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. 2023 Apr 4;14:1872. doi: 10.1038/s41467-023-37608-4

Fig. 5. Extracellular electron-mediated photosynthesis-independent extended hydrogen production.

Fig. 5

a Schematic illustration of hydrogen production (paired cyan circles) arising from surface-augmented algal cells with the addition of EY and TEOA under hypoxic conditions. The electrons are directly transferred to hydrogenase via molecular diffusion; right panel shows the site of interaction with extracellular electrons. Molecular graphics for EY, TEOA and ascorbate are shown. b Time-dependent production of hydrogen for PPy/CaCO3-coated Chlorella cells with periodic addition of TEOA at intervals of 6 d from the time point of 12 d. The culture medium containing EY and TEOA is also refreshed (arrows) along with regeneration of the outer CaCO3 shell. The final used concentrations of EY and TEOA at 72 d are 0.23 and 16.8 mg/mL; 126 d, 0.23 and 13.9 mg/mL; 168 d, 0.23 and 11.0 mg/mL; and 204 d, 0.23 and 9.52 mg/mL. Average chlorophyll content obtained within 204 d, 38.3 mg/L. The decrease on the hydrogen production rate is due to normal apoptosis of the Chlorella cells. c Time-dependent chlorophyll fluorescence kinetics curves for PPy/CaCO3-coated Chlorella cells with the addition of EY and TEOA. d Time-dependent measurements of cell viability for PPy/CaCO3-coated Chlorella cells with or without the addition of EY and TEOA. The half-life of the PPy/CaCO3-coated Chlorella cells was ~128 d. e Time-dependent measurements of hydrogen production for dead PPy/CaCO3-coated Chlorella cells with the addition of EY and TEOA. The final used concentrations of EY and TEOA are 0.24 and 1.65 mg/mL, respectively. All samples are cultivated in sealed vials with sodium ascorbate-containing TAP culture medium and exposed to the daylight with an intensity of 65 μE m–2 s–1. Data in b, d, and e are presented as mean values ± SD, error bars indicate standard deviations (n = 3, biologically independent samples). All relevant experiments are performed independently at least three times with similar results. Source data are provided as a Source Data file.