Improved Oxygen Redox Activity by High-Valent Fe and Co<sup>3+</sup> Sites in the Perovskite LaNi<sub>1–<i>x</i></sub>Fe<sub>0.5<i>x</i></sub>Co<sub>0.5<i>x</i></sub>O<sub>3</sub>
Anjaiah Sheelam, Sakthipriya Balu, Adil Muneeb, Khasim Saheb Bayikadi, Namasivayam Dhenadhayalan, Erakulan E. Siddharthan, Arif I. Inamdar, Ranjit Thapa, Ming‐Hsi Chiang, Song‐Jeng Huang, Raman Sankar
Abstract
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+Δ, Co3+, and partially oxidized Ni3+ states, which is susceptible to tune the eg-orbital filling for superior oxygen redox activity.