High Surface Area Perovskite Oxide-Based Oxygen Reduction Reaction Electrocatalysts

Development of effective precious-metal free oxygen reduction reaction (ORR) electrocatalysts is highly desirable as projections indicate that the costs associated with Pt can contribute up to half of the overall cost of low-T fuel cells and electrolyzers. Development of inexpensive and effective catalysts for the ORR also has ramifications for other applications, including metal-air batteries and water splitting. There exists a variety of chemistries and classes of non-precious catalyst materials used for the ORR in alkaline media, including non-precious metal alloys, perovskite oxides, spinels and pyrolyzed metal macrocycles. For perovskite oxide (ABO₃) catalysts, activity is strongly affected by the B cation and activity can be tuned by A and/or B-site doping. Therefore, identification of doping strategies to tune the perovskite catalyst structure and chemistry to achieve maximum intrinsic catalytic activity is of major importance. Performance of these materials is also limited by the very low surface areas yielded by current synthesis methods. Current soft-chemistry approaches that allow high surface areas are generally only successful for the production of simple (e.g. binary) oxides.

Our catalyst development approach involves i) doping strategies to tune the perovskite catalyst structure and chemistry to achieve maximum intrinsic catalytic activity; ii) novel synthesis processes for the production of compositionally-complex perovskite oxide catalysts with magnitude higher surface areas than those reported in the literature using current techniques; and iii) functionalization of the carbon support to create composite C/oxide catalysts with optimized performance. Combined, these advances allow for greatly improved ORR performance as demonstrated in Figure 1, which shows the evolution of ORR activity for a Ca_0.9La_0.1Al_0.1Mn_0.9O_3-δcatalyst (as quantified by rotating disc electrode) after successive implementation of the strategies discussed above. Structure-property correlations to address the interdependence between catalytic activity and variables related to materials composition, structure, and morphology will be presented. 

Figure 1. Oxygen reduction mass activities of Ca_0.9La_0.1Al_0.1Mn_0.9O_3-δ