Composite Bifunctional Electrocatalyst for the Oxygen Reduction and Evolution Reactions.

Bifunctional oxygen electrocatalysts are subjected to stringent performance and stability criteria. The catalyst must achieve high oxygen evolution reaction (OER) activity while in electrolyzer operation, as well as high oxygen reduction reaction (ORR) activity while in fuel cell operation. Additionally, the catalyst must be stable over a wide potential range and withstand alternating reducing and oxidizing potentials. In this work, a composite NiFeO/NiCoO is rigorously tested as a bifunctional catalyst for anion exchange membrane (AEM) fuel cell and electrolyzer operation. An alternating potential stability test is performed, which unveils the areas where the bifunctional catalyst needs improvement. The OER activity of the catalyst is not hindered by the harsh conditions. However, the ORR activity deteriorates. Both the fundamental rotating disk electrode (RDE) methodology and AEM single-cell testing are used to evaluate the electrode activity and stability. The difference in results between the two techniques emphasizes the importance of evaluating the catalyst under applied conditions. The results of this study provide guidance for the development of new high-performing bifunctional catalysts.