Yin Song, Varun Penmasta and Chunlei Wang

Florida International University

USA

0. Introduction

The global energy demands have increased significantly every year and current reliance on fossil fuels is unsustainable due to finite supplies from environment. In addition, the products from using fossil fuels cause pollution and global warming. Fuel cells offer an alternative solution to this issue. A fuel cell is an electrochemical cell that converts chemical energy from a fuel to electrical energy. In a fuel cell, an oxidation reaction occurs at the anode generating electrons that transfer to the cathode through the external circuit and a reduction reaction occurs at the cathode. Conventional fuel cells, for example, can be operated by using hydrogen or methanol (MeOH) as fuels to produce energy, releasing water and carbon dioxide as by-products. However, hydrogen is gaseous which gives rise to safety issues in storage and transport. Besides, many of the alternative fuels that can be used for fuel cells still rely on petroleum products. Therefore, it is well recognized that alternative sources of renewable energy are urgently required. Numerous efforts have been made to develop different power sources alternatives that are capable of performing in physiological conditions for prolonged lifetime without recharging. More recently, miniaturized medical implants such as pacemaker, defibrillator, insulin pumps, sensor-transmitter systems for animals and plants, nano-robots for drug delivery and health monitoring systems gain increasing attention which led to an upsurge in research and development in micropower source, especially, biofuel cells (Ramanavicius, 2005; Liu & Dong, 2007; Zhu et al., 2007; Moehlenbrock & Minteer, 2008 and Wang et al., 2009). Biofuel cell is a particular kind of fuel cell, which converts biochemical energy to electrical energy by using biocatalysts (Palmore & Whitesides, 1994). The two major types of biofuel cells are microbial fuel cells and enzymatic biofuel cells. Microbial fuel cells employ living cells such as microorganism as the catalyst to convert chemical energy into electricity while enzymatic biofuel cells use enzymes to catalyze the redox reaction of the fuels. In this chapter, we will first introduce both kinds of biofuel cells along with the type of catalysts used, electron transfer mechanism, electrode materials and cell performance. Then we will briefly review recent progress in miniaturized biofuel cells, which offer possibilities for implantable devices within the human body. Carbon-microelectromechanical system (C-MEMS) based miniaturized enzymatic biofuel cells are also highlighted in the chapter.