Electrophoretic Deposition of Two-Dimensional Titanium Carbide (MXene) Thick Films

Abstract

Herein, we demonstrate the fabrication of Ti 3 C 2 T x MXene films using electrophoretic deposition (EPD). A systematic study under constant voltage conditions from aqueous and propylene carbonate-based suspensions was performed to investigate the effects of the EPD process parameters on film morphology, flake orientation, and functional properties. From measured suspension properties, the kinetics of deposition from both suspension media were successfully described by the well-established Sarkar model of EPD. Remarkably, EPD-processed films have electrical conductivities of 7400 S/cm, on par with the highest values reported in the literature for Ti 3 C 2 T x MXene. When employed as electrochemical capacitor electrodes in 1 M H 2 SO 4 , the capacitances were comparable to literature values. Given the process scalability and the morphological control that is possible, these results bode well for EPD as a fast, high-throughput method for making MXene films. Electrophoretic deposition (EPD) is a process wherein an electric field is applied to a stable colloidal suspension in between two electrodes.1 As a consequence, two distinct processes occur, as shown in Figure 1a: (1) charged particles in the colloid move toward the electrode of opposite polarity to that of the particles' surface charge (electrophoresis) and, (2) a solid deposit is formed by coagulation at the suspension-electrode interface (deposition). This technique is well-studied and successfully implemented for high-throughput production of dense, void-free ceramic structures ranging from thin coatings to bulk layers several centimeters thick.2 Because of the flexibility and scalability of the deposition apparatus (e.g. power sources and size/shape of deposition electrodes and cell), fast deposition rates, and excellent microstructural control compared to other processing methods, EPD has been used for commercial-scale production of various engineering and traditional ceramics. [2][3][4] In recent years, EPD has also become a versatile technique for making monolithic films and nanocomposites of two-dimensional (2D) materials -such as graphene, transition metal dichalcogenides, and layered transition metal oxides 5-10 -due to advances in colloidal processing. Recently, we discovered a new family of two-dimensional (2D) early transition metal carbides and nitrides, that we labeled MXene, because they are derived from the MAX phases and share properties similar to graphene. 11,12 The MAX phase composition is M n+1 AX n , where M is an early transition metal, A is an A-group element (mostly group 13 and 14 elements), X is carbon and/or nitrogen, and n = 1 to 3. The exfoliation process is carried out by selectively etching away the 'A' layers by hydrofluoric acid (HF) alone or by hydrochloric acid (HCl) combined with pre-dissolved fluoride salts. [13][14][15][16] The resulting material consists of loosely bonded layers of M n+1 X n T x , where T represents surface functionalization by -OH, -F and/or -O groups, [17][18][19] that can subsequently be delaminated...

Tailoring Structure, Composition, and Energy Storage Properties of MXenes from Selective Etching of In‐Plane, Chemically Ordered MAX Phases

“…Still, the values are, respectively, close to 100%, 70%, and 40% higher than those reported for Mo 2 C (open circles in Figure d), Ti 3 C 2 (open triangles in Figure d), and Mo 1.33 C (open squares in Figure d) tested in H 2 SO 4 . As expected, the capacitance decreases with scan rate, however, even at 200 mV s −1 the capacitance is above 900 F cm −3 , which is at the level of the maximum values reported for Ti 3 C 2 clay, which in turn has a gravimetric capacitance comparable to delaminated Ti 3 C 2 “paper” electrodes from electrophoretic deposition . The here obtained results are in the same range as the best results of Ti 3 C 2 MXene hydrogels, which were reported to achieve a volumetric capacitance of ≈1500 F cm −3 …”

“…As expected, the capacitance decreases with scan rate, however, even at 200 mV s −1 the capacitance is above 900 F cm −3 , which is at the level of the maximum values reported for Ti 3 C 2 clay, [15] which in turn has a gravimetric capacitance comparable to delaminated Ti 3 C 2 "paper" electrodes from electrophoretic deposition. [36] The here obtained results are in the same range as the best results of Ti 3 C 2 MXene hydrogels, which were reported to achieve a volumetric capacitance of ≈1500 F cm −3 . [37] For comparison, the capacitance of the vacancy-ordered Mo 1.33 C (from the procedure used in ref.…”

Edge Capping of 2D‐MXene Sheets with Polyanionic Salts To Mitigate Oxidation in Aqueous Colloidal Suspensions

“…It is noteworthy (and again in total accord with the XRD diffraction results) that no salt crystals are seen in the SEM or TEM images,f urther confirming that the salts were washed off.A part from the TiO 2 nanoparticles,t he planar morphology seen in all 4S EM images (Figures 3a,b;S upporting Information, Figures S2a,b) is typical of vacuum-filtered MXene films in which the 2D MXene sheets re-stack densely on top of each other. [11,28] Themicrographs of FV samples also show nanometer sized particles over the surface,w hich are possibly oxide particles (Supporting Information , Figure S3a). Ther eason they do not result in XRD peaks is most probably because of their poor crystallinity and/or low concentration.…”

Variable range hopping and thermally activated transport in molybdenum-based MXenes

“…In general, compared to Ti 3 C 2 T z , Mo-based MXenes are more resistive (see, e.g., [24,32]). The lowest room-temperature (RT) resistivity, ρ, values obtained to date are of the order of 6.6 μ m [37]; for Ti 3 C 2 T x films, the corresponding value is 1.3 μ m [38,39]. Another important distinction between Ti 3 C 2 T z and Mo-based MXenes is the fact that for the latter ρ increases with decreasing temperatures [24,32].…”