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Electrocatalytic water splitting, as a sustainable, pollution-free and convenient method of hydrogen production, has attracted the attention of researchers. However, due to the high reaction barrier and slow four-electron transfer process, it is necessary to develop and design efficient electrocatalysts to promote electron transfer and improve reaction kinetics. Tungsten oxide-based nanomaterials have received extensive attention due to their great potential in energy-related and environmental catalysis. To maximize the catalytic efficiency of catalysts in practical applications, it is essential to further understand the structure–property relationship of tungsten oxide-based nanomaterials by controlling the surface/interface structure. In this review, recent methods to enhance the catalytic activities of tungsten oxide-based nanomaterials are reviewed, which are classified into four strategies: morphology regulation, phase control, defect engineering, and heterostructure construction. The structure–property relationship of tungsten oxide-based nanomaterials affected by various strategies is discussed with examples. Finally, the development prospects and challenges in tungsten oxide-based nanomaterials are discussed in the conclusion. We believe that this review provides guidance for researchers to develop more promising electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

Constructing a heterogeneous interface using different components is one of the effective measures to achieve the bifunctionality of nanocatalysts, while synergistic interactions between multiple interfaces can further optimize the performance of single-interface nanocatalysts. The non-precious metal nanocatalysts MoS2/NiSe2/reduced graphene oxide (rGO) bilayer sandwich-like nanostructure with multiple well-defined interfaces is prepared by a simple hydrothermal method. MoS2 and rGO are layered nanostructures with clear boundaries, and the NiSe2 nanoparticles with uniform size are sandwiched between both layered nanostructures. This multiple-interfaced sandwich-like nanostructure is prominent in catalytic water splitting with low overpotential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and almost no degradation in performance after a 20 h long-term reaction. In order to simulate the actual overall water splitting process, the prepared nanostructures are assembled into MoS2/NiSe2/rGO||MoS2/NiSe2/rGO modified two-electrode system, whose overpotential is only 1.52 mV, even exceeded that of noble metal nanocatalyst (Pt/C||RuO2~1.63 mV). This work provides a feasible idea for constructing multi-interface bifunctional electrocatalysts using nanoparticle-doped bilayer-like nanostructures. [ABSTRACT FROM AUTHOR]

Li et al. [[3]] fabricated a CoFe SB 2 sb O SB 4 sb /g-C SB 3 sb N SB 4 sb composite catalyst with CoFe SB 2 sb O SB 4 sb particles supported on the flaky g-C SB 3 sb N SB 4 sb using a scalable facile method. However, currently, Li-S batteries suffer from low volumetric energy density and poor cycling stability due to the intrinsic low conductivity of sulfur and its discharge product, lithium polysulfide shuttle effect, and so on. Developing efficient and low-cost energy conversion and storage devices and technologies is all-important issue in order to achieve a low-carbon society, whose performance essentially depends on the properties of materials. Zhao et al. [[8]] designed a single-atom catalyst Au/WSSe by filling the single Au atom at the S vacancy site in the Janus WSSe monolayer. [Extracted from the article]

As a typical two-dimensional (2D) MXene, Ti3C2O2 has been considered as a potential material for high-performance hydrogen evolution reaction (HER) catalyst, due to its anticorrosion and hydrophilic surface. However, it is still a challenge to improve the Ti3C2O2 surficial HER catalytic activity. In this work, we investigated the HER activity of Ti3C2O2 after the surface was doped with S, Se, and Te by the first principles method. The results indicated that the HER activity of Ti3C2O2 is improved after being doped with S, Se, Te because the Gibbs free energy of hydrogen adsorption (ΔGH) is increased from −2.19 eV to 0.08 eV. Furthermore, we also found that the ΔGH of Ti3C2O2 increased from 0.182 eV to 0.08 eV with the doping concentration varied from 5.5% to 16.7%. The HER catalytic activity improvement of Ti3C2O2 is attributed to the local crystal structure distortion in catalytic active sites and Fermi level shift leads to the p-d orbital hybridization. Our results pave a new avenue for preparing a low-cost and high performance HER catalyst. [ABSTRACT FROM AUTHOR]

Transition metal sulfides have attracted a lot of attention as potential oxygen evolution reaction (OER) catalysts. Bimetallic sulfide possesses superior physicochemical properties due to the synergistic effect between bimetallic cations. By introducing a metal-semiconductor interface, the physicochemical properties of transition metal sulfide can be further improved. Using the solvothermal method, Au@NiCo2S4 core-shell heterostructure nanoparticles (NPs) and bare NiCo2S4 NPs were prepared. The measurement of the OER catalytic performance showed that the catalytic activity of Au@NiCo2S4 core-shell heterostructure was enhanced compared to bare NiCo2S4 NPs. At the current density of 10 mA cm−2, the overpotential of Au@NiCo2S4 (299 mV) is lower than that of bare NiCo2S4 (312 mV). The Tafel slope of Au@NiCo2S4 (44.5 mV dec−1) was reduced compared to that of bare NiCo2S4 (49.1 mV dec−1), indicating its faster reaction kinetics. Detailed analysis of its electronic structure, chemical state, and electrochemical impedance indicates that the enhanced OER catalytic performances of bare Au@NiCo2S4 core-shell NPs were a result of its increased proportion of high-valance Ni/Co cations, and its increased electronic conductivity. This work provides a feasible method to improve OER catalytic performance by constructing a metal-semiconductor core-shell heterostructure. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal carbides and nitrides (MXenes) hold promise as electrode materials for alkali metal ion batteries on account of some fascinating peculiarities. However, the high temperature required in the synthesis of the MAX phase severely hinders its further development. Herein, MAX phase (Ti 2 AlC) is first grown on carbon cloth (CC) by molten salt method at a milder temperature, then the hierarchical structure that Ti 2 C sheets arrayed on the carbon fibers can be obtained after HF treatment, demonstrating 269 mA h g−1 after 400 cycles at 1 mA cm−2 for lithium-ion storage and 206 mA h g−1 after 100 cycles at 0.1 mA cm−2 for sodium-ion storage when served as freestanding anode. Meanwhile, in-situ and ex-situ characterization techniques are employed to monitor the possible phase transitions in the electrochemical process. In addition, the kinetics for carrier diffusion in the electrochemical process is also studied. This work endows edification for configuration of MXene-based freestanding electrode. [Display omitted] • MAX phase would be grown directly on the carbon cloth by molten-salt method. • Neoteric MXene-based freestanding anode can be structured. • The electrode without binder shows distinguished electrochemical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • An exquisite externally layered and internally hollow CoP@MoS 2 electrocatalyst was successfully prepared. • CoP can effectively enhance the catalytic ability of MoS 2 on hydrogen evolution reaction. • The externally layered and internally hollow nanostructure can accelerate the transfer of charge and mass. As the star material among nonprecious electrocatalysts, molybdenum disulfide (MoS 2) has received much attention. However, the catalytic inertness of the basal plane, low conductivity of its steady state (2H phase), and the agglomeration of lamellar structures have seriously hindered its catalytic performance. It is very essential to design and modulate the morphology and phase of MoS 2 to improve the above issues by synergistic regulation of electrical structure and defect engineering. Herein, MoS 2 was delicately composited on CoP nanoframe derived from a typical metal–organic frame nanostructure (ZIF-67), forming the hollow CoP@MoS 2 hetero-nanoframe. This exquisite externally layered and internally hollow CoP@MoS 2 electrocatalyst demonstrated excellent catalytic performance for the hydrogen evolution reaction, with a low overpotential of 119 mV at 10 mA cm−2, a small Tafel slope of 49 mV dec−1, a large electric double-layer capacitance of 10.28 mF cm−2, and prominent long-term stability. The remarkable catalytic performance of hollow CoP@MoS 2 hetero-nanoframe can be attributed to the unique architecture of the hetero-nanostructures, appropriate component ratios, strong interaction between CoP and MoS 2 , and large-scale defects and disorder. First-principles density-functional theory calculations can prove the above arguments adequately, the hydrogen adsorption free energy of CoP@MoS 2 is close to zero. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2), as a classic two-dimensional material, is limited in applications with its relatively poor conductivity and chemical instability due to its single morphology/phase structure in electrocatalytic activity and specific capacitance. Moreover, up to date, it is still an open area in establishing cost-effective approaches to fabricate exotic MoS 2 nanostructures with desired morphology and phase component for exhibiting excellent performance in energy conversion and storage. Herein, only using extremely ordinary sources of molybdenum and sulfur and a simple one-pot hydrothermal method, we efficiently and economically synthesized two types of stable MoS 2 nanostructures with a certain percentage of the metastable metallic (1T) phase, i.e., spherical nanoflowers (SNF) and random nanosheets (RNS). Both SNF–MoS 2 and RNS-MoS 2 exhibited excellent electrocatalytic activity for hydrogen evolution reaction with ultra-high stability and high specific capacitance. These remarkable properties are due to the dramatically increased number of active sites in these unique nanostructures and their enhanced electric conductivities due to the metallic 1T phase. Furthermore, when these two types of nanostructures are physical decorated with carbon black, their electrocatalysis is further enhanced. Our findings offer an economical approach to fabricate stable MoS 2 -based nanomaterials for practical applications with highly efficient energy conversion and energy storage. Image 1 • Spherical nanoflower and random nanosheet MoS 2 are mixed with 1T phase. • The preparation method is extremely simple and cost effective. • SNF- and RNS-MoS 2 possess significant HER and supercapacitors performance. • HER performance is enhanced upon the physical mixing of carbon black. • Excellent stability is surveyed for HER. [ABSTRACT FROM AUTHOR]

• Interface controlled Au-NiS x heterostructures were prepared by solvothermal method. • The presence of Au improves the HER properties of NiS x. • Electron transfer along the interface mainly determines the catalytic properties. Nickel sulfides (NiS x) as promising catalysts for hydrogen evolution reaction (HER) have attracted much interest. However, the HER catalytic activities of NiS x reported are relatively low for their poor electrical conductivity. The HER catalytic performance of NiS x is expected to be further enhanced by increasing their electronic conductivity. Constructing heterostructures consisting of noble metal and semiconductor has been proven to be an efficient method to promote their physicochemical performances benefitting from synergistic effects along the metal-semiconductor interface. Here, Au-NiS x heterostructures including core@shell, yolk-shell, and oligomer-like structures have been designed and synthesized by different solvothermal methods. A formation mechanism involving the Kirkendall effect has been proposed for the yolk-shell structure with an empty space around the Au core rather than the seeded grown core@shell structure. Catalytic performance measurements indicate that the Au@NiS x core@shell nanoparticles (NPs) exhibit superior HER catalytic property to Au-NiS x yolk-shell, oligomer-like structures, and "pure" NiS x NPs, resulting from the electron transfer between Au and NiS x interfaces. The overpotentials of Au-NiS x NPs with core@shell and yolk-shell nanostructures are 253 mV and 263 mV at 10 mA/cm2, respectively, which are lower than those of oligomer-like Au-NiS x (283 mV) and pure NiS x (321 mV) NPs. The Tafel slope of Au@NiS x core@shell structure (43.7 mV/dec) is also the lowest. These results demonstrate that the core@shell NPs possess the best HER performances, followed by their yolk-shell and oligomer-like counterparts. These findings confirm that the physicochemical performances of the metal-semiconductor heterostructures can be efficiently optimized by adjusting the electron transfer through the interface structure control. [ABSTRACT FROM AUTHOR]