Pollen-inspired synthesis of porous and hollow NiO elliptical microstructures assembled from nanosheets for high-performance electrochemical energy storage

Numerous efforts have recently been focused on designing and synthesizing efficient nanostructures electrode materials for high-efficiency energy storage. Herein, hierarchical porous and hollow NiO elliptical microstructures constructed from nanosheets are synthesized by utilizing the renewable, cost-effective and widespread native rape pollen grains as template. Benefiting from the unique morphology, pollen-templated NiO shows outstanding electrochemical performances as electrode of supercapacitor, such as high specific capacitance (198.7 mAh g⁻¹ at 1 A·g⁻¹), excellent rate capability (89.2 mAh g⁻¹ at 30 A·g⁻¹) and long cycling life. Besides, asymmetric supercapacitor device was assembled by using pollen-templated NiO and activated carbon, which deliver excellent cycling stability (103.3% retention after 10,000 cycles) as well as high energy/power density (a high energy density of 66.4 Wh kg⁻¹ and power density of 22.2 kW kg⁻¹). Moreover, the low-cost pollen template-based strategy is found to be a versatile method to prepare other porous and hollow elliptical microstructure of transition-metal oxides.