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Mixed-Cation Perovskite La0.6Ca0.4Fe0.7Ni0.3O2.9 as a Stable and Efficient Catalyst for the Oxygen Evolution Reaction

Cite this: ACS Catal. 2021, 11, 13, 8338–8348
Publication Date (Web):June 23, 2021
https://doi.org/10.1021/acscatal.1c00796
Copyright © 2021 American Chemical Society
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Abstract

The La0.6Ca0.4Fe0.7Ni0.3O2.9 perovskite was synthesized using a modified ultrasonic spray pyrolysis technique with sorbitol as the fuel and ozone as the oxidizer, resulting in chemically homogeneous hollow spheres with a specific surface area as high as ∼15 m2 g–1. The crystal structure and the chemical composition were determined with powder X-ray diffraction, electron diffraction, aberration-corrected scanning transmission electron microscopy, energy-dispersive X-ray mapping, 57Fe Mössbauer spectroscopy, iodometric titration, and X-ray photoelectron spectroscopy. Being employed as a catalyst for the oxygen evolution reaction (OER) in 1 M NaOH, La0.6Ca0.4Fe0.7Ni0.3O2.9 demonstrates a mass activity of ∼400 A g–1oxide at 1.61 V vs RHE and a low 52 ± 2.6 mv dec–1 Tafel slope without noticeable degradation. The superior activity of La0.6Ca0.4Fe0.7Ni0.3O2.9 compared to that of undoped LaFe0.7Ni0.3O3 was rationalized by the comparison of DFT-calculated electronic structures. The Ca doping increases Ni and Fe oxidation states, enhances covalency of the Ni/Fe-O bonds, shifts the center of the O 2p band closer to the Fermi level thus decreasing formation energy of the oxygen vacancies, and activates the lattice oxygen mechanism of the OER, which enhances the catalytic activity. Yet, an optimal balance between stability and activity ensures that the thin and stable active layer of Ni-Fe (oxy)hydroxide is supported by the preserved perovskite structure.

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscatal.1c00796.

  • PXRD refinement of La0.6Ca0.4Fe0.7Ni0.3O2.9 perovskite before and after soaking in 1 M NaOH, Mössbauer spectra of La0.6Ca0.4Fe0.7Ni0.3O2.9 and LaFe0.7Ni0.3O3, HAADF-STEM images of synthesized samples, list of samples, electrochemical data for the optimization of perovskite-to-VC ratios and mass loading, comparison of the mass activities at 1.61 V with the literature data, HAADF-STEM images of soaked sample, XPS spectra and calculated stoichiometry, Faradaic efficiency calculated under potentiostatic conditions, galvanostatic test, HAADF-STEM images after polarization, calculation of charge from redox transition, models of the La0.6Ca0.4Fe0.7Ni0.3O2.9 and LaFe0.7Ni0.3O3 for DFT-U calculations, and local spin-polarized PDOS for La0.625Ca0.375Fe0.75Ni0.25O3 and La0.625Sr0.375Fe0.75Ni0.25O3 (PDF)

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