Unveiling the critical role of W doping in enhancing oxygen reduction activity of SrCo0.7Fe0.3O3−δ cathodes for intermediate-temperature SOFCs

Abstract

Cobalt-based composite cathodes, composed of single perovskite (SP) and double perovskite (DP) phases, represent promising candidate materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, the rational design of the SP–DP composite composition requires fundamental insights into the relationship between doping cations and their defect chemistry and oxygen reduction reaction (ORR). To address this, we investigated SrCo_0.7Fe_0.3−xW_xO_3−δ (SCFW, x = 0, 0.1, 0.15, 0.2 and 0.3), a prototypical SP–DP composite, using in situ/ex situ characterization to assess its microstructure, surface oxygen species, bulk oxygen vacancies, and electrochemical performance. It was found that partial substitution of Fe by W in SCF induced microphase separation into SP and DP structures. The DP/SP ratio increased with W doping content but remained temperature-independent. Coexisting SP and DP phases synergistically boosted oxygen permeation flux, oxygen vacancy concentration and surface oxygen reactivity. This synergy enhanced oxygen diffusion through the surface and bulk phases, thereby accelerating ORR kinetics and enabling high electrocatalytic activity. At 640 °C, the area-specific resistance of the SCFW-0.2 cathode was 0.051 Ω cm², significantly lower than that of the undoped SrCo_0.7Fe_0.3O_3−δ cathode. These findings provide critical insights into the enhanced electrochemical activity of W-doped SCF cathodes and offer pathways to tailor surface oxygen species and oxygen vacancies for practical IT-SOFC applications.