Fabrication of Co doped MoS2 nanosheets with enlarged interlayer spacing as efficient and pH-Universal bifunctional electrocatalyst for overall water splitting

Exploring inexpensive and active bifunctional electrocatalysts to produce hydrogen and oxygen from water at all pHs is highly desirable. Herein, we report a facile one-step method to prepare vertically aligned Co doped MoS₂ nanosheets with extended interlayer distance on carbon cloth (Co–MoS₂@CC) for full hydrolysis in both alkaline and acidic medium. Co–MoS₂@CC exhibits long-term durability with overpotentials of 56.6 mV and 130 mV for hydrogen generation and 242 mV and 201 mV for oxygen production at 10 mA cm^?2 in basic and acidic conditions, respectively. Moreover, we achieve low voltages of 1.585 V and 1.55 V in basic and acidic conditions respectively for the overall water splitting. We assume that such excellent property of Co–MoS₂@CC may be ascribed to the uncovering of more active sites and high porosity resulted from Co doping, which boosts the conductivity and thus reduces MoS₂ hydrogen adsorption free energy in HER, as well as benefits to catalytic active sites in OER. This one-step doping approach opens up new ways to regulate the intrinsic catalytic activity to catalyze total hydrolysis at all PHs.     

MoSe1.48S0.52@C as cathode material for rechargeable aluminum-ion batteries and Al–S batteries

Transition metal chalcogenides (TMDCs) present an excellent initial discharge capacity for aluminum ion batteries (AIBs). However, its strong acting force with Al³⁺ and poor electrical conductivity hinder the further application of TMDCs in high-capacity AIBs. In this work, Peony-like MoSe_1.48S_0.52@C was prepared for AIBs cathode by hydrothermal method. The outsourced carbon reduces the agglomeration of MoSe_1.48S_0.52. Meanwhile, the S doping to form Se_1.48S_0.52 interlayer ligands, together with the Se presence to lower the band gap, enhances electrons transport and storage performance of aluminum. In addition, the material MoSe_1.48S_0.52@C can stably accommodate S nanoparticles and anchor aluminum sulfide to enhance the electrochemical stability of the cathode. The electrochemical test result shows that the specific capacitance of MoSe_1.48S_0.52@C reaches 300.8 mAh g^?1 at 100 mA g^?1. Note that the specific capacity for MoSe_1.48S_0.52@C@S is up to 1000 mAh g^?1 at 200 mA g^?1.     

Electrospinning Ru doped Co3O4 porous nanofibers as promising bifunctional catalysts for oxygen evolution and oxygen reduction reactions

Enhancing the catalytic activity for oxygen evolution and oxygen reduction reactions is critical for rechargeable metal-air batteries. Herein, coral-like Ru-doped cobalt oxide nanofibers are prepared by electrospinning and subsequent heat treatment, which reduce the charge transfer resistance of cobalt oxide and optimize its active sites. Moreover, the large specific surface area and rich porosity of the one-dimensional nanomaterials prepared by the electrospinning method markedly improved the catalytic activity. Under the same catalyst load, Ru-doped cobalt oxide nanofibers have an overpotential of 300 mV, which is smaller than that of ruthenium oxide. In the oxygen reduction reaction, the positive half-wave potential of Ru-doped cobalt oxide nanofibers and Pt/C is the same (0.81 V). This work combines the strategies of doping and the advantages of electrospinning nanofibers to make a breakthrough in the catalytic activity of doped cobalt oxide nanofibers, and provides a new basis for the design of one-dimensional nanofiber bifunctional catalysts.     

P-doped MoS2/Ni2P/Ti3C2Tx heterostructures for efficient hydrogen evolution reaction in alkaline media

By combining the advantages of doping to change the electronic structure of molybdenum disulfide (MoS₂), transition metal phosphides, and MXene, we proposed the idea of designing and preparing a new type of composite material, P-doped MoS₂/Ni₂P/Ti₃C₂T_x heterostructures (denoted as P@MNTC), to serve as the hydrogen evolution reaction (HER) catalyst of electrochemical water splitting. The as-prepared P@MNTC heterostructures show a significant HER activity with an overpotential of 120 mV at 10 mA cm^–2 in alkaline electrolyte, with decreasing 105 and 125 mV compared with those of MoS₂ and MXene, respectively. The density functional theory indicates that the P doping and synergy effect of Ti₃C₂T_x can enhance the activation of MoS₂ and thus promote dissociation and absorption of H₂O during HER process. This strategy provides a promising way to develop high-efficiency MoS₂- and Ti₃C₂T_x-based composite catalysts for alkaline HER.     

Characterization of hydrogen evolution on cobalt electrodeposits in water electrolysis

The hydrogen evolution reaction (HER) on cobalt electrodes has been investigated in both alkaline (30 wt% KOH) and acid (1m H₂SO₄) media at 25°C. The electrocatalytic cobalt materials were produced under different electrodeposition conditions, namely deposition in the absence or presence of bubbling oxygen or nitrogen gas with two gas flow rates (80 and 230 ml min^–1) and at different current densities (50–800 A m^–2) and deposition in a cobalt powder-containing bath. It has been shown that the electrocatalytic behaviour of the cobalt deposits can be significantly affected by deposition current density via a change of surface area of the cobalt deposits. A considerable HER overpotential decrease (up to 150mV) has been achieved on the highly porous and active cobalt electrodes deposited in the presence of bubbling oxygen and chloride ions in deposition solution. However, the HER overpotential was increased on the cobalt electrodes deposited with bubbling nitrogen in the bath.     

Mixed 3D/2D dimensional TiO2 nanoflowers/MoSe2 nanosheets for enhanced photoelectrochemical hydrogen generation

Recently, v arious kinds of methods have been implemented to broaden the visible light response and fasten the carrier's separation of TiO₂-based photoanodes. As a promising hydrogen evolution reaction catalyst, MoSe₂ is rarely investigated especially combined with TiO₂ photoanode. In this study, we report a composite photoanode of MoSe₂ nanosheets (with 1T and 2H phase)-modified 3D TiO₂ nanoflowers (NFs).The hybrid of 3D TiO₂ NFs/2D MoSe₂ holds great promise in boosting the PEC water splitting performance. TiO₂ NFs/MoSe₂-15 showed the largest photocurrent density of 1.40 mA/cm², which was five times higher than that of pure TiO₂ NFs under AM1.5G illumination. Moreover 10 times improvement in current density was observed for the TiO₂ NFs/MoSe₂-15 under visible light. This increase could be ascribed to synergistic effects of light absorption enhancement and more efficient carrier separation after MoSe₂ modification. This study not only provides a reference to boost the photoelectrochemical performance of photoelectrodes but also renders a perspective on the potential applications of MoSe₂ nanosheets.     

Efficient solar-light-driven photoelectrochemical water oxidation of one-step in-situ synthesized Co-doped g-C3N4 nanolayers

Cobalt-doped g-C₃N₄ (Co-g-CN) nanolayers were prepared by a single-step thermal treatment with urea and cobalt nitrate. Different amounts of cobalt nitrate were tested to optimize the amount of cobalt dopant in the g-C₃N₄ (g-CN) matrix. Several characterization methods were used to explore the structural and optical properties along with the photoelectrochemical (PEC) performance. X-ray diffraction and Fourier transform infrared studies confirmed that g-CN nanolayers were successfully doped with cobalt without disturbing the basic 2-D structure and tris-triazine units of g-CN. Furthermore, microscopy images demonstrated that the cobalt effectively transformed the short nanosheets into long nanolayers. The cobalt-doping enhanced the visible absorption of g-CN and tuned the bandgap from 2.71 to 2.62 eV. An X-ray photoelectron spectroscopy (XPS) investigation discovered that cobalt entered into the g-CN network as Co²⁺ ions. XPS valence band spectra gave information on the modification in the valence and conduction band edge potentials due to cobalt doping. The photoluminescence intensity from the Co-g-CN samples was lesser than that from g-CN nanosheets, and the PEC activity of the Co-g-CN nanolayers was greater than that of as-prepared g-CN nanosheets. Co-g-CN samples prepared with 15 mg of cobalt nitrate hexahydrate showed a PEC performance of 3.2522 mA/cm², which was greater than that of g-CN nanosheets (1.9246 mA/cm²). The better PEC performance was ascribed to the synergistic consequence of the higher visible absorption obtained by tuning the bandgap and the host–guest interactions between cobalt and g-CN.     

铁硼基海绵催化电极的制备及其高效析氢性能

采用温和化学镀法在非导电基底材料聚氨酯海绵(PU)上成功制备了NiB@Fe–B/PU催化电极,并通过掺杂少量第三种元素,如钴、钼等金属元素制备了NiB@Fe–Co–B/PU和NiB@Fe–Mo–B/PU催化电极。结果表明,掺杂钴、钼可明显提升NiB@Fe–B/PU催化电极的析氢性能,其中掺杂钴的性能更优。在0.5 mol/L缓冲液(磷酸缓冲盐溶液,PBS)中,NiB@Fe–Co–B/PU电极的析氢反应(HER)过电位仅为161 mV(电流密度, j=50 mA/cm2),塔菲尔斜率为68.24 mV/dec,且在过电位为61 mV下能够稳定工作24 h以上,电化学稳定性良好。     

A biotemplate synthesized hierarchical Sn-doped TiO2 with superior photocatalytic capacity under simulated solar light

Despite a number of studies have been carried out on TiO₂ based materials as photocatalysts for water pollutant treatment, it still needs sustained effort to extend the optical range of the photocatalysts and inhibit the recombination of photo-induced carriers to improve their catalytic activities under solar light. In this work, a series of Sn-doped TiO₂ with different amounts of Sn doping (1, 5, 10 and 20 mol%) were biomimetically synthesized by a facile sol–gel method using cellulosic cotton as biotemplate. The Sn-doped TiO₂ materials possess a typical three-dimensional hierarchical structure of microtubes consisting of interwoven nanofibers. The photocatalytic performance was evaluated via the degradation of methylene blue (MB) (10.0 mg L^?1) under Xenon lamp simulated solar irradiation. The results show that Sn(5)-TiO₂ (5 mol% Sn doping) sample exhibits an outstanding photocatalytic capacity with a superior degradation rate of higher than 98% within 30 min and a good reusability without significant decrease of activity after reused for four cycles. The most significantly improved photocatalytic capacity of TiO₂ is ascribed to more extra surface hydroxyl groups and accessible active sites provided by the relatively high surface area, and a higher light capturing and utilization efficiency with less recombination of the photogenerated electron-hole pairs endowed by the good synergistic effect of the special hierarchically porous microstructure and the appropriate amount of Sn doping. Whereas, the excessive Sn doping reduces the photocatalytic activity obviously, resulting from the phase transformation of TiO₂ generating more rutile phase with less reactivity, the phase separation with clear grain boundary blocking the active sites, and the extra Sn⁴⁺ acting as the recombination center. This research presents a facile biomimetic synthesis strategy combined with the traditional sol–gel method to develop various ion doped metal oxides as photocatalysts with enhanced activity.     

Effective hydrolysis of sodium borohydride driven by self-supported cobalt oxide nanorod array for on-demand hydrogen generation

Hydrogen storage, distribution and controlled release are of important concerns for hydrogen based economy. Sodium borohydride (NaBH₄) is one of the mostly studied chemical hydrides used for hydrogen storage and generation. However, it requires efficient catalysts to accelerate its dehydrogenation for controllable hydrogen production. In this paper, we demonstrate that the dehydrogenation of NaBH₄ in alkaline solutions can be driven by self-supported cobalt oxide nanorod array on Ti sheet (Co₃O₄ NA/Ti). Such Co₃O₄ NA/Ti shows high catalytic performance with a maximum hydrogen generation rate of 1940 mL/min/g_Co3O4 and an activation energy of 59.84 kJ/mol under ambient condition. Moreover, this catalyst exhibits no mass or activity loss even after 5 cycles with an obvious advantage of easy separation from the fuel solution. This development offers us a cost-effective and recyclable catalytic material toward hydrolytic hydrogen production for applications.     

Structure and catalytic activity correlation of CoAlPO4 in the synthesis of N,N-biphenyl urea via alkylation of aniline using dimethyl carbonate

Two sets of cobalt aluminophosphate materials, one at different pH (4.5, 7, 10, and 11.5) and the other containing different percentage of cobalt (0.5–20) were prepared by co-precipitation method. All the materials were characterized by XRD, SEM, ²⁷Al MASS NMR, TGA and DSC, FTIR, for their textural and structural properties. The surface area of the samples was determined by BET method and total surface acidity by n-butylamine titration method. The CoAlPO₄ obtained under acidic pH were found to be crystalline AlPO₄ with nonmicroporous tridymit structure associated with cobalt phosphate, whereas the one obtained under alkaline pH were amorphous aluminophosphate and also associated with cobalt phosphate. Tridymit-AlPO₄ crystals exhibited Al atom in a tetrahedral environment of phosphate groups. In the amorphous material the Al atoms were in a mixed tetrahedral and octahedral environment. The concentration of acid sites were found to be higher in the sample obtained under alkaline pH. This has been attributed due to the partial coordination of hydroxyl groups in the octahedral aluminum sites. The amorphous materials obtained under alkaline pH were found to be thermally stable up to 900 °C.The catalytic activity of all the materials was investigated in aniline alkylation using dimethyl/ethyl carbonates (DMC/DEC) under refluxing conditions. N-methyl/ethyl aniline (NMA/NEA) and biphenyl urea (BPU) were formed as the major products with the catalysts prepared at acidic and alkaline pH, respectively. A good correlation has been observed between the catalytic activity of CoAlPO₄ materials towards their selectivity for NMA/NEA and/or BPU and their textural and structural properties. Reaction conditions such as the amount of the catalyst, duration of the reaction, reusability and efficiency of the catalyst have also been evaluated. CoAlPO₄ prepared under alkaline pH with 5% of cobalt has been found to be the best catalyst for BPU synthesis from aniline and DMC/DEC under refluxing conditions.     

Structural,optical, morphological properties of silver doped cobalt oxide nanoparticles by microwave irradiation method

The synthesis of silver doped cobalt oxide nanoparticles by microwave-assisted method and their structural, optical, antibacterial activities are presented in this study. The doping concentrations were chosen as 5, 10, 15, and 20 wt percentages. The sample was undergone powder X-ray diffraction studies and the result shows the good crystalline nature of the sample. Also, the average crystallite size increases from 13.95 nm, 21.26 nm, 26.13 nm, and 28.35 nm with different doping concentrations. The transmission electron microscopy image shows cubic and spherical morphology. The optical properties were tested by UV–vis–NIR absorption spectrum. It indicates the decrease of band gap value. From the antibacterial activity studies, the 20 wt % Ag doped nanoparticles exhibit better activity.     

ZSM-5 Supported Cobalt Catalyst for the Direct Production of Gasoline Range Hydrocarbons by Fischer–Tropsch Synthesis

Abstract  

Fischer–Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C₅–C₉) from syngas was investigated on cobalt-based FTS catalyst supported on the ZSM-5 possessing a four different Si/Al ratio. The FTS catalysts were prepared by impregnation method using cobalt nitrate precursor in a slurry of ZSM-5, and they were characterized by surface area, XRD, H₂-TPR and NH₃-TPD. Cobalt supported catalyst on ZSM-5 having a low Si/Al ratio of 15 was found to be superior to the other catalysts in terms of better C₅–C₉ selectivity due to the formation of small cobalt particle and the presence of larger number of weak acidic sites. It also exhibited the highest catalytic activity because of the higher reducibility and the small cobalt particle size.     

The influence of different zeolitic supports on hydrogen production and waste degradation

The photocatalyst composition affects the chemical–physical properties and directly impacts photocatalytic activity, both in the hydrogen production and degradation of organic contaminants. In this work, the influence of zeolitic structures NaA, NaY, and ZSM-5 combined with a 10% active phase, TiO₂ catalyst doped with 1% copper, and cobalt cocatalysts was tested to mineralize the reactive blue dye (CI250) and to produce hydrogen by photocatalysis under ultraviolet radiation. The band gap energy was affected mainly by the cocatalyst, while the Brunauer-Emmett-Teller method (BET) area was affected by the zeolite structure as well as the X-ray diffraction (XRD). The most active catalyst was the Cu@TiO₂/NaY, which promoted a hydrogen production rate of 240 μmolH₂gcat⁻¹ using 10% ethanol (v/v) aqueous solution as a sacrificial agent and mineralization of 53% of the organic dye, followed by the catalysts impregnated on ZSM-5 zeolites, which had discolouration up to 50% and hydrogen evolution of 92.6 and 109.7 μmolH₂gcat⁻¹ for the catalyst doped with Cu and Co, respectively.     

Cobalt Porphyrins Immobilized on Polymer Microspheres as Catalysts for the Oxidation of 2-naphthol to 2-hydroxy-1,4-naphthoquinone by Molecular Oxygen

Abstract  

Three types of porous polymer microspheres immobilized with cobalt porphyrins appending p–H, p-Cl and p-NO₂ phenyl substituents (designated as CoPP-GMA/MMA, CoCPP-GMA/MMA and CoNPP-GMA/MMA, respectively) were prepared. Their catalytic activities on the oxidation of 2-naphthol to 2-hydroxy-1,4-naphthoquinone by molecular oxygen were investigated in alkaline methanol. The experimental results showed that the porous microsphere supported cobalt porphyrin catalysts could effectively activate molecular oxygen, and 2-naphthol was selectively oxidized to 2-hydroxy-1,4-naphthoquinone with high conversion in alkaline methanol. A phenomenon of distance-dependent catalytic activity was observed and a critical distance of 3.8 nm between porphyrins was determined for the porous polymer microsphere supported catalyst. More interestingly, the activity of the recycled catalyst increased gradually with the increased times of reuse. These results may be helpful in designing highly efficient metalloporphyrin catalysts.     

电催化析氢催化剂研究进展

氢能热值高和环境友好性强等特点使其成为未来能源界最具发展潜力的能源之一。电催化析氢反应（hydrogen evolution reaction,HER）作为一种绿色、可持续的产氢方法成为近年来广泛研究的主题。发展高性能、低成本、高活性的析氢催化剂是目前该领域面临的主要挑战。本文总结了近年来高性能催化剂用于HER反应的进展,重点介绍HER反应的基本原理,评估HER催化剂催化性能的典型方法,过渡金属以及化合物、非金属催化剂以及单原子催化剂等电催化析氢催化剂的最新研究进展,系统讨论了催化活性与催化剂形态、结构、组成和合成方法之间的联系,并对催化剂的合成策略、活性位点的固有活性、如何提高活性中心的内在活性和活性位点的数量进行了展望。     

Fabrication of porous Cu supported Ni-P/CeO2 composite coatings for enhanced hydrogen evolution reaction in alkaline solution

Cost-effective electrodes with high activity for hydrogen evolution reaction (HER) and durability are required to develop clean and renewable hydrogen energy. In this work, a porous Cu supported Ni-P/CeO₂ composite coating was fabricated by a facile electrodeposition technique. Owing to the contribution from the 3D porous Cu support and the incorporating agglomeration-free and uniformly distributed CeO₂ particles into the Ni-P matrix, the optimal composite coating (porous Cu supported Ni-P/CeO₂ (20 g L^-1)) exhibits outstanding electrocatalytic performance with small overpotentials (η) of 118 and 320 mV at a cathodic current density of 10 and 100 mA cm². Moreover, the composite electrode also presents excellent electrochemical stability in the alkaline solution. This work provides a feasible option to fabricate composite electrodes that may have desirable electrochemical properties for HER.     

Structural,magnetic and electrical properties along with antifungal activity & adsorption ability of cobalt doped manganese ferrite nanoparticles synthesized using combustion route

Ultrafine powders of Cobalt doped manganese ferrite with elemental composition Mn_1-xCo_xFe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) were synthesized using combustion method. The formation of the pure cubic spinel phase of ferrite structure was confirmed using X-ray diffraction and Fourier transform infrared spectroscopy. Structural parameters such as lattice constant, X-ray density, mass density, porosity, and cell volume were seen to be greatly influenced by cobalt doping. The surface morphology of the nanocrystalline samples was studied using a scanning electron microscope. The particle size distribution was determined using a Transmission electron microscope and nanograins of the samples were found to have dimensions in the range 15 nm–30 nm. It also showed its dependence on the extent of cobalt inclusion. Variation of magnetization and magnetic moment as a function of magnetic field and temperature was investigated using a vibrating sample magnetometer (VSM). The parameters such as saturation magnetization ‘M_S’ and inversion temperature T_I were seen to depend upon Co⁺² concentration. The variation dielectric constant ‘Ԑ’ as a function of frequency was studied. Antifungal activity of these ferrite nanoparticles against Rhizopus fungi was also investigated at room temperature. The antifungal activity was seen to increase with increasing Co⁺² content in the manganese ferrite structure and hence cobalt doped manganese ferrites are proposed as a candidate material for industries manufacturing antifungal products. The adsorption studies were also investigated using Methylene dye as the adsorbate.     

Tuning the electronic structure of NiCoP arrays through V doping for pH-universal hydrogen evolution reaction electrocatalyst

The exploration of cost-effective, high-performance, and stable electrocatalysts for the hydrogen evolution reaction (HER) over wide pH range (0–14) is of paramount importance for future renewable energy conversion technologies. Regulation of electronic structure through doping vanadium atoms is a feasible construction strategy to enhance catalytic activities, electron transfer capability, and stability of the HER electrode. Herein, V-doped NiCoP nanosheets on carbon fiber paper (CFP) (denoted as V_x-NiCoP/CFP) were constructed by doping V modulation on NiCoP nanosheets on CFP and used for pH-universal HER. Benefiting from the abundant catalytic sites and optimized hydrogen binding thermodynamics, the resultant V₁₅-NiCoP/CFP demonstrates a significantly improved HER catalytic activity, requiring overpotentials of 46.5, 52.4, and 85.3 mV to reach a current density of 10 mA·cm^–2 in 1 mol·L^–1 KOH, 0.5 mol·L^–1 H₂SO₄, and 1 mol·L^–1 phosphate buffer solution (PBS) electrolytes, respectively. This proposed cation-doping strategy provides a new inspiration to rationally enhance or design new-type nonprecious metal-based, highly efficient, and pH-universal electrocatalysts for various energy conversion systems.     

Toward enhancement of TiO2 surface defect sites related to photocatalytic activity via facile nitrogen doping strategy

This study examined the catalytic activities of three distinct N–Pd@TiO₂ nanoparticles, post-annealed (at 700, 800, and 900 °C) after fabrication on silicon substrates. Systematically, HRPES and SPEM indicated that nitrogen was predominantly doped around PdO nanostructure. Particularly, we prove that photocatalytic activity in effective nitrogen doped surface area is far higher than in undoped area of Pd@TiO₂ nanoparticles by measuring for oxidation reaction of benzenethiol, thioacetic acid, and thiobenzoic acid. Besides to the band gap narrowing, nitrogen doping leads to generate Ti^3 + species or oxygen vacancies site of the surface, which leads to enhance the activity of surface photocatalysis.