Polar Aromatic Two-dimensional Dion-Jacobson Halide Perovskites for Efficient Photocatalytic H₂ Evolution

Polar materials with spontaneous polarization (P_s) have emerged as highly promising photocatalysts for efficient photocatalytic H₂ evolution owing to the P_s-enhanced photogenerated carrier separation. However, traditional inorganic polar materials often suffer from limitations such as wide band gaps and poor carrier transport, which hinders their photocatalytic H₂ evolution efficiency. Here, we rationally synthesized a series of isostructural two-dimensional (2D) aromatic Dion-Jacobson (DJ) perovskites, namely (2-(2-Aminoethyl)pyridinium)PbI₄ (2-APDPI), (3-(2-Aminoethyl)pyridinium)PbI₄ (3-APDPI), and (4-(2-Aminoethyl)pyridinium)PbI₄ (4-APDPI), where 2-APDPI and 4-APDPI crystalize in polar space groups with piezoelectric constants (d₃₃) of approximately 40 pm V^-1 and 3-APDPI adopts a centrosymmetric structure. Strikingly, owing to the P_s-facilitated separation of photogenerated carriers, polar 2-APDPI and 4-APDPI exhibit a 3.9- and 2.8-fold increase, respectively, in photocatalytic H₂ evolution compared to the centrosymmetric 3-APDPI. As a pioneering study, this work provides an efficient approach for exploring new polar photocatalysts and highlights their potential in promoting photocatalytic H₂ evolution.