Stabilizing sulfur vacancy defects by performing "click" chemistry of ultrafine palladium to trigger a high-efficiency hydrogen evolution of MoS2

Scalable Bottom-Up Synthesis of High-Purity 1T-MoS2 Assisted by Na2SO4 Template

MoS2 is a promising layered material for energy storage fields owing to its phase-dependent physicochemical properties. However, the scalable synthesis of 1T-MoS2 is challenging due to the inherently high generation energy. Inspired by alkali-metal-induced phase transitions of 2H-MoS₂, we developed a sodium-mediated synthesis strategy using Na2SO4 as the phase transition inducer, growth template and S source for the bottom-up synthesis of 1T-MoS2. Theoretical calculations showed that the distortion of Mo─Mo and Mo─S bonds and the change of the formation energy of 2H- and 1T-MoS2 caused by the adsorption of electron donating Na were the fundamental reasons for the formation and stability of octahedral 1T-MoS2. In situ analysis confirmed that Na2SO4 guided the epitaxial growth of MoS2 by slowly releasing H2S, and the formation of intermediates NaMoOx and NaMoSx were the key to the generation of 1T phase. Systematic optimization identified 16-18 vol% hydrogen concentration as the critical parameter for achieving high-phase-purity metallic MoS₂. As a catalyst for hydrogen evolution reaction, the overpotential and Tafel slope of 1T-MoS2 is 37.4 mV and 32.2 mV/dec, respectively. This preparation strategy enables large-scale production of metastable MoS2 while maintaining exceptional crystallinity and phase purity, providing new opportunities for phase engineering of transition metal dichalcogenide.

Harnessing Near-Infrared Light for Highly Efficient Photocatalysis

Near-infrared (NIR) light, accounting for approximately 50 % of solar light, cannot directly excite photocatalytic reactions due to its lower energy, which severely restricts the photocatalytic solar energy conversion efficiency and hinders the application of photocatalysis. To overcome this dilemma, some viable strategies have been proposed to harness NIR light for enhancing photocatalytic performance based on material structure, composition, and function designs, and obvious progresses have been witnessed. In this review, the basic principles and representative advances in photocatalyst heterojunction designs (including p-n junctions, S-scheme, Z-scheme, and type-ІІ heterojunctions), photocatalyst composition and function designs (such as preparing rare earth element doped upconversion photocatalysts, rare earth upconversion photocatalytic hybrids and triplet-triplet annihilation upconversion photocatalytic composites), and photothermal-photocatalytic bifunction designs for NIR light utilization are exclusively scrutinized. Meanwhile, the applications of the above-mentioned NIR responsive photocatalyst composites in energy and environmental fields are summarized. Importantly, the challenges and outlooks in the field of NIR light harnessing for efficient photocatalysis are proposed, which may provide theoretical and experimental guidance to those working in solar energy conversion and utilization and other related fields.

Enhancing Hydrogen Evolution Reaction Activity of Palladium Catalyst by Immobilization on MXene Nanosheets

Efficient catalysts with minimal content of catalytically active noble metals are essential for the transition to the clean hydrogen economy. Catalyst supports that can immobilize and stabilize catalytic nanoparticles and facilitate the supply of electrons and reactants to the catalysts are needed. Being hydrophilic and more conductive compared with carbons, MXenes have shown promise as catalyst supports. However, the controlled assembly of their 2D sheets creates a challenge. This study established a lattice engineering approach to regulate the assembly of exfoliated Ti3C2Tx MXene nanosheets with guest cations of various sizes. The enlargement of guest cations led to a decreased interlayer interaction of MXene lamellae and increased surface accessibility, allowing intercalation of Pd nanoparticles. Stabilization of Pd nanoparticles between interlayer-expanded MXene nanosheets improved their electrocatalytic activity. The Pd-immobilized K+-intercalated MXene nanosheets (PdKMX) demonstrated exceptional electrocatalytic performance for the hydrogen evolution reaction with the lowest overpotential of 72 mV (@10 mA cm-2) and the highest turnover frequency of 1.122 s-1 (@ an overpotential of 100 mV), which were superior to those of the state-of-the-art Pd nanoparticle-based electrocatalysts. Weakening of the interlayer interaction during self-assembly with K+ ions led to fewer layers in lamellae and expansion of the MXene in the c direction during Pd anchoring, providing numerous surface-active sites and promoting mass transport. In situ spectroscopic analysis suggests that the effective interfacial electron injection from the Pd nanoparticles strongly immobilized on interlayer-expanded PdKMX may be responsible for the improved electrocatalytic performance.

Stable Mo/1T-MoS2 Monolith Catalyst with a Metallic Interface for Large Current Water Splitting

To achieve global carbon neutrality, the realization of highly active and stable catalysts is critical for water splitting to produce green hydrogen (H₂). MoS₂ is considered to be the most promising non-precious metal catalyst for H₂ evolution because of its excellent properties. Herein, we report a metal-phase MoS₂ (1T-MoS₂) synthesized using a simple hydrothermal method. Using a similar procedure, we synthesize a monolithic catalyst (MC) in which 1T-MoS₂ is vertically bonded to a metal molybdenum plate via strong covalent bonds. These properties endow the MC with an extremely low-resistance interface and mechanical robustness, equipping it with outstanding durability and fast charge transfer. Results show that the MC can achieve stable water splitting at 350 mA cm^-2 current density with a low 400 mV overpotential. The MC exhibits negligible performance decay after 60 h of operation at a large current density of 350 mA cm^-2. This study provides a novel possible MC with robust and metallic interfaces to achieve technically high current water splitting to produce green H₂.

A Metal-Organic Frameworks Derived 1T-MoS2 with Expanded Layer Spacing for Enhanced Electrocatalytic Hydrogen Evolution

Metal phase molybdenum disulfide (1T-MoS₂ ) is considered a promising electrocatalyst for hydrogen evolution reaction (HER) due to its activated basal and superior electrical conductivity. Here, a one-step solvothermal route is developed to prepare 1T-MoS₂ with expanded layer spacing through the derivatization of a Mo-based organic framework (Mo-MOFs). Benefiting from N,N-dimethylformamide oxide as external stress, the interplanar spacing of (002) of the MoS₂ catalyst is extended to 10.87 Å, which represents the largest one for the 1T-MoS₂ catalyst prepared by the bottom-up approach. Theoretical calculations reveal that the expanded crystal planes alter the electronic structure of 1T-MoS₂ , lower the adsorption-desorption potentials of protons, and thus, trigger efficient catalytic activity for HER. The optimal 1T-MoS₂ catalyst exhibits an overpotential of 98 mV at 10 mA cm^-2 for HER, corresponding to a Tafel slope of 52 mV dec^-1 . This Mo-MOFs-derived strategy provides a potential way to design high-performance catalysts by adjusting the layer spacing of 2D materials.

Engineering Interface on a 3D CoxNi1-x(OH)2@MoS2 Hollow Heterostructure for Robust Electrocatalytic Hydrogen Evolution

Clarifying the responsibilities and constructing the synergy of different active phases are of great significance but still an urgent challenge for the heterostructure catalyst to improve the hydrogen evolution reaction (HER) process. Here, three-dimensional (3D) Co_xNi_(1-x)(OH)₂ hollow structure integrating MoS₂ nanosheet catalysts [Co_xNi_(1-x)(OH)₂@MoS₂] were ingeniously designed and prepared. This unique structure has realized the construction of a dual active phase for the optimized stepwise-synergetic hydrogen evolution process over a universal pH range through interface assembly engineering. Meanwhile, the 3D hollow heterostructure with a high surface-to-volume ratio can effectively avoid the agglomeration of MoS₂ and enhance the Co_xNi_(1-x)(OH)₂-MoS₂ heterointerfaces. Thus, superior HER activity and stability were obtained over the universal pH range. Density functional theory calculation reveals that Co_xNi_(1-x)(OH)₂ and MoS₂ phases provide efficient active sites for rate-determining water dissociation and H* adsorption/H₂ generation on Co_xNi_(1-x)(OH)₂-MoS₂ heterointerfaces, respectively, resulting in an optimized energy barrier for HER. This work proposes a constructive strategy to design highly efficient electrocatalysts based on the heterointerface with a defined responsible active phase of electrocatalysts.

Ultrahigh activity of molybdenum/vanadium-doped Ni-Co phosphides nanoneedles based on ion-exchange for hydrogen evolution at large current density

Heteroatom doping is a promising strategy to optimize the electronic structure of transition metal phosphides so enhancing the hydrogen evolution reaction (HER). However, complex and harsh experimental design is often required to achieve homogeneous doping of corresponding elements while achieving the best regulating effect. Herein, a facile ion-exchange (IE) strategy is applied to dope Mo/V species evenly into Ni-Co phosphides under mild conditions while maintaining the nanoneedle morphology. The electrochemical characterization verifies Mo dopants have a better electronic regulation effect on NiCoP crystal than V dopants, corresponding to the better hydrogen evolution performance of Mo-NiCoP/NF. Notably, due to the highly dispersed nanoneedle morphology, the synergistic effect of Ni-Co phosphides, and the optimized electronic structure, Mo-NiCoP/NF demonstrates a higher activity than that of the noble metal Pt/C at the high current density (>99 mA cm^-2). The present work is supposed to open new sights for the development of high-performance catalysts by ion-exchange strategy.

Flower-like 1T-MoS2/NiCo2S4 on a carbon cloth substrate as an efficient electrocatalyst for the hydrogen evolution reaction

The 1T-MoS₂/NiCo₂S₄ composite in situ grown on carbon cloth (CC) was successfully prepared by a two-step hydrothermal method as an efficient electrode for the hydrogen evolution reaction. The morphology and composition characterization show that the composite has a flower-like structure with a large number of edges and surfaces exposed, and the content of the 1T phase in MoS₂ is 63%. 1T-MoS₂/NiCo₂S₄/CC exhibits an overpotential of 107 mV at 10 mA cm^-2, and a Tafel slope of 66.4 mV dec^-1 in an alkaline electrolyte. After continuous electrolysis for 24 h at an overpotential of 170 mV, 86% of the original current density was retained in an chronoamperometry measurement. The outstanding catalytic performance of the composite is ascribed to its unique structure, high 1T-MoS₂ content and the synergistic catalysis between 1T-MoS₂ and NiCo₂S₄. This work provides a facile and effective strategy for fabricating the 1T-MoS₂/NiCo₂S₄/CC composite and demonstrates that the composite is expected to be a competitive non-noble HER catalyst.

Ferromagnetism of two-dimensional transition metal chalcogenides: both theoretical and experimental investigations

In recent years, with the fast development of integrated circuit electronic devices and technologies, it has become urgent to improve the density of data storage and lower the energy losses of devices. Under these circumstances, two-dimensional (2D) materials, which have a smaller size and lower energy loss compared with bulk materials, are becoming ideal candidates for future spintronic devices. Among them, 2D transition metal chalcogenides (TMCs), which have excellent electronic and optical properties, have attracted great attention from researchers. However, most of them are intrinsically non-magnetic, which severely hinders their further applications in spintronics. Therefore, introducing intrinsic room-temperature ferromagnetism into 2D TMC materials has become an important issue in spintronics. In this work, we review the introduction of intrinsic ferromagnetism into typical 2D TMCs using various strategies, such as defect engineering, doping with transition metal elements, and phase transfer. Additionally, we found that their ferromagnetism could be adjusted via changing the experimental conditions, such as the nucleation temperature, ion irradiation dose, doping amount, and phase ratio. Finally, we provide some insight into prospective solutions for introducing ferromagnetism into 2D TMCs, hoping to shed some light on future spintronics development.

Engineering sulfur vacancies into Fe9S10 nanosheet arrays for efficient alkaline hydrogen evolution

The development of Earth-abundant transition metal sulfide electrocatalysts with excellent activity and stability toward the alkaline hydrogen evolution reaction (HER) is critical but challenging. Iron-based sulfides are favored due to their economic benefits and good stability, but their intrinsic catalytic activity still needs to be improved urgently. Herein, we successfully prepared Fe₉S₁₀ nanosheet arrays on iron foam (Fe₉S₁₀/IF) through a simple one-step method and utilized plasma treatment to introduce S vacancies (Fe₉S₁₀-V_s/IF) to regulate their intrinsic catalytic activity. The final materials demonstrate excellent HER performance, and only need 149 mV to drive a current density of 10 mA cm^-2 and a small Tafel slope of 50 mV dec^-1. The experimental results show that the existence of S vacancies can enhance their intrinsic electrocatalytic activity. This work provides a reference value for the future regulation of iron-based sulfides and is devoted to the development of non-precious metal catalysts toward the HER.