Construction of Cu-Doped Ni–Co-Based Electrodes for High-Performance Supercapacitor Applications

Abstract

Element doping is an effective method to improve the specific capacity and ion transfer rate of binary metal compounds. In this study, Cu-doped Ni–Co-based electrode materials were synthesized by a hydrothermal process and subsequent annealing treatment. The experimental results show that the nanocone-like Cu-doped Ni–Co carbonate hydroxides (Ni–Co–Cu CH) with high mass loading and the Cu-doped Ni–Co oxide (Ni–Co–Cu oxide) electrode with abundant oxygen defects achieve high area specific capacities of 6.31 F/cm2 and 6.54 F/cm2 at 3 A/g, respectively, which are about 2.5 times larger than the area specific capacity of the undoped nanorod-like Ni–Co precursor electrode (2.51 F/cm2 at 3 A/g). The quasi-solid-state asymmetric supercapacitors (ASCs) Ni–Co–Cu CH//AC and Ni–Co–Cu oxide//AC also achieved high energy densities of 36.9 Wh/kg and 42.1 Wh/kg at power densities of 374.2 W/kg and 374.9 W/kg, respectively, which can light up a red light emitting didode for ∼8 min and ∼11 min, respectively. Cu doping not only changes the morphology and defect state of a Ni–Co bimetallic compound electrode but also improves its electricity conduction and electrochemical performance. This strategy has important reference significance for the preparation of excellent performance supercapacitor energy storage materials in the future.

Electrostructural Compatibility of Battery-Type Diffuse-Porous Co9S8–NiCo2S4/Defective Reduced Graphene Oxide and Flaky FeS/Nitrogen-Doped Defective Reduced Graphene Oxide for Ultra-High-Performance All-Solid-State Hybrid Pseudocapacitors

“…The average crystallite sizes of Co 9 S 8 and NiCo 2 S 4 in the composite are estimated to be ∼15 nm, which was evaluated using the essential parameters of the highest-intensity diffraction peaks of Co 9 S 8 and NiCo 2 S 4 in the Scherrer equation. The small crystallite size of Co 9 S 8 –NiCo 2 S 4 is ascribed to the dimethyl urea induced kinetically controlled precipitation of NiCo precursor in the presence of NH 4 F in the reaction medium. ,, In the PXRD profile, the peaks corresponding to Co 9 S 8 are of significantly lower intensity than those corresponding to NiCo 2 S 4 , which accentuates the lower fraction of Co 9 S 8 than NiCo 2 S 4 in the Co 9 S 8 –NiCo 2 S 4 /D-rGO sample.…”

“…Notably, in sulfides of first row transition metals, multireactive equivalents in the form of variably valent metal ions facilitate compound redox reactions, leading to greater charge storage efficiencies . In this context, Co 9 S 8 –NiCo 2 S 4 is a model electrode material owing to inherent multireactive equivalents, higher electronic conductivity, and enhanced pseudocapacitive charge storage efficiency. , Recent reports show that Co 9 S 8 –NiCo 2 S 4 -based positive electrode materials offer enhanced charge storage efficiency compared to Co/Ni-based monometallic oxide and sulfide materials . Still, the low intrinsic conductivity and constrained bulk diffusivity leading to inferior charge storage efficiency are the major inadequacies of Co 9 S 8 –NiCo 2 S 4 for its integration in high-performance pseudocapacitors .…”

Cation-exchange and oxygen vacancies triggered capacity in hierarchical α-Ni1−xCuxMoO4@CC flexible electrodes for energy-storage applications

“…The greater capacity result is commonly attributed to the synergistic effect of Cu ions in the pristine a-NiMoO 4 @CC electrode. 12,14,46 As is known, the introduction of some metal ions or mixed transition metal oxides with comparable ionic sizes and favorable solubility properties is expected to enhance the pristine metal oxide ionic conductivity, boosting the capacitive performance through the synergistic effect. 12,14 Meanwhile, during the cation-exchange process between Ni and Cu metals, the dopants could disturb or reduce the adjacent metal atom vacancies to balance the local charge.…”

“…12,14,46 As is known, the introduction of some metal ions or mixed transition metal oxides with comparable ionic sizes and favorable solubility properties is expected to enhance the pristine metal oxide ionic conductivity, boosting the capacitive performance through the synergistic effect. 12,14 Meanwhile, during the cation-exchange process between Ni and Cu metals, the dopants could disturb or reduce the adjacent metal atom vacancies to balance the local charge. Such disturbance in valency states leads to the development of OVs (a-Ni 0.95 Cu 0.05 MoO 4−y @CC), which markedly enhances the electrical conductivity of the electrode through the increase of the number of active sites.…”

“…Recently, cation-doping in single and bimetallic oxide-based compositions has attracted much attention and is found to be a good technique to increase electrical conductivity, charge transfer ability, and capacitance. [12][13][14] It has been well proved that introducing a foreign transition metal ion into a selective host matrix can overcome the existing drawbacks in electronic states and trigger electrode reactivity by improving the iondiffusion kinetics, and further it also opens an avenue to develop new approaches. 12,15,16 Among the various metal ions, Cu possesses good electrical conductivity, and it is available at a cheap cost and is recommended for doping.…”