Binder-free electrode materials offer
high active material mass
loading and usage rate, excellent connectivity between active materials
and current collectors, and efficient electron and ion transport inside
the electrodes. Herein, we demonstrate a binder-free in situ synthesis of microstructures of CuCo2O4/CuO
composites grown on the Ni foam (CCO/NF) by wet chemical methods.
Two different morphologies of microspheres (CCO/NF-IPA) and cross-linked
microsheets (CCO/NF-DIW) result from solvents of isopropyl alcohol
and deionized water, respectively. Using X-ray techniques, the nonstoichiometry
of Cu, Co, and O in composites is measured. In the backdrop of the
supercapacitor application, even though both electrodes have consistent
electrochemical performance, the Co-excess of the CCO/NF-IPA composite
has a higher specific capacity (369.6 C g–1 at 1
A g–1) and an extended cyclic performance (98% retention
after 5000 cycles) compared to the other. The all-solid-state CCO/NF-IPA//activated
carbon (AC) asymmetric supercapacitor (ASC) device with a full operating
potential window of 0–1.5 V has exhibited a high specific capacity
of 162.6 C g–1 at 1 A g–1. The
ASC device retains its initial capacity of 97% over 5000 cycles and
renders a notable energy density of 43.7 Wh kg–1 at 752.4 W kg–1 power density.
Binder-free
2D nanosheet Ni3V2O8/Ni-foam (NVO/Ni)
and Ni3V2O8 (NVO)
nanoparticles were synthesized using a facile hydrothermal technique
for electrochemical capacitor applications. Both the NVO and NVO/Ni
samples, produced using 1 M LiOH as a reducing agent during the synthesis,
belong to the Ni3V2O8 phase. The
electrochemical traits of these electrodes revealed that the NVO/Ni
electrodes performed significantly better than the 3D NVO electrodes.
The NVO/Ni electrode provided a specific capacitance of 1300 F/g at
a current density of 1 A/g with high cycling stability (80.62% at
4 A/g) after 7000 cycles due to structural advantages. Moreover, the
NVO/Ni//AC asymmetric supercapacitor device delivered a high energy
density of 33.2 Wh/kg at a power density of 2.4 kW/kg and high cycling
stability over 10,000 cycles in the 1.2 V working potential window.
The device also showed a considerably high maximum power density of
7.2 kW/kg at a 13.62 Wh/kg energy density and remained stable even
after 10,000 cycles. The energy–power performance depicted
nearly 200% power gain over a mere 59% energy expense, indicating
its potential applications in practical devices.
Intriguing cationic defects with hollow nano-/microstructures are a critical challenge but a potential strategy to discover electrochemical energy conversion and storage devices with improved electrochemical performances. Herein, we successfully produced a highly porous, and large surface area of self-templated CuCo 2 O 4 hollow spheres (CCOHSs) with cationic defects via a solvothermal route. We hypothesized that the inside-out Ostwald ripening mechanism of the template-free strategy was the framework for forming the CCOHSs. Cationic defects (Cu) within the CCOHSs were identified by employing various analytical techniques, including energy-dispersive X-ray spectroscopy analysis of both scanning and transmission electron microscopy, X-ray photon spectroscopy, and inductively coupled plasma− atomic emission spectroscopy. The resulting CCOHSs had significant properties, such as a high specific surface area of 98.32 m 2 g −1 , rich porosity, and battery-type electrode behavior in supercapacitor applications. Notably, the CCOHSs demonstrated an outstanding specific capacity of 1003.7 C g −1 at 1 A g −1 , with excellent structural integrity and cycle stability. Moreover, the fabricated asymmetric CCOHS//activated carbon device exhibited a high energy density of 65.2 Wh kg −1 at a power density of 777.8 W kg −1 .
Metal co-doping of metal oxide nanostructures is a promising approach for enhancing the electrochemical performance of supercapacitors. Herein, calcium (Ca) and cobalt (Co) co-doped ZnO capsules (Ca-Co@ZnO) were fabricated using a facile and single-step hydrothermal process. The physical, chemical, and morphological properties of the Ca-Co@ZnO were analyzed using a range of characterization techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. Ca-Co@ZnO showed a remarkable supercapacitor performance in a 3 M KOH aqueous electrolyte. The specific capacitance was 1020 F/g at a current density of 0.75 A/g, which was 3.2, 1.7, and 1.6 times higher than the pristine ZnO, Ca-ZnO, and Co-ZnO capsules, respectively. Ca-Co@ZnO showed more than 50% capacity retention at a higher current density and strong cycling stability up to 5000 cycles with only 8% capacity loss. The Ca-Co@ZnO//Ca-Co@ZnO symmetric performance was also investigated. This device showed a specific capacitance of 187 F/g at a current density of 1 A/g and an energy density of 25.9 Wh/kg at a power density of 556.6 W/kg.The superior performance was attributed to the fast electron accessibility, strong ion diffusion, and higher active sites. Overall, the superior electrochemical performance and novel structures could be beneficial for developing metal co-doped metal oxide electrodes for supercapacitor applications.
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