Nickel–Cobalt Oxide Nanoparticle-Induced Biohydrogen Production

[Image: see text] 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 (NiCo(2)O(4)) NPs were prepared to increase H(2) 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 NiCo(2)O(4) 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 NiCo(2)O(4) NPs increased the abundance of the dominant H(2)-producing Clostridium sensu stricto1 by 23.05%. The gene prediction also showed that NiCo(2)O(4) 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 H(2) evolution was also increased at different levels.