All Pseudocapacitive MXene‐RuO₂ Asymmetric Supercapacitors

Abstract

2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high‐rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti3C2Tx) can operate at negative potentials in acidic electrolyte is exploited, to design an all‐pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO2) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene‐based supercapacitors. The complementary working potential windows of MXene and RuO2, along with proton‐induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm−2 at a power density of 40 mW cm−2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon‐based materials in asymmetric electrochemical capacitors, leading to an increased energy density.

Extraordinary Areal and Volumetric Performance of Flexible Solid‐State Micro‐Supercapacitors Based on Highly Conductive Freestanding Ti3C2Tx Films

“…The obtained freestanding MXene films confidently possess ultrahigh electric conductivity up to 1.25 × 10 5 S m −1 and sheet resistance of 0.015 Ω □ −1 confirmed by four-point probe method (Table S1 and Figure S1, Supporting Information). [29] After etching for 45 h, this product was well stratified as the scanning electron microscope (SEM) image shown (Figure 2a). [29] After etching for 45 h, this product was well stratified as the scanning electron microscope (SEM) image shown (Figure 2a).…”

“…[23] The chemical formula of these materials can be represented by M n+1 X n T z , where M refers to early transition metals (such as Ti, Zr, Hf, V, Nb, Ta, Cr, Sc, etc. [29,30] In addition, freestanding MXene films with outstanding flexibility can be easily obtained by vacuum-assisted filtration. [24][25][26][27][28] Ti 3 C 2 T x is the first and also the most studied MXene for energy storage application.…”

Antimonene Engineered Highly Deformable Freestanding Electrode with Extraordinarily Improved Energy Storage Performance

“…[54,55] While since Ti 3 C 2 T x shows hydrogen evolution under modest negative potentials in low-pH media, the resulted device can only be operated at voltages of no more than 1.6 V. As for neutral salt electrolyte, although a much widened negative potential window can be obtained, the present performance of currently available choices for negative electrodes cannot match most positive electrodes in capacitance. To widen the operating voltage window of the device, there are several works reporting the application of Ti 3 C 2 T x as negative electrode for asymmetric supercapacitors with H 2 SO 4 electrolyte.…”

MXene‐Based Composites: Synthesis and Applications in Rechargeable Batteries and Supercapacitors

“…[136] The substrate loading method is utilized to deposit MXene on a base with excellent flexibility. [292] In addition to carbon fiber, MXene can also be Adv. Figure 12k shows a thin layer of Ti 3 C 2 T x distributed on the carbon fiber.…”

“…a) Schematic of the preparation process of the PCL/Ti 3 C 2 T x /SCNT composite by electrostatic spray method. [292] Copyright 2018, John Wiley and Sons. c) Photograph of twisted (up to 100 times) (MWCNT/Ti 3 C 2 T x ) 2 -PCL films and the corresponding circuits built from them to light up a blue LED.…”