α-Fe2O3 Surface Research Articles

Revealing the inner rules of PREN from electronic aspect by first-principles calculations

This study provides insight into the empirical PREN formula by studying the effects of alloying elements (Cr, Mo, N, Ti) on the surface acidity and electronic structures of α-Fe2O3. Incorporation of Cr, Mo and N into α-Fe2O3 (0001) surface can weaken the surface acidity and reduce the susceptibility to Cl−, while the influence of Ti is opposite. The doped N into α-Fe2O3 behaves as an acceptor and lowers the concentration of electron carriers due to compensation. A negatively-charged center has formed to repel Cl− after the compensation and ionization of acceptor. The mechanism of pitting resistance improving by Cr, Mo or N is proposed.

Boosting photoanodic activity for water splitting in carbon dots aqueous solution without any traditional supporting electrolyte

We present a PEC water oxidation system with boosting activity in Carbon Dots (CDs) aqueous solution directly without any traditional supporting electrolyte. For α-Fe2O3 photoanode, photocurrent was significantly enhanced by dozens of folds compared to that in Na2SO4 solution under similar conditions. Based on electrochemical impedance spectroscopy, energy alignment measurements, photovoltage decay and Mott-Schottky plot, mechanism for charge transfer and function of CDs was well characterized. As semiconductors, CDs can combine with α-Fe2O3 into heterojunction for charge separation. As electrolyte, it can induce downward shift in conduction band of α-Fe2O3, allowing for stronger driving force for charge migration. Since CDs solution possesses a negative Zeta potential, it is proposed that during PEC proceeding, static interaction between CDs and positively charged photoanodic substrate can induce a dynamic balance of CDs absorbing or desorbing on/off α-Fe2O3 surface, which accounts for fast charge transfer, boosted photocurrent and high stability in PEC water splitting.

DFT study on the interaction of H2O and O2 with α-Fe2O3 (001) surface

The interactions of H2O and O2 with α-Fe2O3 (001) surface were studied using density functional theory (DFT). The surface structures of α-Fe2O3 changed a lot after H2O and O2 molecules adsorption, and the O–Fe bonds of α-Fe2O3 surface are weakened. The oxygen atom of H2O molecule are bonded to iron atom of α-Fe2O3 surface, and one H–O bond is broken to form hydroxyl group (−OH). Two oxygen atoms of O2 molecule are bonded the same iron atom of α-Fe2O3 surface. The adsorption energy of O2 on the α-Fe2O3 surface is −170 kJ/mol, which is larger than that of H2O on the α-Fe2O3 surface (−130 kJ/mol). The charge transfers occur from H2O molecule to α-Fe2O3 surface during H2O molecule adsorption, while from α-Fe2O3 surface to O2 molecule for O2 molecule adsorption. The value of charge transfer from α-Fe2O3 surface to O2 molecule (−0. 47 e) is larger than that from H2O to α-Fe2O3 surface (+0.06 e). This study provides a microcosmic explanation for the effect of H2O and O2 on α-Fe2O3 surface, and thus on the photocatalytic mechanism, which has important guiding significance for the industrial application of α-Fe2O3 as a photocatalyst.

Сравнительное исследование осаждения наноразмерных интермедиатов Au—S из водных растворов на поверхности CuO, TiO2 и α-Fe2O3

Методами рентгеновской фотоэлектронной спектроскопии (РФЭС), спектроскопии около­пороговой области рентгеновского поглощения Cu L-, Fe L-, Ti L-, O K-края (TEY XANES) в сочетании с просвечивающей электронной микроскопией изучены продукты взаимодействия дисперсных оксидов меди(II), железа(III) (гематита) и титана(IV) (рутила) с водными растворами, содержащими жидкие преднуклеационные интермедиаты, образующиеся в реакции между HAuCl4 и сульфидом натрия с начальным мольным отношением реагентов 1:3. Установлено, что по сравнению с обработкой подложек раствором HAuCl4 количество осажденного золота в присутствии сульфид-ионов заметно увеличивается. На трех изученных оксидах в качестве продукта разложения сильно разупорядоченного сульфида золота(I) образуются наночастицы золота, покрытые адсорбированной серой. На оксиде меди наблюдались заметно более крупные наночастицы золота (диаметром около 10 нм против 3—5 нм на гематите и на рутиле); имела место сульфидизация поверхности подложки.

Interaction of beta-lactoglobulin and bovine serum albumin with iron oxide (α-Fe2O3) nanoparticles in the presence and absence of pre-adsorbed phosphate

Dynamic changes in the secondary structures of BSA and β-LG observed when adsorbed onto nanoscale α-Fe2O3 surfaces. Adsorbed phosphate, a common oxyanion found in the environment, impacts protein surface coverage and modulates protein structure.

Enhancing [formula omitted]-Fe2O3(0 0 0 1) surfaces reactivity through lattice-strain control

In-plane strain-engineered water adsorption on Fe- and O3-terminated α-Fe2O3(0 0 0 1) surfaces was investigated using dispersion corrected density functional theory. We found that in order to enhance the water adsorption capacity different type of in-plane strain is needed to be applied on the two surfaces. On Fe-terminated surface increasing compressive strain facilitates water molecular adsorption. We demonstrate that this result mainly comes from the structural behavior of the outmost Fe cation on clean Fe-terminated surface. On the contrary, in-plane tensile strain favors water adsorption and dissociation on the O3-terminated surface. We discuss in details the possible reasons of this difference between the two surfaces in terms of structural parameters. Furthermore, we found that the two surfaces can represent two competitive molecular adsorption sites at a certain tensile strain in mixed surfaces. Finally, while strain is found to have a wide influence on the dissociation of water on the O3 termination, its effect is less pronounced on the Fe terminated one. According to our results strain-engineering on hematite surfaces represents a feasible way to enhance the reactivity.

Influence of hematite morphology on the CO oxidation performance of Au/α-Fe2O3

Controlling the interaction between metal nanoparticles and the support is a means to tune catalytic activity and stability. Herein we investigated the influence of the morphology of hematite on the performance of gold for CO oxidation. Nanosphere and nanorod forms of hematite, α-Fe2O3(S) and α-Fe2O3(R) respectively, were used to support gold nanoparticles. The surface of α-Fe2O3(R) was more corrugated than that of α-Fe2O3(S). These defects provide anchoring sites for gold nanoparticle deposition and stabilization. Due to the stronger gold-support interactions, Au/α-Fe2O3(R) contained smaller and more hemispherical gold particles than Au/α-Fe2O3(S). Au/α-Fe2O3(R) was not only more active in CO oxidation but also much more stable as evident from the small change in gold particle size during reaction. The higher reducibility of Au/α-Fe2O3(R) also contributed to the higher CO oxidation activity.

Photoelectrochemical performance of α-Fe2O3@NiOOH fabricated with facile photo-assisted electrodeposition method

This study adopted a photo-assisted electrodeposition method to fabricate NiOOH on α-Fe2O3 photoanode. The detailed microstructure and chemical composition characterizations suggested that the NiOOH particles were selectively deposited on the α-Fe2O3 surface to form hybrid nanocomposites. Photoelectrochemical measurements revealed the important role of NiOOH as a cocatalyst for water splitting under visible light illumination. The prepared photoanode exhibited essentially enhanced photoelectrochemical activity, which was about fourfold higher than that of α-Fe2O3 photoanode. Further study suggested that loading NiOOH by photo-assisted electrodeposition method on α-Fe2O3 surface can facilitate the water splitting process by providing substantial active reaction sites and promoting the transfer and consumption of photogenerated holes. Contribution of this work is to supply a facile method to develop efficient photoelectrochemical anode.

Understanding the formation of nanorods on hematite (α-Fe2O3) in the presence of surfactants: A molecular dynamics simulation study

Molecular dynamics (MD) simulations are applied to understand the morphology of adsorbed surfactants and formation of nanorods on (010) surface of hematite (α-Fe2O3). Three different surfactants are used, anionic - Sodium dodecyl sulphate (SDS), non-ionic - Octyl glucoside (OGA) and cationic - Hexadecyltrimethylammonium bromide (HDAB). The analysis has suggested that SDS has highest interaction among all the surfactants. As a result, it leads to the formation of nanorods on (010) plane of α-Fe2O3. The surfactant aggregates are formed in HDAB and OGA. These two surfactants differ in their tail length. As a result, there would be differences in hydrophobic interaction among the tails of the HDAB and OGA. There is a high tendency for the tails of the HDAB to aggregate and form spherical morphology on the α-Fe2O3 surface. On the other hand, a weak coupling is observed among the carbon atoms in the tails of the OGA surfactants. Hence, the absorption of OGA effectively evolves as the simulation proceeds. The differences in the morphology of different categories of surfactants lead us to explain the formation of nanorods for α-Fe2O3 nanoparticles (NPs).

Nitrogen-Doped Carbon Nanolayer Coated Hematite Nanorods for Efficient Photoelectrocatalytic Water Oxidation

To improve the charge carrier transfer ability in the bulk and at the surface of α-Fe2O3 and accelerate the water oxidation kinetics at the photoanode/electrolyte interface, herein, starting with Ti-doped α-Fe2O3 nanorods, a nitrogen (N) doped carbon (C) nanolayer was coated on the surface of nanorods through a facile hydrothermal method, following a thermal treatment in Ar atmosphere. It was revealed that the N-doped C nanolayer, acting as the passivation layer and/or the water oxidation catalyst, could efficiently extract and collect photoexcited holes from the bulk of α-Fe2O3 and then inject them into the electrolyte for the accelerated water oxidation reaction, by inhibiting both the bulk and surface charge carrier recombination. As a result, the photocurrent density of Ti-doped α-Fe2O3 nanorods coated with N doped C nanolayer was increased by ∼2.7 folds at 1.8 V vs. RHE, as compared with the pristine one.

Adsorption kinetics, conformational change, and enzymatic activity of β-glucosidase on hematite (α-Fe2O3) surfaces

Substantial fractions of extracellular enzymes are intimately associated with soil minerals, which may protect enzymes from denaturation, precipitation, proteolysis, or microbial consumption in soil environments. However, how mineral surface properties affect enzyme-mineral interactions and enzymatic activity of enzymes associated to mineral surface is still unclear. In the present study, adsorption behavior, conformational change, and enzymatic activity of β-glucosidase (BG) on hematite (001) face and (104) face, respectively, were investigated using in situ attenuated total reflectance FTIR spectroscopy and batch experiments. β-glucosidase undergoes greater conformational changes upon adsorption onto hematite (104) face than on hematite (001) face, probably due to the stronger protein-surface interactions on (104) face with the relatively higher surface hydroxyl density. On the other hand, the amount of BG sorbed on hematite (001) face was nearly two times higher than that on hematite (104) at the end of the 150-min adsorption experiments, due to the higher extent of conformational change in β-glucosidase on hematite (104) face. Correspondingly, the initial rate of cellobiose hydrolysis by per gram of β-glucosidase adsorbed on hematite (104) face was 1.7 times higher than that on hematite (001) face. However, when the density of hematite particles was same, the extent of cellobiose hydrolysis was 1.2 times higher on hematite (001) face than that on the (104) face, because of the higher adsorbed amount of β-glucosidase on the former. This study decoupled the effects of mineral surface properties on adsorption kinetics and conformational changes of soil enzymes bound to soil minerals and provided new insights into the correlation between mineral surface properties and catalytical activity of mineral-associated enzymes in soil environments.

Modeling of Formaldehyde Adsorption on Hematite (100) Surface with Reaxff Molecular Dynamics

Introduction Iron oxide (α-Fe2O3, hematite) is a multi-functional n-type material, which has been used in the detection of formaldehyde and other gases [1, 2], but the gas sensing mechanism is not clear yet. In this paper, the adsorption of HCHO molecules on α-Fe2O3 (100) surface are studied by ReaxFF (Reactive Force Field) through MD simulations (molecular dynamics) for the first time. Both pure HCHO gas and the gas mixture of HCHO with the environment gases of O2, H2O and H2 are studied. The adsorption structures and energies are calculated at various temperatures. The results show that the HCHO molecules are completely and directly adsorbed on the hematite (100) surface without desorption for all temperatures and models. Oxygen do not obviously affect the adsorption of formaldehyde on iron oxide, which is differ from ZnO or SnO2. RDF (radical distribution function) data show that the presence of water makes formaldehyde adsorbed more tightly on the hematite (100) surface. The dissociation of the HCHO on the Fe2O3 surface with the H2O is observed at 600 K, and the adsorption energy is the smallest among all temperatures. A possible dissociation process of formaldehyde on the surface of α-Fe2O3 with H2O is presented according to the absorption structures. Method Materials Studio is used to establish the models. The MD simulations are performed using the LAMMPS package and the ReaxFF [3] is employed to describe the atomic interactions among Fe, C, O, H atoms. The systems with pure HCHO, and gas mixtures (HCHO, H2O, O2, and H2) are studied. Figure 1 (a) shows the initial structure of the α-Fe2O3 (100) surface and the gas before adsorption. The initial pressure of the gas mixtures is about 0.76 MPa and the gas molecules are put 0.5 nm above the surface. Periodic boundary conditions, NVT ensemble and an integration timestep of 1 fs are used in the simulations. The systems are thermostatted for 60 ps at temperatures of 300 K, 400 K, 500 K, 600 K and 700 K, respectively. Results and Conclusions The dynamic adsorption processes of gas molecules on α-Fe2O3 can be clearly observed by MD simulations, and Figure 1 (b)-(f) presents the snapshots of the systems after adsorption. The adsorption energy shown in Figure 2 is calculated by Ead = Egas/Fe2O3 - Egas - EFe2O3 where Egas/Fe2O3 is the energy of the system after adsorption, Egas and EFe2O3 represent the energy of gas and Fe2O3 before adsorption, respectively. The negative Ead indicates that formaldehyde molecules can be spontaneously adsorbed on the (100) surface at any temperature. In the gas mixture adsorption system, setting 0.2 nm as the distance threshold from Fe2O3, the atom numbers adsorbed on the surface are shown in Table 1. Among the four gases in this work, HCHO is the easiest to adsorb on (100) surface of hematite, followed by water, then hydrogen, and finally oxygen, as shown in Figure 1 and 2, and Table 1. It is well-known that oxygen plays an important role for the surface adsorption of reducing gases on the n-type SnO2 and ZnO, and Barik [1] tried to explain the reaction of HCHO on hematite surface in the same way, however, the simulation results in this work show that O2 has no observable influence on the adsorption of HCHO and the HCHO is directly adsorbed on hematite (100) surface with the typical structure shown in Figure 3 (a).Comparing the adsorption results of pure HCHO and the gas mixture of HCHO and H2O, the present of water makes the chemical adsorption of HCHO on the hematite (100) surface much stronger, as the O atoms in HCHO bind more tightly to the Fe atoms with the presence of H2O for all temperatures according to the RDF results, while it is not stable for pure HCHO adsorption system when the temperature increases. The adsorption energy is the lowest at 600 K for the system with gas mixture of H2, O2, H2O and HCHO. A new adsorption structure of HCHO is found at this temperature: when a HCHO is close to a H2O molecule, the HCHO can be decomposed into a CH2 group and an O atom, and the O atom takes one H atom from the H2O molecule to form the OHgroup, as shown in Figure 3 (b). Based on this adsorption structure, we haveHCHO + H2O → CH2 + 2 OHThis phenomenon is only observed at 600 K, which leads to the lowest adsorption energy. The results indicate that humidity plays an important role in the chemical reaction between α-Fe2O3 (100) surface and formaldehyde.This work is supported by the Nature Science Foundation of China (61874018 and 61274076), the Fundamental Research Funds for the Central Universities, and the Nature Science Foundation of Liaoning (20180550923).

The Effect of Surface Defects on Chloride-Induced Depassivation of Iron—A Density Functional Theory Study

Chloride-induced depassivation is a large contributor to the degradation of metals, but defects are likely to play a key role in that process. Here density functional theory calculations are used to investigate the mechanism of the initial stages of chloride-induced depassivation of iron by studying the Cl interactions with stepped α-Fe2O3 (0001) surfaces and how that can lead to degradation of the passive oxide film. The low coordinated Fe sites near the step edge and O vacancies facilitate high local coverages of adsorbed Cl, which enhance surface Fe vacancy formation significantly. The step edge also lowers the Cl insertion energy, relative to the flat surface, but insertion by exchange with O is still endothermic. This study illustrates the importance of surface defects, step edges, and O vacancies in the depassivation mechanism, but the findings generally support the point defect model as a description of the depassivation mechanism.

Catalytic function of ferric oxide and effect of water on the formation of sulfur trioxide

Sulfur trioxide (SO3) is not only environmentally harmful but also highly corrosive, taking a great threat to the safe operation of coal-fired power plants. A dominant pathway of SO3 formation in coal-fired power plant is through the catalytic oxidation of SO2 (SO2+1/2O2→SO3) on the surfaces of ash particles containing Fe2O3. The catalytic formation of SO3 could be affected by complex atmosphere, where the effect from H2O is still debatable. In this paper, density functional theory (DFT) is employed to explore the reaction pathway of SO3 formation catalyzed by α-Fe2O3 in complex atmosphere containing O, O2, SO2 and H2O. In order to get the stable adsorption sites of these species, the adsorption energy of potential adsorption configurations on the α-Fe2O3 (001) surface is calculated. The dissociations of O2 molecule on complete and defect α-Fe2O3 (001) surfaces with O vacancy are calculated, and the Langmuir-Hinshelwood and Eley-Rideal mechanisms for the O(ads) reaction with SO2(ads) or SO2 are compared. The effect of H2O besides of SO2 and O2 on the formation of SO3 is especially discussed. The DFT calculation results show that for the formation of SO3 in gas phase, the energy barrier of ‘SO2+1/2O2→SO3’ is 436.75 kJ mol−1, in contrast, for the catalytic formation of SO3 on α-Fe2O3 surfaces, this energy barrier becomes an order of magnitude smaller, 24.82 kJ mol−1. O2 molecules can dissociate on the defect α-Fe2O3 (001) surface with O vacancy spontaneously, indicating that the defect α-Fe2O3 is favorable for the dissociation of O2, thereby promotes the formation of SO3. The energy barrier of ‘SO2(ads)+O(ads)→SO3(ads)’ through Langmuir-Hinshelwood mechanism is much higher than that of ‘SO2+O(ads)→SO3(ads)’ through Eley-Rideal mechanism. The adsorption energy on the α-Fe2O3 (001) surface of H2O is much smaller than that of SO2 and O2, indicating that H2O has little effect on the adsorption of O, O2, SO2 and eventually the heterogeneous formation of SO3. The DFT analysis results in this study provide a deep understanding on the reaction pathway of SO3 catalytic formation by Fe2O3.

Removal of phenol from aqueous solution by adsorption onto hematite (α-Fe2O3): Mechanism exploration from both experimental and theoretical studies

Iron oxides in general and especially hematite, α-Fe2O3 have been proved promising materials for efficient removal of various organic pollutants. Herein, we report a successful preparation of hematite (α-Fe2O3) by a facile precipitation method and its potential application in the removal of phenol from wastewater. The prepared material was subjected to extensive characterization using a variety of techniques such as scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), and the Brunauer Emmett Teller (BET) method. The operating conditions were optimized to improve the adsorption process efficiently. The adsorption analysis showed an adsorption capacity of 16.17 mg g−1 towards phenol at 30 °C. The reaction kinetics and potential rate-limiting steps were studied by Lagergren's pseudo-first-order and pseudo-second-order models, and it was found that the pseudo-second-order accurately described the adsorption kinetics. Freundlich and Langmuir adsorption isotherms models were applied, and the quality of the fittings clearly shows that the Langmuir model well describes the phenol adsorption on the hematite. The interaction mechanism between phenol and α-Fe2O3(0 0 1) surface was further addressed by Density Functional Theory (DFT) calculations and molecular dynamics (MD) simulations. Experimental and theoretical results indicate that there is strong evidence for the decisive effect of π–π interactions and H-bonds on the adsorption capacity.

Improved description of hematite surfaces by the SCAN functional.

Controversies on the surface termination of α-Fe2O3 (0001) focus on its surface stoichiometry dependence on the oxygen chemical potential. Density functional theory (DFT) calculations applying the commonly accepted Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional to a strongly correlated system predict the best matching surface termination, but would produce a delocalization error, resulting in an inappropriate bandgap, and thus are not applicable for comprehensive hematite system studies. Besides, the widely applied PBE+U scheme cannot provide evidence for existence of some of the successfully synthesized stoichiometric α-Fe2O3 (0001) surfaces. Hence, a better scheme is needed for hematite DFT studies. This work investigates whether the strongly constrained and appropriately normed (SCAN) approximation reported by Perdew et al. could provide an improved result for the as-mentioned problem, and whether SCAN can be applied to hematite systems. By comparing the results calculated with the PBE, SCAN, PBE+U, and SCAN+U schemes, we find that SCAN and SCAN+U improves the description of the electronic structure of different stoichiometric α-Fe2O3 (0001) surfaces with respect to the PBE results, and that they give a consistent prediction of the surface terminations. Besides, the bulk lattice constants and the bulk density of states are also improved with the SCAN functional. This study provides a general characterization of the α-Fe2O3 (0001) surfaces and rationalizes how the SCAN approximation improves the results of hematite surface calculations.

Sucrose-templated interconnected meso/macro-porous 2D symmetric graphitic carbon networks as supports for α-Fe2O3 towards improved supercapacitive behavior.

In this study, ultrahigh electrochemical performance for interconnected meso/macro-porous 2D C@α-Fe2O3 synthesized via sucrose-assisted microwave combustion is demonstrated. Hematite (α-Fe2O3) synthesized via the same approach gave an encouraging electrochemical performance close to its theoretical value, justifying its consideration as a potential supercapacitor electrode material; nonetheless, its specific capacitance was still low. The pore size distribution as well as the specific surface of bare α-Fe2O3 improved from 145 m2 g−1 to 297.3 m2 g−1 after it was coated with sucrose, which was endowed with ordered symmetric single-layer graphene (2D graphene). Accordingly, the optimized hematite material (2D C@α-Fe2O3) showed a specific capacitance of 1876.7 F g−1 at a current density of 1 A g−1 and capacity retention of 95.9% after 4000 cycles. Moreover, the material exhibited an ultrahigh energy density of 93.8 W h kg−1 at a power density of 150 W kg−1. The synergistic effect created by carbon-coating α-Fe2O3 resulted in modest electrochemical performance owing to extremely low charge transfer resistance at the electrode–electrolyte interface with many active sites for ionic reactions and efficient diffusion process. This 2D C@α-Fe2O3 electrode material has the capacity to develop into a cost-effective and stable electrode for future high-energy-capacity supercapacitors.

Synergies of co-doping in ultra-thin hematite photoanodes for solar water oxidation: In and Ti as representative case.

Solar energy induced water splitting in photoelectrochemical (PEC) cells is one of the most sustainable ways of hydrogen production. The challenge is to develop corrosion resistant and chemically stable semiconductors that absorb sunlight in the visible region and, at the same time, have the band edges matching with the redox level of water. In this work, hematite (α-Fe2O3) thin films were prepared onto an indium-doped tin oxide (ITO; In:SnO2) substrate by e-beam evaporation of Fe, followed by air annealing at two different temperatures: 350 and 500 °C. The samples annealed at 500 °C show an in situ diffusion of indium from the ITO substrate to the surface of α-Fe2O3, where it acts as a dopant and enhances the photoelectrochemical properties of hematite. Structural, optical, chemical and photoelectrochemical analysis reveal that the diffusion of In at 500 °C enhances the optical absorption, increases the electrode–electrolyte contact area by changing the surface topology, improves the carrier concentration and shifts the flat band potential in the cathodic direction. Further enhancement in photocurrent density was observed by ex situ diffusion of Ti, deposited in the form of nanodisks, from the top surface to the bulk. The in situ In diffused α-Fe2O3 photoanode exhibits an improved photoelectrochemical performance, with a photocurrent density of 145 μA cm−2 at 1.23 VRHE, compared to 37 μA cm−2 for the photoanode prepared at 350 °C; it also decreases the photocurrent onset potential from 1.13 V to 1.09 V. However, the In/Ti co-doped sample exhibits an even higher photocurrent density of 290 μA cm−2 at 1.23 VRHE and the photocurrent onset potential decreases to 0.93 VRHE, which is attributed to the additional doping and to the surface becoming more favorable to charge separation.

First-principles studies on α-Fe2O3 surface slabs and mechanistic elucidation of a g-C3N4/α-Fe2O3 heterojunction

First-principles calculations were carried out to explore the surface energies and electronic properties of α-Fe2O3 surface slabs. Further, to enhance the photocatalytic activity of Fe2O3, an alternative effective strategy was to examine Fe2O3-based heterostructures.

Combined Density Functional Theory and Reduction Kinetics Investigation of Enhanced Adsorption of Hydrogen onto Fe2O3 by Surface Modification with Nickel

Based on the density functional theory, the geometric structure, adsorption energy and density of states of H2/α-Fe2O3 (001) system and (H2 + Ni)/α-Fe2O3 (001) system were determined. The results showed that the absolute value of adsorption energy between H2 molecule and α-Fe2O3 (001) surface and the bond length of H2 molecule were increased by the presence of Ni atom. The presence of Ni atom promotes the adsorption of H2 molecule on α-Fe2O3 (001) surface. Reduction behavior of iron and nickel oxides in H2 atmosphere was determined by thermogravimetric analysis. The samples included Fe2O3, Fe2O3-NiO and Fe2O3-Ni systems. The effect of Ni and NiO on the reduction behavior of Fe2O3 was investigated. The ease of reduction within the following three systems decreases sequentially: Fe2O3-Ni > Fe2O3-NiO > Fe2O3. The activation energy of Fe2O3-Ni, Fe2O3-NiO and Fe2O3 systems at two temperature stages (viz. < 400 °C and > 400 °C) were 172 kJ·mol−1, 197 kJ·mol−1 and 263 kJ·mol−1 respectively.