Fuel cells: Status and challenges in materials and technologies

Abstract

Fuel cells are electrochemical devices that directly convert the chemical energy in incoming fuel (hydrogen or a hydrogen rich reformate) into electrical energy via ionic conducting electrolyte membranes. Depending on the electrolyte used, fuel cells can be classified into a number of types. Two major types of fuel cells, polymeric-electrolyte-membrane fuel cell (PEMFC) and solid-oxide fuel cell (SOFC), have attracted the most recent attention and are the subject of extensive R&D efforts worldwide. PEMFCs are typically based on a proton conductive sulphonated fluoropolymer membrane such as Nafion? and operate in the 60-80 C temperature range. On the other hand, SOFCs are constructed from an oxygen ion conductive membrane, such as YSZ (yttria stabilized zirconia), and operate in the range of 600-1,000 C. To build up a useful voltage, a series of cells, comprised of an anode and a cathode in addition to the electrolyte, are electrically connected and integrated into a stack via interconnects or bi-polar plates. For designs such as the planar one, seals are required in the stack to prevent leakage and to separate the fuel at the anode side from the oxygen or air at the cathode side.