Spray-Flame Synthesis of LaFexCo1- xO3 (x = 0.2, 0.3) Perovskite Nanoparticles for Oxygen Evolution Reaction in Water Splitting: Effect of Precursor Chemistry (Acetates and Nitrates)

Steven Angel; Michael Braun; Baris Alkan; Joachim Landers; Soma Salamon; Heiko Wende; Corina Andronescu; Christof Schulz; Hartmut Wiggers

doi:10.1021/acs.jpca.2c06601

Spray-Flame Synthesis of LaFe_xCo_{1- x}O₃ (x = 0.2, 0.3) Perovskite Nanoparticles for Oxygen Evolution Reaction in Water Splitting: Effect of Precursor Chemistry (Acetates and Nitrates)

J Phys Chem A. 2023 Mar 23;127(11):2564-2576. doi: 10.1021/acs.jpca.2c06601. Epub 2023 Mar 10.

Authors

Steven Angel¹, Michael Braun², Baris Alkan³, Joachim Landers⁴, Soma Salamon⁴, Heiko Wende^{4

5}, Corina Andronescu^{2

5}, Christof Schulz^{1

5}, Hartmut Wiggers^{1

5}

Affiliations

¹ EMPI, Institute for Energy and Materials Processes - Reactive Fluids, University of Duisburg-Essen, 47048 Duisburg, Germany.
² Chemical Technology III, University of Duisburg-Essen, 47048 Duisburg, Germany.
³ Fritz-Haber-Institut der Max-Planck Gesellschaft, Departments of Physical Chemistry and Inorganic Chemistry, Faradayweg 4-6, 14195 Berlin, Germany.
⁴ Experimental Physics, Faculty of Physics, University of Duisburg-Essen, 47048 Duisburg, Germany.
⁵ CENIDE, Center for Nanointegration, University of Duisburg-Essen, 47048 Duisburg, Germany.

PMID: 36896577
DOI: 10.1021/acs.jpca.2c06601

Abstract

The product properties of mixed oxide nanoparticles generated via spray-flame synthesis depend on an intricate interplay of solvent and precursor chemistries in the processed solution. The effect of two different sets of metal precursors, acetates and nitrates, dissolved in a mixture of ethanol (35 Vol.%) and 2-ethylhexanoic acid (2-EHA, 65 Vol.%) was investigated for the synthesis of LaFe_xCo_1-xO₃ (x = 0.2, 0.3) perovskites. Regardless of the set of precursors, similar particle-size distributions (d_p = 8-11 nm) were obtained and a few particles with sizes above 20 nm were identified with transmission electron microscopy (TEM) measurements. Using acetates as precursors, inhomogeneous La, Fe, and Co elemental distributions were obtained for all particle sizes according to energy dispersive X-ray (EDX) mappings, connected to the formation of multiple secondary phases such as oxygen-deficient La₃(Fe_xCo_1-x)₃O₈ brownmillerite or La₄(Fe_xCo_1-x)₃O₁₀ Ruddlesden-Popper (RP) structures besides the main trigonal perovskite phase. For samples synthesized from nitrates, inhomogeneous elemental distributions were observed for large particles only where La and Fe enrichment occurred in combination with the formation of a secondary La₂(Fe_xCo_1-x)O₄ RP phase. Such variations can be attributed to reactions in the solution prior to injection in the flame as well as precursor-dependent variations in in-flame reactions. Therefore, the precursor solutions were analyzed by temperature-dependent attenuated total reflection Fourier-transform infrared (ATR-FTIR) measurements. The acetate-based precursor solutions indicated the partial conversion of, mainly La and Fe, acetates to metal 2-ethylhexanoates. In the nitrate-based solutions, esterification of ethanol and 2-EHA played the most important role. The synthesized nanoparticle samples were characterized by BET (Brunauer, Emmett, Teller), FTIR, Mössbauer, and X-ray photoelectron spectroscopy (XPS). All samples were tested as oxygen evolution reaction (OER) catalysts, and similar electrocatalytic activities were recorded when evaluating the potential required to reach 10 mA/cm² current density (∼1.61 V vs reversible hydrogen electrode (RHE)).