NiCo2O4 spinel oxide with oxygen vacancies as a promising catalyst for oxygen reduction reaction

초록

As environmental problems arise from the excessive use of fossil fuels such as global warming, energy conversion systems (ECS) and storage systems (ESS) have been of great interest. Oxygen reduction reaction (ORR) plays an important role in ECS and ESS such as fuel cells and metal-air batteries. Usually, noble metal such as Pt was used as cathode in fuel cell, but high price limits its applications. In this work, NiCo2O4 spinel-type oxide with oxygen vacancies was synthesized by using hydrothermal method, and partial reduction of as-synthesized NiCo2O4 with hydrogen treatment. To observe the surface morphology of NiCo2O4, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) were employed. The structure and surface compositions of catalyst were investigated by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterizations were conducted by using a potentiostat with rotating disk electrode (RDE). These uniquely designed NiCo2O4 with appropriate oxygen vacancies generated from mild reduction showed an enhanced performance and stability for ORR, which was ascribed to enhanced conductivity derived from oxygen vacancies in NiCo2O4 nanoparticles.