Interfacial coupling in CsSnCl 3 − MoS 2 composite for enhanced aqueous pseudocapacitive performance

The electrochemical instability of Sn-based halide perovskites in aqueous media is commonly linked to surface electron accumulation and defect-assisted oxidation of Sn^2+ to Sn^4+. Here, we examine how interfacial coupling in a cesium tin chloride (CsSnCl₃) -molybdenum disulfide (MoS₂) (CSC--MS, 10%) composite electrode influences charge distribution and electrochemical behavior. Electrochemical and spectroscopic measurements indicate trends consistent with effective electronic redistribution at the interface between n-type CsSnCl₃ and p-type 2H-MoS₂, suggestive of a type-II--like alignment. Mott-Schottky analysis yields an apparent flat-band offset on the order of several hundred millivolts, which reflects an effective interfacial capacitance response rather than a uniquely defined junction potential in the heterogeneous composite electrode. Correlated trends in x-ray photoelectron spectroscopy, impedance spectroscopy, and kinetic analyses support reduced near-surface electron density in CsSnCl₃ and an enhanced pseudocapacitive response. In addition, MoS₂ contributes hydrophobic basal planes and electronically active edge states that cooperatively improve interfacial stability, electronic percolation, and charge transport. As a result, the composite exhibits a kinetically extended aqueous operating window approaching 2. 3 V under scan conditions and mixed charge-storage behavior in which reversible Sn^2+/Sn^4+ redox processes are contributory but not exclusive. These results provide a physically consistent, though not uniquely resolved, picture of how interfacial coupling and composite engineering can enhance the aqueous pseudocapacitive performance of lead-free halide perovskite electrodes.