Cocatalyst-Free Carbon Nitride/ Shewanella oneidensis MR-1 Biohybrids for Cyclic Light–Dark Hydrogen Evolution with Reversible Electron Storage

Semiartificial photosynthesis represents a promising strategy for converting solar energy into storable chemical fuels, yet its practical implementation is hindered by solar intermittency and the reliance on precious metal cocatalysts. Here, we report a cocatalyst-free biohybrid system constructed by coupling cyanamide-functionalized polymeric carbon nitride (NCN-CNx) with the electroactive bacterium Shewanella oneidensis MR-1, enabling continuous hydrogen evolution across alternating light-dark cycles. Under visible-light irradiation (λ ≥ 400 nm), the hybrid system achieves a sustained hydrogen production rate of 204.88 μmol g-1hLight-1 with a quantum efficiency of 2.04%. Notably, photogenerated charges are stored within the cyano-functionalized electron reservoirs of NCN-CNx during illumination, driving an additional dark-phase hydrogen evolution of 39 μmol g-1 following light termination. Mechanistic studies demonstrate dual-mode electron transfer across the bacteria-photocatalyst interface. Photogenerated electrons drive hydrogenase-mediated proton reduction during illumination, while stored charges discharge through conserved microbial conduits in darkness. The system exhibits exceptional biocompatibility, maintaining beyond 90% bacterial viability after multiple operational cycles. By decoupling light harvesting from catalytic turnover through reversible electron storage and eliminating the need for external cocatalysts, this work establishes a robust platform for all-weather solar-driven hydrogen production.