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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Nb4C3 by Materials Project

Nb4C3 is MAX Phase-derived structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Nb4C3 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Nb3+ sites. In the first Nb3+ site, Nb3+ is bonded to six C4- atoms to form a mixture of edge and corner-sharing NbC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.24 Å) and three longer (2.27 Å) Nb–C bond lengths. In the second Nb3+ site, Nb3+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Nb–C bond lengths are 2.17 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to six Nb3+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the second C4- site, C4- is bonded to six equivalent Nb3+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb4C3 by Materials Project

Nb4C3 is MAX Phase-derived structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Nb4C3 sheets oriented in the (0, 0, 1) direction. there are four inequivalent Nb3+ sites. In the first Nb3+ site, Nb3+ is bonded to six C4- atoms to form a mixture of distorted edge and corner-sharing NbC6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.27 Å) and three longer (2.28 Å) Nb–C bond lengths. In the second Nb3+ site, Nb3+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Nb–C bond lengths are 2.16 Å. In the third Nb3+ site, Nb3+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Nb–C bond lengths are 2.18 Å. In the fourth Nb3+ site, Nb3+ is bonded to six C4- atoms to form a mixture of edge and corner-sharing NbC6 octahedra. There are three shorter (2.24 Å) and three longer (2.26 Å) Nb–C bond lengths. There are three inequivalent C4- sites. In the first C4- site, C4- is bonded to six Nb3+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the second C4- site, C4- is bonded to six Nb3+ atoms to form a mixture of edge, corner, and face-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 47°. In the third C4- site, C4- is bonded to six Nb3+ atoms to form a mixture of edge, corner, and face-sharing CNb6 octahedra. The corner-sharing octahedra tilt angles range from 1–47°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb4C3 by Materials Project

Nb4C3 crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. there are two inequivalent Nb3+ sites. In the first Nb3+ site, Nb3+ is bonded in a square co-planar geometry to four equivalent C4- atoms. All Nb–C bond lengths are 2.24 Å. In the second Nb3+ site, Nb3+ is bonded to six equivalent C4- atoms to form corner-sharing NbC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Nb–C bond lengths are 2.24 Å. C4- is bonded to six Nb3+ atoms to form a mixture of corner and edge-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb4SiC3 by Materials Project

Nb4C3Si is MAX Phase structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two silicon molecules and two Nb4C3 sheets oriented in the (0, 0, 1) direction. In each Nb4C3 sheet, there are two inequivalent Nb2+ sites. In the first Nb2+ site, Nb2+ is bonded to six C4- atoms to form a mixture of edge and corner-sharing NbC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.25 Å) and three longer (2.28 Å) Nb–C bond lengths. In the second Nb2+ site, Nb2+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Nb–C bond lengths are 2.20 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to six equivalent Nb2+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the second C4- site, C4- is bonded to six Nb2+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Vanadium and Niobium MXenes—Bilayered V 2 O 5 Asymmetric Supercapacitors

MXenes offer high metallic conductivity and redox capacitance that are attractive for high-power, high-energy storage devices. However, they operate limitedly under high anodic potentials due to irreversible oxidation. Pairing them with oxides to design asymmetric supercapacitors may expand the voltage window and increase the energy storage capabilities. Hydrated lithium preintercalated bilayered V 2 O 5 ( δ-Li x V 2 O 5 ·nH 2 O) is attractive for aqueous energy storage due to its high Li capacity at high potentials; however, its poor cyclability remains a challenge. To overcome its limitations and achieve a wide voltage window and excellent cyclability, it is combined with V 2 C and Nb 4 C 3 MXenes. Asymmetric supercapacitors employing lithium intercalated V 2 C (Li-V 2 C) or tetramethylammonium intercalated Nb 4 C 3 (TMA-Nb 4 C 3 ) MXenes as the negative electrode, and a δ-Li x V 2 O 5 ·nH 2 O composite with carbon nanotubes as the positive electrode in 5 m LiCl electrolyte operate over wide voltage windows of 2 and 1.6 V, respectively. The latter shows remarkably high cyclability—capacitance retention of ≈95% after 10 000 cycles. Here, this work highlights the importance of selecting appropriate MXenes to achieve a wide voltage window and a long cycle life in combination with oxide anodes to demonstrate the potential of MXenes beyond Ti 3 C 2 in energy storage.

36 MATERIALS SCIENCE↗