Fabrication of a mesoporous Ba_0.5Sr_0.5Co_0.8Fe_0.2O_{3-: δ} perovskite as a low-cost and efficient catalyst for oxygen reduction

A precious metal-free cathode catalyst, mesoporous Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (m-BSCF), with a well crystallized perovskite framework and a porous structure (pore size of ∼10 nm) has been synthesized by a one-step co-nanocasting method. The obtained mesoporous perovskite m-BSCF demonstrated a much higher oxygen reduction reaction catalytic activity than its macroporous (CS-BSCF of ∼5 μm pore size) and nonporous counterparts (SG-BSCF). The mesoporous structure and oxygen vacancies endowed the obtained perovskite oxide m-BSCF with an approximate 4e^- pathway for the ORR comparable to the benchmark 20 wt% Pt/C and a stable electro-catalytic activity with 91% current density being retained after 5000 cycles, and excellent methanol tolerance. The redox couples Co⁴⁺/Co³⁺ and Fe³⁺/Fe²⁺ are proposed to accelerate the ORR on active species, i.e., MOOH (M = Co, Fe) groups produced by the substitution species of Co and Fe in the B-site of perovskite m-BSCF, and in the meantime oxygen vacancies generated by the redox couples play a key role in activating the oxygen molecules.