2020 Volume 31 Issue 4

MXenes-The fastest growing materials family in the twodimensional world
Xu Bin , Gogotsi Yury
2020, 31(4): 919-921  doi: 10.1016/j.cclet.2020.03.054
[Abstract](418) [FullText HTML] [PDF 623KB](4)
A mini-review on MXenes as versatile substrate for advanced sensors
Ali Soomro Razium , Jawaid Sana , Zhu Qizhen , Abbas Zaheer , Xu Bin
2020, 31(4): 922-930  doi: 10.1016/j.cclet.2019.12.005
[Abstract](851) [FullText HTML] [PDF 1084KB](5)
MXenes have emerged as versatile 2D materials that are already gaining paramount attention in the areas of energy, catalyst, electromagnetic shielding, and sensors. The unique surface chemistry, graphene-like morphology, high hydrophilicity, metal-like conductivity with redox capability identifies MXenes, as an ideal material for surface-related applications. This short review summarizes the most recent reports that discuss the potential application of MXenes and their hybrids as a transducer material for advanced sensors. Based on the nature of transducing signals, the discussion is categorized into three sections, which include electrochemical (bio) sensors, gas sensors, and finally, electro-chemiluminescence & fluorescent sensors. The review provides a concise summary of all the analytical merits obtained subsequent to the use of MXenes, followed by endeavors that have been made to accentuate the future perspective of MXenes in sensor devices.
Recent progress of MXenes as the support of catalysts for the CO xidation and oxygen reduction reaction
Zhang Yiying , Zhang Xilin , Cheng Cheng , Yang Zongxian
2020, 31(4): 931-936  doi: 10.1016/j.cclet.2019.12.010
[Abstract](991) [FullText HTML] [PDF 1024KB](10)
MXenes, the new family of two-dimensional (2D) transition metal carbides/nitrides, can serve as the substrate materials for the catalysts due to the large specific surface area, tunable electronic structures and thermal stability. The first 2D layered MXene, Ti3C2, was successfully obtained by selective etching of the A element from the MAX phases using hydrofluoric acid (HF) at room temperature in 2011. In this review, we summarize the preparation, structure of MXenes and discuss the recent progress in potential application of MXenes in catalysis, mainly in CO oxidation and oxygen reduction reaction (ORR), from the views of both experimental and theoretical investigations. The outlook of the major challenges and future directions on research of MXenes is also included.
Chemistry of two-dimensional MXene nanosheets in theranostic nanomedicine
Wang Yuemei , Feng Wei , Chen Yu
2020, 31(4): 937-946  doi: 10.1016/j.cclet.2019.11.016
[Abstract](982) [FullText HTML] [PDF 1289KB](8)
Transition metal carbide, carbonitride and nitride MXenes, as the emerging two-dimensional (2D) nanomaterials, have aroused burgeoning research interest in a broad range of applications ranging from energy conversion to biomedicines attributing to their distinctive planar nanostructure, physiochemical properties and biological effects. They are featured with fascinating electronic, optical, magnetic, mechanical and thermal properties, which exert significant roles in biomedical applications of 2D MXenes. In this review, we briefly summarize the recent research progress of 2D MXenes and highlight their intrinsic chemistry in theranostic nanomedicines, focusing on the synthetic chemistry for MXenes construction, surface chemistry for surface engineering, physiochemical property for theranostic application and biological chemistry for biosafety evaluation. Furthermore, based on the current achievements on MXenes, their potential research direction, critical challenges and future development in biomedicine are also discussed. It is highly expected that 2D MXene-based nanosystems would have a broad application prospect in theranostic biomedicine provided the current facing critical issues and challenges are adequately solved.
Two-dimensional hybrid nanomaterials derived from MXenes (Ti3C2Tx) as advanced energy storage and conversion applications
Zhao Sen , Nivetha Ravi , Qiu Yu , Guo Xiaohui
2020, 31(4): 947-952  doi: 10.1016/j.cclet.2019.11.045
[Abstract](677) [FullText HTML] [PDF 1251KB](3)
The development of two-dimensional hybrid nanomaterial derived from MXenes as high performance electrode material is the key component for the advanced energy storage and conversion systems. In the past decades, MXene derived nanomaterials have attracted greatly interest in scientific activity and potential applications because of their unique synergistic properties such as high thermal stability, excellent electrical conductivity, large surface area, easy to handle and outstanding electro and photo chemical properties. This review is focused on the synthesis of hybrid nanomaterials from MXene (Ti3C2Tx) for renewable energy conversion and storage application including hydrogen evolution reaction, supercapacitor, lithium-ion batteries and photocatalysis. Finally, we also summarized the prospect and opportunities of novel two-dimensional hybrid nanomaterials derived MXene (Ti3C2Tx) for futuristic sustainable energy technology
Recent advances of MXene as promising catalysts for electrochemical nitrogen reduction reaction
Sun Jie , Kong Wenhan , Jin Zhaoyong , Han Yaqian , Ma Liangyu , Ding Xiaoteng , Niu Yusheng , Xu Yuanhong
2020, 31(4): 953-960  doi: 10.1016/j.cclet.2020.01.035
[Abstract](865) [FullText HTML] [PDF 1340KB](5)
Electrochemical reduction of N2, as an eco-friendly alternative, not only allows the use of protons in water as a source of hydrogen under mild conditions but also can be driven by renewable electric energy. The major challenge is to identify high-efficiency electrocatalysts. MXene is a new class of 2D transition metal carbides, nitrides, and carbonitrides that have received significant attention in electrocatalysis. The investigations on MXene in electrocatalytic nitrogen fixation are rapidly proceeding, and some breakthroughs have emerged very recently due to MXenes' satisfactory catalytic activity. Here, the recent progress concerning the MXene-based catalysts for electrochemical N2 reduction reaction (NRR) is highlighted. In regards to giving guidelines for exploring more efficient MXene-based catalysts for the NRR, the fabrication and surface modification of MXene are discussed. Besides, the shortcomings and challenges of current research are summarized and the future research directions are prospected.
Intercalated MXene-based layered composites: Preparation and application
Wu Shumeng , Wang He , Li Li , Guo Meixia , Qi Zhichong , Zhang Qingyou , Zhou Yanmei
2020, 31(4): 961-968  doi: 10.1016/j.cclet.2020.02.046
[Abstract](1131) [FullText HTML] [PDF 1036KB](2)
Combining high conductivity, hydrophilicity and excellent electrochemical performance in one, MXenes have attracted increasing attention since their inception. However, easy to stack caused by the van der Waals' force between the layers limits their practical application. Fortunately, intercalating other substances between layers of MXenes and getting intercalated MXene-based layered composites (IMLCs) with open structure can improve their physical and chemical properties effectively. Larger available surface helps expose more active sites and enlarged layer spacing facilitates ion transport. In addition, other substances fixed in the interlayers by MXenes' two-dimensional confinement effect can produce synergistic effect and expand their applicable range greatly. This review is dedicated to summarizing the preparation methods and applications of IMLCs, emphasizing the advantages of them in the fields of energy storage, catalysis, sensors, electromagnetic interference (EMI) shielding and biomedicine. Furthermore, prospects and further developments in these gratifying fields are also commented.
Cation-intercalated engineering and X-ray absorption spectroscopic characterizations of two dimensional Mxenes
Wang Changda , Wei Shiqiang , Zhang Pengjun , Zhu Kefu , Song Pin , Chen Shuangming , Song Li
2020, 31(4): 969-979  doi: 10.1016/j.cclet.2019.08.045
[Abstract](988) [FullText HTML] [PDF 1728KB](3)
The geometrically multiplied development of 2D MXenes has already promoted the prosperity of various fields of scientific researches especially but not limited in energy storage and conversion. Notably, cation intercalation can improve the interlayer spacing of MXenes resulting in tunable physical and chemical properties. Moreover, the synchrotron radiation X-ray characterizations have also shown high potential on exploring the property and structure of cation intercalated MXenes. This review is mainly focused on the recent achievements of cation intercalated MXenes through different methods on energy storage systems. Synchrotron-based X-ray absorption spectroscopic characterizations are emphasized to probe the local coordination and electronic structure in intercalated MXenes. The outlook of cation intercalation on MXenes and their applications are also discussed.
Scalable construction of SiO/wrinkled MXene composite by a simple electrostatic self-assembly strategy as anode for high-energy lithium-ion batteries
Wei Chuanliang , Fei Huifang , Tian Yuan , An Yongling , Tao Yuan , Li Yuan , Feng Jinkui
2020, 31(4): 980-983  doi: 10.1016/j.cclet.2019.12.033
[Abstract](696) [FullText HTML] [PDF 924KB](3)
Available onlineSilicon monoxide (SiO) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity (~2400 mAh/g), low working potential (< 0.5 V vs. Li+/Li), low cost, easy synthesis, nontoxicity, abundant natural source and smaller volume expansion than Si. However, low intrinsic electrical conductivity, low initial Coulombic efficiency (ICE) and inevitable volume expansion (~200%) impede its practical application. Here we fabricate SiO/wrinkled MXene composite (SiO-WM) by an electrostatic self-assembly method. Importantly, this method is simple, scalable and taking into account all the issues of SiO. As a result, the SiO-WM exhibits improved rate capability, cycling performance and ICE than bare SiO.
Two-dimensional vanadium carbide (V2CTx) MXene as supercapacitor electrode in seawater electrolyte
He Hongtian , Xia Qixun , Wang Bingxin , Wang Libo , Hu Qianku , Zhou Aiguo
2020, 31(4): 984-987  doi: 10.1016/j.cclet.2019.08.025
[Abstract](636) [FullText HTML] [PDF 1023KB](2)
In this study, two-dimensional V2CTx MXene has been prepared by selectively etching Al layers from V2AlC MAX phase by NaF+HCl etching at 90 ℃ for 72 h and its performance as supercapacitor (SC) electrode were tested using simulating seawater as electrolyte. V2CTx MXene-based electrodes shows a good capacitance of 181.1 F/g, which is in accordance with the volumetric specific capacitance of 317.8 F/cm3, and with 89.1% capacitance retention even after 5000 cycle. Compared with other MXenes, V2CTx have better electrochemical performance as SC electrode. This work provides an innovative strategy to apply V2CTx MXene as SC electrode in safety and effective seawater electrolyte.
Pt immobilized spontaneously on porous MXene/MAX hybrid monolith for hydrogen evolution reaction
Cui Cong , Cheng Renfei , Zhang Chao , Wang Xiaohui
2020, 31(4): 988-991  doi: 10.1016/j.cclet.2019.08.026
[Abstract](627) [FullText HTML] [PDF 799KB](1)
Designing efficient electrocatalysts with low Pt loadings for hydrogen evolution reaction (HER) is urgently required for renewable and sustainable energy conversion. Here, we report a strategy that Pt nanoparticulates are spontaneously immobilized on porous MXene/MAX monolith as HER catalysts by utilizing the redox reaction between Ti3C2Tx MXene and [PtCl4]2- in H2PtCl6 aqueous solution. By taking advantage of homogeneously distributed Pt nanoparticulates on highly electrically conductive porous Ti3C2Tx/Ti3AlC2 monolith, the as-prepared electrocatalysts show high catalytic performance for hydrogen evolution. Specifically, the binder-free electrocatalysts have Pt loadings as low as 8.9 μg/cm2, with low overpotential of 43 mV at a current density of 10 mA/cm2 and low Tafel slope that three times lower than porous Ti3C2Tx/Ti3AlC2 without Pt loading. This strategy offers a new approach to constructing ultra-low Pt-loading HER catalysts on the basis of in situ redox reaction between noble metal ions and MXenes.
Highly efficient catalytic performances of nitro compounds via hierarchical PdNPs-loaded MXene/polymer nanocomposites synthesized through electrospinning strategy for wastewater treatment
Yin Juanjuan , Zhan Fangke , Jiao Tifeng , Deng Huizhen , Zou Guodong , Bai Zhenhua , Zhang Qingrui , Peng Qiuming
2020, 31(4): 992-995  doi: 10.1016/j.cclet.2019.08.047
[Abstract](627) [FullText HTML] [PDF 971KB](2)
The problem of water pollution has become increasingly serious, and it has already threatened the survival of mankind and has become an obstacle to the healthy development of human health. Here, we prepared a novel polyvinyl alcohol (PVA)/polyacrylic acid (PAA)/MXene fiber membrane by electrospinning. After heat treatment of film and subsequent modification with Pd nanoparticles, PVA/PAA/MXene@PdNPs composite nanofiber membrane with high specific surface area and excellent catalytic performance was finally prepared. The uniform distribution of MXene sheets in the composite fiber membrane not only solves the problem that the MXene sheet is not easy to be monolayerized, but also can grow the self-reduced Pd nanoparticles on the MXene sheets. In addition, the composite nanofiber membrane exhibits excellent catalytic ability and cycle stability for 4-nitrophenol (4-NP) and 2-nitrophenol (2-NA), providing new strategy for the study of catalytic composite materials related to degradation of wastewater.
Nanostructured Ni/Ti3C2Tx MXene hybrid as cathode for lithium-oxygen battery
Wen Caiying , Zhu Tianjiao , Li Xingyu , Li Huifeng , Huang Xianqiang , Sun Genban
2020, 31(4): 1000-1003  doi: 10.1016/j.cclet.2019.09.028
[Abstract](602) [FullText HTML] [PDF 954KB](1)
Ti3C2 belongs to MXenes family, which is a new two-dimensional material and has been applied in many fields. With simple method of hydrothermal and high temperature calcination, nanostructured Ni/Ti3C2Tx hybrid was synthesized. The stable layer structure of Ti3C2 MXene providing high surface area as well as excellent electronic conductivity are beneficial for deposition and decomposition of discharge product Li2O2. Furthermore, possessing special catalytic activity, Ni nanoparticles with size of about 20 nm could accelerate Li2O2 breaking down. Taking advantage of two kinds of materials, Ni/Ti3C2Tx hybrid as cathode of Li-O2 battery can achieve a maximal specific capacity of 20, 264 mAh/g in 100 mA/g and 10, 699 mAh/g in 500 mA/g at the first cycle. This work confirms that the prepared Ni/Ti3C2Tx hybrid exhibiting better cycling stability points out a new guideline to improve the electrochemical performance of lithium-oxygen batteries.
Porous and free-standing Ti3C2Tx-RGO film with ultrahigh gravimetric capacitance for supercapacitors
Fang Yongzheng , Yang Bowen , He Dongtong , Li Huipeng , Zhu Kai , Wu Lin , Ye Ke , Cheng Kui , Yan Jun , Wang Guiling , Cao Dianxue
2020, 31(4): 1004-1008  doi: 10.1016/j.cclet.2019.08.043
[Abstract](599) [FullText HTML] [PDF 1235KB](1)
MXene-based electrode materials exhibit favorable supercapacitor performance in sulfuric acid due to praised pseudocapacitance charge storage mechanism. However, self-stacking of conventional MXene electrodes severely restricts their electrochemical performance, especially at high loading. Herein, a flexible cross-linked porous Ti3C2Tx-MXene-reduced graphene oxide (Ti3C2Tx-RGO) film is skillfully designed and synthesized by microscopic explosion of graphene oxide (GO) at sudden high temperature. The generated chamber structure between layers could hold a few of electrolyte, leading to a close-fitting reaction at interlayer and avoiding complex ions transmission paths. The Ti3C2Tx-RGO film displayed a preferable rate performance than that of pure Ti3C2Tx film and a high capacitance of 505 F/g at 2 mV/s. Furthermore, the uniform intralayer structure and unique energy storage process lead to thickness-independenct electrochemical performances. This work provides a simple and feasible improvement approach for the design of MXene-based electrodes, which can be spread other electrochemical systems limited by ions transport, such as metal ions batteries and catalysis.
Accordion-like titanium carbide (MXene) with high crystallinity as fast intercalative anode for high-rate lithium-ion capacitors
Li Chen , Zhang Xiong , Wang Kai , Sun Xianzhong , Ma Yanwei
2020, 31(4): 1009-1013  doi: 10.1016/j.cclet.2019.09.056
[Abstract](695) [FullText HTML] [PDF 860KB](1)
Two-dimensional transition-metal carbide materials, or MXenes, have attracted great attention in energy-related fields due to their excellent electrical conductivity, and large interlayer spacing. In this work, a simple method involving combustion synthesis and acid treatment to prepare accordion-like Ti3C2Tx MXene with open structure and high crystallinity, which is employed as anode materials in lithium-ion capacitors. Due to the improved ion diffusion and electron transportation of Ti3C2Tx anode, the mismatched electrode kinetics can be largely alleviated to acquire an enhanced power performance. The assembled Ti3C2Tx-based lithium-ion capacitors provides a maximum energy density of 106 Wh/kg and still exhibits a superior energy density of 79 Wh/kg even at a higher power density of 5.2 kW/kg, which provides a new platform for MXene materials with porous and crystalline features toward both high energy and power densities.
Robust and easily retrievable Pd/Ti3C2Tx⊂graphene hydrogels for efficient catalytic hydrogenation of nitroaromatic compounds
Xie Xiuqiang , Wu Zhenjun , Zhang Nan
2020, 31(4): 1014-1017  doi: 10.1016/j.cclet.2019.10.012
[Abstract](613) [FullText HTML] [PDF 808KB](1)
Ti3C2Tx has been emerging as an attractive platform to prepare composite catalysts, and their assembly into integrated catalytic materials represents a key step forward toward practical applications. However, the swelling behavior of Ti3C2Tx leads to significant structure change, which challenges the stability of Ti3C2Tx-based integrated functional materials for catalytic applications. Here we report a facile synthesis of Pd/Ti3C2Tx⊂graphene hydrogels in which Pd/Ti3C2Tx are spatially encapsulated in the 3D porous graphene framework. The porous interconnected structure not only affords efficient mass transfer and desirable functional accessibility to catalytic active sites, but also effectively buffers the swelling behavior of Ti3C2Tx. When applied for catalytic hydrogenation of nitroaromatic compounds, the mechanically robust Pd/Ti3C2Tx⊂graphene hydrogels exhibit efficient activities, easy separability, and good cyclability. This work is expected to promote the application of Ti3C2Tx-based functional materials for practical applications involving interactions with salt solutions, such as supercapacitors, catalysis, and water purification.
Ti3C2Tx/PEDOT: PSS hybrid materials for room-temperature methanol sensor
Wang Xiaofeng , Sun Kaiming , Li Ke , Li Xu , Gogotsi Yury
2020, 31(4): 1018-1021  doi: 10.1016/j.cclet.2019.11.031
[Abstract](645) [FullText HTML] [PDF 822KB](3)
It is essential to develop a methanol gas sensor with high selectivity and low working temperature for human health and environmental monitoring. In this work, a blend of PEDOT:PSS and Ti3C2Tx with the mass ratio of 4:1 is used to fabricate a methanol gas sensor. It possesses a high response ratio of the largest response and the second largest response (5.54) and an enhanced response compared to pure PEDOT:PSS and pure Ti3C2Tx tested at room temperature. These findings may pave the way towards design of the MXenes based high-performance gas-sensing materials in the future.
Mechanical properties and frictional resistance of Al composites reinforced with Ti3C2Tx Mxene
Hu Jie , Li Shibo , Zhang Jing , Chang Qiuying , Yu Wenbo , Zhou Yang
2020, 31(4): 996-999  doi: 10.1016/j.cclet.2019.09.004
[Abstract](582) [FullText HTML] [PDF 871KB](2)
Two-dimensional (2D) Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient, but also used in composites due to its high aspect ratio and rich surface functional groups. So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx. Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites. Ti3C2Tx/Al composites were designed and prepared by pressureless sintering followed by hot extrusion technique. The prepared composites exhibit a homogeneous distribution of Ti3C2Tx. The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content. A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt% Ti3C2Tx/Al composite. The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding. A low friction coefficient of 0.2, twice lower than that of pure Al, was achieved in the 3 wt% Ti3C2Tx/Al composite. Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite, improving the frictional properties of Al matrix composites.
Ternary BiOBr/TiO2/Ti3C2Tx MXene nanocomposites with heterojunction structure and improved photocatalysis performance
Xu Tianxiang , Wang Jiapei , Cong Ye , Jiang Song , Zhang Qin , Zhu Hui , Li Yanjun , Li Xuanke
2020, 31(4): 1022-1025  doi: 10.1016/j.cclet.2019.11.038
[Abstract](558) [FullText HTML] [PDF 883KB](6)
The rational design and construction of heterojunction structure is an effective strategy to improve the photocatalytic performance. Herein, a series of BiOBr nanosheets-immobilized TiO2/Ti3C2Tx MXene hybrid materials with heterojunction structure were synthesized by a facial one-step hydrothermal method. The ternary composites show outstanding performance as photocatalysts for the degradation of rhodamine B due to the optimized synergetic effects of BiOBr, TiO2 and Ti3C2Tx. The improved photocatalytic performance is remarkably attributed to the construction of a heterojunction between TiO2 and BiOBr due to their well-matching of energy band position, which can enhance the absorption for visible light and promote the transfer of photo-generated charge carriers. Moreover, Ti3C2Tx acts as an electron trap to further accelerate the separation of photo-generated electrons and holes.
Electromagnetic interference shielding Ti3C2Tx-bonded carbon black films with enhanced absorption performance
Fan Xiaomeng , Li Minghang , Li Xin , Ye Fang , Xue Jimei , Zhang Litong , Cheng Laifei
2020, 31(4): 1026-1029  doi: 10.1016/j.cclet.2020.01.030
[Abstract](552) [FullText HTML] [PDF 872KB](2)
The demand for flexible and freestanding electromagnetic interference (EMI) shielding materials are more and more urgent to combat with serious electromagnetic (EM) radiation pollution. Twodimensional Ti3C2Tx is considered as promising EMI shielding material to graphenes because of the low cost and high electrical conductivity. However, the shielding performance still needs to be optimized to decrease the reflection effectiveness (SER) and increase absorption effectiveness (SEA). Herein, we prepared Ti3C2Tx-bonded carbon black films with a porous structure. The SER decreased from 20 dB to 12 dB and the SEA increased from 31 dB to 47 dB. The best EMI shielding effectiveness can be as high as 60 dB with SEA of 15 dB and SER of 45 dB. Their calculated specific shielding effectiveness can be as high as 8718 dB cm2/g. These results indicate that the porous structure can enhance the absorption of the EMI shielding films, resulting from the enhanced scattering and reflection. Consequently, this work provides a promising MXene-based EMI shielding film with lightweight and flexibility.
Facile hydrothermal construction of Nb2CTx/Nb2O5 as a hybrid anode material for high-performance Li-ion batteries
Qin Li , Xu Senyang , Liu Yang , Zhu Shuhao , Hou Linrui , Yuan Changzhou
2020, 31(4): 1030-1033  doi: 10.1016/j.cclet.2020.03.006
[Abstract](567) [FullText HTML] [PDF 800KB](2)
Herein, a simple yet efficient hydrothermal strategy is developed to in-situ convert multi-layered niobium-based MXene (Nb2CTx) to hierarchical Nb2CTx/Nb2O5 composite. In the hybrid, the Nb2O5 nanorods are well dispersed in and/or on the Nb2CTx. Thanks to the synergetic contributions from the high capacity of Nb2O5 and superb electrical conductivity of the two-dimensional Nb2CTx itself, the resultant Nb2CTx/Nb2O5 hybrid exhibits excellent rate behaviors and stable long-term cycling behaviors, when evaluated as anodes for Li-ion batteries.
Additive-free porous assemblies of Ti3C2Tx by freeze-drying for high performance supercapacitors
Yang Yue , Wu Lili , Li Lu , Lin Shuangyan , Bai Lina , Ma Xinzhi , Shao Zhitao , Zhang Xitian
2020, 31(4): 1034-1038  doi: 10.1016/j.cclet.2020.02.027
[Abstract](635) [FullText HTML] [PDF 1061KB](5)
Ti3C2Tx has shown great potential in energy storage filed, but the restacking between Ti3C2Tx nanosheets seriously hampers the maximization of its capacitance. In this study, we rationally designed and synthesized porous Ti3C2Tx assemblies without any additive by introducing ice as spacers using a facile freeze-drying method. The porous Ti3C2Tx assemblies have a three-dimensional network structure, which consists of ultra large Ti3C2Tx lamellar walls and lots of macro- and mesopores. It has been proven that there are more-O groups on the surface of the porous Ti3C2Tx assemblies than the Ti3C2Tx film. The porous Ti3C2Tx assemblies deliver a maximum areal capacitance of 1668 mF/cm2 when the mass loading is 8.4 mg/cm2, an optimized specific capacitance of 247.2 F/g when the mass loading is 5.3 mg/cm2, and 87% capacitance retention over 10000 cycles. The symmetric solid-state supercapacitors based on the porous Ti3C2Tx assemblies show an areal capacitance of 355.8 mF/cm2, the maximum power density of 50 mW/cm2 and an outstanding flexibility under different deformation.
Achieving high yield of Ti3C2Tx MXene few-layer flakes with enhanced pseudocapacior performance by decreasing precursor size
Xu Jianguang , Zhu Jiale , Gong Chen , Guan Zexin , Yang Dan , Shen Zhihan , Yao Wei , Wu Haijiang
2020, 31(4): 1039-1043  doi: 10.1016/j.cclet.2020.02.050
[Abstract](650) [FullText HTML] [PDF 957KB](5)
Ti3C2Tx, a most studied member of MXene family, shows promise as a candidate electrode for pseudocapacitor due to its electronic conductivity and hydrophilic surface. However, the unsatisfactory yield of Ti3C2Tx few-layer flakes significantly restricted it in real applications. Here, we proposed a simple solution to boost the yield of Ti3C2Tx few-layer flakes by decreasing precursor size. When using the small 500 mesh Ti3AlC2 powders as raw material, high yield of 65% was successfully achieved. Moreover, the asreceived small flakes also exhibit an enhanced pseudocapacior performance owing to their excellent electrical conductivity, expanded interlayer space and more O content on the surface. This work not only sheds light on the cost effective mass production of Ti3C2Tx few-layer flakes, but also provides an efficient solution for the design of MXene electrodes with high pseudocapacior performance.
From high-yield Ti3AlCN ceramics to high-quality Ti3CNTx MXenes through eliminating Al segregation
Chen Ningjun , Huang Haichao , Xu Zhong , Xie Yanting , Xiong Da , Chu Xiang , Gu Bingni , Zheng Bo , Deng Weili , Zhang Haitao , Yang Weiqing
2020, 31(4): 1044-1048  doi: 10.1016/j.cclet.2019.10.004
[Abstract](591) [FullText HTML] [PDF 1049KB](6)
Ti3CNTx MXenes with unique electrical conductivity can be widely applied for supercapacitors and electromagnetic shielding. However, its relatively low-yield quaternary nitrogen-containing Ti3AlCN ceramics precursor (less than 50%), due to the inevitable Al segregation during the synthesizing process, significantly hindered its widely commercial applications. Herein, we employed the controllable AlNoversaturation precursor strategy to precisely tune the phase transition point of quaternary Ti3AlCN ceramics to obtain high-yield Ti3AlCN precursor for the purpose of high conductivity Ti3CNTx MXenes. Combined energy dispersive X-ray spectrometer (XRD) with X-ray photoelectron spectroscopy (XPS) characterizations, the yield of the quaternary nitrogen-containing Ti3AlCN ceramics was evidently proved to be up to 70%, which is 1.4 times than that of previously reported works. Such relatively highyield quaternary Ti3AlCN is mainly ascribed to the elimination of Al segregation. Based on it, we further developed accordion-like two-dimensional (2D) MXene via hydrofluoric acid etch and vacuum freezedry. This novel accordion-like 2D Ti3CNTx MXene possesses high electrochemical capacitive properties (209 F/g). Therefore, this controllable AlN-oversaturation precursor strategy will pave a way to exploit costly high-yield MAX ceramics precursor for high conductivity MXenes and also play a powerful role in promoting their practical applications including electrical and magnetic engineering fields.
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