Microbial fuel cells were first suggested before the First World War, but it is a technology that is yet to reach maturity more than a century later. However, researchers at The University of Rochester, New York, USA, believe that MFCs still hold great promise, perhaps for niche applications where conventional fuel cells or batteries are too risky to use. The researchers have now made such significant progress towards an efficient and viable MFC that they may well have found the niche that could take this field forwards.
Chemistry professor Kara Bren and postdoctoral fellow Peter Lamberg have developed a bioelectrochemical system that uses bacteria found in wastewater and an electrode made from paper coated with carbon paste. They use this proof-of-concept system to propose that carbon paste paper electrodes could be used to build a tenable MFC. Until now, the electrodes used in fuel cells running with wastewater have been made of metal which is prone to rapid corrosion, others have used carbon felt, which is less costly but becomes clogged up and ineffective. The Rochester team's solution was to simply replace the carbon felt with paper coated with a carbon paste, basically a mixture of graphite and mineral oil. This carbon paste-paper electrode is not only cheaper and easier to prepare but outperforms the carbon felt, the team reports. Indeed, "the paper electrode has more than twice the current density than the felt model," explains Bren. [Lamberg et al., ACS Energy Lett (2016), 1(5), 895-898; DOI: 10.1021/acsenergylett.6b00435]
The team built their electrode with a layered sandwich of paper, carbon paste, a conducting polymer, and a film of the bacteria. This is easily constructed but despite its simplicity has an output of 2.24 Amps per square meter. By comparison felt anodes in their system have a current density of just 0.94 Amps per square meter.
The carbon paste is essential to the functionality of the fuel cell because it can suck up the electrons released by bacterial metabolic action. In the present example, Bren used Shewanella oneidensis MR-1, a microbial species found in wastewater that can sequester toxic heavy metal ions and in so doing releases electrons. Once transferred to the carbon coating of the anode, those electrons will wend their way to the platinum cathode whereby a current flows as the electrochemical counter reaction occurs on the platinum surface.
"We've come up with an electrode that's simple, inexpensive, and more efficient," explains Lamberg. "As a result, it will be easy to modify it for further study and applications in the future."
Bren points out that the ease of preparation of these electrodes facilitates making different derivatives."We would like to test how different additives may enhance biofilm growth and longevity and extracellular electron transfer," she says. "In addition, we are interested in using systems like this to provide electrons to chemical reactions of interest." Ultimately, of course, the experiments were undertaken as a way to develop and test a cheap and easy to construct new anode material that could be used in MFCs.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".