Huarong Peng

Branched ultra-fine nickel oxide/manganese dioxide core–shell nanosheet arrays for electrochemical capacitors

We demonstrate the fabrication of ultra-fine hierarchical NiO@MnO2 core–shell nanosheet arrays on carbon fiber paper via a facile and two-step hydrothermal method as the electrode for supercapacitors. Owing to the unique hierarchical core–shell heterostructured nanosheet array configuration and synergetic contribution from the NiO core and MnO2 shell, the as-prepared hybrid nanosheet arrays exhibited a high specific capacitance of 494.8 F g−1 and good rate capability, which are better than those of the obtained individual component of the NiO nanosheets. More importantly, the asymmetric supercapacitor, composed of NiO@MnO2 core–shell nanosheet arrays as the positive electrode and activated carbon as the negative electrode delivers a specific capacitance of 86.3 F g−1 and reaches up to an energy density of 30.6 W h kg−1 and power density of 400 W kg−1. The improved performance of the NiO@MnO2 core–shell nanosheet arrays demonstrates that rational design of electrode structure is an effective way to fabricate a high-performance electrode for supercapacitors.

Investigating the effect of sulfur and selenium on the electrochemical properties of nickel–cobalt oxides: enhanced charge capacity and composition–property relationships

Nickel and cobalt oxides, sulfides, selenides are widely studied as active materials in the application of energy storage and enhanced capacity are obtained as the atomic number of the non-metal element increase. In this study, Nickel and cobalt oxides (NiCoO2), sulfides and selenides are prepared via ion-exchange method and they are investigated as electrode materials for aqueous battery applications. From the perspective of electrochemistry, a detailed study of the fundamental relationships between composition, properties, and electrochemical performance are carried out. The results reveal that the enhanced charge capacity is associated with a more active property of nickel and cobalt as well as higher diffusivity of electrolyte after introducing different anions (S or Se). However, the reversible specific capacity decreases for sulfides and selenides and X-ray photoelectron spectroscopy results after long-term cycling tests indicate that the dissolution of S and Se may be responsible for the severe degrading in charge capacity.

Controlled growth of hierarchical nickel and cobalt hybrid inorganic–organic nanosheet-supported nanowires for energy storage

Hierarchical nickel and cobalt inorganic–organic nanostructures on carbon fiber paper have been fabricated by a one-step hydrothermal approach directed by hexamethylenetetramine (HMT). The morphology and evolution of these single-crystalline inorganic–organic nanosheets–nanowires (IOSW) are investigated. Results show that HMT plays a vital role in the secondary growth of single-crystalline nanowires. Besides, HMT molecules intercalate within the interlayers of inorganic materials, forming single-crystalline organo-LDH (layered double hydroxide) nanosheets and organo-carbonate hydroxide nanowires. Furthermore, the electrode is employed for battery-like energy storage applications. The interconnected nanosheet–nanowire structure affords rich open spaces and efficient passways for ion diffusion and electron transport. A specific capacitance of 1308 F g−1 (1.7 F cm−2, at the current density of 4 mA cm−2) and excellent long-term cycling performance (94% retention after 10 000 cycles) are achieved. The high stability of the electrode could be attributed to the interactions between HMT and nickel/cobalt within the interlayer. In addition, a two-electrode device consisting of nickel and cobalt IOSW as the positive electrode and commercial active carbon as the negative electrode is fabricated and reaches a maximum energy density of 32.3 W h kg−1 (8 A g−1).

In Situ Growth of Zeolitic Imidazolate Framework-67-derived Nanoporous Carbon@K0.5Mn2O4 for High-Performance 2.4 V Aqueous Asymmetric Supercapacitors

Aqueous asymmetric supercapacitors (ASCs) with a wide voltage window can effectively improve energy storage capacity of energy storage devices. Zeolitic imidazolate framework-67 (ZIF-67) was used as a precursor to prepare nanoporous carbon (NC), and K0.5 Mn2 O4 nanosheets were subsequently grown on the NC surface through a facile in situ redox process (denoted as NCMO). The electrode potential window of NCMO was extended to 1.2 V in a three-electrode system and the value of the potential window was higher than that of most reported manganese oxides. To assemble the asymmetric supercapacitor with a high voltage range, the as-prepared NCMO and NC (with a potential window of -1.2-0 V) were used as the positive and negative electrode, respectively. A 2.4 V NCMO//NC aqueous ASC was constructed and displayed a large energy density of 60 Wh kg-1 at a power density of 1200 W kg-1 and excellent rate performance (41 Wh kg-1 even at a specific power density of 12.3 kW kg-1 ) as well as good cycling stability (92.6 % capacitance retention over 10 000 cycles at 10 A g-1 ). This work provides new opportunities for the development of high voltage ASCs with a high energy density for further practical application.