Mechanism of Iron Integration into LiMn_1.5Ni_0.5O₄ for the Electrocatalytic Oxygen Evolution Reaction

Abstract

Spinel-type LiMn1.5Ni0.5O4 has been paid temendrous consideration as an electrode material because of its low cost, high voltage, and stabilized electrochemical performance. Here, we demonstrate the mechanism of iron (Fe) integration into LiMn1.5Ni0.5O4 via solution methods followed by calcination at a high temparature, as an efficient electrocatalyst for water splitting. Various microscopic and structural characterizations of the crystal structure affirmed the integration of Fe into the LiMn1.5Ni0.5O4 lattice and the constitution of the cubic LiMn1.38Fe0.12Ni0.5O4 crystal. Local structure analysis around Fe by extended X-ray absorption fine structure (EXAFS) showed Fe3+ ions in a six-coordinated octahedral environment, demonstrating incorporation of Fe as a substitute at the Mn site in the LiMn1.5Ni0.5O4 host. EXAFS also confirmed that the perfectly ordered LiMn1.5Ni0.5O4 spinel structure becomes disturbed by the fractional cationic substitution and also stabilizes the LiMn1.5Ni0.5O4 structure with structural disorder of the Ni2+ and Mn4+ ions in the 16d octahedral sites by Fe2+ and Fe3+ ions. However, we have found that Mn3+ ion production from the redox reaction between Mn4+ and Fe2+ influences the electronic conductivity significantly, resulting in improved electrochemical oxygen evolution reaction (OER) activity for the LiMn1.38Fe0.12Ni0.5O4 structure. Surface-enhanced Fe in LiMn1.38Fe0.12Ni0.5O4 serves as the electrocatalytic active site for OER, which was verified by the density functional theory study.

LaCoO3 Perovskite Nanoparticles Embedded in NiCo2O4 Nanoflowers as Electrocatalysts for Oxygen Evolution

“…The peaks located at binding energies of 779.17 and 794.54 eV and 781.31 and 796.424 eV are assigned to the Co 3+ and Co 2+ oxidation states, respectively. The high-resolution Ni 2p spectra show two peaks at 854.02 and 871.77 eV associated with Ni 2+ , whereas the peaks that appear at 855.98 and 873.82 eV are attributed to Ni 3+ , respectively. , Another peak doublet at 861.34 and 879.19 eV is assigned as satellite peaks. , The main peak of La 3d 5/2 is unfolded into bimodal double peaks at 833.62 and 837.81 eV due to orbital spin splitting, which corresponds to the energy loss phenomena caused by intense O 2p–La 4f charge events or the presence of a mixture of electronic configurations is induced. , Thus, the high-resolution XPS analysis of La 3d confirms that La is in the 3+ oxidation state in the LaCoO 3 /NiCo 2 O 4 composite structure. In general, La 3d 3/2 and Ni 2p 3/2 appear in the same binding energy region.…”

“…39,40 Another peak doublet at 861.34 and 879.19 eV is assigned as satellite peaks. 32,41 The main peak of La 3d 5/2 is unfolded into bimodal double peaks at 833.62 and 837.81 eV due to orbital spin splitting, which corresponds to the energy loss phenomena caused by intense O 2p−La 4f charge events or the presence of a mixture of electronic configurations is induced. 42,43 Thus, the high-resolution XPS analysis of La 3d confirms that La is in the 3+ oxidation state in the LaCoO 3 /NiCo 2 O 4 composite structure.…”

NiS/MoS2 Anchored Multiwall Carbon Nanotube Electrocatalyst for Hydrogen Generation and Energy Storage Applications

“…This result implies that the transfer of electrons occurs from Mo 4+ to Ni 2+ sites in the composite structure, which further resulted in a low valence state and electron‐rich structure at Ni 2+ sites [44] . Using the relative atomic sensivity factor and the respective areas of the deconvoluted Ni 2p 1/2 and Ni 2p 3/2 , the calculated surface atomic ratio of Ni 2+ /Ni 3+ in pure NiS and composite system are 2.05 and 1.64 respectively [45] . The HRXPS Mo 3d spectrum (Figure 3b) in pure MoS 2 (deconvoluted w.r.t 2H MoS 2 as XRD results suggest) shows the presence of two distinct characteristic peaks at 232.1 and 229.0 eV owing to Mo 3d 3/2 and 3d 5/2 orbitals of Mo 4+ respectively with a spin‐orbit splitting separation energy of 3.1 eV.…”

Facile Fabrication of Ni9S8/Ag2S Intertwined Structures for Oxygen and Hydrogen Evolution Reactions

“…Whereas IrO 2 shows an overpotential of 354 mV to generate the same current density. [76] To assess the OER kinetics of the catalysts we have calculated the Tafel slopes. The Tafel slope of Ni 9 S 8 /Ag 2 S composite nanostructure was found to be 72 mV dec À 1 (Figure 9b), which was lower than commercial IrO 2 (78 mV dec À 1 ), Ni 9 S 8 (125 mV dec À 1 ), and Ag 2 S (161 mV dec À 1 ).…”