La, Ni-Based Metal Oxides As Bifunctional Catalysts for the Oxygen Reduction and Evolution Reactions in Alkaline Medium

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the fundamental processes occurring at the air electrode of metal-air batteries and reversible fuel cells. [1,2] However, the performance of those devices is hindered by the sluggish kinetics of both OER and ORR, and by the low stability and high cost of the catalysts. Here, we will present our recent studies on the one-dimensional (1D) La, Ni-based metal oxide [3] bifunctional catalysts which are characterized by excellent OER and ORR electrocatalytic activity and outstanding stability. The catalysts were prepared by hydrothermal method and, by controlling the KOH concentration, 1D hydroxide precursors with different aspect ratios were synthesized. By using graphene (G) as the supporting material, a variety of La, Ni-based metal oxides such as Ni+La 2 O 3 /G, LaNiO 3 , and La 2 NiO 4 +NiO/G were synthesized, Figure 1. Electrochemical characterization of the catalysts showed that the aspect ratio of the materials has a significant effect on their electrocatalytic activity. Namely, Ni+La 2 O 3 /G nanorods have proven to be electrochemically active for ORR with a half-wave potential (E 1/2 ) of 0.715 V vs RHE, and for OER with 1. 574 V vs RHE at 10.0 mA cm −2 (E 10 ) in 0.1 M KOH. The performance of Ni+La 2 O 3 /G is close to that of commercial Pt/C (E 1/2 =0.830V) which is the most efficient catalyst of ORR, and significantly higher than commercial RuO 2 (E 10 =1.633 V) and IrO 2 (E 10 =1.663 V) for OER. The unique structural, morphological and electrocatalytic properties of the Ni+La 2 O 3 /G catalysts will be presented and discussed. 1. Sui, S.; Wang, X.; Zhou, X.; Su, Y.; Riffat, S.; Liu, C.-j., A comprehensive review of Pt electrocatalysts for the oxygen reduction reaction: Nanostructure, activity, mechanism and carbon support in PEM fuel cells. Journal of Materials Chemistry A 2017 , 5 (5), 1808-1825. 2. Cheng, F.; Shen, J.; Peng, B.; Pan, Y.; Tao, Z.; Chen, J., Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts. Nature chemistry 2011, 3 (1), 79. 3. Singh, Sarika, Daria Zubenko, and Brian A. Rosen. "Influence of LaNiO3 shape on its solid-phase crystallization into coke-free reforming catalysts." ACS Catalysis 2016 , 7 4199-4205. Figure 1