Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Low-spin state of Fe in Fe-doped NiOOH electrocatalysts.

ABSTRACT: Doping with Fe boosts the electrocatalytic performance of NiOOH for the oxygen evolution reaction (OER). To understand this effect, we have employed state-of-the-art electronic structure calculations and thermodynamic modeling. Our study reveals that at low concentrations Fe exists in a low-spin state. Only this spin state explains the large solubility limit of Fe and similarity of Fe-O and Ni-O bond lengths measured in the Fe-doped NiOOH phase. The low-spin state renders the surface Fe sites highly active for the OER. The low-to-high spin transition at the Fe concentration of ~ 25% is consistent with the experimentally determined solubility limit of Fe in NiOOH. The thermodynamic overpotentials computed for doped and pure materials, η = 0.42 V and 0.77 V, agree well with the measured values. Our results indicate a key role of the low-spin state of Fe for the OER activity of Fe-doped NiOOH electrocatalysts.

SUBMITTER: He ZD

PROVIDER: S-EPMC10264450 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Low-spin state of Fe in Fe-doped NiOOH electrocatalysts.

He Zheng-Da ZD Tesch Rebekka R Eslamibidgoli Mohammad J MJ Eikerling Michael H MH Kowalski Piotr M PM

Nature communications 20230613 1

Doping with Fe boosts the electrocatalytic performance of NiOOH for the oxygen evolution reaction (OER). To understand this effect, we have employed state-of-the-art electronic structure calculations and thermodynamic modeling. Our study reveals that at low concentrations Fe exists in a low-spin state. Only this spin state explains the large solubility limit of Fe and similarity of Fe-O and Ni-O bond lengths measured in the Fe-doped NiOOH phase. The low-spin state renders the surface Fe sites hi ...[more]

PMID: 37311755

Similar Datasets

A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts.

Project description:Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N4 ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen2N2)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen2N2)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen2N2)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen2N2)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.

| S-EPMC7572418 | biostudies-literature

Toward Simulation of Fe(II) Low-Spin → High-Spin Photoswitching by Synergistic Spin-Vibronic Dynamics.

Project description:A new theoretical approach is presented and applied for the simulation of Fe(II) low-spin (LS, singlet, t2g6eg0) → high-spin (HS, quintet, t2g4eg2) photoswitching dynamics of the octahedral model complex [Fe(NCH)6]2+. The utilized synergistic methodology heavily exploits the strengths of complementary electronic structure and spin-vibronic dynamics methods. Specifically, we perform 3D quantum dynamics (QD) and full-dimensional trajectory surface hopping (TSH, in conjunction with a linear vibronic coupling model), with the modes for QD selected by TSH. We follow a hybrid approach which is based on the application of time-dependent density functional theory (TD-DFT) excited-state potential energy surfaces (PESs) and multiconfigurational second-order perturbation theory (CASPT2) spin-orbit couplings (SOCs). Our method delivers accurate singlet-triplet-quintet intersystem crossing (ISC) dynamics, as assessed by comparison to our recent high-level ab initio simulations and related time-resolved experimental data. Furthermore, we investigate the capability of our simulations to identify the location of ISCs. Finally, we assess the approximation of constant SOCs (calculated at the Franck-Condon geometry), whose validity has central importance for the combination of TD-DFT PESs and CASPT2 SOCs. This efficient methodology will have a key role in simulating LS → HS dynamics for more complicated cases, involving higher density of states and varying electronic character, as well as the analysis of ultrafast experiments.

| S-EPMC8908767 | biostudies-literature

In-Situ Construction of Fe-Doped NiOOH on the 3D Ni(OH)2 Hierarchical Nanosheet Array for Efficient Electrocatalytic Oxygen Evolution Reaction.

Project description:Accessible and superior electrocatalysts to overcome the sluggish oxygen evolution reaction (OER) are pivotal for sustainable and low-cost hydrogen production through electrocatalytic water splitting. The iron and nickel oxohydroxide complexes are regarded as the most promising OER electrocatalyst attributed to their inexpensive costs, easy preparation, and robust stability. In particular, the Fe-doped NiOOH is widely deemed to be superior constituents for OER in an alkaline environment. However, the facile construction of robust Fe-doped NiOOH electrocatalysts is still a great challenge. Herein, we report the facile construction of Fe-doped NiOOH on Ni(OH)2 hierarchical nanosheet arrays grown on nickel foam (FeNi@NiA) as efficient OER electrocatalysts through a facile in-situ electrochemical activation of FeNi-based Prussian blue analogues (PBA) derived from Ni(OH)2. The resultant FeNi@NiA heterostructure shows high intrinsic activity for OER due to the modulation of the overall electronic energy state and the electrical conductivity. Importantly, the electrochemical measurement revealed that FeNi@NiA exhibits a low overpotential of 240 mV at 10 mA/cm2 with a small Tafel slope of 62 mV dec-1 in 1.0 M KOH, outperforming the commercial RuO2 electrocatalysts for OER.

| S-EPMC11434255 | biostudies-literature

Photoinduced Low-Spin → High-Spin Mechanism of an Octahedral Fe(II) Complex Revealed by Synergistic Spin-Vibronic Dynamics.

Project description:The Fe(II) low-spin (LS; 1A1g, t2g6eg0) → high-spin (HS; 5T2g, t2g4eg2) light-induced excited spin state trapping (LIESST) mechanism solely involving metal-centered states is revealed by synergistic spin-vibronic dynamics simulations. For the octahedral [Fe(NCH)6]2+ complex, we identify an initial ∼100 fs 1T1g → 3T2g intersystem crossing, controlled by vibronic coupling to antisymmetric Fe-N stretching motion. Subsequently, population branching into 3T1g, 5T2g (HS), and 1A1g (LS) is observed on a subpicosecond time scale, with the dynamics dominated by coherent Fe-N breathing wavepackets. These findings are consistent with ultrafast experiments, methodologically establish a new state of the art, and will give a strong impetus for further intriguing dynamical studies on LS → HS photoswitching.

| S-EPMC8456406 | biostudies-literature

Defying the inverse energy gap law: a vacuum-evaporable Fe(ii) low-spin complex with a long-lived LIESST state.

Project description:The novel vacuum-evaporable complex [Fe(pypypyr)2] (pypypyr = bipyridyl pyrrolide) was synthesised and analysed as bulk material and as a thin film. In both cases, the compound is in its low-spin state up to temperatures of at least 510 K. Thus, it is conventionally considered a pure low-spin compound. According to the inverse energy gap law, the half time of the light-induced excited high-spin state of such compounds at temperatures approaching 0 K is expected to be in the regime of micro- or nanoseconds. In contrast to these expectations, the light-induced high-spin state of the title compound has a half time of several hours. We attribute this behaviour to a large structural difference between the two spin states along with four distinct distortion coordinates associated with the spin transition. This leads to a breakdown of single-mode behaviour and thus drastically decreases the relaxation rate of the metastable high-spin state. These unprecedented properties open up new strategies for the development of compounds showing light-induced excited spin state trapping (LIESST) at high temperatures, potentially around room temperature, which is relevant for applications in molecular spintronics, sensors, displays and the like.

| S-EPMC10321519 | biostudies-literature

Crystallographic Detection of the Spin State in FeIII Complexes.

Project description:We report a single example of thermal spin crossover in a series of FeIII complexes, [FeIII(R-sal2323)]+, which typically stabilize the low-spin (S = 1/2) state. Single-crystal X-ray diffraction analysis of 53 such complexes with varying "R" groups, charge-balancing anions, and/or lattice solvation confirms bond lengths in line with an S = 1/2 ground state, with only the [FeIII(4-OMe-sal2323)]NO3 complex (1a) exhibiting longer bond lengths associated with a percentage of the spin sextet form at room temperature. Structural distortion parameters are investigated for the series. A magnetic susceptibility measurement of 1a reveals a gradual, incomplete transition, with T 1/2 = 265 K in the solid state, while Evans method NMR reveals that the sample persists in the low-spin form in solution at room temperature. Computational analysis of the spin state preferences for the cations [FeIII(4-OMe-sal2323)]+ and [FeIII(sal2323)]+ confirmed the energetic preference for the spin doublet form in both, and the thermal spin crossover in complex 1a is therefore attributed to perturbation of the crystal packing on warming.

| S-EPMC9634697 | biostudies-literature

Low-spin pseudotetrahedral iron(I) sites in Fe₂(μ-S) complexes.

Project description:Fe(I) centers in iron-sulfide complexes have little precedent in synthetic chemistry despite a growing interest in the possible role of unusually low valent iron in metalloenzymes that feature iron-sulfur clusters. A series of three diiron [(L3Fe)2(μ-S)] complexes that were isolated and characterized in the low-valent oxidation states Fe(II)-S-Fe(II), Fe(II)-S-Fe(I), and Fe(I)-S-Fe(I) is described. This family of iron sulfides constitutes a unique redox series comprising three nearly isostructural but electronically distinct Fe2(μ-S) species. Combined structural, magnetic, and spectroscopic studies provided strong evidence that the pseudotetrahedral iron centers undergo a transition to low-spin S=1/2 states upon reduction from Fe(II) to Fe(I). The possibility of accessing low-spin, pseudotetrahedral Fe(I) sites compatible with S(2-) as a ligand was previously unknown.

| S-EPMC4155920 | biostudies-literature

Outer-sphere effects on ligand-field excited-state dynamics: solvent dependence of high-spin to low-spin conversion in [Fe(bpy)3]2.

Project description:In condensed phase chemistry, the solvent can have a significant impact on everything from yield to product distribution to mechanism. With regard to photo-induced processes, solvent effects have been well-documented for charge-transfer states wherein the redistribution of charge subsequent to light absorption couples intramolecular dynamics to the local environment of the chromophore. Ligand-field excited states are expected to be largely insensitive to such perturbations given that their electronic rearrangements are localized on the metal center and are therefore insulated from so-called outer-sphere effects by the ligands themselves. In contrast to this expectation, we document herein a nearly two-fold variation in the time constant associated with the 5T2 → 1A1 high-spin to low-spin relaxation process of tris(2,2'-bipyridine)iron(ii) ([Fe(bpy)3]2+) across a range of different solvents. Likely origins for this solvent dependence, including relevant solvent properties, ion pairing, and changes in solvation energy, were considered and assessed by studying [Fe(bpy)3]2+ and related derivatives via ultrafast time-resolved absorption spectroscopy and computational analyses. It was concluded that the effect is most likely associated with the volume change of the chromophore arising from the interconfigurational nature of the 5T2 → 1A1 relaxation process, resulting in changes to the solvent-solvent and/or solvent-solute interactions of the primary solvation shell sufficient to alter the overall reorganization energy of the system and influencing the kinetics of ground-state recovery.

| S-EPMC8159330 | biostudies-literature

Spin-Dependent Transport in Fe/GaAs(100)/Fe Vertical Spin-Valves.

Project description:The integration of magnetic materials with semiconductors will lead to the development of the next spintronics devices such as spin field effect transistor (SFET), which is capable of both data storage and processing. While the fabrication and transport studies of lateral SFET have attracted greatly attentions, there are only few studies of vertical devices, which may offer the opportunity for the future three-dimensional integration. Here, we provide evidence of two-terminal electrical spin injection and detection in Fe/GaAs/Fe vertical spin-valves (SVs) with the GaAs layer of 50 nanometers thick and top and bottom Fe electrodes deposited by molecular beam epitaxy. The spin-valve effect, which corresponds to the individual switching of the top and bottom Fe layers, is bias dependent and observed up to 20 K. We propose that the strongly bias- and temperature-dependent MR is associated with spin transport at the interfacial Fe/GaAs Schottky contacts and in the GaAs membranes, where balance between the barrier profiles as well as the dwell time to spin lifetime ratio are crucial factors for determining the device operations. The demonstration of the fabrication and spin injection in the vertical SV with a semiconductor interlayer is expected to open a new avenue in exploring the SFET.

| S-EPMC4949422 | biostudies-literature

MOF-Derived Co and Fe Species Loaded on N-Doped Carbon Networks as Efficient Oxygen Electrocatalysts for Zn-Air Batteries.

Project description: Not available

| S-EPMC9372253 | biostudies-literature