Unlocking the\nPotential of Ni/Fe<sub>2</sub>O<sub>3</sub> Bimetallic Nanoparticles\nfor Fermentative Biohydrogen Production

The coordinated system of inorganic nanoparticle-intact\nliving\ncells has shown great potential in fermentative hydrogen (H<sub>2</sub>) production. Meanwhile, sluggish electron transfer and energy loss\nduring transmembrane diffusion restrict the production of biohydrogen\n(BioH<sub>2</sub>). Herein, iron oxide, nickel oxide, and Ni/Fe<sub>2</sub>O<sub>3</sub> bimetallic nanocomposites were prepared through\nthe coprecipitation method to investigate their potential effect on\nthe dark fermentative hydrogen production (DFHP) system. The results\nshowed that BioH<sub>2</sub> production could be enhanced by using\nnickel and iron oxide composites in DFHP, surpassing the performance\nof individual iron oxide or nickel oxide and their physical mixture.\nSpecifically, Ni/Fe<sub>2</sub>O<sub>3</sub>-5% added to the feed\nat 150 mg/L increased the BioH<sub>2</sub> yields by 51.24% compared\nto that in its controlled experiment. The microbial community analysis\nconfirmed a significant change in compositional proportions of the\nmicrobiome structure of DFHP in response to Ni/Fe<sub>2</sub>O<sub>3</sub>-5 wt %. The Enterobacter species proportions increased from\n32.0% to 39.0%, along with some unclassified genera of microbial communities,\nfrom 34.0% to 42.0%, by supplementation of the nanomaterials. Enterobacter\nspecies are versatile facultative hydrogen producers and can use various\norganic wastes as the sole carbon source. The results suggested that\nthe supplemented Ni/Fe<sub>2</sub>O<sub>3</sub>-5% induced the glycolytic\nefficacy and Fe and Ni availability, thereby increasing the hydrogenase\nactivities. This study provided novel insights into integrating Ni/Fe<sub>2</sub>O<sub>3</sub> into the DFHP system and depicted its potential\nas an excellent catalyst to increase BioH<sub>2</sub> production.\nThe distinctive microbial communities, unidentified hydrogen-producing\nbacteria, and increased BioH<sub>2</sub> yield due to the presence\nof Ni/Fe<sub>2</sub>O<sub>3</sub> in the DFHP system suggest unique\nand substantial advantages for the sustainable use of bimetallic nanomaterials\nin fermentation technology.