Organic Semiconducting Hydrogel with Integrated Microbes and Enzymes for Selective Solar CO₂ Conversion

Integrating synthetic light-harvesting materials with biological CO₂-fixing catalysts offers a promising route to efficient and selective solar-to-chemical conversion under mild conditions. However, progress remains limited by the lack of photocatalytic materials that combine biocompatibility, strong electronic coupling with biocatalysts, high biocatalyst loading capacity, and facile product separation. Here we introduce an organic semiconducting hydrogel synthesized from a rationally designed conjugated polyelectrolyte featuring visible-light absorption, water-processability, and covalent cross-linkability. The resulting macroporous, positively charged hydrogel scaffold immobilizes both microbes and enzymes, promoting intimate abiotic-biotic interactions throughout the three-dimensional hydrogel matrix. This platform supports two distinct modes of sacrificial CO₂ reduction: mediated electron transfer via photogenerated H₂ to drive acetate synthesis in the microbe Clostridium ljungdahlii, and direct electron transfer from photoexcited polymer domains to the isolated enzyme formate dehydrogenase for formate synthesis. By coupling the molecular programmability of organic semiconductors with the selectivity of biocatalysts, this work establishes a versatile class of soft biohybrid materials for solar fuel production through semiartificial photosynthesis.