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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.

Utilizing the latest SCAN-rVV10 density functional, we thoroughly assess the electrochemical properties of 35 Mo-based ordered double transition metal MXenes including clean Mo2MC2 (M = Sc, Ti, V, Zr, Nb,...

Using the SCAN-rVV10 density functional, the electrochemical properties of bare Mo-based ordered double-transition metal MXenes (Mo2MC2, M = Sc, Ti, V, Zr, Nb, Hf, Ta) as aluminum-ion battery anode materials are studied. By calculating the average adsorption energy for each layer in a symmetric multilayer adsorption configuration, we find that all investigated MXene structures could adsorb three layers of Al atoms on both upper and lower surfaces, leading to the high theoretical capacities ranging from 888.98 mAh g–1 (Mo2TaC2) to 1170.33 mAh g–1 (Mo2ScC2). The formation of a multilayer adsorption configuration for Al atoms on Mo-based MXenes is mainly attributed to the gradual decreasing of the valence charge transfer from the adsorption layer to the substrate. Then, the CI-NEB method is used to assess the diffusion performance of Al atoms adsorbed on MXenes for energy favorable zig-zag like migration pathways. It is revealed that the migration energy barrier is no larger than 0.20 eV for all seven Mo-based MXenes. Therefore, the intrinsic Mo-based double-transition metal MXenes are promising anode materials possessing both high energy storage density and fast ion diffusion dynamics for Al-ion batteries.

The doping effect of graphene nanoplatelets (GNPs) on electrical insulation properties of polyethylene (PE) was studied by combining experimental and theoretical methods. The electric conduction properties and trap characteristics were tested for pure PE and PE/GNPs composites by using a direct measurement method and a thermal stimulated current (TSC) method. It was found that doping smaller GNPs is more beneficial to decrease the conductivity of PE/GNPs. The PE/GNPs composite with smaller size GNPs mainly introduces deep energy traps, while with increasing GNPs size, besides deep energy traps, shallow energy traps are also introduced. These results were also confirmed by density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) method calculations. Therefore, doping small size GNPs is favorable for trapping charge carriers and enhancing insulation ability, which is suggested as an effective strategy in exploring powerful insulation materials.