RESUMO
The use of nanoporous carbon for energy storage has seen a significant rise due to its exciting properties such as high surface area, hierarchical porosity and exceptional electrochemical properties. These unique advantages of exceptional surface and electrochemical properties of these porous carbon nanostructures can be coupled with the individual doping of heteroatoms for achieving high energy storage capacity and stability. Herein, we integrated the synthesis of carbon nitride (CN) and borocarbonitride (BCN) with solid state activation for introducing multiple heteroatoms (B, N, O and S) onto the nanoporous carbon frameworks. The produced materials exhibit abundance of micro and mesoporosity, a high surface area of 2909 m2 g-1, and a pore volume of 0.87 cm3 g-1. Also, it offers an exceptional capacitance of 233.5 F g-1 at 0.5 A g-1 with 3M KOH as electrolyte. Further, the optimised material was explored as cathode in zinc ion capacitor which delivers an energy and power density of 50.4 Wh kg-1 and 400 W kg-1 respectively in addition to high cyclability. Studies on the formation of the intermediate phases during charging/discharging of the cell through ex situ characterization result in some useful insights into the stability of ZIC.
RESUMO
Iron (Fe) sites play a critical role in boosting the catalytic activity of transition metal layered double hydroxide (LDH) electrocatalysts for the oxygen evolution reaction (OER), but the contribution of the Fe content to the catalysis of Fe-doped LDHs is still not well understood. Herein, a series of two-dimensional (2D) Fe-doped MFe-LDHs (M = Co, Ni, Cu, and Mn) was synthesized via a general molecular self-assembly method to track the role of Fe in their electrocatalytic OER activities. Besides the revelation of the intrinsic activity trend of NiFe > CoFe > MnFe > CuFe, volcano-shaped relationships among the catalytic activity descriptors, i.e., overpotential, Tafel slope, and turnover frequency (TOF), and the Fe-content in MFe-LDHs, were identified. Specifically, a â¼20% Fe content resulted in the highest OER performance for the LDH, while excess Fe compromised its activity. A similar volcano relationship was determined between the intermediate adsorption and Fe content via operando impedance spectroscopy (EIS) measurements, and it was shown that the intermediate adsorption capacitance (CPEad) can be a new activity descriptor for electrocatalysts. In this work, we not only performed a systematic study on the role of Fe in 2D Fe-doped LDHs but also offer some new insights into the activity descriptors for electrocatalysts.
RESUMO
2D tin diselenide and its derived 2D heterostructures have delivered promising potentials in various applications ranging from electronics to energy storage devices. The major challenges associated with large-scale fabrication of SnSe2 crystals, however, have hindered its engineering applications. Herein, a tin-extraction synthetic method is proposed for producing large-size SnSe2 bulk crystals. In a typical synthesis, a Sn-containing MAX phase (V2 SnC) and a Se source are heat-treated under a reducing atmosphere, by which Sn is extracted from the V2 SnC phase as a rectified Sn source to form SnSe2 crystals in the cold zone. After the following liquid exfoliation, the obtained 2D SnSe2 nanosheets have a lateral size of a few centimeters and an atomic thickness. Furthermore, by coupling with 2D graphene to form 2D/2D SnSe2 /graphene heterostructured electrodes, as validated by theoretical calculation and experimental studies, the superior Li-/Na-ion storage performance with ultralow surface/interface ion transport barriers are achieved for rechargeable Li-/Na-ion batteries. This innovative synthetic strategy opens a new avenue for the large-scale synthesis of selenides and offers more options into the practical application of emerging 2D/2D heterostructure for electrochemical energy storage.
