Investigation Of The Performance Of Calcium Ion-doped Ni_xMg_1-xO-based SOCs Oxygen Electrode Materials

As an efficient electrochemical energy conversion and storage device,solid oxide cells（SOCs）can not only solve the problems such as intermittency of renewable energy,but also has the characteristics of high conversion efficiency,wide range of fuel selection and strong modular structure.In this paper,Nd Ba Co₂O_5+δ,a layered and ordered bicalcite oxygen electrode material,was used as the research object to investigate the oxygen catalytic activity and stability of the oxygen electrode material at medium temperature by using calcium doping method to synthesize novel materials,and t provide an effective way for the development of high performance SOC oxygen electrode.Novel perovskite type A-site calcium-doped Nd_1–xCa_xBa Co₂O_5+δ（x=0–0.3）oxides were investigated for oxygen electrode materials for SOC.The electrode of x≤0.2 was composed of a tetragonal perovskite structure with a P4/mmm space group.Ca²⁺doping was used to reduce the coefficient of thermal expansion（TEC）,and improve conductivity and electrochemical properties of the Nd Ba Co₂O_5+δoxides,with TEC and conductivity values of Nd_1–xCa_xBa Co₂O_5+δof 17.5–16.2×10^-6K^-1and 960.4–1,068 S cm^-1,respectively.The X-ray photoelectron spectroscopy results indicated that Ca²⁺doping has a beneficial influence on the surface oxygen adsorption properties and the increase in the concentration of Co⁴⁺.Theoretical calculations indicate that doping with Ca²⁺leads to easier oxygen release and uptake.x=0.2,the oxygen electrode exhibits the best electrochemical performance.The area specific resistance（ASR）is 0.058Ωcm²at 700°C.The maximum power density using H₂as fuel is 740 m W cm^-2at 800°C,and the current density for electrolysis of pure CO₂is–1.68 A cm^-2at 1.5 V.Based on the excellent properties of NCBC,the calcium ion co-doped layered double perovskite oxides Nd_0.8Ca_0.2Ba_1-xCa_xCo₂O_5+δ（x=0–0.2,NCBCC）were synthesized by the glycine-nitrate method.When x≤0.1,the sample has a tetragonal chalcogenide structure with a space group structure of P4/mmm.The conductivity of the Nd_0.8Ca_0.2Ba_0.9Ca_0.1Co₂O_5+δ（NCBCC1）oxygen electrode was higher than 230 S cm^-1in the range of 25–850°C at x=0.1 and showed good compatibility with commonly used electrolyte materials.The TEC of the calcium ion co-doped NCBCC1(17.3×10^-6K^-1)sample was slightly decreased.At 700°C,the ASR value of the NCBCC1 sample decreased from 0.26（NBC）to 0.083Ωcm².The NCBCC1 electrode exhibited good stability in a pure O₂environment,indicating that calcium ion introduction is effective for improving cation bias on the perovskite surface.Using NCBCC1 as an oxygen electrode,the MPD reached762 m W cm^-2at 800°C in SOFC mode;the current density was–1.51 and–1.85 A cm^-2in SOEC mode at an electrolytic voltage of 1.5 V and a temperature of 800°C,fueled by pure CO₂and H₂containing 30%water vapor,respectively.The above results indicate that the stability of the electrochemical performance of the oxygen electrode can be effectively improved by a proper doping strategy of calcium ions in layered bicaluminite,which is a proven option in the optimization of the performance of SOC oxygen electrodes.