In recent years, MXene 2D materials have shown great application potential in catalysis, electrochemical energy storage, sensors and other fields due to their excellent electrical conductivity, high specific surface area and abundant surface functional groups. In order to further improve the performance of MXene, researchers have tried to combine various components, such as organic molecules, polymers, metals and semiconductor materials, with MXene to form MXene composites. However, the problems of MXene oxidation and nanoparticle agglomeration in the synthesis of MXene composites by the traditional solution method limit its application. Therefore, it is of great significance to develop a green and efficient synthesis method for MXene composites.

To address the above problems, Hee-Tae Jung et al., Korea Advanced Institute of Science and Technology (KAIST), proposed a solution-free composite hybrid nanostructure synthesis method of MXene, which uses rapid Joule heating technology to overcome the shortcomings of MXene oxidation in the synthesis process of traditional solution method. MXene composite hybrid nanostructures containing Pt, Co, Cu, Ni, Fe, Pd and their alloys were synthesized by loading precursors onto MXene substrates and applying rapid thermal shock. The experimental results show that the rapid Joule heating technique has many advantages, including minimization of MXene oxidation, uniform distribution of hybrid components without severe agglomeration, and homogeneity of multicomponent alloy synthesis. The effectiveness of this method was demonstrated by the synthesis of Pt-MXene nanocomposites, which showed excellent electrocatalytic activity and stability in the hydrogen precipitation reaction (HER). This technology not only retains the unique properties of MXene, but is also suitable for a variety of application scenarios, especially in areas where the synergies of MXene composites can bring significant performance improvements. 

1. Solution-free synthesis method: Rapid Joule heating technology is used to avoid the problems of MXene oxidation and nanoparticle agglomeration in the traditional solution method, and the excellent performance of MXene is retained.

2. Uniform dispersion: The uniform distribution of metal nanoparticles on the surface of MXene is realized, the agglomeration phenomenon is avoided, and the electrocatalytic activity of the material is improved.

3. Multi-element alloy synthesis: binary, ternary, quaternary, five-element and six-element metal alloy nanoparticles have been successfully synthesized, providing more possibilities for the performance regulation of MXene composites.

4. Excellent HER catalytic performance: The synthetic Pt-MXene composite material shows excellent catalytic activity of hydrogen evolution reaction, low overpotential, good stability, and has broad application prospects.

Figure 1 Outlines the process of preparing MXene nanocomposites using a rapid Joule heating technique. In this study, Ti3C2Tx MXene was obtained by chemical wet etching, and its surface was verified by XPS to be rich in oxygen and hydroxyl groups. The method is also applicable to other MXene materials, such as Ti2CTx. MXene aerogel is used as the substrate, which provides abundant active sites to support metal nanoparticles due to its high specific surface area. Rapid Joule heating technology rapidly raises the temperature of the substrate by applying a high electrical pulse, lasting only 75 milliseconds. During this process, metal precursors migrate along the substrate surface and deposit rapidly at defect sites, thus forming uniformly distributed metal nanoparticles (NPs) on the surface of MXene. The TEM image of Figure 1B shows the uniform distribution of Pt nanoparticles on Ti3C2Tx MXene, and the presence and distribution of Pt nanoparticles are verified by HRTEM and TEM-EDS mapping.

FIG. 2 compares the surface structure and morphology of Pt-Ti3C2Tx MXene composite nanostructures prepared by rapid heating and traditional solution treatment. The Pt nanoparticles prepared by the rapid heating method showed high uniform dispersion, while the solution treatment method resulted in severe aggregation of Pt nanoparticles on the surface of MXene. In addition, the rapid heating method significantly reduced the oxidation of MXene, while the solution treatment method resulted in the oxidation of MXene to TiO2. XPS and XRD analysis further confirmed the protective effect of rapid heating method on MXene during the synthesis process and reduced oxidation.

Figure 3 shows the performance of rapidly heated Pt-MXene as an electrocatalyst in HER. Rapidly heated PT-Mxene exhibits low overpotential and high catalytic activity, with higher mass activity and lower Tafel slope compared to commercial Pt/C. This is attributed to the uniform distribution of Pt nanoparticles and the protection of the MXene surface during synthesis, thus maximizing the exposure of the catalytic active site. In addition, rapidly heated Pt-MXene showed excellent stability in long-term stability tests, far exceeding that of solution-treated Pt-MXene.

Figure 4 shows the ability of multiple multi-element metal nanoparticles synthesized by rapid Joule heating technique on MXene aerogel. By adjusting the ratio of metal precursors, metal nanoparticles ranging from binary to six-element alloys were synthesized successfully, and no significant phase separation was observed in the alloys. The HAADF-STEM and EDS mapping images confirm the successful synthesis of alloy nanoparticles, showing that the method is capable of synthesizing a wide range of alloy combinations while maintaining minimum oxidation of MXene, providing a broad space for adjusting material properties.

In conclusion, this study proposed a synthesis method of MXene composites based on rapid Joule heating technology, which can effectively avoid MXene oxidation and nanoparticle agglomeration, and achieve uniform distribution of metal nanoparticles on the surface of MXene. The results show that Pt-MXene composites synthesized by this method show excellent catalytic performance of hydrogen evolution reaction, low overpotential and good stability. In addition, the method can also be used to synthesize multi-metal alloy nanoparticles, which provides more possibilities for the property regulation of MXene composites. This study provides a new idea for the green and efficient synthesis of MXene composites, and is expected to promote its application in catalysis, electrochemical energy storage and other fields.