Influence of intrinsic spin ordering in La0.6Sr0.4Co0.8Fe0.2O3−δ and Ba0.6Sr0.4Co0.8Fe0.2O3−δ towards electrocatalysis of oxygen redox reaction in solid oxide cell

Abstract

The redox reaction of oxygen (OER & ORR) forms the rate determining step of important processes like cellular respiration and water splitting. Being a spin relaxed process governed by quantum spin exchange interaction, QSEI (the ground triplet state in O₂ is associated with singlet oxygen in H₂O/OH⁻), its kinetics is sluggish and requires inclusion of selective catalyst. Functionality and sustainability of solid oxide cell involving fuel cell (FC) and electrolyzer cell (EC) are also controlled by ORR (oxygen redox reaction) and OER (oxygen evolution reaction). We suggest that, presence of inherent spin polarization within La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF6482) (15.86 emu g⁻¹) and Ba_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (BSCF6482) (3.64 emu g⁻¹) accounts for the excellent selective electrocatalysis towards ORR and OER. QSEI forms the atomic level basis for OER/ORR which is directly proportional to spin ordering (non-zero magnetization) of the active electrocatalyst. LSCF6482 exhibits (21.5 kJ mol⁻¹@0.8 V for ORR compared to 61 kJ mol⁻¹@0.8 V for OER) improved ORR kinetics whereas BSCF6482 (18.79 kJ mol⁻¹@0.8 V for OER compared to 32.19 kJ mol⁻¹ for ORR@−0.8 V) is best suited for OER under the present stoichiometry. The findings establish the presence of inherent spin polarization of catalyst to be an effective descriptor for OER and ORR kinetics in solid oxide cell (SOC).