Charge Storage Mechanism via Vacancy-Mediated Anion Intercalation in a Two-Dimensional Cs2PbI2Cl2 Ruddlesden–Popper Perovskite

This research delves into the exploration of the electrochemical charge storage mechanism and supercapacitive behavior exhibited by 2D Ruddlesden–Popper (RP) halide perovskites. The mechanochemically synthesized Cs2PbI2Cl2 perovskite, characterized by its tetragonal phase and I4/mmm space group symmetry, has been investigated as a promising electrode material for energy storage applications. In our investigation, we probed the charge storage mechanism within Cs2PbI2Cl2 by employing a 1 M KOH aqueous electrolyte in a three-electrode setup. This system operated within the potential window of 0.0–0.6 V vs Ag/AgCl. The pseudocapacitive behavior of the Cs2PbI2Cl2 perovskite arises from anion (OH– ion) intercalation from the electrolyte into vacant sites within the electrode material, accompanied by redox transformations of Pb ions. Specifically, the Cs2PbI2Cl2 perovskite exhibits a specific capacitance of 2017 F g–1 at a scan rate of 2 mV s–1. Furthermore, we fabricated an asymmetric supercapacitor device with the configuration of a Cs2PbI2Cl2/PVA-KOH gel/activated carbon. This device delivers an energy density of 67 Wh kg–1 and a power density of 794 W kg–1 at a current density of 1 A g–1, with ∼75% capacitive retention after 8000 charge–discharge cycles. These compelling electrochemical findings strongly support the feasibility of utilizing a low-dimensional Cs2PbI2Cl2 perovskite as an electrode material for advanced supercapacitor electrodes.