Effect Of Electrochemical Performance Of La_0.6PrSr_0.4NiO₄Electrode Under Polarization Condition

Cathode plays a key role of electrochemical performance of cell, which is as animportant part of solid oxide fuel cell (SOFC). And in recent years, the research ofLa0.6PrSr0.4NiO4(LPSN) material with K2NiF4perovskite-like structure of perovskitestructure material, has made great progress. LPSN material is has the a layeredstructure with AO salt layers and ABO3perovskite layers arranged alternately. It ishas high mixed electronic and ionic conductivity in medium the intermediatetemperature range, and it also has a strong catalytic ability for O2reduction. So,LPSN is a considerable as a potential candidate for intermediate temperature SOFCelectrode material.When LPSN electrode is in operation condition as a cathode of SOFC, LPSNitself is in the state of polarization, whose current direction from electrolyte toelectrode. In order to study the electrochemical properties of LPSN electrode inoperation condition of SOFC and solid oxide electrolysis cell (SOEC) for a long time,in this paper, the electrochemical performances were tested via3-electrode method.In the cell, Ce0.9Gd0.1O1.95(GDC) was selected as electrolyte since it matches thecoefficient of thermal expansion LPSN working electrode, and Ag was employed asthe counter electrode and reference electrode. Thus La0.6PrSr0.4NiO4(LPSN)electrodes is processed under cathode and anode current with same current density,and once for a while, its electrochemical performance was tested.LPSN and GDC power materials were synthesized by sol-gel method,. and thephase temperatures of LPSN powders were pre-calcined at900C and1050C,respectively. After55h–annealing at700C in air, the polarization resistance of TheLPSN electrode coated was prepared on the GDC electrolyte, and increases from0.31Ω cm2(as prepared) to0.90Ω cm2(after55h)，was investigated by testing theelectrochemical performance in annealing treatment at700C for55h. Before theannealing treatment polarization resistance of LPSN electrode is obtained0.31Ωcm2,and measured0.90Ωcm2after annealing55h,i.e. an increases of190%.; Meanwhile,the ohmic resistance was changed from1.36Ω cm2, to1.62Ω cm2, i.e. by an increaseof19%. The electrochemical impedance spectroscopy (EIS) results showed that boththe ohmic resistance and polarization resistance of the electrode increased with theincrease of annealing time, it means the electrochemical performance of the LPSNelectrode is degradation. And Scanning electron microscopy (SEM) observationshowed shows that LPSN electrode particles grow significantly after long annealing treatment, and particles aggregate is increased.,Thus the effective area of theelectrode contacted with the electrolyte is reduced, and resulting in the increasing ofpolarization resistance and ohmic resistance, as well as the degradation ofelectrochemical performance of LPSN electrode.The electrode behavior of LPSN was investigated under cathodic polarizationconditions with a constant current density of417mA cm-2at700C in air. Thepolarization resistance increased from0.35Ω cm2to0.84Ω cm2after cathodic currentfor55h, increasing140%, at the same time, the ohmic resistance (RΩ) increased from1.44Ω cm2to1.85Ω cm2, increasing28%. The results showed that electrochemicalbehavior of LPSN electrode declined under cathodic current treatment. Whilecompared with the annealing treatment at the same temperature and atmospherecondition, the increase of polarization resistance of the LPSN electrode undercathodic current treatment is slower. The SEM photos indicated that the aggregate ofLPSN electrode was vanished, and particles size decreased significantly, it means thatcathodic current treatment can help to inhibit the grain growth of electrode at hightemperature for a long time. At the same time, the weak contact caused by particlefragmentation results in the increase of ohmic resistance.LPSN electrode was treated under a anodic current to simulate the workingconditions of SOEC. The polarization resistance of LPSN electrode increased from0.39Ω cm2to0.52Ω cm2after anodic anodic current treatment for55h, by33%, whileRΩalmost remained the same value at~1.1Ω cm2. These results indicated that anodiccurrent treatment resulted in an increase of polarization resistance and degradation ofelectrochemical performance of LPSN electrode, but no significant effect on theohmic resistance.The SEM photo showed the aggregate of LPSN electrode wasvanished, and particles size decreased significantly, while the contact interface of theelectrolyte and electrode kept stable.In summary, compared to annealing and electrode polarization process under thesame temperature and time, the increase of the ohmic resistance and the polarizationresistance are far less than the annealing and cathodic polarization current treatment.So LPSN is a potential material of anode of SOEC.