Xianfeng Yang

Seaweed-Derived Route to Fe2O3 Hollow Nanoparticles/N-Doped Graphene Aerogels with High Lithium Ion Storage Performance

We developed a nanoscale Kirkendall effect assisted method for simple and scalable synthesis of three-dimensional (3D) Fe2O3 hollow nanoparticles (NPs)/graphene aerogel through the use of waste seaweed biomass as new precursors. The Fe2O3 hollow nanoparticles with an average shell thickness of ∼6 nm are distributed on 3D graphene aerogel, and also act as spacers to make the separation of the neighboring graphene nanosheets. The graphene-Fe2O3 aerogels exhibit high rate capability (550 mA h g(-1) at 5 A g(-1)) and excellent cyclic stability (729 mA h g(-1) at 0.1 A g(-1) for 300 cycles), outperforming all of the reported Fe2O3/graphene hybrid electrodes, due to the hollow structure of the active Fe2O3 NPs and the unique structure of the 3D graphene aerogel framework. The present work represents an important step toward high-level control of high-performance 3D graphene-Fe-based NPs aerogels for maximizing lithium storage with new horizons for important fundamental and technological applications.

Scalable and Cost-Effective Synthesis of Highly Efficient Fe2N-Based Oxygen Reduction Catalyst Derived from Seaweed Biomass

A simple and scalable synthesis of a 3D Fe2N-based nanoaerogel is reported with superior oxygen reduction reaction activity from waste seaweed biomass, addressed the growing energy scarcity. The merits are due to the synergistic effect of the 3D porous hybrid aerogel support with excellent electrical conductivity, convenient mass transport and O2 adsorption, and core/shell structured Fe2N/N-doped amorphous carbon nanoparticles.

Seaweed biomass derived (Ni,Co)/CNT nanoaerogels: efficient bifunctional electrocatalysts for oxygen evolution and reduction reactions

Developing earth-abundant, active and stable electrocatalysts which operate in two-electrode rechargeable metal–air batteries, including both oxygen evolution and reduction reactions (OER and ORR), is vital for renewable energy conversion in real application. Here, we demonstrate a three-dimensional (3D) bifunctional nanoaerogel electrocatalyst that exhibits good electrocatalytic properties for both OER and ORR. This material was fabricated using a scalable and facile method involving the pyrolysis of (Ni,Co)/CNT alginate hydrogels derived from sustainable seaweed biomass after an ion exchange process. The bifunctionality for oxygen electrocatalysis as shown by the OER–ORR potential difference (ΔE, the OER and ORR potentials are taken at the current densities of 10 mA cm−2 and −3 mA cm−2 in 0.1 M KOH, respectively) could be reduced to as low as 0.87 V, comparable to the state-of-the-art non-noble bifunctional catalysts. The good performance was attributed to the ternary Ni/NiO/NiCo2O4 catalytic center for charge transfer and 3D hierarchical mesoporous hybrid framework for efficient mass transport. More importantly, the Zn–air battery fabricated with the hybrid nanoaerogel as a bifunctional electrocatalyst displays very high energy efficiency (58.5%) and long-term stability. Prospectively, our present work may pave a new way to develop earth-abundant and low cost high-performance bifunctional electrocatalysts for rechargeable metal–air batteries.

Architecture-controlled synthesis of MxOy (M = Ni, Fe, Cu) microfibres from seaweed biomass for high-performance lithium ion battery anodes

The increasing demand for high performance lithium ion batteries (LIBs) has aroused great interest in developing high specific capacity, cycle performance and rate capability anode materials. Transition metal oxides (TMOs) have attracted much attention as promising anode materials for rechargeable LIBs owing to their high theoretical capacity. Here, a general strategy has been developed to fabricate high-performance fibrous TMO anodes such as elemental Ni doped NiO fibre (NiO/Ni/C-F), yolk–shell structured carbon@Fe2O3 fibre (C@Fe2O3-F), and hollow CuO fibre (CuO-HF) with controllable nanostructures by using alginate microfibres as templates. The key to the formation of various TMO micro-/nano-structures is the templating ability of the natural structure of long alginate molecular chains, where the metal cations can be confined in an “egg-box” via coordination with negatively charged α-L-guluronate blocks. When tested as anode materials for LIB half cells, these fibrous electrodes deliver excellent cycling performance with no capacity decrease after 200 cycles (793 mA h g−1, NiO/Ni/C-F, 0.072 A g−1; 1035 mA h g−1, C@Fe2O3-F, 0.1 A g−1; 670 mA h g−1, CuO-HF, 0.067 A g−1), and demonstrate great rate performance at different current densities. This finding highlights a general, green and eco-friendly strategy for the scale-up production of potential high-performance TMO anodes for LIBs.

Double-Helix Structure in Carrageenan–Metal Hydrogels: A General Approach to Porous Metal Sulfides/Carbon Aerogels with Excellent Sodium-Ion Storage

The metal sulfide-carbon nanocomposite is a new class of anode material for sodium ion batteries, but its development is restricted by its relative poor rate ability and cyclic stability. Herein, we report the use of double-helix structure of carrageenan-metal hydrogels for the synthesis of 3D metal sulfide (Mx Sy ) nanostructure/carbon aerogels (CAs) for high-performance sodium-ion storage. The method is unique, and can be used to make multiple Mx Sy /CAs (such as FeS/CA, Co9 S8 /CA, Ni3 S4 /CA, CuS/CA, ZnS/CA, and CdS/CA) with ultra-small nanoparticles and hierarchical porous structure by pyrolyzing the carrageenan-metal hydrogels. The as-prepared FeS/CA exhibits a high reversible capacity and excellent cycling stability (280u2005mAu2009h-1 at 0.5u2005Au2009g-1 over 200u2005cycles) and rate performance (222u2005mAu2009h-1 at 5u2005Au2009g-1 ) when used as the anode material for sodium-ion batteries. The work shows the value of biomass-derived metal sulfide-carbon heterostuctures in sodium-ion storage.

Highly stable supercapacitors with MOF-derived Co9S8/carbon electrodes for high rate electrochemical energy storage

Co9S8 has received intensive attention as an electrode material for electrical energy storage (EES) systems due to its unique structural features and rich electrochemical properties. However, the instability and inferior rate capability of the Co9S8 electrode material during the charge/discharge process has restricted its applications in supercapacitors (SCs). Here, MOF-derived Co9S8 nanoparticles (NPs) embedded in carbon co-doped with N and S (Co9S8/NS–C) were synthesized as a high rate capability and super stable electrode material for SCs. The Co9S8/NS–C material was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). It was found that the Co9S8/NS–C material possessed a unique nanostructure in which Co9S8 NPs were encapsulated in porous graphitic carbon co-doped with N and S. The N/S co-doped porous graphitic carbon of composite led to improved rate performance by enhancing the stability of the electrode material and shortening the ion diffusion paths due to a synergistic effect. The as-prepared Co9S8/NS–C-1.5 h material exhibited a high specific capacitance of 734 F g−1 at a current density of 1 A g−1, excellent rate capability (653 F g−1 at 10 A g−1) and superior cycling stability, i.e., capacitance retention of about 99.8% after 140u2006000 cycles at a current density of 10 A g−1. Thus, a new approach to fabricate promising electrode materials for high-performance SCs is presented here.

Triple-walled SnO2@N-doped carbon@SnO2 nanotubes as an advanced anode material for lithium and sodium storage

Triple-walled SnO2@N-doped carbon@SnO2 nanotubes are synthesized by a facile process with high-quality PPy nanotubes as the template. This structure has SnO2 nanoparticles closely attached to both the external and internal surfaces of N-doped carbon nanotubes, thus assuring good charge-transfer kinetics to all the SnO2 nanoparticles. Meanwhile, it doubles the loading density of SnO2 in the nanocomposite, and offers adequate room to accommodate the volume deformation of SnO2 on/in the nanotubes. All these features make the nanocomposite well fitted for lithium or sodium storage. It is found that this nanocomposite as an anode material for lithium ion batteries can deliver a reversible capacity of 935 mA h g−1 after 100 cycles at 200 mA g−1, or 658 mA h g−1 after 300 cycles at 2000 mA g−1. In the case of sodium ion batteries, its capacity could be still preserved at 492 mA h g−1 after 50 cycles at a current density of 25 mA g−1.

Multishelled Ni-Rich Li(NixCoyMnz)O2 Hollow Fibers with Low Cation Mixing as High-Performance Cathode Materials for Li-Ion Batteries

A simple seaweed biomass conversion strategy is proposed to synthesize highly porous multishelled Ni‐rich Li(NixCoyMnz)O2 hollow fibers with very low cation mixing. The low cation mixing results from the cation confinement by the novel “egg‐box” structure in the alginate template. These hollow fibers exhibit remarkable energy density, high‐rate capacity, and long‐term cycling stability when used as cathode material for Li‐ion batteries.

Interface engineering of 3D BiVO4/Fe-based layered double hydroxide core/shell nanostructures for boosting photoelectrochemical water oxidation

Photoelectrochemical water oxidation driven by photocatalysts is one of the most effective ways for converting solar energy into fuels and chemicals. However, to date, the solar conversion efficiency using the established photocatalysts is still low. Herein, we report a new strategy for making a class of three-dimensional (3D) BiVO4/Fe-based (Ni1−xFex and Co1−xFex) layered double hydroxide (LDH) interface heterostructures for boosting the photoelectrocatalytic water oxidation performance. Compared with the BiVO4, the BiVO4/Ni0.5Fe0.5–LDH interface photoanode exhibits about 4-fold photocurrent enhancement at 1.23 V vs. the reversible hydrogen electrode and remarkable negative shift (320 mV) of the onset potential for the oxygen evolution reaction (OER). Theoretical calculations reveal that the enhanced photocatalysis for the OER is mainly attributed to the optimal light absorption and the acceleration of electron–hole separation enabled by the strong electronic coupling at the BiVO4/NiFe–LDH interface. The present work first highlights the importance of tuning the light absorption and the separation of carriers using interface engineering in enhancing the solar photocatalytic performance.

Chestnut-Like TiO2@α-Fe2O3 Core–Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO2@α-Fe2O3 core-shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO2 and α-Fe2O3 are observed and supposed to provide synergistic effect. The TiO2 microsphere framework significantly improves the mechanical stability, while the α-Fe2O3 provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g-1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g-1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe0 phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe2O3-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs.