Direct Conversion of Carbon Fuels in a Molten Carbonate Fuel Cell

Abstract

Anodes of elemental carbon may be discharged in a galvanic cell, using molten carbonate electrolyte, at power densities of 40-100 mW/cm2. 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/cm2 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 cm2 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.