Hot-Injection-Driven Interfacial Stabilization of Lead-Free Halide Perovskites via Sulfur-Vacancy-Rich MoS2 Toward Aqueous Electrocatalysis.

Halide perovskites exhibit exceptional optoelectronic and catalytic properties but remain chemically fragile, rapidly degrading under moisture or alkaline conditions. Here, we introduce a synthesis-driven interfacial engineering strategy that stabilizes the intrinsically unstable lead-free CsSnBr 3 perovskite by coupling nucleation and heterointerface formation within a single liquid-phase hot-injection process. During crystal growth, sulfur-vacancy-rich MoS 2 nanosheets conformally encapsulate CsSnBr 3 nanocrystals, forming coherent 2D-3D p-n heterojunctions that suppress Sn 2 + oxidation, limit moisture penetration, and enable directional charge transport. The resulting heterostructure exhibits a built-in potential of 0.67 V, generating an internal electric field that promotes efficient charge separation and enhanced redox stability. Under alkaline conditions, the synthesis-driven heterointerface sustains bifunctional water splitting in both freshwater and seawater for over 24 h without chlorine evolution or structural degradation. More broadly, this approach provides a generalizable synthesis paradigm for stabilizing moisture- and oxidation-sensitive halide perovskites, enabling their integration into chemically robust and electronically coupled systems for aqueous electrocatalysis and other demanding environments.