Highlights
Interface engineering of heterogeneous CoS/CoO nanocrystals and N-doped graphene composite facilitates high-performance oxygen reduction reaction and oxygen evolution reaction.
Density ...functional theory calculations and experimental results confirm the enhanced electrocatalytic performances via the proposed interface engineering.
The bifunctional oxygen electrocatalyst exhibits excellent performances in rechargeable Zn–air batteries.
Low cost and green fabrication of high-performance electrocatalysts with earth-abundant resources for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for the large-scale application of rechargeable Zn–air batteries (ZABs). In this work, our density functional theory calculations on the electrocatalyst suggest that the rational construction of interfacial structure can induce local charge redistribution, improve the electronic conductivity and enhance the catalyst stability. In order to realize such a structure, we spatially immobilize heterogeneous CoS/CoO nanocrystals onto N-doped graphene to synthesize a bifunctional electrocatalyst (CoS/CoO@NGNs). The optimization of the composition, interfacial structure and conductivity of the electrocatalyst is conducted to achieve bifunctional catalytic activity and deliver outstanding efficiency and stability for both ORR and OER. The aqueous ZAB with the as-prepared CoS/CoO@NGNs cathode displays a high maximum power density of 137.8 mW cm
−2
, a specific capacity of 723.9 mAh g
−1
and excellent cycling stability (continuous operating for 100 h) with a high round-trip efficiency. In addition, the assembled quasi-solid-state ZAB also exhibits outstanding mechanical flexibility besides high battery performances, showing great potential for applications in flexible and wearable electronic devices.
Being simple, inexpensive, scalable and environmentally friendly, microporous biomass biochars have been attracting enthusiastic attention for application in lithium-sulfur （Li-S） batteries. Herein, ...porous bamboo biochar is activated via a KOH/annealing process that creates a microporous structure, boosts surface area and enhances electronic conductivity. The treated sample is used to encapsulate sulfur to prepare a microporous bamboo carbon-sulfur （BC-S） nanocomposite for use as the cathode for Li-S batteries for the first time. The BC-S nanocomposite with 50 wt.% sulfur content delivers a high initial capacity of 1,295 mA-h/g at a low discharge rate of 160 mA/g and high capacity retention of 550 mA-h/g after 150 cycles at a high discharge rate of 800 mA/g with excellent coulombic efficiency （995%）. This suggests that the BC-S nanocomposite could be a promising cathode material for Li-S batteries.
In this work, we synthesized graphene oxide (GO) using the improved Hummers’ oxidation method. TiO2 nanoparticles can be anchored on the GO sheets via the abundant oxygen-containing functional groups ...such as epoxy, hydroxyl, carbonyl, and carboxyl groups on the GO sheets. Using the TiO2 photocatalyst, the GO was photocatalytically reduced under UV illumination, leading to the production of TiO2-reduced graphene oxide (TiO2-RGO) nanocomposite. The as-prepared TiO2, TiO2-GO, and TiO2-RGO nanocomposite were used to fabricate lithium ion batteries (LIBs) as the active anode materials and their corresponding lithium ion insertion/extraction performance was evaluated. The resultant LIBs of the TiO2-RGO nanocomposite possesses more stable cyclic performance, larger reversible capacity, and better rate capability, compared with that of the pure TiO2 and TiO2-GO samples. The electrochemical and materials characterization suggest that the graphene network provides efficient pathways for electron transfer, and the TiO2 nanoparticles prevent the restacking of the graphene nanosheets, resulting in the improvement in both electric conductivity and specific capacity, respectively. This work suggests that the TiO2 based photocatalytic method could be a simple, low-cost, and efficient approach for large-scale production of anode materials for lithium ion batteries.
Blue hydrogenated rutile TiO2 nanoparticles (blue TiO2) are prepared by treating white rutile via an enhanced hydrogenation process (i.e., high pressure and temperature). The materials ...characterization results demonstrate that the hydrogenation process leads to the increase in the unit cell volume and decrease in the size compared with the untreated white TiO2. The electrochemical impedance spectra analyses and theoretical energy calculations using density functional theory (DFT) suggest that the hydrogenation process not only improves electronic conductivity due to the formation of oxygen vacancy in the hydrogenation process but also dramatically augments lithium-ion mass transport within the crystalline lattice due to the introduction of oxygen vacancy and crystalline dislocation. Because of these characteristics resulting from the hydrogenation process, the blue TiO2 based lithium ion batteries (LIBs) possess significantly higher energy capacity and better rate performance than the white TiO2 based LIBs. In particular, at the rate of 0.1 and 5 C (1 C = 336 mAh g–1), the discharge capacities of the blue rutile are maintained at ca.179.8 and 129.2 mAh g–1, while the capacities of the white TiO2 are just ca. 119.6 and 55.5 mAh g–1, respectively.
The high rate applications such as electric vehicles of the traditional lithium ion batteries (LIBs) are commonly limited by their insufficient electron conductivity and slow mass transport of ...lithium ions in bulk electrode materials. In order to address these issues, in this work, a simple and up-scalable wet-mechanochemical (wet-ball milling) route has been developed for fabrication of amorphous porous TiO2@nitrogen doped graphene (TiO2@N-G) nanocomposites. The amorphous phase, unique porous structure of TiO2 and the surface defects from nitrogen doping to graphene planes have incurred surface controlled reactions, contributing pseudocapacitance to the total capacity of the battery. It plays a dominant role in producing outstanding high rate electrochemical performance, e.g., 182.7mAh/g (at 3.36A/g) after 100 cycles. The design and synthesis of electrode materials with enhanced conductivity and surface pseudocapacitance can be a promising way for high rate LIBs.
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•3D porous carbon nanosheets with expanded interlayer is successfully synthesized.•The PCNs-C600 exhibits a superior capacitive Na-ion storage.•The SIC device delivers high ...energy/power densities of 128 Wh kg−1/17034 W kg−1.•The SIC device exhibits superior rate capability and long-term cycle life.
Hard carbon anodes are deemed to be the best choice for sodium-ion capacitors (SICs). However, hard carbon still suffers from low specific capacity and poor rate capability, arising from its bulk structure with nonporous surface. Herein, we disclose the importance of utilizing ascorbic acid (AA) with polyvinyl alcohol (PVA) to synthesize 3D porous carbon nanosheets (PCNs) for SIC. The physical studies reveal that AA is operative to increase the specific surface area (373.7 m2 g−1) as well as to enlarge the interlayer spacing (0.41 nm). As anode for sodium-ion storage, PCNs-C600 achieves a high specific capacity of 307 mAh g−1 at 0.1 A g−1, superior rate performance of 121 mAh g−1 at 10 A g−1, as well as outstanding cycling stability at 1.0 A g−1 with virtually no decay over 5000 cycles. Accordingly, the SIC device is assembled by using PCNs-C600 as anode, which displays high energy/power densities of 128 Wh Kg−1/17034 W Kg−1 with superior rate capability and remarkable cyclability (83% retention over 8000 cycles at 1.0 A g−1). These results open a new pathway towards generating a high-performance sodium-ion capacitor.
Carbon nanotube (CNT) and TiO2 nanofibre composite films are prepared and used as anode materials for lithium ion batteries (LIBs) without the use of binders and conventional copper current ...collector. The preliminary experimental results from X-ray diffraction, scanning electron microscopy and transmission electron microscopy suggest that the TiO2 nanofibres were well-dispersed and interwoven by the CNTs, forming freestanding, bendable and light weighted composite. In comparison with TiO2 nanofibre based LIBs, the CNTs could significantly improve the battery performance due to their high conductivity property and 3D network morphology. In both 1–3V and 0.01–3V testing voltage ranges, the as-prepared composites show excellent reversible capacity and capacity retention. The superior lithium storage capacity of the CNT/TiO2 composite was mainly attributed to dual functions of the CNTs – the CNTs not only provide conductive networks to assist the electron transfer but also facilitate lithium ion diffusion between the electrolyte and the TiO2 active materials by preventing agglomeration of TiO2 nanofibres. This work demonstrates that the CNT–TiO2 composite film could be one type of potential electrode material for large-scale LIB applications.
In this study, well-dispersed gold nanoparticles were prepared by the reduction of HAuCl
4
in sodium bis(2-ethylhexyl)sulfosuccinate/isooctane reverse micelles system using ascorbic acid as reducing ...agent. The properties of the obtained nanoparticles were characterized with transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and UV–vis absorption spectrophotometer. Due to its high water solubility, biodegradability, and low toxicity, ascorbic acid could be used as a benign naturally available reducing agent to synthesize gold nanoparticles.
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