Cytosine assisted aqueous synthesis of AgPt hollow alloyed nanostructures as highly active electrocatalyst for ethylene glycol oxidation and hydrogen evolution

Herein, a simple one-pot aqueous method was developed for synthesis of AgPt hollow alloyed nanostructures (AgPt HANS) with polyvinylpyrrolidone (PVP) and cytosine as the dispersing agent and eco-friendly growth-director, respectively. The synthesized architectures displayed the improved catalytic performance toward ethylene glycol oxidation reaction (EGOR) relative to commercial Pt black in alkaline media. Meanwhile, the catalyst exhibited the enhanced catalytic activity for hydrogen evolution reaction (HER) with the positive onset potential (E_onset, ?39 mV) and a small Tafel slope (40 mV dec^?1) relative to commercial Pt/C (20 wt%, ?31 mV, 33 mV dec^?1) in 0.5 M H₂SO₄, along with the more positive E_onset (?34 mV) and a smaller Tafel slope (59 mV dec^?1) in 0.5 M KOH compared with Pt/C (?35 mV, 85 mV dec^?1).     

Nickel foam-supported NiFe layered double hydroxides nanoflakes array as a greatly enhanced electrocatalyst for oxygen evolution reaction

In this work, nickel-iron layered double hydroxides nanoflakes are grown on nickel foam by a facile in-situ complexation precipitation method. The fabricated nickel-iron layered double hydroxides/nickel foam with special 3D structure with large electrochemical activated surface area is proposed as a greatly enhance electrode material for oxygen evolution reaction. The electrochemical properties of the as-fabricated nickel-iron layered double hydroxides/nickel foam electrode are evaluated using 1 mol L^?1 KOH as electrolyte. The obtained electrochemical results show that the fabricated nickel-iron layered double hydroxides/nickel foam electrode exhibits a low overpotential of 245 mV at current density of 10 mA cm^?2 with small Tafel slope of 27 mV dec^?1. Also, it displays a much longer durability of 20 h with very small decay of 0.02% as compared with 3D nickel foam, IrO₂ and the related catalysts reported. Therefore, this study indicates that the nickel-iron layered double hydroxides/nickel foam is a promising electrode material for oxygen evolution reaction due to its facile preparation method, low cost and environmentally friendly nature.     

Straightforward preparation of nickel selenide nanosheets supported on nickel foam as a highly efficient electrocatalyst for oxygen evolution reaction

The development of economical, durable, and efficient oxygen evolution reaction (OER) electrocatalysts is essential for large-scale industrial water electrolysis. Here, a straightforward strategy is proposed to synthesize a series of nickel selenide nanosheets supported on nickel foam (NiSe₂/NF) materials by directly selenizing nickel foam substrates at different temperatures under an inert atmosphere. When evaluated as electrocatalysts in OER, the optimal self-supported NiSe₂/NF-350 shows an excellent performance in 1.0 M KOH medium with an overpotential of 458 mV at 100 mA cm^?2, a small Tafel slope of 45.8 mV dec^?1, and a long-term stability for 36 h. Furthermore, the structural and compositional preservation for NiSe₂/NF-350 after stability test was also verified by various characterizations.     

Porous nickel telluride nanostructures as bifunctional electrocatalyst towards hydrogen and oxygen evolution reaction

Electrochemical water splitting technology has attracted researchers for the development of next generation fuels. Herein, we report the synthesis of nanostructured porous hollow nickel telluride nanosheets and their use as bifunctional electrocatalyst towards hydrogen and oxygen evolution reaction, anticipating an enhanced performance owing to their 2D sheet like morphology, conductivity, porous nature providing larger catalytic surface for water splitting reaction. In this regard, nickel telluride nanostructures were synthesized via an anion-exchange-reaction between pre-synthesized nickel hydroxide hexagonal nanosheets and tellurium ions under hydrothermal conditions. The as-synthesized nanostructures were characterized for structural, morphological and compositional properties using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Nickel telluride modified electrodes were tested as bifunctional electrocatalyst under acidic and alkaline conditions, through linear sweep voltammetry and constant current chronopotentiometry methods. The modified electrodes revealed an onset potential of ?422 mV and 87.4 mV dec^?1 Tafel slope towards HER and overpotential of 679 mV and 151 mV dec^?1 Tafel slope towards OER. The lower onset potentials are complimented with excellent electrocatalytic stability.     

Hollow hexagonal NiSe–Ni3Se2 anchored onto reduced graphene oxide as efficient electrocatalysts for hydrogen evolution in wide-pH range

Integrating transition metal complexes with carbon-based materials, especially graphene, is a useful strategy for synthesizing effective hydrogen evolution catalysts. Herein, we report a design of hollow hexagonal NiSe–Ni₃Se₂ nanosheets grown on reduced graphene oxide (NiSe–Ni₃Se₂/rGO) by a simple hydrothermal method as an effective catalyst for hydrogen evolution reaction (HER) in the full pH range. In 0.5 M H₂SO₄, the NiSe–Ni₃Se₂/rGO possesses 112 mV to achieve 10 mA cm^?2 and a small Tafel slope (61 mV dec^?1). In 1.0 M PBS and 1.0 M KOH, the overpotentials are 261 and 188 mV at 10 mA cm^?2, and Tafel slopes are 103 and 92 mV dec^?1, respectively. Meanwhile, it owns good cycle stability and durability over 20 h in the whole pH range (0-14). In all solutions, the HER performance of NiSe–Ni₃Se₂/rGO is better than that of NiSe–Ni₃Se₂. This is because the rGO substrate accelerates the electron transfer and improves the electrical conductivity, increasing HER activity of catalyst.     

Synthesis of nitrogen-doped MoSe2 nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction

Benefiting from improved electrical conductivity, the N-doped MoSe₂ nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately ?135 mV and a smaller Tafel slope of 62 mV dec^?1, which exhibiting enhanced catalytic performance compared with that of pure MoSe₂. The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe₂-based electrocatalyst.     

Flower-like CoS2/MoS2 nanocomposite with enhanced electrocatalytic activity for hydrogen evolution reaction

Molybdenum sulfide (MoS₂) has received tremendous attracts for its promising performance in the aspects of hydrogen evolution reaction (HER). To improve the HER activity of MoS₂, we designed a flower-shaped CoS₂/MoS₂ nanocomposite with enhanced HER electroactivity compared with MoS₂ nanosheets by a simple one-step hydrothermal method. The facile approach brings about distinct transformation of the morphology from nanosheets to nanoflower structures. The introduction of Co element into MoS₂ results in the larger active surface area, more edge-terminated structures, and higher conductivity of the CoS₂/MoS₂ nanocomposite, which are good for improving the HER electroactivity. In brief, the optimized catalyst exhibits the low overpotential of 154 mV at 10 mA cm^?2, small Tafel slope of 61 mV dec^?1, and excellent stability in acidic solution.     

Novel strongly coupled tungsten-carbon-nitrogen complex for efficient hydrogen evolution reaction

Alternatives to noble metal based electrocatalysts are vitally necessary to produce hydrogen from water at low overpotentials. Earlier research on tungsten based electrocatalyst has been mainly concentrated towards tungsten carbide (WC) and tungsten nitride (WN) as the potential electrocatalysts for hydrogen evolution reaction (HER), whereas tungsten carbide (W₂C) has been least focused upon. Herein, we report a highly active novel strongly coupled tungsten-carbon-nitrogen complex (W₂C-NC-WN complex) prepared by in situ carbonization method. This W₂C-NC-WN complex exhibits a remarkable electrochemical performance for HER with a small onset potential of 33 mV vs. RHE and requires an overpotential (η) of 145 mV vs. RHE to render ?10 mA cm^?2 current density. The Tafel analysis demonstrates a slope of 96 mV dec^?1 which is much better than WN (109.6 mV dec^?1) and WC (142.4 mV dec^?1). The strong coupling of W₂C and WN within N-doped carbon (NC) framework brings about a significant enhancement in HER kinetics and faster electron transport due to the remarkable reduction in charge transfer resistance. The facile synthetic approach reported here, provides a powerful tool for the structurally controlled modification of the catalyst while simultaneously introducing active species.     

3D hierarchical network NiCo2S4 nanoflakes grown on Ni foam as efficient bifunctional electrocatalysts for both hydrogen and oxygen evolution reaction in alkaline solution

The development of cost-effective and high-efficiency electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) still remains highly challenging. Exposing as many active sites as possible is the key method to improve activity of HER and OER performance. In this communication, we demonstrate a novel 3D hierarchical network NiCo₂S₄ nanoflake grown on Ni foam (NiCo₂S₄-NF) as a highly efficient and stable electrochemical catalyst. The NiCo₂S₄-NF exhibits overpotentials as low as 289 and 409 mV at 100 mA cm^?2, superior long-term durability during a 20 h measurement, and a low Tafel slope of 89 and 91 mV dec^?1 for HER and OER in 1.0 M NaOH solution. The outstanding performance is owe to the inherent activity of ultrathin NiCo₂S₄ nanoflakes and the special structure of NiCo₂S₄-NF that can provide a huge number of exposed active sites, accelerate the transfer of electrons, and facilitate the diffusion of electrolyte simultaneously.     

Ni–MoS2 composite coatings as efficient hydrogen evolution reaction catalysts in alkaline solution

It remains an important project for the development of water splitting electrolyze to design and synthesis of more efficient non-noble metal catalyst. In this work, a structured Ni–MoS₂ composite coating has been synthesized under supergravity fields with nickel sulphamate bath containing suspended MoS₂ submicro-flakes. X-ray diffraction patterns indicate that the MoS₂ submicro-flakes have been successfully incorporated into the Ni matrix. Additionally, SEM shows that the prepared Ni–MoS₂ composite coatings display finer grain size than the pure Ni coatings, which can increase the electrochemistry surface area and the active site of hydrogen evolution reaction. Therefore, due to the synergistic effect of molybdenum disulfide and nickel, the Ni–MoS₂ composite coatings are directly used as binder-free electrode, which exhibits outstanding electrocatalytic activity for HER in 1.0 M NaOH solution at room temperature. The Ni–MoS₂ composite coatings demonstrated an outstanding performance toward the electrocatalytic hydrogen production with low overpotential (100 mA cm^?2 at η = 207 mV), a Tafel slope as small as 65 mV dec^?1, and stable cycling performance (1200 cycles). The preeminent HER performance of this catalyst suggests that it may hold great promise for practical applications.     

Hierarchical MoS2 nanoflowers on carbon cloth as an efficient cathode electrode for hydrogen evolution under all pH values

In this paper, a facile hydrothermal synthetic strategy was developed for MoS₂ nanoflowers with enlarged interlayer spacing on the carbon cloth (CC) as a high efficiency cathode electrode for hydrogen evolution reaction (HER) under wide pH condition. It was observed that the loading amount of MoS₂ has a major impact on the HER performance, where the optimized MoS₂/CC exhibited a low onset potential of 94 mV and a small Tafel slope of 50 mV dec^?1 in strong acid solution (pH = 0). The improved HER performance can be contributed to the enlarged interlayer spacing, abundant defects and more exposed active sites in the small size MoS₂ nanosheets as revealed by XRD and HRTEM. Meanwhile, it also exhibited relatively good performance for HER under basic and neutral conditions with the overpotentials of 188 (pH = 14) and 230 (pH = 7) mV to achieve current density of 10 mA cm^?2 and the Tafel slopes of 52 and 84 mV dec^?1, respectively.     

One-step synthesis of the 3D flower-like heterostructure MoS2/CuS nanohybrid for electrocatalytic hydrogen evolution

In this work, a facile one-step hydrothermal method was developed to fabricate three types different of nanomaterials: the two-dimension (2D) of MoS₂ nanosheets; 3D spherical CuS nanoparticles; and 3D flower-like heterostructure of MoS₂/CuS nanohybrid, respectively. The as-synthesized MoS₂, CuS and MoS₂/CuS were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM) and X-ray diffraction (XRD) etc. The morphology of the MoS₂/CuS nanohybrid is different from the MoS₂ nanosheets and CuS nanoparticles. The hydrogen evolution reaction (HER) activity of MoS₂ nanosheets, CuS nanoparticles and MoS₂/CuS nanohybrid, were investigated by the Linear Sweep Voltammetry (LSV) and Tafel slope. The HER activity of MoS₂/CuS nanohybrid is better than those of MoS₂ nanosheets and CuS nanoparticles, which can be attributed to the good electron-transport ability of CuS and the strong reduction ability of hydrogen ions by MoS₂. Thus, MoS₂/CuS nanohybrid exhibited excellent activity for HER with a small onset potential of 0.15 V, a low Tafel slope of 63 mV dec^?1, and relatively good stability. However, the MoS₂ nanosheets and CuS nanoparticles respectively shows a bigger onset potential of 0.25 V and 0.35 V, a higher Tafel slope of 165 and 185 mV dec^?1. This 3D flower-like heterostructure of MoS₂/CuS nanohybrid catalyst exhibits great potential for renewable energy applications.     

Phosphorus-doped nickel selenides nanosheet arrays as highly efficient electrocatalysts for alkaline hydrogen evolution

Earth-abundant transition-metal dichalcogenides are considered as promising electrocatalysts to accelerate the hydrogen evolution reaction （HER）. Among them, the pyrite nickel diselenide (NiSe₂) has been received special attention due to its low cost and high conductivity, but it suffers a poor HER performance in alkaline media possibly attributed to its inadequate hydrogen adsorption free energies. Here, we report a novel P-doped NiSe₂ nanosheet arrays anchored on the carbon cloth with an obviously optimized HER performance. The catalyst only needs a low overpotential of 86 mV at a current density of 10 mA cm^?2 and a Tafel slop of 61.3 mV dec^?1，as well as maintains a long-term durability for 55 h in 1.0 M KOH, which is superior to the pristine NiSe₂ (135 mV@10 mA cm^?2) and most recently reported non-noble metal electrocatalysts. The XRD, EDS, TEM and XPS results validated the successful doping of P element into NiSe₂ nanosheet, while the density functional theory (DFT) calculation demonstrated the P doping can optimize the electronic structures and the hydrogen adsorption free energy of NiSe₂. This work thus opens up new ways for rationally designing high-efficient HER electrocatalysts and beyond.     

Mo incorporated W18O49 nanofibers as robust electrocatalysts for high-efficiency hydrogen evolution

Creation of robust and stable electrocatalysts is a persistent objective for high-efficiency hydrogen evolution by water splitting. We present here the experimental realization of one-dimensional Mo incorporated W₁₈O₄₉ nanofibers (NFs) by a template-free solvothermal method. When utilized as electrocatalysts for hydrogen evolution through water splitting, the preliminary results demonstrate that the optimized catalytic electrode from 1 at% Mo doped W₁₈O₄₉ NFs yields an onset overpotential of 89 mV and Tafel slope of 49 mV dec^?1 as well as maximal exchange current density up to 1.60 × 10^?2 mA cm^?2. An overpotential as low as 462 mV is required to attain current density of 50 mA cm^?2 in comparison with 587 mV for pristine W₁₈O₄₉ NFs. Moreover, the Mo doped W₁₈O₄₉ NFs display relative stability by applying a potential of 503 mV and a current density of 80 mA cm^?2 over 24 h in 0.5 M H₂SO₄ aqueous solution, making them promising in practical applications.     

MoS2 supported on MOF-derived carbon with core-shell structure as efficient electrocatalysts for hydrogen evolution reaction

In this work, the porous carbon polyhedra were firstly obtained by carbonizing the zeolite imidazole framework (ZIF-8). Then the carbon polyhedra and precursors of MoS₂ were successfully combined by a hydrothermal reaction, forming the C-MoS₂ composites with different carbon contents. The well-tuned C-MoS₂ sample possesses a core-shell morphology, in which the carbon substrate is well decorated by vertically aligned MoS₂ ultrathin nanosheets. The resulting composites can be used as electrocatalysts of hydrogen evolution reaction (HER), displaying significantly superior activities to pure MoS₂ and carbon. It's found that the carbon content largely affects the architectures and HER behaviors of catalysts. In particular, the optimized catalyst yields the best catalytic activity with the lowest onset potential (35 mV), smallest Tafel slope (53 mv dec^?1), lowest overpotential (200 mV at 10 mA cm^?2), as well as extraordinary long-term stability in H₂SO₄. The enhanced HER activity can be attributed to the unique core-shell structure, where abundant active edge sites of MoS₂ are exposed and the underlying carbon substrate effectively improves the conductivity of the electrode.     

Co Nanoparticles@N-doped carbon coated on carbon Nanotube@Defective silica as non-noble photocathode for efficient photoelectrochemical hydrogen generation

The development of photoelectrodes capable of light-driven hydrogen evolution from water with non-noble metals is an important approach for the storage of solar energy in the form of a chemical energy carrier. In this study, we report Co nanoparticles@N-doped carbon coated on carbon nanotube@defective-silica (CNTs@Co@NC/D-SiO₂), which are composed of Co nanoparticles@N-doped carbon as electrocatalyst, defective-silica as photocatalyst and carbon nanotube as conductive substrates. The obtained non-noble photocathode possesses the high performance for efficient photoelectrochemical hydrogen evolution reaction. When evaluated for hydrogen evolution reaction electrocatalysis, CNTs@Co@NC/D-SiO₂ exhibits a small onset overpotential of 104 mV (J = 1 mA cm^?2), a Tafel slope of 69.1 mV dec^?1 and outstanding long-term cycling stability. The P type semiconductor characteristics of CNTs@Co@NC/D-SiO₂ due to defective-silica with carrier concentration of 3.53 × 10¹⁹ cm^?3 is measured, which produces a significant positive shift of overpotential of 40 mV (J = 10 mA cm^?2) under 100 mW cm^?2 simulated sunlight irradiation. These findings provide a straightforward and effective route to produce cheap and efficient photo-electro-catalyst for water splitting.     

Hierarchical self-supported NiSe2/TiN@Ni12P5 on nickel foam for the urea oxidation reaction

The development of high-performance, low-cost, and non-noble metal catalysts for the urea oxidation reaction (UOR) as an alternative to oxygen evolution reaction (OER) has received much attention but remains a huge challenge. In this work, NiSe₂/TiN@Ni₁₂P₅/NF catalysts with a stalactite structure were prepared by chemical vapor deposition to obtain the integrated electrode Ni₁₂P₅/NF on the nickel foam (NF), and subsequently NiSe₂/TiN was formed on the Ni₁₂P₅/NF surface by the hydrothermal method. The designed catalyst delivers an ultra-low potential of 1.270 V at 10 mA cm^?2, and a Tafel slope of 33.3 mV dec^?1 for UOR. Furthermore, the catalyst only shows a 1.7% decrease in potential after an 80-h stability test, which demonstrates its excellent stability. The prepared NiSe₂/TiN@Ni₁₂P₅/NF shows a high specific surface area, and the strengthening effect between TiN and NiSe₂, endowing the catalyst a high activity and durability.     

A high active hydrogen evolution reaction electrocatalyst from ionic liquids-originated cobalt phosphide/carbon nanotubes

Ionic liquid/carbon nanotubes (IL/CNTs) composite was applied as the precursor to prepare CNTs-supported cobalt phosphide via low-temperature phosphidation. CoP_(MBMG)/CNTs, generated from N,N-bis(4-(methoxycarbonyl)benzyl)-N-methyl-d-glucaminium dibromodichlorocobaltate(II) (MBMG)₂-CoCl₂Br₂), exhibits the best catalytic activity toward hydrogen evolution reaction with an onset overpotential of 55 mV, a Tafel slope of 58 mV dec^?1, 95% Faradaic efficiency (FE), current densities of 10 and 20 mA cm^?2 at overpotentials of 135 and 160 mV, and it can maintain the catalytic activity for at least 27 h. FT-IR, Raman spectroscopy, XPS and XRD were utilized to investigate the phosphidation process. All experimental results confirmed that anion from (MBMG)₂-CoCl₂Br₂ can form CoP and glucaminium-based cation can become amorphous carbon after phosphidation to obtain the high HER activity of CoP_(MBMG)/CNTs.     

Syntheses of nickel sulfides from 1,2-bis(diphenylphosphino)ethane nickel(II)dithiolates and their application in the oxygen evolution reaction

In this work, four heteroleptic Ni(II)dppe dithiolates complexes, [Ni(NED)(dppe)] (Ni-NED), [Ni(ecda)(dppe)] (Ni-ecda), [Ni(i-mnt)(dppe)] (Ni-i-mnt) and [Ni(cdc)(dppe)] (Ni-cdc) (dppe = 1,2-bis(diphenylphosphino)ethane; NED = 1-nitroethylene-2,2-dithiolate; ecda = 1-ethoxycarbonyl-1-cyanoethyelene-2,2-dithiolate; i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and cdc = cyanodithioimidocarbonate), have been synthesized and characterized by analytical and spectroscopic techniques (Elemental analysis, vibrational, electronic absorption and multinuclear NMR spectroscopy). Structural characterization of all the four complexes by single crystal X-ray diffraction study suggests distortion in regular square planar geometry at Ni(II) center by coordination with two phosphorus of the dppe and two sulfur of the dithiolate ligands, respectively. The decomposition of all four complexes have been done to produce nickel sulfides and the resulting nickel sulfides have been utilized for electrocatalytic oxygen evolution reaction (OER). The nickel sulfide obtained by decomposing Ni-cdc shows best activity with overpotential η = 222 mV at j = 10 mA cm^?2 and a Tafel slope of 44.2 mV dec^?1 while other catalysts shows η > 470 mV at j = 5 mA cm^?2 and η > 600 mV at j = 10 mA cm^?2 at loading of 1.3 mg cm^?2.     

Cobalt carbonate hydroxide mesostructure with high surface area for enhanced electrocatalytic oxygen evolution

Hydrogen energy utilization from water splitting relies on the successful development of earth-abundant, efficient, and stable electrocatalysts for oxygen evolution reaction (OER). Herein, novel cobalt carbonate hydroxide nanorods are synthesized by facile low-temperature precipitation. The nanorods are networked to form mesoporous structure with a large surface area (291.4 m² g^?1) and high pore volume (1.06 cm³ g^?1). The obtained catalyst reaches a current density of 10 mA cm^?2 with an overpotential of a 320 mV and a Tafel slope of 39 mV dec^?1. Moreover, OER activity is improved after stability test, while the overpotential drops down to 313 mV. This increase in activity is explained by in-situ conversion from carbonate to hydroxide, resulting in an increase of active sites. The synthesis route allows an efficient way for obtaining novel cobalt-based OER electrocatalyst, and the enhancement in catalytic activity after stability test also gives a new insight for designing high-performance OER electrodes.