RESUMO
Integrating the battery behavior and supercapacitor behavior in a single electrode to obtain better electrochemical performance has been widely researched. However, there is still a lack of research studies on an integrated battery-capacitor supercapacitor electrode (BatCap electrode). In this work, an integrated BatCap electrode porous carbon-coated Mn-Ni-layered double oxide (Mn-Ni LDO-C) was fabricated successfully using controllable heat treatment of polypyrrole-precoated Mn-Ni-layered double hydroxide (Mn-Ni LDH@PPy). This Mn-Ni LDO-C electrode was grown on Ni foam directly and possessed a hierarchical structure that consisted of a pyridinic N (N-6)-doped porous carbon shell and a Mn-Ni LDO core within abundant oxygen vacancies. Benefiting from the synergistic effect of N-6-doped porous carbon and increased oxygen vacancies, Mn-Ni LDO-C exhibited excellent electrochemical performance. The capacity of Mn-Ni LDO-C reached 2.36 C cm-2 (1478.1 C g-1) at 1 mA cm-2 and remained at 92.1% of the initial capacity after 5000 cycles at a current density of 20 mA cm-2. The aqueous battery-supercapacitor hybrid device Mn-Ni LDO-C//active carbon (Mn-Ni LDO-C//AC) also presented superior cycle stability: it retained 85.3% of the original capacity after 5000 cycles at 2 A g-1. Meanwhile, Mn-Ni LDO-C//AC could work normally under a wider potential window (2.0 V), so that the device held the highest energy density of 78.2 Wh kg-1 at a power density of 499.7 W kg-1 and retained 39.1 Wh kg-1 at the highest power density of 31.3 kW kg-1. Two Mn-Ni LDO-C//AC devices connected in series could light a light-emitting diode (LED) bulb easily and keep the LED brightly illuminated for more than 10 min. In general, this work synthesized an integrated BatCap electrode Mn-Ni LDO-C; the integrated electrode exhibited high electrochemical performance, thus has a promising application prospect in the field of energy storage.
RESUMO
Self-assembly of nanoscale building units into mesoscopically ordered superstructures opens the possibility for tailored applications. Nonetheless, the realization of precise controllability related specifically to the atomic scale has been challenging. Here, first, we explore the key role of a molecular surfactant in adjusting the growth kinetics of two-dimensional (2D) layered SnS2. Experimentally, we show that high pressure both enhances the adsorption energy of the surfactant sodium dodecylbenzene sulfonate (SDBS) on the SnS2(001) surface at the initial nucleation stage and induces the subsequent oriented attachment (OA) growth of 2D crystallites with monolayer thickness, leading to the formation of a monolayer amorphous carbon-bridged nanosheet mesocrystal. It is notable that such a nanosheet-coalesced mesocrystal is metastable with a flowerlike morphology and can be turned into a single crystal via crystallographic fusion. Subsequently, direct encapsulation of the mesocrystal via FeCl3-induced pyrrole monomer self-polymerization generates conformal polypyrrole (PPy) coating, and carbonization of the resulting nanocomposites generates Fe-N-S-co-doped carbons that are embedded with well-dispersed SnS/FeCl3 quantum sheets; this process skillfully integrated structural phase transformation, pyrolysis graphitization, and self-doping. Interestingly, such an integrated design not only guarantees the flowerlike morphology of the final nanohybrids but also, more importantly, allows the thickness of petalous carbon and the size of the nanoconfined particles to be controlled. Benefiting from the unique structural features, the resultant nanohybrids exhibited the brilliant electrochemical performance while simultaneously acting as a reliable platform for exploring the structure-performance correlation of a Li-ion battery (LIB).
RESUMO
Porous Co3O4/SnO2 quantum dot (QD) heterojunctions with a strong synergistic effect are successfully synthesized in this paper. Owing to the strong synergistic effect between Co3O4 and SnO2QDs, Co3O4/SnO2QD heterostructures possess more Co2+ ions for a faster Co2+/Co0 redox reaction in the process of sensing of reducing gases and electrochemical reactions, and more oxygen vacancies for more active sites and reduced charge transfer resistance on the surface. These advantages are demonstrated to significantly enhance the gas sensitivity to xylene and greatly improve the catalysis for the oxygen evolution reaction (OER). As a catalyst for the OER, Co3O4/SnO2QD (1 : 1) heterostructures exhibit the highest current density, lowest onset potential, largest active surface area and remarkable durability in alkaline electrolytes. The sensitivity of Co3O4/SnO2QD (1 : 1) heterostructures to 100 ppm xylene is almost 10 times higher than that of pure Co3O4 nanosheets and 3 times higher than that of SnO2QDs. In addition, Co3O4/SnO2QD (1 : 1) heterostructure sensors exhibit excellent gas selectivity, long-term stability and markedly high response to low concentrations of xylene at low operating temperatures.