Morphology and phase composition of the scales formed on 316L stainless steel in an environment simulating a solid oxide fuel cell (SOFC) interconnect were determined towards the corrosion behavior study of commercial and new alloys for SOFC stack and balance-of-plant (BOP) applications. The simulated SOFC environment consisted of a dual exposure condition with air on one side of the specimen and mixtures of hydrogen and water vapor on the other side at 907 oK. Surface characterization techniques, such as optical and scanning electron microscopy, energy dispersive X-ray spectroscopy as well as X-ray diffraction analysis were used in this study. Also, an attempt was made to correlate the experimental results with thermodynamic calculations.
Fuel cells are galvanic cells, in which the free energy of a chemical reaction is converted into electrical energy via an electrical current. The anode reaction in fuel cells can be a direct oxidation of hydrogen, or the oxidation of methanol. An indirect oxidation via a steam-reforming step of hydrocarbons into a mixture of hydrogen and carbon monoxide can also occur. The cathode reaction is oxygen reduction, in most cases from air.1
The main characteristics of fuel cells is to convert chemical energy without the need of combustion, giving much higher conversion efficiencies than conventional methods, such as gas turbines because fuel cells are not subject to Carnot limit. Fuel cells utilize electrochemical oxidation so they have much lower carbon dioxide emissions than combustion-based technologies for the same power output. They also produce negligible amounts of environmentally unfriendly SOx and NOx, which are the main constituents of acid rain.1
There are several major types of fuel cells that are currently exist 1-4 namely:
Alkaline Fuel Cells (AFC)
Proton Exchange Membrane Fuel Cells or Polymer Electrolyte Membrane Fuel Cells (PEMFC)
Direct Methanol Fuel Cells (DMFC)
Phosphoric Acid Fuel Cells (PAFC)
Molten Carbonate Fuel Cells (MCFC)
Solid Oxide Fuel Cells (SOFC)
The main difference between the different fuel cells is the material used for the electrolyte, and, therefore their operating temperature. An exception to this classification is the DMFC, where the fuel, methanol, is directly supplied to the anode. Table 1 shows an overview of the fuel cells listed above:
TABLE 1
Overview of Fuel Cells currently in Use 1
