Red-Light-Driven Biophotochemical Diode Based on a Microorganism–Silicon Nanowire Interface for Stable and Efficient Bias-Free CO2 Reduction

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.