Properties Of Bismuth Ion-doped Layered Double Perovskite Cathode Materials

Solid oxide fuel cell（SOFC）is an efficient and green all-solid-state power generation device that can directly convert chemical energy into electrical energy.In this paper,we focus on the double-pervoskite electrode material as the research object,and use doping and modification means to synthesize novel materials to explore the oxygen-catalytic activity and stability at intermediate and low temperatures,so as to develop IT-SOFC cathode materials with application potential.Firstly,the Nd³⁺-deficient Nd_1-xBa Co₂O_5+δwas synthesized by the glycine nitrate method（GNP）,followed by the synthesis of a novel Nd_1-xBa Co₂O_5+δ+x/2Bi₂O₃（x=0.05;NBC95+B）composite cathode material by introducing bismuth oxide one-pot method.The XRD shows the presence of some trace bismuth ions into the lattice in the composite.The results of iodine titration and XPS analysis indicate that the bismuth oxide composite contributes to the increase of Co⁴⁺concentration.Moreover,the introduction of bismuth oxide reduced the thermal expansion coefficient（TEC）of the material(17.1×10^-6→16.6×10^-6K^-1)and improved the ORR catalytic activity.The polarization impedance（ASR）and maximum power density（MPD）of the NBC95+B cathode were 0.026Ωcm^-2and 720m W cm^-2at 800°C.The good electrochemical performance of the NBC95+B composite cathode was attributed to the combined effect of the introduction of Nd cation defects and the suboxidation state of Bi cations.In addition,the NBC95+B cathode also exhibited good resistance to CO₂poisoning and stability.Based on the characteristics of cationic defects in improving the electrochemical performance of the material,high concentration Nd cation-deficient Nd_0.9Ba Co₂O_5+δ（NBC90）nanocomposites were synthesized by the glycine nitrate method.XRD studies revealed the presence of a double pervoskite structure（93.82%）as well as a single pervoskite phase（6.18%）solved in the form of nanoparticles（NPs）in NBC90.This approach accelerated the ORR catalytic capacity,and the surface specific resistance（ASR）of NBC90 dropped to 0.023Ωcm-2 at 800°C.In order to improve the stability and electrochemical performance of NBC90,NBC90+0.05Bi₂O₃（NBC90+B）nanocomposites cathode was synthesized using bismuth ion modification.The NBC90+B electrode material is spontaneously assembled to form NBC90（91.43%）and bismuth-doped Ba Co_1-yM_yO_3-x（M=Bi）pervoskite NPs（8.57%）due to the penetration of bismuth ions inside the lattice regulating its smart assembly and surface segregation.It was shown that the nanostructured Ba Co_1-yM_yO_3-x（M=Bi）formed by anisotropic growth could exhibit an extremely strong surface oxygen catalytic activity with the multiple heterointerfaces constructed by the parent material.As a result,the ASR decreased to 0.014Ωcm^-2at 800°C.Meanwhile,the integrated synthetic assembled composites effectively improved the electrical conductivity of the samples,which was 563.7 S cm^-1at 600°C,significantly better than that of NBC(424.8 S cm^-1)and NBC90(412.5 S cm^-1).In addition,a synergistic effect of the penetration of highly acidic Bi ions and the multiple interfaces of the two phases significantly enhanced the structural stability and resistance to CO₂poisoning of the cathode（700°C,～110 h）.B-site Bi ion-doped Nd Ba Co_2-xBi_xO_5+δ（x=0.05-0.2;NBCBx）cathode materials were synthesized by the glycine nitrate method.XRD analysis showed that x=0.05 and 0.1bismuth ions were successfully doped into the Co site and did not change the double perovskite structure（P4/mmm）.The introduction of Bi³⁺ions with large ionic radius and high bonding energy can improve the ionic conductivity of the sample as well as the stability of the material.The electrochemical tests revealed that the best material performance was achieved at a Bi doping content of 0.05,with an ASR of 0.019Ωcm²and an MPD of 798 m W cm^-2at 800°C.The best catalytic activity of NBCB0.05 was attributed to the appropriate amount of Bi³⁺doping,which provided the active site for oxygen reduction and facilitated oxygen transport.In addition,NBCB0.05 also shows excellent stability under CO₂atmosphere and a stable operation time of～70 h for a single cell.