Direct Conversion of Carbon Fuels in a Molten Carbonate Fuel Cell

Anodes of elemental carbon may be discharged in a galvanic cell, using molten carbonate electrolyte, at power densities of 40-100 mW/cm 2 . We report cell polarization, surface area, primary particle size, and crystallization index for nine particulate carbon samples derived from fuel oil, methane, coal, biochar, and petroleum coke. At 800°C, 50-125 mA/cm 2 current densities were measured at a cell voltage of 0.8 V. Power densities were nearly the same on scales of 2.8 and 60 cm 2 active area. Constant current operation of a small cell was accompanied by constant voltage during multiple tests of 10-30 h duration. Cell voltage fell off after the carbon inventory was consumed. Three cathode structures are compared, indicating improved rates for a Lawrence Livermore National Laboratory-fabricated porous nickel electrode with <10 μm pores compared with nickel foam with 100-300 μm pores. Petroleum coke containing substantial sulfur and ash discharges at a slightly lower rate than purified petroleum coke. Sulfur degrades the anode current collector over time. A conceptual model for electrochemical reactivity of carbon is presented, and indicates the importance of ( i ) bulk lattice disorder, which continually provides surface reactive sites during anodic dissolution, and electrical conductivity, which lowers the ohmic component of anode polarization. © 2004 The Electrochemical Society. All rights reserved.