Design of chitosan gel pore structure: towards enzyme catalyzed flow-through electrodes

To improve power density derived from biofuel cell electrodes, multi-dimensional and multi-directional pore structures are highly desirable to provide mesopores, for enzyme immobilization, and highly interconnected macropores that balance the need between smaller pores that provide large active surface areas, for enhanced enzyme loading, and larger pores that provide spacious pore channels, for reduced drag on the mass transport of liquid phase fuels. Chitosan and its derivatives are considered attractive materials to achieve such objectives because the process of thermal induced phase separation can be used to fabricate porous scaffolds of defined pore structure. In this work, we discuss the fundamentals of this fabrication technique and how key process variables - freezing temperature, freezing time, acetic acid concentration, and chitosan concentration - affect the final pore structure. We also show, through proof-of-concept experimentation, that the chitosan scaffold can be used to create a working enzymatic electrode that can oxidize glucose and produce electrical current more effectively than if the same electrode was made of a chitosan film using the drop-casting technique. Future applications include the development of "flow-through'' electrodes for use in biofuel cells.