Improved Oxygen Redox Activity by High-Valent Fe and Co3+ Sites in the Perovskite LaNi1-xFe0.5xCo0.5xO3

Tuning the electronic structure of perovskite oxides via aliovalent substitution is a promising strategy to attain inexpensive and efficient electrocatalysts for energy conversion and storage devices. Herein, following the d-band center positions and using a simple sol-gel method followed by a pyrolysis step, LaNi1-xCo0.5xFe0.5xO3 (LNFCO-x; x = 0.0, 0.4, 0.5, and 0.6) electrocatalysts are designed and synthesized for oxygen redox reactions in 1 M KOH. Among them, LNFCO-0.5 has exhibited the lowest overpotential and the highest charge transfer kinetics in oxygen redox reactions. Overall, a 90 mV lower overpotential was observed in oxygen redox activity of LNFCO-0.5 compared to that of pristine LaNiO3. The mass activity of LNFCO-0.5 in the oxygen reduction reaction (at 0.7 V vs RHE) and oxygen evolution reaction (1.60 V vs RHE) was calculated to be 2.5 and 2.13 times higher than that of LaNiO3, respectively. The bifunctionality index (potential difference between the oxygen evolution at a current density of 10 mA cm(-2) and the oxygen reduction at a current density of -1 mA cm(-2)) of LNFCO-0.5 was found to be 0.98. The substitution of Fe and Co for the Ni-site shifted the d-band center close to the Fermi level, which can increase the binding strength of the *OH intermediate in the rate-determining step. Also, the surface was enriched with Fe3+Delta, Co3+, and partially oxidized Ni3+ states, which is susceptible to tune the eg-orbital filling for superior oxygen redox activity.

Automated summary

By synthesizing LaNi1-xCo0.5xFe0.5xO3 electrocatalysts, high activity in oxygen reduction and oxygen evolution reactions was achieved. The substitution of Fe and Co can shift the d-band center, enhancing the binding strength of reaction intermediates and improving oxygen redox activity.