I imagine you’re all pretty familiar with fuel cell technology at this point. It’s been around for quite some time and is often heralded as the answer to green, renewable energy. For the most part that is quite true, as there are a number of advantages that this technology has over current combustion-based options. It not only produces smaller amounts of greenhouse gases, but none of the air pollutants associated with health problems.
That being said, the technology isn’t perfect, with many improvements still to be made. One problem is that a fuel cell’s environmental impact depends greatly on how the fuel is acquired. For example, the by-products of a Hydrogen (H2) fuel cell may only be heat and water, but if electricity from the power grid is used to produced the H2 fuel then CO2 emissions are still too high.
The technology also requires the use of expensive or rare materials. Platinum (Pt) is easily the most commonly used catalyst in current fuel cell technology, and this is a rare metal often costing around 1000 US dollars per ounce. This really hurts the commercial viability of the fuel cell, but research regarding alternative materials is progressing.
While I’m certain these kinks will be worked out eventually, it is still worth considering other options. One such option is the Microbial Fuel Cell (MFC), a bio-electrochemical device that uses respiring microbes to convert an organic fuel into electrical energy. These already have several advantages over conventional fuel cell technology, primarily due to the fact that bacteria are used as the catalyst.
The basic structure of an MFC is shown in Figure 1, and you can see that it closely resembles that of a conventional fuel cell. In fact the method by which it produces electricity is exactly the same, the only differences are the fuel and the catalyst.
The fuel for an MFC is often an organic molecule that can be used in respiration. In the figure it is shown to be glucose, and you can see that its oxidation yields both electrons and protons. It is worth noting that the species shown as “MED” is a mediator molecule used to transfer the electrons from the bacteria to the anode. Such molecules are no longer necessary, as most MFCs now use electrochemically active bacteria known as “Exoelectrogens”. These bacteria can directly transfer electrons to the anode surface via a specialised protein.
As I mentioned before, this technology has several advantages over conventional fuel cell technology in terms of cost and environmental impact. Not only are bacteria both common and inexpensive when compared to Pt, but some can respire waste molecules from other processes. This not only means that less waste would be sent to a landfill, but would actually be a source of energy. This has already be applied in some waste-water treatment plants, with the MFCs producing a great deal of energy while also removing waste molecules.
Now you’re probably thinking, “Nathan, this is all well and good, but it’s not exactly new technology”. You’d be right there, but some scientists from the Universities of Bristol and West England have made a big improvement. They have designed an MFC that is entirely biodegradable! The research was published in the journal ChemSusChem in July of 2015, and it represents a great improvement in further reducing the environmental impact of these fuel cells.
Many materials were tried and tested during the construction process. Natural rubber was used as the membrane (see Figure 1), the frame of the cell was produced from polylactic acid (PLA) using 3D printing techniques, and the anode was made from Carbon veil with a polyvinyl alcohol (PVA) binder. All of these materials are readily biodegradable with the exception of the Carbon veil, but this is known to be benign to the environment.
The cathode proved to be more difficult, with many materials being tested for conductivity and biodegradability. The authors noted that conductive synthetic latex (CSL) can be an effective cathode material, but lacks the essential biodegradability. While this meant it couldn’t be used in the fuel cell, it was used as a comparison when measuring the conductivity of other materials.
Testing then continued with egg-based and a gelatin-based mixtures being the next candidates. While both of these were conductive, they weren’t nearly good enough to be used. CSL actually performed 5 times better than either of them. But science can not be beaten so easily! Both mixtures were improved by modification with lanolin, a fatty substance found in Sheep wool, which is known to be biodegradable. This caused a drastic increase in performance for both mixtures, with the egg-based one outperforming CSL! This increase easily made it the best choice for the cathode.
With all the materials now decided, it was time to begin construction on the fuel cell. A total of 40 cells were made and arranged in various configurations. These are shown in Figure 2, and each configuration was tested to determine its performance. Of these three, the stack shown in Figure 2C was found to be able to continuously power an LED that was directly connected. It was also connected to some circuitry that harvested and stored the energy produced, and the authors report that the electricity produced by this method could power a range of applications.
While there is much to celebrate here, the authors also address some of the concerns associated with this technology. The most notable concern is how long the fuel cells can operate, and the authors report that after 5 months of operation the stacks were still producing power. This could potentially be longer in an application, as the operational environment of a fuel cell rarely mimics natural conditions.
They also discuss how these MFCs didn’t perform as well as some produced in other studies, but these were the first to be made from cheap, environmentally friendly materials. If anything, this research shows that such fuel cells can at least be functional, and are an excellent target for further research.
So we’ll have to wait for more research to see if this technology will actually take off, and given the timescale of this study it’s likely that we’ll be waiting quite some time. Even so, this is an important step on the road to completely sustainable living, as it shows that even our power sources could be made from completely environmentally friendly materials. Now we just have to hope people take notice. Let’s make sure they do!
Sources not mentioned in text:
- Altenergy.org,. What are Microbial Fuel Cells? – How do fuel cells work, Info on Microbial Fuel Cells. Retrieved 26 January 2016, from http://www.altenergy.org/renewables/what-are-microbial-fuel-cells.html
- Empa. (2015, July 15). Are fuel cells environmentally friendly? Not always.ScienceDaily. Retrieved January 26, 2016 from http://www.sciencedaily.com/releases/2015/07/150715113313.htm
- National Geographic,. Fuel Cells Information, Fuel Cells Facts, Fuel Cells Technology – National Geographic. Retrieved 26 January 2016, from http://environment.nationalgeographic.com/environment/global-warming/fuel-cell-profile/
- Rahimnejad, M., Adhami, A., Darvari, S., Zirepour, A., & Oh, S. (2015). Microbial fuel cell as new technology for bioelectricity generation: A review. Alexandria Engineering Journal, 54(3), 745-756. http://dx.doi.org/10.1016/j.aej.2015.03.031