Preparation of low internal resistance electrode material with multistage interconnected pores from coffee grounds

Using biomass waste materials to prepare electrode materials with excellent properties is an effective strategy for solving current energy and environmental problems. In this work, coffee grounds were pretreated with Co(NO3)2 and Ni(NO3)2, then KOH was used to activate the pretreated coffee grounds at a high temperature to obtain a foam-like electrode material with interconnected microporous-mesoporous-macroporous hierarchical channels. This preparation method is simple and has low energy consumption, and the resulting material has an ultra-low internal resistance of 0.31 Ω. The specific capacitance of CGC-2 is 302.65 F g−1 at a current density of 1 A g−1. The low internal resistance and high electrical conductivity of this activated material are attributed to the presence of Co2+ and Ni2+ during carbonization, whose catalytic effect leads to a relatively ordered lattice structure. The interconnected structure of the final product is mainly caused by the strong activation function of KOH generating many pores. The prepared material exhibits good rate performance and cycling stability, and it has a Coulombic efficiency of nearly 93%. This work provides a novel idea for using biomass materials to fabricate high-performance electrode materials for supercapacitors.