In situ characterizations of porous media for applications in biofuel cells: Issues and challenges

Porous media in either electrode configurations or membranes used in biofuel cell applications are often required to have specific functionalities for use in aqueous solutions at nearly neutral pH (Atanassov et al. 2007). These unique requirements and operating conditions can only be better understood by in situ characterizations that combine both physical and chemical analyses in a noninvasive manner (Minteer et al. 2007; Cooney and Liaw 2008). The functionalities of these porous media also need to be studied in small physical dimensions from biological species on the order of a few nanometers to pore structures covering the entire range of micropores to macropores; that is, a wide range of volume, surface area, or thickness shall be involved. Some of the characterizations (in situ in solutions) can hardly be achieved by conventional physical or chemical characterization techniques (e.g., porosimetry or nanoscale imaging), nor can they be accomplished easily with sufficient accuracy. Furthermore, additional issues with ex situ characterizations can also emerge. For instance, misleading results associated with exposure to the ex situ environment during sample preparation or characterization may inhibit interpretations of the underlying surface or interface phenomena. Facing these problems, one shall find that in situ characterizations are thus more desirable, critical, and necessary for defining the properties of the porous media used in such applications.