UC Berkeley

Artificial photosynthesis offers a promising route for sustainable liquid fuel and feedstock production, yet integrating efficient CO₂ reduction catalysts with light-harvesting systems remains challenging. Here, we present a biophotochemical diode that couples microorganism-driven CO₂ reduction with glycerol oxidation, enabled by silicon nanowire photoelectrodes under varying red-light intensities. Tuning the biotic-abiotic interface─by increasing biocatalyst loading and adjusting the catholyte pH to mitigate local alkalization─significantly improves performance and stability. The enhanced-loading biocathode maintains a high faradaic efficiency across a wide potential range, even under elevated light intensities. At 60 mW/cm², the system achieves a bias-free current density of 3.5 mA/cm². Long-term stability testing at 40 mW/cm² demonstrates stable operation for over 100 h. The photoanode generates valuable C₃ products, primarily glycerate and lactate, enhancing the economic viability. This work showcases the importance of microenvironmental control at the biotic-abiotic interface and establishes a scalable platform for light-driven CO₂ reduction using earth-abundant silicon.