Defect-based chemical regulation and electrochemical performance of In³⁺-doped BaCe_0.36Fe_0.64O_3-δ cobalt-free cathodes

To address the limitations of the cobalt-free cathode BaCe_0.36Fe_0.64O_3-δ for proton-conducting solid oxide fuel cells, namely low proton conductivity and poor chemical stability, an In³⁺ doping strategy at the B-site was adopted in this work. A series of BaCe_0.36-xFe_0.64In_xO_3-δ cathode materials were synthesized via the sol-gel method, and the effects of In³⁺ doping on crystal structure, oxygen vacancy concentration, conductive behavior, and single-cell performance were systematically investigated. The results show that In³⁺ doping induces lattice expansion and increases the cubic phase content. Charge compensation is achieved through the reduction of Fe, leading to a marked increase in oxygen vacancy concentration. Among all samples, BCFI10 exhibits the lowest average Fe valence state of 2.57, the highest oxygen vacancy concentration, and a conductivity of 4.71×10⁻² S·cm⁻¹ in humid air at 600℃. At 800℃, its hydrogen permeation flux reaches 2.37×10⁻⁸ mol·cm⁻²·s⁻¹, representing a substantial improvement over undoped BCF. A single cell employing BCFI10 as the cathode achieves a peak power density of 279 mW·cm⁻² at 700℃, which is 123% higher than that of BCF, and shows no current density decay during a 100-hour constant-voltage test. Appropriate In³⁺ doping effectively enhances the triple conductivity and single-cell output performance of the BCF-based cathode by optimizing defect chemistry, offering a new route for developing low-cost high-performance H-SOFC cathode materials.