Electrochemical removal of NO_x by La_0.8Sr_0.2Mn_1−xNi_xO₃ electrodes in solid electrolyte cells: Role of Ni substitution

Electrochemical removal of nitrogen oxides (NO_x) by solid electrolyte cells (SECs) is a promising technology due to no required reductant. Herein, a series of La_0.8Sr_0.2Mn_1−xNi_xO₃ (0 ≤ x ≤ 0.5) perovskites were first synthesized and utilized as the electrode materials of SECs. The role of Ni substitution in electrode performance and NO_x reduction mechanism were revealed by various experimental characterization and first-principle calculations. The results indicate that the moderate Ni substitution (x ≤ 0.3) increased the NO_x conversion of electrodes while reduced the polarization resistance. The further investigation shows that this improvement was attributed to the more surface oxygen vacancies, better reducibility and higher Mn⁴⁺ proportion of the Ni-substituted perovskites. The electrochemical impedance spectroscopy (EIS) shows that these changes facilitated the NO_x adsorption and dissociation processes on the electrode. According to first-principle calculations, the Ni-substituted perovskite had a lower formation energy of surface oxygen vacancy, while the NO molecule adsorbed on defect surface gained more electrons thus was easier to be reduced and dissociated. Finally, the electrode performance at different operating temperatures and the operational stability were verified.