Facile synthesis of NiS2 nanowires and its efficient electrocatalytic performance for hydrogen evolution reaction

Recently, the first-row transition metal dichalcogenides MX₂ (M = Fe, Co, Ni; X = S, Se) have been widely reported as promising catalysts for hydrogen evolution reaction (HER) because of its excellent catalytic activity and earth-abundance. The rational nanostructure designs have been proved as an effective way to improve their catalytic performance. However, the reported one dimension (1D) NiS₂ nanowires for HER suffer from a large Tafel slope. Here, we report a facile synthesis of 1D NiS₂ nanowires and its high efficient catalytic activity in HER. This nanowire structure with large surface area and active sites enables highly efficient electrocatalytic performance in HER with a much smaller Tafel slope (83.5 mV/dec) compared to that of bulk NiS₂ (136 mV/dec) as well as long-term stability. Our work builds up a structure–performance relationship and enriches the synthetic strategy to other efficient catalysts such as first-row transition metal dichalcogenides or transition metal phosphide.     

Surfactant-assisted hydrothermal synthesis of nitrogen doped Mo2C@C composites as highly efficient electrocatalysts for hydrogen evolution reaction

We describe a facile surfactant-assisted hydrothermal route to synthesize nitrogen doped Mo₂C@C composites in the presence of cetyltrimethylammonium bromide (CTAB) as carbon source and structure guiding agent. The resulting Mo₂C@C composites consist of Mo₂C nanocrystals with sheet-like morphology and well-dispersed nitrogen element doping. Controllable experiments indicate that the additive amount of CTAB can efficiently tune porous structure and electrochemical activity of the as-prepared Mo₂C@C materials. This unique nitrogen doped Mo₂C@C composite provides several advantages for electrocatalytic applications: (1) nitrogen doped carbons can prevent the aggregation of Mo₂C nanocrystals and render it high conductivity; (2) the homogeneous dispersion of Mo₂C nanocrystals provides abundant active sites; (3) 2D morphology, the hierarchical porosity, and high surface areas allow large exposed field of active sites and facilitate mass transfer. As a result, the nitrogen doped Mo₂C@C composites deliver superior HER electrocatalytic activities with a low overpotential of only 100 mV and also a low Tafel slope of 53 mV/dec in alkaline condition. Such CTAB-assisted strategy may open up an opportunity towards synthesis of low cost and high performance Mo-based electrocatalysts for various applications, such as water splitting.     

Facile synthesis of MoS2/CuS nanoflakes as high performance electrocatalysts for hydrogen evolution reaction

The fabrication of metal sulfides heterostructure is a promising strategy for enhancing catalytic activity. Herein, the MoS₂/CuS heterostructure was successfully grown on carbon cloth (MoS₂/CuS/CC) through an efficient method. The SEM results confirmed that the fabricated MoS₂/CuS/CC composites have a flake morphology, which can not only improves the surface area but also offers ample surface catalytic active sites. Particularly, the optimized MoS₂/CuS/CC-2 electrocatalyst showed a small overpotential of 85 mV@10 mA cm^?2 and exceptional long-term cycling durability for hydrogen evolution in 1 M KOH. The outstanding catalytic activity is attributed to the fact that the combination of MoS₂ with CuS can greatly enhance the charge transport rate and improve the structural stability. These results suggest that the MoS₂/CuS/CC heterostructure is a potential electrocatalyst for hydrogen production.     

Facile synthesis of carbon encapsulated RuO2 nanorods for supercapacitor and electrocatalytic hydrogen evolution reaction

In this work, carbon encapsulated RuO₂ nanorods (RuO₂ NRs/C) has been synthesized by thermolysis of ruthenium chloride and Punica granatum (P. granatum) peel under N₂ atmosphere. The synthesized RuO₂ NRs/C was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction method (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) analyses. The FT-IR results suggested that the organic constituents of P. granatum have been carbonized and encapsulated over RuO₂ nanorods (RuO₂ NRs). The XRD pattern of RuO₂ NRs/C revealed its crystalline nature and carbon encapsulation. The synthesized RuO₂ NRs/C has been well dispersed with the average width of 20 nm, exposed from the FE-SEM and HR-TEM images. The EDS results of RuO₂ NRs/C showed the existence of three elements viz., Ru, O and C. Further, the supercapacitor and electrocatalytic hydrogen evolution reaction (HER) activities of RuO₂ NRs/C were studied using standard electrochemical methods. The synthesized RuO₂ NRs/C offered a maximum specific capacitance of 151.3 F g⁻¹ at a scan rate of 5 mV s⁻¹, obtained from the cyclic voltammetry results. The onset over potential and Tafel slope of synthesized RuO₂ NRs/C for HER were −0.099 V_RHE and −99.4 mV dec⁻¹, respectively. The present study revealed that RuO₂ NRs/C as a better candidate for supercapacitor and HER.     

Facile hydrothermal synthesis of combined MoSe2PS nanostructures on nickel foam with superior electrocatalytic properties for hydrogen evolution reaction

Producing an efficient and inexpensive electrocatalyst for use in the water electrolysis process is the most efficient and logical way to industrialize this method to produce hydrogen as a clean and alternative fuel for fossil fuels. In this study, combined and unique MoSe₂PS nanostructures are synthesized on nickel foam by three steps hydrothermal process. Microstructural observations reveal the unique morphology of the petals covered by the elongated nano-blades. A high electrocatalytic performance is attained with this nanostructure in hydrogen evolution reaction, so that the 90 mV overpotential is achieved at a current density of ?10 mA/cm². The near-platinum activity is due to the unique and combined nanostructure due to the synergistic properties of S and P on MoSe₂ as well as the high electrochemical active sites in the specimen. Additionally, excellent stability of the synthesized electrocatalyst is observed in the alkaline medium for 30 h, which confirms its potential application in relevant industries such as fuel cells and transportation.     

Facile synthesis of tubular CoP as a high efficient electrocatalyst for pH-universal hydrogen evolution

A facile three-step approach for tubular CoP preparation and its catalytic activity for HER and OER are reported. The CoP microtubes show superior HER performance in a wide pH range with low overpotentials of 91, 101 and 113 mV at 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively. Additionally, it also depicts superior OER performance with an overpotential of 300 mV at 10 mA cm^?2, which is lower than reported precious metal oxides. The improved electrocatalytic performance of tubular CoP is likely attributed to the porous tube-like structural features, which not only afford rich exposed active sites, but also accelerate the charge or mass transfer efficiency, and thus efficiently promote the HER performance. The synthesis of tubular CoP confirms the importance of morphology features and provides a new insight to rationally design and synthesize highly effective non-noble metal phosphide-based pH-universal electrocatalysts for HER.     

Facile synthesis of porous 3D CoNiCu nano-network structure and their activity towards hydrogen evolution reaction

Nanostructured alloys have recently attracted great attention for hydrogen evolution due to their unique electron structure and large surface area. Herein, we reported a facile electrochemical method to prepare three-dimensional (3D) nano-network structures and demonstrated their feasibility as efficient electrocatalyst for hydrogen evolution. These 3D CoNiCu nano-network structure exhibited good performance in hydrogen evolution reaction (HER).     

One-pot wet-chemical synthesis of uniform AuPtPd nanodendrites as efficient electrocatalyst for boosting hydrogen evolution and oxygen reduction reactions

Uniform trimetallic AuPtPd nanodendrites (NDs) were synthesized by a simple and quick method, using l-proline and ascorbic acid (AA) as eco-friendly structure-guiding agent and reducing agent, respectively. The obtained AuPtPd NDs displayed greatly enlarged electrochemically active surface area (27.65 m² g^?1_metal) relative to home-made AuPt nanocrystals (NCs, 21.76 m² g^?1_metal), AuPd NCs (3.91 m² g^?1_metal), Pt black (20.88 m² g^?1_metal) and Pd black (8.30 m² g^?1_metal). For hydrogen evolution and oxygen reduction reactions, AuPtPd NDs showed excellent catalytic performances relative to the referenced catalysts. These results reveal the practical applications of the as-obtained catalyst in energy storage and conversion.     

Facile one-step synthesis of nitrogen-doped carbon sheets supported tungsten carbide nanoparticles electrocatalyst for hydrogen evolution reaction

Exploring non-precious metal catalysts with high activity and stability to replace Pt-based materials is vital for electrochemical water splitting. In this work, a facile one-step method was put forward to synthesize WC/NC composite. Due to the couple effect of KCl/NaCl salt and dicyandiamide, pure WC phase was obtained at 900 °C. Meanwhile, KCl/NaCl salt eliminated the runaway pyrolysis expansion of glucose. Besides contributing to the special surface area, dicyandiamide as N source significantly alleviated W mass loss trigged by KCl/NaCl salt and ensured the appropriate WC content in WC/NC composite. As a HER electrocatalyst in acid media, WC/NC composite exhibits the small overpotential of 156 mV at a current density of 10 mA cm⁻², the low Tafel slope of 64 mV dec⁻¹, as well as the robust stability. This work offers a feasible option to fabricate low-cost and effective transition metal carbide electrocatalysts on a large-scale for hydrogen evolution reaction.     

Ru/MoO2 decorated on CNT networks as an efficient electrocatalyst for boosting hydrogen evolution reaction

Generally, electrochemical hydrogen evolution reaction (HER) is hampered by slow kinetics and low round-trip efficiency. Electrocatalysts with a hierarchical structure and large surface area are expected to overcome these problems. Herein, we prepared a Ru/MoO₂/carbon nanotubes (RMC) hybrid with a hierarchical structure by a convenient solid-phase reaction (SPR) method, and studied the electrochemical activity for HER. After annealing as-prepared RuO₂/MoO₂/carbon nanotubes (ROMC) precursor in a tubular furnace under Ar atmosphere, RuO₂ and MoS₂ were in-situ transformed into Ru metal and MoO₂ phase by the redox SPR. Through various tests, we have confirmed that the new formed Ru metal and MoO₂ phase are combined and uniformly coated on the outer surface of CNTs. Interestingly, the RMC-500 exhibits the best HER performance with a low overpotential of 16 mV at l0 mA cm^?2, small Tafel slope of 45 mV dec^?1, higher electrochemical active surface area, and long-time durability in alkaline electrolyte.     

In-situ anion exchange synthesis of copper selenide electrode as electrocatalyst for hydrogen evolution reaction

Efficient and robust Earth-abundant catalysts for hydrogen evolution reaction (HER) is one of the key components for clean energy technologies aimed at reducing future carbon emissions. Here, an in-situ anion exchange approach to prepare hierarchical nanostructures consisting of ultrathin Cu_2-xSe nanosheet is reported. With the aid of the selenylation process and the hierarchical ultrathin nanostructure, the nanostructured Cu_2-xSe/Cu foam electrode achieved considerably enhanced HER performance with a large geometric current density of ?100 mA cm^?2 at a small overpotential of 313 mV and outstanding long-term operational stability. Significant improvement of electrocatalytic activity for Cu_2-xSe catalyst could be attributed to the promoted mass diffusion/transfer properties, which results from its special structural feature. Meanwhile, the overpotential associated with the catalyst/substrate interface could be effectively eliminated due to the self-supported construction. We believe that this work will lead towards the further development of Cu-based chalcogenides for applications in electrocatalysis and energy conversion.     

Facile and large-scale preparation of Co/Ni-MoO2 composite as high-performance electrocatalyst for hydrogen evolution reaction

Facile fabrication of high-performance catalyst based on low-cost metals for sustainable hydrogen evolution is still a matter of cardinal significance. However, synthetic approaches for electrocatalyst are usually complicated and the yields are often low. Herein, we report a one-step simple method for the large-scale synthesis of Co/Ni-MoO₂ composite as efficient and stable hydrogen evolution reaction (HER) electrocatalyst to drive 10 mA cm^?2 current density with a low overpotential of 103 mV in basic media. Co-MoO₂ and Ni-MoO₂ were also prepared using this method with overpotential of 137 and 130 mV, respectively, to gain the same current density. These results indicate that this facile synthesis approach is of great practical importance as it can be easily used for large-scale preparation of electrocatalysts in industry.     

Hydrogen evolution reaction activity and stability of sintered porous Ni-Cu-Ti-La2O3 cathodes in a wide pH range

Finding a low-cost, efficient, stable, and workable electrode for the production of hydrogen based on the hydrogen evolution reaction (HER) is particularly critical. At present, the use of Pt/C electrodes is under development, but the expensive cost hinders its wide application in the HER field. Herein, a novel porous Ni-Cu-Ti-La₂O₃ cathode with a porosity of 29.07% was proved to be an excellent substitute for the HER, which was fabricated by vacuum sintering based on powder metallurgy. The hydrogen evolution efficiency is superior to that of commercial 20% Pt/C under pH = 14.1 condition (2.67 mol/L KOH). The HER activity is also close to commercial 20% Pt/C under pH = 0.1 (1 mol/L HCl) and pH = 8.1 (3.34% simulated seawater) conditions and exceeds it after reaching a high potential. Meanwhile, it can achieve good HER stability within 48 h and maintain its HER activity after 1000 continuous cycle electrolysis.     

Facile synthesis of self-supported intertwined columnar NiCoP as a high efficient electrocatalyst for hydrogen evolution reaction

A new self-supported nickel-cobalt phosphide (NiCoP) on Ni foam (NiCoP/NF) is fabricated by simple immersion in Co(NO₃)₂ solution followed by subsequent phosphorization. NiCoP/NF displays intertwined and porous columnar morphology derived from topological transformation of corresponding columnar amorphous hydroxides precursor. NiCoP/NF manifests the most prominent hydrogen evolution reaction (HER) performance in both 0.5 M H₂SO₄ and 1 M KOH with the overpotentials of 49 and 57 mV to achieve 10 mA cm^?2, respectively. Also, NiCoP/NF showed excellent oxygen evolution reaction (OER) performance, requiring 256 mV to achieve 10 mA cm^?2, even superior to that of RuO₂ and IrO₂. Such impressive HER performance of NiCoP/NF is mainly attributed to the collective effects of enlarged surface area and enriched exposed active sites, affording faster charge transfer kinetic in HER process. This simple immersion method offers a new insight to design cost-effective and efficient electrocatalysts for large scale application.     

Facile synthesis of porous dendritic Pt68Ag32 nanodandelions for greatly boosting electrocatalytic activity towards oxygen reduction and hydrogen evolution

Contrary to single counterparts, Pt-based bimetallic nanocrystals are attractive and feasible to decrease the cost, improve the catalytic activity and enhance the stability via morphology-, structure- and composition-engineering. Herein, porous dendritic alloyed Pt₆₈Ag₃₂ nanodandelions (NDs) were synthesized by a one-pot successive co-reduction method, using amrinone as the new stabilizer and structure director, without any template, seed or complicated instrument. The correlative shapes, composition, and crystalline structure were examined by a range of characterization techniques. It is found that the molar ratio of the precursors (AgNO₃ and H₂PtCl₆), the dosage of amrinone, and different reductants play the essential roles during the synthesis process. The Pt₆₈Ag₃₂ NDs exhibited dramatically enlarged electrochemically active surface area, enhanced catalytic activity and stability for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) as compared to commercial Pt/C, Pt black, home-made Pt₇₅Ag₂₅ nanocrystals (NCs) and Pt₅₆Ag₄₄ NCs catalysts.     

NiCoP nanoarchitectures: One-step controlled electrodeposition and their application as efficient electrocatalysts for boosting hydrogen evolution reaction

Designing non-precious and long-lasting electrocatalysts with enhanced catalytic properties for hydrogen evolution reaction (HER) is a fundamental approach to address the needs for hydrogen industry and overcome the current challenges in sustainable energy generation. Herein, we present ternary NiCoP nanostructures synthesized through a direct and controlled electrochemical deposition at room temperature as highly efficient electrocatalysts for HER. Different Ni/Co ratios in the alloy were investigated resulting in different nanoarchitectured morphologies, chemical compositions and HER performances, in turn. The NiCoP–I alloy exhibited a nanoparticulated morphology comprising well-defined nanoparticles of ～20–30 nm which evolved to nanoparticulated caps at prolonged electrodeposition times presenting a large electrochemical surface area of 526 cm². The NiCoP–I electrocatalyst demonstrated a small Tafel slope of 49 mV dec^?1 and an ultra-low overpotential of 68 mV vs. RHE at ?10 mA cm^?2 in alkaline solution which well rivals to that of Pt foil and outmatches its binary alloy counterparts.     

Facile synthesis of MoS2/N-doped macro-mesoporous carbon hybrid as efficient electrocatalyst for hydrogen evolution reaction

A novel three-dimensional (3D) hybrid consisting of molybdenum disulfide nanosheets (MoS₂) uniformly bound at N-doped macro-mesoporous carbon (N-MMC) surface was fabricated by the solvothermal method. The resulting MoS₂/N-MMC hybrid possesses few-layer MoS₂ nanosheets structure with abundant edges of MoS₂ exposed as active sites for hydrogen evolution reaction (HER), in sharp contrast to large aggregated MoS₂ nanoflowers without N-MMC. The high electric conductivity of N-MMC and an abundance of exposed edges on the MoS₂ nanosheets make the hybrid excellent electrocatalytic performance with a low onset potential of 98 mV, a small Tafel slope of 52 mV/decade, and a current density of 10 mA cm^?2 at the overpotential of 150 mV. Moreover, the MoS₂/N-MMC hybrid exhibits outstanding electrochemical stability and structural integrity owing to the strong bonding between MoS₂ nanosheets and N-MMC.     

Facile synthesis of electrospun C@NiO/Ni nanofibers as an electrocatalyst for hydrogen evolution reaction

Hydrogen evolution reaction (HER) is considered to be one of the most important electrochemical reactions from both fundamental and application perspective to produce hydrogen. Polyacrylonitrile (PAN) based carbon (C)@NiO/Ni nanofibers were fabricated via simple electrospinning method. The as-prepared C@NiO/Ni nanofibers were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectra. The SEM and TEM analyses revealed that NiO/Ni nanoparticles distributed on the PAN based carbon nanofibers. EDS, XPS and XRD results confirm the presence of the nanoparticles. The catalytic activity and durability of C@NiO/Ni nanofibers containing different weight ratio of Ni salt content (2%, 3%, & 4%) were examined for HER in 1 M KOH solution. It has been observed that C@NiO/Ni nanofibers containing Ni content (4%) showed the highest catalytic activity. It indicates that the catalytic activity of electrocatalyst can be enhanced by increasing the effective active sites. Noteworthy to mention here that the nanofibers catalyst reached a current density of 60 mA/cm². The as-prepared catalyst showed remarkable stability up to 22 h and retained 99% of its initial activity even after 16 h of reaction.     

Ion exchange synthesis of Fe-doped clustered CoP nanowires as superior electrocatalyst for hydrogen evolution reaction

Green hydrogen production from electrochemical water splitting currently suffers from the key issues of high energy consumption and cost. Herein, we demonstrated the synthesis of highly efficient and stable clustered CoP nanowires electrocatalysts on nickel foam. Moreover, an ion exchange strategy was proposed to precisely control the doping content of iron to further modify the intrinsic electrochemical activity of CoP nanowires. The introduction of iron effectively alters the surface atomic configuration and electronic structure of CoP and increases the active sites, thus accelerating the overall reaction rate and enhancing the catalytic performance. It has been demonstrated that the CoFeP-30-30/NF electrode exhibits platinum-like catalytic activity with only an overpotential of 29.8 mV at 10 mA·cm⁻² and outstanding stability toward hydrogen evolution reaction. The synthetic strategy of CoFeP/NF electrode proposed in this work will significantly promote the development of highly efficient transition metal phosphides electrocatalysts with lower overpotential and better stability.     

Facile synthesis of molybdenum-based layered double hydroxide nanorods for boosting water oxidation reaction

Exploiting environmentally friendly and robust oxygen evolution reaction (OER) electrodes is still a great difficulty to promote the water oxidation for electrocatalytic water splitting. In the work, molybdenum-doped nickel copper hydrotalcite (NiCuMo_x LDH) nanoarrays have been firstly in situ grown on nickel foam (NF) via a typical hydrothermal process. When NiCuMo_0.2 LDH/NF was used as a OER electrocatalyst, it displays superior electrocatalytic performance with the need of small overpotentials of only 290 mV to drive 40 mA cm⁻² and a low Tafel slope of 39.8 mV dec⁻¹, which are almost one of the best water oxidation activities reported so far. The enhanced electrocatalytic performance is attributed to unique urchin-like structure, more exposure to active sites and enhanced charge transfer rate owing to the synergistic effect of Mo doping and NiCu LDH. The work put forward a new method for the development of efficient water oxidation electrocatalysts, which will fill the gap for the exploitation of trimetal LDH-based electrodes in large-scale water splitting applications in the future.