Researchers develop efficient biohydrogen production technique based on microbial electrolysis cell

Scientists from Penn State University have developed a technique to efficiently produce hydrogen from biomass via a process based on the way microbial fuel cells (MFCs) work. Bruce E. Logan, the Kappe professor of environmental engineering, and Shaoan Cheng, research associate, report the method in today's early edition of the Proceedings of the National Academy of Sciences. The report titled 'Sustainable and efficient biohydrogen production via electrohydrogenesis' is an open access article.

The new biohydrogen production method is considerably more efficient than the electrolysis of water, which, in order to produce renewable and clean hydrogen would have to rely on electricity from solar, wind, biomass or nuclear power plants.

The new technique is capable of directly generating renewable hydrogen in an environmentally friendly way from cellulose and other biodegradable organic materials. The researchers state that, contrary to cellulosic ethanol production which makes use of agricultural residues or dedicated non-food energy crops but which is at least a decade away, the biohydrogen production method can use this abundant source of biomass already today. They suggest blending the biohydrogen with methane from natural gas or biogas as a transport fuel.

The researchers used naturally occurring bacteria in a microbial electrolysis cell (MEC, picture, click to enlarge) with acetic acid – the acid found in vinegar. Acetic acid is also the predominant acid produced by fermentation of glucose or cellulose. The anode was granulated graphite, the cathode was carbon with a platinum catalyst, and they used an off-the-shelf anion exchange membrane. In other words, they basically set up a microbial fuel cell (more about MFCs here). The bacteria consume the acetic acid and release electrons and protons creating up to 0.3 volts. When more than 0.2 volts are added from an outside source, hydrogen gas bubbles up from the liquid.

The process produces 288 percent more energy in hydrogen than the electrical energy that is added to the process. Water hydrolysis, a standard method for producing hydrogen, is only 50 to 70 percent efficient. Even if the microbial electrolysis cell process is set up to bleed off some of the hydrogen to produce the added energy boost needed to sustain hydrogen production, the process still creates 144 percent more available energy than the electrical energy used to produce it:
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For those who think that a hydrogen economy is far in the future, Logan suggests that hydrogen produced from cellulose and other renewable biomass could be blended with natural gas for use in natural gas vehicles.

We drive a lot of vehicles on natural gas already. Natural gas is essentially methane. Methane burns fairly cleanly, but if we add hydrogen, it burns even more cleanly and works fine in existing natural gas combustion vehicles. - Bruce E. Logan, lead author

The range of efficiencies of hydrogen production based on electrical energy and energy in a variety of organic substances is between 63 and 82 percent. Both lactic acid and acetic acid achieve 82 percent, while unpretreated cellulose is 63 percent efficient. Glucose is 64 percent efficient.

Another potential use for microbial-electrolysis-cell produced hydrogen is in fertilizer manufacture. Currently fertilizer is produced in large factories and trucked to farms. With microbial electrolysis cells, very large farms or farm cooperatives could produce hydrogen from wood chips and then through a common process, use the nitrogen in the air to produce ammonia or nitric acid. Both of these are used directly as fertilizer or the ammonia could be used to make ammonium nitrate, sulfate or phosphate.

The researchers have filed for a patent on this work. Air Products and Chemicals, Inc. and the National Science Foundation supported the research.

According to large well-to-wheel studies, the production of hydrogen from biomass is the most efficient and cleanest production pathway out of 28 options, including hydrogen from wind, nuclear, and electricity mixes (previous post and here for a large EU-funded WTW study). For this reason, some have suggested that biohydrogen is the most feasible way of reviving the idea of the 'hydrogen economy' (earlier post).


Picture: A microbial electrolysis cell (MEC) shown with the power source used to augment the voltage produced by the bacteria. Bacteria grow in the anode chamber, forming a biofilm on graphite granules, while hydrogen gas is released at the cathode and bubbles up and into the tube on top of the reactor. Credit: Photograph by Shaoan Cheng, Penn State University

References:
Shaoan Cheng and Bruce E. Logan, "Sustainable and efficient biohydrogen production via electrohydrogenesis" [open access], Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0706379104, Published online before print November 13, 2007

Penn State Live: Clean, carbon-neutral hydrogen on the horizon - November 12, 2007.

Biopact: Microbial fuel cell development speeds up: from biopower in space to the developing world - September 30, 2007

Biopact: Biohydrogen, a way to revive the 'hydrogen economy'? - August 20, 2006