Enhanced Graphite Fiber Electrodes for a Microbial Biofuel Cell Employing Marine Sediments
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Enhanced Graphite Fiber Electrodes for a Microbial Biofuel Cell Employing Marine Sediments Gregory Konesky ATH Ventures Inc., 3 Rolling Hill Rd. Hampton Bays, NY 11946 ABSTRACT A microbial biofuel cell has been demonstrated utilizing organic material in the sediment as fuel and dissolved oxygen in the overlying seawater as the oxidizer. A graphite electrode placed in the sediment acts as the anode and collects electrons both by mediated and non-mediated processes. Another graphite electrode suspended in the seawater above the sediment acts as the cathode and transfers these electrons to oxygen in the seawater. The sediment serves as a natural permeable membrane that permits hydrogen ions to flow from within the sediment and combine with the oxygen to produce water. Electrons which flow from the anode to the cathode through an interconnecting wire are used to power external circuits. Both fuel and oxidizer are naturally present and self-renewing, and the graphite electrodes are inexpensive and non-toxic. Overall, this is a very “green” fuel cell. A significant improvement in collection efficiency is demonstrated by using graphite fiber electrodes.
INTRODUCTION Microbial biofuel cells function in a similar manner to traditional hydrogen/oxygen fuel cells. In the latter case, electrons are catalytically removed from hydrogen, producing hydrogen ions (protons). The liberated electrons are collected by an electrode and flow through an external circuit, developing useable power. They then return from the circuit to a second electrode where they are transferred to oxygen. The hydrogen ions migrate across an ion-permeable membrane separating the two electrodes, where these ions combine with the oxygen to create water. In microbial biofuel cells, nutrients from the surrounding environment are metabolized by respiratory enzymes, liberating electrons. These electrons are ultimately transferred to Terminal Electron Acceptor Processes (TEAP) [1]. In aerobic organisms (such as ourselves), oxygen is the TEAP, and again, water is created. Anaerobic organisms have a much wider range of TEAPs including nitrates, sulfates and a variety of metal ions. Microorganisms in biofuel cells have their respiratory electrons “stolen” from them, either by mediated or non-mediated processes, and are transferred to a collection electrode. These electrons power an external circuit and then return to a second electrode where they are transferred to a TEAP. A microbial biofuel cell may employ oxygen as the TEAP, even though the microorganism itself is anaerobic, so that ambient air can be used as a source of oxygen. This is possible since the respiratory electron transfer occurs remotely, through a wire, so to speak, rather than by direct exposure to oxygen, which the anaerobic microorganism might find fatal. Transfer of respiratory electrons to the collection electrode may be significantly enhanced by the use of mediators. These are molecules that penetrate the cell wall of the microorganism and collect electrons from respiratory enzymes. T
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