Computational design and experimental realization of Zn substitution in Cr-poisoning resistant LaNi0.6Fe0.4O3-δ solid oxide fuel cell cathode for enhanced performance and durability

Abstract

Chromium poisoning rapidly degrades the performance of solid oxide fuel cell (SOFC) cathode materials with superior oxygen reduction kinetics, such as La0·6Sr0·4Co0·2Fe0·8O3 and La0·6Sr0·4CoO3. Previously, LaNi0.6Fe0.4O3 (LNF) demonstrated excellent resistance to chromium poisoning; however, it has relatively low electrocatalytic activity. Here, we investigate the effect of Zn substitution on the B-site of LNF cathode and deliver La(Ni0·6Fe0.4)1-xZnxO3-δ cathode materials with enhanced electrical and electrochemical properties. The ab initio first-principles calculations showed charged oxygen-vacancy defect formation energies of Zn-doped LNF (2.07 eV for La8Ni5Fe2Zn1O24 and 1.83 eV for La8Ni4Fe3Zn1O24) are lower than those of undoped LNF (2.92 eV for La8Ni5Fe3O24). Various Zn-doped LNF materials are synthesized and tested for experimental validation of the DFT results. Electrical conductivity relaxation, temperature-programmed oxygen desorption, and electrochemical impedance spectroscopy analysis indicate enhanced oxygen reduction kinetics for LNFZ3 (La(Ni0·6Fe0.4)0.97Zn0·03O3-δ). At 700 °C, LNFZ3 has 25.4% less polarization resistance and 52.3% higher maximum power density of an anode-supported SOFC than LNF. Moreover, LNFZ3 has the lowest polarization resistance compared with various studies reporting LNF cathode material. Furthermore, LNFZ3 shows highly robust operation under accelerated chromium-poisoning conditions at 700 °C. The high performance and durability synergy makes the newly developed LNFZ3 a promising cathode material for further commercial validation studies.