2D early transition metal carbide and nitride MXenes have intriguing properties for electrochemical energy storage and electrocatalysis. These properties can be manipulated by modifying the basal plane chemistry. Here, mixed transition metal nitride MXenes, M‐Ti4N3Tx(M = V, Cr, Mo, or Mn; Tx= O and/or OH), are developed by modifying pristine exfoliated Ti4N3TxMXene with V, Cr, Mo, and Mn salts using a simple solution‐based method. The resulting mixed transition metal nitride MXenes contain 6–51% metal loading (cf. Ti) that exhibit rich electrochemistry including highly tunable hydrogen evolution reaction (HER) electrocatalytic activity in a 0.5
Here it is shown that Ti3C2T
- Award ID(s):
- 1740795
- NSF-PAR ID:
- 10455652
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 30
- Issue:
- 43
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract m H2SO4electrolyte as follows: V‐Ti4N3Tx> Cr‐Ti4N3Tx> Mo‐Ti4N3Tx> Mn‐Ti4N3Tx> pristine Ti4N3Txwith overpotentials as low as 330 mV at −10 mA cm−2with a charge‐transfer resistance of 70 Ω. Scanning electrochemical microscopy (SECM) reveals the electrochemical activity of individual MXene flakes. The SECM data corroborate the bulk HER activity trend for M‐Ti4N3Txas well as provide the first experimental evidence that HER results from catalysis on the MXene basal plane. These electrocatalytic results demonstrate a new pathway to tune the electrochemical properties of MXenes for water splitting and related electrochemical applications. -
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, Ti3C2T
x , 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−3and 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. -
Abstract MXenes, a family of 2D transition‐metal carbides and nitrides, have excellent electrical conductivity and unique optical properties. However, MXenes oxidize in ambient conditions, which is accelerated upon heating. Intercalation of water also causes hydrolysis accelerating oxidation. Developing new tools to readily characterize MXenes’ thermal stability can enable deeper insights into their structure–property relationships. Here, in situ spectroscopic ellipsometry (SE) is employed to characterize the optical properties of three types of MXenes (Ti3C2T
x , Mo2TiC2Tx , and Ti2CTx ) with varied composition and atomistic structures to investigate their thermal degradation upon heating under ambient environment. It is demonstrated that changes in MXene extinction and optical conductivity in the visible and near‐IR regions correlate well with the amount of intercalated water and hydroxyl termination groups and the degree of oxidation, measured using thermogravimetric analysis. Among the three MXenes, Ti3C2Tx and Ti2CTx , respectively, have the highest and lowest thermal stability, indicating the role of transition‐metal type, synthesis route, and the number of atomic layers in MXene flakes. These findings demonstrate the utility of SE as a powerful in situ technique for rapid structure–property relationship studies paving the way for the further design, fabrication, and property optimization of novel MXene materials. -
Restacking of two-dimensional (2D) flakes reduces the accessibility of electrolyte ions and is a problem in energy storage and other applications. Organic molecules can be used to prevent restacking and keep the interlayer space open. Here, we report on a combined theoretical and experimental investigation of the interaction between 2D titanium carbide (MXene), Ti 3 C 2 T x , and glycine. From first principle calculations, we presented the functionalization of glycine on the Ti 3 C 2 O 2 surface, evidenced by the shared electrons between Ti and N atoms. To experimentally validate our predictions, we synthesized flexible freestanding films of Ti 3 C 2 T x /glycine hybrids. X-ray diffraction and X-ray photoelectron spectroscopy confirmed the increased interlayer spacing and possible Ti–N bonding, respectively, which agree with our theoretical predictions. The Ti 3 C 2 T x /glycine hybrid films exhibited an improved rate and cycling performances compared to pristine Ti 3 C 2 T x , possibly due to better charge percolation within expanded Ti 3 C 2 T x .more » « less
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