Penn State Researchers Develop Efficient Microbial Electrolysis Cell for Hydrogen Production from a Range of Organic Substances

12 November 2007

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

Researchers at Penn State University have developed a method based on their successful work with microbial fuel cells (MFCs) (earlier post) to convert cellulose and other biodegradable organic materials directly into hydrogen. The work on microbial electrolysis cells by Bruce Logan and colleagues at Penn State University is published online in the Proceedings of the National Academy of Sciences.

The researchers used naturally occurring bacteria in a microbial electrolysis cell 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.

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.

—Bruce Logan

Water hydrolysis, a standard method for producing hydrogen, is only 50-70% 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% more available energy than the electrical energy used to produce it, according to the researchers.

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

Resources

• NSF press release