Direct Conversion of Carbon Fuels in a Molten Carbonate Fuel Cell

Abstract

Anodes of elemental carbon may be discharged in a galvanic cell using a molten carbonate electrolyte, a nickel-foam anode-current collector, and a porous nickel air cathode to achieve power densities of 40-100 mW/cm 2 . We report cell and anode polarization, surface area, primary particle size and a crystallization index for nine particulate carbon samples derived from fuel oil, methane, coal, charred biological material and petroleum coke. At 800 °C, current densities of 50-125 mA/cm 2 were measured at a representative cell voltage of 0.8 V. Power densities for cells with two carbon-anode materials were found to be 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 hour duration. Cell voltage fell off after the carbon inventory was consumed. Three different cathode structures are compared, indicating that an LLNL fabricated porous nickel electrode with <10 µm pores provides improved rates 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. The sulfur leads to degradation of the anode current collector over time. A conceptual model for electrochemical reactivity of carbon is presented which indicates the importance of (1) bulk lattice disorder, which continually provides surface reactive sites during anodic dissolution and (2) electrical conductivity, which lowers the ohmic component of anode polarization.

Effect of structural properties of carbon-based fuels on efficiency of direct carbon fuel cells

“…Weaver et al [21] were perhaps the first to recognize that the polarization of the carbon anode in the carbonate melt depended not on the specific surface area but rather on the degree of disorder. Cherepy et al [22] conducted a more thorough examination of the dependence of the anode oxidation rate on the fixed polarization.…”

Application of infiltrated LSCM–GDC oxide anode in direct carbon/coal fuel cells

“…According to literature, the peak at 2θ = 20-30 o can be ascribed to (002) reflection with the one at 2θ = 40-50 o to (100) reflection for carbon materials [3][4] . These two peaks are very broad in the XRD pattern of xerogel sample, indicating a very disordered structure that is beneficial for carbon oxidation in DCFC.…”

“…These two peaks are very broad in the XRD pattern of xerogel sample, indicating a very disordered structure that is beneficial for carbon oxidation in DCFC. It has been agreed by several researchers that less crystalline carbon tends to have more edges sites and defects which are considered reactive sites for carbon oxidation in DCFC [3][4]13 . One may argue that xerogel has quite low fixed carbon (53.6%) and a very high amount of volatile matter (46.4%), both of which were believed to impact DCFC performance negatively 13 The enhanced performance from the DCFC with a GDC-LSCM SOFC anode is probably attributed to the high ionic conductivity and electro-catalytic activity the oxide anode offers.…”

“…Different types of DCFCs are in use depending on the electrolyte, for instance, molten carbonate [3][4][5] , molten hydroxide 6 , and solid oxide 7 etc. The hybrid DCFCs (HDCFCs) have gained increasing interest due to the benefits it brings 8 .…”

Clean energy from a carbon fuel cell

“…The experimental results obtained so far by several authors, e.g. [6][7][8][9], are quite promising and thus further investigations are led with increased interest [1,3,4,10,11]. The DCFC provides excellent conditions for direct conversion of fuel's chemical energy into electricity without the combustion process and with no use of any 'intermediate' technologies or machinery (e.g.…”