Fe2O3-Based Microbial Hybrids for Enhancing Dark Fermentation Hydrogen Production: Performance and Mechanistic Insights

• • At 300 mg/L Fe2O3 (S300), hydrogen yield reached 2.94 mol/mol glucose, achieving 73.5% of theoretical maximum and 1.59× higher than control (S0), demonstrating a significant enhancement in fermentative H2 production efficiency. • • S300 biohybrid exhibited a 4.09-fold increase in ATP content and 1.30-fold rise in total protein, indicating enhanced microbial metabolic activity and biomass synthesis, critical for scaling up industrial fermentation. • • Hydrogenase and dehydrogenase activities were boosted by 24.62% and 63.11%, respectively, while electron transfer system activity increased 3.44-fold with reduced charge transfer resistance, directly addressing the electron transfer bottleneck in dark fermentation. • • Fe2O3 addition enriched Clostridium by 9.75 percentage points to 42.60% relative abundance, underscoring a microbial community shift favorable for hydrogen production, which is essential for process stability in continuous systems.