Rational design of 3D porous niobium carbide MXene/rGO hybrid aerogels as promising anode for potassium-ion batteries with ultrahigh rate capability

An effective method is designed to construct three-dimensional (3D) Nb₂C/reduced graphene oxide (rGO) hybrid aerogels through a low-temperature graphene oxide (GO)-assisted hydrothermal self-assembly followed by freeze-drying and annealing. The intimately coupled Nb₂C/rGO hybrid aerogel combines the advantages of large specific surface area and rich 3D interconnected porous structure of aerogel as well as high conductivity and low potassium diffusion energy barrier of Nb₂C, which not only effectively prevents the self-restacking of Nb₂C nanosheets to allow more active sites exposed and accommodate the volume change during the charge/discharge process, but also increases the accessibility of electrolyte and promotes the rapid transfer of ions/electrons. As a result, Nb₂C/rGO-2 as the anode of potassium ion batteries (KIBs) delivers a large reversible specific capacity (301.7 mAh·g⁻¹ after 500 cycles at 2.0 A·g⁻¹), an ultrahigh rate capability (155.5 mAh·g⁻¹ at 20 A·g⁻¹), and an excellent long-term large-current cycle stability (198.8 mAh·g⁻¹ after 1,000 cycles at 10 A·g⁻¹, with a retention of 83.3%). Such a high-level electrochemical performance, especially the ultrahigh rate capability, is the best among transition metal carbides and nitride (MXene)-based materials reported so far for KIBs. The diffusion kinetics of K⁺ is investigated thoroughly, and the synergetic charge–discharge mechanism and the structure–performance relationship of Nb₂C/rGO are revealed explicitly. The present work provides a good strategy to solve the self-restacking problem of two-dimensional materials and also enlarges the potential applications of MXenes.