The Influence Of Toluene On SOFC Performance And Modification Of Anodic Catalysts

Solid oxide fuel cell?SOFC?is a clean power generation system with all-in-solid and high efficiency due to the direct conversion from chemical energy in fuels to electricity.Fuel flexibility is an attractive advantage of SOFC when compared to low temperature fuel cells.High temperature raw coke-oven-gas?COG?is a promising fuel for SOFC because it is rich in H₂?55–60%?and CH₄?23–27%?.However,unsaturated hydrocarbons such as tar in COG limit its direct power generation using the state-of-art SOFC based on Ni cermet anode due to severe coking.Based on this situation,a tar model?toluene?is investigated to study the influence of tar on performance and stability of the state-of-art SOFC.In this work,we use the 8%Y₂O₃stabilized ZrO₂?YSZ?as the electrolyte,NiO-YSZ as the SOFC anode,Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-??BSCF?as the SOFC cathode,Sm_0.2Ce_0.8O_1.9?SDC?as the buffer layer,and fabricate an anode-supported SOFC with the configuration of NiO-YSZ/YSZ/SDC/BSCF-SDC.Simultaneously,loading three different catalysts as the independent catalyst layers which is separated from SOFC anode,respectively.Results indicate that applying of the catalyst layers is an effective way to reduce the negative effect of toluene on the anode can be improved.1.Preparation and characterization of three catalysts.La_0.7Sr_0.3MnO₃?LSM?and La_0.6Sr_0.4Co_0.2Fe_0.8O₃?LSCF?powders were synthesized by a combined ethylene diamine tetraacetic acid?EDTA?–citric acid?CA?complex method,and NiO/BaO/CeO₂?NBC?was synthesized by glycine-nitrate combustion method.The structures of the three catalysts before and after reduction were characterized by XRD.The three catalysts and the substrate were co-compressed to form a double-layer sheet,respectively,as an independent catalyst layer.This structure avoids the mismatch of thermal expansion coefficient between anode and catalyst materials under the premise of ensuring that the catalytic activity and conductivity of the nickel-based anode can not be affected.2.The influence of toluene on SOFC anode materials.When using 45 g Nm^-33 toluene-contaminated wet H₂ fuel,the maximum power density of the cell decreases from 1.251 W cm^-2 to 0.996 W cm^-2 at 800°C,and the polarization resistance increases from 0.461?cm² to 0.876?cm².In other word,the performance drops drastically.At the same time,in the discharge test under constant current,a significant voltage drop occurs from 0.7 V to 0V within 1.4 h for the cell.Based on the SEM/EDX analysis,it is found that a large amount of carbon deposits on the anode surface of the cell.3.Improving the coking-resistance of a Ni-based anode using three different catalysts.LSM,LSCF and NBC are used as independent catalyst layers,respectively.A conventional cell without the catalyst layer is used for comparison.Using 45 g Nm^-3 toluene-contaminated wet H₂ fuel,the catalyst-modified cells show a stable running for nearly 110 h under a constant current density of 300 mA/cm² at 800°C.The surface of the anode and the catalyst layer before and after the aging test are analyzed by SEM/EDX.Only a small amount of carbon deposition exists on the anode surface and the catalyst surface of LSM and LSCF.A large number of carbon nanotubes are observed on the catalyst surface of NBC.It indicates that all three catalysts have a positive effect on the oxidation of toluene.This work provides a good way for the coke-oven-gas utilization as SOFC fuel,and also provides an effective method to resist carbon deposition for SOFC.