Yuanyuan Guo

Co9S8/MoS2 Yolk–Shell Spheres for Advanced Li/Na Storage

Uniform sized Co9 S8 /MoS2 yolk-shell spheres with an average diameter of about 500 nm have been synthesized by a facile route. When evaluated as anodes for lithium-ion and sodium-ion batteries, these Co9 S8 /MoS2 yolk-shell spheres show high specific capacities, excellent rate capabilities, and good cycling stability.

Controllable Preparation of Square Nickel Chalcogenide (NiS and NiSe2) Nanoplates for Superior Li/Na Ion Storage Properties

A facile and bottom-up approach has been presented to prepare 2D Ni-MOFs based on cyanide-bridged hybrid coordination polymers. After thermally induced sulfurization and selenization processes, Ni-MOFs were successfully converted into NiS and NiSe2 nanoplates with carbon coating due to the decomposition of its organic parts. When evaluated as anodes of Li-ion batteries (LIBs) and Na-ion batteries (NIBs), NiS and NiSe2 nanoplates show high specific capacities, excellent rate capabilities, and stable cycling stability. The NiS plates show good Li storage properties, while NiSe2 plates show good Na storage properties as anode materials. The study of the diffusivity of Li(+) in NiS and Na(+) in NiSe2 shows consistent results with their Li/Na storage properties. The 2D MOFs-derived NiS and NiSe2 nanoplates reported in this work explore a new approach for the large-scale synthesis of 2D metal sulfides or selenides with potential applications for advanced energy storage.

Hexagonal-Phase Cobalt Monophosphosulfide for Highly Efficient Overall Water Splitting

The rational design and synthesis of nonprecious, efficient, and stable electrocatalysts to replace precious noble metals are crucial to the future of hydrogen economy. Herein, a partial sulfurization/phosphorization strategy is proposed to synthesize a nonstoichiometric pyrrhotite-type cobalt monophosphosulfide material (Co0.9S0.58P0.42) with a hexagonal close-packed phase for electrocatalytic water splitting. By regulating the degree of sulfurization, the P/S atomic ratio in the cobalt monophosphosulfide can be tuned to activate the Co3+/Co2+ couples. The synergy between the nonstoichiometric nature and the tunable P/S ratio results in the strengthened Co3+/Co2+ couples and tunable electronic structure and thus efficiently promotes the oxygen/hydrogen evolution reaction (OER/HER) processes toward overall water splitting. Especially for OER, the Co0.9S0.58P0.42 material, featured with a uniform yolk-shell spherical morphology, shows a low overpotential of 266 mV at 10 mA cm-2 (η10) with a low Tafel slope of 48 mV dec-1 as well as high stability, which is comparable to that of the reported promising OER electrocatalysts. Coupled with the high HER activity of Co0.9S0.58P0.42, the overall water splitting is demonstrated with a low η10 at 1.59 V and good stability. This study shows that phase engineering and composition control can be the elegant strategy to realize the Co3+/Co2+ couple activation and electronic structure tuning to promote the electrocatalytic process. The proposed strategy and approaches allow the rational design and synthesis of transition metal monophosphosulfides toward advanced electrochemical applications.

Sn Nanoparticles Encapsulated in 3D Nanoporous Carbon Derived from a Metal–Organic Framework for Anode Material in Lithium-Ion Batteries

Three-dimensional nanoporous carbon frameworks encapsulated Sn nanoparticles (Sn@3D-NPC) are developed by a facile method as an improved lithium ion battery anode. The Sn@3D-NPC delivers a reversible capacity of 740 mAh g-1 after 200 cycles at a current density of 200 mA g-1, corresponding to a capacity retention of 85% (against the second capacity) and high rate capability (300 mAh g-1 at 5 A g-1). Compared to the Sn nanoparticles (SnNPs), such improvements are attributed to the 3D porous and conductive framework. The whole structure can provide not only the high electrical conductivity that facilities the electron transfer but also the elasticity that will suppress the volume expansion and aggregation of SnNPs during the charge and discharge process. This work opens a new application of metal-organic frameworks in energy storage.

From fibrous elastin proteins to one-dimensional transition metal phosphides and their applications

One-dimensional (1D) carbon-supported nanostructured CoP and FeP4 were prepared using fibrous elastin proteins that served as starting materials through an oil-phase method and the as-synthesized products were investigated for their lithium and sodium storage properties. The 1D CoP and FeP4 are composed of nanosized particles decorated on carbon supports. The 1D CoP and FeP4 nanostructures are ∼2 μm in length and 20–50 nm in diameter. The particles on the exterior of the 1D structure are 5–10 nm in diameter. To investigate the as-synthesized 1D TMPs in energy storage applications, the as-synthesized 1D CoP nanostructures are applied as an anode material in half-cells for LIBs and SIBs. For lithium storage performances, the anode delivers a specific capacity as high as ∼740 mAh g−1 at 0.2C and shows good rate performance and capacity retention as well as high rate capability (e.g. a stable specific capacity of ∼365 mAh g−1 for 120 cycles at 3.0C). In SIBs, at 0.2 and 5.0C, the specific capacities of 491.60 and 314.84 mAh g−1 are delivered, respectively. When tested at 1.0, 2.0, and 5.0C, the specific capacities are stable at ∼400, 360, and 300 mAh g−1 over 250, 250, and 1000 cycles, respectively.

Tunable Co3O4 hollow structures (from yolk–shell to multi-shell) and their Li storage properties

In this work, we report a facile approach to synthesize uniform Co3O4 hollow spheres with tunable shell numbers via controllably annealing cobalt(II) complex precursors at different heating rates. When evaluated as anodes for LIBs, the multi-shelled Co3O4 spheres exhibit high specific capacity, good rate capabilities and excellent cycling stability (1058 mA h g−1 over 100 cycles at 1 A g−1).

Cobalt silicate hierarchical hollow spheres for lithium-ion batteries

In this paper, the synthesis of cobalt silicate novel hierarchical hollow spheres via a facile hydrothermal method is presented. With a unique hollow structure, the Co2SiO4 provides a large surface area, which can shorten the lithium ions diffusion length and effectively accommodate the volumetic variation during the lithiation/de-lithiation process. Serving as an anode material in lithium-ion battery application, the Co2SiO4 electrode demonstrates a high reversible specific capacity (first-cycle charge capacity of 948.6 mAh g(-1) at 100 mA g(-1)), a cycling durability (specific capacity of 791.4 mAh g(-1) after 100 cycles at 100 mA g(-1)), and a good rate capability (specific capacity of 349.4 mAh g(-1) at 10 A g(-1)). The results indicate that the cobalt silicate hierarchical hollow sphere holds the potential applications in energy storage electrodes.

Using elastin protein to develop highly efficient air cathodes for lithium-O2 batteries

Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O2 batteries. It has been discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12,441 mAh g(-1) at a current density of 100 mA g(-1). When they were cycled at a limited capacity of 800 mAh g(-1) at current densities of 200 or 400 mA g(-1), these cathodes showed stable charge voltages of ∼3.65 or 3.90 V, corresponding to energy efficiencies of ∼71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O2 battery cathodes.