Some Basic Concepts Related to Fuel Cells with a Focus on Microbial and Enzymatic Fuel Cells Nevin Longenecker John Adams High School

The PURPOSES of this investigation were to examine and evaluate variables associated with increasing the efficiency of a microbial fuel cell . propose and construct a prototype enzymatic fuel cell based on the previous findings. describe in an educational science journal an inexpensive fuel cell which could be easily constructed and used in a classroom. The operation of such a cell would have diverse applications in many sciences and would integrate mathematical principles from calculus, statistics, algebra and geometry.

Advantages of Fuel Cells vs. Internal Combustion Engines Unlimited supply of fuel No reliance on foreign oil Little or no pollutants Much higher energy conversion % No moving parts No noise

How Does it Work? ^ V V Anode Chamber Often Platinum Catalyst Cathode Chamber Exposed to air <-- Anode Chamber Stores fuel --> ^ Membrane - Allows for H+ passage

Microbial Fuel Cells

Procedures A prototype microbial fuel cell was designed and built. (next slide) Factors affecting microbial fuel cell efficiency were measured and evaluated. Surface area of electrodes Bacterial conc. on anode/in solution Aerobic vs anaerobic conditions Supplemental O2 sources Single and mixtures of enzymes were tested in the prototype cell to compare power output.

Significant Factors Affecting Microbial Fuel Cell Operation Type of electrodes Surface area of electrodes Use of catalysts on electrodes and PEM Conc. of hydrocarbon in anode chamber Agitation of hydrocarbon molecules Rate of replacement of hydrocarbons Types of microbes/enzymes Conc. of microbes/enzymes

Examples of microbial-based fuel cells Microbe Substrate Mediator Anode Voltage E coli Glucose Methylene Blue Pt- C-cloth 625mV Bacillus subtilis Thionine Vitreous Carbon 640mV Acetate Neutral red Graphite felt 250mV Pseudomona s methanica Methane 1-Naphthol-2- Sulfonate indo- 2,6 dichlorophenol Pt-black 550mV Proteus vulgaris Sucrose Carbon rod 350mV

Significant Factors Affecting Microbial Fuel Cell Operation Types of mediators Conc. of mediators Distance between electrode and PEM Type of proton exchange membrane(PEM) Surface area of PEM Source of oxygen Temperature effects

Pseudomonas sp.

Mediator Shuttling Electrons

Types of Electrodes

Power Output C rod vs C cloth -aerobic E coli

Carbon Rod and Carbon Fiber Electrodes

Power Output of C rod Biofilm vs C rod Solution –anaerobic Ecoli

Proposed Advantages of Enzyme Use 1. Immediate contact with substrate 2. Elimination of metabolism of substrate by bacteria 3. Elimination of possible mixing of hazardous bacterial types 4. If immobilized on electrodes, no mediators are required.

Immobilized Enzyme /Cathode Interaction

Glucose Dehydrogenase

Partial Composition of PEB Enzyme Solution Lipase Protease Amylase Hydrolase Likely-dehydrogenases, lactase, decarboxylase, invertase Supplied by Enzyme Solutions, Inc

PEB EnzymeTrial –anaerobic-C rod

PEB Trial C rod Cathode vs Pt Cathode

Total Power Output in 22 hrs

Long Term PEB Enzyme Action

PEB Investigation Trends and Conclusions 1. Optimum power output developed in 2hrs Whole Ecoli cells PEB solution 0.2 watts/m2 2.1 watts/m2 2. Prolonged power output at 24 hrs 0.14 watts/m2 2.05 watts/m2 3. Prolonged optimum power output continued for 5 days. 4. Pt. coating on the anode did not improve the efficiency of the enzymatic cell.

Uses for Implantable Enzymatic Fuel Cells (To utilize arterial glucose and oxygen with immobilized enzymes on electrodes in a noncompartmentalized cell) Micropumps-insulin, pain meds, arthritis Current for-nerve stimulation, hearing aids Heart pacemaker (cells in series)

Immobilized Enzymes on Electrodes

Implantable Arterial Fuel Cell

Additional Uses of Enzymatic Fuel Cells Space-regeneration of human waste Treatment of human waste in developing countries Treatment of household wastes in place of landfills Industry-detoxify chemical wastes Portable units- power generation

Acknowledgments University of Notre Dame RET Program Dr. Alex Hahn Dr. Robert Nerenberg Dr. Valli Sarveswaran