Diverse Pyrochlore Materials for Oxygen Reduction and Evolution Reaction in Alkaline Medium

Abstract

The oxygen reduction and evolution reactions (ORR and OER) have proven to be the limiting factors on the development of rechargeable metal-air batteries. Numerous research work has been carried out on the improvement of cathode technologies in order to reduce the voltage loss associated with the oxygen reactions. ORR and OER have proven to be a catalytic electrochemical process, and thus, the catalytic material in the cathode plays an important role in the performance of such batteries.Current catalysts used for air cathodes can be classified into noble metals and metal alloys, carbons, and transition metal oxides. Platinum and platinum-based electrodes such as Pt-nanopartices dispersed on a carbon support have been the primary choice to catalyze the ORR because of their known superior electrocatalytic activity. Other Pt-based alloys, Pt3M (where M can be Fe, Co among others) have also shown superior ORR activities. Carbonaceous materials have also emerged as an alternative for metal-free electrodes. Some of the best performing carbonaceous materials are vertically aligned nitrogen doped carbon nanotubes (VA-NCNT), nitrogen doped porous carbons and graphenes which have exhibit comparable activity to that of the Pt-based electrodes [1]. However, in order to fully develop the applicability of metal-air batteries, bifunctional electrodes are essential.In the present research, a group of pyrochlore materials, A2B2O7-δOδ, have being synthesized, characterized and studied for bifunctional oxygen electrode applications. Among the characteristics that make pyrochlores attractive for air cathodes, is the unusual framework containing oxygen vacancy ordering. Lanthanum, lead and bismuth-based pyrochlores has been synthesized by the well-known Pechini, solid state, and stearic acid methods.All the samples were characterized by XRD for phase analysis, and electrochemical performance has been investigated by means of cyclic voltammetry. The effect of dopant concentration on the electronic conductivity as well as oxygen activity will be presented. Acknowledgements This work is supported by the IGERT-NSF fellowship and partially funded by the US Dept. of Energy/NETL, Oak Ridge Institute for Science and Education (ORISE) fellowship.