Mingjun Pang

Mesoporous NiCo2O4 nanospheres with a high specific surface area as electrode materials for high-performance supercapacitors

Ternary nickel cobaltite (NiCo2O4) has attracted more and more attention as a promising electrode material for high performance supercapacitors (SCs) due to its high theoretical capacity, unique crystal structure and excellent electronic conductivity. In this study, a template-free chemical co-precipitation method as a general strategy has been easily developed to fabricate mesoporous NiCo2O4 nanospheres with a high specific surface area of 216 m2 g−1, which can be further self-assembled into 3D frameworks. The key to the formation of mesoporous NiCo2O4 nanospheres with a desired pore-size distribution centered at ∼2.4 nm is a unique preparation method assisted with sodium bicarbonate as a complex agent. When tested as electrode materials for SCs, the NiCo2O4 electrodes delivered excellent electrochemical performances with high specific capacitance (842 F g−1 at a current density of 2 A g−1), superior cycling stability with no capacity decrease after 5000 cycles (103% initial capacity retention), and great rate performance at a 10-time current density increase (79.9% specific capacitance retention). Furthermore, as expected in a NiCo2O4-based asymmetric supercapacitor device, a superior energy density as high as 29.8 W h kg−1 at a power density of 159.4 W kg−1 could be achieved. These results highlight a general, eco-friendly, template-free strategy for the scale-up fabrication of a promising mesoporous NiCo2O4 electrode material for high-performance SC applications.

Experimental and theoretical studies of nonlinear dependence of the internal resistance and electrode thickness for high performance supercapacitor

In this study, the internal resistance with the increasing of electrode thickness in a typical nanoporous carbon-based supercapacitor and their corresponding electrochemical performances were designed and investigated in detail. As for the carbon-based double electrode layer electrochemical system, electrochemical experiments greatly support the fact of nonlinear dependence and indicate that the curve of internal resistance vs. electrode thickness can have a minimum value when the thickness increasing from 10 to 140 μm. To explain the underlying mechanisms responsible for the nonlinear dependence, a theoretical model based on a porous electrode/electrolyte electrochemical system was proposed. As expected, the results of calculations carried out in the framework of the proposed model can be very good agreement with the experimental data. According to the calculation, the optimized electrode thickness is 53.1 μm corresponding to the minimum value of SC internal resistance. Obviously, the current research results might greatly support the nonlinear conclusion instead of linear relationship between the internal resistance and the electrode thickness and may shed some light on the fabrication and exploration of supercapacitors with high power density.

Layered perovskite GdBa0·5Sr0·5CoCuO5+δ as cathode material for intermediate-temperature solid oxide fuel cells

Abstract Layered GdBa0·5Sr0·5CoCuO5+δ(GBSCCu) perovskite oxide is synthesised using an ethylenediaminetetraacetic acid (EDTA)–citrate combined method. Electrochemical performances are investigated as a novel cathode material for intermediate-temperature solid oxide fuel cells. The cathode GBSCCu chemical compatibility with Gd0·1Ce0·9O1·95 (GDC) electrolyte is examined below 950°C. The electrical conductivity value of the GBSCCu sample reaches a maximum of 147 Scm−1 at 750°C in air. The thermal expansion coefficient of the GBSCCu sample is 16·9×10−6 K−1 between 30°C and 900°C. The polarisation resistance of GBSCCu on the GDC electrolyte is 0·102 Ω cm2 at 800°C. The maximum power density of a single cell with a GBSCCu–GDC composite cathode on the 300 μm thick GDC electrolyte reaches 402 mW cm−2. These results indicate that GBSCCu is a potential cathode material for GDC electrolyte intermediate-temperaturte solid oxide fuel cells(IT-SOFCs).

Designed fabrication of three-dimensional δ-MnO2-cladded CuCo2O4 composites as an outstanding supercapacitor electrode material

Three-dimensional δ-MnO2-cladded CuCo2O4 composites are designed and grown in situ on Ni foam via a simple hydrothermal reaction and subsequent one-pot chelation-mediated aqueous processes. The electrode architecture can take good advantage of the synergistic effects contributed by both the porous CuCo2O4 nanoflake core and the δ-MnO2 shell layer. When δ-MnO2-cladded CuCo2O4 composites, along with porous Ni foam, are employed as a binder-free electrode for supercapacitors, the hybrid electrode shows higher specific capacitances and a better rate capability than the single CuCo2O4 nanoflake electrode. A maximum specific capacitance of 1180 F g−1 is achieved at a current density of 1 A g−1 and 81.7% of this value remains at a high current density of 10 A g−1. Moreover, the δ-MnO2-cladded CuCo2O4 electrode also delivers an excellent cycling stability, maintaining 93.2% at 15 A g−1 after 5000 galvanostatic charge–discharge cycles. Moreover, according to electrochemical impedance spectroscopy (EIS) analysis, the δ-MnO2-cladded CuCo2O4 electrode possesses a lower equivalent series resistance of 0.78 Ω and a charge transfer resistance of 0.09 Ω. In view of its cost-effective fabrication process and excellent energy storage properties, this unique integrated nanoarchitecture would hold great promise in the field of electrochemical energy storage.