| Solid oxide fuel cell (SOFC) is an energy conversion device converting chemical energy of fuels into electricity by electrochemical reactions. It’s clean without pollution, quiet without noise and has a high degree of modularization; it’s capable of being used in high population areas as well as a dependent electricity station for remote areas. Tubular SOFC has advantages on sealing and fuel applicability over planar design, especially for solid fuels utilization. Direct carbon solid oxide fuel cell (DCSOFC) is a promising technology directly using solid carbonaceous fuels for electicity generation with easy CO2 separation. Liquid antimony anode direct carbon solid oxide fuel cell (LAA-DCSOFC) has unique working mechanisms in those DCSOFC blue prints. Electrochemically formed Sb2O3 and Sb are liquid above 660 ℃ and will detach from each other driving by density difference; fuels are consumed by reducing Sb2O3, ensuring Sb looping. Cell structure and fuel properties have significant influence on cell running performance. Current researches on LAA-DCSOFC are mainly using electrolyte supported planar button cells, the further researches on praperation and operation characteristics of tubular LAA-DCSOFC must be carried out.In this paper, tubular SOFCs with Ni-YSZ anode, YSZ electrolyte and LSM-YSZ or Pd+LSM-YSZ cathode and YSZ supported tubular LAA-DCSOFCs with LSCF-10GDC cathode were fabricated by a novel slurry-casting method. The discharging performance and long-term durability of tublar SOFCs was tested. The electrochemical reaction characteristics, discharging and running performance, refueling feasibility, biomass carbon fuels applicability, fuel and temperature influence, anode chemical reactions, fuel utilization and cell efficiency, exhaust gas consist and it’s reusing of tubular LAA-DCSOFC were investigated detailed. The main conclusions are summarized as follow:(1) Tubular Ni-YSZ/YSZ/LSM-YSZ cell was fabricated by a slurry-casting method and showed no degradation in the 192 h’s test. The peak power density of Pd+LSM-YSZ cathode cell at 750 ℃ increased from 280 m W·cm-2 to 828 m W·cm-2 by PdO infiltration. Tested at 750 ℃ and 0.7 A·cm-2, the voltage degradation rate decreased from 0.39 mV-h-1 in the former 170 h to 0.17 mVh-1 in the later 100 h; performance degradation was maily due to the aggragation and growing of nano-sized PdO particles.(2) Tubular LAA-DCSOFC was fabricated by a slurry-casting method and a peak power density of 114,196, and 304 mW-cm-2 was achieved at 700,750, and 800 ℃, respectively. Sb2O3 with a smaller density was converged to the top of Sb rather than mixed with each other. Biomass carbon fuels were successfully used as fuels for LAA-DCSOFC and fuels acted as a reducer for Sb looping. The cell performance decreased fast after fuels used up and the decreased cell performance was recovered to original level by directly refueling at working temperature, showing good refueling feasibility.(3) Fuel utilization and energy conversion efficiency of tubular LAA-DCSOFC could be evaluated easily by introducing "stable ruuning time per gram fuel" (tg). Better cell performance but lower fuel utilization was achieved at higher temperature; at the same temperature, a higher current density would lead a lower tg. Efficiency was related to working conditions:a higher current density would lead to a lower efficiency at a constant temperature. When biomass carbon fueled tubular LAA-DCSOFC worked at 750-800 ℃ and 0.4 A cm-2, the energy conversion efficiency was 25.6%-32.2%.(4) Tubular LAA-DCSOFC was inherently electrochemical-looping combustion of carbon fuels, coupling of CLC and SOFC with SOFC as oxygen captor and Sb2O3 as oxygen carriers. The fluxes of CO and CO2 in the exhaust gas were 2.00±0.04 and 1.79±0.04 ml min-1 respectively when tubular LAA-DCSOFC was working at 800 ℃ and 0.4 A·cm-2. Sereis power generation was achieved by reusing the exhaust gas by a tubular SOFC, the energy conversion efficiency increased from 27.8% to 38.9%. |
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