Yuanjuan Bai

Designed synthesis of hollow Co3O4 nanoparticles encapsulated in a thin carbon nanosheet array for high and reversible lithium storage

The design and fabrication of novel composite nano-architectures is crucial for their applications in energy storage devices such as lithium ion batteries (LIBs). Herein, a thin carbon nanosheet array with encapsulated hollow Co3O4 nanoparticles is successfully fabricated on 3D Ni foam by using electrodeposited Co(OH)2 nanosheets as templates and followed by a two step annealing process. When used as an anode material in LIBs, the hollow Co3O4/carbon nanosheet composite displays an excellent performance with a high reversible capacity, excellent cycling stability and rate capability. This work is helpful for the design of an advanced electrode for LIBs, supercapacitors, electrochemical sensors, etc.

A General Strategy Towards Encapsulation of Nanoparticles in Sandwiched Graphene Sheets and the Synergic Effect on Energy Storage

A novel and universal approach towards the unique encapsulation of nanoparticles in the sandwiched graphene sheets is presented here. In the method, a low-cost, sustainable and environmentally friendly carbon source, glucose, is firstly applied to yield the high-quality, uniform and coupled graphene sheets in a large scale, and the pre-fabricated hydrated nanosheets act as the sacrificial templates to generate the enveloped metallic nanoparticles. After controllable oxidation or removal of the encapsulated nanoparticles, sandwiched nanocomposite with oxidizes nanoparticles encapsulated in graphene sheets or pure phase of sandwich-like and coupled graphene sheets would be achieved. Moreover, the synergic effect on energy storage via Li-ion batteries is solidly verified in the Co(3)O(4)@graphene nanocomposite. More importantly, the unique structure of the nanoparticles-encapsulated sandwiched graphene sheets will definitely result in additional applications, such as biosensors, supercapacitors and specific catalyses. These results have enriched the family of graphene-based materials and recognized some new graphene derivatives, which will be considerably meaningful in chemistry and materials sciences.

Novel peapod NiO nanoparticles encapsulated in carbon fibers for high-efficiency supercapacitors and lithium-ion batteries

Nickel oxide is regarded as one of the most promising electrodes in energy storage. In this report, a special peapod NiO/C is successfully designed and fabricated for the first time through a simple hydrothermal method by using green glucose as the carbon source. This unique structure can not only provide a large contact area between the electrolyte and active materials so as to promote fast ion and electron exchange, but also digest possible volume changes during long-time reactions so that it can lead to superior cyclic stability. Importantly, the porous structure can effectively accelerate ion diffusion, further enhancing the electrochemical performances. In this work, our peapod NiO/C exhibits excellent performances in both supercapacitors (SCs) and lithium-ion batteries (LIBs).

Novel peapod array of Ni2P@graphitized carbon fiber composites growing on Ti substrate: a superior material for Li-ion batteries and the hydrogen evolution reaction

A novel one-dimensional (1-D) peapod array of nickel phosphide (Ni2P)@graphitized carbon fiber composites consisting of graphitized carbon fiber and the encapsulated Ni2P nanoparticles has been designed and synthesized on titanium foil substrate. This smart and elaborate architecture design offers several remarkable advantages, including large interfacial area, short charge transporting path, strong physical adhesion with the current collector and large electrolyte diffusion pathway between the peapod array. When used for lithium ion batteries, excellent electrochemical performances such as a high capacity of 634 mA h g−1 at a current density of 200 mA g−1, long-term cycling stability and outstanding rate capability, are obtained. In 0.5 M sulfuric acid, as an electrocatalyst for hydrogen evolution reaction, the peapod array of Ni2P@graphitized carbon fiber composites gives a current density of 10 mA cm−2 at a small over-potential of 45 mV and a small Tafel slope of ∼46 mV decade−1. More importantly, the sample exhibits exceptional stability in an acidic environment. Furthermore, it is believed that the idea to prepare the 1-D peapod array on a conductive substrate is generic and could be extended to be used with other materials.

Tunable and Specific Formation of C@NiCoP Peapods with Enhanced HER Activity and Lithium Storage Performance.

The superior properties of nanomaterials with a special structure can provide prospects for highly efficient water splitting and lithium storage. Herein, we fabricated a series of peapodlike C@Ni2-x Cox P (x≤1) nanocomposites by an anion-exchange pathway. The experimental results indicated that the HER activity of C@Ni2-x Cox P catalyst is strongly related to the Co/Ni ratio, and the C@NiCoP got the highest HER activity with low onset potential of ∼45 mV, small Tafel slope of ∼43 mV dec(-1) , large exchange current density of 0.21 mA cm(-2) , and high long-term durability (60 h) in 0.5 m H2 SO4 solutions. Equally importantly, as an anode electrode for lithium batteries, this peapodlike C@NiCoP nanocomposite gives excellent charge-discharge properties (e.g., specific capacity of 670 mAh g(-1) at 0.2 A g(-1) after 350 cycles, and a reversible capacity of 405 mAh g(-1) at a high current rate of 10 A g(-1) ). The outstanding performance of C@NiCoP in HER and LIBs could be attributed to the synergistic effect of the rational design of peapodlike nanostructures and the introduction of Co element.

Designed Functional Systems for High-Performance Lithium-Ion Batteries Anode: From Solid to Hollow, and to Core–Shell NiCo2O4 Nanoparticles Encapsulated in Ultrathin Carbon Nanosheets

Binary metal oxides have been considered as ideal and promising anode materials, which can ameliorate and enhance the electrochemical performances of the single metal oxides, such as electronic conductivity, reversible capacity, and structural stability. In this research, we report a rational method to synthesize some novel sandwich-like NiCo2O4@C nanosheets arrays for the first time. The nanostructures exhibit the unique features of solid, hollow, and even core-shell NiCo2O4 nanoparticles encapsulated inside and a graphitized carbon layers coating outside. Compared to the previous reports, these composites demonstrate more excellent electrochemical performances, including superior rate capability and excellent cycling capacity. Therefore, the final conclusion would be given that these multifarious sandwich-like NiCo2O4@C composites could be highly qualified candidates for lithium-ion battery anodes in some special field, in which good capability and high capacity are urgently required.

Sandwich-like CoP/C nanocomposites as efficient and stable oxygen evolution catalysts

Nowadays, the sluggish kinetics of the oxygen evolution reaction (OER) has been a bottleneck factor in water electrolysis. Designing and synthesizing some materials, with novel and specific morphology, may hopefully relieve the present puzzle. Herein, a novel sandwich-like CoP/C nanocomposite was developed by a low-temperature phosphorization method using a carbon-encapsulated Co-based nanosheet as a precursor. The cross-section images directly show that the monodispersed CoP nanoparticles are sandwiched between two thin carbon layers. The outer coating of CoP nanoparticles serves as an efficient protective layer and conductive medium in the process of water electrolysis. Remarkably, the sandwich-like CoP/C obtains a small overpotential of only 330 mV (1.56 V vs. RHE) at a current density of 10 mA cm−2, which is favorably compared with the commercial IrO2/C (400 mV), sandwich-like CoO/C (450 mV) and macroporous CoP (610 mV) catalysts we prepared. This CoP/C nanocomposite also presents better stability in alkaline solution than that of CoO/C and macroporous CoP. What is important is that this excellent OER performance has exceeded most Co-based materials reported thus far. The sandwich-like CoP/C material we obtained affords the possibility of the pursuit of robust, low-cost and high-effective OER catalysts.

Designed Synthesis of Transition Metal/Oxide Hierarchical Peapods Array with the Superior Lithium Storage Performance

In this report, a novel hierarchical peapoded array with Co3O4 nanoparticles encapsulated in graphitized carbon fiber is introduced for the first time. The unique peapoded structure is suitable for the excellent anode in LIBs and demonstrates enhanced rate capability, cyclability and prolonged lifespan, e.g. the specific capacity can reach up to 1150 mAh/g. All the enhanced electrochemical performance is reasonably derived from the peapod-like and aligned conformation. Furthermore, due to the specialty of the structure and the versatility of Co3O4, the composite will find more applications in specific catalysis, biomedicine, electronics, optoelectronic engineering and gas sensing. The fabrication strategy developed here is also a rational and universal approach towards peapod-like architecture and has significantly widened the specific functional material domain we created before. In our design, more peapod-like aligned samples with various nanoparticles, e.g. oxides, phosphides, even nitrides, encapsulated in graphitized carbon fibers, have been lifted on the research agenda and the results will be presented soon.

Unique synthesis of mesoporous peapod-like NiCo2O4–C nanorods array as an enhanced anode for lithium ion batteries

A novel peapod-like NiCo2O4–C nanorods array on a 3D Ni-foam was synthesized for the first time and used as an anode for lithium ion batteries. The nanorods array was grown directly on a 3D Ni-foam by a facile route, including a hydrothermal reaction and subsequent annealing at a setting temperature. In contrast to previous reports, the as-prepared peapod-like NiCo2O4–C composite in our experiments exhibited both mesoporosity and excellent conductivity; moreover, the stable core–shell structure allowed improved electron transfer and electrolyte penetration when applied to lithium ion batteries. When tested in an electrochemical system, the as-prepared samples demonstrated excellent electrochemical performance such as enhanced rate capability (a reversible capability of 664 mA h g−1 at 2000 mA g−1) as well as a high coulombic efficiency (coulombic efficiency of 97% can be obtained after 200 cycles at 100 mA g−1).

Strengthened Synergistic Effect of Metallic MxPy (M = Co, Ni, and Cu) and Carbon Layer via Peapod-Like Architecture for Both Hydrogen and Oxygen Evolution Reactions

The smooth electric transmission is crucial for the high-efficient electrocatalysis. Herein, a series of peapod-like metallic Mx Py /C (M = Co, Ni, and Cu) composites is developed as bifunctional catalysts toward hydrogen and oxygen evolution reactions. For the first time, the metallic property of Cu3 P is confirmed through the theoretical calculation. The in-depth composition, structural and catalytic mechanism analysis of Mx Py /C discloses that the comparable activity and considerable durability of these catalysts mainly result from the strengthened synergistic effect between metallic Mx Py and carbon layer based on the unique peapod-like architecture. Especially, the atomic contact between Mx Py and carbon not only provides an open channel for electronic transmission but also ensures the integrity of peapod-like structure. Furthermore, the high electric conductivity of the inner metallic Mx Py and the outer carbon layer endows the Mx Py /C catalyst with rapid charge migration during the electrocatalytic pathway. These findings shed light on the origin of high catalytic activity of Mx Py /C and open a path for purposefully rationally synthesizing superior electrocatalysts.