Open Access Research Article Issue
Synthesis of Mo2C MXene with high electrochemical performance by alkali hydrothermal etching
Journal of Advanced Ceramics 2023, 12 (10): 1889-1901
Published: 25 October 2023
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Two-dimensional MXenes are generally prepared by the etching of acid solutions. The as-synthesized MXenes are terminated by acid group anions (F, Cl, etc.), which affect the electrochemical performance of MXenes. Here, we report a novel method to prepare Mo2C MXene from Mo2Ga2C by the hydrothermal etching of alkali solutions. Highly pure Mo2C MXene was successfully synthesized by the etching of NaOH, while the etchings of LiOH and KOH were failed. The concentration of NaOH, temperature, and time strongly affect the purity of as-prepared MXene. Pure Mo2C MXene could be synthesized by the etching of 20 M NaOH at 180 ℃ for 24 h. After intercalation by hexadecyl trimethyl ammonium bromide at 90 ℃ for 96 h, few-layer Mo2C MXene was obtained. The Mo2C MXene made by NaOH etching after intercalation exhibited excellent performance as anode of lithium-ion battery, compared with general Mo2C MXene made by HF etching and the Mo2C MXene reported in literature. The final discharge specific capacity was 266.73 mAh·g−1 at 0.8 A·g−1, which is 52% higher than that Mo2C made by HF etching (175.77 mAh·g−1). This is because Mo2C MXene made by NaOH etching has lager specific surface area, lower resistance, and pure O/OH termination without acid anion termination. This is the first report to make Mo2C MXene by alkali etching and the samples made by this method exhibited significantly better electrochemical performance than the samples made by general HF etching.

Open Access Research Article Issue
Construction and performance of CdS/MoO2@Mo2C-MXene photocatalyst for H2 production
Journal of Advanced Ceramics 2022, 11 (9): 1431-1444
Published: 04 August 2022
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Nowadays, photocatalytic technologies are regarded as promising strategies to solve energy problems, and various photocatalysts have been synthesized and explored. In this paper, a novel CdS/MoO2@Mo2C-MXene photocatalyst for H2 production was constructed by a two-step hydrothermal method, where MoO2@Mo2C-MXene acted as a binary co-catalyst. In the first hydrothermal step, MoO2 crystals with an egged shape grew on the surface of two-dimensional (2D) Mo2C MXene via an oxidation process in HCl aqueous solution. In the second hydrothermal step, CdS nanorods were uniformly assembled on the surface of MoO2@Mo2C-MXene in ethylenediamine with an inorganic cadmium source and organic sulfur source. The CdS/MoO2@Mo2C-MXene composite with MoO2@Mo2C-MXene of 5 wt% exhibits an ultrahigh visible-light photocatalytic H2 production activity of 22,672 μmol/(g·h), which is ~21% higher than that of CdS/Mo2C-MXene. In the CdS/MoO2@Mo2C-MXene composite, the MoO2 with metallic nature separates CdS and Mo2C MXene, which acts as an electron-transport bridge between CdS and Mo2C MXene to accelerate the photoinduced electron transferring. Moreover, the energy band structure of CdS was changed by MoO2@Mo2C-MXene to suppress the recombination of photogenerated carriers. This novel compound delivers upgraded photocatalytic H2 evolution performance and a new pathway of preparing the low-cost photocatalyst to solve energy problems in the future.

Open Access Review Issue
From structural ceramics to 2D materials with multi-applications: A review on the development from MAX phases to MXenes
Journal of Advanced Ceramics 2021, 10 (6): 1194-1242
Published: 10 November 2021
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MAX phases (Ti3SiC2, Ti3AlC2, V2AlC, Ti4AlN3, etc.) are layered ternary carbides/nitrides, which are generally processed and researched as structure ceramics. Selectively removing A layer from MAX phases, MXenes (Ti3C2, V2C, Mo2C, etc.) with two-dimensional (2D) structure can be prepared. The MXenes are electrically conductive and hydrophilic, which are promising as functional materials in many areas. This article reviews the milestones and the latest progress in the research of MAX phases and MXenes, from the perspective of ceramic science. Especially, this article focuses on the conversion from MAX phases to MXenes. First, we summarize the microstructure, preparation, properties, and applications of MAX phases. Among the various properties, the crack healing properties of MAX phase are highlighted. Thereafter, the critical issues on MXene research, including the preparation process, microstructure, MXene composites, and application of MXenes, are reviewed. Among the various applications, this review focuses on two selected applications: energy storage and electromagnetic interference shielding. Moreover, new research directions and future trends on MAX phases and MXenes are also discussed.

Open Access Research Article Issue
Synthesis and electrochemical properties of V2C MXene by etching in opened/closed environments
Journal of Advanced Ceramics 2020, 9 (6): 749-758
Published: 15 November 2020
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The effect of etching environment (opened or closed) on the synthesis and electrochemical properties of V2C MXene was studied. V2C MXene samples were synthesized by selectively etching of V2AlC at 90 ℃ in two different environments: opened environment (OE) in oil bath pans under atmosphere pressure and closed environment (CE) in hydrothermal reaction kettles under higher pressures. In OE, only NaF (sodium fluoride) + HCl (hydrochloric acid) etching solution can be used to synthesize highly pure V2C MXene. However, in CE, both LiF (lithium fluoride) + HCl and NaF+HCl etchant can be used to prepare V2C MXene. Moreover, the V2C MXene samples made in CE had higher purity and better-layered structure than those made in OE. Although the purity of V2C obtained by LiF+HCl is lower than that of V2C obtained using NaF+HCl, it shows better electrochemical performance as anodes of lithium-ion batteries (LIBs). Therefore, etching in CE is a better method for preparing highly pure V2C MXene, which provides a reference for expanding the synthesis methods of V2C with better electrochemical properties.

Open Access Research Article Issue
Carbon dioxide adsorption of two-dimensional carbide MXenes
Journal of Advanced Ceramics 2018, 7 (3): 237-245
Published: 10 October 2018
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Two-dimensional carbide MXenes (Ti3C2Tx and V2CTx) were prepared by exfoliating MAX phases (Ti3AlC2 and V2AlC) powders in the solution of sodium fluoride (NaF) and hydrochloric acid (HCl). The specific surface area (SSA) of as-prepared Ti3C2Tx was 21 m2/g, and that of V2CTx was 9 m2/g. After intercalation with dimethylsulfoxide, the SSA of Ti3C2Tx was increased to 66 m2/g; that of V2CTx was increased to 19 m2/g. Their adsorption properties on carbon dioxide (CO2) were investigated under 0–4 MPa at room temperature (298 K). Intercalated Ti3C2Tx had the adsorption capacity of 5.79 mmol/g, which is close to the capacity of many common sorbents. The theoretical capacity of Ti3C2Tx with the SSA of 496 m2/g was up to 44.2 mmol/g. Additionally, due to high pack density, MXenes had very high volume-uptake capacity. The capacity of intercalated Ti3C2Tx measured in this paper was 502 V·v–1. This value is already higher than volume capacity of most known sorbents. These results suggest that MXenes have some advantage features to be researched as novel CO2 capture materials.

Open Access Research Article Issue
Electrochemical performance of Ti3C2 supercapacitors in KOH electrolyte
Journal of Advanced Ceramics 2015, 4 (2): 130-134
Published: 30 May 2015
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Two-dimensional (2D) carbide Ti3C2 was synthesized by exfoliating Ti3AlC2 in HF solution and used for supercapacitive performance investigation in 3 M KOH electrolyte. The specific surface area (SSA) of as-synthesized Ti3C2 was 22.35 m2/g. Ti3C2-based supercapacitor electrodes exhibited good energy storage ability and had a volumetric capacitance 119.8 F/cm3 at the current density of 2.5 A/g. Moreover, the addition of carbon black into Ti3C2 powders greatly improved the performance of Ti3C2-based capacitors because carbon black restrained the preferred orientation of 2D Ti3C2, providing fast ion transport channels, and in turn, decreasing electrical resistance from 16.7 Ω to 3.5 Ω.

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