3D graphite exhibit very diverse properties. Among these, 2D graphene has gained the most popularity due to its unique properties and technological impact. [1] The discovery of fascinating properties in graphene has led to the exploration of other 2D materials, such as silicene, germanene, transition metal dichalcogenides, and, very recently, MXenes.MXenes, a 2D material based on carbides, carbonitrides, and nitrides, were first reported in 2011, and are typically synthesized from their parent 3D MAX phases through exfoliation in hydrofluoric acid (HF). [2] As one of the most novel and versatile members of the 2D material family, MXenes have been drawing significant interest from various fields due to their wide range of applicability. The general formula for MXenes is M n + 1 X n T x , in which M, X, and T x represent early d-block transition metals, C and/or N atoms, and the surface termination groups (F, OH, and/or O), respectively. Through a top-down synthesis approach, A-layer atoms (i.e., Al, Si, and Ga) can be selectively etched from the structure of the MAX phase, leaving behind loosely stacked 2D MX layers, which can then be further exfoliated into single-layer MXene flakes. [3] To date, the MXene family includes more than 30 stoichiometric compositions that have been experimentally synthesized, with many more theoretically possible, each with distinct electronic, physical, and (electro)chemical properties. [4] Currently, there are at least 28 nitride MAX and 17 nitride MXene phases that have been reported to exist and be thermodynamically stable, but these mostly exist only in the theoretical realm due to difficulty of MAX phase synthesis and etching (Scheme 1). In addition, about 20 kinds of solid solutions on both the M and X sides have also been reported. The compositional diversity as well as surface chemistry modifications have resulted in numerous new materials, which are being explored for multitudinous applications, including energy storage, optoelectronics, wireless communication, catalysis, sensing, and medicine, as well as being explored for in situ/operando spectroelectrochemistry (Scheme 1). [5][6][7][8][9][10] Carbide versusNitride: What's the Holdup in Nitride MXenes? While a vast majority of the MXene work focuses on carbides (with hundreds of publications presently), especially Ti 3 C 2 , As nanomaterials are becoming a key component in various electronics, 2D nanomaterials are emerging and attracting tremendous attention in the scientific community due to their unique physical, chemical, and structural properties. In recent years, a new family of 2D carbides and nitrides, known as MXenes, has become the center of attention for many electrochemical energy storage and conversion systems. While nitride MXenes have some publications centered around them, the overwhelming majority revolve around carbide and their direct application to systems without understanding the underlying mechanism behind their performance. The lack of publications in both of these fields, nitrides and mechanistic u...
Decarbonizing the chemical industry and achieving carbon-neutral energy is paramount to the sustainability of the human species on earth. Electrocatalysis using transition metalbased catalysts plays a major role in achieving this task. In this work, we present an overview on the application of transition metal-based catalysts in electrocatalytic reactions. We particularly focus on the advancement of the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO 2 RR) using transition metal electrocatalysts. We also aim to highlight the major achievements in these fields and the limitations in their large-scale industrial applications. Different transition metal catalysts are discussed, from 3-dimensional to 1-to 0-dimensional structures. We place special attention to the emerging transition metal catalysts such as 2dimensional carbide and nitride MXenes and single atom catalysts. Lastly, we offer recommendation for future research directions for the aforementioned electrocatalysis fields using transition metal electrocatalysts. This work will ultimately help both existing and incoming researchers in these fields in providing the state-of-the-art research findings and identifying the major challenges that must be addressed in order to attain carbon-neutral energy.
Two-dimensional (2D) carbide and nitride MXenes possess properties that are desirable for a broad range of electrocatalytic applications including the hydrogen evolution reaction (HER). These properties include high surface area, hydrophilicity, heterogeneity of redox-active transition metals, and tunable surface functionalities allowing for low HER overpotentials. In this paper, we report on the cathodic etching and À O/À OH functionalization of hybrid Ti 3 CN upon the application of an external potential for improved HER performance and show that the active sites for HER on this MXene catalyst are located primarily on the À OÀ and À OH functional groups. The overpotential for the hybrid Ti 3 CN improves by 350 mV upon in-situ À O/À OH functionalization and etching, reaching À 0.46 V vs. RHE at a current density of 10 mA cm À 2 , much lower than those reported for the benchmark Ti 3 C 2 carbide MXene. These results provide a path forward to tuning the electrocatalytic activity of MXenes and related electrocatalysts for water splitting.
Two-dimensional (2D) carbide and nitride MXenes possess properties that are desirable for a broad range of electrocatalytic applications including hydrogen evolution reaction (HER). These properties include high surface area, hydrophilicity, heterogeneity of redox-active transition metals, and tunable surface functionalities allowing for low HER overpotentials. In this presentation, I will report on the -O functionalization of Ti3CNTx (Tx = -O, -F, -OH) upon the application of external potential for improved HER performance and show that the active sites for HER on this MXene catalyst are located primarily on the O functional groups. The overpotential for the Ti3CN improves by 350 mV upon in-situ -O functionalization and reaches -0.46 V vs. RHE at a current density of 10 mA cm-2. Structural and electrochemical characterization results showed that the functionalized Ti3CNTx MXene catalyst is structural and electrochemically stable. Further insights into the mechanism of HER were provided by in-situ/operando Raman spectroelectrochemistry and the results will be presented. Ultimately, these findings provide a path forward to tuning the electrocatalytic activity of MXenes and related electrocatalysts for water splitting.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.