Charging Temperature Dependence of the Fuel Utilization and Ratio of Residual Carbon after Power Generation in Rechargeable Direct Carbon Fuel Cells

Abstract

Rechargeable Direct Carbon Fuel Cells (RDCFC) with Ni/GDC-cermet anodes were developed. RDCFCs with a Ni/GDC (gadolinium-doped ceria) anode and 0.3-mm-thick ScSZ (scandia-stabilized zirconia) electrolyte charged with propane for 5 min at 600° exhibited a stable, maximum power density of 200 mW/cm2 for more than 1 h at operating temperature of 900°. The effect of charging temperature on the properties of charged carbon and on power generation was studied here. When the charging temperature was decreased from 900° to 750°, power generation time increased by more than a factor of 10, from 22 to 280 min. Based on the TG-DTA results, carbon charged at 600° could easily be oxidized, and CO supply by the Boudouard reaction was improved. This led to an improved power density and fuel utilization.

Effects of Gas Composition Just before Fuel Pulses on Power Generation Characteristics at Different Fuel Supply Frequency in Pulse Jet-Rechargeable Direct Carbon Fuel Cells

“…Thus, the achievable efficiency of a RDCFC approaches 1, and power generation at high efficiency is expected. Our research succeeded in achieving stable power generation of 200 mW/cm 2 for more than 1 h with 5 min charging of propane (20). However, RDCFCs have several drawbacks.…”

“…Our research group previously considered the efficient use of solid carbon as fuel and proposed a new type of SOFC in which the solid carbon deposited on the anode by thermal decomposition of hydrocarbon is used as fuel (12)(13)(14)(15)(16)(17)(18)(19)(20)(21). These fuel cells are called "Rechargeable Direct Carbon Fuel Cells (RDCFCs)".…”

Power Generation of Rechargeable Direct Carbon Fuel Cells with Batch-Type Charging System

“…), producing CO 2 in the anode (CO 2 a ) in the total reaction [8].Theoretical OCV of a DCFC can be calculated from molar Gibbs free energy change ( ) of the total reaction [8] using the Nernst equation [9] as follows: [10] where ΔG of the total reaction is expressed as standard ( ) of the reaction (C graphite + O 2 → CO 2 , 1 atm, 1173 K,), activity of solid carbon ( ), partial pressure of CO 2 in the anode side (…”

“…Our group proposed a Rechargeable Direct Carbon Fuel Cells (RDCFC), which is an SOFC-based new type of DCFC using pyrolytic carbon as fuel (5)(6)(7)(8)(9)(10)(11)(12)(13). RDCFCs use hydrocarbon for power generation as follows.…”

“…However, an RDCFC using a charging method that continuously introduces propane [48 ccm under standard temperature and pressure (STP)] for 5 min at 900 ºC has a low conversion efficiency (5%) from hydrocarbon to solid carbon, and has a propane-based fuel utilization of only about 3% (6,9). To improve propane-based fuel utilization, the conversion rate of hydrocarbon to solid carbon must be increased.…”