Transition metal carbides and nitrides (MXenes), a family of two-dimensional (2D) inorganic compounds, are materials composed of a few atomic layers of transition metal carbides, nitrides, or carbonitrides. Ti3C2, the first 2D layered MXene, was isolated in 2011. This material, which is a layered bulk material analogous to graphite, was derived from its 3D phase, Ti3AlC2 MAX. Since then, material scientists have either determined or predicted the stable phases of >200 different MXenes based on combinations of various transition metals such as Ti, Mo, V, Cr, and their alloys with C and N. Extensive experimental and theoretical studies have shown their exciting potential for energy conversion and electrochemical storage. To this end, we comprehensively summarize the current advances in MXene research. We begin by reviewing the structure types and morphologies and their fabrication routes. The review then discusses the mechanical, electrical, optical, and electrochemical properties of MXenes. The focus then turns to their exciting potential in energy storage and conversion. Energy storage applications include electrodes in rechargeable lithium- and sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. In terms of energy conversion, photocatalytic fuel production, such as hydrogen evolution from water splitting, and carbon dioxide reduction are presented. The potential of MXenes for the photocatalytic degradation of organic pollutants in water, such as dye waste, is also addressed, along with their promise as catalysts for ammonium synthesis from nitrogen. Finally, their application potential is summarized.

Applications of 2D MXenes in energy conversion and storage systems

Ti3 C2 Tx , a typical representative among the emerging family of 2D layered transition metal carbides and/or nitrides referred to as MXenes, has exhibited multiple advantages including metallic conductivity, a plastic layer structure, small band gaps, and the hydrophilic nature of its functionalized surface. As a result, this 2D material is intensively investigated for application in the energy storage field. The composition, morphology and texture, surface chemistry, and structural configuration of Ti3 C2 Tx directly influence its electrochemical performance, e.g., the use of a well-designed 2D Ti3 C2 Tx as a rechargeable battery anode has significantly enhanced battery performance by providing more chemically active interfaces, shortened ion-diffusion lengths, and improved in-plane carrier/charge-transport kinetics. Some recent progresses of Ti3 C2 Tx MXene are achieved in energy storage. This Review summarizes recent advances in the synthesis and electrochemical energy storage applications of Ti3 C2 Tx MXene including supercapacitors, lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries. The current opportunities and future challenges of Ti3 C2 Tx MXene are addressed for energy-storage devices. This Review seeks to provide a rational and in-depth understanding of the relation between the electrochemical performance and the nanostructural/chemical composition of Ti3 C2 Tx , which will promote the further development of 2D MXenes in energy-storage applications.

Recent Advances in Layered Ti 3 C 2 T x MXene for Electrochemical Energy Storage

MXene-based materials for electrochemical energy storage

MXene, an important and increasingly popular category of postgraphene 2D nanomaterials, has been rigorously investigated since early 2011 because of advantages including flexible tunability in element composition, hydrophobicity, metallic nature, unique in-plane anisotropic structure, high charge-carrier mobility, tunable band gap, and favorable optical and mechanical properties. To fully exploit these potentials and further expand beyond the existing boundaries, novel functional nanostructures spanning monolayer, multilayer, nanoparticles, and composites have been developed by means of intercalation, delamination, functionalization, hybridization, among others. Undeniably, the cutting-edge developments and applications of clay-inspired 2D MXene platform as electrochemical electrode or photo-electrocatalyst have conferred superior performance and have made significant impact in the field of energy and advanced catalysis. This review provides an overview of the fundamental properties and synthesis routes of pure MXene, functionalized MXene and their hybrids, highlights the state-of-the-art progresses of MXene-based applications with respect to supercapacitors, batteries, electrocatalysis and photocatalysis, and presents the challenges and prospects in the burgeoning field.

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Clay-Inspired MXene-Based Electrochemical Devices and Photo-Electrocatalyst: State-of-the-Art Progresses and Challenges.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.201801897

2D Metal Carbides and Nitrides (MXenes) as High‐Performance Electrode Materials for Lithium‐Based Batteries

Preparation of Ultrathin 2D MoS2/Graphene Heterostructure Assembled Foam-like Structure with Enhanced Electrochemical Performance for Lithium-ion Batteries

SnO2 nanoparticle-modified Ti3C2 MXene (SnO2–Ti3C2) nanocomposites have been synthesized via hydrothermal method and subsequently used as anode material for lithium-ion batteries (LIBs) with enhanced electrochemical performance. The results of the microstructure analysis indicate that the introduction of SnO2 nanoparticles enlarged the d-spacing of Ti3C2 layers and increased the Li+ storage. Meanwhile, SnO2 nanoparticles improve the electrochemical performance based on the alloying mechanism. Electrochemical results reveal that SnO2–Ti3C2 nanocomposites can greatly improve the reversible capacity compared with pure Ti3C2Tx particles. Remarkably, SnO2–Ti3C2 nanocomposites show outstanding initial capacity of 1030.1 mAh g−1 at 100 mA g−1, and the capacity can remain about 360 mAh g−1 after 200 cycles. The SnO2–Ti3C2 nanocomposites demonstrate a stable cycle performance and high reversible capacity for lithium storage.

Facile synthesis SnO2 nanoparticle-modified Ti3C2 MXene nanocomposites for enhanced lithium storage application

One dimensional (1D) hierarchical core–shell structures (MoO3@MoS2) constructed by perpendicular growth of few-layered MoS2 nanosheets on MoO3 nanowires were successfully fabricated by a direct anion-exchange reaction of the inorganic MoO3 nanowire precursor. The morphology and structure of the products can be controlled by adjusting the hybrid solvent in the anion-exchange process, and the contents of MoS2 and MoO3 in the core–shell nanowires can be easily tuned by adding a varied amount of thiourea. Although the organic–inorganic precursor was not used, the 1D structure of the inorganic MoO3 nanowire was still maintained. An amazing feature of the MoO3@MoS2 nanowire was its 1D hierarchical core–shell structure integrated with two-dimensional (2D) ultrathin MoS2 nanosheets and 1D MoO3 nanowires. The numerous few-layered MoS2 nanosheets grew perpendicularly on the MoO3 nanowires, providing plenty of diffusion channels for Li+ during the insertion/extraction process. Due to the abundant hardly stacked MoS2 nanosheets and the synergistic effects between MoO3 nanowires and MoS2 nanosheets, this unique MoO3@MoS2 nanowire showed greatly improved Li+ storage properties when evaluated as an anode material for lithium ion batteries (LIBs).

Perpendicular growth of few-layered MoS2 nanosheets on MoO3 nanowires fabricated by direct anion exchange reactions for high-performance lithium-ion batteries

Xianjin Chen

Papers

Preparation of Ultrathin 2D MoS2/Graphene Heterostructure Assembled Foam-like Structure with Enhanced Electrochemical Performance for Lithium-ion Batteries

Facile synthesis SnO2 nanoparticle-modified Ti3C2 MXene nanocomposites for enhanced lithium storage application

Perpendicular growth of few-layered MoS2 nanosheets on MoO3 nanowires fabricated by direct anion exchange reactions for high-performance lithium-ion batteries

Three-dimensional elastic ultrathin reduced graphene oxide coating SnS2 hierarchical microsphere as lithium ion batteries anode materials

A novel nitrite biosensor based on the direct electron transfer hemoglobin immobilized in the WO3 nanowires with high length-diameter ratio.