Shengjue Deng

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.

Hollow TiO2@Co9S8 Core–Branch Arrays as Bifunctional Electrocatalysts for Efficient Oxygen/Hydrogen Production

Abstract Designing ever more efficient and cost‐effective bifunctional electrocatalysts for oxygen/hydrogen evolution reactions (OER/HER) is greatly vital and challenging. Here, a new type of binder‐free hollow TiO2@Co9S8 core–branch arrays is developed as highly active OER and HER electrocatalysts for stable overall water splitting. Hollow core–branch arrays of TiO2@Co9S8 are readily realized by the rational combination of crosslinked Co9S8 nanoflakes on TiO2 core via a facile and powerful sulfurization strategy. Arising from larger active surface area, richer/shorter transfer channels for ions/electrons, and reinforced structural stability, the as‐obtained TiO2@Co9S8 core–branch arrays show noticeable exceptional electrocatalytic performance, with low overpotentials of 240 and 139 mV at 10 mA cm−2 as well as low Tafel slopes of 55 and 65 mV Dec−1 for OER and HER in alkaline medium, respectively. Impressively, the electrolysis cell based on the TiO2@Co9S8 arrays as both cathode and anode exhibits a remarkably low water splitting voltage of 1.56 V at 10 mA cm−2 and long‐term durability with no decay after 10 d. The versatile fabrication protocol and smart branch‐core design provide a new way to construct other advanced metal sulfides for energy conversion and storage.

Hierarchical porous Ti2Nb10O29 nanospheres as superior anode materials for lithium ion storage

Lithium ions batteries (LIBs) with high power/energy densities largely rely on the innovation of electrode materials. Herein, for the first time, we rationally construct novel titanium niobium oxide (Ti2Nb10O29, TNO) nanospheres with a three-dimensional porous structure consisting of cross-linked nanoparticles by a simple solvothermal method combined with heat treatment. Compared to bulk TNO microrods, the obtained TNO nanospheres show a larger specific surface area and richer/shorter transfer channels for ions/electrons. Owing to these advantages, the TNO nanosphere electrode exhibits noticeable exceptional electrochemical performance with superior high-rate capability (241 mA h g−1 at 10C, and 208 mA h g−1 at 20C) and ultra-long life with a capacity of 215 mA h g−1 after 500 cycles at 10C, much better than the TNO microrod counterparts. Our findings may pave a new way for the design/fabrication of the state-of-the-art electrodes for electrochemical energy storage.

Phase Modulation of (1T‐2H)‐MoSe2/TiC‐C Shell/Core Arrays via Nitrogen Doping for Highly Efficient Hydrogen Evolution Reaction

Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase- and morphology-modulated N-doped MoSe2 /TiC-C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC-C nanorod arrays serve as the backbone for MoSe2 nanosheets to form high-quality MoSe2 /TiC-C shell/core arrays. Impressively, continuous phase modulation of MoSe2 is realized on the MoSe2 /TiC-C arrays. Except for the pure 1T-MoSe2 and 2H-MoSe2 , mixed (1T-2H)-MoSe2 nanosheets are achieved in the N-MoSe2 by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer HSe bond length, and diminished bandgap endow N-MoSe2 /TiC-C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N-MoSe2 /TiC-C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm-2 , and a small Tafel slope of 32 mV dec-1 . Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.

Boosting sodium ion storage by anchoring MoO2 on vertical graphene arrays

Developing high-capacity anodes is of great importance for the advancement of sodium ion batteries. In this work, we report a powerful combined method of plasma enhanced chemical vapor deposition–electrodeposition (PECVD–ED) to construct high-quality vertical graphene/MoO2 (VG/MoO2) core/shell arrays. The conductive MoO2 (n-type semiconductor) shell is uniformly electrodeposited on the VG core to form a binder-free integrated electrode. Compared with carbon fibre cloth-supported MoO2 film (CFC/MoO2), the obtained VG/MoO2 core/shell arrays display a higher surface area, better mechanical stability and improved electrical conductivity. Due to these positive advantages, the VG/MoO2 arrays show enhanced sodium ion storage performance with a reversible capacity of 678 mA h g−1 (vs. 542 mA h g−1 for CFC/MoO2) at the current density of 100 mA g−1, and a stable cycling life with a capacity retention of 81.7% (vs. 62.1% for CFC/MoO2) after 500 cycles. Our results provide a new route for the synthesis of high-capacity anodes for sodium ion batteries.

A synergistic vertical graphene skeleton and S–C shell to construct high-performance TiNb2O7-based core/shell arrays

Bespoke synthesis of wide-temperature high-power electrodes is of great importance for the development of advanced power-type lithium ion batteries (LIBs). Herein, we report a powerful combined solvothermal-electrodeposition (ST-ED) method to construct titanium niobium oxide (TiNb2O7) arrays sandwiched between a highly conductive vertical graphene (VG) skeleton and S–C shell forming a binder-free VG/TiNb2O7@S–C electrode. VG and S–C work cooperatively to establish an omnibearing conductive network on TiNb2O7 through internal and external integration. Positive advantages including large porosity, improved conductivity and enhanced structural stability are obtained in the VG/TiNb2O7@S–C core/shell arrays. Consequently, excellent electrochemical high-power performance at medium–high temperature (25 to 70 °C) is demonstrated for the designed VG/TiNb2O7@S–C electrodes, which show a high capacity from 284 to 354 mA h g−1 at 1C, and 181 to 241 mA h g−1 at 160C as the working temperature increases from 25 to 70 °C. Additionally, a remarkable high-temperature (70 °C) cycling span is proven for the VG/TiNb2O7@S–C electrode with a capacity of 203 mA h g−1 at 40C after 5000 cycles. The synergistic positive effect from the VG and S–C shell is responsible for the enhancement of high-power capability. Our work paves the way for the fabrication of novel high-power electrodes for electrochemical energy storage.

Spore Carbon from Aspergillus Oryzae for Advanced Electrochemical Energy Storage

Development of novel advanced carbon materials is playing a critical role in the innovation of electrochemical energy storage technology. Hierarchical porous spore carbon produced by Aspergillus oryzae is reported, which acts as a biofactory. Interestingly, the spore carbon not only shows a porous maze structure consisting of crosslinked nanofolds, but also is intrinsically N and P dual doped. Impressively, the spore carbon can be further embedded with Ni2 P nanoparticles, which serve as porogen to form a highly porous spore carbon/Ni2 P composite with increased surface area and enhanced electrical conductivity. To explore the potential application in lithium-sulfur batteries (LSBs), the spore carbon/Ni2 P composite is combined with sulfur, forming a composite cathode, which exhibits a high initial capacity of 1347.5 mAh g-1 at 0.1 C, enhanced cycling stability (73.5% after 500 cycles), and better rate performance than the spore carbon/S and artificial hollow carbon sphere/S counterparts. The synergistic effect on suppressing the shuttle effect of intermediate polysulfides is responsible for the excellent LSBs performance with the aid of a physical blocking effect arising from the electrical maze porous structure and the chemical adsorption effect originating from N, P dual doping and polarized compound Ni2 P.