li symmetric battery can operate stably for more than 800 h. At 2C rate, Li‖ILCPE‖LiFePO4 cell delivered a high specific discharge capacity of 156.5 mA h g−1 and 130 mA h g−1 at 55 °C and 25 °C, respectively, and obtained high capacity retention of 95.5% after 300 charge–discharge cycles at 25 °C. [ABSTRACT FROM AUTHOR]

In this study, FeOx and CoOx thin films were successively and uniformly coated on high-surface-area carbon nanotubes by plasma-enhanced atomic layer deposition, which formed a heterojunction of the two oxides. As an electrocatalyst in the oxygen evolution reaction (OER), CoOx/FeOx/CNTs showed excellent electrocatalytic performance in terms of catalytic activity and stability. The overpotential of CoOx/FeOx/CNTs in OER was only 308 mV at 10 mA cm−2, which was lower than those of the pure oxides: CoOx/CNTs (392 mV) and FeOx/CNTs (406 mV). The as-prepared electrocatalyst also displayed better stability than the reference RuO2 material, with almost no attenuation of current density in contrast to the 10% loss seen with RuO2. The OER performance of CoOx/FeOx/CNTs was superior to those of its oxide components due to the formation of heterojunction, which led to a smoother reaction path and a lower overpotential for OER compared to pure oxides, as supported by the density-functional theory (DFT) calculations. These results provide a new direction for the preparation of electrocatalysts for metal–air batteries and water splitting reactions. [ABSTRACT FROM AUTHOR]

Photocatalytic systems capable of precisely regulating oxygen vacancy (OV) concentrations, which could help illuminate the effects of the OV concentration on N2 fixation activity, are still scarce. Here, we demonstrate that excessive OVs in TiO2, while increasing the adsorption activation capacity of N2 molecules, exhibit disappointing activity due to a decrease in charge separation efficiency. With optimized OV concentration, TiO2 can increase the charge separation efficiency 3-fold and show significant activation towards N2 molecules. The normalized N2 photofixation rate is 324.86 μmol h−1 g−1 (full spectrum) and the corresponding apparent quantum yield (AQY) under 365 nm illumination reaches 1.1%, which are relatively high levels compared to reports in the literature. The origin of this excellent activity is clearly attributable to the OV defect structures, which coordinate the charge separation efficiency and the dissociative adsorption capacity of N2. This work establishes the relationship between OV concentration and activity, and helps to construct a highly efficient nitrogen-fixing photocatalyst by optimizing the OV concentration. [ABSTRACT FROM AUTHOR]

CuOx–Co3O4 heterostructure arrays are grown on 3D porous nitrogen-doped carbon nanofiber (PNCNF) substrates by electrospinning and solvothermal methods. When the CuOx–Co3O4@PNCNF composite is employed as a free-standing anode for lithium-ion batteries, it exhibits discharge capacity of 1122 mA h g−1 at current density of 200 mA g−1 after 100 cycles; the reversible capacity is 668 mA h g−1 after long-term 1000 cycles even at a high current density of 2 A g−1. This outstanding performance can be attributed to the rational design of the electrode structure and the fascinating synergetic contributions from the CuOx–Co3O4 heterostructure in addition to the 3D substrate, which can shorten the Li+ diffusion path, expand interfacial contact, and provide increased electrochemically active sites for lithium storage. The reaction mechanisms are investigated by ex situ XPS and FESEM, confirming the phase transformation of CuOx–Co3O4 and verifying the structural stability during cycling. This work not only proposes a high-performance lithium-ion anode, but also provides ideas to design and reveal the reaction mechanisms of other metal-oxide heterostructures for use in various energy storage materials. [ABSTRACT FROM AUTHOR]

Over the past few decades, owing to their unique functional properties such as physical, chemical, optical and electronic properties, spinel materials have attracted significant scientific attention in heterogeneous photocatalyst research. Here, we review the main fundamental understanding of the correlations between the performance of spinel structures and their particle shape, size, chemical composition, and photo-Fenton reactions for photocatalytic applications; these include photocatalytic dye degradation for environmental remediation, photocatalytic hydrogen generation, CO2 reduction and photoelectrochemical water splitting. In addition, the key factors and essential strategies to improve their performance and functionality are discussed in detail. Future research pathways and perspectives on the progress of these high performance and cost effective renewable energy materials are provided, along with the improvements in material properties that are necessary to replace current commercial energy materials. It is envisioned that further investigations should focus on surface modification, integrating conductive matrixes and regulating the spinel composition, which will make spinels promising photocatalysts. [ABSTRACT FROM AUTHOR]

A novel free-standing and binder-free air electrode with excellent electrochemical performance was designed for highly reversible Li–O2 batteries. The 3D hierarchically N, S co-doped macro–mesoporous carbon (NSMmC) was deposited on carbon paper (CP) via a template method, and then uniformly decorated with PdNi nanoparticles. The macropores of the porous carbon can provide enough space to accommodate discharge products, while the interconnected pores and channels efficiently facilitate oxygen and electrolyte diffusion. The introduction of PdNi nanoparticles greatly reduce the charge transfer resistance, resulting in the improvement of electron mobility of the whole cathode. Compared with Pd–NSMmC/CP and NSMmC/CP cathodes, the PdNi–NSMmC/CP cathode shows considerable enhancement of Li–O2 battery performance. The ultrafine and evenly distributed PdNi nanoparticles can not only provide enough catalytic sites, but can also tailor the discharge products into a cage-like morphology, which provides enough channels for electron and lithium ion transport. Moreover, the smaller size of the cage-like Li2O2 makes it decompose more easily, resulting in lower charge overpotential. This study provides a promising strategy to design 3D structured air cathodes for Li–O2 batteries with high electrocatalytic performance. [ABSTRACT FROM AUTHOR]