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.