CoFe_2O_4/carbon nanotube aerogels as high performance anodes for lithium ion batteries

High-performance lithium ion batteries(LIBs) require electrode material to have an ideal electrode construction which provides fast ion transport, short solid-state ion diffusion, large surface area, and high electric conductivity. Herein, highly porous three-dimensional(3D)aerogels composed of cobalt ferrite(CoFe_2O_4, CFO) nanoparticles(NPs) and carbon nanotubes(CNTs) are prepared using sustainable alginate as the precursor. The key feature of this work is that by using the characteristic egg-box structure of the alginate, metal cations such as Co^(2+)and Fe^(3+) can be easily chelated via an ion-exchange process, thus binary CFO are expected to be prepared. In the hybrid aerogels, CFO NPs interconnected by the CNTs are embedded in carbon aerogel matrix, forming the 3D network which can provide high surface area, buffer the volume expansion and offer efficient ion and electron transport pathways for achieving high performance LIBs. The as-prepared hybrid aerogels with the optimum CNT content(20 wt%) delivers excellent electrochemical properties, i.e., reversible capacity of 1033 mAh g^(-1) at 0.1 A g^(-1) and a high specific capacity of 874 mAh g^(-1) after 160 cycles at 1 A g^(-1). This work provides a facile and low cost route to fabricate high performance anodes for LIBs.

Phosphorus oxoanion-intercalated layered double hydroxides for high-performance oxygen evolution

Rational design and controlled fabrication of efficient and cost-effective electrodes for the oxygen evolution reaction （OER） are critical for addressing the unpre- cedented energy crisis. Nickel-iron layered double hydroxides （NiFe-LDHs） with specific interlayer anions （i.e. phosphate, phosphite, and hypophosphite） were fabricated by a co-predpitation method and investigated as oxygen evolution electrocatalysts. Intercalation of the phosphorus oxoanion enhanced the OER activity in an alkaline solution; the optimal performance （i.e., a low onset potential of 215 mV, a small Tafel slope of 37.7 mV/dec, and stable electrochemical behavior） was achieved with the hypophosphite-intercalated NiFe-LDH catalyst, demonstrating dramatic enhancement over the traditional carbonate-intercalated NiFe-LDH in terms of activity and durability. This enhanced performance is attributed to the interaction between the intercalated phosphorous oxoanions and the edge-sharing MO6 （M = Ni, Fe） layers, which modifies the surface electronic structure of the Ni sites. This concept should be inspiring for the design of more effective LDH-based oxygen evolution electrocatalvsts.

Tuning oxygen vacancies in two-dimensional iron-cobalt oxide nanosheets through hydrogenation for enhanced oxygen evolution activity

The oxygen evolution reaction （OER） represents the rate-determining step of electrocatalytic water splitting into hydrogen and oxygen. Creating oxygen vacancies and adjusting their density has proven to be an effective strategy to design high-performance OER catalysts. Herein, a hydrogenation method is applied to treat a two-dimensional （2D） iron-cobalt oxide （Fe1Co1Ox-origin）, with the purpose of tuning its oxygen vacancy density. Notably, compared with Fe1Co1Ox-origin, the iron-cobalt oxide hydrogenated at 200℃ and 2.0 MPa optimized conditions exhibits a markedly improved OER activity in 1.0 M KOH （with an overpotential 17 of 225 mV at a current density of 10 mA.cm^-2） and a rapid reaction kinetics （with a Tafel slope of 36.0 mV·dec^-1）. Moreover, the OER mass activity of the hydrogenated oxide is 1.9 times that of Fe1Co1Ox-origin at an overpotential of 350 mV. The experimental results, combined with density functional theory （DFT） calculations, reveal that the optimal control of oxygen vacancies in 2D Fe1Co1Ox via hydrogenation can improve the electronic conductivity and promote OH- adsorption onto nearby low-coordinated Co^3＋ sites, resulting in a significantly enhanced OER activity.

Enhanced photodynamic therapy of mixed phase TiO2（B）/anatase nanofibers for killing of HeLa cells

Photodynamic therapy （PDT）, which is a procedure that uses photosensitizing drug to apply therapy selectively to target sites, has been proven to be a safe treatment for cancers and conditions that may develop into cancers. Nano-sized TiO2 has been regarded as potential photosensitizer for UV light driven PDT. In this study, four types of TiO2 nanofibers were prepared from proton tri-titanate （H2T3O7） nanofiber. The as-obtained nanofibers were demonstrated as efficient photosensitizers for PDT killing of HeLa cells. MTT assay and flow cytometry （FCM） were carried out to evaluate the biocompatibility, percentage of apoptotic cells, and cell viability. The non-cytotoxicity of the as-prepared TiO2 nanofibers in the absence of UV irradiation has also been demonstrated. Under UV light irradiation, the TiO2 nanofibers, particularly the mixed phase nanofibers, displayed much higher cell-killing efficiency than Pirarubicin （THP）, which is a common drug to induce the apoptosis of HeLa cells. We ascribe the high cell- killing efficiency of the mixed phase nanofibers to the bandgap edge match and stable interface between TiO2（B） and anatase phases in a single nanofiber, which can inhibit the recombination of the photogenerated electrons and holes. This promotes the charge separation and transfer processes and can produce more reactive oxygen species （ROS） that are responsible for the killing of HeLa cells.

How heteroatoms(Ge,N,P) improve the electrocatalytic performance of graphene:theory and experiment

The oxygen reduction reactions(ORR)play a crucial role in the electrochemical energy storage devices,such as fuel cell,metal-air batteries[1–3].However,their larger scale applications are hindered by the sluggish slow kinetics of the ORR.Up to now,platinum(Pt)-based catalysts are still known as the best

Epitaxial growth of hyperbranched Cu/Cu2O/CuO coreshell nanowire heterostructures for lithium-ion batteries

The careful design of nano-architectures and smart hybridization of expected active materials can lead to more advanced properties. Here we have engineered a novel hierarchical branching Cu/Cu2O/CuO heteronanostructure by combining a facile hydrothermal method and subsequent controlled oxidation process. The fine structure and epitaxial relationship between the branches and backbone are investigated by high-resolution transmission electron microscopy. Moreover, the evolution of the branch growth has also been observed during the gradual oxidation of the Cu nanowire surface. The experimental results suggest that the surface oxidation needs to be performed via a two-step exposure process to varying humidity in order to achieve optimized formation of a core-shell structured branching architecture. Finally, a proof-of-concept of the function of such a hierarchical framework as the anode material in lithium-ion batteries is demonstrated. The branching core-shell heterostructure improves battery performance by several means： （i） The epitaxially grown branches provide a high surface area for enhanced electrolyte accessibility and high resistance to volume change induced by Li^＋ intercalation/extraction; （ii） the core-shell structure with its well-defined heterojunction increases the contact area which facilitates effective charge transport during lithiation; （iii） the copper core acts as a current collector as well as providing structural reinforcement.

Narrow-bandgap Nb_2O_5 nanowires with enclosed pores as high-performance photocatalyst

Porous niobium oxide nanowires synthesized via a solvothermal method exhibited decreased bandgap,en- hanced light absorption and reduced charge-recombination rate.The porous Nb2O5 nanowires showed increased performance for the photocatalytic H2 evolution and photo- degradation of rhodamine B,as compared to their solid counterparts,which could be ascribed to the peculiar porous nanostructure.