Ionic Cocrystal Programming of Spatial Ionic Organization in Carbon Nitrides Enables Highly Efficient H 2 O 2 Photosynthesis

ABSTRACT Controlling the spatial organization of ions in polymeric photocatalysts remains a fundamental challenge for optimizing charge transport and catalytic selectivity in solar‐driven hydrogen peroxide (H 2 O 2 ) synthesis. In conventional poly(heptazine imide) (PHI), alkali cations are incorporated through molten‐salt‐mediated equilibration, producing statistically distributed ionic environments with little spatial correlation. Here, we demonstrate that organic‐inorganic ionic cocrystals (ICCs) serve as molecularly preorganized precursors that promote spatially correlated ionic environments during framework formation, enabling controlled incorporation of Li + into imide‐bridged N sites. This ICC‐programmed architecture decouples composition from photocatalytic function, demonstrating that photocatalytic activity is governed by the ion incorporation pathway and the resulting spatial ionic organization, rather than cation identity or content alone. The resulting ionic carbon nitride, CALiK, achieves an apparent quantum yield of 58% at 410 nm, the highest among the benchmarked state‐of‐the‐art photocatalysts, while requiring substantially lower inorganic salt loading than conventional ionothermal synthesis. Operando‐relevant spectroscopic and electrochemical analyses reveal directional charge migration driven by internal electrostatic polarization and enhanced accumulation of long‐lived photogenerated electrons. Representative density functional theory models suggest that spatially correlated ionic motifs and cyano‐derived electron‐accepting domains generate polarized charge landscapes that lower the energetic barrier for the two‐electron oxygen reduction pathway.