Zhujun Yao

Directional Construction of Vertical Nitrogen‐Doped 1T‐2H MoSe2/Graphene Shell/Core Nanoflake Arrays for Efficient Hydrogen Evolution Reaction

The low utilization of active sites and sluggish reaction kinetics of MoSe2 severely impede its commercial application as electrocatalyst for hydrogen evolution reaction (HER). To address these two issues, the first example of introducing 1T MoSe2 and N dopant into vertical 2H MoSe2 /graphene shell/core nanoflake arrays that remarkably boost their HER activity is herein described. By means of the improved conductivity, rich catalytic active sites and highly accessible surface area as a result of the introduction of 1T MoSe2 and N doping as well as the unique structural features, the N-doped 1T-2H MoSe2 /graphene (N-MoSe2 /VG) shell/core nanoflake arrays show substantially enhanced HER activity. Remarkably, the N-MoSe2 /VG nanoflakes exhibit a relatively low onset potential of 45 mV and overpotential of 98 mV (vs RHE) at 10 mA cm-2 with excellent long-term stability (no decay after 20 000 cycles), outperforming most of the recently reported Mo-based electrocatalysts. The success of improving the electrochemical performance via the introduction of 1T phase and N dopant offers new opportunities in the development of high-performance MoSe2 -based electrodes for other energy-related applications.

Rational construction of a metal core for smart combination with Li4Ti5O12 as integrated arrays with superior high-rate Li-ion storage performance

Directional design/fabrication of advanced high-rate electrodes is critical for the development of high-performance electrochemical energy storage devices with large energy/power densities. In this work, we for the first time realize a bamboo joint-like metal Co core for smart combination with spinel lithium titanate (Li4Ti5O12, LTO) in free-standing core/shell arrays with the help of atomic layer deposition (ALD) plus lithiation. Combined properties such as improved electrical conductivity, enhanced structural stability, and large hollow structures are achieved in the Co/LTO core/shell architecture. Owing to the well-designed structure, the binder-free core/shell arrays of Co/LTO exhibit impressive performance with excellent high-rate performance (146 mA h g−1 at 50C and 143 mA h g−1 at 100C) and remarkable cycle life (142 mA h g−1 after 3000 cycles at 20C with 90% retention). Our newly developed metal-based core/shell arrays have put on a new look on the construction of advanced hetero-structured electrodes.

Encapsulating silicon nanoparticles into mesoporous carbon forming pomegranate-structured microspheres as a high-performance anode for lithium ion batteries

It is a research hotspot to develop advanced anodes with high capacity and good high-rate cyclability for lithium ion batteries. In this work, we develop a facile way to design and fabricate a silicon/carbon spherical composite by encapsulating Si nanoparticles into a mesoporous carbon matrix via a one-step hydrothermal method. Interestingly, the pomegranate structure is realized in the silicon/carbon (Si/C) composite spheres, in which Si nanoparticles of 50–100 nm are just like “pomegranate seeds” embedded into the mesoporous “pomegranate carbon chamber” with pores of 3–4 nm. This unique porous pomegranate structure can not only ensure good electrical conductivity for active Si, but also accommodate the huge volume change during cycles as well as facilitate the fast diffusion of Li ions. When evaluated as an anode for LIBs, the designed pomegranate-structured Si/C composite spheres deliver an excellent cycling stability of 581 mA h g−1 at a current density of 0.2 A g−1 after 100 cycles and achieve a noticeable high-rate capacity of 421 mA h g−1 even at a high current density of 1 A g−1, much better than those of the bare silicon electrode. Our developed facile synthetic strategy shows a new way for large-scale production of high-performance anodes for electrochemical energy storage.

Hybrid vertical graphene/lithium titanate–CNTs arrays for lithium ion storage with extraordinary performance

In the present study, we report a synthetic strategy for the direct fabrication of hybrid vertical graphene/lithium titanate–CNTs arrays via atomic layer deposition in combination with chemical vapor deposition. A novel array architecture was formed where active lithium titanate (Li4Ti5O12, LTO) was uniformly sandwiched by a vertical graphene backbone and an interconnected CNTs shell. The hybrid omnibearing conductive network was identified to be an extremely stable porous structure and demonstrated superior ultra-high rate capability (146 mA h g−1 at 50C and 131 mA h g−1 at 100C) with a capacity of 136 mA h g−1 at 20C after 10 000 cycles when used as an electrode in lithium ion batteries. This special electrode construction strategy is expected to provide a new route for the manufacture of electrochemical energy storage with ultra-high rate capability and ultra-stability.

Pine-Needle-Like Cu-Co Skeleton Composited with Li4Ti5O12 Forming Core-Branch Arrays for High-Rate Lithium Ion Storage

High-performance of lithium-ion batteries (LIBs) rely largely on the scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. In this work, the pine-needle-like Cu-Co skeleton is reported to support highly active Li4 Ti5 O12 (LTO) forming Cu-Co/LTO core-branch arrays via a united hydrothermal-atomic layer deposition (ALD) method. ALD-formed LTO layer is uniformly anchored on the pine-needle-like heterostructured Cu-Co backbone, which consists of branched Co nanowires (diameters in 20 nm) and Cu nanowires (250-300 nm) core. The designed Cu-Co/LTO core-branch arrays show combined advantages of large porosity, high electrical conductivity, and good adhesion. Due to the unique positive features, the Cu-Co/LTO electrodes are demonstrated with enhanced electrochemical performance including excellent high-rate capacity (155 mAh g-1 at 20 C) and noticeable long-term cycles (144 mAh g-1 at 20 C after 3000 cycles). Additionally, the full cell assembled with activated carbon positive electrode and Cu-Co/LTO negative electrode exhibits high power/energy densities (41.6 Wh kg-1 at 7.5 kW kg-1 ). The design protocol combining binder-free characteristics and array configuration opens a new door for construction of advanced electrodes for application in high-rate electrochemical energy storage.

Porous carbon hosts for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are considered to be one of the most promising alternatives to the current lithium-ion batteries (LIBs) to meet the increasing demand for energy storage owing to their high energy density, natural abundance, low cost, and environmental friendliness. Despite great success, LSBs still suffer from several problems, including undermined capacity arising from low utilization of sulfur, unsatisfactory rate performance and poor cycling life owing to the shuttle effect of polysulfides, and poor electrical conductivity of sulfur. Under such circumstances, the design/fabrication of porous carbon-sulfur composite cathodes is regarded as an effective solution to overcome the above problems. In this review, different synthetic methods of porous carbon hosts and their corresponding integration into carbon-sulfur cathodes are summarized. The pore formation mechanism of porous carbon hosts is also addressed. The pore size effect on electrochemical performance is highlighted and compared. The enhanced mechanism of the porous carbon host on the sulfur cathode is systematically reviewed and revealed. Finally, the combination of porous carbon hosts and high-profile solid-state electrolytes is demonstrated, and the challenges to realize large-scale commercial application of porous carbon-sulfur cathodes is discussed and future trends are proposed.