Investigating the NH₄⁺ Preintercalation and Surface Coordination Effects on MnO₂ for Ammonium-Ion Supercapacitors

Ion preintercalation is an effective method for fine-tuning the electrochemical characteristics of electrode materials, thereby enhancing the performance of aqueous ammonium-ion hybrid supercapacitors (A-HSCs). However, much of the current research on ion preintercalation lacks controllability, and the underlying mechanisms remain unclear. In this study, we employ a two-step electrochemical activation approach, involving galvanostatic charge-discharge and cyclic voltammetry, to modulate the preintercalation of NH₄⁺ in MnO₂. An in-depth analysis of the electrochemical activation mechanism is presented. This two-step electrochemical activation approach endows the final MnO₂/AC electrode with a high capacitance of 917.4 F g^-1, approximately 2.4 times higher than that of original MnO₂. Furthermore, the MnO₂/AC electrode retains approximately 93.4% of its capacitance after 10 000 cycles at a current density of 25 mA cm^-2. Additionally, aqueous A-HSC, comprising MnO₂/AC and P-MoO₃, achieves a maximum energy density of 87.6 Wh kg^-1. This study offers novel insights into the controllable ion preintercalation approach via electrochemical activation.