(29a) Pem Fuel Cells - Challenge in Science and Technology

Fuel cells are moving past the development stage and into trials for real applications. They are the most promising energy source for transportation, heating and power generation. In a fuel cell, hydrogen is ionized to produce an electrical current and then the hydrogen ion reacts with oxygen to form water and heat. The perceived benefits include high efficiency, efficiency relatively independent of load, reduced pollution, high power density, no moving parts, very low noise output, short start-up time and capable of automatic operation. The immediate difficulties to overcome include: difficult fuel storage, sensitivity to fuel impurities, maintaining proper moisture control of the membrane, market penetration and high cost to produce. There are a variety of fuel cells in different stages of development and they can be classified by the ion transportation separator that is used to facilitate the electrochemical reactions. The most common classification of fuel cells is by the type of electrolyte in the cells and includes 1) proton exchange membrane (polymer) electrolyte fuel cell (PEMFC); 2) alkaline fuel cell (AFC); 3) phosphoric acid fuel cell (PAFC); 4) molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC). PEMFC will be the fuel cell type primarily discussed in the chapter. PEMFC produce electricity via a direct electrochemical energy conversion process rather than a combustion process typical of the current fossil fuel power plants. These fuel cells operate at low temperature allowing for faster start-up and immediate response to changes in demands for power. The PEMFC system is seen as the system of choice for vehicular power applications, small stationary power applications and as battery replacements in small, hand-held devices. These fuel cells typically operate on hydrogen or methanol as fuel. This paper discusses the challenges in science and technology facing this industry.