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Figure 1 Apparatus of the hydrogen production assay.
Figure 2 Hydrogen evolution curve with nanorods bound to biofilm beads.
During the period with lighting, the hydrogen production increases, until we shut off the light at points that correspond to the tips. The curve then goes downward, showing that the hydrogen concentration is lowered, an evidence of the bidirectional catalytic activity of hydrogenase. It is noteworthy that the hydrogenase shows the greatest production rate at the beginning of lighting: a transient sharp rise can be observed at the valleys. It is also obvious that each period of “light-on light-off” gives similar curves, which implies that our hydrogenase is stable. In our experiment, we find that despite the reported affected catalytic ability of FeFe hydrogenase due to oxygen, non-strict anaerobic and short-term exposure to oxygen does not cause detrimental effects on the enzyme activity of producing hydrogen. This can be explained by the high catalytic ability and the segregation layer from the atmosphere provided by the hydrogen it produces. Meanwhile, the electron sacrificial agent VitaminC also adds to the “protection layer” of the hydrogenase in our system.
Figure 3 Hydrogen evolution curve with free-flowing nanorods.
Another point to note between our two systems is that in the process of hydrogen generation without biofilm-anchored CdS, a stir bar with a necessary speed of 800 RPM was needed. But in Figure 2, the system with biofilm, a stir bar was not used. It is likely because the aggregates of NR have a bigger chance in colliding with E. coli to transfer electrons. b) Calculating the hydrogen evolution rate of our integrated system. We are particularly interested in learning what our efficiency is compared to one study reported this year. See reference 1. In calculating the efficiency, we chose the data from the first hydrogen production period. We converted the data in mV into umol/L. The standard curve is provided by the lab who supervised our assay apparatus.
Figure Standard Relationship between voltage data and concentration.
Thus, we obtain the rate of hydrogen evolution: the tip of the first period is 7.061 mV at 500s. This corresponds to 2.179 (0.3086*7.061) umol/L at 500s. Thus the rate is 0.0126 (2.179/500*3mL*1000) umol/s, for 0.1g E. Coli. In comparison with the rate from reference 1, 0.0086mol umol/s. This 46% increase in the efficiency shows that our system not only works, but is also a progress for the study of artificial hydrogen production system.Given that our system has been proved to work with repeatability and its intrinsic characteristics for massive application, we think our project is a successful applied design. Here, we summarize the qualification and merits of our design in the following figure. Meanwhile, we also point out the lack of our design and some future works that are needed to improve our Solar Hunter.
