Nitrogen- and fluorine-doped bimetallic carbide as active and stable oxygen reduction reaction electrocatalyst.

Nitrogen- and fluorine-doped bimetallic carbide composites with graphite matrix (abbreviated as C19Cr7Mo24/NG and C19Cr7Mo24/FG) are synthesized through carbonization at 1300 °C. The C19Cr7Mo24/NG displays an initial half-wave potential (E1/2) of 0.873 V and suffers merely 3 mV decrease in E1/2 within 60,000 CV cycles for oxygen reduction reaction (ORR) in alkaline media. A H2/O2 fuel cell testing system using the C19Cr7Mo24/NG as cathode maintains 95.9% of the initial peak power density (1.08 W cm-2) within 60,000 cycles. The C19Cr7Mo24/FG shows higher ORR activity than the C19Cr7Mo24/NG. The positive and negative charge centers caused by the N or F dopants are the critical reasons to their high activities. While F and bimetallic carbide more favor electron transfer respectively than the N and monometallic carbide. Their excellent stabilities originate from interactions among atoms due to electron transfer and the intrinsic chemical inertness of graphite and bimetallic carbides.

Cu-Based Materials for Enhanced C2+ Product Selectivity in Photo-/Electro-Catalytic CO2 Reduction: Challenges and Prospects.

Carbon dioxide conversion into valuable products using photocatalysis and electrocatalysis is an effective approach to mitigate global environmental issues and the energy shortages. Among the materials utilized for catalytic reduction of CO2, Cu-based materials are highly advantageous owing to their widespread availability, cost-effectiveness, and environmental sustainability. Furthermore, Cu-based materials demonstrate interesting abilities in the adsorption and activation of carbon dioxide, allowing the formation of C2+ compounds through C-C coupling process. Herein, the basic principles of photocatalytic CO2 reduction reactions (PCO2RR) and electrocatalytic CO2 reduction reaction (ECO2RR) and the pathways for the generation C2+ products are introduced. This review categorizes Cu-based materials into different groups including Cu metal, Cu oxides, Cu alloys, and Cu SACs, Cu heterojunctions based on their catalytic applications. The relationship between the Cu surfaces and their efficiency in both PCO2RR and ECO2RR is emphasized. Through a review of recent studies on PCO2RR and ECO2RR using Cu-based catalysts, the focus is on understanding the underlying reasons for the enhanced selectivity toward C2+ products. Finally, the opportunities and challenges associated with Cu-based materials in the CO2 catalytic reduction applications are presented, along with research directions that can guide for the design of highly active and selective Cu-based materials for CO2 reduction processes in the future.

Boosting activity on copper functionalized biomass graphene by coupling nanocrystalline Nb2O5 as impressive rate capability for supercapacitor and outstanding catalytic activity for oxygen reduction.

A novel and hierarchical porous but cross-linked copper-doped biomass graphene (Cu@HPBG) combined with Nb2O5 (denoted as Nb2O5/Cu@HPBG) is successfully fabricated on a large-scale using fig peels as biomass carbon and copper as the graphitization catalyst. During the synthesis process, basic copper carbonate serves dual functions of pore-forming agent, as well as homogeneous copper provider, and NH3 is employed as a defect-forming agent and N dopant. Owing to the porous hierarchical structure increased availability of contact interface and pseudo capacitance active sites provided by copper and Nb2O5, the assembled asymmetrical supercapacitor (ASC) employing Nb2O5/Cu@HPBG as positive electrode and HPBG as negative electrode can not only widen the stability window range of 0～1.9 V, but also deliver a maximum gravimetric energy density of 82.8 W h kg-1 at the power density of 950.0 W kg-1 and maintain a remarkable cycling stability of 97.1% after 15,000 cycles. Impressively, due to the synergistic enhancement of Cu@HPBG and Nb2O5, the resulting Nb2O5/Cu@HPBG hybrid displays more positive half wave potential (∼0.85 V) and a long-life stability than Pt/C electrode toward oxygen reduction reaction (ORR). Our research provides a feasible strategy to fabricate renewable biomass graphene electroactive composites for large-scale supercapacitor electrodes and efficient ORR catalysts toward energy applications.

Cs3Cu2I5/ZnO Heterostructure for Flexible Visible-Blind Ultraviolet Photodetection.

Wearable, portable, and biocompatible optoelectronic devices made of all-green and abundant materials and fabricated by low-temperature solution method are the key point in the development of next generation of intelligent optoelectronics. However, this is usually limited by the weaknesses of mono-component materials, such as non-adjustable photoresponse region, high carrier recombination rate, high signal-to-noise ratio, as well as the weak mechanical flexibility of bulk films. In this work, the Cs3Cu2I5/ZnO heterostructure flexible photodetectors were constructed by a low-temperature solution method combined with spin-coating technique. The heterostructure combines the low dark current and strong deep ultraviolet absorption of Cs3Cu2I5 quantum dots with the high carrier mobility of ZnO quantum dots as well as the efficient charge separation of the vertical p-n junction, to improve the photodetection performance. The heterostructure shows enhanced light/dark current ratio and ultraviolet-to-visible rejection ratios. Under an illumination of 280 nm light, an optical detectivity as high as 1.26 × 1011 Jones was obtained; the optical responsivity and response time are much better than those of control devices. After 300 times of 180° bending cycles, the photocurrent had no obvious change. The results demonstrate that the Cs3Cu2I5/ZnO heterostructure has great potential in wearable and portable visible-blind ultraviolet optoelectronic devices.

Chrysanthemum-like FeS/Ni3S2 heterostructure nanoarray as a robust bifunctional electrocatalyst for overall water splitting.

The development of a scalable strategy to prepare highly efficient and stable bifunctional electrocatalysts is the key to industrial electrocatalytic water splitting cycles to produce clean hydrogen. Here, a simple and quick one-step hydrothermal method was used to successfully fabricate a three-dimensional core chrysanthemum-like FeS/Ni3S2 heterogeneous nanoarray (FeS/Ni3S2@NF) on a porous nickel foam skeleton. Compared with the monomer Ni3S2@NF, the chrysanthemum-like FeS/ Ni3S2@NF heterostructure nanomaterials have improved catalytic performance in alkaline media, showing low overpotentials of 192 mV (η10) and 130 mV (η-10) for OER and HER, respectively. This study attests that integrated interface engineering and precise morphology control are effective strategies for activating the Ni3+/Ni2+ coupling, promoting charge transfer and improving the intrinsic activity of the material to accelerate the OER reaction kinetics and promote the overall water splitting performance. The scheme can be reasonably applied to the design and development of transition metal sulfide-based electrocatalysts to put into industrial practice of electrochemical water oxidation.

Graphene Nanosphere as Advanced Electrode Material to Promote High Performance Symmetrical Supercapacitor.

To get carbon electrode with both excellent gravimetric and volumetric capacitances at high mass loadings is critical to supercapacitors. Herein, cracked defective graphene nanospheres (GNS) well meet above requirements. The morphology and structure of the GNS are controlled by polystyrene sphere template/glucose ratio, microwave heating time, and Fe content. The typical GNS with specific surface area of 2794 m2 g-1 , pore volume of 1.48 cm3 g-1 , and packing density of 0.74 g cm-3 performs high gravimetric and volumetric capacitances of 529 F g-1 and 392 F cm-3 at 1A g-1 with a capacitance retention of 62.5% at 100 A g-1 in a three-electrode system in 6 mol L-1 KOH aqueous electrolyte. In a two-electrode system, the GNS possesses energy density of 18.6 Wh kg-1 (13.8 Wh L-1 ) at the power density of 504 W kg-1 , which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density, in aqueous solution, as far as it is known. A structural feature of carbon materials that possess both high energy density and high power density is pointed out here.

Size-controllable synthesis of zinc ferrite/reduced graphene oxide aerogels: efficient electrochemical sensing of p-nitrophenol.

In this study, a nonaqueous method for the synthesis of size-controlled highly crystalline zinc ferrite/reduced graphene oxide (ZFO/rGO) aerogel was provided by using benzyl alcohol as the medium. In our findings, benzyl alcohol was introduced not only as the solvent, but the structure-directing agent and strong reducing agent during the nucleation and growth of ZnFe2O4 nanoparticles (NPs). The characterization analysis indicated that ZnFe2O4 NPs were immobilized on the multilayer rGO with a controllable size of 12 nm. Moreover, the 3D ZFO/rGO aerogel shows excellent electrochemical property as a facile electrochemical sensor for the detection of p-nitrophenol (p-NP). The ZFO/rGO electrochemical sensing offers the advantages of wide linear range (1-500 µmol l-1), excellent sensitivity (23.985 mA mM-1 cm-2), good stability and selectivity (<8.8%). In addition, the possible reaction mechanism of 3D ZFO/rGO aerogel was explained during the detection process under acidic condition. Significantly, our results not only provided insight into the possible reaction mechanism of 3D ZFO/rGO nanocomposite, but proposed the way for the synthesis of highly crystalline materials through a benzyl alcohol-mediated method.

In situ confined vertical growth of a 1D-CuCo2S4 nanoarray on Ni foam covered by a 3D-PANI mesh layer to form a self-supporting hierarchical structure for high-efficiency oxygen evolution catalysis.

Inspired by the patchwork of artificial turf, where planting in a smaller area can result in a more uniform lawn that grows in one direction, here, we defined the growth position and orientation of a CuCo2S4 nanoarray for the first time by electroplating a PANI mesh layer onto a Ni foam to obtain a self-supporting hierarchical electrode material. The nitrogen species derived from the PANI building blocks act as bridging sites to bind with metal ions, which provides a strong coupling effect for the in situ growth of CuCo2S4. At the same time, the mesh structure of PANI divides the growable location into smaller blocks. Compared with a mesh plane with uniformly distributed nitrogen sites, only a small portion of the nitrogen sites are located on the narrow-width fence structure, which may make it difficult for CuCo2S4 to grow onto the fence structure, thereby limiting the self-growth space and confining CuCo2S4. The uniformly distributed growth sites direct CuCo2S4 to grow perpendicular to the plane while limiting their growth size. The excellent structural features further enhance the electrochemical oxygen evolution activity, and the oxygen evolution overpotential at a current density of 100 mA cm-2 is only 291 mV, which is superior to that of the currently known cobalt-copper-based catalyst materials. In addition, the stable structure provides excellent electrode cyclic stability. The preparation of hierarchical self-supporting cobalt-copper bimetallic sulfide nanoarrays provided a reference direction for other transition metal catalytic materials and provided a basis for industrial applications.

Cu2O-Au nanowire field-effect phototransistor for hot carrier transfer enhanced photodetection.

In metal-semiconductor hybrid nanostructures, metal absorbs incident photons and generates hot carriers. The hot carriers are injected into the adjacent semiconductor and subsequently contribute to photocurrent. This process increases the conversion efficiency of optoelectronic devices and provides a new path of photodetectors. In this work, we report an enhanced photodetector by hot holes transfer, which is based on Au nanoparticles decorated p-type Cu2O nanowires. The photodetector achieves an enhanced photo-responsivity up to 0.314 A W-1, a higher detectivity of 3.7 × 1010 Jones. The response time and external quantum efficiency of the Cu2O-Au nanowires photodetector are 3.7 times faster and 18.2 times higher than that of the Cu2O nanowires, respectively. The findings indicate that Cu2O-Au nanowires would be a promising candidate in developing novel plasmonic hot carrier devices.

Selective adsorption of organic dyes by porous hydrophilic silica aerogels from aqueous system.

Hydrophilic silica aerogel (HSA) was obtained by sol-gel method and dried at ambient conditions and further studied for the removal of organic dyes in water. Silica aerogel was characterized by its morphology, porous structure, specific surface area and particle size distribution by scanning electron microscopy, Brunauer-Emmett-Teller and pore size distribution. The HSA after calcination had a specific surface area of 888.73 m2/g and an average particle size of 2.6341 nm. Moreover, adsorption properties of the HSA toward organic dyes - adsorption conditions, kinetics data, and equilibrium model - were investigated. The removal rate of cationic dyes (rhodamine B (RhB), methylene blue (MB) and crystal violet (CV)) by HSA was up to 90%, while the removal rate of anionic dye (acid orange 7) was not more than 30%. The maximum adsorptions were: RhB 191.217 mg/g, MB 51.1601 mg/g and CV 24.85915 mg/g, respectively. Based on the adsorption mechanism of HSA for cationic/anionic dyes, the conclusion confirmed the prospect of HSA as effective adsorbent to treat cationic dyes wastewater.

A novel route for synthesis of UV-resistant hydrophobic titania-containing silica aerogels by using potassium titanate as precursor.

Developing a novel and facile way to synthesize composite aerogels plays an important role in the applications of aerogels. UV-resistant hydrophobic titania-containing silica aerogels are prepared for the first time using potassium titanate as precursor by a modified ambient pressure drying method. The well established silica-titania networks, which can be tuned from 10 to 30 nm by adjusting the precursor content in the preparation process, provide effective confinement of spherical solid clusters. The UV-resistant hydrophobic composite aerogels show excellent photocatalytic dye degradation activity under visible light irradiation. This can be ascribed to the insert of suitable titania into the silica organizational structure. The present work gives a promising method of one pot synthesis and surface modification of aerogel composite structures, which have a broader application as photocatalyst.

Nanosized tungsten carbide synthesized by a novel route at low temperature for high performance electrocatalysis.

Tungsten carbide (WC) is a widely used engineering material which is usually prepared at high temperature. A new mechanism for synthesizing nanoscaled WC at ultralow temperature has been discovered. This discovery opens a novel route to synthesize valuable WC and other carbides at a cost-efficient way. The novel formation mechanism is based on an ion-exchange resin as carbon source to locally anchor the W and Fe species. As an intermediate, FeWO4 can be formed at lower temperature, which can be directly converted into WC along with the carbonization of resin. The size of WC can be less than 2 nm. The catalyst made with Pt nanoparticles supported on nanosized WC-GC (WC-graphitized carbon) shows enhanced electrocatalytic activity for oxygen reduction reaction. The result also indicates that the Pt nanoparticles deposited on WC-GC are dominated by Pt (111) plane and shows a mass activity of 257.7 mA mg(-1)Pt@0.9 V.

Nano-architectures of ordered hollow carbon spheres filled with carbon webs by template-free controllable synthesis.

Hollow carbon spheres with a carbon network structure inside have been synthesized in the absence of templates for the first time. The samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, N(2) adsorption-desorption, and thermogravimetric analyses. The experimental results indicate that the core and the shell of this new structure contain both mesopores and micropores. Furthermore, the inner space and thickness of the hollow carbon spheres can be controlled by adjusting the molar ratio of the glucose and Na(2)SnO(3)·H(2)O. Moreover, a possible formation mechanism has been suggested on the basis of time-dependent experiments. The electrocatalytic activity of methanol oxidation on Pt supported on HC electrocatalyst (Pt/HC@C) is 1.8 times higher than that of Pt supported on commercial Vulcan XC-72 carbon (Pt/C) electrocatalyst at the same Pt loadings.

Ion-exchange-assisted synthesis of Pt-VC nanoparticles loaded on graphitized carbon: a high-performance nanocomposite electrocatalyst for oxygen-reduction reactions.

Carbide-based electrocatalysts are superior to traditional carbon-based electrocatalysts, such as the commercial Pt/C electrocatalysts, in terms of their mass activity and stability. Herein, we report a general approach for the preparation of a nanocomposite electrocatalyst of platinum and vanadium carbide nanoparticles that are loaded onto graphitized carbon. The nanocomposite, which was prepared in a localized and controlled fashion by using an ion-exchange process, was an effective electrocatalyst for the oxygen-reduction reaction (ORR). Both the stability and the durability of the Pt-VC/GC nanocomposite catalyst could be enhanced compared with the state-of-the-art Pt/C. This approach can be extended to the synthesis of other metal-carbide-based nanocatalysts. Moreover, this straightforward synthesis of high-performance composite nanocatalysts can be scaled up to meet the requirements for mass production.

A universal method to synthesize nanoscale carbides as electrocatalyst supports towards oxygen reduction reaction.

We have developed a general ion-exchange method of preparing a composite of low nanometre size carbide particles with controllable size less than 10 nm on carbon foams. The nanoarchitectures of the carbide nanoparticles on carbon foam are used to load Pt nanoparticles as electrocatalysts which show enhanced activity for the oxygen reduction reaction.