SnO x /graphene anode material with multiple oxidation states for high-performance Li-ion batteries.

Tin and its oxides are promising anode materials owing to their high theoretical capacity, rich resource, and environmental benignity. To achieve low cost and green synthesis, a facile synthetic route of SnO x /graphene composites is proposed, using a simple galvanic replacement method to quickly obtain abundant foamed tin as raw material and ball milling method to realize a mechanochemical reaction between SnO x (0 ≤ x ≤ 2) and graphene. Under different annealing conditions, the foamed tin is converted to tin oxides with multiple oxidation states (Sn3O4, SnO, and SnO2). These unique components can greatly affect the electrochemical performance of the electrode in LIBs. The as-prepared electrode (SnO x -300/G) obtained by annealing foamed tin at 300 °C for 4 h and combining SnO x powders with graphene via ball milling shows great cycling stability, retaining a high capacity of 786 mA h g-1 at 0.1 A g-1 after 150 cycles, and its initial Coulombic efficiency can reach 84.03%. Thus, this facile synthesis can provide an environmentally friendly route for commercial production of high-performance energy storage materials.

Diblock copolymers directing construction of hierarchically porous metal-organic frameworks for enhanced-performance supercapacitors.

A rationally designed strategy is developed to synthesize hierarchically porous Fe-based metal-organic frameworks (P-Fe-MOF) via solution-based self-assembly of diblock copolymers. The well-chosen amphiphilic diblock copolymers (BCP) of polystyrene-block-poly(acrylic acid) (PS-b-PAA) exhibits outstanding tolerance capability of rigorous conditions (e.g. strong acidity or basicity, high temperature and pressure), steering the peripheral crystallization of Fe-based MOF by anchoring ferric ions with outer PAA block. Importantly, the introduction of BCP endows MOF materials with additional mesopores (∼40 nm) penetrating whole crystals, along with their inherent micropores and introduced macropores. The unique hierarchically porous architecture contributes to fast charge transport and electrolyte ion diffusion, and thus promotes their redox reaction kinetics processes. Accordingly, the resultant P-Fe-MOF material as a new electrode material for supercapacitors delivers the unprecedented highest specific capacitance up to 78.3 mAh g-1 at a current density of 1 A g-1, which is 9.8 times than that of Fe-based MOF/carbon nanotubes composite electrode reported previously. This study may inspire new design of porous metal coordination polymers and advanced electrode materials for energy storage and conversion field.

Pre-Polymerization Enables Controllable Synthesis of Nanosheet-Based Porphyrin Polymers towards High-Performance Li-Ion Batteries.

The precise regulation of nucleation growth and assembly of polymers is still an intriguing goal but an enormous challenge. In this study, we proposed a pre-polymerization strategy to regulate the assembly and growth of polymers by facilely controlling the concentration of polymerization initiator, and thus obtained two kinds of different nanosheet-based porphyrin polymer materials using tetrakis-5,10,15,20-(4-aminophenyl) porphyrin (TAPP) as the precursor. Notably, due to the π-π stacking and doping of TAPP during the preparation process, the obtained PTAPP-nanocube material exhibits a high intrinsic bulk conductivity reaching 1.49×10-4  S m-1 . Profiting from the large π-conjugated structure of porphyrin units, closely stacked layer structure and excellent conductivity, the resultant porphyrin polymers, as electrode materials for lithium ion batteries, deliver high specific capacity (≈650 mAh g-1 at the current density of 100 mA g-1 ), excellent rate performance and long-cycle stability, which are among the best reports of porphyrin polymer-based electrode materials for lithium-ion batteries, to the best of our knowledge. Therefore, such a pre-polymerization approach would provide a new insight for the controllable synthesis of polymers towards custom-made architecture and function.

Hollow Bio-derived Polymer Nanospheres with Ordered Mesopores for Sodium-Ion Battery.

Bio-inspired hierarchical self-assembly provides elegant and powerful bottom-up strategies for the creation of complex materials. However, the current self-assembly approaches for natural bio-compounds often result in materials with limited diversity and complexity in architecture as well as microstructure. Here, we develop a novel coordination polymerization-driven hierarchical assembly of micelle strategy, using phytic acid-based natural compounds as an example, for the spatially controlled fabrication of metal coordination bio-derived polymers. The resultant ferric phytate polymer nanospheres feature hollow architecture, ordered meso-channels of ~ 12 nm, high surface area of 401 m2 g-1, and large pore volume of 0.53 cm3 g-1. As an advanced anode material, this bio-derivative polymer delivers a remarkable reversible capacity of 540 mAh g-1 at 50 mA g-1, good rate capability, and cycling stability for sodium-ion batteries. This study holds great potential of the design of new complex bio-materials with supramolecular chemistry.

One-Step In Situ Self-Assembly of Cypress Leaf-Like Cu(OH)2 Nanostructure/Graphene Nanosheets Composite with Excellent Cycling Stability for Supercapacitors.

Transition metal hydroxides and graphene composite holds great promise to be the next generation of high performance electrode material for energy storage applications. Here we fabricate the cypress leaf-like Cu(OH)2 nanostructure/graphene nanosheets composite through one-step in situ synthesis process, employed as a new type of electrode material for high efficiency electrochemical energy storage in supercapacitors. A solution-based two-electrode system is applied to synthesize Cu(OH)2/graphene hybrid nanostructure, where anodic graphene nanosheets firmly anchor cathodic Cu(OH)2 nanostructure due to the electrostatic interaction. The in situ self-assembly of Cu(OH)2/graphene ensures good structural robustness and the cypress leaf-like Cu(OH)2 nanostructure prompt to form the open and porous morphology. The hybrid structure would facilitate charge transport and effectively mitigate the volume changes during long-term charging/discharging cycles. As a consequence, the Cu(OH)2/graphene composite exhibits the highest capacitance of 317 mF/cm2 at the current density of 1 mA/cm2 and superior cyclic stability with no capacitance decay over 20,000 cycles and remarkable rate capability at increased current densities.

NiO/Ni x Co3-x O4 porous ultrathin nanosheet/nanowire composite structures as high-performance supercapacitor electrodes.

The demand for a new generation of high-safety, long-lifespan, and high-capacity power sources increases rapidly with the growth of energy consumption in the world. Here we report a facile method for preparing architecture materials made of NiO/Ni x Co3-x O4 porous nanosheets coupled with NiO/Ni x Co3-x O4 porous nanowires grown in situ on nickel foams using a hydrothermal method without any binder followed by a heat treatment process. The nanosheet-shaped NiO/Ni x Co3-x O4 species in the nanosheet matrix function well as a scaffold and support for the dispersion of the Ni x Co3-x O4 nanowires, resulting in a relatively loose and open structure within the electrode matrix. Among all composite electrodes prepared, the one annealed in air at 300 °C displays the best electrochemical behavior, achieving a specific capacitance of 270 mF cm-2 at 5 mA cm-2 while maintaining excellent stability (retaining ≈ 89% of the max capacitance after 20 000 cycles), demonstrating its potential for practical application in power storage devices.

A one-step method to fabricate novel three-dimensional GaP nanopore arrays for enhanced photoelectrochemical hydrogen production.

Gallium phosphide nanopore arrays with unique three-dimensional interior architectures (3D GaP NPs) are fabricated by electrochemical etching in a neutral solution. As the photoanodes for photoelectrochemical (PEC) hydrogen production, the 3D GaP NPs exhibited a larger photocurrent density (5.65 mA cm-2 at 0 V vs. RHE, which is 58.3 and 2.3 times as large as that of the planar wafer and the NPs reported by our group in our previous work respectively) and a lower onset potential (-0.58 V vs. RHE, shifting negatively nearly 300 mV compared with its counterparts in the previous work). Besides the excellent light-trapping characteristics of the nanostructures, electrochemical impedance spectroscopy (EIS) further confirmed that the enhanced PEC performance was ascribed to the more efficient charge separation and transfer, and the increased surface area with the unique 3D NP arrays. Furthermore, the efficient charge separation may be attributed to the passivated surface states by the neutral solution.

Nickel skeleton three-dimensional nitrogen doped graphene nanosheets/nanoscrolls as promising supercapacitor electrodes.

A novel nickel skeleton 3D nitrogen doped graphene (N-GR/NF) superstructure with interconnected graphene nanosheets and nanoscrolls was synthesized using a facile two-step method. By varying the precursor concentration, the assembly of a graphene aerogel can be easily regulated, yielding different micro-structures and morphologies which accelerate the fast electron/ion transportation. The N-GR/NF composites demonstrate enhanced capacitance of 250 F g-1 at 5 A g-1, good rate performance (237 F g-1 at the current density of 12 A g-1) and cycle stability (90.9% retention after 5000 cycles) in 1 M KOH electrolyte. This study provides a new strategy for the microporous engineering of graphene gel, promising for further exploitation in various other applications.

Galvanic displacement assembly of ultrathin Co3O4 nanosheet arrays on nickel foam for a high-performance supercapacitor.

High-performance supercapacitors are very desirable for many portable electronic devices, electric vehicles and high-power electronic devices. Herein, a facile and binder-free synthesis method, galvanic displacement of the precursor followed by heat treatment, is used to fabricate ultrathin Co3O4 nanosheet arrays on nickel foam substrate. When used as a supercapacitor electrode the prepared Co3O4 on nickel foam exhibits a maximum specific capacitance of 1095 F g-1 at a current density of 1 A g-1 and good cycling stability of 71% retention after 2000 cycling tests. This excellent electrochemical performance can be ascribed to the high specific surface area of each Co3O4 nanosheet that comprises numerous nanoparticles.

Synchronous exfoliation and assembly of graphene on 3D Ni(OH)2 for supercapacitors.

Nowadays, new approaches to fabricate high-performance electrode materials are of vital importance in the renewable energy field. Here, we present a facile synthesis procedure of 3D Ni(OH)2/graphene hybrids for supercapacitors via synchronous electrochemical-assisted exfoliation and assembly of graphene on 3D Ni(OH)2 networks. With the assistance of an electric field, the electrochemically exfoliated high-quality graphene can be readily, uniformly assembled on the surfaces of 3D Ni(OH)2. When serving as electrode materials for supercapacitors, the resulting 3D Ni(OH)2/graphene composites exhibited excellent specific capacitance (263 mF cm-2 at 2 mA cm-2), remarkable rate capability and super-long cycle life (retention of 94.1% even after 10 000 continuous charge-discharge cycles), which may be attributed to their highly porous, stable 3D architecture as well as uniform, firm anchoring of ultrathin graphene on their surfaces. Therefore, our approach provides a facile strategy for the large-scale synthesis of high-quality graphene based composites towards various applications.