Electrochemical oxidation of urea plays a significant role in electrochemical removal urea in the waste-water and energy conversation and storage. Here we demonstrated that nickel-molybdenum oxide ...nanorods were efficient catalysts for urea electro-oxidation. Nickel-molybdenum oxide nanorods were prepared with various Ni/Mo molar ratios in the precursors and the crystal structure, morphology and surface elements compositions of the nickel-molybdenum oxide nanorods were characterized by X-ray diffraction, Raman spectrum, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The catalytic performance of urea oxidation and kinetics analysis were measured by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy; the process of urea catalyzed by nickel-molybdenum oxide was proposed to follow an electrochemical-chemical reaction mechanism in which urea oxidation happened accompanying the redox of NiOOH/Ni(OH)2 at high potentials. The catalytic ability for urea oxidation was varied by changing the ratio of Ni/Mo in the precursors, and the rapid kinetics, small charge transfer resistance and low Tafel slope consistently supported NiMoO4-C (Ni/Mo = 2) materials as the best catalyst for urea electro-oxidation. The desirable electrocatalytic activity, stability and tolerance towards urea oxidation indicated its promising applications in sustainable energy techniques and alleviating water contamination.
•Nickel-molybdenum oxide nanorods are efficient catalysts for urea electro-oxidation.•Catalytic ability is varied by changing Ni/Mo ratio in the precursors.•NiMoO4-2-C (Ni/Mo = 2) is best for urea electro-oxidation.•Redox of NiOOH/Ni(OH)2 is significant to urea electro-oxidation.
•2D/2D MXene/MoS2 heterostructure was successfully prepared by a facile hydrothermal method.•Visualizing charge distribution was firstly characterized at 2D interface by electron holography.•The ...synergistic effects between two different 2D materials is detailed analyzed.•The MXene-MoS2 composites exhibit the excellent MA performance (RL= -46.72 dB, EAB =4.32 GHz).
The MXene-MoS2 composite with massive 2D/2D heterostructures holds the excellent microwave absorption performance accompanied by the superior RL (−46.72 dB) and the distinct EAB (4.32 GHz) at only 2 mm thickness. Display omitted
The unique 2D/2D heterostructures can fully combine their respective 2D properties and exhibit enhanced performance due to its synergistic effect. However, how to effectively introduce other foreign 2D materials on the 2D MXene substrate, as well as research on their detailed synergistic effects, is still in lack. Herein, 3D conductive interconnected network with massive 2D/2D heterostructures in MXene-MoS2 composites are constructed by a facile hydrothermal reaction, and the microwave absorption mechanism accompanying the synergistic effect is detailed analyzed. Impressively, the unique off-axis electron holography is firstly used to visually characterize the distribution of charge density at the 2D interface, which constructs an effective relationship between the charge density distribution at the 2D/2D heterostructures and the strength of the microwave absorption performance. In addition, the confined space provided by each independent accordion-like multilayered MXene facilitates the heterogeneous coupling between the layers to increase its dielectric loss capability. Accordingly, the MXene-MoS2 composite holds the excellent microwave absorption performance accompanied by the superior reflection loss (RL) (−46.72 dB) and the distinct effective absorption bandwidth (EAB) (4.32 GHz) at only 2 mm thickness. This work refers an archetype for studying the synergistic effect between 2D/2D heterostructures.
Highlights
The rGO/CoNi nanosheets embedded between the MXene layers can continue to serve as a conductive channel, ensuring carrier migration and proper conductive loss capability.
Owing to the ...strong magnetic coupling between the magnetic FeCo alloy nanoparticles on the rGO substrate, the entire MXene-rGO/CoNi film exhibits a strong magnetic loss capability.
Self-assembly MXene-rGO/CoNi films hold excellent microwave absorption performance − 54.1 dB at 13.28 GHz.
MXene, as a rising star of two-dimensional (2D) materials, has been widely applied in fields of microwave absorption and electromagnetic shielding to cope with the arrival of the 5G era. However, challenges arise due to the excessively high permittivity and the difficulty of surface modification of few-layered MXenes severely, which infect the microwave absorption performance. Herein, for the first time, a carefully designed and optimized electrostatic self-assembly strategy to fabricate magnetized MXene-rGO/CoNi film was reported. Inside the synthesized composite film, rGO nanosheets decorated with highly dispersed CoNi nanoparticles are interclacted into MXene layers, which effectively suppresses the originally self-restacked of MXene nanosheets, resulting in a reduction of high permittivity. In addition, owing to the strong magnetic coupling between the magnetic FeCo alloy nanoparticles on the rGO substrate, the entire MXene-rGO/CoNi film exhibits a strong magnetic loss capability. Moreover, the local dielectric polarized fields exist at the continuous hetero-interfaces between 2D MXene and rGO further improve the capacity of microwave loss. Hence, the synthesized composite film exhibits excellent microwave absorption property with a maximum reflection loss value of − 54.1 dB at 13.28 GHz. The electromagnetic synergy strategy is expected to guide future exploration of high-efficiency MXene-based microwave absorption materials.
Highlights
Benefiting from the possible “seed-germination” effect, the “seeds” Ni
2+
grow into “buds” Ni nanoparticles and “stem” carbon nanotubes (CNTs) from the enlarged “soil” of MXene skeleton.
...Compared with the traditional magnetic agglomeration, the MXene-CNTs/Ni hybrids exhibit the highly spatial dispersed magnetic architecture.
3D MXene-CNTs/Ni composites hold excellent microwave absorption performance (−56.4 dB at only 2.4 mm).
Ti
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C
2
T
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MXene is widely regarded as a potential microwave absorber due to its dielectric multi-layered structure. However, missing magnetic loss capability of pure MXene leads to the unmatched electromagnetic parameters and unsatisfied impedance matching condition. Herein, with the inspiration from dielectric-magnetic synergy, this obstruction is solved by fabricating magnetic CNTs/Ni hetero-structure decorated MXene substrate via a facile in situ induced growth method. Ni
2+
ions are successfully attached on the surface and interlamination of each MXene unit by intensive electrostatic adsorption. Benefiting from the possible “seed-germination” effect, the “seeds” Ni
2+
grow into “buds” Ni nanoparticles and “stem” carbon nanotubes (CNTs) from the enlarged “soil” of MXene skeleton. Due to the improved impedance matching condition, the MXene-CNTs/Ni hybrid holds a superior microwave absorption performance of − 56.4 dB at only 2.4 mm thickness. Such a distinctive 3D architecture endows the hybrids: (i) a large-scale 3D magnetic coupling network in each dielectric unit that leading to the enhanced magnetic loss capability, (ii) a massive multi-heterojunction interface structure that resulting in the reinforced polarization loss capability, confirmed by the off-axis electron holography. These outstanding results provide novel ideas for developing magnetic MXene-based absorbers.
The oxide perovskite family holds great promise for diverse applications on account of their unique chemical and physical properties. However, owing to the inadequate Li+‐storage sites, the ...insertion‐type perovskite anodes for lithium‐ion batteries (LIBs) are limited. A‐site deficient perovskites with rich intrinsic vacancies and ion transport channels are believed to be the desirable hosts of superior Li+ storage. Herein, the perovskite Li0.1La0.3NbO3 (LLNO) is designed and demonstrated as the remarkable anode for LIBs with a high specific capacity, a safe operating voltage, an excellent rate performance, and a long cycling life. More importantly, the outstanding cycling stability of LLNO is originated from its low strain characteristic with a maximum volume change of only 1.17%. The exceptional rate performance can be explained by the unconventional Li+ transport pathways with external → grain boundaries → lattice deficiencies. These results not only reveal that A‐site deficient perovskite LLNO is a promising anode for LIBs but also provide fundamental insights into the Li+ ions transport mechanism, facilitating the development of high‐performance perovskite anodes.
A‐site deficient perovskite Li0.1La0.3NbO3 is designed as the anode for Li+ storage, exhibiting high reversible capacity, safe operating potential, excellent rate, and cycling performance. The maximum volume change is only 1.17%, showing a low strain characteristic. The fast Li+ transport pathways with external → grain boundaries → lattice deficiencies are demonstrated, which leads to excellent electrochemical performance.
Niobates with shear ReO3 crystal structures are remarkably promising anode materials for Li+ batteries due to their large capacities, inherent safety, and high cycling stability. However, they ...generally suffer from limited rate capabilities rooted in their insufficient electronic and Li+ conductivities. Here, micrometer‐sized copper niobate (Cu2Nb34O87) bulk as a new anode material having a high electronic conductivity of 2.1 × 10−5 S cm−1 and an impressive average Li+ diffusion coefficient of ≈3.5 × 10−13 cm2 s−1 is exploited, which synergistically leads to an excellent rate capability (184 mAh g−1 at 10 C) while remaining a large reversible capacity and superior cycling stability. Moreover, the fast Li+ transport pathways of grain boundary (micrometer scale) → lattice deformation area (nanometer scale) → (010) crystallographic plane (angstrom scale) are demonstrated in Cu2Nb34O87. Therefore, these results could pave the way for practical application of Cu2Nb34O87 in high‐performance Li+ batteries.
Microsized Copper Niobate having a high electronic conductivity and an impressive average Li+ diffusion coefficient is fabricated via a conventional solid‐state reaction, which exhibits superior electrochemical performance as an anode material. Research on the Li+ transport reveals the fast Li+ transport pathways of the grain boundary (micrometer scale) → lattice deformation area (nanometer scale) → (010) crystallographic plane (angstrom scale).
Zirconium-based metal–organic frameworks (Zr-MOFs) have aroused enormous interest owing to their superior stability, flexible structures, and intriguing functions. Precise control over their ...crystalline structures, including topological structures, porosity, composition, and conformation, constitutes an important challenge to realize the tailor-made functionalization. In this work, we developed a new Zr-MOF (PCN-625) with a csq topological net, which is similar to that of the well-known PCN-222 and NU-1000. However, the significant difference lies in the conformation of porphyrin rings, which are vertical to the pore surfaces rather than in parallel. The resulting PCN-625 exhibits two types of one-dimensional channels with concrete diameters of 2.03 and 0.43 nm. Furthermore, the vertical porphyrins together with shrunken pore sizes could limit the accessibility of substrates to active centers in the framework. On the basis of the structural characteristics, PCN-625(Fe) can be utilized as an efficient heterogeneous catalyst for the size-selective 4 + 2 hetero-Diels–Alder cycloaddition reaction. Due to its high chemical stability, this catalyst can be repeatedly used over six times. This work demonstrates that Zr-MOFs can serve as tailor-made scaffolds with enhanced flexibility for target-oriented functions.
“Zero‐strain” materials with little lattice strain and volume change during long‐term cycling are ideal electrode choices for long‐life lithium‐ion batteries. However, the very limited “zero‐strain” ...materials explored generally show small capacities (<200 mAh g−1), and the origin of “zero‐strain” is still unclear. Here, Na2Ca(VO3)4 (NCVO) nanowires are explored as a new anode material capable of keeping single‐phase‐transition “zero‐strain” during large‐capacity (381 mAh g−1) Li+ intercalation. NCVO owns a crystal structure with isolated V4O124− tetracycles separated by large‐sized NaO6 octahedra and CaO8 square antiprism decahedra, generating large‐sized quadrilateral and hexagonal channels (≈3.6 Å). During lithiation, two‐electron transfer per vanadium is accomplished, introducing a large amount of Li+ into interstitial sites and increasing the size of reduced vanadium ions. The former and latter expansion effects are eliminated by the superior volume‐buffering capabilities of the sufficiently large interstitial sites and electrochemical inactive Na‐/Ca‐based polyhedra, respectively, thus achieving “zero‐strain” with the maximum volume variation of only 0.039% and mean strain of only 0.060%. Therefore, the NCVO nanowires exhibit exceptional cyclic stability, as demonstrated by 93.8%/93.2%/94.7% capacity retention over 2000/2000/7000 cycles at 1C/2C/10C. The understanding of the crystal‐structural features for “zero‐strain” provides a guide for the future designs of “zero‐strain” energy‐storage materials.
Single‐phase‐transition “zero‐strain” and a large reversible capacity (381 mAh g−1) harmoniously coexist in a new Na2Ca(VO3)4‐nanowire Li+‐storage material. Due to the volume‐buffering capabilities of the large interstitial sites and electrochemical inactive Na‐/Ca‐based polyhedra in Na2Ca(VO3)4, its volume variation and lattice strain are the smallest among the explored Li+‐storage materials, leading to its excellent cyclic stability for thousands of cycles.
“Zero‐strain” compounds are ideal energy‐storage materials for long‐term cycling because they present negligible volume change and significantly reduce the mechanically induced deterioration during ...charging–discharging. However, the explored “zero‐strain” compounds are very limited, and their energy densities are low. Here, γ phase Li3.08Cr0.02Si0.09V0.9O4 (γ‐LCSVO) is explored as an anode compound for lithium‐ion batteries, and surprisingly its “zero‐strain” Li+ storage during Li+ insertion–extraction is found through using various state‐of‐the‐art characterization techniques. Li+ sequentially inserts into the 4c(1) and 8d sites of γ‐LCSVO, but its maximum unit‐cell volume variation is only ≈0.18%, the smallest among the explored “zero‐strain” compounds. Its mean strain originating from Li+ insertion is only 0.07%. Consequently, both γ‐LCSVO nanowires (γ‐LCSVO‐NW) and micrometer‐sized particles (γ‐LCSVO‐MP) exhibit excellent cycling stability with 90.1% and 95.5% capacity retention after as long as 2000 cycles at 10C, respectively. Moreover, γ‐LCSVO‐NW and γ‐LCSVO‐MP respectively deliver large reversible capacities of 445.7 and 305.8 mAh g−1 at 0.1C, and retain 251.2 and 78.4 mAh g−1 at 10C. Additionally, γ‐LCSVO shows a suitably safe operating potential of ≈1.0 V, significantly lower than that of the famous “zero‐strain” Li4Ti5O12 (≈1.6 V). These merits demonstrate that γ‐LCSVO can be a practical anode compound for stable, high‐energy, fast‐charging, and safe Li+ storage.
Conductive γ‐Li3.08Cr0.02Si0.09V0.9O4 is explored as a new Li+‐storage compound with a “zero‐strain” characteristic. Li+ sequentially inserts into its 4c(1) and 8d sites, but its maximum unit‐cell volume variation is only ≈0.18%. It is the only “zero‐strain” anode compound with comprehensively good electrochemical properties, including a large reversible capacity, low but safe operating potential, high rate performance, and excellent cycling stability.
Large interfacial resistance plays a dominant role in the performance of all‐solid‐state lithium‐ion batteries. However, the mechanism of interfacial resistance has been under debate. Here, the Li+ ...transport at the interfacial region is investigated to reveal the origin of the high Li+ transfer impedance in a LiCoO2(LCO)/LiPON/Pt all‐solid‐state battery. Both an unexpected nanocrystalline layer and a structurally disordered transition layer are discovered to be inherent to the LCO/LiPON interface. Under electrochemical conditions, the nanocrystalline layer with insufficient electrochemical stability leads to the introduction of voids during electrochemical cycles, which is the origin of the high Li+ transfer impedance at solid electrolyte‐electrode interfaces. In addition, at relatively low temperatures, the oxygen vacancies migration in the transition layer results in the formation of Co3O4 nanocrystalline layer with nanovoids, which contributes to the high Li+ transfer impedance. This work sheds light on the mechanism for the high interfacial resistance and promotes overcoming the interfacial issues in all‐solid‐state batteries.
This work shows the solid‐solid interface inside the all‐solid‐state battery is composed of a previously unreported nanocrystalline layer and transition layer. Both the nanocrystalline layer with insufficient electrochemical stability and the transition layer with thermal stability are the origin of high Li+ transfer impedance in all‐solid‐state batteries.
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