Superior Thermoelectric Performance of Ordered Double Transition Metal MXenes: Cr₂TiC₂T₂ (T = −OH or −F)

Abstract

Using SCAN-rVV10+U, we show Cr2TiC2 and Cr2TiC2T2 (T = −F and −OH) MXenes are moderate band gap semiconductors mostly in the antiferromagnetic state. All investigated MXene structures show large Seebeck coefficients (>400 μV/K), especially Cr2TiC2 (>800 μV/K) and Cr2TiC2F2 (>700 μV/K). The hole relaxation time of p-type Cr2TiC2(OH)2 is found to be ∼8 ps, ensuring its superior electron transport properties in comparison to other investigated MXenes. It is also discovered that the surface functionalization could decrease the phonon thermal conduction and that Cr2TiC2(OH)2 has the smallest lattice thermal conductivity (∼6.5 W/m·K) and the largest electron thermal conduction (>50 W/m·K with n = 1019 cm–3). We predict the ZT value of p-type Cr2TiC2(OH)2 can reach 3.0 at 600 K with the maximum thermoelectric conversion efficiency of 20%. Overall, the thermoelectric property of Cr-based ordered double transition metal MXenes is far superior to that of any known two-dimensional structures in the MXene family.

Progress and biomedical applications of MXenes

“…[ 56 ] It is worth noting that Ti 2 CO 2 , Zr 2 CO 2 , Hf 2 CO 2 , Sc 2 CO 2 , Sc 2 C(OH) 2 , Cr 2 C(OH) 2 , Cr 2 CF 2 , and Sc 2 CF 2 are considered to be semiconductors and non‐magnetic among MXenes. [ 57 ] The magnetic properties of MXenes include ferromagnetic(such as Cr 2 C [ 58 ] )and antiferromagnetic (such as Ti 3 C 2 , Cr 2 TiC 2 F 2 [ 59 ] ). [ 60 ] Similar to the optical and electrical properties, the magnetic properties of MXenes are also affected by many factors such as the composition of “M” and surface termination.…”

Nb2CTx MXene as High-Performance Energy Storage Material with Na, K, and Liquid K–Na Alloy Anodes

“…; n = 1, 2, 3; X = C or N; and T represents terminal groups, like OH, O, F, Cl, etc. − The variety of terminal groups enables it to own great hydrophilicity and compatibility with many solvents. , Previous research studies proved that MXenes have a much lower diffusion barrier for ions with larger diameters, such as Na + and K + , with real benefits to fast charging/discharging processes for battery systems except Li-ion batteries. − Its interlamellar space is open for ions to intercalate. , Moreover, MXene is metallic, with good electrical conductivity and mechanical flexibility, so it can serve as a promising candidate in numerous applications, such as alkali-ion battery systems, − supercapacitation, , sensing, , H 2 storage, , catalysis, , etc. Apart from the first-reported Ti 3 C 2 T x , many other Mxenes have been successfully prepared and reported over the years, such as Ti 2 CT x , Ti 2 NT x , V 2 CT x , Mo 2 TiC 2 T x , V 4 C 3 T x , Nb 4 C 3 T x , Ta 4 C 3 T x , Ti 3 CNT x , Cr 2 TiC 2 T x , Zr 3 C 2 T x , Hf 3 C 2 T x , etc. − Besides, plenty of MXene-based composite materials have been developed and utilized in various fields. − When used in energy storage systems, including all kinds of batteries and supercapacitors, MXenes, as well as its composites, show extremely remarkable electrochemical performance, − even though exploitation of more high-performance MXene materials and their study is far from enough.…”

High Thermoelectric Performance in the Cubic Inorganic Cesium Iodide Perovskites CsBI3 (B = Pb, Sn, and Ge) from First-Principles

“…Such an unprecedented progress in PSCs is mainly associated with the unique physicochemical properties of HPMs, including large light absorption coefficients, defect tolerance, , tunable band gap, and diversity in crystal structure. Moreover, it was found that HPMs exhibit ultralow thermal conductivity and high carrier mobility, − which promise them as potential alternatives to the conventional thermoelectric materials (TMs). − …”