Structural bidimensional transition-metal carbides and/or nitrides (MXenes) have drawn the attention of the material science research community thanks to their unique physical-chemical properties. ...However, a facile and cost-effective synthesis of MXenes has not yet been reported. Here, using elemental precursors, we report a method for MXene synthesis via titanium aluminium carbide formation and subsequent in situ etching in one molten salt pot. The molten salts act as the reaction medium and prevent the oxidation of the reactants during the high-temperature synthesis process, thus enabling the synthesis of MXenes in an air environment without using inert gas protection. Cl-terminated Ti
C
T
and Ti
CT
MXenes are prepared using this one-pot synthetic method, where the in situ etching step at 700 °C requires only approximately 10 mins. Furthermore, when used as an active material for nonaqueous Li-ion storage in a half-cell configuration, the obtained Ti
CT
MXene exhibits lithiation capacity values of approximately 280 mAh g
and 160 mAh g
at specific currents of 0.1 A g
and 2 A g
, respectively.
MXenes, a rapidly growing family of 2D transition metal carbides, carbonitrides, and nitrides, are one of the most promising high‐rate electrode materials for energy storage. Despite the significant ...progress achieved, the MXene synthesis process is still burdensome, involving several procedures including preparation of MAX, etching of MAX to MXene, and delamination. Here, a one‐pot molten salt electrochemical etching (E) method is proposed to achieve Ti2C MXene directly from elemental substances (Ti, Al, and C), which greatly simplifies the preparation process. In this work, different carbon sources, such as carbon nanotubes (CNT) and reduced graphene oxide (rGO), are reacted with Ti and Al micro‐powders to prepare Ti2AlC MAX with 1D and 2D tuned morphology followed by in situ electrochemical etching from Ti2AlC MAX to Ti2CTx MXene in low‐cost LiCl‐KCl. The introduction of the O surface group via further ammonium persulfate (APS) treatment can act in concert with Cl termination to activate the pseudocapacitive redox reaction of Ti2CClyOz in the non‐aqueous electrolyte, resulting in a Li+ storage capacity of up to 857 C g−1 (240 mAh g−1) with a high rate (86 mAh g−1 at 120 C) capability, which makes it promising for use as an anode material for fast‐charging batteries or hybrid devices in a non‐aqueous energy storage application.
A one‐pot molten salt electrochemical etching (E) method is proposed to achieve Ti2C MXene directly from elemental substances (Ti, Al, and C), which greatly simplifies the preparation process. By using carbon sources with different morphologies, such as carbon nanotubes and reduced graphene oxide, MAX and MXene with tuned morphology are prepared based on the “carbon‐template‐growth” mechanism.
The unique properties of 2D MXenes, such as metal‐like electrical conductivity and versatile surface chemistry, make them appealing for various applications, including energy storage. While surface ...terminations of 2D MXene are expected to have a key influence on their electrochemical properties, the conventional HF‐etching method limits the surface functional groups to F, OH, and O. In this study, O‐free, Cl‐terminated MXenes (noted as Ti3C2Clx) are first synthesized by a molten salt (FeCl2) etching route. Then, a substitution of surface termination from Cl to N is performed via post‐thermal treatment of Ti3C2Clx in Li3N containing molten salt electrolytes. While the Cl‐terminated pristine material does not show electrochemical activity, the surface‐modified, N‐containing Ti3C2Tx exhibits a unique capacitive‐like electrochemical signature in sulfuric acid aqueous electrolyte with rate performance—more than 300 F g−1 (84 mAh g−1) at 2 V s−1. These results show that control of the MXene surface chemistry enables the preparation of high‐performance electrodes in a previously not accessed limit of energy storage.
Surface termination substitutions from Cl to N is performed via post thermal treatment of Ti3C2Clx in Li3N containing molten salt electrolyte. While the Cl‐terminated pristine material does not show electrochemical activity, the surface‐modified, N‐containing Ti3C2Tx MXenes exhibit a unique electrochemical signature in sulfuric acid aqueous electrolyte with a high‐rate, capacitive‐like redox process within the full voltage window.
Recently, rechargeable zinc‐ion batteries in mild acidic electrolytes have attracted considerable research interest as a result of their high sustainability, safety, and low cost. However, the use of ...conventional Zn‐ion storage materials is hindered by insufficient specific capacity, sluggish reaction kinetics, or poor cycle life. Here, these limitations are addressed by pre‐intercalating alkali ions and water crystals into layered δ‐MnO2 (birnessite) to prepare K0.27MnO2·0.54H2O (KMO) and Na0.55Mn2O4·1.5H2O with ultrathin nanosheet morphology via a rapid molten salt method. In these materials, alkali ions and water crystals act as pillars to stabilize the layered structures, which can enable rapid diffusion of cations in the KMO structure, resulting in high power capability (90 mAh g−1 at 10 C) and good cycling stability. Furthermore, electrochemical quartz crystal microbalance measurements shed light on the charge storage mechanism of KMO in an aqueous Zn‐ion battery which, combined together with in‐operando X‐ray diffraction techniques, suggests that the charge storage process is dominated by the (de)intercalation of H3O+ with further dissolution–precipitation of Zn4(OH)6(SO4)·5H2O solid product on the KMO surface during cycling.
A molten salt‐prepared K0.27MnO2·0.54H2O cathode achieves a high capacity of 288 mAh g−1 at C/3 and high‐power capability (88 mAh g−1 at 10 C) in an aqueous Zn‐ion battery configuration. The combination of in situ XRD and electrochemical quartz crystal microbalance reveal a charge storage process dominated by (de)intercalation of (hydrated) protons with further dissolution–precipitation of Zn4(OH)6(SO4)·5H2O.
In this study, we used 2‐Dimmensionnal Ti3C2 MXene as model materials to understand how the surface groups affect their electrochemical performance. By adjusting the nature of the surface ...terminations (Cl‐, N/O‐, and O‐) of Ti3C2 MXene through a molten salt approach, we could change the spacing between MXene layers and the level of water confinement, resulting in significant modifications of the electrochemical performance in acidic electrolyte. Using a combination of techniques including in‐operando X‐ray diffraction and electrochemical quartz crystal microbalance (EQCM) techniques, we found that the presence of confined water results in a drastic transition from an almost electrochemically inactive behavior for Cl‐terminated Ti3C2 to an ideally fast pseudocapacitive signature for N,O‐terminated Ti3C2 MXene. This experimental work not only demonstrates the strong connection between surface terminations and confined water but also reveals the importance of confined water on the charge storage mechanism and the reaction kinetics in MXene.
A transition from electrochemically inactive Cl‐terminated Ti3C2 to fast, pseudocapacitive behavior is reported for N,O‐terminated Ti3C2 MXene, attributed to the presence of confined water between the MXene layers. This study evidences the crucial role surface terminations and confined water in charge storage and reaction kinetics in MXene materials.
Pseudocapacitive materials that store charges by fast redox reactions are promising candidates for designing high energy density electrochemical capacitors. MXenes – recently discovered ...two-dimensional carbides, have shown excellent capacitance in aqueous electrolytes, but in a narrow potential window, which limits both the energy and power density. Here, we investigated the electrochemical behavior of Ti3C2 MXene in 1M solution of 1-ethly-3-methylimidazolium bis- (trifluoromethylsulfonyl)-imide (EMITFSI) in acetonitrile and two other common organic electrolytes. This paper describes the use of clay, delaminated and composite Ti3C2 electrodes with carbon nanotubes in order to understand the effect of the electrode architecture and composition on the electrochemical performance. Capacitance values of 85 F g−1 and 245 F cm−3 were obtained at 2 mV s−1, with a high rate capability and good cyclability. In situ X-ray diffraction study reveals the intercalation of large EMI+ cations into MXene, which leads to increased capacitance, but may also be the rate limiting factor that determines the device performance.
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•3 types of Ti3C2 electrodes were prepared: clay, delaminated and CNT composite.•Capacitance up to 245 F cm−3 in 1 M EMITFSI solution in acetonitrile was achieved.•Imidazolium (EMI+) ions intercalation was demonstrated by in situ XRD.
The development of the basic understanding of the charge storage mechanisms in electrodes for energy storage applications needs deep characterization of the electrode/electrolyte interface. In this ...work, we studied the charge of the double layer capacitance at single layer graphene (SLG) electrode used as a model material, in neat (EMIm‐TFSI) and solvated (with acetonitrile) ionic liquid electrodes. The combination of electrochemical impedance spectroscopy and gravimetric electrochemical quartz crystal microbalance (EQCM) measurements evidence that the presence of solvent drastically increases the charge carrier density at the SLG/ionic liquid interface. The capacitance is thus governed not only by the electronic properties of the graphene, but also by the specific organization of the electrolyte side at the SLG surface originating from the strong interactions existing between the EMIm+ cations and SLG surface. EQCM measurements also show that the carbon structure, with the presence of sp2 carbons, affects the charge storage mechanism by favoring counter‐ion adsorption on SLG electrode versus ion exchange mechanism in amorphous porous carbons.
The charge of the double layer capacitance at a single layer graphene (SLG) electrode was studied in neat (EMIm‐TFSI) and solvated (with acetonitrile) ionic liquid electrodes. Electrochemical impedance spectroscopy and gravimetric electrochemical quartz crystal microbalance measurements evidence that the presence of solvent drastically increases the charge carrier density at the SLG/ionic liquid interface.
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