The insufficient energy density of electrode materials has hindered the popularity and application of supercapacitors. The construction of hybrid supercapacitors offers an ideal solution by combining transition-metal hydroxides with high specific capacity and biochar with excellent conductivity. In this study, an electrode material (β-Ni(OH) 2 @AC 22 composite) was created by in situ growth flower-like β-Ni(OH) 2 nanosheets on biochar (AC) that extracted from the seed coat of Xanthoceras sorbifolium Bunge . This β-Ni(OH) 2 @AC 22 composite exhibited a remarkable specific capacity of 617.5C g −1 (1 A g −1 ), nearly four times that of AC, and remarkable cycling stability (85.6 % retention after 5000 cycles). Using this composite as the positive electrode and biochar as the negative electrode, the assembled battery-type hybrid supercapacitors (HSCs) achieved a specific capacity of 92.75C g −1 (1 A g −1 ). The HSCs demonstrated a specific energy of 57.9 Wh kg −1 , a specific power of 750.9 W kg −1 , and even maintained 42.2 Wh kg −1 at a maximum specific power of 6049.4 W kg −1 . The device maintained a specific capacity of about 78.7 % after 7000 charging/discharging cycles, demonstrating good practical performance. These results highlight the practical application potential of the prepared composites in supercapacitors, with biochar serving as a basis for enhancing the electrochemical performance of supercapacitors.
Yafeng Wang,Xian Luo,Wenjie Lu,Bin Huang,Yanqing Yang
In this study, β-Ni(OH)2 with a unique flower-like morphology was synthesized through a hydrothermal method. The doping of Rh in β-Ni(OH)2 was achieved by a reduction method. The as-synthesized catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy for the crystal structure, morphology, composition, and chemical state analysis. The electrochemical tests revealed that the doping of Rh can significantly increase the electrocatalytic performance of β-Ni(OH)2 in 1.0 M KOH solution. The methanol oxidation peak current density of Rh-doped β-Ni(OH)2 reached 95 mA cm–2 with a Tafel slope of 40 mV dec–1. The reason for these improvements is that Rh can suppress the phase transformation of NiOOH from β to α. Meanwhile, the electronic structure change of nickel in β-Ni(OH)2 and the defect ratio increase caused by Rh doping are beneficial to methanol oxidation reaction (MOR) catalytic activity. Furthermore, the synergistic effect between Rh and Ni(OH)2 improved the surface activity of β-NiOOH. The doping of Rh in β-Ni(OH)2 is initiative in this work, which provides a new strategy to design highly efficient and cost-effective MOR electrocatalysts for alkaline DMFCs.
Hexagonal β-Ni(OH) 2 nanosheets with thickness of ∼12 nm were synthesized by a hydrothermal method at 150 °C using nickel chloride as nickel source and morpholine as alkaline. Electrodes for application in pseudocapacitor were assembled through a traditional technique: pressing a mixture of β-Ni(OH) 2 nanosheets and acetylene black onto nickel foam. Due to the hexagonal shape of rigid β-Ni(OH) 2 nanosheet and the mediation of surface-modified glycerol during electrochemical charge–discharge cycles, a nanostructure of electrode material with facile interior pathway for the transfer of electrolyte was formed. As a result, the as-formed electrodes presented high specific capacitance of 1,917 F g −1 at current density of 1.6 A g −1 in 3 mol L −1 KOH solution. At high charge and discharge current density of 31.3 A g −1 , the electrodes still remained a high specific capacitance of 1,289 F g −1 . The interesting results obtained from this investigation may provide a new insight for the synthesis of electrode materials with high electrochemical performance.
Weijun Liang,Senlin Wang,Yanxiu Zhang,Jian Gu,Kaida Zhu,Jing Zhong,Xinru Wang
β-Ni(OH) 2 with good crystallinity is grown on the surface of the flower-like α-Ni(OH) 2 to form a 3D α@β-Ni(OH) 2 material by a two-step hydrothermal method . The synthesized β-Ni(OH) 2 is nanometer size and strong alkali stability, while the α-Ni(OH) 2 has a large specific surface, high specific capacity and good electrical conductivity , so there are multiple synergistic effects between the β-Ni(OH) 2 coating and the α-Ni(OH) 2 core. Coupled with a 3D flower-like structure, the obtained α@β-Ni(OH) 2 electrode shows a high capacity of 431 mAh g −1 at a current density of 1 A g −1 . Furthermore, we use the α@β-Ni(OH) 2 electrode and the activated carbon (AC) electrode to assemble an asymmetric supercapacitor (ASC) device. This ASC shows the excellent energy density of 53 Wh kg −1 at a power density of 875 W kg −1 and capacity retention rate of 78% after 5000 cycles. Finally, metal hydride (MH) is used to replace the AC negative electrode, and a cell with a high energy density of 100.17 Wh kg −1 at a power density of 424.75 W kg −1 is obtained. The results show that α@β-Ni(OH) 2 electrode has better electrochemical performance than commercial electrodes and has application prospects in energy storage.
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