Assembling 2D MXenes into Highly Stable Pseudocapacitive Electrodes with High Power and Energy Densities

Abstract

Electrochemical capacitors (ECs) that store charge based on the pseudocapacitive mechanism combine high energy densities with high power densities and rate capabilities. 2D transition metal carbides (MXenes) have been recently introduced as high‐rate pseudocapacitive materials with ultrahigh areal and volumetric capacitances. So far, 20 different MXene compositions have been synthesized and many more are theoretically predicted. However, since most MXenes are chemically unstable in their 2D forms, to date only one MXene composition, Ti3C2Tx, has shown stable pseudocapacitive charge storage. Here, a cation‐driven assembly process is demonstrated to fabricate highly stable and flexible multilayered films of V2CTx and Ti2CTx MXenes from their chemically unstable delaminated single‐layer flakes. The electrochemical performance of electrodes fabricated using assembled V2CTx flakes surpasses Ti3C2Tx in various aqueous electrolytes. These electrodes show specific capacitances as high as 1315 F cm−3 and retain ≈77% of their initial capacitance after one million charge/discharge cycles, an unprecedented performance for pseudocapacitive materials. This work opens a new venue for future development of high‐performance supercapacitor electrodes using a variety of 2D materials as building blocks.

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

“…Because the V 2 CT z flakes in the colloidal suspension, in which no salt was added, completely dissolved (see inset (ii)in Figure 2b), no diffraction patterns could be obtained from this sample.T his probably is due to dissolution of the vanadium pentoxide formed. Va hidMohammadi et al in their study [27] showed asimilar dissolution of V 2 CT z flakes that they ascribed to the formation of V 2 O 5 .O nt he other hand, the 0.1 PV and the FV (Figure 2b)s amples show the (002) and (110) peaks near 68 8 and 648 8 respectively,t hat are typical of V 2 CT z .Noother peaks were observed, implying that, at least at the XRD level, the oxidation was undetectable in both cases.…”

Ti3C2Tx (MXene)‐Silicon Heterojunction for Efficient Photovoltaic Cells

“…Notably, the XPS spectrum of the 7-d old film confirmed the partial oxidation of Ti 3 C 2 T x MXene ( Figure S3b, Supporting Information). [41] Compared to the starting efficiency of graphene/Si (1.5%) [47] and perovskite solar cells (3.8%) [48] in their first reports, as-prepared Ti 3 C 2 T x /Si solar cells have already shown comparable efficiencies. This can also be observed from the C 1s spectrum ( Figure S3e, Supporting Information), showing increased intensity of CC peak after 7 d. In the C case, there is little doubt some of the increase is simply due to the deposition of adventitious material from the environment but we would suggest there is a contribution from MXene oxidation as well.…”

“…The degradation of the films was expected and is probably due to the oxidation of MXene caused by the moisture and oxygen in the air. [41] This clearly can change the structure, morphology and properties of the MXene. [41] This clearly can change the structure, morphology and properties of the MXene.…”

Recent Advances of Two‐Dimensional Nanomaterials for Electrochemical Capacitors

“…Beidaghi et al synthesized highly stable and flexible multilayered films of V 2 CT x andT i 2 CT x MXenesb yacation-drivena ssembly process in alkali chloride solutions, which paved the way to designing next-generation pseudocapacitive materials for ECs ( Figure 11 a-e). [77]…”