Nanobiocatalysis For Biofuel Cells

Research Objectives:

The objectives of this research are to understand, characterize, and improve enzymatic biofuel cell (BFC) systems with the long term goal being to eventually develop the knowledge necessary to commercialize miniature systems for in vivo applications. In order to realize this long term goal, improving enzyme immobilization techniques to increase its direct electron transfer (DET) efficiency and/or mediated electron transfer (MET) efficiency as well as it long term stability are our primary focus.

What is a Biofuel Cell?

A biofuel cell is simply a fuel cell which uses some biological product to catalyze the anode and/or cathode reactions. Two major classes are enzyme based cells and microorganism based cells. We are focused on cells which utilize glucose oxidase (GOx) as a model enzyme to catalyze the glucose oxidation and generate the electrical power from sugars. We have chosen GOx because glucose, the fuel which GOx oxidizes, is abundant in nature, including plants and animals. GOx is also one of the most studied enzymes; a breadth of knowledge about this molecule is currently available. Figure 1 is an image a BFC with a footprint smaller than a US penny which we have created and optimized. The design is quite simple, consisting of a fuel storage reservoir, anode and cathode current collectors, and a membrane electrode assembly (MEA). A schematic is also shown in Figure 2(A).

Figure 1: Penny Sized Biofuel Cell	Figure 2: (A) Biofuel Cell Assembly Diagram and (B) Its VI and Power Density Plots

How does a Biofuel Cell Work?

The biofuel cells (BFCs) shown above convert sugar (glucose) and atmospheric oxygen to gluconolactone and water, while producing electrical power in the process. At the anode, immobilized GOx reacts with glucose to release two electrons and two protons. These electrons are then captured by benzoquinone (BQ) which shuttles the electrons to the anode current collector. Meanwhile, the protons diffuse through the membrane portion of the MEA. At the cathode, the protons combine with electrons and oxygen to form water, which then evaporates away. A schematic of this process is shown in Figure 3.

Figure 3: Working Principle of Biofuel Cell

The two largest obstacles with BFCs which must be overcome are increasing the power density and increasing the enzyme stability. In collaboration with Dr. Kim of Korean University (Seoul, South Korea), we have developed and characterized a novel enzyme immobilization technique which we have named “crosslinked enzyme clusters” or CEC (See Figure 4). Through the procedure shown in Figure 4 we are able to precipitate GOx and then crosslink them to create enzyme aggregates which show an unprecedented level of stability and also an impressive activity.

Figure 4: Nanobiocatalysis	Figure 5: Schematic Diagram of Biofuel Cell Powering Glucose Sensor in Human Blood Stream. (A) Schematic Diagram and (B) AFM Image of Our Nanobiocatalysis (GOx on CNT via CEC method)

Applications of Biofuel Cells:

The most probable application of BFCs will be to use miniature cells to derive power from plants/animals to power small devices. It is believed that miniature biofuel cells could be placed within a human patient to power micro sensor/transmitter devices (such as glucose sensors for diabetics) to provide a doctor with pressure, temperature, concentration, etc. data or to power a pacemaker or bladder control valve. It is also believed that these miniature BFCs could be used by the military to derive power from either trees or insects to power chemical or biological agent sensing devices.

Figure 6: Overview of Biofuel Cell Research at WSU