3D printed microbial fuel cells for customized design and volume manufacturing

With the increased global population, we need clean water and energy more than ever. While nearly two third of our earth surface is covered with sea or ocean water, due to high salinity and impurity, we need means to purify it. All available options including widely used Reverse Osmosis consume large-scale power while purifying the water. Thus, it becomes a nefarious water-energy nexus for many countries to optimally manage their bioresource. In that regard, Microbial Fuel Cells (MFCs) offer promise to serve the purpose of purification in an energy efficient manner as it can generate power during the purification process. However, due to its fundamental dependency on bio-electrochemical reaction, research and development is inherently slow. It is exemplified by complex manufacturability of the cells too. Here we show, introduction of additive manufacturing process like 3D printing to rapidly prototype MFCs with uncompromised performance when compared to traditional MFCs. With 150 W, the obtained maximum power density of the 3D printed MFC is 633 mW/m2, the current density is 1.5 A/m2 and the cell potential was 0.30 V, whereas the traditional MFC shows the maximum power density of 505 mW/m2 and the maximum current density of 1.08 A/m2 and the cell potential was 0.32 V. Voltammetry analysis of the anodic biofilms for the two types of MFC reactors showed similar voltammetric response.

Rapid Evaluation of Power Degradation in Series Connection of Single Feeding Microsized Microbial Fuel Cells

We have developed a sustainable, single feeding, microsized, air-cathode and membrane-free microbial fuel cells with a volume of 40 μL each, which we have used for rapid evaluation of power generation and viability of a series array of three cells seeking higher voltage levels. Contrary to expectations, the achieved power density was modest (45 mW m−3), limited due to non-uniformities in assembly and the single-channel feeding system. 

Rojas, J. P., Alqarni, W. and Hussain, M. M. (2014), Rapid Evaluation of Power Degradation in Series Connection of Single Feeding Microsized Microbial Fuel Cells. Energy Technology, 2: 673–676. doi:10.1002/ente.201402035 

Sustainable Design of High Performance Micro-sized Microbial Fuel Cell with Carbon Nanotube Anode and Air Cathode 

Microbial fuel cells (MFCs) are a promising alternative energy source that both generates electricity and cleans water. Fueled by liquid wastes such as wastewater or industrial wastes, the microbial fuel cell converts waste into energy. Microsized MFCs are essentially miniature energy harvesters that can be used to power on-chip electronics, lab-on-a-chip devices, and/or sensors. As MFCs are a relatively new technology, microsized MFCs are also an important rapid testing platform for the comparison and introduction of new conditions or materials into macroscale MFCs, especially nanoscale materials that have high potential for enhanced power production. Here we report a 75 μL microsized MFC on silicon using CMOS-compatible processes and employ a novel nanomaterial with exceptional electrochemical properties, multiwalled carbon nanotubes (MWCNTs), as the on-chip anode. We used this device to compare the usage of the more commonly used but highly expensive anode material gold, as well as a more inexpensive substitute, nickel. This is the first anode material study done using the most sustainably designed microsized MFC to date, which utilizes ambient oxygen as the electron acceptor with an air cathode instead of the chemical ferricyanide and without a membrane. Ferricyanide is unsustainable, as the chemical must be continuously refilled, while using oxygen, naturally found in air, makes the device mobile and is a key step in commercializing this for portable technology such as lab-on-a-chip for point-of-care diagnostics. At 880 mA/m2 and 19 mW/m2 the MWCNT anode outperformed the others in both current and power densities with between 6 and 20 times better performance. All devices were run for over 15 days, indicating a stable and high-endurance energy harvester already capable of producing enough power for ultra-low-power electronics and able to consistently power them over time. 

J. E. Mink, M. M. Hussain 

ACS Nano, 2013, 7 (8), pp 6921–6927 DOI: 10.1021/nn402103q

Graphene-Based Flexible Micrometer-Sized Microbial Fuel Cell

Microbial fuel cells harvest electrical energy produced by bacteria during the natural decomposition of organic matter. We report a micrometer-sized microbial fuel cell that is able to generate nanowatt-scale power from microliters of liquids. The sustainable design is comprised of a graphene anode, an air cathode, and a polymer-based substrate platform for flexibility. The graphene layer was grown on a nickel thin film by using chemical vapor deposition at atmospheric pressure. Our demonstration provides a low-cost option to generate useful power for lab-on-chip applications and could be promising to rapidly screen and scale up microbial fuel cells for water purification without consuming excessive power (unlike other water treatment technologies). 

Mink, J. E., Qaisi, R. M. and Hussain, M. M. (2013), Graphene-Based Flexible Micrometer-Sized Microbial Fuel Cell. Energy Technology, 1: 648–652. doi:10.1002/ente.201300085 

Role of metal/silicon semiconductor contact engineering for enhanced output current in micro-sized microbial fuel cells

We show that contact engineering plays an important role to extract the maximum performance from energy harvesters like microbial fuel cells (MFCs). We experimented with Schottky and Ohmic methods of fabricating contact areas on silicon in an MFC contact material study. We utilized the industry standard contact material, aluminum, as well as a metal, whose silicide has recently been recognized for its improved performance in smallest scale integration requirements, cobalt. Our study shows that improvements in contact engineering are not only important for device engineering but also for microsystems. 

Mink, J., Rojas, J., Rader, K. and Hussain, M. M. (2014), Role of metal/silicon semiconductor contact engineering for enhanced output current in micro-sized microbial fuel cells. Phys. Status Solidi A, 211: 551–554. doi:10.1002/pssa.201330233 

Vertically grown multi-walled carbon nanotube anode and nickel silicide integrated high performance micro-sized (1.25 mL) microbial fuel cell

Microbial fuel cells (MFCs) are an environmentally friendly method for water purification and self-sustained electricity generation using microorganisms. Microsized MFCs can also be a useful power source for lab-on-a-chip and similar integrated devices. We fabricated a 1.25 μL microsized MFC containing an anode of vertically aligned, forest type multiwalled carbon nanotubes (MWCNTs) with a nickel silicide (NiSi) contact area that produced 197 mA/m2 of current density and 392 mW/m3 of power density. The MWCNTs increased the anode surface-to-volume ratio, which improved the ability of the microorganisms to couple and transfer electrons to the anode. The use of nickel silicide also helped to boost the output current by providing a low resistance contact area to more efficiently shuttle electrons from the anode out of the device. 

J. E. Mink, J. P. Rojas, B. E. Logan, M. M. Hussain

Nano Lett., 2012, 12 (2), pp 791–795 DOI: 10.1021/nl203801h