Synergizing Phase‐Change Thermal Buffering with Heterojunction Band Engineering for High‐Performance Photocatalytic CO ₂ Reduction

ABSTRACT Photocatalytic CO 2 reduction is hindered by rapid deactivation due to localized photothermal heating, coupled with inefficient charge separation and uncontrolled selectivity. Herein, we design a thermoregulatory photocatalytic microcapsule that, for the first time, integrates phase‐change thermal buffering with heterojunction band engineering within a single hierarchical architecture (MEPCM@ZIF‐8@PPy). The n‐Docosane core confers a high latent heat capacity (124.12 J g −1 ), maintaining the catalyst at ∼50 °C under illumination, while the Type‐II ZIF‐8/PPy heterojunction affords broad‐spectrum light harvesting and efficient charge separation. In a sacrificial agent‐free, gas‐solid system using only CO 2 and water vapor, the composite achieves a CO evolution rate of 433.01 µmol g −1 h −1 with ≈99.5% selectivity, outperforming most state‐of‐the‐art MOF‐based photocatalysts. In situ DRIFTS and real‐time infrared thermal imaging reveal that the PCM core not only prevents thermal degradation but actively steers the reaction pathway by suppressing *CO hydrogenation, thus enabling near‐unity CO selectivity. This work establishes a new paradigm wherein thermal management materials actively direct reaction selectivity, offering a broadly applicable strategy for durable solar fuel production.