Construction of hierarchical porous two-dimensional Zn-MOF-based heterostructures for supercapacitor applications

Recently, two-dimensional metal-organic frameworks (2D MOFs) are drawing increasing attention in energy storage area. Specially, hybrid 2D MOF-based heterostructures have greatly promoted the development of MOF-based electrode materials. However, the underutilization of both abundant active sites and high surface area causes 2D MOFs poor performance and thus restricts their practical application. Herein, to shorten the ion transport paths and enhance the ion diffusion ability, mesopores were introduced into 2D Zn-MOF sheets to construct a hierarchical porous Zn-MOF-based heterostructure. The energy-storage mechanism in the heterostructures was deeply investigated and the importance of the introduced-mesopores on enhancing the electrochemical behaviors was confirmed. With the optimized design, the obtained Meso-Zn-MOF@rGO-PBA delivered outstanding electrochemical performance, including a high capacitance (292.8 F g−1 at 0.2 A g−1), an excellent rate capacity (268.1 F g−1 at 5 A g−1) and a good cycling stability (83.2 % retention after 2000 cycles). Furthermore, the practical applicability of Meso-Zn-MOF@rGO-PBA was researched by assembling an asymmetric supercapacitor using activated carbon as the other electrode, achieving a satisfied specific capacitance of 54.9 F g−1 with an energy density of 19.5 Wh kg−1 (1 A g−1). Our observation provides a strategic design idea for high-performance supercapacitor electrode materials.