Bipolar plates (BPs) are a major component of polymer electrolyte membrane fuel cells (PEMFCs). BPs play a multifunctional character within a PEMFC stack. It is one of the most costly and critical part of the fuel cell, and hence the development of efficient and cost-effective BPs is of much interest for the fabrication of next-generation PEMFCs in future. Owing to high electrical conductivity and chemical inertness, graphene is an ideal candidate to be utilized in BPs. This paper reviews recent advances in the area of graphene-based BPs for PEMFC applications. Various aspects including the momentous functions of BPs in the PEMFC, favorable features of graphene-based BPs, performance evaluation of various reported BPs with their advantages and disadvantages, challenges at commercial level products and future prospects of frontier research in this direction are extensively documented.
Zwitterionic Gemini surfactants have the Gemini molecular structure in which there are both multiple lipophilic groups and multiple hydrophilic groups. However, their hydrophilic groups have different charges. Due to the special molecular structure, this kind of surfactants possesses excellent properties, including high surface activities, isoelectric point (IP), low critical micelle concentration (CMC), less toxicity, low irritating, biodegradability, bioactive, interface modification, and so on. In this review, synthetic strategies of three kinds of zwitterionic Gemini surfactants, i.e., anionic– cationic, cationic–nonionic and anionic–nonionic Gemini surfactants, are discussed, and their potential applications in life sciences, chemical industry and enhanced oil recovery (EOR) are illustrated. Their future development is also prospected.
An aligned composite film was fabricated via the deposition of carboxylic graphene oxide (C-GO) and polypyrrole (PPy) nanoparticles on aligned poly(L-lactic acid) (PLLA) fiber-films (named as C-GO/PPy/PLLA), which has the core (PLLA)–sheath (C-GO/PPy) structure, and the composition of C-GO (~4.8 wt.% of PPy sheath) significantly enhanced the tensile strength and the conductivity of the PPy/PLLA film. Especially, after 4 weeks of immersion in the PBS solution, the conductivity and the tensile strength of C-GO/PPy/PLLA films still remained ~6.10 S/cm and 28.9 MPa, respectively, which could meet the need of the sustained electrical stimulation (ES) therapy for nerve repair. Moreover, the neurite length and the neurite alignment were significantly increased through exerting ES on C-GO/PPy/PLLA films due to their sustained conductivity in the fluid of cell culture. These results indicated that C-GO/PPy/PLLA with sustained conductivity and mechanical property possessed great potential of nerve repair by exerting lasting-ES.
The growth direction, morphology and microstructure of carbon nanotubes (CNTs) play key roles for their potential applications in electronic and energy storage devices. However, effective synthesis of CNTs in high crystallinity and desired microstructure still remains a tremendous challenge. Here we introduce an electric field for controlling the microstructure formation of CNTs. It reveals that the electric field not only make CNTs aligned parallel but also improve the density of CNTs. Especially, the microstructures of CNTs gradually change under electrical field. That is, graphite sheets are transformed from the “herringbone” structure to a highly crystalline structure, facilitating the transportation of electrons. Due to the improved aligned growth direction, high density and highly crystalline microstructure, the electrochemical performance of CNTs is greatly improved. When the CNTs are applied in supercapacitors, they present a high specific capacitance of 237 F/g, three times higher than that of the CNTs prepared without electrical field. Such microstructure modulation of CNTs by electric field would help to construct high performance electronic and energy storage devices.
No-precious bifunctional catalysts with high electrochemical activities and stability were crucial to properties of rechargeable zinc–air batteries. Herein, LaNiO3 modified with Ag nanoparticles (Ag/LaNiO3) was prepared by the co-synthesis method and evaluated as the bifunctional oxygen catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Compared with LaNiO3, Ag/LaNiO3 demonstrated the enhanced catalytic activity towards ORR/OER as well as higher limited current density and lower onset potential. Moreover, the potential gap between ORR potential (at −3 mA·cm−2) and OER potential (at 5 mA·cm−2) was 1.16 V. The maximum power density of the primary zinc–air battery with Ag/LaNiO3 catalyst achieved 60 mW·cm−2. Furthermore, rechargeable zinc–air batteries operated reversible charge–discharge cycles for 150 cycles without noticeable performance deterioration, which showed its excellent bifunctional activity and cycling stability as oxygen electrocatalyst for rechargeable zinc–air batteries. These results indicated that Ag/LaNiO3 prepared by the co-synthesis method was a promising bifunctional catalyst for rechargeable zinc–air batteries.
In this work, the Ag loaded Ce-based catalyst was synthesized (by the sol−gel method) and its performance was studied by TG, H2-TPR, XRD, SEM, TEM, BET and XPS. The results show that Ag nanoparticles be successfully loaded onto the CeO2 surface and the relative content of Ag nanoparticles is about 10.22 wt.% close to the theoretical value (10%). XPS shows that Ag nanoparticles induce a great number of oxygen vacancies in the CeO2 lattice through the electronic transfer, and H2-TPR indicates that the Ag-assisted CeO2 catalyst exhibits a better reduction performance and Ag nanoparticles can promote O− transform into O2−. The catalytic activity for soot oxidation was studied by TG under air atmosphere and the activity was found to be obviously enhanced when Ag nanoparticles be load on the surface of CeO2 (T10 = 386 °C, T90 = 472.5 °C, Tm = 431 °C). The reaction mechanism was also presented and O2− species is regarded as the determinant factor for the catalytic activity.
The present study describes the facile preparation of acid/CO2 stimuli-responsive sheddable nanoparticles based on carboxymethylated chitosan (CMCS). Commercially available CMCS was grafted with monomethoxy polyethylene glycol (mPEG) chains via an acid/CO2 responsive linker, i.e., benzoic-imine, and then was used for the cross-linking with CaCl2. With a high CMCS concentration up to 7 mg/mL, stable nanoparticles were successfully prepared. The particle size grew slightly with increasing the molecular weight of mPEG. When the concentration of CaCl2 and the feed ratio of CMCS to mPEG increased, the particle size decreased at first and then increased after reaching a minimum size. When the particles were stimulated by CO2 or acid, benzoic-imine cleaved quickly, and mPEG fell off the nanoparticles simultaneously, and then flocculation and precipitation occurred. These sheddable nanoparticles might have potential application in the biomedical field including the intelligent drug delivery system.
Multifunctional wearable e-textiles have been a focus of much attention due to their great potential for healthcare, sportswear, fitness, space, and military applications. Among them, electroconductive textile yarn shows great promise for use as the next-generation flexible sensors without compromising properties and comfort of usual textiles. Recently, a myriad of efforts have been devoted to improving performance and functionality of wearable sensors. However, the current manufacturing process of metal-based electroconductive textile yarn is expensive, unscalable, and environmentally unfriendly. In this work, we report the preparation of multifunctional reduced graphene oxide/linen (RGO/LN) fabrics through the reduction and the followed suction filtration. As-prepared RGO/LN fabric could serve as the methane gas sensor, which exhibited high sensitivity, remarkable reliability and feasibility. Furthermore, the RGO/LN fabric sensor exhibited good moisture permeability and air permeability. The present work reveals that RGO/LN fabric has great potential as wearable smart devices in personal healthcare applications.
In this work, a method to acquire freestanding GaN by using low temperature (LT)-GaN layer was put forward. To obtain porous structure and increase the crystallinity, LT-GaN layers were annealed at high temperature. The morphology of LT-GaN layers with different thickness and annealing temperature before and after annealing was analyzed. Comparison of GaN films using different LT-GaN layers was made to acquire optimal LT-GaN process. According to HRXRD and Raman results, GaN grown on 800 nm LT-GaN layer which was annealed at 1090 °C has good crystal quality and small stress. The GaN film was successfully separated from the substrate after cooling down. The self-separation mechanism of this method was discussed. Cross-sectional EBSD mapping measurements were carried out to investigate the effect of LT-buffer layer on improvement of crystal quality and stress relief. The optical property of the obtained freestanding GaN film was also determined by PL measurement.
A simplified analysis method based on micromagnetic simulation is proposed to investigate effects of nonmagnetic particles on the demagnetizing field of a permanent magnet. By applying the additivity law of the demagnetizing field, the complicated demagnetizing field of the real magnet could be analyzed by only focusing on the stray field of the reserved magnet. For a magnet with nonmagnetic particles inside, the particle size has no significant effect on the maximum value of the demagnetization field, but the area of the affected region by the particle is proportional to the particle size. A large particle produces a large affected area overlapped with those influenced by other particles, which leads to the large demagnetization field. With increasing the length of the particle along the magnetization direction, the demagnetization field on the pole surface increases. The pole surface with a convex shape will increase the demagnetization field. The demagnetizing field near the nonmagnetic particle will be further increased by the large macroscopic demagnetizing field near the pole surface. This work suggests some practical approaches to optimize the microstructure of permanent magnets.