Influence of Pamoic Acid as a Complexing Agent in the Thermal Preparation of NiO Nanoparticles: Application to Electrochemical Water Oxidation

We developed a thermal decomposition method for preparing NiO nanoparticles (NiONPs) using disodium salt of pamoic acid (Na₂PA) as a complexing agent and Ni(NO₃)₂⋅6H₂O as a nickel precursor. Prior to thermal decomposition, Ni(NO₃)₂⋅6H₂O was mixed with Na₂PA in ethanol, and the ethanol was evaporated succesively. The dried reaction mass was characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. Thermal decomposition was then performed in air to obtain the NiONPs. The role of Na₂PA in the synthesis of NiONP was evaluated by preparing NiONPs according to the protocol described above without the addition of Na₂PA. The X-ray diffraction data indicated that crystalline NiO (bunsenite, cubic crystal system) formed with or without Na₂PA; however, field emission scanning electron microscopy images showed that smaller monodisperse NiONPs formed only with the addition of Na₂PA. Without Na₂PA, the obtained NPs were quite large and polydisperse. The sizes of the NiONPs prepared in the presence of Na₂PA were determined using transmission electron microscopy imaging to be 19.1 ± 3.2 nm. The electrocatalytic activity of the NiONPs toward water oxidation under alkaline conditions was evaluated by immobilizing the NPs onto an in-house prepared filter paper derived carbon electrode, and compared.