High-quality mesoporous graphene particles as high-energy and fast-charging anodes for lithium-ion batteries.

The application of graphene for electrochemical energy storage has received tremendous attention; however, challenges remain in synthesis and other aspects. Here we report the synthesis of high-quality, nitrogen-doped, mesoporous graphene particles through chemical vapor deposition with magnesium-oxide particles as the catalyst and template. Such particles possess excellent structural and electrochemical stability, electronic and ionic conductivity, enabling their use as high-performance anodes with high reversible capacity, outstanding rate performance (e.g., 1,138 mA h g-1 at 0.2 C or 440 mA h g-1 at 60 C with a mass loading of 1 mg cm-2), and excellent cycling stability (e.g., >99% capacity retention for 500 cycles at 2 C with a mass loading of 1 mg cm-2). Interestingly, thick electrodes could be fabricated with high areal capacity and current density (e.g., 6.1 mA h cm-2 at 0.9 mA cm-2), providing an intriguing class of materials for lithium-ion batteries with high energy and power performance

A Review of the Transition Region of Membrane Electrode Assembly of Proton Exchange Membrane Fuel Cells: Design, Degradation, and Mitigation

As the core component of a proton exchange fuel cell (PEMFC), a membrane electrode assembly (MEA) consists of function region (active area), structure region, and transition region. Situated between the function and structure regions, the transition region influences the reliability and durability of the MEA. The degradation of the electrolyte membrane in this region can be induced by mechanical stress and chemical aggression. Therefore, prudent design, reliable and robust structure of the transition region can greatly help avoid early failure of MEAs. This review begins with the summarization of current structural concepts of MEAs, focusing on the transition region structures. It can be seen that aiming at better repeatability and robustness, partly or total integration of the materials in the transition region is becoming a development trend. Next the degradation problem at the transition region is introduced, which can be attributed to the hygro-thermal environment, free radical aggression, air pressure shock, and seal material decomposition. Finally, the mitigation approaches for the deterioration at this region are summarized, with a principle of avoiding the exposure of the membrane at the edge of the catalyst-coated membrane (CCM). Besides, durability test methods of the transition region are included in this review, among which temperature and humidity cycling are frequently used

Oxygen-doped carbon host with enhanced bonding and electron attraction abilities for efficient and stable SnO2/carbon composite battery anode

The coupling between electrochemically active material and conductive matrix is vitally important for high efficiency lithium ion batteries (LIBs). By introducing oxygen groups into the nanoporous carbon framework, we accomplish sustainably enhanced electrochemical performance for a SnO2/carbon LIB. 2-5 nm SnO2 nanoparticles are hydrothermally grown in different nanoporous carbon frameworks, which are pristine, nitrogen-or oxygen-doped carbons. Compared with pristine and nitrogen-doped carbon hosts, the SnO2/oxygen-doped activated carbon (OAC) composite exhibits a higher discharge capacity of 1,122 mA h g(-1) at 500 mA g(-1) after 320 cycles operation and a larger lithium storage capacity up to 680 mA h g(-1) at a high rate of 2,000 mA g(-1). The exceptional electrochemical performance originated from the oxygen groups, which could act as Lewis acid sites to attract electrons effectively from Sn during the charge process, thus accelerating reversible conversion of Sn to SnO2. Meanwhile, SnO2 nanoparticles are effectively bonded with carbon through such oxygen groups, thus preventing the electrochemical sintering and maintaining the cycling stability of the SnO2/OAC composite anode. The high electrochemical performance, low biomass cost, and facile preparation renders the SnO2/OAC composites a promising candidate for anode materials

Oxygen-doped carbon host with enhanced bonding and electron attraction abilities for efficient and stable SnO2/carbon composite battery anode

The coupling between electrochemically active material and conductive matrix is vitally important for high efficiency lithium ion batteries (LIBs). By introducing oxygen groups into the nanoporous carbon framework, we accomplish sustainably enhanced electrochemical performance for a SnO2/carbon LIB. 2-5 nm SnO2 nanoparticles are hydrothermally grown in different nanoporous carbon frameworks, which are pristine, nitrogen-or oxygen-doped carbons. Compared with pristine and nitrogen-doped carbon hosts, the SnO2/oxygen-doped activated carbon (OAC) composite exhibits a higher discharge capacity of 1,122 mA h g(-1) at 500 mA g(-1) after 320 cycles operation and a larger lithium storage capacity up to 680 mA h g(-1) at a high rate of 2,000 mA g(-1). The exceptional electrochemical performance originated from the oxygen groups, which could act as Lewis acid sites to attract electrons effectively from Sn during the charge process, thus accelerating reversible conversion of Sn to SnO2. Meanwhile, SnO2 nanoparticles are effectively bonded with carbon through such oxygen groups, thus preventing the electrochemical sintering and maintaining the cycling stability of the SnO2/OAC composite anode. The high electrochemical performance, low biomass cost, and facile preparation renders the SnO2/OAC composites a promising candidate for anode materials

High-Performance Sodium-Ion Pseudocapacitors Based on Hierarchically Porous Nanowire Composites

Electrical energy storage plays an increasingly important role in modern society. Current energy storage methods are highly dependent on lithium-ion energy storage devices, and the expanded use of these technologies is likely to affect existing lithium reserves. The abundance of sodium makes Na-ion-based devices very attractive as an alternative, sustainable energy storage system. However, electrodes based on transition-metal oxides often show slow kinetics and poor cycling stability, limiting their use as Na-ion-based energy storage devices. The present paper details a new direction for electrode architectures for Na-ion storage. Using a simple hydrothermal process, we synthesized interpenetrating porous networks consisting of layer-structured V₂O₅ nanowires and carbon nanotubes (CNTs). This type of architecture provides facile sodium insertion/extraction and fast electron transfer, enabling the fabrication of high-performance Na-ion pseudocapacitors with an organic electrolyte. Hybrid asymmetric capacitors incorporating the V₂O₅/CNT nanowire composites as the anode operated at a maximum voltage of 2.8 V and delivered a maximum energy of ∼40 Wh kg^–1, which is comparable to Li-ion-based asymmetric capacitors. The availability of capacitive storage based on Na-ion systems is an attractive, cost-effective alternative to Li-ion systems

Tailoring of Single-Crystalline Complex Ta₅Si₃ Nanostructures: From Networked Nanowires to Nanosheets

Single-crystalline Ta₅Si₃ nanostructures with a complex morphology were synthesized through a catalyst-free, chemical vapor deposition method under low pressures. The morphology, structure, and composition of deposited nanostructures were studied by scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. These nanostructures have lengths of up to several tens of micrometers and an average thickness of 13 nm. It was found that the formation of networked Ta₅Si₃ nanostructures is highly sensitive to the vapor pressure of tantalum chloride and silica and is based on a vapor–solid mechanism. Results indicate that, with the decrease of silica vapor pressure, the Ta₅Si₃ networked nanowires evolve into networked nanoribbons and nanosheets via two-dimensional growth. Cyclic voltammetry measurements of the Ta₅Si₃ nanostructures show superior electrochemical capacitance properties of nanosheets compared to nanowires. It is expected that these nanostructures have great potential applications for nanodevices in electronic and energy related applications