Nickel–Cobalt Oxide Nanoparticle-Induced Biohydrogen Production

The positive effects of metal oxide nanoparticles (NPs) on dark fermentation (DF) for biohydrogen synthesis have been increased, and the mechanism still needs to be further revealed. In this study, nickel-cobalt oxide (NiCo2O4) NPs were prepared to increase H2 yield via DF. The highest (259.67 mL/ g glucose) and the lowest (188.14 mL/g glucose) yields were achieved at 400 and 800 mg/L NiCo2O4 NPs added, respectively, with their corresponding 33.97% increase and 2.93% decrease compared with the control yield (193.82 mL/g glucose). Meanwhile, the microbial community further confirmed that NiCo2O4 NPs increased the abundance of the dominant H2-producing Clostridium sensu stricto1 by 23.05%. The gene prediction also showed that NiCo2O4 NPs increased the abundance of genes encoding the rate-limiting enzyme pyruvate kinase in glycolysis, thus increasing the substrate conversion. Moreover, the gene abundance of key enzymes directly related to H2 evolution was also increased at different levels.