Carbon-based lanthanum nickelate material La2−x−yNdxPryNiO4+δ (x = 0, 0.3, and 0.5; y = 0 and 0.2) as a bifunctional electrocatalyst for oxygen reduction in alkaline media

Abstract

The kinetics and mechanism of oxygen reduction reaction (ORR) in alkaline medium are studied on lanthanum nickelate materials La2−x−yNdxPryNiO4±δ (x = 0, 0.3 and 0.5; y = 0 and 0.2) using the electrochemical technique of the rotating disk electrode in a 0.5-M solution of NaOH. The oxide powders are synthesized by the citrate–nitrate method. Structural and surface characterizations are performed by X-ray diffraction (XRD) and X-ray photoelectron spectrometry (XPS), while the morphology is studied by scanning electron microscopy (SEM). Electrochemical studies are carried out by linear voltamperometry, cyclic voltamperometry, and impedance spectroscopy. The doped and undoped electrocatalyst composites (La2−x−yNdxPryNiO4±δ/C), made of the rare earth nickel oxides mixed with carbon black (Vulcan XC-72(C)), are deposited as a thin layer on a glassy carbon substrate. At room temperature, the undoped electrocatalyst La2NiO4±δ material shows single-step kinetics unlike the doped materials. The doping by the rare earths Nd or/and Pr significantly enhances the electrical conductivity of the electrode under air and the diffusion of oxygen. On the other hand, the steric hindrance between the atomic oxygen orbital (π-orbital (O2)–π-orbital (O2)) and the dz2–orbital (Ni)–π-orbital (O2) influences the training model of the liaison (dz2(Ni)–π (O2)). The structure, oxygen adsorption, and oxidation states of the catalyst elements have a large influence on the mechanism and kinetics of the ORR. The LNNO3/C and LNPNO5/C electrocatalysts have better electrocatalytic performances, which allow them to be used as a bifunctional electrocatalyst for the reduction of oxygen in alkaline media.