Understanding Integrated Graphene–MOF Nanostructures as Binder- and Additive-Free High-Performance Supercapacitors at Commercial Scale Mass Loading

Supercapacitors are energy storage devices that can deliver rapid power but have found limited application due to their inferior capacitive performance at a higher mass loading required for commercial application. Herein we have synthesized a graphene–MOF aerogel (GMA) from a chemical synthesis route between graphene and a metal–organic framework (MOF) which has been demonstrated as an efficient binder and additive-free electrode material for supercapacitor applications with gradual increments in mass loading. The integration of the high conductivity, mechanical strength, and chemical stability of graphene along with the excellent pseudocapacitive nature of the MOF led to the superlative performance of the composite as a high-mass-loading supercapacitor. Remarkably, even after a 233% increase in mass loading from 3 mg cm–2 to 10 mg cm–2, only a 23% reduction in specific capacitance was observed. At the lowest mass loading, specific capacitance was calculated to be 98 F g–1 for the full cell, whereas at the highest mass loading, it was found to be 75 F g–1. Additionally, the material exhibited 100% stability after 25 000 cycles. Electrochemical impedance spectroscopy revealed that equivalent series resistance and resistance for ion adsorption were lowered due to excellent electrical conductivity of the material (1.15 Sm–1). Notably, the integrated nature of the material made double-layer charging and charge transfer at the interface rapid, while pseudocapacitive charging representing electron transfer inside the nanomaterial was also efficient due to hydrogen bonded network between the MOF and graphene. The composite showed a high energy density of 10.4 Wh kg–1 at the highest mass loading without the presence of any dead components. This energy density value was higher than that observed for comparable materials even at a lower mass loading.