Moisture-Stable CsSnBr<sub>2</sub>Cl Halide Perovskite:\nElectrochemical Insights in Aqueous Environments

In this investigation, moisture-stable CsSnBr<sub>2</sub>Cl nanoparticles\nwere synthesized by incorporating Cl into CsSnBr<sub>3</sub> halide\nperovskite using the hot injection method. Various analyses including\nXRD, XPS, UV–vis absorbance, photoluminescence, and Mott–Schottky\nhave confirmed that the structural properties, chemical states, optical\nproperties, and electronic band structure of CsSnBr<sub>2</sub>Cl\nnanoparticles remain intact even after 75 days of water immersion,\nthereby conclusively demonstrating their moisture stability. In a\nthree-electrode system, the comparative electrochemical performance\nof pristine CsSnBr<sub>3</sub> nanoparticles and moisture-stable Cl-incorporated\nCsSnBr<sub>2</sub>Cl nanoparticles was evaluated in various aqueous\nelectrolytes, including HCl, Na<sub>2</sub>SO<sub>4</sub>, and KOH.\nThe results indicate that the CsSnBr<sub>2</sub>Cl electrode material\nexhibits superior electrochemical properties, such as a larger integrated\ncyclic voltammetry (CV) area, a wider potential window, longer charge–discharge\ntimes, and lower impedance parameters compared to the pristine CsSnBr<sub>3</sub> nanoparticles. The electrochemical performance of CsSnBr<sub>2</sub>Cl nanoparticles was evaluated for potential applications\nin batteries, supercapacitors, fuel cells, and water splitting, with\na focus on reaction kinetics, charge storage mechanisms, and impedance\nparameters. The electrochemical properties of the nanoparticles were\nassessed using a three-electrode configuration across various 0.5\nM aqueous electrolytes (HCl, Na<sub>2</sub>SO<sub>4</sub>, and KOH).\nIn HCl, the nanoparticles demonstrated impressive charge storage capability,\nachieving a capacitance of 474 F g<sup>–1</sup> at 1 A g<sup>–1</sup>, affirming their suitability for energy storage devices.\nIn Na<sub>2</sub>SO<sub>4</sub>(aq.), the nanoparticles exhibited\nexcellent stability for supercapacitors, operating up to 1.6 V without\nsignificant oxygen evolution. Notably, in KOH, they demonstrated potential\nas effective water-splitting electrodes. The practical applicability\nof the nanoparticles was evaluated using a symmetric two-electrode\nconfiguration with HCl and Na<sub>2</sub>SO<sub>4</sub> electrolytes.\nThe capacitance values were 117 F g<sup>–1</sup> in HCl and\n70 F g<sup>–1</sup> in Na<sub>2</sub>SO<sub>4</sub> at 1 A\ng<sup>–1</sup>. Notably, after 5000 GCD cycles in HCl(aq.),\nthe nanoparticles retained 93% of their capacitance and maintained\n91% Coulombic efficiency. They also demonstrated stable operation\nacross a temperature range of 3 to 60 °C, achieving an energy\ndensity of 5.83 W h kg<sup>–1</sup> at a power density of 600\nW kg<sup>–1</sup>. This study emphasizes the considerable potential\nof CsSnBr<sub>2</sub>Cl nanoparticles in advancing electrochemical\nenergy storage technologies and sets a solid foundation for future\nresearch and development in metal halide perovskites.