Partially Substituted La for Sm in Sm0.8Sr0.2NiO3: An Efficient Electrocatalyst Towards Alkaline Water Splitting

Abstract

Perovskite-type oxides having composition La_xSm_0.8−xSr_0.2NiO₃ (0 ≤ x ≤ 0.6) were explored for their ability to act as facilitators for oxygen evolution reaction (OER) in alkaline media. Synthesis of the materials was conducted through a sol-gel procedure via malic acid. The materials underwent advanced physicochemical characterization utilizing techniques, namely transmission electron microscope (TEM), scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS), inductively coupled plasma – mass spectrometry (ICP-MS) and X-ray diffraction (XRD). These analyses provided crucial details about the material’s particle size, surface morphology/chemical composition and crystalline structure, opening up exciting possibilities for their diverse applications. From TEM analysis, the average particle size of the oxide materials has been estimated and found to be 5.9 nm for Sm_0.8Sr_0.2NiO₃ and 4.8 nm for La_0.6Sm_0.2Sr_0.2NiO₃. The particle size of the oxide material decreases when La was partially substituted for Sm in Sm_0.8Sr_0.2NiO₃. Cyclic voltammetry and Tafel plot were observed for the electrochemical analysis in 1 M KOH (25 °C). An investigation on the anodic polarization of oxides revealed an increased electrocatalytic activity when La was partially substituted for Sm in Sm_0.8Sr_0.2NiO₃. La_0.6Sm_0.2Sr_0.2NiO₃ was found to be most active at 800 mV with a current density, j = 184.1 mA/cm². The Tafel experiment was conducted in 1M KOH at varying temperatures to determine thermodynamic properties like standard electrochemical energy of activation ($$), standard enthalpy of activation (ΔH°^#), and standard entropy of activation (ΔS°^#).