MXene-based 3D porous macrostructures for electrochemical energy storage

Abstract

2D transition metal carbides and nitrides (MXenes) have shown outstanding potential as electrode materials for energy storage applications due to a combination of metallic conductivity, wide interlayer spacing, and redox-active, metal oxide-like surfaces capable of exhibiting pseudocapacitive behavior. It is well known that 2D materials have a strong tendency to restack and aggregate, due to their strong van der Waals interactions, reducing their surface availability and inhibiting electrochemical performance. In order to overcome these problems, work has been done to assemble 2D materials into 3D porous macrostructures. Structuring 2D materials in 3D can prevent agglomeration, increase specific surface area and improve ion diffusion, whilst also adding chemical and mechanical stability. Although still in its infancy, a number of papers already show the potential of 3D MXene architectures for energy storage, but the impact of the processing parameters on the microstructure of the materials, and the influence this has on electrochemical properties is still yet to be fully quantified. In some situations the reproducibility of works is hindered by an oversight of parameters which can, directly or indirectly, influence the final architecture and its properties. This review compiles publications from 2011 up to 2020 about the research developments in 3D porous macrostructures using MXenes as building blocks, and assesses their application as battery and supercapacitor electrodes. Recommendations are also made for future works to achieve a better understanding and progress in the field. carbon and/or nitrogen and T x represents surface terminations which vary depending on the synthesis method used (for example, hydroxyl, oxygen, or fluorine) [10].With less than 10 years since their discovery, efforts are still mainly pointed towards the assessment of its potentialities and exploration of its properties, while their integration and application in various engineering fields are still very much in their infancy. Nevertheless, investigations have shown very competitive results in energy storage devices attracting a lot of interest in the field. In particular, the inner conductive metal carbide layers provide fast electron supply to electrochemically active sites, and functional groups on the surface, allow water intercalation and fast redox activity for pseudocapacitive energy storage [11][12][13]. Besides energy storage, MXenes also showed promising properties and have been researched for a variety of other areas, such as electromagnetic shielding, environmental, sensors, optoeletronic devices, and renewable energy [9,[14][15][16].For most practical applications, the MXene powders must be assembled or processed into a macroscopic sample such as, for example, an electrode. Conventionally this is done either by mixing it with a solvent to form a slurry which is painted over a substrate, by directly vacuum filtration, by spin coating, or by spraying the MXene suspension to form a compact film. During these processes, there i...

Heteroatom‐Doped and Oxygen‐Functionalized Nanocarbons for High‐Performance Supercapacitors

“…Readers are encouraged to follow the general guidelines for supercapacitor research, such as reporting normalized capacitance minimum at the scan rate of 10 mV s −1 or the current density of 2 A g −1 , providing information on Self-discharge or leakage current, from relevant references. [47,90,[285][286][287][288] Below we formulate and refine the following general guidelines related to the supercapacitor research involving doping processes in electrode preparation.…”

“…[54] In addition, the BET surface area often overestimates the actual surface area of the sample. [52,260,286] Hence, establishing the correlation between electroactive surface area with the supercapacitive performance could provide a more in-depth understanding. In order to estimate the electroactive surface area, one can find out the double layer capacitance C dl (mF) from the capacitive charging-discharging current (i C ) versus the scan rate (v in V s −1 ) plot ( C dl = i C /v) and divide it by the general specific capacitance 40 µF cm −2 in 1 m NaOH or 35 µF cm −2 in 1 m H 2 SO 4 electrolytes.…”

Controlling the Porosity and Biocidal Properties of the Chitosan-Hyaluronate Matrix Hydrogel Nanocomposites by the Addition of 2D Ti3C2Tx MXene

“…The mechanism of gelation is self-assembly, as thoroughly described by Tontini et al [ 66 ]. He noted that the disadvantage of MXenes was their low capability to gelation which appears as a reduction of the interconnectivity between 2D flakes.…”

“…This problem was partially solved by using various additives such as ethylenediamine (EDA) [ 68 ], thiourea dioxide, ammonia [ 69 ], polyacrylic acid (PAA) [ 70 ], or divalent metal ions. The additives enhance the interconnectivity between material branches during gelation by simply filling the available space, inducing chemical cross-linking, chemical reduction or enhancing electrostatic interactions between the chemical groups of the mixed agents [ 66 ]. In this study, we took advantage of the electrostatic interactions between the mixed and then freeze-dried materials.…”

Filtration Materials Modified with 2D Nanocomposites—A New Perspective for Point-of-Use Water Treatment

“…The induction of oxidative stress associated with the generation of reactive oxygen species (ROS) and silver ion release should also be considered [ 38 , 39 , 40 , 41 ]. On the other hand, the tendency of Ti 3 C 2 MXenes to agglomerate [ 42 ] due to strong van der Waals interactions helps keep the metal nanoparticles inside the agglomerates, which decreases their diffusion potential and impact on bacterial cells.…”