Molecular Design of Glucose Biofuel Cell Electrodes

The possibility to harvest energy out of nontoxic and noncombustible compounds such as sugar opened the way for glucose biofuel cells, a research field with steady growing interest. Biological catalysts, enzymes, have the capacity to efficiently oxidize sugars and, in particular, glucose, mostly in a two-electron oxidation process, at neutral pH and ambient temperature with high efficiencies and a unique selectivity. Such enzymes can be used as catalysts in isolated form (enzymatic biofuel cells) or even in cells (microbial fuel cells). Enzymatic biofuel cells provide promising power densities and can be integrated in miniaturized portable devices, whereas microbial biofuel cells win over lifetime due to the natural regeneration of living cells. However, one constant challenge of these power generators is the transfer of electrons involved in the redox reactions to an external circuit. Small redox-active molecules with appropriate redox potentials might be the solution for this drawback. Furthermore, molecular functions can specifically interact with a domain of the protein shell of enzymes that enables oriented immobilization leading to a direct electron transfer between the enzyme and the electrode material. This chapter reviews the principles and promising examples of molecular designs for glucose biofuel cells emphasizing enzymatic biofuel cells.