“All power created in this device is useable because no electricity is needed to run the fluids through the device. This is crucial in the advancement of these devices and the expansion of their applications.”Nastaran Hashemi
Scientists from Iowa State University have demonstrated a 3D paper-based microbial fuel cell (MFC) that uses capillary action to guide the liquids through the MFC system, doing away with the need for an external power source. The proof-of-concept findings indicate that the MFCs can develop power in an environmentally friendly way operating under continuous flow condition.
As reported in TECHNOLOGY [Hashemi et al. Technology (2016) DOI 10.1142/S2339547816400124], the device was shown to run for five days due to the production of current as a result of biofilm formation on the anode. Previous studies on power production from paper-based MFCs did not run for as long and, with insufficient time for the biofilm to form, the reported current and power data would mostly be associated with extracellular electron transfer, which does not fully represent the electrical producing capabilities of MFCs.
Although MFCs have become more used as a viable and environmentally friendly alternative for energy production, and interest in the role of paper as a main platform or part of energy storage and conversion has increased, there remain challenges in miniaturizing the system for application in smaller devices. In addition, the short duration of operation have limited their application.
The length of time in this study meant the team could fully investigate the role of biofilm formation on the anode and its effect of electron transport mechanisms. As senior author Nastaran Hashemi points out, “All power created in this device is useable because no electricity is needed to run the fluids through the device. This is crucial in the advancement of these devices and the expansion of their applications.”
The biofilm formation on the carbon cloth offers greater proof that the current measured was due to the bio-chemical reaction taking place, key as the biofilm plays an important role in the production of MFCs. Larger and thicker biofilms could lead to increased current production. Single bacterial cells metabolize electron-rich substances in a process that involves numerous enzyme-catalyzed reactions, allowing the electrons to move to the anode.
For the S. Oneidensis MR-1 used, the best known means of moving electrons from bacteria cells to the anode are through direct contact, biological nanowires or excreted soluble redox molecules, with the last of these seen as serving the extracellular electron shuttling that comprises up to 70% of electron transfer mechanisms from individual bacterial cells to the electrode.
The team is now looking to identify ways to better control the voltage output and create constant current, as this will help in the regulation of the systems output and provide more stable results, and also to explore the design of materials with specific properties to further enable such technology.