Dual-Doping Strategy for Lowering the Thermal Expansion Coefficient and Promoting the Catalytic Activity in Perovskite Cobaltate Air Electrodes for Solid Oxide Cells

Abstract

Lowering the thermal expansion coefficient (TEC) and promoting the catalytic activity of cobalt-based perovskite air electrodes is crucial for efficient solid oxide cells (SOCs) devices. However, the co-achievement of both merits has usually been largely compromised in most scenarios. Herein, a dual-doping strategy to manipulate the properties of perovskite cobaltate electrocatalyst is reported in which a high valence element of Ta⁵⁺ is incorporated into B-site to significantly suppress the dynamic reduction of Co⁴⁺ species and reduces the TEC value from PrBaCo₂O_5+δ (PBC, 17.8 × 10^⁻6 K⁻¹) to PrBaCo_1.96Ta_0.04O_5+δ (PBCT, 12.5 × 10⁻⁶ K⁻¹) and suppresses the oxygen loss in SOCs operation condition, revealing the improved structural stability. Meanwhile, the Ca²⁺ is doped into A-site of Ta-incorporated candidate, further decreasing the covalency of Co─O bonds and facilitating the formation of oxygen vacancies, benefiting the oxygen exchange kinetics and leading to a low polarization resistance of 0.026 Ω cm² (800 °C) in as-prepared PrBa_0.8Ca_0.2Co_1.96Ta_0.04O_5+δ (PBCCT) electrode. The cell with PBCTT demonstrates remarkable robustness during a 50 h thermal cycling test (25 cycles). Moreover, it delivers a high current density of 1.44 A cm⁻² (1.6 V, 800 °C), as well as attractive durability over 100 h for pure CO₂ electrolysis.