The concentration of benzoic acid was found to exercise efficient control over the formation of either MIL-101(Cr) or MIL-88B(Cr) under otherwise similar hydrothermal synthetic conditions. Nanocrystals of MIL-101(Cr) with ∼100 nm average size and excellent SBET = 3467 m2 g−1 are obtained at lower concentrations of benzoic acid, while at higher concentrations the microparticulated MIL-88B(Cr) product is formed. Hereby a new efficient synthetic method towards the elusive MIL-88B(Cr), yet reported only once without synthetic details, is proposed. The obtained MIL-88B(Cr) has an interesting and potentially valuable property of retaining its high-volume form (Vcell ∼ 2000 Å3) after thermal activation. The degassing of MIL-88B(Cr) in a vacuum at 250 °C yields a porous material with a SBET area of 1136 m2 g−1, which is around the theoretical maximum. The transition to the denser ‘closed’ form (Vcell ∼ 1500 Å3) occurs only at 350 °C, when all of the benzoate/benzoic acid, hindering the process, is removed.
Triboelectric Nanogenerators (TENGs), as a novel tool that is capable of harnessing ubiquitous mechanical energy, have gained tremendous attention in recent years. Developing flexible and transparent TENGs with high triboelectric output performance is a major challenge towards adaptable and invisible energy harvesters. Previously developed transparent TENGs are normally used in a single electrode working mode or have relatively low output. Herein, a flexible semitransparent dual-electrode hydrogel-based TENG (DH-TENG) with high output was developed. The DH-TENG contains a thermoplastic polyurethane (TPU) tribopositive layer and a polydimethylsiloxane (PDMS) tribonegative layer. Both materials are highly transparent. NaCl containing polyacrylamide (PAM) hydrogels were used as electrodes, and polyethylene terephthalate (PET) sheets were used to provide mechanical stiffness. A benzophenone (BP) grafting method was used to enhance the interfacial bonding between hydrophobic triboelectric materials and hydrophilic hydrogels, which realized a significant improvement in tear strength of over 12 times. The DH-TENG demonstrated a high instant voltage and current of 311.5 V and 32.4 μA respectively. A maximum power density of 2.7 W m−2 was achieved on a 4.7 MΩ resistor. Furthermore, the DH-TENG showed a highly stable output under continuous running and demonstrated the capability to charge capacitors and power small electronics such as a timer, pedometer, and digital watch.
In recent years, aqueous zinc ion batteries (ZIBs) have attracted much attention due to their high safety, low cost, and environmental friendliness. Owing to the unique layered structure and more desirable layer spacing, transition metal dichalcogenide (TMD) materials are considered as the comparatively ideal cathode material of ZIBs which facilitate the intercalation/ deintercalation of hydrated Zn2+ between layers. However, some disadvantages limit their widespread application, such as low conductivity, low reversible capacity, and rapid capacity decline. In order to improve the electrochemical properties of TMDs, the corresponding modification methods for each TMDs material can be designed from the following modification strategies: defect engineering, intercalation engineering, hybrid engineering, phase engineering, and in-situ electrochemical oxidation. This paper summarizes the research progress of TMDs as cathode materials for ZIBs in recent years, discusses and compares the electrochemical properties of TMD materials, and classifies and introduces the modification methods of MoS2 and VS2. Meanwhile, the corresponding modification scheme is proposed to solve the problem of rapid capacity fading of WS2. Finally, the research prospect of other TMDs as cathodes for ZIBs is put forward.
29 October 2019 in Journal of Applied Polymer Science