X-Functionality–Driven Photocatalytic Hydrogen Evolution in 2D 4-X-PEA₂SnI₄ Perovskites

Two-dimensional (2D) Sn-halide perovskites (Sn-HPs) have emerged as promising candidates for efficient optoelectronic devices, owing to their suitable charge carrier mobility and tunable optical properties achievable via chemical composition. These characteristics make them ideal for extending their application to aqueous solar-driven photocatalysis; however, the oxidation of Sn²⁺ hinders their use in chemical reactions, making the stabilization of Sn²⁺ a big challenge. Here, we demonstrate a novel synthetic procedure for growing water-stable, red-emitting 2D Sn-HPs microcrystals and their use as raw materials for H₂ evolution. By introducing 4-X-phenethylammonium (PEA) cation derivatives (X = fluorine, F; methoxy, MeO; and their combination), Sn-HPs show a modulable band structure for carrying out hydrogen evolution reaction, achieving a maximum evolved H₂ of 19.3 µmol·g⁻¹, a H₂ evolution rate of 6.98 µmol·g⁻¹·h⁻¹, maintaining their structural integrity over four On light cycles during HI splitting. The presence of organic functionalities in the para (p)-position of the PEA cation restrains the [SnI₆]⁴⁻ octahedra distortion, while the presence of I⁻ prevents the rapid iodide consumption in the perovskite. This synergy enhances both the stability in aqueous solutions and electron accumulation, thus favoring the photocatalytic H₂ generation.