Topological Modulation of Heteroanionic Motifs in a Novel Oxysulfide Sr ₃ in ₄ O ₄ S ₅ for Synchronized Charge Dynamics and Enhanced Solar Fuel Generation

The chemistry of oxysulfides integrates the merits of sulfides and oxides through fully hybridized S─O states, rendering them promising for photocatalytic water splitting. Precise control over heteroanionic coordination is a cornerstone for tailoring their functional properties, yet it remains a profound synthetic challenge. Here, the first discovery of a novel indium oxysulfide, Sr 3 In 4 O 4 S 5 , is reported, presenting a unique one‐dimensional structure built from fully heteroanionic [InO 2 S 3 ] 7 − motifs, ensuring complete S─O orbital hybridization. Beyond structural novelty, a groundbreaking topological acid‐exfoliation strategy is introduced that enables postsynthetic tuning of local anion ratios within these motifs. This process transforms the crystalline surface into an amorphous, reconstructed network, narrowing the optical bandgap from 3.20 to 2.47 eV. More importantly, the reconstructed motifs can function as exceptional electron sinks, accelerating charge trapping and extending carrier lifetimes by an order of magnitude, thereby resolving the critical kinetic mismatch between bulk charge dynamics and surface reactions. This coordination engineering unlocks unprecedented photocatalytic performance, yielding a record‐high apparent quantum yield of 2.74% at 420 nm for H 2 evolution among non‐Ti‐based oxysulfides. This work not only reports a high‐performance photocatalyst but also establishes a generalizable paradigm for topological heteroanionic coordination tuning, aiding in the rational design of advanced catalysts and tunable semiconductors.