Abstract:
A microbial fuel cell apparatus and system suitable for use for off-grid rural or remote power applications in developing countries, among others.

Description:
RELATED APPLICATION 
       [0001]    This application claims benefit of priority to Provisional U.S. Patent Application No. 60/995,482, filed Sep. 27, 2007, entitled MICROBIAL FUEL CELL WITH ANION EXCHANGE MEMBRANE AND SOLID OXIDE CATALYST; the aforementioned priority application being hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments described herein pertain to renewable fuel cells, and more particularly, to microbial fuel cells. 
       BACKGROUND 
       [0003]    A microbial fuel cell a device that converts chemical energy to electrical energy by the catalytic reaction of bacterial enzymes. A typical microbial fuel cell consists of anode and cathode chambers separated by a proton exchange membrane which allows protons to pass between the chambers. 
         [0004]    In the anode chamber, in an electro-oxidation process, organic matter, such as glucose or cellulose is oxidized by the bacterial enzymes, generating electrons and protons. Electrons are transferred to the cathode chamber through an external electric coupling, and the protons are transferred to the cathode compartment through the proton exchange membrane. Electrons and protons are consumed in an electro-reduction process at the cathode compartment, where protons react with the electrons developed from the electro-oxidation process at the anode. Taken in total, the electro-oxidation and electro-reduction processes at the anode and cathode respectively create a potential difference whereby an electrical current may be driven through the external electrical coupling. 
         [0005]    Typically a platinum catalyst has been used in conjunction with a graphite cathode to enhance the energy density of the electro-reduction process at the cathode, thereby resulting in a fuel cell having increased power. 
         [0006]    Otherwise, the low cost of biological catalysts utilized in the anode chamber and the availability of carbohydrate feedstocks make microbial fuel cells an attractive technology for off-grid rural or remote power applications in developing countries. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals indicate corresponding, analogous or similar elements, and in which: 
           [0008]      FIG. 1  is a conceptual illustration of an exemplary arrangement of a cathode-membrane assembly of the microbial fuel cell apparatus; 
           [0009]      FIG. 2  is a conceptual illustration of an exemplary arrangement of a cathode-membrane assembly integrated with an anode assembly; and 
           [0010]      FIG. 3  is a conceptual illustration of an exemplary cathode-membrane assembly and anode assembly integrated with peripheral hardware components. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  is a conceptual illustration of an exemplary arrangement of a cathode-membrane assembly  100  of the microbial fuel cell apparatus. Cathode electrode  101  may be composed of carbon, such as a graphite fabric or other forms of carbon such as activated carbon, carbon powder, carbon cloth, carbon felt, carbon particles or carbon nanotubes. The porosity of cathode electrode  101  may range from about 1% to 80% of the structure. A solid oxide catalyst  105  may be interspersed generally uniformly within the cathode. The solid oxide catalyst may be mixed to form a porous composite structure composed of an electronic material such as carbon, graphite, Pt, Au to allow ease of electron transfer in and out of the oxide cathode catalyst. The particle size of the cathode oxide catalyst may range from 1 nm to 1000 micrometers. The solid oxide catalyst may also comprise a thin film coating on cathode electrode  101 , ranging in thickness from 1 nm to 1000 micrometers generally. 
         [0012]    Examples of solid oxide catalysts which may be suitable for cathode  101  of the microbial fuel cell include materials such as the family of perovskites with ABO 3-d  composition such as Sm x Sr y CoO 3-d , Ba x La y CoO 3-d , Gd x Sr y CoO 3-d , Sr-doped Lanthanide transition metal oxides such as Ln 1-x Sr x (TM)O 3-d  where Ln=Ba, La, Ca, Sm and TM=Cr, Mn, Fe, Co, Ni, or mixtures of these. Other cathode catalysts may comprise similar Sr-doped perovskites with two TM elements at the b-site such as, for example, La 1-x Sr x (Co 1-y Fe y )O 3-d  or Ba 1-x Sr x (Co 1-y Fe y )O 3-d . Other transition metal oxides with the A 2 BO 4-d  composition such as LnSr(TM)O 4-d  where Ln=Ba, La, Ca, Sm and TM=Cr, Mn, Fe, Co, Ni, Cu, Ru. 
         [0013]    Electron collector medium  104  is in physical contact with cathode  101  to collect charge therefrom, and may be composed of a steel mesh material or other electronic conducting material, or a gas diffusion electrode. 
         [0014]    Anion exchange membrane  102  may be any anion conducting material such as Selemion anion membrane from Asahi Glass Co. Ltd. of Japan, Neosepta anion membrane from Tokuyama Soda Co. Ltd. of Japan, Morgane anion membrane from Solvay SA of Belgium and other similar anion conducting membranes used in chemical separation, alkaline fuel cells and desalination systems. Other materials used may be aqueous-based, such as water and KOH solution, or composite mixtures of ion exchange/inert backbone material. 
         [0015]    A retaining layer  103 , composed for example of a plastic net material, may be optionally used to complete the cathode-membrane assembly  100  by keeping the cathode-membrane assembly  100  components compactly together. 
         [0016]      FIG. 2  is a conceptual illustration of an exemplary arrangement of a cathode-membrane assembly  100  integrated with an anode assembly. The anode electrode  201  is typically composed of carbon, such as of a porous carbon foam material, carbon cloth, carbon felt, carbon particles, activated carbon, carbon nanotubes, such as of a porous carbon foam material that maximizes its surface area. Anode  201  resides in a chamber  202  which is filled with an aqueous-based electrolyte medium, and anode  201  is receptive to electrons developed from a reaction of bacterial anode enzyme with organic nutrient in chamber  202 . The organic fuel that can be utilized in the microbial fuel cell can be composed of any organic matter that comprises hydrogen and oxygen or carbon. Examples of this would be cellulose, ethanol, acetate, alcohols, human waste, agricultural waste, starch, farm animal waste, and industrial organics waste. 
         [0017]    The bacterial anode enzyme utilized in the microbial fuel cell can be composed of a singular organism or a community culture that metabolizes the organic fuel and converts this into lower molecular weight organics such as alcohols with evolution of by products such as CO2 gas, CH4 gas, protons and electrons. 
         [0018]    For single organism cultures, examples such as the Genus  Clostridium , such as  Clostridium cellulovorans, Clostridium celluliticum , that digest cellulose directly would be utilized to produce protons and electrons for reaction in the MFC and electrons to power the external load. 
         [0019]    For community cultures, mixtures that contain bacteria such as  E. Coli , Genus  Clostridium , Genus  Rhodoferax  such as  Rhodoferax Ferireducens, Geobacter metallireducens  to breakdown cellulose and its sub-units to produce protons for reaction in the microbial fuel cell and electrons to flow around a complete electrical circuit. Resistive load  203  provides an electrical coupling from anode  201  to electron collector medium  104  at cathode  101 . Resistive load  203  may also be directly coupled to cathode  101 , alternatively. 
         [0020]      FIG. 3  is a conceptual illustration of an exemplary cathode-membrane assembly  100  and anode assembly integrated with peripheral hardware components. Lid  301  and sealing gasket  303  provide the means to secure the cathode-membrane assembly  100  to chamber  202 . Lid  301  may be of plastic material, such as acrylic, and of slotted construction to allow availability of oxygen from the air for the electro-reduction process at cathode  101 . The complete cathode-membrane assembly  100  disposed on lid  301  may be affixed onto chamber  202  by use of a suitable quick-release locking mechanisms, such as thumbscrews. This would allow easy access to chamber  202  for replenishing the organic fuel and bacterial enzyme mixture. 
         [0021]    Sealing gasket  304  may be disposed on rim  302  of chamber  202 , to enable the cathode-membrane assembly  100  to be compressively sealed against chamber  202 . In this way, it would also be possible to aerobically seal chamber  202 , to allow bacterial enzyme in chamber  202  to undergo anaerobic respiration in aid of the electro-oxidation process at anode  201 . 
         [0022]    Another embodiment of the invention provides a method of generating electrical power for an electrical charging device, such as for powering a cell phone charger. In this case, electrical power generated by operation of the microbial fuel cell is used to power a cell phone charger device, represented by resistive load  203 . The electrical coupling may be adapted to include leads  204  and  205  from the cathode and anode respectively with suitable commercial terminations to enable easy and rapid plug-in or connection to the electrical charging device. 
         [0023]    Another embodiment of the invention provides a method of generating electrical power for direct use in operating a light emitting device such as a bulb or LED. This can also be used to directly operate a radio and other electronic appliances, represented by resistive load  203 . 
         [0024]    Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments. As such, many modifications and variations will be apparent to practitioners skilled in this art. Accordingly, it is intended that the scope of the invention be defined by the following claims and their equivalents. Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mentioned of the particular feature. Thus, the absence of describing combinations should not preclude the inventor from claiming rights to such combinations.