NiS2–MXene hybrid composite: Facile synthesis and improved hydrogen storage properties of magnesium hydride

Abstract

We employed a one-step hydrothermal method to in situ grow spherical NiS2 nanoparticles on the surface of MXene, successfully constructing a NiS2–MXene hybrid composite. This study demonstrates that the integration of a NiS2–MXene hybrid composite into MgH2 substantially improves its hydrogen storage performance. Specifically, the composite reduces the initial dehydrogenation temperature of MgH2 by 118°C, lowering it from 310°C (pure MgH2) to 192°C. At 300°C, it can release 5.87wt% of hydrogen within 12 min. Furthermore, it demonstrates the ability to absorb hydrogen under ambient temperature conditions, with approximately 2.96wt% of hydrogen being absorbed as the temperature increases from room temperature to 50°C. The activation energies for hydrogenation and dehydrogenation of the NiS2–MXene–MgH2 composite reduced by 33.7 and 40.6 kJ·mol−1, respectively, in comparison to those of pure MgH2. Mechanistic studies demonstrate that NiS2–MXene enhances hydrogen storage performance through multiple synergistic effects. Specifically, the multivalent titanium in MXene establishes efficient electron transport pathways, promoting hydrogen binding and dissociation. Moreover, the in situ formation of Mg2Ni/Mg2NiH4 and MgS creates numerous phase interfaces, offering abundant active sites that facilitate both the dissociation and recombination of hydrogen molecules. Furthermore, the high specific surface area of MXene effectively inhibits agglomeration between the catalyst and Mg/MgH2, thereby maintaining structural stability and reactivity.

1. Introduction

Hydrogen energy is recognized as a clean energy source and has attracted significant interest owing to its environmentally friendly nature and high efficiency. However, its application in the transportation sector remains considerably constrained, primarily due to unresolved safety challenges associated with hydrogen storage and transportation. Among various types of hydrogen storage materials, NaBH4 and AlH3 offer certain advantages, yet their widespread use is limited by issues such as poor reversibility and demanding reaction conditions. As a result, magnesium-based materials have emerged as a promising research focus owing to their superior overall performance [1–6]. Nonetheless, their practical deployment still suffers from issues such as high hydrogenation/dehydrogenation temperatures and sluggish kinetics.

To overcome these drawbacks, researchers have proposed various modification strategies, including alloying [7–10], nanostructuring [11–13], and the addition of catalysts [14–20]. Among these approaches, the introduction of catalysts has emerged as one of the most effective methods for improving the hydrogen storage capabilities of magnesium-based materials due to its simplicity and significant impact. In recent years, the development of catalysts for MgH2 has evolved from the use of single metals or simple compounds to the design of composite catalyst systems that leverage synergistic effects among multiple components and interfaces. This shift aligns with the trends reviewed in recent literature [21], which systematically summarizes the research progress in multi-component materials and high-entropy materials for catalyzing Mg-based hydrogen storage systems, with a focus on catalyst categories and performance optimization strategies, and further outlines prospective research directions for advancing their practical application. In addition, as summarized in earlier literature [22–25], a variety of catalysts—including carbon-based materials, metal oxides, high-entropy borides, and emerging MXenes—have effectively enhanced the hydrogen sorption kinetics of MgH2 through mechanisms such as facilitating hydrogen diffusion pathways, increasing active sites, promoting electron migration, and weakening Mg–H bonds.

Beyond these conventional strategies, interface engineering has emerged as a paradigm shift recognized as a key approach to fundamentally transforming magnesium-based hydrogen storage systems [26]. Jiang et al. [27] emphasized in their forward-looking review that precise design of one-dimensional, two-dimensional, and three-dimensional interface structures can modulate hydrogen storage kinetics while achieving an optimal balance between thermodynamic instability and kinetic enhancement. This framework opens new perspectives for designing next-generation high-performance hydrogen storage materials. Shi et al. [26] designed transition metal oxides through anionic modulation (fluorination), significantly improving the hydrogen storage performance of MgH2. This work reported for the first time on the interaction between partially reduced fluorinated titanium dioxide and MgH2