Understanding the etching mechanisms of MXene and obtaining direct insights into the influence of etchants on structural features and defects are of critical importance for improving MXene ...properties, optimization of etching protocols, and exploring new MXene compositions. Despite their importance, such studies have been challenging because of the monoatomic thickness of the A-element layers being etched and aggressive etchants that hinder in situ studies. Here, we visualize the etching behavior of the Ti3AlC2 MAX phase in different etchants at the atomic scale using focused ion beam and electron microscopy. We also report on the structural changes in the Ti3AlC2 phase as a function of etching time and etchant type (LiF/HCl, HF, or NH4HF2) to reveal the etching mechanism for the first time. Interestingly, direct visualization reveals an unexpected stepwise etching where the edge Al atoms at the middle layers of the MAX particle are not etched despite contact with the acidic etchant counterintuitively. Also, while the propagation of the etching front occurs in the direction normal to the inner basal plane for all etchants, we reveal that HF and NH4HF2 etch the grain boundaries of polycrystal MAX particles to expose more edge sites to the etchant, which is not observed for LiF/HCl.
Two-dimensional (2D) transition metal carbides (MXenes) exhibit outstanding performances in many applications, such as energy storage, optoelectronics, and electrocatalysts. However, colloidal ...solutions of Ti3C2Tx MXene flakes deteriorate rapidly under ambient conditions due to the conversion of the titanium carbide to titanium dioxide. Here, we discuss the dominant factors influencing the rate of oxidation of Ti3C2Tx MXene flakes, and present guidelines for their storage with the aim of maintaining the intrinsic properties of the as-prepared material. The oxidation stability of the Ti3C2Tx flakes is dramatically improved in a system where water molecules and temperature were well-controlled. It was found that aqueous solutions of Ti3C2Tx MXene can be chemically stable for more than 39 weeks when the storage temperature (−80 °C) is sufficiently low to cease the oxidation processes. It was also found that if the Ti3C2Tx flakes are dispersed in ethanol, the degradation process can be significantly delayed even at 5 °C. Moreover, the oxidation stability of the Ti3C2Tx flakes is dramatically improved in both cases, even in the presence of oxygen-containing atmosphere. We demonstrate practical applications of our approach by employing Ti3C2Tx in a gas sensor showing that when oxidation is inhibited, the device can retain the original electrical properties after 5 weeks of storage.
Two-dimensional (2D) transition metal carbides (MXenes) exhibit outstanding performances in many applications, such as energy storage, optoelectronics, and electrocatalysts. However, colloidal ...solutions of Ti3C2Tx MXene flakes deteriorate rapidly under ambient conditions due to the conversion of the titanium carbide to titanium dioxide. Here, we discuss the dominant factors influencing the rate of oxidation of Ti3C2Tx MXene flakes, and present guidelines for their storage with the aim of maintaining the intrinsic properties of the as-prepared material. The oxidation stability of the Ti3C2Tx flakes is dramatically improved in a system where water molecules and temperature were well-controlled. It was found that aqueous solutions of Ti3C2Tx MXene can be chemically stable for more than 39 weeks when the storage temperature (-80 °C) is sufficiently low to cease the oxidation processes. It was also found that if the Ti3C2Tx flakes are dispersed in ethanol, the degradation process can be significantly delayed even at 5 °C. Moreover, the oxidation stability of the Ti3C2Tx flakes is dramatically improved in both cases, even in the presence of oxygen-containing atmosphere. We demonstrate practical applications of our approach by employing Ti3C2Tx in a gas sensor showing that when oxidation is inhibited, the device can retain the original electrical properties after 5 weeks of storage.
Decreasing the size of portable, wearable, and integrated electronics requires subsequent reduction in the accompanying energy storage devices. To further decrease the size of supercapacitors without ...compromising device performance, adequate materials are required as well as appropriate device design. Traditionally, carbon nanomaterials have been utilized within high-performance electrochemical energy storage applications, however carbides, specifically two-dimensional (2D) transition metal carbides and or nitrides (MXenes) have shown promise. Herein, a focused-ion-beam (FIB) process is used for patterning of titanium carbide (Ti3C2) carbon nanotube (CNT) electrodes into a finely controlled coplanar interdigitated configuration. The symmetric micro supercapacitors produced have a narrow, 500 nm gap between the electrode fingers and exhibit high areal capacitance of ~317 mF cm−2 at a scan rate of 50 mV s−1 and still retain >30% of their capacitance (~104 mF cm−2) at 100 V s−1. In addition, electron beam lithography and photolithography are utilized to create almost-invisible devices with ultra-small footprints (0.04 mm2 device areas) that can be used for securing electronic components. This study provides a simple and reliable method for fabrication of on-chip symmetric MSCs with coplanar interdigitated electrodes.
MXene/CNT based coplanar interdigitated on-chip micro supercapacitors (MSCs) are demonstrated by utilizing a FIB process. The devices prepared by the FIB process feature a gap of 500 nm between fingers, achieving a higher spatial resolution compared to other methods shown before. The MXene/CNT MSCs exhibit excellent areal capacitance and superior rate capability, and their power performance benefits from the hybridization of materials with different and from the sub-500 nm finger interspacing. Display omitted
•MXene/CNT based micro supercapacitors (MSCs) are demonstrated by utilizing a FIB process.•The MSCs demonstratedhave a narrow, 500 nm gap between the electrode fingers.•The MXene/CNT based MSCs with 500 nm gap exhibit high areal capacitance of ~317 mF cm−2 at a scan rate of 50 mV s−1.
Oxidation-resistant titanium carbide MXene films Lee, Yonghee; Kim, Seon Joon; Kim, Yong-Jae ...
Journal of materials chemistry. A, Materials for energy and sustainability,
2020, Letnik:
8, Številka:
2
Journal Article
Recenzirano
Two-dimensional transition metal carbides (MXenes) have attracted much attention due to their excellent electrical conductivity and outstanding performances in energy storage, telecommunication, and ...sensing applications. It is known that MXene flakes are readily oxidized in either humid air or aqueous environments. While the chemical instability of MXenes may limit their use in applications involving ambient environments and long-term operation, oxidation behaviour of MXene films has not been addressed. In this work, we demonstrate a hydrogen annealing method to increase the oxidation stability of Ti
3
C
2
MXene in two different aspects: (1) dramatic improvement in the oxidation stability of pristine MXene films against harsh conditions (100% relative humidity, 70 °C), and (2) large recovery in the electrical conductivity of previously oxidized Ti
3
C
2
MXene films. We also demonstrate an electric-field-induced heater capable of stable operation under highly oxidizing conditions, based on the oxidation-resistant MXene film. A total loss of heat generation ability was observed for the as-prepared MXene film, while the hydrogen-annealed one maintained its bright infrared radiation, under the highly oxidizing conditions. This work offers a solution to industrial applications of unprotected MXene films, securing their stable and long-term operation in humid conditions.
We have demonstrated a highly stable electric heater made of oxidation-resistant MXene film, which was capable of stable operation in air under highly oxidizing conditions (70 °C, 100% RH).
2D transition metal carbides (MXenes) obtained from bulk Mn+1AXn (n = 1, 2, 3, or 4) phases are an intriguing class of crystalline solids with unique physicochemical properties for promising ...applications such as batteries, capacitive energy storage, and electrocatalysis. One of the obstacles that must be overcome for technical applications is that MXene flakes delaminated in aqueous conditions suffer from phase transition and/or structural decomposition over time. Herein, a simple but powerful strategy to enhance their stability by passivating vulnerable edges on the delaminated MXene (Ti3C2Tx) with heterocyclic aromatic amines is reported. In particular, pyrrole‐functionalized MXenes are found to facilitate anti‐oxidation in aqueous solutions at room temperature over 700 days, at 70 °C over 42 days, and even with a strong oxidizer (H2O2, 9.70 mmol) over 50 days. On the other hand, the as‐prepared MXene solution lost its color within a month at room temperature, a day at 70 °C, and 5 min in the presence of H2O2 (9.70 mmol). Density functional theory calculations indicate that chemical interactions between MXene and pyrrole are extremely strong and involve the formation of TiC bonds. Furthermore, pyrrole‐functionalized MXenes exhibit higher electrochemical performance than pristine MXenes as a supercapacitor.
2D titanium carbide (Ti3C2Tx) MXenes with outstanding chemical stability are realized by passivation of the vulnerable edges on the MXene with heterocyclic aromatic amines. Pyrrole‐functionalized MXenes show great conservation against water attacks at room temperature, at 70 °C, and even under hydrogen peroxide. Furthermore, the unique functionalization of pyrrole based on TiC bonds enhances the electrochemical capacitive performances.
Ultra‐Stable MXenes
In article number 2203296, Yonghee Lee, Chi Won Ahn, Mu‐Hyun Baik, and co‐workers demonstrate a simple and powerful strategy in the preservation of titanium carbide MXene ...(Ti3C2Tx) phases with long‐lasting stability in aqueous environments. Pyrrole‐functionalized MXenes were found to facilitate anti‐oxidation at room temperature over 700 days, at 70 °C over 42 days, and even with a strong oxidizer (H2O2) over 50 days.
Two-dimensional (2D) transition metal carbides (MXenes) exhibit outstanding performances in many applications, such as energy storage, optoelectronics, and electrocatalysts. However, colloidal ...solutions of Ti
3
C
2
T
x
MXene flakes deteriorate rapidly under ambient conditions due to the conversion of the titanium carbide to titanium dioxide. Here, we discuss the dominant factors influencing the rate of oxidation of Ti
3
C
2
T
x
MXene flakes, and present guidelines for their storage with the aim of maintaining the intrinsic properties of the as-prepared material. The oxidation stability of the Ti
3
C
2
T
x
flakes is dramatically improved in a system where water molecules and temperature were well-controlled. It was found that aqueous solutions of Ti
3
C
2
T
x
MXene can be chemically stable for more than 39 weeks when the storage temperature (−80 °C) is sufficiently low to cease the oxidation processes. It was also found that if the Ti
3
C
2
T
x
flakes are dispersed in ethanol, the degradation process can be significantly delayed even at 5 °C. Moreover, the oxidation stability of the Ti
3
C
2
T
x
flakes is dramatically improved in both cases, even in the presence of oxygen-containing atmosphere. We demonstrate practical applications of our approach by employing Ti
3
C
2
T
x
in a gas sensor showing that when oxidation is inhibited, the device can retain the original electrical properties after 5 weeks of storage.
We discuss the dominant factors influencing the rate of oxidation of Ti
3
C
2
T
x
MXene flakes, and present guidelines for their storage with the aim of maintaining the intrinsic properties of the as-prepared material.
