Halide Perovskites for Solar Hydrogen Production: Moving from Hydrohalic Acid toward Water Splitting

ConspectusThe conversion of solar energy into chemical fuels via photocatalytic water splitting represents a promising pathway to sustainable hydrogen production. Halide perovskites (HPs) have emerged as remarkable photocatalysts owing to their strong visible-light absorption, tunable bandgaps, long carrier diffusion lengths, and defect-tolerant electronic structures. The photocatalytic hydrogen evolution in aqueous solution was first reported in 2016, wherein the inherent aqueous instability of HPs was addressed through a dissolution-precipitation dynamic equilibrium between the halide perovskite (HP) powders and HP-saturated hydroiodic acid (HI) solution. Early systems, however, faced fundamental limitations: (1) limited charge utilization due to the high carrier recombination and insufficient surficial reactive sites; (2) restriction to the hydrogen evolution half-reaction in concentrated HI solution, which was an uneconomical material source and also caused thermodynamic inefficiency for I^- oxidation instead of water splitting.Over the past decade, our research has focused on addressing these challenges through a combination of material- and system-level innovations. On the materials side, we have explored cocatalyst loading, heterostructure and composite construction, and compositional tuning at the A-, B-, and X-sites to improve carrier utilization efficiency and accelerate surface reaction kinetics, thereby improving photocatalytic performance. These efforts have enabled solar-to-hydrogen (STH) conversion efficiencies exceeding 5% for HI splitting and set the foundation for further advancements. At the system level, we pioneered a solar-driven decoupled water-splitting platform by integrating HP-based photocatalytic hydrogen evolution with spatially separated electrocatalytic or photoelectrocatalytic water oxidation via an I₃^-/I^- redox shuttle. This design resolved critical issues of instability and thermodynamic limitation of HPs for direct water splitting, enabling sustained and stoichiometric hydrogen and oxygen evolution. Building on this, we introduced hydrolytically stable HPs through organic macromolecule incorporation and paired them with complementary oxygen evolution photocatalysts to establish Z-scheme configurations operating in mildly acidic media. Together, these advances in HP-based systems have enabled solar-driven overall water splitting, with STH efficiencies exceeding 2%.This Account summarizes the evolution of HP photocatalysis from early sacrificial hydrohalic acid splitting to integrated solar-driven overall water splitting, highlighting the interplay between material modifications and system designs in overcoming key bottlenecks. We conclude by discussing persistent challenges, including long-term stability, morphology and particle-size control, and interfacial charge management, while outlining future research directions toward translating laboratory advances into practical and scalable solar hydrogen production.