Kan Liu,Wenli Zhang,Man Tang,Zhipeng Wang,Yanqin Yang,Songzhan Li,Hao Long
The performance of supercapacitors not only depends on the structure of the electrode but also relates to the composition of electrode material. The binder-free integrated electrodes were obtained from NiCo 2 O 4 nanosheets grown on nitrogen-doped carbon and Co aggregation (NC/Co) nanowires through a hydrothermal process and subsequent annealing. The NiCo 2 O 4 @NC/Co composite presents the stereostructure with NC/Co nanowire supports and intertwined NiCo 2 O 4 ultrathin nanosheets. The NiCo 2 O 4 @NC/Co electrode demonstrates excellent electrochemical capacitive performances and cycling stability, where it illustrates a splendid specific capacitance of 1112 F g −1 at 1 A g -1 and maintains around 90.7 % of the maximum capacitance after 5000 cycles. Besides, the functionalized asymmetric supercapacitor (ASC) was fabricated based on NiCo 2 O 4 @NC/Co and NC with KOH-PVA solid electrolyte. The NiCo 2 O 4 @NC/Co // NC ASC possesses a stabilized operating potential range of 1.6 V and retains around 81.1 % retention after 5000 cycles. This makes a great potential for Ni-Co multiple compound electrodes for high-performance energy storage systems.
Exploring advanced electrocatalysts for the hydrazine oxidation reaction (HzOR) could expedite the applications of direct hydrazine fuel cells (DHzFCs) for zero-carbon economics. Herein, we report a remarkable HzOR electrocatalyst based on low-coordinated Co arrays supported on Cu foam (p-Co/CF). The low-coordinated Co arrays were synthesized by the reduction of the Co(OH)F precursor with H2 plasma to induce numerous few-atom vacancies, producing low-coordinated surface Co atoms as catalytic active sites. The as-prepared p-Co/CF electrode exhibits a low onset potential of −0.15 V (vs. RHE) and a small Tafel slope of 8.83 mV dec−1 in 0.05 M N2H4/1 M KOH electrolyte, which are superior to those of most reported electrocatalysts toward the HzOR. Density functional theory (DFT) calculations have been employed to elucidate the HzOR process on metallic Co catalysts, suggesting that the improved catalytic activity would be attributed to the weakened adsorption of N2H3* on low-coordinated Co sites. Benefited by the superior catalytic activity of p-Co/CF, a prototype DHzFC has been demonstrated to deliver a high open circuit voltage of 1.1 V and a maximal power density of 186 mW cm−2 at ambient temperatures. This work provides guidance for designing high-performance non-noble metal electrocatalysts toward viable direct hydrazine fuel cells.
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