AFM: Large layer pitch flexible Nb4C3Tx film suitable for high performance supercapacitors

source：beike new material Views：3952time：2020-08-10 QQ Academic Group: 1092348845

【Introduction】

Mxene derived from 413 Max phase has a thick single layer (four-layer transition metal and three-layer carbon or nitrogen), so it may have excellent electrical and mechanical properties. In this study, Nb 4 C 3 T x -MXene nanosheets were layered, and an independent film with a layer spacing of 1.77 nm was obtained, which is thicker than most previous MXene nanosheets. When Nb 4 C 3 T x independent films were tested as supercapacitor electrodes, Nb 4 C 3 T x showed high-capacity capacitance in 1 m H 2 SO 4 , 1 m KOH, and 1 m MgSO 4 . During the cycling process, because the space between the MXene layers is sufficient to accommodate the insertion and deintercalation of cations, there is almost no change in the 21Å layer spacing, which makes the performance of the Nb 4 C 3 T x -MXene energy storage device tend to be stable.

【Background Introduction】

1. Application of supercapacitors in flexible materials

The development of portable wearable electronic devices makes people put forward higher requirements for clean energy. There are many ways to meet the requirements of charging, such as secondary batteries (lithium, sodium, potassium, etc.), fuel cells, and various ion capacitors. However, compared with other reported energy storage devices, supercapacitors can be quickly charged and discharged to complete the energy supply. Supercapacitors mainly rely on two different energy storage methods: electrostatic adsorption on the electrode / electrolyte surface and rapid surface redox reaction. Pseudo-capacitance. At present, finding flexible materials with high volume performance suitable for supercapacitors has become an important research goal.

2. Excellent performance of MXenes in supercapacitors

In the field of nanomaterials, two-dimensional materials are important energy storage materials due to their large specific surface area and good electrical conductivity. One of the most striking is MXene, which is etched from a ternary transition metal carbonitride. There are currently more than 30 known MXene materials, the general chemical formula is M n + 1 X n T x , where M is a transition metal, X is carbon and / or nitrogen, and T x is a surface termination (OH, O, F). MXenes such as Ti 2 CT x , Ti 3 C 2 T x , V 2 CT x , Nb 4 C 3 T x , Nb 2 CT x have a good reputation and application prospect in the field of hydrogen storage. MXenes and its composite materials have excellent capacitance performance in the application of supercapacitors in the fields of photocatalysis, solar cells, sewage treatment, and especially energy storage. Taking Ti 3 C 2 T x as an example, previous reports indicate that at 1 m H 2 SO 4The medium capacitance is up to 900 F cm -3 and the capacitance is up to 1500 F cm -3 in 3 m H 2 SO 4 . In 6 m KOH, the capacitance is 393 F cm -3 (d-Ti 3 C 2 / CNT) and 528 F cm -3 (Ti 3 C 2 T x / PVA-KOH) in 1 m KOH; at 1 m The capacitance in MgSO 4 is approximately 280 F cm -3 . These capacitance values are higher than most other supercapacitor electrodes.

Figure 1. Mxene material principle.

【Introduction】

Recently, Yury Gogotsi, Yu Gao, and Yohan Dall‘Agnese and others published the title "Flexible Nb 4 C 3 T x Film with Large Interlayer Spacing for High-Performance " in the internationally renowned journal Advanced Functional Materials (2018 Impact Factor: 15.62) Supercapacitors "research paper. The first author of this article is Shuangshuang Zhao.

The authors say that among many members of the MXene family, Nb-based materials are less studied than Ti-based MXene. The performance and electrochemical behavior of Nb 4 C 3 T x nanosheets as supercapacitor materials are still in the exploration stage, which may be because their thicker single layer makes MXene delamination more challenging. In lithium-ion batteries, multilayer Nb 4 C 3 T x materials exhibit better cycle performance and rate performance than other MXene materials, so the authors expect their layered monomolecular films may perform well.

In this study, Nb 4 C 3 T x was layered for the first time , and the electrochemical behavior and capacitance of its flexible self-supporting membrane in acidic, alkaline and neutral electrolytes were studied. In-situ X-ray diffraction (XRD) was used to study the reaction mechanism in different electrolytes. The chemical and structural stability of the Nb 4 C 3 T x aqueous suspension and flexible membrane were studied, which will lay the foundation for the energy storage and further application of Nb 4 C 3 T x .

Figure 2. Characterization of Nb 4 C 3 T x structure and morphology

a) XRD pattern of Nb 4 C 3 T x film. Inset shows a digital photo.

b) SEM image of a Nb 4 C 3 T x film in cross-section (inset shows SEM image of a single fkake) and c) TEM image of a Nb 4 C 3 T x flake. Inset in (c) shows a selected area electron diffraction pattern

Figure 3. Characterization of Nb 4 C 3 T x structure and morphology

a) XRD patterns of Nb 4 C 3 T x films treated at different temperatures in nitrogen.

b) Thermogravimetric curve.

c, d) SEM images after treatment in nitrogen c) at 400 ° C and d) at 800 ° C

Figure 4. Nb 4 C 3 T x structure vs. temperature

a) In situ XRD patterns of a Nb 4 C 3 T x film at different temperatures in vacuum.

b) Temperature dependence of c-lattice parameter calculated from (002) peak position

Figure 5. Electrochemical properties of Nb 4 C 3 T x materials

Electrochemical performance of Nb 4 C 3 T x film. CVs at different scan rates in

a) 1 m H 2 SO 4 ,

b) 1 m KOH, and

c) 1 m MgSO 4 .

d) Specific capacitance measured from corresponding CVs.

e) Cycle lives measured from galvanostatic charge–discharge at 2 A g ⁻¹ and

f) profiles in 1 m H 2 SO 4 .

Article link:

https://onlinelibrary.wiley.com/doi/10.1002/adfm.202000815

Source of information: Scientific Materials Station

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