Bio micro fuel cell grand challenge final report.

Abstract

Executive SummaryThis LDRD was conceived to develop a power system that could harvest the energy from carbohydrate fuels that are readily available and can be harvested from biological sources. This included the possibilities of generating power from harvested tree sap, sugars, and even mammalian blood. Since the biological host continues to produce and/or replace these fuels as part its normal biological processes, this approach enables a very long lived, power microsystem. Fuel cells were identified as the energy conversion systems most likely to take advantage of the opportunities of a continuous fuel supply, and therefore the project started from an existing foundation in traditional fuel cell operations.Six basic subtasks were identified for this project; harvesting, membrane separation, catalysis, architecture, enzymology, and power management. Harvesting targeted both harvesting from a tree using a simple spile arrangement, and harvesting through the skin of mammalian hosts using a microneedle patch. Membrane separation provided a physical separator between the anode oxidation of the fuel and the cathodic reduction of oxygen. The catalysis team targeted both the development of new, poison resistant, highly active noble metal catalysts that could readily oxidize the carbohydrate fuel without poisoning the catalysts, and also worked to develop mediator molecules to transport oxidized electrons from enzyme catalysts to anode electrode surfaces. The enzymology team developed protocols for the genetic engineering of enzymes capable of oxidizing the carbohydrates, and also looked into the requirements to immobilize these enzymes against an electrode, together with the catalysis team. The architecture team was tasked with developing a small architecture that could take in these other components and assemble them into working fuel cells running on glucose (a simple carbohydrate) and oxygen. The power management task, added after the initial program was started, focused on handling the variation in the power output from the fuel cells and in turn producing stable, electronic grade power to supply to an external circuit.At the end of the project, the best power generated from a single, 15mm x 21mm x 1mm fuel cell was about 7 mW/cm 2 running on 1 molar (M) glucose in water and oxygen at room temperature. This was achieved using a noble metal catalyst. The best enzymatic fuel cell using an anode based on glucose oxidase was able to demonstrate 5 250μW/cm 2 of power from a 50 millimolar glucose solution. In both cases, however, the lifetime was limited to a few minutes . In the noble metal case, oxidation byproducts quickly poison the catalysts. However, a system solution for in situ cleaning of the anode with little power penalty eventually extending the lifetime to about 700 hours (nearly one month) while producing about 2 mW/cm 2 . In the enzymatic case, the lifetime was limited to minutes of operation by the loss of enzyme and mediator to the flowing fuel.Significant progress was made in stabilizing the enzyme, bu...