Over the last decade, there has been substantial research on immobilizing enzymes at electrode surfaces for use in biofuel cells [12,14-15]. These immobilization strategies have been successful at increasing biofuel cell lifetimes to 7-10 days

[15]. Therefore, one of the main obstacles that is still plaguing enzyme-based biofuel cells is the ability to immobilize the enzyme in a membrane at the electrode surface that will extend the lifetime of the enzyme and form a mechan­ically and chemically stable layer, while not forming a capacitive region at the electrode surface.

The problem associated with bioelectrodes as reported in the literature is ineffective techniques for enzyme immobilization [16]. The most common tech­niques used are sandwich [17] or wired [16,18]. However, sandwich and wired techniques still leave the enzyme exposed to the matrix, so the enzyme’s three­dimensional configuration can change due to the harsh physical and chemical forces resulting in the loss of optimal enzymatic activity [14,16,18,19].

To solve these issues and offer a more stable enzyme immobilization, researchers have employed a micellar polymer (Nafion®). Nafion® is a perfluori — nated ion exchange polymer that has excellent properties as an ion conductor and has been widely employed to modify electrodes for a variety of sensor and fuel cell applications. The molecular structure of Nafion® is shown in Figure 12.2. Nafion® is a cation exchange polymer that has superselectivity against anions. Nafion® also preconcentrates cations at the electrode surface and serves as a protective coating for the electrode. A simple approach to obtain selective elec­trodes is performed by solvent casting of the Nafion® polymer directly onto the electrode surface. Nafion® can be employed for enzyme immobilization in three different ways by employing either the wired technique, sandwich technique, or entrapment technique [20].