Crystallographic Properties Research Articles

Thermodynamic and magnetotransport properties of EuAg2Ge2 single crystals

Here, we report the crystallographic, thermodynamic, and magnetotransport properties of flux grown EuAg2Ge2 single crystals using X-ray diffraction, anisotropic magnetic susceptibility, and magnetization, heat capacity, electrical resistivity, and magnetoresistance measurements. The room temperature powder X-ray diffraction pattern confirms that EuAg2Ge2 crystallizes in a body-centered tetragonal ThCr2Si2–type structure (space group I4/mmm) with lattice parameters, a = 4.401 Å and c = 10.845 Å. The magnetic susceptibility data reveal two subsequent antiferromagnetic transitions at TN1 ∼ 8.3 K, and TN2 ∼ 6.2 K. For H‖c at T = 5 K, the magnetization data show the spin-flop like metamagnetic transition around the critical field of 1.4 T. The existence of antiferromagnetic transitions is further confirmed by the heat capacity measurements, which display two anomalies around TN1 = 8.3 K and TN2 = 6.1 K. The electrical resistivity data show the metallic behavior of the compound, which is best described by the Bloch-Grüneisen model above 30 K. At low temperatures, the antiferromagnetic transition manifests through a slight upturn around 8 K, followed by a sharp drop in the resistivity data. The transverse magnetoresistance (MR) measured for H‖c below TN first increases, showing a broad maximum at critical field strength that shifts towards lower fields with increasing temperature. With further increasing fields beyond the maximum, MR decreases, and changes its value from positive to negative. The evolution of MR from positive to negative could be associated with the metamagnetic transition in EuAg2Ge2. In the paramagnetic region, MR remains negative across the entire field range.

Stress distribution variations during nanoindentation failure of hard coatings on silicon substrates

Regarding quality inspection of technologically important nanocomposite hard coatings based on Ti, B, Si, C, and N and bioceramics such as hydroxyapatite that are used in small-scale high-precision devices and bio-implants, it is essential to study the failure mechanisms associated with nanoindentation, such as fracture, delamination, and chipping. The stress imposed by the indenter can affect the fracture morphology and the interfacial fracture energy, depending on indenter shape, substrate type, crystallographic properties, pre-existing flaws, internal micro-cracks, and pre-strain. Reported here are finite-element-based fracture studies that provide insights into the different cracking mechanisms related to the aforementioned failure process, showing that the fracture morphology is affected by the interaction of different cracking events. The interfacial fracture energy, toughness, and residual stress are calculated using existing models with minor adjustments, and it is found that increasing the indenter sharpness improves the shear stress distribution, making the coating more prone to separation. Depending on the prevailing type of stress, the stress distribution beneath the depression results in either crack formation or a dislocation pile-up leading to strain hardening. Different forms of resistances resulting from the indentation process are found to affect the tip–sample conduction, and because of its stronger induced plasticity than that of a Berkovich indenter tip, a sharper cube-corner tip produces more resistance.

High-Rate One-Dimensional α-MnO2 Anode for Lithium-Ion Batteries: Impact of Polymorphic and Crystallographic Features on Lithium Storage.

Manganese dioxide (MnO2) exists in a variety of polymorphs and crystallographic structures. The electrochemical performance of Li storage can vary depending on the polymorph and the morphology. In this study, we present a new approach to fabricate polymorph- and aspect-ratio-controlled α-MnO2 nanorods. First, δ-MnO2 nanoparticles were synthesized using a solution plasma process assisted by three types of sugars (sucrose, glucose, and fructose) as reducing promoters; this revealed different morphologies depending on the nucleation rate and reaction time from the molecular structure of the sugars. Based on the morphology of δ-MnO2, the polymorphic-transformed three types of α-MnO2 nanorods showed different aspect ratios (c/a), which highly affected the transport of Li ions. Among them, a relatively small aspect ratio (c/a = 5.1) and wide width of α-MnO2-S nanorods (sucrose-assisted) induced facile Li-ion transport in the interior of the particles through an increased Li-ion pathway. Consequently, α-MnO2-S exhibited superior battery performance with a high-rate capability of 673 mAh g-1 at 2 A g-1, and it delivered a high reversible capacity of 1169 mAh g-1 at 0.5 A g-1 after 200 cycles. Our findings demonstrated that polymorphs and crystallographic properties are crucial factors in the electrode design of high-performance Li-ion batteries.

Accelerated multi-property screening of Fe–Co–Ni alloy libraries by hyper-heuristic combinatorial flow synthesis and high-throughput spark plasma sintering

High-throughput (HT) chemical synthesis facilitates accelerated materials discovery products. However, HT methods are limited by the need for expensive robotic systems, complicated methodology, and low yield. Hence, we developed a hyper-heuristic combinatorial flow synthesis (HCFS) device capable of composition gradient generation and production of an adequate mass of Fe–Co–Ni alloy nanoparticles. A library of 91 Fe–Co–Ni powder compositions was synthesized using this technique. A high-throughput spark plasma sintering (HT-SPS) methodology, along with the die design, was developed for combinatorial screening of multiple properties. 56 compositions were down-selected and consolidated into compositionally graded bulk samples using HT-SPS and subsequent annealing. The crystallographic, magnetic, electrical, and magnetic properties of the bulk library were assessed. The saturation magnetization (Ms) varied from 83.3 emu/g to 225.2 emu/g, coercivity (Hc) from 17.5 Oe to 78.4 Oe, resistivity (ρ) from 17.2 μΩ·cm to 986.7 μΩ·cm, and Vickers hardness (HV) from 41.9 HV to 281.7 HV. Novel Fe–Co–Ni compositions, e.g., Fe36.5Co55.1Ni8.4 and Fe22.6Co73.4Ni4, with a promising multi-property set, were identified for the first time. This study demonstrated that promising new compositions exhibiting multi-property optimization can be successfully discovered by our hyper-heuristic combinatorial chemical synthesis methodology.

Hot-Pressing Deformation Yields Fine-Grained, Highly Dense and (002) Textured Ru Targets.

Ruthenium (Ru) is a refractory metal that has applications in the semiconductor industry as a sputtering target material. However, conventional powder metallurgy methods cannot produce dense and fine-grained Ru targets with preferred orientation. Here, we present a novel method of hot-pressing deformation to fabricate Ru targets with high relative density (98.8%), small grain size (~4.4 μm) and strong (002) texture. We demonstrate that applying pressures of 30-40 MPa at 1400 °C transforms cylindrical Ru samples into disk-shaped targets with nearly full densification in the central region. We also show that the hardness and the (002)/(101) peak intensity ratio of the targets increase with the pressure, indicating enhanced mechanical and crystallographic properties. Our study reveals the mechanisms of densification and texture formation of Ru targets by hot-pressing deformation.

Stabilization of the tetragonal phase in ZrO2 thin films according to ozone concentration using atomic layer deposition

In this study, we investigated the crystallographic and electrical properties of ZrO2 thin films prepared by an ozone-based atomic layer deposition process. Cyclopentadienyl tris(dimethylamino) zirconium [CpZr(NMe2)3] was used as the Zr precursor, and O3 was used as the reactant. ZrO2 films were produced using O3 in various concentrations from 100 to 400 g/m3. These thin films were used to fabricate metal–oxide–semiconductor capacitors, whose electrical properties were evaluated and correlated with crystallographic analysis. As the O3 concentration increased, the tetragonal phase of the ZrO2 film stabilized and the dielectric constant improved. However, the leakage current density characteristics concurrently deteriorated due to the high concentration of O3, increasing the number of grain boundaries in the ZrO2 film by increasing crystallinity. Thus, the concentration of O3 can control the number of OH groups of the ZrO2 film, affecting the device characteristics.

Sol-gel synthesis and characterization of foamed Ni3Pt alloys

This study focuses on the preparation of Ni3Pt nanoporous alloy foams through the annealing of a colloid composed of Ni(NO3)2, H2PtCl6, and starch under an argon gas atmosphere. Field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were employed to analyze the chemical composition, structure, and crystallographic properties of the obtained products. The product exhibits a three-dimensional foam structure comprising open pores with an average pore size of 300 nm. Additionally, it possesses structural supports with a thickness of approximately 140 nm within the open-pore configuration. XRD analysis confirms that the obtained product exhibits a face-centered cubic phase, indicating that it is a Ni3Pt alloy. This result is further supported by reductions insurface atomic ratio and Pt binding energy observed in the XPS analysis. The resulting open-cell Ni3Pt alloy foam exhibits a homogeneous and well-defined three-dimensional structure, offering a high specific surface area. These characteristics reveal the excellent potential of the Ni3Pt alloy foam for application in battery and electrode materials.

Morphology tuned plasmonic TiN nanostructures formed by angle-dependent sputtering process for SERS measurements

Nowadays, most SERS platforms are based on plasmonic metals like silver and gold. The current scientific achievement is to construct SERS non-metallic platform with SERS activity not worse than in case of standard metallic platforms. The prominent combination of opto-electronic properties of TiN (titanium nitride) makes it a promising alternative plasmonic material for noble metals. So far, the TiN nanostructures are widely tested in catalysis, especially in photocatalysis. Despite the TiN potential in SERS sensing applications, there are still several fundamental issues preventing its wide practical application. In this work, the surface morphology of TiN layers was tuned from planar 2D to a high aspect ratio 1D nanorod-like structures by industrially scalable normal and glancing angle deposition (GLAD) pulsed DC reactive sputtering. The morphology of formed samples was studied by SEM microscopy, while the crystallographic properties were examined by Raman and XRD method. The opto-electrical parameters measured by spectroscopic ellipsometry, and DRS spectroscopy revealed substantial changes in optical properties of the TiN films with the variation of glancing angle. This in turn opened the way for tailoring the surface plasmon resonance and hence for SERS activity.

Green Luminescence in Zero-Dimensional Lead bromide hybrid material (C5H9N3)2PbBr6: Experimental and Theoretical Studies

In this work, we describe the preparation of a new zero-Dimensional (0D) lead bromide hybrid material, with the structural formula (C5H9N3)2PbBr6, of which crystallographic, thermal, optical, and electrical properties have been studied and analyzed. Single crystals of (C5H9N3)2PbBr6 material were grown using a slow evaporation solution method at room temperature. The molecular structure reveals that the crystal packing is made of isolated [PbBr6]4− units into which organic (C5H9N3)2+ cations are embedded and linked by a combination of N/C-H…Br hydrogen bonds and stacking interactions forming a three-dimensional network. The Hirshfeld surface analysis and fingerprint plots facilitates a quantification of non-covalent intermolecular interactions, which are crucial in building the supramolecular architectures. Upon photoexcitation, the crystals exhibit an efficient green emission band covering a large spectral region from 400 to 700 nm peaking at 592 nm. The optical band gap was calculated to be Eg = 3.45 eV. The electrical conductivity of this material shows that the most suitable equivalent circuit is represented by a single parallel cell formed by (Rg∥CPEg), the value of the activation energy is 1.18 eV. Thermal analysis reveals that the decomposition of the sample starts from 275 K. Density functional theory (DFT) was performed to determine the electronic structure of the tilted compound. The DFT calculation shows that the title compound is direct semiconductor with a band gap energy of about 2.97 eV.

Insight on Atomically Dispersed Cu Catalysts for Electrochemical CO2 Reduction.

Electrochemical CO2 reduction (ECO2R) with renewable electricity is an advanced carbon conversion technology. At present, copper is the only metal to selectively convert CO2 into multicarbon (C2+) products. Among them, atomically dispersed (AD) Cu catalysts have received great attention due to the relatively single chemical environment, which are able to minimize the negative impact of morphology, valence state, and crystallographic properties, etc. on product selectivity. Furthermore, the completely exposed atomic Cu sites not only provide space and bonding electrons for the adsorption of reactants in favor of better catalytic activity but also provide an ideal platform for studying its reaction mechanism. This review summarizes the recent progress of AD Cu catalysts as a chemically tunable platform for ECO2R, including the atomic Cu sites dynamic evolution, the catalytic performance, and mechanism. Furthermore, the prospects and challenges of AD Cu catalysts for ECO2R are carefully discussed. We sincerely hope that this review can contribute to the rational design of AD Cu catalysts with enhanced performance for ECO2R.

Modification of the electronic structure of g-C3N4 using urea to enhance the visible light-assisted degradation of organic pollutants.

Graphitic carbon nitride has been proven to be a good candidate for using solar energy for photo-induced pollutant degradation. However, the high photo-induced holes-electron recombination rate, unfavorable morphology, and textural properties limited their application. In this study, we present a novel g-C3N4 with a novel electronic structure and physiochemical properties by introducing a single nitrogen in the graphitic network of the g-C3N4 through a novel method involving step-by-step co-polycondensation of melamine and urea. Through extensive characterization using techniques such as XPS, UPS-XPS, Raman, XRD, FE-SEM, TEM, and N2 adsorption-desorption, we analyze the electronic and crystallographic properties, as well as the morphology and textural features of the newly prepared g-C3N4 (N-g-C3N4). This material exhibits a lower C/N ratio of 0.62 compared to conventional g-C3N4 and a reduced band gap of 2.63 eV. The newly prepared g-C3N4 demonstrates a distinct valance band maxima that enhances its photo-induced oxidation potential, improving photocatalytic activity in degrading various organic pollutants. We thoroughly investigate the photocatalytic degradation performance of N-g-C3N4 for Congo red (CR) and sulfamethoxazole (SMX), and removal of up to 90 and 86% was attained after 2 h at solution pH of 5.5 for CR and SMX. The influence of different parameters was examined to understand the degradation mechanism and the influence of reactive oxygenated species. The catalytic performance is also evaluated in the degradation of various organic pollutants, and it showed a good performance.

Relationship between Copper(II)-Lactate Complexes and Cu2O Electrodeposited Using Highly Concentrated Alkaline Solutions

The direct or indirect effects of two different copper(II)-lactate complex species, Cu(H–1L)L– and Cu(H–1L)2 2–, on the orientation and electrical properties of Cu2O electrodeposits were examined, where L– = CH3CH(OH)COO– and H–1L2– = CH3CH(O–)COO–. To investigate the relationships between the copper(II)-lactate complex species and several properties of Cu2O, a set of Cu2O layers was electrodeposited from thermodynamically well-stabilized electrolytes of different pHs with unified overpotentials. The Cu2O layers obtained at pH <9.5 had the 〈100〉 preferential orientation, whereas the orientation changed to the 〈111〉 preferential orientation at pH >9.5. In addition, marked differences were observed in the resistivity and carrier density of Cu2O layers bordering pH 9.5, indicating the presence of a strong relationship between copper(II)-lactate complexes and these crystallographic or electrical properties. In terms of the cathodic reactivity of copper(II)-lactate complexes and changes in local pH in the vicinity of the cathode upon electrodeposition, we suggest that the two copper(II)-lactate complexes directly affected the electrical properties of Cu2O and indirectly affected its crystallographic orientation.

Towards the extraction of the crystal cell parameters from pair distribution function profiles.

The approach based on atomic pair distribution function (PDF) has revolutionized structural investigations by X-ray/electron diffraction of nano or quasi-amorphous materials, opening up the possibility of exploring short-range order. However, the ab initio crystal structural solution by the PDF is far from being achieved due to the difficulty in determining the crystallographic properties of the unit cell. A method for estimating the crystal cell parameters directly from a PDF profile is presented, which is composed of two steps: first, the type of crystal cell is inferred using machine-learning approaches applied to the PDF profile; second, the crystal cell parameters are extracted by means of multivariate analysis combined with vector superposition techniques. The procedure has been validated on a large number of PDF profiles calculated from known crystal structures and on a small number of measured PDF profiles. The lattice determination step has been benchmarked by a comprehensive exploration of different classifiers and different input data. The highest performance is obtained using the k-nearest neighbours classifier applied to whole PDF profiles. Descriptors calculated from the PDF profiles by recurrence quantitative analysis produce results that can be interpreted in terms of PDF properties, and the significance of each descriptor in determining the prediction is evaluated. The cell parameter extraction step depends on the cell metric rather than its type. Monometric, dimetric and trimetric cells have top-1 estimates that are correct 40, 20 and 5% of the time, respectively. Promising results were obtained when analysing real nanocrystals, where unit cells close to the true ones are found within the top-1 ranked solution in the case of monometric cells and within the top-6 ranked solutions in the case of dimetric cells, even in the presence of a crystalline impurity with a weight fraction up to 40%.

Influence of A-Site Modifications on the Electrical and Crystallographic Properties of Ln0.2Sr0.7-XCaxTi0.95Fe0.05O3-δ (Ln=La, Nd) Based Fuel Electrode for Solid Oxide Cell

Perovskite oxides, in particular SrTiO3–based compounds have attracted particular attention over the past years due to their decent conductivity, good dimensional stability and high tolerance and resistance towards sulfur poisoning and carbon depositions [1, 2]. Optimal doping and stoichiometry levels on A- (La, Nd etc.) and B-sites (Fe, Ni etc.) of SrTiO3 based compounds allow to improve catalytic activity, electrical conductivity and chemical stability [2]. In addition, doping of A-site with calcium is predicted to enhance the electronic conductivity because it should decrease the unit cell volume bringing the conduction orbitals of titanium closer to each other [3].In this research influence of chemical composition of A-site on electrical and electrochemical performance of Ln0.2Sr0.7-xCaxTi0.95Fe0.05O3-δ (Ln=La, Nd) (x=0.35, 0.45) (LSCTF-x, NSCTF-x) hydrogen electrode has been investigated. The crystal structure and microstructure have been studied using X-ray diffraction and SEM to confirm the phase purity and visualize the microstructure of studied electrode layers. To understand the influence of MIEC material composition on electrical conductivities of LSCFT and NSCTF, the DC four-probe conductivity measurements of porous electrode layers has been performed. Conductivities have been measured at two different atmospheres: 1% H2 + 3% H2O + 96% Ar and 97% H2 + 3% H2O. It has been shown that the both LSCTF and NSCTF materials behave like semiconductor and the conductivity is significantly dependent on composition. The maximal total electrical conductivity of porous electrode layers were 5.5 S cm− 1 and 4.8 S cm− 1 at 850 °C characteristic for the La0.2Sr0.25Ca0.45Ti0.95Fe0.05O3-δ (LSCTF-45) and Nd0.2Sr0.35Ca0.35Ti0.95Fe0.05O3-δ (NSCTF-35) materials, respectively, in 97% H2 + 3% H2O atmosphere. Keywords: solid oxide fuel cell; perovskite; fuel electrode; MIEC; LST. [1] X. Li, H. Zhao, X. Zhou, N. Xu, Z. Xie, N. Chen, Electrical conductivity and structural stability of La-doped SrTiO3 with A-site deficiency as anode materials for solid oxide fuel cells, international journal of hydrogen energy 35 (2010) 7913-7918.[2] A. Gondolini, E. Mercadelli, G. Constantin, L. Dessemond, V. Yurkiv, R. Costa, A. Sanson, On the manufacturing of low temperature activated Sr0.9La0.1TiO3-δ-Ce1-xGdxO2-δ anodes for solid oxide fuel cell, Journal of the European Ceramic Society, 38 (2018) 153–161.[3] A.D. Aljaberi, J.T.S. Irvine, Ca-substituted, A-site deficient perovskite La0.2Sr0.7TiO3 as a potential anode material for SOFCs. J. Mater. Chem. A 2013, 1, 5868-5874.

Influence of A-Site Deficiency and B-Site Composition on the Electrical and Crystallographic Properties of (La0.25Sr0.25Ca0.45)yTi0.95Ni0.05-xMnxO3-δ Solid Oxide Fuel Cell Anode

(La,Sr)TiO3-δ has attracted specific attention over the past years due to its superior dimensional stability, high conductivity, and significant tolerance against sulfur poisoning and carbon depositions. To increase the catalytic activity and chemical stability, many different doping levels and stoichiometries for LaxSr1-xTiO3-δ (LST) have been investigated [1, 2]. Doping of B-site with Mn has been shown to promote electroreduction under SOFC conditions [3]. Furthermore, Mn is known to accept lower coordination numbers in perovskites, especially for Mn3+ (3d4), and so may enhance oxide-ion migration [4]. In addition, MnO is clearly stable under fuel conditions unlike Co or Ni oxides [4].In this research influence of A-site deficiency and B-site chemical composition on electrical performance of La0.25Sr0.25Ca0.45Ti0.95Ni0.05-xMnxO3-δ (x=0-0.05) (LSCTNM-x) hydrogen electrode has been studied. The crystal structure and microstructure have been studied using X-ray diffraction and SEM to confirm the phase purity and visualize the microstructure of studied electrode layers. To understand the influence of MIEC material composition on electrical conductivities of LSCTNM, the DC four-probe conductivity measurements of porous electrode layers has been performed. Conductivities have been measured at two different atmospheres: 1% H2 + 1.7% H2O + 97.3% Ar and 98.3% H2 + 1.7% H2O. It has been shown that all materials with LSCTNM compositions behave like semiconductor and the conductivity is significantly dependent on composition. The maximal total electrical conductivity of porous electrode layers was characteristic for the LSCTNM materials with 10% A-site deficiency, in 98.3% H2 + 1.7% H2O atmosphere. Keywords: solid oxide fuel cell; conductivity; perovskite; fuel electrode; MIEC.[1] X. Li, H. Zhao, X. Zhou, N. Xu, Z. Xie, N. Chen, Electrical conductivity and structural stability of La-doped SrTiO3 with A-site deficiency as anode materials for solid oxide fuel cells, international journal of hydrogen energy 35 (2010) 7913-7918.[2] A. Gondolini, E. Mercadelli, G. Constantin, L. Dessemond, V. Yurkiv, R. Costa, A. Sanson, On the manufacturing of low temperature activated Sr0.9La0.1TiO3-δ-Ce1-xGdxO2-δ anodes for solid oxide fuel cell, Journal of the European Ceramic Society, 38 (2018) 153–161.[3] P. Holtappels, J. Bradley, J.T.S. Irvine, A. Kaiser, M. Mogensen, Electrochemical characterization of ceramic SOFC anodes, J. Electrochem. Soc. A 148 (2001) 923–929.[4] S. Tao, J.T.S. Irvine, A redox-stable efficient anode for solid-oxide fuel cells, nature materials, 2 (2003) 320-323.

Orientation-dependent crystallographic properties in osteocyte-associated bone revealed by nano-scanning X-ray diffraction and fluorescence with a sub-50 nm X-ray beam

Orientation-dependent crystallographic properties in osteocyte-associated bone revealed by nano-scanning X-ray diffraction and fluorescence with a sub-50 nm X-ray beam

Crystallographic, structural, optical, and dielectric properties of aniline and aniline halide imprinted hydrogels for optoelectronic applications

Crystallographic, structural, optical, and dielectric properties of aniline and aniline halide imprinted hydrogels for optoelectronic applications

Upconversion nanoparticles: influence of the host lattices on crystallographic and luminescent properties

Upconversion nanoparticles: influence of the host lattices on crystallographic and luminescent properties

Semiconductor-ferromagnetic nature of rare-earth based ferrocobaltite SmFe0.5Co0.5O3

Materials in which electronic spin manipulation is possible for the tuning of charge and spin currents are intensively pursued due to the multifunctionality of their potential applications in spintronics technology. In this work, the synthesis and characterization of the crystallographic, optical, electrical and magnetic properties of SmFe0.5Co0.5O3 material is reported. Structural analysis reveals its crystallization in an orthorhombic cell (Pnma space group) with disordered distribution of Fe and Co cations. The optical response evidences the occurrence of a bandgap Eg= 1.0 eV, typical of semiconductor materials, which is corroborated by electrical resistivity measurements and J-E curves, where a varistor-type curve is recorded. Magnetic analysis suggests a predominant antiferromagnetic behavior at low temperatures with weak ferromagnetic response, which strengthens at high temperatures as a result of interactions described by the super-exchange model. Ab-initio calculations of the density of states and electronic band structure predict the semiconductor type response, with an asymmetry of the bandgap between the two spin polarizations, opening channels for tuning polarized spin currents, which is characteristic of ferromagnetic semiconductor type materials.

Investigation of the properties influencing the deactivation of iron electrodes in iron-air batteries

Iron-air batteries hold the potential to be a key technology for energy storage, thanks to their energy density, low cost, safety and abundance of their materials. In order to scale the technology up and optimize the cell formulations, it is key to obtain a clear understanding of how the physical-chemical properties of the electrode influence their electrochemical behaviour, in particular, the capacity loss. In this work, we propose for the first time mathematical correlations between textural and crystallographic properties of iron electrodes and their electrochemical stability. By adjusting synthesis parameters, we were able to tune pore size and volume, surface area and crystal size of iron oxides, and found that stability is highly correlated to both surface area and pore size. Large surface area and small average pore size provide electrodes with enhanced stability. We hypothesize that the cause for deactivation is the passivation of the electrodes ascribed to the formation of a non-conductive, non-reactive iron (II) hydroxide layer during discharge, which then cannot be reduced to iron again. We validate this hypothesis with electrochemical impedance spectroscopy studies, which show that, in the more stable electrodes, the charge transfer resistance in the Fe(OH)2 to Fe reduction does not significantly change after cycling, contrary to the behaviour of the less stable electrodes, corroborating our hypothesis. Furthermore, the electrode with the best properties was cycled 100 times, retaining almost 75% of its initial capacity at the end of the 100 cycles. These results are highly relevant for the future design and operation of iron-air batteries.