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The development of nonprecious metal-based electrocatalysts for oxygen reduction reaction (ORR) is a central task in renewable electrochemical energy conversion and storage technologies. Iron-nitrogen doped carbon-based (Fe−N/C) materials are promising alternatives to Pt-based ORR electrocatalysts. Owing to large specific surface area and outstanding electrical conductivity, carbon black is an inborn support for electrocatalysts. Unfortunately, the direct incorporation of Fe−Nx moieties onto the surface of carbon black has not been realized to date. Herein, Fe−Nx moieties are directly incorporated onto the surface of carbon black through surface modification and the following Fe and N co-doping. The obtained Fe and N co-doped carbon back (Fe−N/CB) catalyst has very large specific surface area and abundant accessible Fe−Nx moieties. As a result, Fe−N/CB electrocatalyst exhibits a more positive half-wave potential (0.86 V) than Pt/C. The Fe−N/CB catalyst also displays better stability and methanol resistance than Pt/C. The Zn-air battery with Fe−N/CB as cathodic catalyst shows a maximum power density of 68 mW cm−2 and a specific capacity of 676 mAh gZn-1. Our finding provides a convenient and low-cost approach to fabricating efficient M−N/C-based catalysts and will be helpful to the development of renewable electrochemical energy conversion and storage technologies.

Transition metal- and N-codoped carbon nanotubes (CNTs) have superior catalytic activity because the curling surface enhances the bonding ability of atoms within CNTs to other species. However, it is a great challenge to prepare CNTs with transition metal- and N-doped at high level during the growth of CNTs. Here, (Fe,N-codoped CNT)/(Fe-based nanoparticle) (Fe,N-CNT/FeNP) hybrid nanostructures are for the first time prepared through the carbonization of Fe-doped g-C3N4. The doping of Fe and N is simultaneously realized during the formation of CNTs. Meanwhile, the abundant and homogeneous Fe and N in Fe-doped g-C3N4 ensure high-level and uniform doping of Fe and N in CNTs. The Fe,N-CNT/FeNP hybrid nanostructures have several types of active components, including homogeneously distributed coordinating Fe moieties (FeCxNy or FeNx) and CFe15.1 nanoparticles embedded in Fe,N-CNTs, towards oxygen reduction reaction (ORR). A superior ORR electrocatalytic performance is therefore obtained on the Fe,N-CNT/FeNP nanohybrids. Our preparation method opens an avenue to preparation of CNTs with transition metal- and N-doping at high-level, and the superior performance of Fe,N-CNT/FeNP nanostructures for ORR will be very helpful to the development of fuel cells and metal-air batteries.

Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible hybrid film with outstanding flexibility and electrochemical performance is prepared via a vacuum filtration method. The three-dimensional interconnect structure is constructed by reduced graphene oxide and single-walled carbon nanotube, and Mn3O4 nanoplates with pesudocapacitance are embedded into the interconnect structure. The regular interconnect structure and a synergetic effect between graphene oxide/single-walled carbon nanotube and Mn3O4 make the Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible film electrode exhibit a large areal capacitance of 796 mF cm−2. All-solid-state Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible supercapacitor is prepared by using the hybrid film as electrodes and sandwiching the PVA–KOH gel electrolyte, it exhibits a large area specific capacitance of 360 mF cm−2 and the capacitance maintains 95% after 5000 charge/discharge cycles. The assembled supercapacitor exhibits both outstanding mechanical performance and a high areal energy density of 32 μW h cm−2 at an areal power density of 0.392 mW cm−2. The Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible supercapacitors exhibit significant potentiality in flexible and wearable electronics owing to their excellent flexibility, high energy density and long cycle life.

Vanadium pentoxide/single-walled carbon nanotube (V 2 O 5 -SWCNT) hybrid fibers with good electrochemical performance and flexibility are firstly prepared by using wet-spinning method. V 2 O 5 nanobelt suspension is obtained by mixing V 2 O 5 bulk, 30% H 2 O 2 , H 2 O and followed by hydrothermally treating at 190 °C for 15 h. SWCNT suspension is suspended into V 2 O 5 nanobelt suspension under vigorous stirring, the V 2 O 5 -SWCNT homogenous suspension is obtained. It is injected into a coagulation bath composed of 5 wt % CaCl 2 ethanol-water solution using syringe pump, V 2 O 5 -SWCNT hybrid fibers are prepared by washing with deionized water and drying at room temperature. Reduced graphene oxide (RGO)-SWCNT hybrid fibers are also prepared by the similar wet-spinning approach and followed by reducing GO-SWCNT hybrid fibers in an aqueous solution of hydriodic acid. All solid-state asymmetric V 2 O 5 /SWCNT//RGO/SWCNT fiber supercapacitors are assembled with V 2 O 5 -SWCNT fiber as positive electrode and RGO-SWCNT fiber as negative electrode by using PVA-H 3 PO 4 as gel electrolyte. The assembled device not only shows maximum volumetric energy density of 1.95 mW h cm −3 at a volumetric power density of 7.5 mW cm −3 , superior rate performance and cycling stability, but also exhibits remarkable flexibility to tolerate long-term and repeated bending. This work will open a new application filed of V 2 O 5 -based fibers in wearable energy storage devices.

Three fused-ring nonfullerene electron acceptors are designed and synthesized by combining side chain effect and terminal group modification. The 2-ethylhexyl substituent is employed to replace the commonly used n-hexyl or n-hexylphenyl side chains. Three acceptor units, 2-(3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (IC), 2-(6-oxo-5,6-dihydro-4H-cyclopenta [c]thiophen-4-ylidene) malononitrile (CPTCN), and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC–2Cl) are used as the terminal groups and the three fused-ring nonfullerene acceptors, IDTC8-IC, IDTC8-Th, and IDTC8-4Cl are developed, respectively. The thermal, photophysical, electrochemical and photovoltaic properties of the three acceptors are systematically studied in view of the influence of the side chain and the terminal group. The three acceptors exhibit strong absorption ranging from 500 nm to 720 nm in solution with high molar extinction coefficients. The large bandgap polymer PM6 is chosen as the donor to blend with the acceptors, due to the complementary absorption bands and well-matched energy levels. The optimized organic solar cell based on PM6:IDTC8-IC exhibits a power conversion efficiency (PCE) of 8.56% with an open-circuit voltage (VOC) of 0.98 V, a short-circuit current density (JSC) of 13.93 mA cm−2, and a fill factor (FF) of 62.42%. The PM6:IDTC8-4Cl device demonstrates the best performance with a PCE of 9.79%, a VOC of 0.82 V, a JSC of 17.40 mA cm−2, and a FF of 68.67%. The impacts of carrier mobility, film morphology, and molecular packing properties of the blend films on photovoltaic performances are systematically investigated. The results imply that the synergistic effect of alkyl chains on the central core and modification of the terminal groups yields improved photovoltaic performance of nonfullerene acceptors.

Nanostructures made of dielectric materials with high or moderate refractive indexes can support strong electric and magnetic resonances in the optical region. They can therefore function as nanoresonators. In addition to plasmonic metal nanostructures that have been widely investigated, dielectric nanoresonators provide a new type of building blocks for realizing powerful and versatile nanoscale light manipulation. In contrast to plasmonic metal nanostructures, nanoresonators made of appropriate dielectric materials are low-cost, earth-abundant and have very small or even negligible light energy losses. As a result, they will find potential applications in a number of photonic devices, especially those that require low energy losses. In this review, we describe the recent progress on the experimental and theoretical studies of dielectric nanoresonators. We start from the basic theory of the electromagnetic responses of dielectric nanoresonators and their fabrication methods. The optical properties of individual dielectric nanoresonators are then elaborated, followed by the coupling behaviors between dielectric nanoresonators, between dielectric nanoresonators and substrates, and between dielectric nanoresonators and plasmonic metal nanostructures. The applications of dielectric nanoresonators are further described. Finally, the challenges and opportunities in this field are discussed.

Exfoliation and assembly of 2-D materials have been extensively investigated to exploit their performances in the area of catalysis, magnetics and electronics etc., but novel strategies are highly desired to shorten their preparing period and to improve their environment-friendliness. Here we introduce a simple and green hydrothermal process to fabricate ultrathin layered β-Ni(OH)2/g-C3N4 nanohybrids for photocatalytic water splitting application. Different from conventionally separated exfoliation and assembly, the exfoliation of g-C3N4, formation of β-Ni(OH)2 as well as their self-assembly can be one-pot achieved by simple hydrothermal treatment of nickel dichloride and bulk g-C3N4 free of any organic agents for 12 h. Moreover, the thickness of β-Ni(OH)2 nanolayer can be adjusted by controlling the concentration of nickel precursors. The as-obtained nanohybrids have been in detail characterized to have a strong interaction of the assembly components, among which the g-C3N4 is active for photocatalytic water splitting, and β-Ni(OH)2 nanolayer is efficient for acceleration of activation of water oxidation. Their photocatalytic water splitting performances are evaluated in the presence of sacrificial agents, based on which the assembly of β-Ni(OH)2 nanolayers on the surface of exfoliated g-C3N4 lamella is found to obviously promote the charge separation, water oxidation kinetics as well as final photocatalytic performances compared to the pristine g-C3N4. The direct water splitting is also achieved with the AQY of 1.48% under 405-nm visible light irradition. The one-pot hydrothermal method introduced here may be an alternative strategy for g-C3N4, a promising photocatalytic water splitting material, to construct highly efficient solar energy conversion composite systems based on its exfoliated lamella.

As a green pollution-free reaction, oxygen reduction reaction (ORR) plays a significant role in many energy storage and conversion devices. Although commercial Pt/C possesses the highest ORR activity (especially in acidic medium), the high cost, low stability and poor methanol tolerance making the development of non-platinum electrocatalysts with high performance especially important. Herein, we design and synthesize a carbon nanofiber decorated by Ti4O7/Ti3O5 dual-phase nanoparticles (CNF/T4/T3) as ORR catalysts with excellent activity. With the employment of electrospinning followed by precisely controlled calcination process, the composite catalysts with uniform fibrous morphology can be obtained. Such CNF/T4/T3 composite catalysts exhibited an improved electrochemical performance with onset and half-wave potential of 0.91 V and 0.78 V respectively in alkaline solution. By comparing the catalytic performance with the pure T4 or T3 phase decorated on the same carbon nanofiber, it is found that the mixture of the two titanium sub-oxide phases can optimize the onset potential and limited current density at the same time. Density functional theory calculations suggest that different steps of ORR take place on T3 and T4 successively, which is the main reason of the excellent ORR performance for the dual-phase structure. This work provided a novel designing concept for the functional electrocatalysts using electrospinning technique for the application of energy storage and conversion.

Rh(1 1 1)-catalyzed methanol dehydrogenation is systematically studied based on density functional (DF) calculations and microkinetic modelings. We find that, compared to those for the same reaction on other transition metal surfaces, e.g., Ni(1 1 1), Pd(1 1 1) and Pt(1 1 1), the adsorption configurations of some relevant intermediates on Rh(1 1 1) are relatively abundant and the adsorption potential energy surfaces (PES) are relatively flat. Transition states for all the possible elementary steps involved are searched. Based on the DF results, we model the reaction at two sets of typical reaction conditions, i.e., the low temperatures in ultrahigh vacuum conditions and the high temperature and high pressure conditions. The DF calculations and microkinetic modelings reveal that paths CH3OH → CH3O → CH2O → CHO → CO and CH3OH → CH2OH → CHOH → CHO → CO are dominant under all the reaction conditions, whereas at the high temperatures and high pressures, paths CH3OH → CH2OH → CH2O → CHO → CO and CH3OH → CH2OH → CHOH → COH → CO are also significant. Under all the considered reaction conditions, apparent activation energy for the methanol decomposition is found to decrease with temperature, and the reaction order of methanol is decreased when increasing its partial pressure. In addition, it is found that it is the very activated adsorption state (η1(C)−η1(O)−η1(H)) for formaldehyde on Rh(1 1 1) that results in the fact that methanol oxidation does not take place at formaldehyde.