Gang Pang

Template-engaged synthesis of uniform mesoporous hollow NiCo2O4 sub-microspheres towards high-performance electrochemical capacitors

An efficient template-engaged synthetic strategy, where silica spheres were applied as hard templates, was developed to synthesize hierarchical mesoporous hollow NiCo2O4 sub-microspheres assembled entirely from ultrathin nanosheets with a thickness of a few nanometers. The as-prepared mesoporous hollow NiCo2O4 sub-microspheres are very uniform in size, mesoporous in textual property, and structurally robust benefiting from the in situ template removal. The morphologies of the hollow sub-microspherical architecture can be tuned easily by varying the concentrations of Ni2+, Co2+, and the precipitant. When evaluated as an appealing electroactive material for electrochemical capacitors (ECs), the as-fabricated hierarchical hollow NiCo2O4 sub-microspheres delivered a specific capacitance (SC) of 678 F g−1 at a current density of 1 A g−1, and even kept it as high as 540 F g−1 at 10 A g−1. Additionally, a desirable cycling stability of 13% SC degradation over 3500 continuous cycles at a current density of 10 A g−1 is observed, suggesting their promising application in advanced ECs.

Hollow mesoporous hetero-NiCo2S4/Co9S8 submicro-spindles: unusual formation and excellent pseudocapacitance towards hybrid supercapacitors

Hierarchical hollow porous architectures with intriguing hetero-interfaces are currently of particular interest in emerging energy-related fields. In this investigation, we report a smart template-free methodology to purposefully fabricate high-quality uniform hollow hetero-NiCo2S4/Co9S8 (NCCS) submicro-spindles with well-dispersed hetero-nanodomains at the nanoscale. High-yield hollow mesocrystal nickel cobalt carbonate spindles are first solvothermally synthesized as the intermediate, and a subsequent shape-preserving conversion into hetero-NCCS submicro-spindles via a hydrothermal anion-exchange reaction occurs. The underlying template-free formation mechanism of the hollow structures is tentatively proposed. When evaluated as a promising electrode for supercapacitors, the resultant hollow mesoporous hetero-NCCS electrode with a mass loading of 5 mg cm−2 delivers a good pseudocapacitance of ∼749 F g−1 at a current rate of 4 A g−1, and holds at approximately 620 F g−1 at 15 A g−1 as a result of intrinsic synergetic contributions from structural/compositional/componental merits. Furthermore, an asymmetric device based on hollow mesoporous hetero-NCCS achieves an encouraging energy density of around 33.5 W h kg−1 at a power density of 150 W kg−1, and exceptional cycling behavior with capacitance degradation of ∼0.007% per cycle over 5000 consecutive cycles at 5 A g−1. Comprehensive investigations unambiguously highlight that the unique hollow mesoporous hetero-NCCS submicro-spindles would be a powerful electrode platform for advanced next-generation supercapacitors.

Mesoporous NaTi2(PO4)3/CMK-3 nanohybrid as anode for long-life Na-ion batteries

In this work, a solvothermal strategy combined with following calcination was developed to synthesize a mesoporous NaTi2(PO4)3/CMK-3 (NTP/C) nanohybrid as a high-performance anode for next-generation Na-ion batteries (NIBs). Physicochemical characterizations demonstrated that NASICON-type structured NaTi2(PO4)3 (NTP) nanoparticles (NPs) with high crystallinity were homogeneously embedded in the mesoporous CMK-3 matrix. The mesoporous NTP/C nanohybrid as the anode for NIBs exhibited excellent electrochemical performance with high charge–discharge capability, good rate performance and long cycle life in non-aqueous electrolytes. The nanohybrid electrode delivered large specific capacities of 101, 76, 58, 39 mA h g−1 at 0.2, 0.5, 1.0 and 2.0 C, respectively, and retained it as high as 62.9 mA h g−1 even after 1000 cycles at 0.5 C. Compared to the pure NTP electrode, the mesoporous NTP/C hybrid anode with unique “meso–nano” architecture exhibited better Na-storage ability and indicated its promising application for rechargeable NIBs.

Self-sacrifice Template Formation of Hollow Hetero-Ni7S6/Co3S4 Nanoboxes with Intriguing Pseudo-capacitance for High-performance Electrochemical Capacitors

Herein, we report a simple yet efficient self-sacrifice template protocol to smartly fabricate hollow hetero-Ni7S6/Co3S4 nanoboxes (Ni-Co-S NBs). Uniform nickel cobalt carbonate nanocubes are first synthesized as the precursor via solvothermal strategy, and subsequently chemically sulfidized into hollow heter-Ni-Co-S NBs through anion-exchange process. When evaluated as electrode for electrochemical capacitors (ECs), the resultant hetero-Ni-Co-S NBs visually exhibit attractive pesudo-capacitance in KOH just after continuously cyclic voltammetry (CV) scanning for 100 cycles. New insights into the underlying energy-storage mechanism of the hollow hetero-Ni-Co-S electrode, based on physicochemical characterizations and electrochemical evaluation, are first put forward that the electrochemically induced phase transformation gradually occurrs during CV sweep from the hetero-Ni-Co-S to bi-component-active NiOOH and CoOOH, which are the intrinsic charge-storage phases for the appealing Faradaic capacitance (~677 F g−1 at 4 A g−1) of hollow Ni-Co-S NBs at high rates after cycling. When further coupled with negative activated carbon (AC), the AC//hetero-Ni-Co-S asymmetric device with extended electrochemical window of 1.5 V demonstrates high specific energy density of ~31 Wh kg−1. Of significance, we strongly envision that hollow design concept and new findings here hold great promise for enriching synthetic methodologies, and electrochemistry of complex metal sulfides for next-generation ECs.

From biomolecule to Na3V2(PO4)3/nitrogen-decorated carbon hybrids: highly reversible cathodes for sodium-ion batteries

Sodium ion batteries (SIBs) working at room temperature offer promising opportunities for renewable energy storage applications because of the abundant supply and low cost of sodium, low capacity, inferior rate capability and limited cycle life remain a significant challenge in their electrochemical operations. Herein, we report the preparation of hierarchically Na3V2(PO4)3/nitrogen-decorated carbon hybrids via solvothermal reaction using biomolecule of adenosine 5′-triphosphate disodium salt (ATP), as a novel precursor and environmentally friendly multifunctional source, simultaneously including sodium, phosphorus, carbon, nitrogen. The results demonstrate that Na3V2(PO4)3 nanocrystals are encapsulated in interconnected carbon nanosheets with moderate nitrogen doping (2.88%) to form a bundle-like structure, where the carbon nanosheets not only serve as a highly conducting pathway facilitating electron and ion transport, but as a shielding matrix to accommodate volume changes upon electrochemical cycling; thus, improving stability and reversibility of the Na3V2(PO4)3 cathode. Thus, the obtained materials deliver a high reversible capacity of 110.9 mA h g−1 at a low current rate of 0.2 C, as well as outstanding rate performance, suggesting that the Na3V2(PO4)3/nitrogen-doped carbon hybrids are promising cathode materials to be used in high-performance sodium ion batteries.

Scalable Room‐Temperature Synthesis of Mesoporous Nanocrystalline ZnMn2O4 with Enhanced Lithium Storage Properties for Lithium‐Ion Batteries

In this work, we put forward a facile yet efficient room-temperature synthetic methodology for the smart fabrication of mesoporous nanocrystalline ZnMn2O4 in macro-quality from the birnessite-type MnO2 phase. A plausible reduction/ion exchange/re-crystallization mechanism is tentatively proposed herein for the scalable synthesis of the spinel phase ZnMn2O4. When utilized as a high-performance anode for advanced Li-ion battery (LIB) application, the as-synthesized nanocrystalline ZnMn2O4 delivered an excellent discharge capacity of approximately 1288 mAh g(-1) on the first cycle at a current density of 400 mA g(-1), and exhibited an outstanding cycling durability, rate capability, and coulombic efficiency, benefiting from its mesoporous and nanoscale structure, which strongly highlighted its great potential in next-generation LIBs. Furthermore, the strategy developed here is very simple and of great importance for large-scale industrial production.

One-step hydrothermal fabrication of strongly coupled Co3O4 nanosheets–reduced graphene oxide for electrochemical capacitors

In the work, we developed a one-step synthetic strategy to prepare a strongly coupled Co3O4 nanosheets–reduced graphene oxide (Co3O4 NSs–rGO) hybrid, and further utilized it as a promising electroactive material for electrochemical capacitors (ECs). During the hydrothermal procedure, the GO was reduced and Co3O4 NSs were in situ grown on the rGO sheets simultaneously due to the electrostatic interaction between the Co2+ and GO sheets. Electrochemical characteristics indicated that the Co3O4 NSs–rGO hybrid with ∼7.2 wt% Co3O4 loading delivered a specific capacitance (SC) of 187 F g−1 at 1.2 A g−1. Furthermore, the SC degradation of the hybrid was ∼6 and 9% at constant current densities of 1.2 and 5 A g−1 after 1000 continuous charge–discharge cycles, demonstrating its desirable electrochemical stability. The synergetic effect of nanoscale size and good redox activity of the Co3O4 NSs combined with the high electronic conductivity of the rGO resulted in the enhanced electrochemical utilization at high rates. In addition, an activated carbon/Co3O4 NSs–rGO asymmetric EC was further fabricated, and exhibited a specific energy density of ∼13.4 W h kg−1, specific power density of ∼2166 W kg−1 and striking electrochemical stability with ∼11% SC degradation after 1000 cycles.

Flexible metal–organic frameworks as superior cathodes for rechargeable sodium-ion batteries

In response to the ever-increasing demand for grid-scale energy storage systems, sodium ion batteries (SIBs) working at ambient- or room-temperature are gaining much attention as promising alternatives because of the abundance and low cost of sodium resources. However, their adoption is significantly hampered by several issues, especially in terms of sluggish kinetics and capacity retention during cycling. Herein, flexible Prussian blue analogue FeFe(CN)6/carbon cloth composites are synthesized using low temperature strategies and utilized as a potential host for sodium ion insertion. As a proof of concept, the composites demonstrate excellent electrochemical performance: a reversible specific capacity of 82 mA h g−1 at 0.2C, good rate capability and long term cycling life with 81.2% capacity retention over 1000 cycles. Most significantly, this low-cost, scalable and low-temperature synthesis provides guidance for the design of other flexible materials that could have applications in wearable electronics, energy storage and conversion devices.

Facile synthesis of nitrogen-doped carbon derived from polydopamine-coated Li3V2(PO4)3 as cathode material for lithium-ion batteries

Nitrogen-doped, carbon-coated Li3V2(PO4)3 cathode materials were prepared by the oxidative self-polymerization of dopamine on the Li3V2(PO4)3 surface and subsequent carbonization of polydopamine. Field emission scanning electron microscopy (FESEM), scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) and X-ray photoelectron spectroscopy (XPS) were performed to characterize morphologies and structures. The uniform nitrogen-doped, carbon coating provided a continuous electronic conducting network. Furthermore, the existence of nitrogen in the composite can improve electronic conductivity. As cathode materials for lithium-ion batteries, the nitrogen-doped, carbon-coated Li3V2(PO4)3 composites display superior rate performance and excellent cycle performance over the pristine Li3V2(PO4)3 and carbon-coated Li3V2(PO4)3. The electrode delivers high specific capacity of 74 mA h g−1 at 10 C, and still remains at 95.4% of initial capacity after 100 cycles at 1 C.

Prussian Blue Analogue with Fast Kinetics Through Electronic Coupling for Sodium Ion Batteries

Alternative battery systems based on the chemistry of sodium are being considered to offer sustainability and cost-effectiveness. Herein, a simple and new method is demonstrated to enable nickel hexacyanoferrate (NiHCF) Prussian blue analogues (PBA) nanocrystals to be an excellent host for sodium ion storage by functionalization with redox guest molecule. The method is achieved by using NiHCF PBA powders infiltrated with the 7,7,8,8-tetracyanoquinododimethane (TCNQ) solution. Experimental and ab initio calculations results suggest that TCNQ molecule bridging with Fe atoms in NiHCF Prussian blue analogue leads to electronic coupling between TCNQ molecules and NiHCF open-framework, which functions as an electrical highway for electron motion and conductivity enhancement. Combining the merits including high electronic conductivity, open framework structure, nanocrystal, and interconnected mesopores, the NiHCF/TCNQ shows high specific capacity, fast kinetics and good cycling stability, delivering a high specific capacity of 35 mAh g-1 after 2000 cycles, corresponding a capacity loss of 0.035% decay per cycle.