Investigation on the Structure–Performance Correlation of TiC MXenes as Cathode Catalysts for Li-O₂ Batteries

Abstract

Two-dimensional TiC MXenes have high stability and large specific surface area, as well as show great application prospect as cathode catalysts for Li-O 2 batteries. There are at least three different structures of TiC MXenes labeled as Ti 2 C, Ti 3 C 2 , and Ti 4 C 3 MXenes. Understanding the effect of structure on the catalytic activity of TiC MXenes is of great significance for the rational design of catalyst. In this study, the adsorption structures of H, O, F, and OH functional groups upon TiC MXenes under single atom and full coverage were first constructed. The results of first-principles calculation show that O has the highest adsorption energy, which means that O-terminated TiC MXenes are typical structures present. The overpotentials were used to assess the catalytic activity quantitatively for Ti 2 C, Ti 3 C 2 , and Ti 4 C 3 with and without O group. The catalytic activity follows such a trend: Ti 2 C < Ti 3 C 2 < Ti 4 C 3 < Ti 4 C 3 O 2 < Ti 3 C 2 O 2 < Ti 2 CO 2 . The electronic properties of the Ti 3d orbital near Fermi level for Ti 2 CO 2 MXene lead to its high catalytic activity. These findings provide theoretical guidance for the design of TiC MXenes as cathode catalysts in Li-O 2 batteries.

Straintronic Effect on Phonon-Mediated Superconductivity of Nb2CT2 (T = O, S, Se, or Te) MXenes

“…Since the first MXene (2D Ti 3 C 2 ) was reported in 2011, more than 30 MXenes have been experimentally synthesized and over 100 theoretically predicted . The electronic structures of MXenes vary widely from metallic to insulating, and MXenes have been used to produce materials with properties relevant to a variety of applications such as energy storage, − transparent conductors and heaters, − photo-thermal therapy, − photocatalysts, − thermoelectrics, − superconductors, , ferromagnets, , and topological insulators. − …”

Recent Advances in Titanium Carbide MXene (Ti3C2Tx) Cathode Material for Lithium–Air Battery

“…According to the experimental calculations, the estimated theoretical energy storage densities of Ti 4 C 3 O, Ti 3 C 2 O 2 , and Ti 2 CO 2 are 0.562, 0.476, and 0.372 kWh kg –1 , respectively, on the basis of the assumption that their SSA is ≈100 m 2 g –1 . , The study also shows that discharge potential for bare TiC MXene (Ti 3 C 2 ) was about 3.21 and 9.36 for ORR and OER, respectively, while for TiC MXene with O terminations (Ti 3 C 2 O 2 ), it reduced significantly, i.e., 0.18 V for ORR and 0.22 V for OER, concluding that oxygen terminations in TiC MXene have a stronger adsorption capacity to promote catalytic activity and, in turn, reduce the overpotential. , …”

“…65,129 The study also shows that discharge potential for bare TiC MXene (Ti 3 C 2 ) was about 3.21 and 9.36 for ORR and OER, respectively, while for TiC MXene with O terminations (Ti 3 C 2 O 2 ), it reduced significantly, i.e., 0.18 V for ORR and 0.22 V for OER, concluding that oxygen terminations in TiC MXene have a stronger adsorption capacity to promote catalytic activity and, in turn, reduce the overpotential. 48,130 TiC MXenes with different surface terminations effected electrode potential differently, while TiC MXenes with Oterminations had the fastest electronic transmission due to its high electron energy and they form transition metal oxides-like surfaces, which are active for redox reactions. 126,131 It was also revealed that TiC MXenes with O-terminations can provide additional catalytic sites for the formation as well as the decomposition of the deposited Li 2 O 2 and can facilitate growth on the Li 2 O 2 surface.…”

“…These surface terminations are generally a diverse combination of -F/-OH and -O and are attributed to the hydrophilic nature of MXenes. These terminations are difficult to predict prior to synthesis, while etchant and etching time play a significant role . MXenes possess excellent metallic conductivity like their parent MAX phase and can modify toward semiconductor-like behavior upon removal of A-layers. − Since the synthesis of first MXenes, more than 30 different MXenes have been synthesized experimentally from their corresponding parent phases.…”

“…These terminations are difficult to predict prior to synthesis, while etchant and etching time play a significant role . MXenes possess excellent metallic conductivity like their parent MAX phase and can modify toward semiconductor-like behavior upon removal of A-layers. − Since the synthesis of first MXenes, more than 30 different MXenes have been synthesized experimentally from their corresponding parent phases. The order of M atoms varies to maintain its structural stability, between M 2 X, M 3 X 2 , M 4 X 3 , and M 5 X 4 , etc., with a hexagonal crystal structure. , …”