Synergistic zinc doping and defect engineering toward MoS2 nanosheet arrays for highly efficient electrocatalytic hydrogen evolution

Engineering Rich Active Sites and Efficient Water Dissociation for Ni-Doped MoS2/CoS2 Hierarchical Structures toward Excellent Alkaline Hydrogen Evolution

Besides improving charge transfer, there are two key factors, such as increasing active sites and promoting water dissociation, to be deeply investigated to realize high-performance MoS₂-based electrocatalysts in alkaline hydrogen evolution reaction (HER). Herein, we have demonstrated the synergistic engineering to realize rich unsaturated sulfur atoms and activated O-H bonds toward the water for Ni-doped MoS₂/CoS₂ hierarchical structures by an approach to Ni doping coupled with in situ sulfurizing for excellent alkaline HER. In this work, the Ni-doped atoms are evolved into Ni(OH)₂ during alkaline HER. Interestingly, the extra unsaturated sulfur atoms will be modulated into MoS₂ nanosheets by breaking Ni-S bonds during the formation of Ni(OH)₂. On the other hand, the higher the mass of the Ni precursor (m_Ni) for the fabrication of our samples, the more Ni(OH)₂ is evolved, indicating a stronger ability for water dissociation of our samples during alkaline HER. Our results further reveal that regulating m_Ni is crucial to the HER activity of the as-synthesized samples. By regulating m_Ni to 0.300 g, a balance between increasing active sites and promoting water dissociation is achieved for the Ni-doped MoS₂/CoS₂ samples to boost alkaline HER. Consequently, the optimal samples present the highest HER activity among all counterparts, accompanied by reliable long-term stability. This work will promise important applications in the field of electrocatalytic hydrogen evolution in alkaline environments.

meta-Position synergistic effect induced by Ni-Mo co-doped WSe2 to enhance the hydrogen evolution reaction

Transition metal dichalcogenides have been the most attractive two-dimensional layered materials for electrocatalytic hydrogen evolution due to their unique structure and multi-phase electronic states. However, the enhancement of the WSe₂ electrocatalytic hydrogen evolution reaction (HER) performance by bimetal co-doping has been rarely reported. Herein, the NiMo-WSe₂ catalyst has been synthesized by a one-step hydrothermal reaction, with lower overpotentials of 177 and 188 mV at a current density of 10 mA cm^-2 in 0.5 M H₂SO₄ and 1 M KOH, respectively. The large specific surface area and thinner edge morphology provide more active sites for hydrogen production, thereby significantly improving the charge transfer kinetics. Density functional theory calculation results show that under acidic conditions the ΔG_H* values of NiMo-WSe₂ with different structures and hydrogen adsorption sites are also different, when the hydrogen adsorption site was located at the top of the Se-Ni bond, the meta NiMo-WSe₂ has a ΔG_H* value (-0.04 eV) that is closest to 0. Meanwhile, NiMo-WSe₂ (meta) also has a minimum of ΔG_H* under alkaline conditions. DOS confirmed that Ni doping has a large impact on the electronic states at the WSe₂ Fermi level, while NiMo co-doping greatly reduces the potential energy barrier of the HER reaction, jointly increasing the current density, and thus improving the HER performance.

Boosting Highly Active Exposed Mo Atoms by Fine-Tuning S-Vacancies of MoS2-Based Materials for Efficient Hydrogen Evolution

Guided by the theoretical calculation, achieving an efficient hydrogen evolution reaction (HER) by S-vacancy engineering toward MoS₂-based materials is quite challenging due to the contradictory relationship between the adsorption free energy of hydrogen atoms (ΔG_H) of the exposed Mo atoms (EMAs) and the number of EMAs per unit area (N_EMAs). Herein, we demonstrate a novel one-pot incorporating-assisted compositing strategy to realize fine-tuning the concentration of S-vacancies (C_S-vacancies) of MoS₂-based materials to boost highly active EMAs for efficient HER. In our strategy, S-vacancies are modulated into basal planes of MoS₂ via decreasing the formation energy of S-vacancies by oxygen incorporation; moreover, C_S-vacancies of the basal planes is precisely regulated by simply controlling the molar amount of the Co precursor based on the electron injection effect. At low or excessively high C_S-vacancies, the as-synthesized electrocatalysts lack "highly active EMAs" in quantity or nature. The balance between the intrinsic activity of EMAs and N_EMAs is realized for boosting EMAs with high catalytic performance. The optimal electrocatalysts exhibit excellent activity and stability at fine-tuning C_S-vacancies to 9.61%. Our results will pave a novel strategy for unlocking the potential of an inert basal plane in MoS₂ for high-performance HER.

Synergistic Regulation of S-Vacancy of MoS2-Based Materials for Highly Efficient Electrocatalytic Hydrogen Evolution

Low or excessively high concentration of S-vacancy (C_S-vacancy) is disadvantageous for the hydrogen evolution reaction (HER) activity of MoS₂-based materials. Additionally, alkaline water electrolysis is most likely to be utilized in the industry. Consequently, it is of great importance for fine-tuning C_S-vacancy to significantly improve alkaline hydrogen evolution. Herein, we have developed a one-step Ru doping coupled to compositing with CoS₂ strategy to precisely regulate C_S-vacancy of MoS₂-based materials for highly efficient HER. In our strategy, Ru doping favors the heterogeneous nucleation and growth of CoS₂, which leads to a high crystallinity of Ru-doped CoS₂ (Ru-CoS₂) and rich heterogeneous interfaces between Ru-CoS₂ and Ru-doped MoS_2-x (Ru-MoS_2-x). This facilitates the electron transfer from Ru-CoS₂ to Ru-MoS_2-x, thereby increasing C_S-vacancy of MoS₂-based materials. Additionally, the electron injection effect increases gradually with an increase in the mass of Co precursor (m_Co), which implies more S^2- leaching from MoS₂ at higher m_Co. Subsequently, C_S-vacancy of the as-synthesized samples is precisely regulated by the synergistic engineering of Ru doping and compositing with CoS₂. At C_S-vacancy = 17.1%, a balance between the intrinsic activity and the number of exposed Mo atoms (EMAs) to boost highly active EMAs should be realized. Therefore, the typical samples demonstrate excellent alkaline HER activity, such as a low overpotential of 170 mV at 100 mA cm⁻² and a TOF of 4.29 s⁻¹ at -0.2 V. Our results show promise for important applications in the fields of electrocatalysis or energy conversion.

Multi-interface MoS2/Ni3S4/Mo2S3 composite as an efficient electrocatalyst for hydrogen evolution reaction over a wide pH range

The exploitation of cost-efficiently electrocatalysts for hydrogen evolution reaction (HER) over a wide pH range remains a challenge. Herein, we prepared a novel multi-interface MoS₂/Ni₃S₄/Mo₂S₃ composite on carbon cloth (CC) that acts as an efficient electrocatalyst over a wide pH range through a facile one-pot strategy, where (NH₄)₄[NiH₆Mo₆O₂₄]·5H₂O (abbreviated to NiMo₆) as a bimetallic precursor and Ni(NO₃)₂·6H₂O as one of the raw materials and salt are used together with thiourea (TU) for converting them into the MoS₂/Ni₃S₄/Mo₂S₃ load on CC (abbreviated as MoS₂/Ni₃S₄/Mo₂S₃/CC). MoS₂/Ni₃S₄/Mo₂S₃/CC-24 h shows a distinguished electrocatalytic performance towards HER with long-term stability in acid and alkaline media. It presents low overpotentials of 38 mV and 51 mV in 0.5 M H₂SO₄ and 1.0 M KOH at 10 mA cm^-2, respectively. This work can deliver a new idea to fabricate cost-efficient and long-term durability HER electrocatalysts over a broad pH range.