Bifunctional Platinum-Cobal Oxide Catalysts for the Oxygen Reduction and Evolution Reactions

Abstract

A bifunctional catalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) could be employed in a unitized regenerative fuel cell, an energy storage device that can be coupled to intermittent renewable energy such as wind or solar to peak-shift electricity to the grid. Though significant work has been done over the past few decades, no catalyst for both ORR and OER with high activity for both reactions have been discovered. It is well know that platinum or platinum based alloys exhibit the highest activities for ORR among all other catalyst, however they display poor activity for OER. In contrary, transition metal (hydro)oxides, such as iron, nickel, or cobalt (hydro)oxides, always possess highly activities for OER but poor activity for ORR. Due to “migration-effect” of transition metal in ORR, in which the free transition metal (hydro)oxides will move to the surfaces of platinum during electrochemical process and results in the dramatically decrease of the ORR activity of Pt eventually, it is impossible to achieve high activity for both ORR and OER by simply mix platinum or platinum based alloy with transition metal (hydro)oxides together. Inspired by this, we developed a novel method to prepare 7nm platinum nanoparticles doped with atomic sized cobalt oxides for the applications of ORR and OER. Our primary results showed that these hetero-structured materials exhibited higher activity than state-of-the-art commercial platinum for ORR, but also 10 times higher activity for OER than Co3O4. Most importantly, our catalysts also demonstrated excellent stability. Apparently, the interfaces must play a dominated role in both ORR and OER. Investigation of the interfaces between platinum and Co3O4 of our catalyst in atomic scale is crucial to understand how the interfaces worked and what kinds of interfaces are better for both ORR and OER. Our work will advanced the fundamental understanding of the metal-oxide interface in enhancing the ORR and OER, which is envisioned to shed light on the design of advanced catalysts for catalyzing complex chemical processes.