Experimental Descriptors for the Synthesis of Multicationic Nickel Perovskite Nanoparticles for Oxygen Reduction

Abstract

In many liquid-phase synthesis methods developed to produce nanomaterials, the key parameters governing the selective synthesis of solids and compounds are clearly identified, e.g. heat treatment profile, precursors solubility, pH, etc. Most of these wellunderstood approaches rely on relatively low temperature processes, below 400 °C, where conventional solvents are still stable. Interestingly, thermally stable inorganic molten salts enable to widen the temperature range for liquid-phase syntheses. They provide access to other families of crystalline solids requiring higher temperatures, as multicationic oxides. Nonetheless, the mechanisms that govern solid state formation and phase selection when different compounds compete are poorly understood. Herein, we report how experimental parameters, such as temperature, time, reaction medium Page 2 of 43 ACS Paragon Plus Environment ACS Applied Nano Materials 3 composition and solvent oxo-basicity, enable to drive the synthesis mechanisms in molten salts towards nanoscaled multicationic oxides. We especially enlighten the phaseselective synthesis of pseudo-cubic perovskite LaNiO 3 and layered Ruddlesden-Popper phases La NiO and LaSrNiO 4 at the nanoscale, by suggesting that the oxidation state of the metallic precursor plays a key role in the reaction pathway. This allows designing electrocatalysts for oxygen reduction reaction.

Investigation into La(Fe/Mn)O3 Perovskites Formation over Time during Molten Salt Synthesis

“…This confirms that the XRD data of the washed samples (Figures ,,, and ) reliably reflects their compositions. The duration of MSS experiments most commonly ranges from several hours to under 1 h. ,,,− The “feeding-and-sampling” procedure reveals that MSS is remarkably fast, yielding a PTO phase within single minutes.…”

“…In this “mixing” procedure, product formation has been reported to initiate during the heating period, prior to the salts’ melting point. , Thus, the salt composition determines both the chemical environment of MSS and the salts’ melting point, affecting the reaction starting point. , Additionally, MSS durations are often reported as the dwelling time at the synthesis temperature, without considering the lengthy heating period (Figure ). Notably, even extremely high heating rates dictate a heating period of several minutes. − An effective method for minimizing this period is introducing the salt and reagents mixture into a preheated furnace. , Alternatively, reagents can be fed into the molten salt during dwelling at the designated synthesis temperature − (“feeding”Figure ), defining the reaction starting point.…”

Geoinspired syntheses of materials and nanomaterials

“…17C). 170 Again, the analysis of quenched media at different reaction times provided information on reaction mechanisms. We have highlighted the incorporation of nickel ions into La 2 NiO 4 to form LaNiO 3 at low temperatures with retention of particles size and morphology, while higher temperature triggered dissolution of La 2 NiO 4 and re-crystallization of LaSrNiO 4 .…”

High-Efficiency of Bi-Functional-Based Perovskite Nanocomposite for Oxygen Evolution and Oxygen Reduction Reaction: An Overview

“…According to Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), LaNiO 3 is made up of well faceted truncated cubes with an average particle size of 100 nm. Tiny particles as small as 20 nm can also be seen in these micrographs [ 51 ]. Song et al [ 52 ] synthesized Ni/Mn promoted cobaltite by a one-step wet-chemical method.…”