The carbides and nitrides of transition metals known as “MXenes” refer to a fast-growing family of two-dimensional materials discovered in 2011. Thanks to their unique nanolayer structure, superior electrical, mechanical, and thermal properties, MXenes have shown great potential in addressing the critical overheating issues that jeopardize the performance, stability, and lifetime of high-energy-density components in modern devices such as microprocessors, integrated circuits, and capacitors, etc. The outstanding intrinsic thermal conductivity of MXenes has been proved by experimental and theoretical research. Numerous MXenes-enabled high thermal conductivity composites incorporated with polymer matrix have also been reported and widely used as thermal management materials. Considering the booming heat dissipation demands, MXenes-enabled thermal management material is an extremely valuable and scalable option for modern electronics industries. However, the fundamental thermal transport mechanisms behind the MXenes family remain unclear. The MXene thermal conductivity disparities between the theoretical prediction and experimental results are still significant. To better understand the thermal conduction in MXenes and provide more insights for engineering high-performance MXene thermal management materials, in this article, we summarize recent progress on thermal conductive MXenes. The essential factors that affect MXenes intrinsic thermal conductivities are tackled, selected MXenes-polymer composites are highlighted, and prospects and challenges are also discussed.

Atomically thin Pt nanolayers were synthesized on the surface of Mo₂TiC₂ MXenes and used for the catalytic dehydrogenation of ethane and propane into ethylene and propylene, two important chemicals for the petrochemical industry. As compared with Pt nanoparticles, the atomically thin Pt nanolayer catalyst showed superior coke-resistance (no deactivation for 24 h), high activity (turnover frequencies (TOFs) of 0.4–1.2 s⁻¹), and selectivity (> 95%) toward ethylene and propylene. The unique Pt nanolayer has a similar geometric surface to Pt nanoparticles, enabling the investigations of the electronic effect on the catalytic performance, where the geometric effect is negligible. It is found that the electronic effect plays a critical role in dehydrogenative product selectivity and catalyst stability. The metal–support interaction is found dependent on the substrate and metal components, providing wide opportunities to explore high-performance MXene-supported metallic catalysts.

The development of cost-effective electrocatalysts for overall water splitting is highly desirable, remaining a critical challenge at current stage. Herein, a class of composite FeNi@MXene (Mo₂TiC₂T_x)@nickel foam (NF) has been synthesized through introducing Fe²⁺ ions and in-situ combining with surface nickel atoms on nickel foam. The obtained FeNi@Mo₂TiC₂T_x@NF exhibited high activity with overpotentials of 165 and 190 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at a current density of 10 mA·cm^-2, respectively. The synergetic effects of Mo₂TiC₂T_x and FeNi nanoalloys lead to increasing catalytic activities, where MXene provides high active surface area and rich active sites for HER, and FeNi nanoalloys promote the OER. Theoretical simulation of electron exchange capacity between FeNi and MXene in FeNi@Mo₂TiC₂T_x catalyst shows that electrons transferred from surface Mo atoms to the interface between FeNi and MXene, indicating that the electrons are accumulated near the FeNi nanoparticles. This kind of electronic distribution facilitates the formation of intermediate of NiOOH. Correspondingly, (H⁺ + e^-) is more inclined onto Mo–Ni interfaces for HER. The Gibbs free energy changes for H* to HER and potential-limiting step for -OOH intermediate in OER over FeNi@Mo₂TiC₂T_x are much less than those on bare MXene. The catalyst can be further used for overall water splitting in alkaline solution, realizing a current density of 50 mA·cm^-2 at 1.74 V. This work provides a facile strategy to achieve efficient and cheap catalysts for new energy production.

As more than 60% of worldwide consumed energy is unused and becomes waste heat every year, high-efficiency waste heat to power technologies are highly demanded for the conversion of wasted heat to electricity. Thermoelectrics which can convert the wasted heat directly into electricity represent a promising approach for energy recovery. Thermoelectric technology has existed for several decades, but its usage has been limited due to low efficiencies. Recent advances in nanotechnology have enabled the improving of thermoelectric properties which open up the thermoelectrics' feasibility in industry. In this paper, we present an overview of recent progress in increasing the porosity of thermoelectric materials from atomic scale to microscale, leading to the enhancement of figure of merit.

Anisotropy and inhomogeneity are ubiquitous in spark plasma sintered thermoelectric devices. However, the origin of inhomogeneity in thermoelectric nanocomposites has rarely been investigated so far. Herein, we systematically study the impact of inhomogeneity in spark plasma sintered bismuth antimony telluride (BiSbTe) thermoelectric nanocomposites fabricated from solution-synthesized nanoplates. The figure of merit can reach 1.18, which, however, can be overestimated to 1.88 without considering the inhomogeneity. Our study reveals that the inhomogeneity in thermoelectric properties is attributed to the non-uniformity of porosity, textures and elemental distribution from electron backscatter diffraction and energy-dispersive spectroscopy characterizations. This finding suggests that the optimization of bulk material homogeneity should also be actively pursued in any future thermoelectric material research.

Thermoelectric materials, which can convert waste heat into electricity, have received increasing research interest in recent years. This paper describes the recent progress in thermoelectric nanocomposites based on solution-synthesized nanoheterostructures. We start our discussion with the strategies of improving the power factor of a given material by using nanoheterostructures. Then we discuss the methods of decreasing thermal conductivity. Finally, we highlight a way of decoupling power factor and thermal conductivity, namely, incorporating phase-transition materials into a nanowire heterostructure. We have explored the lead telluride–copper telluride thermoelectric nanowire heterostructure in this work. Future possible ways to improve the figure of merit are discussed at the end of this paper.

We synthesized Cu_3.8Ni/CoO and Cu_3.8Ni/MnO nanoparticles via an easy and scalable solution synthesis. The synthesized Cu_3.8Ni/CoO and Cu_3.8Ni/MnO nanoparticles were annealed to remove the organic surfactants without phase transitions or side reactions. Electrons can be transferred via metallic Cu_3.8Ni, which will not react with lithium ions. The heterogeneous structures of Cu_3.8Ni/CoO and Cu_3.8Ni/MnO nanoparticles could enhance the lithium ion mobility and improve the life cycle, and these materials are therefore promising candidates as high- power-density and high-energy-density anode materials for lithium-ion batteries in diverse applications, such as electrical vehicles.

We demonstrate an easy and scalable low-temperature process to convert porous ternary complex metal oxide nanoparticles from solution-synthesized core/shell metal oxide nanoparticles by thermal annealing. The final products demonstrate superior electrochemical properties with a large capacity and high stability during fast charging/discharging cycles for potential applications as advanced lithium-ion battery (LIB) electrode materials. In addition, a new breakdown mechanism was observed on these novel electrode materials.

We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hotpressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit (ZT) of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.