Abstract
In the metal-ion-dominated era of electrochemical energy storage, emerging non-metallic charge carriers like ammonium ion (NH4+), have gained attention for their affordability, sustainability, and compatibility with aqueous electrolytes. Herein, we report morphology-controlled fullerene-derived porous hollow carbon spheres as an anode material for ammonium-ion asymmetric supercapacitors and establish a structure-property relationship by systematically comparing hollow spheres with solid spheres. The porous hollow carbon spheres (HCS_900) exhibited superior electrochemical ammonium-ion storage performance, delivering more than 2-fold higher specific capacitance (134.2 F g(-1)) compared to solid carbon spheres (SCS_900, 51.8 F g(-1)). Moreover, HCS_900 shows higher rate capability (58.4% capacitance retention at a high current density of 10 A g(-1)) than its solid counterparts (50.4%), directly correlating morphology with ion-storage kinetics. An asymmetric device consisting of hollow carbon spheres as the anode and delta-MnO2 as the cathode (HCS_900//delta-MnO2) delivered a decent energy density of 16.5 Wh kg(-1) and sustained a high-power density of 525 W kg(-1), with 65% capacitance retention and >99% coulombic efficiency even after 5000 charge/discharge cycles. This study demonstrated fullerene-derived porous hollow carbon as a potential anode material in an aqueous ammonium-ion supercapacitor and provided fundamental insights into morphology-dependent ammonium-ion energy storage.