Guragain D, Zequine C, Poudel T, Neupane D, Gupta R K, Mishra S R
Department of Physics and Materials Science, The University of Memphis, Memphis, TN 38152, USA.
Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA.
J Nanosci Nanotechnol. 2020 Apr 1;20(4):2526-2537. doi: 10.1166/jnn.2020.17366.
The widespread use of miniature electronic devices calls for energy-dense storage strategies. The supercapacitor-based energy storage devices with high areal capacitance are desired energy storage alternative. It is still a challenge to fabricate supercapacitor-based energy devices with consistent performance. The porous metal oxides with large areal capacitance are desired materials for electrode, but there exists a limited understanding of the influence of synthesis parameters on microstructural properties, which largely govern their electrochemical performance. In the present work, hierarchal spinel nickel cobaltite (NiCo₂O₄) nanostructures were synthesized in the presence of the varying amount of hydrolyzing agent via a simple hydrothermal method coupled with a simple post-annealing process. This work focuses on understanding the influence of hydrolyzing agent in controlling the microstructure and hence ensuing electrochemical properties of the NiCo₂O₄ based electrode. Based on the urea hydrolyzing content, the as synthesized NiCo₂O₄ nanostructure varied from the rod, plate to nanoflower. The mesoporous nanostructures, with urea content 1.49 gm, exhibit a sizeable BJH surface area (79.2 m² g) and high mesopore volume (0.140 cm³ g). Remarkably, the NiCo₂O₄ nanoflower shows high specific capacitance of 3143.451 F/g at 2 mV/s scan rate, 1264.5 F/g at 1 A/g current density, energy density of 56 Wh/kg and power density of 8,400 W/kg in 3 M KOH electrolyte. The capacitance loss after 5000 cycles is 48% at the current density of 10 A/g, indicating their excellent cycling stability. The impressive electrocatalytic activity is largely ascribed to the high intrinsic electronic conductivity, superior mesoporous nanostructures and rich surface Ni active species of the NiCo₂O₄ materials, which can largely boost the interfacial electroactive sites and charge transfer rates indicating promising applications as electrodes in future supercapacitors.
微型电子设备的广泛应用需要能量密集型存储策略。具有高面积电容的基于超级电容器的储能设备是理想的储能替代品。制造性能一致的基于超级电容器的能量设备仍然是一个挑战。具有大的面积电容的多孔金属氧化物是电极的理想材料，但对于合成参数对微观结构性质的影响的理解有限，而微观结构性质在很大程度上决定了它们的电化学性能。在本工作中，通过简单的水热法结合简单的退火后处理工艺，在不同量的水解剂存在下合成了分级尖晶石镍钴矿（NiCo₂O₄）纳米结构。这项工作的重点是了解水解剂在控制微观结构以及由此产生的基于NiCo₂O₄的电极的电化学性质方面的影响。基于尿素水解含量，合成的NiCo₂O₄纳米结构从棒状、板状到纳米花状各不相同。尿素含量为1.49克的介孔纳米结构具有相当大的BJH表面积（79.2平方米/克）和高介孔体积（0.140立方厘米/克）。值得注意的是，NiCo₂O₄纳米花在3M KOH电解液中，在2mV/s扫描速率下显示出3143.451F/g的高比电容，在1A/g电流密度下为1264.5F/g，能量密度为56Wh/kg，功率密度为8400W/kg。在10A/g电流密度下5000次循环后的电容损失为48%，表明其具有优异的循环稳定性。令人印象深刻的电催化活性很大程度上归因于NiCo₂O₄材料的高本征电子导电性、优异的介孔纳米结构和丰富的表面Ni活性物种，这可以大大增加界面电活性位点和电荷转移速率，表明其在未来超级电容器中作为电极具有广阔的应用前景。
