Materials Discovery: Non-Precious Metal Catalysts for the Oxygen Reduction Reaction

The development of active, stable, and low-cost catalysts for the ORR in acid is necessary for the viability of polymer electrolyte membrane fuel cells.¹ A promising class of materials are the TM oxides, which encompass a large phase space due to the variety of possible constituents, stoichiometries, and structures.² These catalysts have however been limited by their poor stability in acid and poor electrical conductivity, which can complicate understanding of the intrinsic activity of the catalyst. In this work, we have devised a two pronged approach to studying oxides that focuses on (1) leveraging our computational expertise to find a composition that is active and conductive, and (2) designing morphological controls to access oxides that are difficult to study due to their insulating nature.

We computationally identified transition metal antimonates (M_xSb_yO_z) as having ORR activity approaching that of the Pt (111) surface, as well as metallic character. We then synthesized nanoparticulate antimonates with different transition metals, (e.g. Mn, Ni), and tested their activity, stability, and selectivity for ORR in acid and alkaline electrolyte. Through loading studies, use of different supports and substrates, and modification via nitridation, we have gained insight into these previously unexplored oxide catalysts for ORR and validated theoretical predictions for novel materials.

V-doped Ta₂O₅ was identified computationally as a promising low-cost acid-stable catalyst, but the bulk conductivity is poor. To overcome this, we developed synthetic methods to control the doping level, crystal structure, and nanoparticle morphology. Utilizing the smallest nanoparticles with carbon and antimony-doped tin oxide supports, we assessed the electrochemical performance of these catalysts for both ORR and OER, validating the predicted stability of these materials over a wide potential range. This combined computation-experimental methodology for identification of promising catalysts provides a roadmap for future materials discovery for a variety of important reactions.

(1)Adv.Mat.2019,31,1807615

(2) Apl.Mater.2013,1(1),011002.