A Highly Efficient Multi-phase Catalyst Dramatically Enhances the Rate of Oxygen Reduction

This work demonstrates that a multi-phase catalyst coating (∼30 nm thick), composed of BaCoO_3−x (BCO) and PrCoO_3−x (PCO) nanoparticles (NPs) and a conformal PrBa_0.8Ca_0.2Co₂O_5+δ (PBCC) thin film, has dramatically enhanced the rate of oxygen reduction reaction (ORR). When applied to a state-of-the-art La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathode in a solid oxide fuel cell (SOFC), the catalyst coating reduced the cathodic polarization resistance from 2.57 to 0.312 Ω cm² at 600°C. Oxygen molecules adsorb and dissociate rapidly on the NPs due to enriched surface oxygen vacancies and then quickly transport through the PBCC film, as confirmed by density functional theory-based computations. The synergistic combination of the distinctive properties of the two separate phases dramatically enhances the ORR kinetics, which is attractive not only for intermediate-temperature SOFCs but also for other types of energy conversion and storage systems, including electrolysis cells and membrane reactors for synthesis of clean fuels. Oxygen reduction reaction (ORR) is an important but sluggish step in many chemical and energy transformation processes; energy loss due to ORR is still significant in the most advanced fuel cells, more so at lower operating temperatures. To make energy conversion and storage devices economically competitive and commercially viable, however, several materials challenges must be overcome, one of which is the creation of durable, low-cost materials and nanostructures of high electrocatalytic activity for ORR at operating temperatures. Here we report our rationally designed multi-phase catalyst, dramatically enhancing the kinetics of oxygen reduction of the state-of-the-art solid oxide fuel cell cathode. It is readily applicable to other energy storage and conversion systems, including metal-air batteries, supercapacitors, electrolyzers, dye-sensitized solar cells, and photocatalysis. A multi-phase catalyst coating, composed of a thin-film PrBa_0.8Ca_0.2Co₂O_5+δ (PBCC) decorated with nanoparticles (NPs) of BaCoO_3−x and PrCoO_3−x, has dramatically enhanced the rate of oxygen reduction reaction. Oxygen molecules adsorb and dissociate rapidly on the NPs due to enriched surface oxygen vacancies, while the dissociated oxygen species transport quickly through the PBCC film into the cathode.