by Allison Kerley (Photo above of Hanyu Wang, first author of this paper at the University of California, Santa Cruz.)
Most hydrogen generating devices require an external addition of a 0.2 to 1.0 V electric potential in order to sustain the hydrogen generation. Wang et al. (2013) explored the feasibility of a self-powering photoelectrochemical-microbial fuel cell (PEC-MFC) hybrid device to generate hydrogen. The PEC-MFC was a combination of a photoelectrochemical fuel cell and a microbial fuel cell. The Hydrogen production of the device was tested when powered by a ferricyanide solution inoculated with a pure strain of Shewanellla oneidensis MR-1 and when powered by microorganisms found naturally occurring in the municipal wastewater. In both scenarios, given replenishments of fuel, the device produced enough voltage to be self-sustaining. However, when the device was powered by wastewater it produced both a lower current and a smaller hydrogen production than when powered by ferricyanide solution. Continue reading →
The paper by Xie et al. (discussed in my August 10 post) didn’t say much about the electrogenic bacteria needed to make their microbial battery work. Just a few days ago, however, researchers in Beijing and Singapore published a paper focussed on such bacteria (Klebsiella sp. in this case) isolated out of a microbial fuel cell, that can do the job in wastewater heavily contaminated with cyanide, almost completely degrading the cyanide in the process. Even without the electricity generation this is interesting, because these bacteria do a better job of removing cyanide than the much more expensive chemical oxidation methods more commonly used by industry. Microbial fuel cells get electricity out of microbes differently than the “microbial battery” of Xie et al.; they consist of two wastewater-filled chambers seperated by a proton exchange membrane. The bacteria in the anode chamber strip protons (hydrogen ions) off the feedstock—a cyanide/glucose mixture in this experiment—and the protons migrate through the membrane to the cathode. The electrons flow as an electrical current from the anode to the cathode in a wire, where they can be used as electricity. Interestingly, the bacteria continued to generate electricity from cyanide alone when they ran out of glucose.
Wang, W., Feng, Y., Tang, X., Li, H., Du, Z., Yang, Z., Du, Y., 2014. Isolation and Characterization of an Electrochemically Active and Cyanide-degrading Bacterium Isolated from a Microbial Fuel Cell. RSC Advances, DOI: 10.1039/C1034RA04090B. Abstract at: http://rsc.li/XbkskA