Unraveling Double-Exchange Effect Coupling Spin Modulation of Sr2Fe1.5Mo0.5O6-δ Electrocatalyst for Solid Oxide Cells

Perovskites are promising electrocatalysts for solid oxide cells (SOCs) due to their tunable structures. The reactivity/stability can be effectively enhanced by tuning the spin, whereas few studies have been able to elucidate the correlation between spin and reactivity/stability. Herein, the double-exchange effect coupling spin modulation is studied for Sr₂Fe_1.3Ni_0.2Mo_0.5O₆, which exhibits a current density of 2.48 A cm^-2 with high stability at 800 °C and 1.5 V as the cathode in CO₂ reduction. Based on Mössbauer spectroscopy, X-ray absorption spectroscopy, and density functional theory calculations, it is revealed that the doped Ni induces an additional double-exchange effect with enhanced conductivity coupling spin modulation. It produces high-spin Fe⁴⁺ (t_2g³e_g¹) with vacant e_g orbitals which can accommodate additional electrons from the lone pairs of oxygen, thus facilitating CO₂ reduction by enhancing CO₂ adsorption and weakening CO adsorption. This work provides a general strategy for the design of SOC electrocatalysts.