Researchers at Penn State Show Increased Hydrogen Yield in Membrane-less Microbial Electrolysis Cell
Researchers at Penn State have obtained hydrogen yields from a membrane-less microbial electrolysis cell (MEC) that is double the amount obtained in previous MEC studies. Prior work has assumed that a membrane is needed in an MEC to avoid hydrogen losses due to bacterial consumption of the product gas.
This new research, led by Dr. Bruce Logan, Kappe Professor of Environmental Engineering, demonstrates that high hydrogen recovery and production rates are possible in a single chamber MEC without a membrane, and suggests the potential reduction in cost of these systems, allowing for new and simpler designs.
In 2007, Logan and his colleagues published a paper in the Proceedings of the National Academy of Sciences describing their development of a method based on their successful work with microbial fuel cells (MFCs) to convert cellulose and other biodegradable organic materials directly into hydrogen. (Earlier post.)
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 production of hydrogen gas by electrohydrogenesis in microbial electrolysis cells (MECs) is at greater yields than fermentation and at greater energy efficiencies than water electrolysis, according to Logan and team’s findings.
With the membrane-less system, the researchers achieved high cathodic hydrogen recoveries (78 ± 1% to 96 ± 1%) despite the absence of a membrane between the electrodes. Through the use of a membrane-less system, a graphite fiber brush anode, and close electrode spacing, hydrogen production rates reached a maximum of 3.12 ± 0.02 m3 H2/m3 reactor per day at an applied voltage of Eap = 0.8 V. This production rate is more than double that obtained in previous MEC studies.
Overall energy efficiency relative to both Eap and energy of the substrate averaged 78 ± 4%, with a maximum of 86 ± 2% (1.02 ± 0.05 m3 H2/m3 day, Eap = 0.4 V).