In the past decade, ferroelectric materials have been intensively explored as promising photocatalysts. An intriguing ability of ferroelectrics is to directly sperate the photogenerated electrons and holes, which is believed to arise from a spontaneous polarization. Understanding how polarization affects the photocatalytic performance is vital to design high-efficiency photocatalysts. In this work, we report a size effect of ferroelectric polarization on regulating the photocatalytic overall water splitting of SrTiO₃/PbTiO₃ nanoplate heterostructures for the first time. This was realized hydrothermally by controlling the thickness and thus spontaneous polarization strength of single-crystal and single-domain PbTiO₃ nanoplates, which served as the substrate for selective heteroepitaxial growth of SrTiO₃. An enhancement of 22 times in the photocatalytic overall water splitting performance of the heterostructures has been achieved when the average thickness of the nanoplate increases from 30 to 107 nm. A combined experimental investigation revealed that the incompletely compensated depolarization filed is the dominated driving force for the photogenerated carrier separation within heterostructures, and its increase with the thickness of the nanoplates accounts for the enhancement of photocatalytic activity. Moreover, the concentration of oxygen vacancies for negative polarization compensation has been found to grow as the thickness of the nanoplates increases, which promotes oxygen evolution reaction and reduces the stoichiometric ratio of H₂/O₂. These findings may provide the opportunity to design and develop high-efficiency ferroelectric photocatalysts.

Developing highly efficient oxygen evolution reaction (OER) catalysts for electrolytic water splitting is urgently desirable but remains a challenge due to sluggish kinetic process of water oxidation. Herein, we report a one-step electrodeposition strategy to prepare Ni(OH)₂ modified with Ir single-atom catalysts (SACs) (Ir SACs/Ni(OH)₂) on an electrically conductive substrate of three dimensional (3D) hierarchical porous nickel foam (HP-NF) as efficient OER electrocatalyst. The HP-NF with abundant open pores can not only enable the full exposure of catalytically active sites but also facilitate the diffusion of electrolyte and release of gaseous oxygen produced. The optimal Ir SACs/Ni(OH)₂@HP-NF exhibits a remarkable catalytic performance and outstanding stability for the OER activity in 1.0 M KOH alkaline media, delivering a low overpotential of ~ 223 mV at a current density of 10 mA·cm⁻² and a low Tafel plot of 58 mV·dec⁻¹. Various characterizations together with control electrochemical experiments demonstrated that the superior activity and robust stability of Ir SACs/Ni(OH)₂@HP-NF for OER are originated from the highly distributed and exposed Ir SACs and 3D interconnected pores of HP-NF with high electric conductivity.