Hydrogen production with a microbial biocathode

This paper, for the first time, describes the development of a microbial biocathode for hydrogen production that is based on a naturally selected mixed culture of electrochemically active micro-organisms. This is achieved through a three-phase biocathode startup procedure that effectively turned an acetate- and hydrogen-oxidizing bioanode into a hydrogen-producing biocathode by reversing the polarity of the electrode. The microbial biocathode that was obtained in this way had a current density of about -1.2 A/m(2) at a potential of -0.7 V. This was 3.6 times higher than that of a control electrode (-0.3 A/m(2)). Furthermore, the microbial biocathode produced about 0.63 m(3) H-2/m(3) cathode liquid volume/day at a cathodic hydrogen efficiency of 49% during hydrogen yield tests, whereas the control electrode produced 0.08 m(3) H-2/m(3) cathode liquid volume/day at a cathodic hydrogen efficiency of 25%. The effluent of the biocathode chamber could be used to inoculate another electrochemical cell that subsequently also developed an identical hydrogen-producing biocathode (-1.1 A/m(2) at a potential of -0.7 V). Scanning electron micrographs of both microbial biocathodes showed a well-developed biofilm on the electrode surface.