In Situ Hard-Template Synthesis of Hollow Bowl-Like Carbon: A Potential Versatile Platform for Sodium and Zinc Ion Capacitors

Metal-ion capacitors are being widely studied to reach a balance between power and energy output by combining the merits of conventional batteries and capacitors. The main challenge for Na-ion capacitors is that the battery-type anode usually has unsatisfactory power density and long-term stability since most Na host materials have a poor kinetic and structural stability. Herein, asymmetric hollow bowl-like carbon (HBC) materials are rationally designed and fabricated through an in situ hard-template approach. The formation originates from a subtle control of capillary force and the mechanical strength of the carbon shell. The HBCs possess abundant mesopores, high volumes of accessible surface area as well as an open macropore network. As a 3D host, MoSe₂ nanocrystals are anchored onto the HBC matrix by a solid-phase reaction. The obtained MoSe₂@HBC nanobowl electrode exhibits pseudocapacitive sodium storage with fast kinetics, improved capacity at high currents, and cycle stability, which is also supported by DFT calculations. Sodium ion capacitor full cells are fabricated using the two bowl-like architectures (MoSe₂@HBC as the anode and HBC as the cathode), which deliver high energy and power densities, long cycle life, and a comparably low self-discharge rate. Moreover, application of the HBC in a zinc-ion capacitor (ZIC) is also demonstrated.