The electrochemical instability of Sn-based halide perovskites in aqueous media is commonly linked to surface electron accumulation and defect-assisted oxidation of ${\mathrm{Sn}}^{2+}$ to ${\mathrm{Sn}}^{4+}$. Here, we examine how interfacial coupling in a cesium tin chloride (${\mathrm{CsSnCl}}_3)$-molybdenum disulfide $\left({\mathrm{MoS}}_2\right)$ (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 ${\mathrm{CsSnCl}}_3$ and $p$-type 2H-${\mathrm{MoS}}_2$, 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 ${\mathrm{CsSnCl}}_3$ and an enhanced pseudocapacitive response. In addition, ${\mathrm{MoS}}_2$ 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 ${\mathrm{Sn}}^{2+}/{\mathrm{Sn}}^{4+}$ 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.

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• Electrochemical properties