Rapid preparation of high efficiency hydrogen evolution catalyst with hydrophilicity.

The electrolytic water method is an outstanding hydrogen production process because of its high stability and no restriction. A low-priced and efficient catalyst for electro-deposition of Ni-Co microspheres and nanoclusters on carbon steel (Ni-Co/CS) has been prepared by the dynamic hydrogen bubble template. In the 6 M KOH solution, Ni-Co/CS only requires an overpotential of 48 mV to provide a current density of 50 mA cm-2. At the same time, it also has a large electrochemically active specific surface area (ECSA) and a hydrophilic surface. In addition, the study about the influence of carbon steel (CS) on Ni-Co coatings and the comparison experiment for different base materials has been completed. The results prove that CS is an excellent base material for hydrogen production. It can help the Ni-Co catalyst to have a stable electrolysis in 6 M KOH for 500 h. The above properties of Ni-Co/CS catalyst make it a new choice of hydrogen production by electrolysis of water in practical applications.

A universal synthesis of MOF-Hydroxyl for highly active oxygen evolution.

Since of their adjustable pore structure and variety of metal sites, MOFs materials have infinite possibilities, but their low intrinsic activity hinders them from being employed in electrolytic water. The sulfurization and oxidation of MOFs has proven to be a feasible technique for producing highly active catalytic materials. Here, the MOFs are completely converted to hydroxide by treatment with alkaline solutions only. Electron microscopy demonstrates that hydroxides generated from various MOFs retain the complete profile of the precursor and contain a two-dimensional lamellar or mesoporous structure. Fe-MIL-88(A)-OH, a two-dimensional structural transformation product generated from Fe-MIL-88(A), demonstrates significant OER performance increase. At the same 300 mV overpotential, Fe-MIL-88(A)-OH delivers 83 times the current density of Fe-MIL-88(A) and 16 times that of commercial IrO2 (22.56 mA cm-2 vs. 0.27 mA cm-2 vs. 1.37 mA cm-2). The alkali treatment strategy proved to be a generally applicable treatment for MOFs, allowing the conversion of nickel- and cobalt-based MOFs to hydroxide with a significant boost in OER performance.

High electrochemical performance of Fe2O3@OMC for lithium-ions batteries.

Fe2O3@OMC (ordered mesoporous carbon) is synthesized using Fe-MOFs (metal-organic frameworks). The Fe2O3@OMC pore size is mostly concentrated at approximately 2-4 nm. Compared to traditional OMC or carbonized Fe-MOFs, Fe2O3@OMC demonstrates a higher capacity (the capacity remains at 1176.6 mAh g-1 after 500 cycles under a current density of 0.1 A g-1) and a longer cycle life. The first cycle capacity of Fe2O3@OMC is ultrahigh at 2448.6 mAh g-1, and the reversible capacity is 1294.1 mAh g-1. Fe2O3@OMC maintains a good performance under current densities of 0.1 A g-1, 0.2 A g-1, 0.5 A g-1, 1 A g-1, 2 A g-1, and 5 A g-1, with electric capacities of 1100.8 mAh g-1, 1017.6 mAh g-1, 849.3 mAh g-1, 690.7 mAh g-1, 506.7 mAh g-1, and 272.1 mAh g-1, respectively. Thus, the material has good rate performance. Combining iron oxide and MOFs is helpful to improve the capacity performance.

Optimized electronic structure and p-band centre control engineering to enhance surface absorption and inherent conductivity for accelerated hydrogen evolution over a wide pH range.

Numerous experiments have demonstrated that an appropriate electronic configuration can effectively activate the electrocatalytic activity. However, systematic studies on the effects of non-metallic elemental doping and its p-orbital center (εp) on electrocatalysis have not yet been carried out. Combining theoretical and experimental methods, we demonstrate an electronic configuration and p-orbital center control engineering for promoting the HER course in both acid and alkaline solutions over group VA elements doped into the inert basal plane of nanoMoS2. In acidic solutions, As-doped MoS2 has the best electrocatalytic activity. Theoretically, the calculated ΔGH of the As atom is only -0.07 eV, indicating that it has excellent catalytic performance. Furthermore, the p-orbital center under and near the Fermi level plays a significant role in the H adsorption course, and the closer the εp value is to the Fermi level, the weaker the H- non-metallic atom bond is. An appropriate εp can insure a proper strength of bond with H and further influence the catalytic activity of the HER. In alkaline solutions, P-doped MoS2 has the best electrocatalytic activity, which is due to the engineering of water dissociation sites by doping P atoms into MoS2 nanosheets. These findings pave the path to develop a rational strategy to trigger the activity of the inert basal plane of MoS2, to enhance the conductivity of inherent MoS2 towards the HER and provide a new idea that can be extended to other layered dichalcogenides.

Environmentally-Friendly Exfoliate and Active Site Self-Assembly: Thin 2D/2D Heterostructure Amorphous Nickel-Iron Alloy on 2D Materials for Efficient Oxygen Evolution Reaction.

A class of 2D layered materials exhibits substantial potential for high-performance electrocatalysts due to high specific surface area, tunable electronic properties, and open 2D channels for fast ion transport. However, liquid-phase exfoliation always utilizes organic solvents that are harmful to the environment, and the active sites are limited to edge sites. Here, an environmentally friendly exfoliator in aqueous solution is presented without utilizing any toxic or hazardous substance and active site self-assembly on the inert base of 2D materials. Benefiting from thin 2D/2D heterostructure and strong interfacial coupling, the resultant highly disordered amorphous NiFe/2D materials (Ti3C2 MXene, graphene and MoS2 ) thin nanosheets exhibit extraordinary electrocatalytic performance toward oxygen evolution reaction (OER) in alkaline media. DFT results further verify the experimental results. The study emphasizes a viable idea to probe efficient electrocatalysts by means of the synergistic effect of environmentally friendly exfoliator in aqueous solution and active site self-assembly on the inert base of 2D materials which forms the unique thin 2D/2D heterostructure in-suit. This new type of heterostructure opens up a novel avenue for the rational design of highly efficient 2D materials for electrocatalysis.

Nitrogen Codoped Unique Carbon with 0.4 nm Ultra-Micropores for Ultrahigh Areal Capacitance Supercapacitors.

A full understanding of ion transport in porous carbon electrodes is essential for achieving effective energy storage in their applications as electrochemical supercapacitors. It is generally accepted that pores in the size range below 0.5 nm are inaccessible to electrolyte ions and lower the capacitance of carbon materials. Here, nitrogen-doped carbon with ultra-micropores smaller than 0.4 nm with a narrow size distribution, which represents the first example of electrode materials made entirely from ultra-microporous carbon, is prepared. An in situ electrochemical quartz crystal microbalance technique to study the effects of the ultra-micropores on charge storage in supercapacitors is used. It is found that ultra-micropores smaller than 0.4 nm are accessible to small electrolyte ions, and the area capacitance of obtained sample reaches the ultrahigh value of 330 µF cm-2 , significantly higher than that of previously reported carbon-based materials. The findings provide a better understanding of the correlation between ultra-micropore structure and capacitance and open new avenues for design and development of carbon materials for the next generation of high energy density supercapacitors.

Ultrathin Wall (1 nm) and Superlong Pt Nanotubes with Enhanced Oxygen Reduction Reaction Performance.

The synthesis of Pt nanotubes catalysts remains a substantial challenge, especially for those with both sub-nanometer wall thickness and micrometer-scale length characteristics. Combining techniques of insulin fibril template with Pd nanowire template, numerous Pt nanotubes with diameter of 5.5 nm, tube-length of several micrometers, and ultrathin wall thickness of 1 nm are assembled. These tubular catalysts with both open ends deliver electrochemical active surface area (ECSA) of 91.43 m2 gpt-1 which results from multiple Pt atoms exposed on the inner and outer surfaces that doubled Pt atoms can participate in catalytic reactions, further with enhanced electrocatalytic performance for oxygen reduction reaction (ORR). The ultrafine Pt nanotubes represent a class of hollow nanostructure with increased Pt-utilization and large ECSA, which is regarded as a type of cost-effective catalysts for ORR.

Preparation of SiO2 nanowire arrays as anode material with enhanced lithium storage performance.

SiO2 nanowire arrays have been prepared by a template-assisted sol gel method and used as a negative electrode material for lithium ion batteries. Amorphous SiO2 was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. The results of scanning electron microscopy and transmission electron microscopy confirmed that the SiO2 nanowire had a diameter of about 100 nm and a length of about 30 µm. Cyclic voltammetry and constant current charge and discharge tests showed the prepared SiO2 nanowire arrays were electrochemically active at a potential range of 0.05-3.0 V. At a current density of 200 mA g-1, the first discharge specific capacity was as high as 2252.6 mA h g-1 with a coulombic efficiency of 60.7%. Even after about 400 cycles, it still maintained 97.5% of the initial specific capacity. Moreover, a high specific capacity of 315 mA h g-1 was exhibited when the current density was increased to 2500 mA g-1. SiO2 nanowire array electrodes with high reversible capacity and good cycle performance provide potential anode materials for future lithium-ion batteries.

Fluorine- and Nitrogen-Codoped MoS2 with a Catalytically Active Basal Plane.

Two-dimensional molybdenum disulfide (2D MoS2) has drawn persistent interests as one of the most promising alternatives to Pt catalysts for the hydrogen evolution reaction (HER). It is generally accepted that the edge sites of 2D MoS2 are catalytically active but the basal planes are inert. Activating the MoS2 basal plane is an obvious strategy to enhance the HER activity of this material. However, few approaches have sought to activate the basal plane. Here, for the first time, we demonstrate that the inert basal planes can be activated via the synergistic effects of nitrogen and fluorine codoping. Our first-principles calculations reveal that nitrogen in the basal plane of the fluorine- and nitrogen-codoped MoS2 (NF-MoS2) can act as a new active and further tuneable catalytic site. The as-prepared NF-MoS2 catalyst exhibited an enormously enhanced HER activity compared to that of pure MoS2 and N-doped MoS2 due to the chemical codoping effect. This work will pave a novel pathway for enhancing the HER activity using the synergistic effects of chemical codoping.

High oxygen-reduction activity and durability of nitrogen and sulfur dual doped porous carbon microspheres.

Nitrogen and sulfur co-doped monodisperse carbon microspheres (NS-CMSs) have been successfully synthesized as a new kind of outstanding metal-free ORR catalyst through a one-pot solvothermal reaction. The as-synthesized heteroatom-doped CMSs have been systematically characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) and by using Raman spectra and nitrogen adsorption and desorption isotherms. Compared with the commercially available 20 wt% Pt/C catalyst, the as-prepared NS-CMSs showed a much better tolerance toward methanol crossover and long-term operation stability for ORR in an alkaline medium.

Ultrahigh volumetric capacitance and cyclic stability of fluorine and nitrogen co-doped carbon microspheres.

Highly porous nanostructures with large surface areas are typically employed for electrical double-layer capacitors to improve gravimetric energy storage capacity; however, high surface area carbon-based electrodes result in poor volumetric capacitance because of the low packing density of porous materials. Here, we demonstrate ultrahigh volumetric capacitance of 521 F cm(-3) in aqueous electrolytes for non-porous carbon microsphere electrodes co-doped with fluorine and nitrogen synthesized by low-temperature solvothermal route, rivaling expensive RuO2 or MnO2 pseudo-capacitors. The new electrodes also exhibit excellent cyclic stability without capacitance loss after 10,000 cycles in both acidic and basic electrolytes at a high charge current of 5 A g(-1). This work provides a new approach for designing high-performance electrodes with exceptional volumetric capacitance with high mass loadings and charge rates for long-lived electrochemical energy storage systems.

Vertically-aligned BCN nanotube arrays with superior performance in electrochemical capacitors.

Electrochemical capacitors (EC) have received tremendous interest due to their high potential to satisfy the urgent demand in many advanced applications. The development of new electrode materials is considered to be the most promising approach to enhance the EC performance substantially. Herein, we present a high-capacity capacitor material based on vertically-aligned BC2N nanotube arrays (VA-BC2NNTAs) synthesized by low temperature solvothermal route. The obtained VA-BC2NNTAs display the good aligned nonbuckled tubular structure, which could indeed advantageously enhance capacitor performance. VA-BC2NNTAs exhibit an extremely high specific capacitance, 547 Fg(-1), which is about 2-6 times larger than that of the presently available carbon-based materials. Meanwhile, VA-BC2NNTAs maintain an excellent rate capability and high durability. All these characteristics endow VA-BC2NNTAs an alternative promising candidate for an efficient electrode material for electrochemical capacitors (EC).