A Research On Surface Segregation Of GdBaCo₂O_5+?-based Oxygen Electrodes And Chromium Deposition

A solid oxide fuel cell?SOFC?is a device which can directly convert chemical energy into electrical energy with many advantages,such as high efficiency,clean,and modularity etc.The solid oxide electrolytic cell?SOEC?,is a device that converts electric energy into chemical energy,which can be used to split H2 O into H2 and O2.The above two are promising technologies for future energy coversion and storage.GdBaCo₂O_5+??GBCO?is a kind of ion electron mixed conductor,for the cathode and anode of SOEC and SOFC,respectively.Many materials in the high temperature annealing as well as the operation of the cell electrode and electrode surface,surface cationic segregation will occur.Previous papers presented,the segregation of the electrode surface can reduce the catalytic activity and thus decrease the power of the cell.GBCO based oxygen electrode may also occur this kind of phenomenon.Therefore,this paper measures annealing and current polarization property on the GBCO based oxygen electrode,and the treated samples were characterized,and detected GBCO electrode surface segregation.F doped GBCO electrodes were synthesized and tested.Not only the segregation occurs in the surface of the electrode will degrade the performance of the electrode,the Cr vapor produced by the interconnect materials of the fuel cell stack will also reduce the performance of the electrode,GBCO chromium poisoning were also analyzed.GdBaCo₂O_5+??GBCO?electrode material was prepared by sol gel method,phase analysis is the first step,then the GBCO acted as electrode on SDC?Sm0.2Ce0.8O1.9?the electrolyte,and the electrochemical performance was evaluated using half cell system.A 40 h annealing test for GBCO was carried out and SEM test reveals that surface segregation was significantly increased compared to the pure electrode.Thus the anode and cathode current polarization were treated by different current density of GBCO half cells.It was found that the polarization performance of the anode decreases and increases the segregation phenomenon of the electrode surface.On the other hand,cathodic polarization can inhibits electrode surface segregation and improves electrode performance.Repeated polarization experiments were conducted to test whether the polarization of the cathode was the result of the electrode recovery.GdBaCo₂O_5+?F_x?x=0.1?0.2?0.3?were synthesized by solid phase reaction,and the phase purity,electrical conductivity and thermal expansion rate in air atmosphere were studied.The electrical conductivity and thermal expansion coefficient is similar with undoped sample.In addition,we found that the polarization resistance of doping one at the same temperature is smaller than the polarization resistance of the regular GBCO,and the smallest polarization resistance of sample?GBCOF0.2?used to measure theanode and cathode polarization test,and the result is similar to the change rule of the GBCO.It is reported that the water vapor content in Cr vapor had the serious influence on electrode degradation,therefore the dry and wet atmosphere Cr poisoning GBCO experiment had been tested and compared.Our results showed that electrode degradation under wet atmosphere is more apparent.In addition,an experiment in the polarization of the GBCO electrode also was found to inhibit Cr poisoning,while the anodic polarization accelerated the level of Cr poisoning.