Incorporation Of Fe Atoms Research Articles

Electronic modulation on allotropic Co2P/CoP heterojunctions with N, P co-doped porous carbon matrix through metal-injection toward high-efficiency water splitting

The interfacial electron modulation of electrocatalysts is a useful technique for promoting catalyst performance for the water-related dissociation reactions. Herein, a high-efficient Fe-doped allotropic Co2P/CoP heterojunction nanoparticles embedded in N, P co-doped carbon matrix was constructed. The intense electrical interfacial contacts between the allotropic heterojunction optimized the reaction kinetics by boosting efficient charged active centers, regulating the intermediate adsorption/desorption. The incorporation of Fe atoms further enhancing the heterointerface contact between CoP and Co2P by providing favorable electronic properties and special coordination environment, causing the interfacial coupling enhancement. Therefore, Fe-Co2P/CoP possesses outstanding performance in both hydrogen evolution reaction and oxygen evolution reaction, with small overpotentials of 174 mV and 286 mV at 10 mA·cm−2 in alkaline medium, respectively. And only 1.71 V battery voltage is needed for the Fe-Co2P/CoP (+, −) cell device with satisfactory durability. This finding provides valuable insights into the engineering of electronic structures of well-designed metal phosphides for water electrolysis.

Dealumination of Y zeolite through an economic and eco‐friendly defect‐engineering strategy

AbstractA sustainable defect‐engineering strategy for the dealumination of Y zeolite is described. This strategy includes the green synthesis of a well‐crystallized Y zeolite with point defects arising from the incorporation of Fe atoms by using Fe‐containing perlite and the subsequent preparation of ultra‐stable Y (USY) zeolite by efficient steaming dealumination. The systematic characterizations verify that Fe atoms originally existing in the perlite are incorporated into the as‐synthesized Y zeolite and function as point defects, leading to the distortion of framework Al. The step‐by‐step investigation of dealumination process shows that vacancies are formed by the extraction of framework Fe in ammonium exchange, and the framework dealumination is promoted under the combined effect of the distorted framework Al and the formed vacancies during steaming treatment. The resulting USY zeolite owns excellent features in (hydro)thermal stability, pore structure and acid property, and exhibits outstanding catalytic performance in the cracking of n‐octane and 1,3,5‐triisopropylbenzene.

Accelerating Electrochemical Water Oxidation Activity by Tailoring Morphology and Electronic Structure of Nickel Organic Framework Nanoarrays with a Fe Etching Effect

Fe-mediated nickel organic framework nanoarrays (NiFe-MOFs NAs) on carbon cloth were successfully constructed from ultrathin nanosheets via an etching effect. This strategy also combined the dissolution and coordination effect of acidic ligand (2,6-naphthalenedicarboxylic acid, NDC) to a self-sacrificial template of Ni(OH)2 NAs. Benefiting from the strong Fe etching effect, dense and thick brick-like Ni-NDC nanoplates were tailored into loose and ultrathin NiFe-NDC nanosheets with abundant squamous nanostructures, which were still tightly attached to carbon cloth. As a consequence, more coordinatively unsaturated metal sites (CUMSs) that served as active centers were exposed to accelerate oxygen production. Meanwhile, the electronic structure of active Ni centers was modulated by the incorporation of Fe atoms. The charge density redistribution between Ni and Fe ultimately optimized the energy barrier of the adsorption/desorption of oxygenated intermediates, promoting the kinetics for water oxidation.

Rational designing Ni3-xFexS2 nanosheet arrays on Ni foam to enhance supercapacitor performance

Supercapacitors are important renewable and sustainable electrochemical energy storage devices with significant advantages including rapid charge/discharge rates, long cycle lifetimes, and high power densities. Herein, to achieve high-performance supercapacitors, Ni3-xFexS2 nanosheet arrays were synthesized on Ni foam with different Ni/Fe ratios. The incorporation of Fe atoms allows the adjustment of the electron configuration of the Ni–Fe bimetal sulfides and thus significantly influenced their electrochemical activity in a supercapacitor system. As expected, compared with the monometal sulfide Ni3S2, the Ni2FeS2-based supercapacitor delivered a superior capacitive performance and rate capability owing to its unique nanosheet array structure and bimetallic composition.

(Invited) Revisiting the Nature of Active Sites in Pyrolyzed Fe-N-C Electrocatalysts: In Situ Monitoring the Structure Evolution of Active Sites in Fe-N-C Catalysts during Pyrolysis

Since it was found in 1980s that pyrolysis of the mixture of Fe, N, and C precursors leads to decent electrocatalysts for the oxygen reduction reaction (ORR), the nature of active sites high inherent ORR activity formed upon the heat treatment remains elusive. This mystery hasn’t been unraveled by recent applications of advanced spectroscopy and microscopy techniques.1-4 Herein, we conducted in situ x-ray absorption spectroscopy on carbon supported iron(II) phthalocyanine (FePc), as well as the mixture of ZIF-8, phenanthroline, Fe(II) acetate (namely MOF-derived catalyst) in a sealed inert gas environment as a function of pyrolysis temperature, in attempt to directly monitor the formation of new active sites. The FePc represents the Fe precursors with preexisting Fe-N4 moieties, and the Fe(II) acetate represents the precursors without. We observed the destruction of the in-plane Fe-N4 sites in FePc as a result of demetalization starting at a low temperature of ~300 ℃. However, we did not see the formation of new Fe-Nx active sites but metallic Fe clusters at elevated temperatures. The maximum of the ORR activity of the FePC/C pyrolyzed at 600 ℃ was attributed to the counterbalance between the loss of Fe-N4 sites and the increase of the carbon porosity caused by the demetalization, plus strengthening of the interactions between the FePc and carbon substrate, rather than creation of new active sites. On the other hand, during the pyrolysis of the MOF-derived catalyst, the XAS reveals the evolution from the Fe-O6 moiety to the Fe-N4 moiety with the local geometry resembling that of FePc but with longer Fe-N bond distance. The formation of metallic Fe clusters was not observed even at a high temperature of 1000 ℃. These results together suggest that the new active sites are likely formed upon the incorporation of Fe atoms into the N-doped carbon matrix during the pyrolysis. Compared to FePc/C, the carbon matrix in the MOF-derived catalyst appears to capture Fe atoms more efficiently forming Fe-N4 sites, owing probably to more abundant C-N cavities. Acknowledgement This work was supported by the US Department of Energy under award number DE-EE0008416. The authors declare no competing financial interests. MRCAT operations are supported by the Department of Energy and the MRCAT member institution. This research used resources of the Advanced Photon Source, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. References (1) Li, J.; Alsudairi, A.; Ma, Z.-F.; Mukerjee, S.; Jia, Q. Asymmetric Volcano Trend in Oxygen Reduction Activity of Pt and Non-Pt Catalysts: In Situ Identification of the Site-Blocking Effect. J. Am. Chem. Soc. 2017, 139, 1384-1387. (2) Li, J.; Ghoshal, S.; Liang, W.; Sougrati, M.-T.; Jaouen, F.; Halevi, B.; McKinney, S.; McCool, G.; Ma, C.; Yuan, X.; Ma, Z.-F.; Mukerjee, S.; Jia, Q. Structural and mechanistic basis for the high activity of Fe-N-C catalysts toward oxygen reduction. Energ Environ Sci 2016, 9, 2418-2432. (3) Jia, Q.; Ramaswamy, N.; Tylus, U.; Strickland, K.; Li, J.; Serov, A.; Artyushkova, K.; Atanassov, P.; Anibal, J.; Gumeci, C.; Barton, S. C.; Sougrati, M.-T.; Jaouen, F.; Halevi, B.; Mukerjee, S. Spectroscopic insights into the nature of active sites in iron–nitrogen–carbon electrocatalysts for oxygen reduction in acid. Nano Energy 2016, 29, 65-82. (4) Jia, Q.; Ramaswamy, N.; Hafiz, H.; Tylus, U.; Strickland, K.; Wu, G.; Barbiellini, B.; Bansil, A.; Holby, E. F.; Zelenay, P.; Mukerjee, S. Experimental Observation of Redox-Induced Fe–N Switching Behavior as a Determinant Role for Oxygen Reduction Activity. ACS Nano 2015, 9, 12496-12505. Figure 1

Structure and gas sensing properties of nanocrystalline Fe-doped ZnO films prepared by spin coating method

Nanocrystalline Fe-doped ZnO films were obtained by spin coating, using zinc acetate and iron acetate as starting materials and N,N-dimethylformamide as solvent. Characteristic XRD patterns indicate that the films under study are single phase with the ZnO-like wurtzite structure. There are not any secondary phases and Fe2+ as well as Fe3+ substitutes for Zn2+ of ZnO host. Atomic force microscopy analysis revealed that the studied films are characterized by high-density columnar structure and the incorporation of Fe atoms into the ZnO lattice modified the surface morphology. The sensitivity, at three different gases, was investigated and it was observed that acetone is the test gas that produces the most significant changes in the electrical resistance of all studied samples. Experimental results indicate that the optimum operating temperature increases for Fe-doped ZnO films by comparison with the undoped one. Also, the values of sensitivity were found to depend on the dopant concentration in ZnO films.

Investigation on Fe-doped ZnO nanostructures prepared by a chemical route

Abstract Zn 1− x Fe x O ( x = 0.03, 0.05 and 0.07) nanoparticles synthesized by a chemical route were characterized by different techniques. The structural characterization by XRD and TEM confirmed the phase purity of the samples and indicated a reduction in particle size with increase in the dopant (Fe) concentration in ZnO. The optical characterization of the nanoparticles by FTIR, PL and UV–visible spectroscopy confirmed the formation of wurtzite structure and incorporation of Fe in the ZnO lattice. Magnetization measurements by VSM and Faraday balance techniques indicate presence of room temperature ferromagnetism in the Fe-doped ZnO samples. Local environment around the Fe atoms has been probed by 57 Fe Mossbauer spectroscopy and the measured isomer shifts confirmed the charge state of iron as Fe 3+ . Positron annihilation lifetime spectroscopy (PALS) measurements confirm the presence of cation vacancies in the nanoparticles and indicate a reduction of overall defect concentration with incorporation of Fe atoms in the ZnO structure.

Ion beam characterization of Fe-implanted GaN

Abstract Fe ion implantation in GaN has been investigated by means of ion beam analysis techniques. Implantations at an energy of 150 keV and fluences ranging from 2 × 10 15 to 1 × 10 16 cm −2 were done, both at room temperature and at 623 K. Secondary Ions Mass Spectrometry was used to determine the Fe implantation profiles, whereas Rutherford Backscattering in channeling conditions with a 2.2 MeV 4 He + beam allowed us to follow the damage evolution. Particle Induced X-ray Emission in channeling conditions with a 2 MeV H + beam was employed to study the lattice location of Fe atoms after implantation. The results show that a high fraction of Fe-implanted atoms are located in high symmetry sites in low fluence implanted samples, where the damage level is lower, whereas the fraction of randomly located Fe atoms increases by increasing the fluence and the resulting damage. Moreover, dynamical annealing present in high temperature implantation has been shown to favor the incorporation of Fe atoms in high symmetry sites.

Epitaxial growth and magnetic properties of a new group‐IV ferromagnetic semiconductor: Ge 1– x Fe x

Epitaxial growth and magnetic properties of group-IV ferromagnetic semiconductor Ge1–xFex thin films were investigated by employing in-situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and magnetic circular dichroism (MCD). When Ge1–xFex films were grown at substrate temperatures (TS) of 100–200 °C, their RHEED pattern showed streaks with a 2×2 reconstruction pattern, indicating two-dimensional growth mode with atomically flat surface morphology. Single-phase crystallographic structure without Fe-Ge intermetallic compounds was observed in the films by TEM. MCD measurements revealed that s,p-d exchange interactions induced by the incorporation of Fe atoms that occupied the substitutional sites of the host Ge matrix cause single-phase ferromagnetic ordering in the Ge1–xFex films. Above TS = 300 °C, the growth mode was changed from two-dimensional growth mode to three-dimensional growth mode. It was found from MCD observations that when Ge1–xFex films are grown at TS = 300–400 °C, phase separation occurs and the films contain ferromagnetic precipitates. A ferromagnetic semiconductor phase was obtained for TS ranging from 100 °C to 200 °C, and higher Curie temperature was obtained for TS = 200 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magneto-optical properties of group-IV ferromagnetic semiconductor Ge1−xFex grown by low-temperature molecular beam epitaxy

Group-IV ferromagnetic semiconductor Ge1−xFex was grown by low-temperature molecular beam epitaxy without precipitation of ferromagnetic Ge–Fe intermetallic compounds. The ferromagnetism of Ge1−xFex films was investigated by magnetic circular dichroism (MCD). In particular, the influence of the Fe content (x=2.0%–17.5%) and growth temperature (100 and 200°C) on the ferromagnetism was carefully studied. The MCD measurements revealed that the overall spectral features reflecting the band structure of the Ge1−xFex films were identical with those in bulk Ge, and that the large spin splitting of the band structure was induced by the incorporation of Fe atoms into the Ge matrix, indicating the existence of s,p-d exchange interactions. The Ge1−xFex films showed ferromagnetic behavior and the ferromagnetic transition temperature linearly increased with increasing the Fe concentration. These results indicate that the epitaxially grown Ge1−xFex is an intrinsic ferromagnetic semiconductor.

Properties of iron-doped Sb2Te3 single crystals

Iron-doped Sb2Te3 single crystals (C Fe = (0–9.5) × 1019 atoms/cm−3) were prepared from elements of semiconductor purity using a modified Bridgman method. The samples of these crystals were characterized by means of X-ray diffraction analysis, measurements of the reflectance in the plasma resonance frequency range ωp, of the Hall constant R H(B ‖ c) and electrical conductivity σ⊥c . It was found that the incorporation of Fe atoms into the Sb2Te3 crystal lattice reduces the volume of the unit cell; the values of ωp and R H(B ‖ c) (i.e. the concentration of holes) increase and the values of σ⊥c decrease with increasing iron content. The observed increase in the hole concentration is explained as due to the incorporation of Fe atoms into the Sb-sublattice creating thus substitutional defects of Fe'Sb. The decrease in the electric conductivity is associated with a decrease in the hole mobility.

Boronizing of steel by outward transport of Fe atoms during dynamic ion mixing

Mild steel substrates were treated by B-ion implantation or dynamic ion mixing in which B-ion implantation and Ti deposition were carried out simultaneously. Before the treatments, some substrates were implanted with C ions to confirm the location of the original substrate surface. The compositional depth profiles of the surface regions were obtained by using Auger electron spectroscopy (AES). For the B-ion implantation, an accumulation of the implanted B species takes place followed by a growth of the B layer as the B fluence is increased. The Fe matrix is separated during the process with outward transport of Fe atoms caused by the growth of the B layer. For the dynamic ion mixing, the outward transport of Fe atoms is enhanced during the process which is thought to be caused by not only the growth of the B layer but also the reaction between the sputtered Fe atoms and the depositing Ti atoms at steel surface. The TiFe reaction causes an incorporation of Fe atoms into the growing B layer resulting in the formation of a several μm thick boronized layer.