Trinary Layered Double Hydroxides as High-Performance Bifunctional Materials for Oxygen Electrocatalysis.

Layered double hydroxides (LDHs) are a family of high-profile layer materials with tunable metal species and interlayer spacing, and herein the LDHs are first investigated as bifunctional electrocatalysts. It is found that trinary LDH containing nickel, cobalt, and iron (NiCoFe-LDH) shows a reasonable bifunctional performance, while exploiting a preoxidation treatment can significantly enhance both oxygen reduction reaction and oxygen evolution reaction activity. This phenomenon is attributed to the partial conversion of Co2+ to Co3+ state in the preoxidation step, which stimulates the charge transfer to the catalyst surface. The practical application of the optimized material is demonstrated with a small potential hysteresis (800 mV for a reversible current density of 20 mA cm−2) as well as a high stability, exceeding the performances of noble metal catalysts (commercial Pt/C and Ir/C). The combination of the electrochemical metrics and the facile and cost-effective synthesis endows the trinary LDH as a promising bifunctional catalyst for a variety of applications, such as next-generation regenerative fuel cells or metal-air batteries. [ABSTRACT FROM AUTHOR]