The Sulfur-poisoning Regeneration Method Of La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ Based Composite Anode For Fuel Cells

The sulfur poisoning and regeneration issue for solid oxide fuel cell(SOFC)when using cheap fuel is always the limiting factor on its commercialization.Therefore,the anode regeneration experiment should be conducted after anode poisoning.Early research found that a single SOFC with a Ni-YSZ cermet anode exposed to a fuel containing 50 ppm H2 S at 800 oC,recovered to 96% of its initial performance after stopping the H2 S exposure.However,sulfides in anode can not be completely removed by this regeneration method,and this regeneration process needs dozens or even hundreds of hours,thus this regeneration method is more time-consuming and it is not the most effective method for the regeneration of poisoned anode.In this paper,a fast oxidation regeneration method for sulfur poisoned oxide anode is proposed-oxidation method,mainly includes the chemical oxidation and electrochemical oxidation method.LSCrM has higher sulfur-tolerant capability compared with Ni based anodes.Most importantly,it possesses higher stability in both oxidation and reduction atmosphere,thus LSCrM becomes a good candidate for poisoning-oxidation regeneration investigation.The voltage degradation rate of LSCrM/YSZ/LSM cell is 3% after poisoned by 50 ppm H2 S at 850 oC about 5 h,the maximum power density(Pmax)of cell reduced to 110 mW?cm-2 from 129 mW?cm-2,the XRD and XPS indicate the poisoning products are adsorbed sulfur,sulfide and sulfite.The chemical oxidation regeneration method can remove sulfur and sulfide in 15 min,and generate the manganese oxide particles on LSCrM anode,the Pmax rise to 158 mW?cm-2 after chemical oxidation regeneration process.The six cycles of poisoning-chemical oxidation regeneration indicate the voltage degradation rate increases with the number of poisoning,the Pmax after the second chemical oxidation regeneration have the highest value,the value is 162 mW?cm-2,though the performance of cell was recovered at different degrees through the followed chemical oxidation regeneration,but the regeneration degree is not good enough.The electrochemical oxidation regeneration method can realize the LSCrM anode regeneration under Ar at 15 min,and the signal of O2 and SO2 can be detected by mass spectrometer during the electrochemical oxidation regeneration process.The Pmax rise to 189 mW?cm-2 after regeneration,the SEM shows that the electrochemical oxidation regeneration method can remove the adsorbed sulfur and sulfide clearly and form the manganese oxide particles on surface of LSCrM anode.The six cycles of poisoning-chemical oxidation regeneration indicate the voltage degradation rate is not increase with the poisoning times,the voltage degradation rate remained about the same in the process of the final three cycles of sulfur poisoning.This paper introduce the Co and Ni catalyst into LSCrM anode in order to improve the anode catalytic ability,the sulfur resistant ability of composite anodes are also studied in this paper,the chemical oxidation and electrochemical oxidation regeneration are used to realize the composite anodes regeneration.The effect of impregnation amount of Co catalyst on the cell performance is evaluated in this study,the introduction of Co significantly reduces the resistance of LSCrM coating,and thus increases electronic conducting performance of Co-impregnated LSCrM,the performance of LSCrM increases with the loading of Co,the performance of LSCrM is optimum when the Co loading is 1.66 mg?cm-2.The impregnation of Co will reduce the sulfur resistant ability of LSCrM anode.The performance of Co-impregnated LSCrM can be recovered by chemical oxidation regeneration method,but the value of Pmax after regeneration can not compared to previous value.The electrochemical oxidation regeneration method can not make the poisoned LSCrM realize regeneration,it will cause the further reduce of electrochemical performance.The impregnation of Ni also will reduce the sulfur resistant ability of LSCrM anode.The performance of Ni-impregnated LSCrM can be recovered by chemical oxidation regeneration method,but the value of Pmax after regeneration can not compared to previous value.The electrochemical oxidation regeneration method can not make the poisoned LSCrM realize regeneration,it will cause the further reduce of electrochemical performance.