Team:Reading/Fuel Cell

Introduction

Contents

All fuel cells adhere to a basic design. On this page we'll introduce how they work, then show you some of our own. You can also check out plans for making a large rooftop panel, and head over to the human practices page to see how we'd pass the regulatory requirements.

1. Introduction
2. Fuel Cell Design
3. Our Fuel Cells
4. Scaling it up

Fuel Cell Design

A fuel cell is different from other cells (like batteries) in that there is a continuously replenished source of energy involved; the most common example of a fuel cell is a Hydrogen Cell, which takes continuous inputs of pure Hydrogen and atmospheric Oxygen to create water, generate energy.

In our cells, microorganisms are constantly doing work to generate energy, but need fuelling over time. Yeast cells are more traditional, requiring sugars to keep alive and generating energy. On the other hand, our cyanobacterial cell uses solar energy to stay alive, only needing an inorganic carbon source (such as carbon dioxide), water, and low levels of minerals to continue to be productive.

Our Fuel Cells

A look at some of our fuel cells, whether they're cyanobacterial, yeast, or just plain ol' mud.

Scaling it up

At a laboratory scale, our cell gets rapidly outperformed by an AA battery. However, our intent was to create a fuel cell that can outperform standard solar cells on cost, ease of use and maintenance, with the aim of providing easy power sources for incredibly remote locations. Since our cells work with minimal media, it is possible to use sterilised pond water as the base, meaning you don't have to transport perfect media to the desired location. We have tested this by UV-sterilising pond water using the SODIS method, then passing the pond water through a rudimentary filter. UV-sterilisation is done using normal PET plastic bottles that would be easily available in less-developed countries. Rags or old pieces of clothing could be used as a filter to remove larger pieces of debris or plant material. We used PET bottles and paper towels, then added our cyanobacteria to the water. We would expect pond water to contain the low levels of iron and minerals required by our organism, though not necessarily in optimal concentrations, allowing Synechocystis to grow. In our experiment, Synechocystis grew as expected; you can our pond water cultures thriving below.

Synechocystis can be frozen for transport or just kept alive on plates for shipping. The benefit of using microorganisms is that large liquid batches do not need to be transported; due to their reasonably fast growth (doubling time is around 12 hours), cultures could grow up in a matter of weeks. This allows scalability based on the needs and available space at the target location. Even in non-remote areas, our fuel cell can out-perform standard solar cells on price, paying for their initial investment in just 30% of the time. With no high cost components, long-term maintenance is also cheap and easy.

We wanted to plan out the system we would set up on each roof. To do this, we envisioned how it would work on a rooftop in our university or on the roof of a person's house. The hypothetical situation we considered is panels large enough to fit on an average roof. The system would be set up by using large, flat, pre-sterilised containers, contained the sterile carbon fibre electrodes. Cyanobacteria would be cultured in a separate facility, and added to the anodic chamber of the container once a suitable density was reached. The electron acceptor, which would probably be potassium ferricyanide, would be added to the cathodic chamber. The two chamber sit horizontally in the panel, with the anode on top. This allows light to penetrate the panel and reach our cyanobacteria, which then donate electrons to the carbon fibre anode that they are growing on. A proton-permeable membrane separates the two compartments, as with a normal fuel cell.

The system would be sealed and transported to the site (either the university or a private property), so that our system is completely sealed when it leaves our factory. As nutrients in the media, and CO₂, would decrease over time, we may need to use a drip in/drip out system, where users would attach a fresh tank of minimal media to drip in, and a waste tank fills up. Waste disposal is a key issue when considering risks associated with GM work. Our system would use a filter, so that the waste water was completely GMM-free and could be disposed of down a normal drain. The filter would need to be replaced at certain points (with the old one being collected for sterilisation) to prevent it clogging. Furthermore, long-term installations would need a source of low-level CO₂. Air level is sufficient for this. We would need to pump sterile air through the panel to maintain low CO₂ conditions; alternatively, sodium hydrogen carbonate could be added in low amounts to the medium prior to shipping. The panel may also need an access point where a maintenance worker could easily, but securely, take a sample from the panel to check that biological controls, such as engineered auxotrophy, were still functional.

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