This article reviews the PEO-based electrolytes for lithium-ion batteries.Poly(ethylene oxide) (PEO) based materials are widely considered as promising candidates of polymer hosts in solid-state electrolytes for high energy density secondary lithium batteries. They have several specific advantages such as high safety, easy fabrication, low cost, high energy density, good electrochemical stability, and excellent compatibility with lithium salt. However, the typical linear PEO does not reach the production requirement because its insufficient ionic conductivity due to the high crystallinity of the ethylene oxide (EO) chains, which can restrain the ionic transition due to the stiff structure especially at low temperature. The scientists have explored different approaches to reduce the crystallinity hence to improve the ionic conductivity of PEO-based electrolytes, including: blending, modifying and making PEO derivatives etc. This review is focused on surveying the recent developments and issues about PEO-based electrolytes for lithium-ion batteries.

The development of bifunctional electrocatalysts with high performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with earth-abundant elements is still a challenge in electrochemical water splitting technology. Herein, we fabricated a free-standing electrocatalyst in the form of vertically oriented Fe-doped Ni3S2 nanosheet array grown on three-dimensional (3D) Ni foam (Fe-Ni3S2/NF), which presented a high activity and durability for both HER and OER in alkaline media. On the basis of systematic experiments and calculation, the Fe-doping was evidenced to increase the electrochemical surface area, improve the water adsorption ability, and optimize the hydrogen adsorption energy of Ni3S2, which resulted in the enhancement of HER activity on Fe-Ni3S2/NF. Moreover, metal sites of Fe-Ni3S2/NF were proved to play a significant role in the HER process. During the catalysis of OER, the formation of Ni–Fe (oxy)­hydroxide was observed on the near-surface section of Fe-Ni3S2/NF, and the introduction of the Fe element dramatically enhanced the OER activity of Ni3S2. The overall water splitting electrolyzer assembled by Fe-Ni3S2/NF exhibited a low cell voltage (1.54 V @ 10 mA cm–2) and a high durability in 1 M KOH. This work demonstrated a promising bifunctional electrocatalyst for water electrolysis in alkaline media with potential application in the future.

Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc. Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH3, NO2, H2, CO, SO2, H2S, as well as vapor of volatile organic compounds. The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.

There remains a great challenge in the sensitive detection of microRNA because of the short length and low abundance of microRNAs in cells. Here, we have demonstrated an ultrasensitive detection platform for microRNA by combining the tetrahedral DNA nanostructure probes and hybridization chain reaction (HCR) amplification. The detection limits for DNA and microRNA are 100 aM and 10 aM (corresponding to 600 microRNAs in a 100 μL sample), respectively. Compared to the widely used supersandwich amplification, the detection limits are improved by 3 orders of magnitude. The uncontrolled surface immobilization and consumption of target molecules that limit the amplification efficiency of supersandwich are eliminated in our platform. Taking advantage of DNA nanotechnology, we employed three-dimensional tetrahedral DNA nanostructure as the scaffold to immobilize DNA recognition probes to increase the reactivity and accessibility, while DNA nanowire tentacles are used for efficient signal amplification by capturing multiple catalytic enzymes in a highly ordered way. The synergetic effect of DNA tetrahedron and nanowire tentacles have proven to greatly improve sensitivity for both DNA and microRNA detection.

Nanoparticles of titanium dioxide co-doped with nitrogen and iron (III) were first prepared using the homogeneous precipitation-hydrothermal method. The structure and properties of the co-doped were studied by XRD, XPS, Raman, FL, and UV-diffuse reflectance spectra. By analyzing the structures and photocatalytic activities of the undoped and nitrogen and/or Fe 3+ -doped TiO 2 under ultraviolet and visible light irradiation, the probable mechanism of co-doped particles was investigated. It is presumed that the nitrogen and Fe 3+ ion doping induced the formation of new states closed to the valence band and conduction band, respectively. The co-operation of the nitrogen and Fe 3+ ion leads to the much narrowing of the band gap and greatly improves the photocatalytic activity in the visible light region. Meanwhile, the co-doping can also promote the separation of the photogenerated electrons and holes to accelerate the transmission of photocurrent carrier. The photocatalyst co-doped with nitrogen and 0.5% Fe 3+ shows the best photocatalytic activity, the degradation efficiencies of which were improved by 75% and 5% under visible and ultraviolet irradiation, respectively, compared with the pure titania.