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Carbonate Fuel Cell Anode: A Review
The molten carbonate fuel cell (MCFC) has emerged as one of the leading devices to convert chemical energy into power. To date 1.9 GWh of electricity has been produced commercially using this new technology. The molten carbonate fuel cell uses a mixture of alkali carbonates as the electrolyte and operates in the temperature range of 550-650°C. The high operating temperature dramatically improves the reaction kinetics and eliminates the need for a noble metal catalyst. During cell operation, hydrogen is oxidized at the anode and oxygen is reduced at the cathode, equations (1) and (2)
H2 + CO32- → H2O + CO2 + 2e- (1)
1/2O2 + CO2 + 2 e- → CO32- (2)
The current carbonate fuel cell design (illustrated in figure 1) has evolved over many years from extensive research conducted in fifteen companies and many prestigious laboratories. The cell hardware is made from stainless steel, the electrodes are nickel based, and the separator called matrix is a porous ceramic. The anode design is an important consideration from both performance and cost considerations.
The state of the art MCFC anode is a porous Ni electrode stabilized against sintering by Cr and/or Al additives. Typical anodes have porosities of 40-60% and 3-6 µm as average pore diameters. To ensure long-term stability against creep, corrosion and oxidation, major considerations need to be taken into account in material selection. Mechanical and chemical stability as well as the electrochemical activity for anode are key factors for performance and life stability.
Accelerated lab-scale technology stacks (30kW) and long-term field tests have shown that the current anode materials have the desired performance and stability of the useful life of >5-7 years. As shown in figure 2, anode maintains stable pore structure and morphology over long-term operation. Parameters such as conductivity, pore size distribution, wetting and electrolyte fill level affect anode performance and its stability. To achieve an