Chunshuang Yan

Layered nickel metal–organic framework for high performance alkaline battery-supercapacitor hybrid devices

Alkaline battery-supercapacitor hybrid devices (ABSHDs) are attracting considerable attention because they combine the advantages of both alkaline batteries and supercapacitors. Herein, a nickel metal–organic framework (Ni-MOF) was demonstrated to have a high specific capacity and could further improve energy storage through a novel strategy: “synergistic effect between Ni-MOF and Fe(CN)64−/Fe(CN)63−”. The unique 2D-layered crystal structure of the Ni-MOF could provide enough space for Fe(CN)64−/Fe(CN)63− storage and diffusion and Fe(CN)64−/Fe(CN)63− could act as an electron relay during charge–discharge processes by coupling Ni(II)/Ni(III) in the Ni-MOF electrode. Moreover, we assembled an Ni-MOF//CNTs-COOH ABSHD in 3 M KOH and 0.1 M K4Fe(CN)6 mixed electrolyte with an extended voltage window of 1.4 V, which resulted in a high energy density (55.8 W h kg−1) and power density (7000 W kg−1) simultaneously. Hence, the results in this study could broaden the applications of MOFs in energy storage devices and provide insightful guidelines for developing other redox additives.

Mixed-metallic MOF based electrode materials for high performance hybrid supercapacitors

Metal–organic frameworks (MOFs) have obtained increasing attention as a kind of novel electrode material for energy storage devices. Yet low capacity in most MOFs largely thwarts their application. In this study, an effective strategy was developed to improve the conductivity of MOFs by partially substituting Ni2+ in the Ni-MOF with Co2+ or Zn2+. The mixed-metal organic frameworks (M-MOFs) showed excellent electrochemical performance, which is attributed not only to the favorable paths for charge transport due to the presence of free pores, but also to the raised electrochemical double-layer capacitance (EDLC) at the enlarged specific surface area of the material. Meanwhile, the cycling stability of the assembled hybrid supercapacitors (M-MOFs//CNTs–COOH) is enhanced due to the alleviation of phase transformation during electrochemical cycling tests. More interestingly, the Co/Ni-MOF//CNTs–COOH also exhibited an excellent energy density (49.5 W h kg−1) and power density (1450 W kg−1) simultaneously. These values demonstrated the better performance of all the MOF materials in supercapacitors at present. In addition to broadening the application of MOFs, our study may open a new avenue for bridging the performance gap between batteries and supercapacitors.

Two-Dimensional Holey Co3O4 Nanosheets for High-Rate Alkali-Ion Batteries: From Rational Synthesis to in Situ Probing

A general template-directed strategy is developed for the controlled synthesis of two-dimensional (2D) assembly of Co3O4 nanoparticles (ACN) with unique holey architecture and tunable hole sizes that enable greatly improved alkali-ion storage properties (demonstrated for both Li and Na ion storage). The as-synthesized holey ACN with 10 nm holes exhibit excellent reversible capacities of 1324 mAh/g at 0.4 A/g and 566 mAh/g at 0.1 A/g for Li and Na ion storage, respectively. The improved alkali-ion storage properties are attributed to the unique interconnected holey framework that enables efficient charge/mass transport as well as accommodates volume expansion. In situ TEM characterization is employed to depict the structural evolution and further understand the structural stability of 2D holey ACN during the sodiation process. The results show that 2D holey ACN maintained the holey morphology at different sodiation stages because Co3O4 are converted to extremely small interconnected Co nanoparticles and these Co nanoparticles could be well dispersed in a Na2O matrix. These extremely small Co nanoparticles are interconnected to provide good electron pathway. In addition, 2D holey Co3O4 exhibits small volume expansion (∼6%) compared to the conventional Co3O4 particles. The 2D holey nanoarchitecture represents a promising structural platform to address the restacking and accommodate the volume expansion of 2D nanosheets for superior alkali-ion storage.

Metallic Transition Metal Selenide Holey Nanosheets for Efficient Oxygen Evolution Electrocatalysis

Catalysts for oxygen evolution reaction (OER) are pivotal to the scalable storage of sustainable energy by means of converting water to oxygen and hydrogen fuel. Designing efficient electrocatalysis combining the features of excellent electrical conductivity, abundant active surface, and structural stability remains a critical challenge. Here, we report the rational design and controlled synthesis of metallic transition metal selenide NiCo2Se4-based holey nanosheets as a highly efficient and robust OER electrocatalyst. Benefiting from synergistic effects of metallic nature, heteroatom doping, and holey nanoarchitecture, NiCo2Se4 holey nanosheets exhibit greatly enhanced kinetics and improved cycling stability for OER. When further employed as an alkaline electrolyzer, the NiCo2Se4 holey nanosheet electrocatalyst enables a high-performing overall water splitting with a low applied external potential of 1.68 V at 10 mA cm-2. This work not only represents a promising strategy to design the efficient and robust OER catalysts but also provides fundamental insights into the structure-property-performance relationship of transition metal selenide-based electrocatalytic materials.

Solid–liquid reaction synthesis and thermalstability of Ti2SnC powders

A novel method based on the solid–liquid reaction in the Ti–Sn–C system was developed for the synthesis of Ti2SnC powders. In this process, Ti–Sn intermetallic compounds were formed in liquid Sn, then they further reacted with graphite powders to form Ti2SnC. The advantages of this solid–liquid reaction based method include low synthesis temperature, short reaction time and less impurity in the as-prepared powders. Investigations on the stability of Ti2SnC powders demonstrated that Ti2SnC was stable in Ar up to at least 1200°C. In air, however, a complex oxidation–decomposition–oxidation process was observed.

Facile solvothermal synthesis and growth mechanism of flower-like PbTe dendrites assisted by cyclodextrin

Three-dimensional (3D) flower-like PbTe dendrites have been successfully fabricated in high yield through a simple, facile solvothermal method in the presence of β-cyclodextrin. The as-prepared products were characterized by means of powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). Some reaction factors influencing the formation of flower-like PbTe dendrites were systematically investigated. The possible growth mechanism of the flower-like PbTe dendrites was proposed to be an oriented attachment accompanied by an Ostwald ripening process. Thermoelectric transport measurements indicated that the obtained PbTe has a Seebeck coefficient of about 313.3 and 349 μV K−1 at the temperatures of 300 and 400 K, up to about 18% and 32% higher than that of the bulk PbTe at room temperature. Our work provides a very simple, convenient, and fast route to synthesize PbTe flower-like dendrites which are potentially useful in thermoelectric devices.

Structural Engineering of 2D Nanomaterials for Energy Storage and Catalysis

Research on 2D nanomaterials is rising to an unprecedented height and will continue to remain a very important topic in materials science. In parallel with the discovery of new candidate materials and exploration of their unique characteristics, there are intensive interests to rationally control and tune the properties of 2D nanomaterials in a predictable manner. Considerable attention is focused on modifying these materials structurally or engineering them into designed architectures to meet requirements for specific applications. Recent advances in such structural engineering strategies have demonstrated their ability to overcome current material limitations, showing great promise for promoting device performance to a new level in many energy-related applications. Existing in many forms, these strategies can be categorized based on how they intrinsically or extrinsically alter the pristine structure. Achieved through various synthetic routes and practiced in a range of different material systems, they usually share common descriptors that predestine them to be effective in certain circumstances. Therefore, understanding the underlying mechanism of these strategies to provide fundamental insights into structural design and property tailoring is of critical importance. Here, the most recent development of structural engineering of 2D nanomaterials and their significant effects in energy storage and catalysis technologies are addressed.

An Amorphous Noble‐Metal‐Free Electrocatalyst that Enables Nitrogen Fixation under Ambient Conditions

N2 fixation by the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to achieve NH3 production, which still heavily relies on the Haber-Bosch process at the cost of huge energy and massive production of CO2 . A noble-metal-free Bi4 V2 O11 /CeO2 hybrid with an amorphous phase (BVC-A) is used as the cathode for electrocatalytic NRR. The amorphous Bi4 V2 O11 contains significant defects, which play a role as active sites. The CeO2 not only serves as a trigger to induce the amorphous structure, but also establishes band alignment with Bi4 V2 O11 for rapid interfacial charge transfer. Remarkably, BVC-A shows outstanding electrocatalytic NRR performance with high average yield (NH3 : 23.21 μg h-1  mg-1cat. , Faradaic efficiency: 10.16 %) under ambient conditions, which is superior to the Bi4 V2 O11 /CeO2 hybrid with crystalline phase (BVC-C) counterpart.

Microwave-assisted synthesis of Bi2Se3 ultrathin nanosheets and its electrical conductivities

Ultrathin Bi2Se3 nanosheets have been successfully fabricated through a microwave-assisted approach in the presence of ethylene glycol (EG) under 1 kW microwave power for 1 minute. The structure and morphology of the obtained products were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected-area electron diffraction (SAED) and Raman spectroscopy techniques. Based on the control experiments, a possible growth mechanism of Bi2Se3 ultrathin nanosheets was proposed. Furthermore, the thermoelectric transport properties of the nanosheets were investigated by measuring the electrical conductivity and the Seebeck coefficient at temperatures ranging from 298 to 523 K. The maximum power factor can reach up to 157 μW m−1 K−2 at 523 K due to the ultrathin nature of the as-prepared sample, indicating that this promising approach can be extended to the synthesis of other thermoelectrical materials.

Engineering 2D Nanofluidic Li-Ion Transport Channels for Superior Electrochemical Energy Storage

Rational surface engineering of 2D nanoarchitectures-based electrode materials is crucial as it may enable fast ion transport, abundant-surface-controlled energy storage, long-term structural integrity, and high-rate cycling performance. Here we developed the stacked ultrathin Co3 O4 nanosheets with surface functionalization (SUCNs-SF) converted from layered hydroxides with inheritance of included anion groups (OH- , NO3- , CO32- ). Such stacked structure establishes 2D nanofluidic channels offering extra lithium storage sites, accelerated Li-ion transport, and sufficient buffering space for volume change during electrochemical processes. Tested as an anode material, this unique nanoarchitecture delivers high specific capacity (1230 and 1011 mAh g-1 at 0.2 and 1 A g-1 , respectively), excellent rate performance, and long cycle capability (1500 cycles at 5 A g-1 ). The demonstrated advantageous features by constructing 2D nanochannels in nonlayered materials may open up possibilities for designing high-power lithium ion batteries.