Fe Surface Research Articles

Investigation of the corrosion inhibition potentials of some 2-(4-(substituted)arylidene)-1H-indene-1,3-dione derivatives: density functional theory and molecular dynamics simulation

BackgroundCorrosion is a threat to material strength and durability. Electron-rich organic inhibitor may offer good corrosion mitigation potentials. In this work, anti-corrosion potentials of nine derivatives of 1H-indene-1,3-dione have been investigated using density functional theory (DFT) approach and molecular dynamics (MD) simulation. Chemical reactivity descriptors like energies of lowest unoccupied molecular orbital (ELUMO), highest occupied molecular orbital (EHOMO), electron affinity (A), ionization potential (I), energy gap (ΔEgap), global hardness (η), global softness (σ), electronegativity (χ), electrophilicity (ω), number of transferred electrons (ΔN) and back-donation (ΔEback-donation) were computed at DFT/B3LYP/6-31G(d) theoretical level. The local reactive sites and the charge partitioning on the compounds were studied using Fukui indices and molecular electrostatic potential (MEP) surface analysis. The adsorption behavior and the binding energy of the inhibitors on Fe (110) surface in hydrochloric acid solution were investigated using MD simulation.ResultsThe high chemical reactivity, kinetic instability and good corrosion inhibition potentials demonstrated by the inhibitors are rationalized based on their high EHOMO, A, σ, ΔN, ΔEback-donation, and low ΔEgap, ELUMO, I and η. A wide difference of approximately 2.4–3.2 eV between the electronegativities of iron and the 1H-inden-1,3-diones suggests good charge transfer tendency from the latter to the low-lying vacant d-orbitals of iron. The heteroatoms (O and N) and the aromatic moieties are the nucleophilic sites on the inhibitors for effective adsorption on the metal surface as shown by condensed Fukui dual functions and MEP analysis. The MD simulation shows good interaction and strong binding energy between the inhibitor and Fe (110) surface.ConclusionsEffective surface coverage and displacement of H3O+, Cl− and water molecules from Fe (110) surface by the inhibitors indicate good corrosion inhibition properties of the inden-1,3-diones. 2-((4,7-dimethylnaphthalen-1-yl)methylene)-1H-indene-1,3(2H)-dione display low energy gap, strongest binding interaction and most stabilized iron-inhibitor configuration, hence, the best anti-corrosion potential.Graphical abstract

Exploring the feasibility of new eco-friendly heterocyclic compounds for establishing efficient corrosion protection for N80 steel in a simulated oil well acidizing environment: From molecular-level prediction to experimental validation

Corrosion inhibitors are an effective and low-cost option to relieve strong acid-induced corrosion during acidizing oil wells. In this work, a computational study was conducted to assess the interaction of newly synthesized eco-friendly compounds namely, (R, E)-N′-(4-(dimethylamino)benzylidene)− 2-(4-isobutylphenyl) propanehydrazide (DBIP) and (R,E)− 2-(4-isobutylphenyl)-N′-(4-nitrobenzylidene) propanehydrazide (INBP) with the steel surface. Theoretical prediction of compounds’ affinity to the steel surface and interaction mechanisms were elucidated at the molecular level using first-principles density-functional tight-binding (DFTB), quantum chemical descriptors (QCDs), Fukui functions (FFs) and molecular dynamics (MD) simulations. Then, the corrosion inhibition performance of selected compounds for N80 steel in 15 wt% HCl solution was investigated using weight loss (WL), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves (PPCs) methods, and field emission scanning electron microscopy (FESEM). A theoretical investigation by DFTB modeling and Partial Density of States (PDOSs) showed the formation of several covalent bonds between inhibitor molecules and Fe(110) surface. Experimental studies revealed an increased inhibition efficiency of both inhibitors DBIP and INBP with increasing concentrations reaching a higher efficiency of 99% at 5 × 10−3 mol/L of DBIP. The PPCs data confirmed the mixed-type nature of inhibition. The adsorption obeyed the Langmuir isotherm model, following a mixed physical and chemical interaction mode. The surface morphology analysis by FESEM showed a protected N80 steel surface in the presence of inhibitors compared to its highly corroded surface in blank solutions. The present results open an interesting approach for developing a highly efficient corrosion inhibitor formulation for oil well acidizing based on low-cost computational prediction.

One-pot H/D exchange and low-coordinated iron electrocatalyzed deuteration of nitriles in D2O to α,β-deuterio aryl ethylamines

Developing a step-economical approach for efficient synthesis of α,β-deuterio aryl ethylamines (α,β-DAEAs) with high deuterium ratios using an easy-to-handle deuterated source under ambient conditions is highly desirable. Here we report a room-temperature one-pot two-step transformation of aryl acetonitriles to α,β-DAEAs with up to 92% isolated yield and 99% α,β-deuterium ratios using D2O as a deuterium source. The process involves a fast α-C − H/C − D exchange and tandem electroreductive deuteration of C ≡ N over an in situ formed low-coordinated Fe nanoparticle cathode. The moderate adsorptions of nitriles/imine intermediates and the promoted formation of active hydrogen (H*) on unsaturated Fe sites facilitate the electroreduction process. In situ Raman confirms co-adsorption of aryl rings and the C ≡ N group on the Fe surface. A proposed H*-addition pathway is confirmed by the detected hydrogen and carbon radicals. Wide substrate scope, parallel synthesis of multiple α,β-DAEAs, and successful preparation of α,β-deuterated Melatonin and Komavine highlight the potential.

(Digital Presentation) Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Ammonia electrosynthesis is considered promising for the production of ammonia as an energy carrier, as the process could provide greater flexibility and compatibility to the fluctuations of renewable energy than the industrial Haber-Bosch process. One approach for enhancing the ammonia formation rate is the electrochemical promotion of catalysis (EPOC) [1], in which a non-faradaic acceleration of ammonia synthesis is observed; however, much of the mechanism remains unclear. Further mechanistic insight would aid in designing better electrode structures that are suited for efficient ammonia electrosynthesis. In this presentation, we explore the mechanism underlying the electrochemical promotion of ammonia synthesis, using electrochemical cells with iron-based cathodes on a proton-conducting BaCe0.9Y0.1O3 (BCY) electrolyte.Previously, our group reported that the ammonia formation rate of a cathodically polarized cell can be enhanced by adding H2 to the cathode gas feed (commonly pure N2) [2, 3]. Further kinetic and isotopic analysis using deuterium showed that the primary hydrogen source for the ammonia produced was the gaseous hydrogen feed, rather than the protons conducted via the electrolyte [4]. Cells with a porous pure Fe cathode resulted in higher ammonia formation rates than those with a porous 10 wt.% Fe-BCY cathode, suggesting that the pure Fe surfaces near the cathode-electrolyte interface, as opposed to the triple phase boundaries, are active for ammonia electrosynthesis [3]. However, the 10 wt.% Fe-BCY cathode, fabricated by the impregnation method, was thought to be limited by lack of Fe network formation needed for electron conduction.In this study, we fabricated a cermet cathode with the composition 56 wt.% Fe-BCY, aiming for Fe and BCY to form separate networks for electron and proton conduction, respectively. Electrochemical cells of the configurations Pt|BCY|Fe and Pt|BCY|Fe-BCY [Fig. 1a], with similar Fe mass (0.5 and 0.4 mg) were compared. Ammonia synthesis was conducted in a single-chamber reactor at 500-600˚C with a 50% H2/50% N2 feed. The gaseous ammonia produced was captured by bubbling into a dilute H2SO4 solution and quantified via high-performance liquid chromatography.Using the pure Fe electrode, an ammonia formation rate of 1.3 × 10-8 mol s-1 cm-2 (26 mmol gFe -1 h-1) was obtained at 600˚C and -1 V [Fig. 1b]. This corresponds to an almost 5-fold increase in ammonia formation compared to the catalytic reaction at 0 V. In contrast, a lower ammonia formation rate of 7.0 × 10-9 mol s-1 cm-2 (17 mmol gFe -1 h-1) was obtained using the Fe-BCY electrode at the same conditions. Despite the cermet electrode having a slightly higher current density, and despite the comparable iron loading on the two cells, the pure Fe cell still resulted in a faster ammonia formation rate per electrode area and per iron mass. As the cermet electrode is expected to have a significantly longer triple phase boundary length, from the comparison of these two electrochemical cells, the triple phase boundaries do not appear to be the primary active sites. We further analyze the roles of the bulk Fe surfaces and the Fe/BCY triple phase boundaries, by examining the effect of the electrode thickness and by post-experiment cross-sectional electron microscopy approaches.AcknowledgementsThis work was supported by JSPS KAKENHI Grant Number JP21H04938.

Pronounced inhibitory mechanism of Cr on vacancy-like defects in Fe9Cr alloy irradiation with helium ions

• First-principles calculations combined with positron annihilation spectroscopy. • The He atoms aggregate among (1 1 0) planes in the perfect Fe and Fe9Cr models. • Fe atoms around the He clusters are inclined to emit spontaneously. • The doping of Cr repels the He atoms and weakens the growth of He clusters. First-principles calculations and positron annihilation spectroscopy were used to investigate the effect of Cr atoms on He-induced vacancy-like defects in pure Fe and Fe9Cr alloys. The He atom is not energetically favorable at both the surface and the subsurface, but it becomes stable under the third atomic layer from the surface. The diffusion of He atoms to the vacuum and aggregation of He atoms into clusters coexist. We observed that the interstitial He n clusters prefer to stay along the (1 1 0) plane. Moreover, the small He n clusters induce strong lattice distortions, and the emission of a self-interstitial Fe atom located at the adjacent He n cluster is energetically favorable for n > 2 and vacancy formation energies of Fe9Cr are higher than that of Fe. This suggests that Cr atoms could effectively enhance the stability of Fe atoms around He n clusters but that the Fe atoms would still like to shift from the vicinity of He n to the surfaces of the models. In the experiment, Fe and Fe9Cr alloys were irradiated with He ions to a dose of 1 × 10 16 cm 2 and the positron annihilation results showed that the Fe9Cr alloy has a smaller relative S (ΔS) parameter value than pure Fe. The experimental results matched well with the theoretical analysis. These results would help provide additional insights into the behavior of He in irradiated Fe and Fe9Cr surfaces, necessary for the interpretation of the growth of the He bubble.

Adsorption of imidazolium-based ionic liquids on the Fe(1 0 0) surface for corrosion inhibition: Physisorption or chemisorption?

The use of imidazolium-based ionic liquids (ILs) as corrosion inhibitors for iron was studied using both first-principles based density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD), to understand their adsorption structure, stability, and mechanism. A total of 36 ionic liquids (ILs) were selected, with various anion type (Cl−, Br−, I−, N(CN)2−, BF4− and PF6−) and alkyl chain length (Cn, n = 0, 1, 2, 4 and 6). Our calculations revealed that the ILs exhibit strong adsorption on the metal surface and is classified as chemisorption under various different criteria. AIMD simulations including explicit solvation effects verified that these adsorption configurations calculated under vacuum are representative of the adsorption process in an aqueous environment. Furthermore, we showed that the basis of this chemisorption interaction is through net electron donation from the iron slab to the imidazolium ring. Employing dispersion corrected DFT methods (DFT-D3), we demonstrated that the alkyl chain length of the cation greatly influences adsorption energy. Finally, we showed that DFT calculations model the adsorption process much more accurately compared to classical molecular dynamics calculations. The results from this computational study agree with past experimental findings and demonstrate that DFT calculations can be used to provide insight into the nature of the adsorption process of the green and sustainable ILs involved in corrosion inhibition.

Self-doped poly(aniline-co-metanilic acid) copolymer coatings for enhancing the corrosion resistance of 304 stainless steel

Self-doped conducting poly(aniline-co-metanilic acid) (SPANI) copolymer coatings are electropolymerized for corrosion protection of 304 stainless steel (304SS) in a 0.3 M HCl solution. The synthesized SPANI coating is more compact and uniform, which exhibits improved barrier resistance to aggressive ions. The potentiodynamic polarization curve and electrochemical impedance spectroscopy results show that the SPANI copolymer coatings significantly suppress the corrosion current density, increase the charge transfer resistance, and effectively inhibit corrosion of the 304SS substrate. In addition, the SPANI copolymer coating exhibits a nondestructive topography after 120 h of immersion in a corrosive environment, which further confirms its superior protection performance. Owing to their enhanced physical barrier effect (compact coating surface with low porosity) and superior anodic protection, SPANI copolymer coatings are more corrosion resistant. Furthermore, the outcomes of the quantum chemical calculation and molecular dynamic simulation indicate that the SPANI copolymer chains are more stabilized and display favorable compatibility with the Fe (1 1 0) surface via electrostatic force. The better surface coverage and higher adsorption activity ensure an excellent chemical-anchor effect on the Fe (1 1 0) plane and thus achieve higher corrosion inhibition efficiency of the SPANI copolymer coatings.

Iron-Based Electrode Structures for Ammonia Electrosynthesis Cells with Proton-Conducting Ceramic Electrolytes

Ammonia electrosynthesis was conducted using proton-conducting ceramic electrolysis cells in a single chamber supplied with mixed N2 and H2, to determine the active electrode regions for the electrochemical promotion of catalysis (EPOC). Cells with Fe-based cathodes of either a metal, cermet, or mixed ionic-electronic conductor (MIEC) structure were compared, to assess whether the triple-phase boundaries (TPBs) or the Fe catalyst surfaces are more effective for ammonia synthesis. Upon cathodic polarization at 600˚C, high ammonia formation rates on the order of 10−8 mol s−1 cm−2 were obtained with both Fe metal and Fe-BaZr0.8Y0.2O3 (Fe-BZY) cermet cathodes. Comparisons of the three electrode structures suggest that when H2 is also supplied to the cathode, ammonia formation occurring on bulk Fe surfaces leads to a greater promotional effect than that at TPBs. There also remains a possibility that the interfacial layer formed at the cathode-electrolyte interface due to cation interdiffusion aids ammonia formation.

Performance and interaction mechanism of a new highly efficient benzimidazole-based epoxy resin for corrosion inhibition of carbon steel in HCl: A study based on experimental and first-principles DFTB simulations

Thanks to their excellent properties, epoxy resins are the first choice for many engineering applications. In this regard, herein, a new epoxy resin, namely 1-(oxiran-2-ylmethyl-1H-benzo[d]imidazole (BIZ epoxy), was synthesized and characterized by nuclear magnetic resonance (1H, 13C NMR) and Fourier transform infrared-attenuated total reflection (FTIR-ATR)) techniques. The corrosion inhibition properties of prepared epoxy resin for carbon steel (CS) in 1.0 mol/L HCl were evaluated using electrochemical and scanning electron microscope (SEM) techniques. Furthermore, reactivity and interaction mechanisms between epoxy resin molecule and the iron surface were investigated using quantum chemical parameters (QCPs) and Density-Functional Tight-Binding (DFTB). Electrochemical studies by potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS) showed that the BIZ epoxy acted as a barrier against the acid corrosion of CS with an inhibition efficiency of 93 % at 1 mmol/L. The adsorption of BIZ epoxy followed the Langmuir adsorption isotherm and was found to be a physicochemical process. The SEM analysis showed a significant difference in surface morphology of CS after inhibition due to the formation of a protective barrier. DFTB simulation of BIZ epoxy – Fe(110) surface revealed the formation of a chemical bond and several long-range van der Waals interactions. The projected density of states (PDOS) of isolated and adsorbed systems confirmed the physicochemical nature of interactions between inhibitor molecule and Fe(110) surface.

Influence of surface treatment on the metal dusting behavior of alloy 699 XA

AbstractMetal dusting attack is a serious problem in processing industries using carbonaceous gases and high temperatures. Ni‐based alloy 699 XA was recently developed as an alloy for these types of environments with high resistance against metal dusting. In this study, different surface treatments of this chromium‐ and aluminum‐rich alloy are shown to have an important influence on the metal dusting onset behavior. It was found that surface treatments that are traditionally considered to be helpful for fatigue performance, for example, shot peening, and pickling were detrimental to the metal dusting performance of alloy 699 XA. Additionally, the shot peening surface treatment promoted Fe surface contamination, resulting in a negative impact on the metal dusting pitting resistance of the alloy. Deformation accompanied by apparent BCC α‐Cr precipitation in the bulk microstructure, but a comparison with cold‐rolled materials shows that the surface treatment dominates the metal dusting resistance.

Computational Design of Anticorrosion Properties of Novel, Low-Molecular Weight Schiff Bases.

Due to the many economic consequences and technological problems caused by the corrosion process, its inhibition is one of the most important aspects of ongoing research. Computer methods, i.e., density functional theory (DFT) methods, are of great importance to the large-scale research being conducted which allows the evaluation of the corrosion inhibition performance without conducting time-consuming, long-term and expensive experimental measurements. In this study, new corrosion inhibitors were designed in three corrosion environments on the basis of their HOMO and LUMO orbital energies—the energy difference between them and their dipole moment. In addition, their interactions with the Fe and Cu surface were modelled on the basis of the number of electrons transferred during the formation of the protective adsorption layer (ΔN) and the initial energy between inhibitor molecule and protected metal surface (Δψ). The obtained results indicate that, among the aliphatic investigated Schiff bases, the N-methylpropan-1-imine (N-MP(1)I) molecule would theoretically have the highest corrosion inhibition efficiency mainly due to its high EHOMO value, relatively low ELUMO value, high chemical reactivity and high polarity.

ReaxFF molecular dynamics investigation on the oxidation mechanism of Fe surface in supercritical CO2 mixed with O2

In the present study, the oxidation reaction of Fe surface in supercritical CO2 (SCO2) mixed with O2 was studied at atomic scale by ReaxFF molecular dynamics simulation. The microscopic oxidation mechanism was explored, the charge evolution was observed and the effects of gas composition and temperature on the oxidation were determined. The results indicate that in the initial stage of the reaction, both of O2 and SCO2 molecules are adsorbed on the Fe surface, and O2 reacts with Fe atoms prior to SCO2. The initial consumption rates of O2 and SCO2 increase with the increase of their content in the system. The reaction degrees of O2 and SCO2 increase with temperature. The consumption of SCO2 is always greater than O2 at different temperatures. The thermal motion of atoms rises significantly with the increase of temperature, which is beneficial to the oxidation reaction.

DFT and Monte Carlo Simulations on the Corrosion Inhibitive Potentials of some Furan-based Carbohydrazide Derivatives

Corrosion is a serious concern for the oil and construction industries. Controlling corrosion, therefore, remains essential in a bid to reduce costs and save lives. The anti-corrosion potentials of seven Furan-based Carbohydrazide derivatives were investigated using the density functional theory (DFT) approach and Monte Carlo (MC) simulation. The energies of the frontier molecular orbitals (FMOs) like the lowest unoccupied molecular orbital energy (ELUMO), highest occupied molecular orbital energy (EHOMO), energy gap (Eg), number of transferred electrons (ΔN), and other reactivity descriptors were computed at DFT/B3LYP/6-31G(d) level of theory. The reactive sites were determined using Fukui indices and molecular electrostatic potential (MESP) surface analysis. The adsorption behavior of the compounds on the Fe (110) surface was investigated in hydrochloric acid solution using MC simulation. The compounds displayed corrosion inhibition potentials as rationalized by their high EHOMO, A, σ, ΔN, ΔEback-donation, and low Eg, ELUMO, I, and η. This is because they showed the ability to donate electrons to the metal’s d-orbital while also accepting electrons via back-donation, as revealed by the MESP surface analysis. The MC simulation revealed good interaction between the compounds (inhibitors) and Fe(110) surface in the HCl medium. These compounds could be used as inhibitors of corrosion in the manufacturing industries.

Investigation of Corrosion Inhibition Potential of Triazolopyrimidinones via Density Functional Theory and Monte-Carlo Simulations

The protection of metal parts from corrosion is important to save the cost of production of goods and lives. Twelve triazolopyrimidinone derivatives were investigated for their ability to inhibit the corrosion of metal via density functional theory and Monte Carlo (MC) simulation approaches. The electronic properties and global and local reactivity descriptors were computed at the B3LYP/6-31G(d) level of theory, using Spartan 14 software. The Mulliken charge distribution and electrostatic potential (ESP) maps were used to locate the reactive sites. The adsorption of the compounds on the surface of the stable Fe(110) was investigated in an aqueous solution using the adsorption locator module on Material Studio software. The values of energies of their frontier molecular orbitals and other reactivity descriptors suggest that these molecules displayed good corrosion inhibition potentials. The Mulliken charge distribution and electrostatic potential maps showed that they can donate electrons to the metal and at the same time accept electrons via back-donation, also rationalized by the values of their electron back-donation calculated. The molecules interacted well with Fe(110) surface in an aqueous medium, as revealed by the MC results.

Insight into the role of debris in the formation of polytetrafluoroethylene film via molecular dynamic simulation of debris adhesion

AbstractIn this paper, the role of debris in the formation of polytetrafluoroethylene (PTFE) film was investigated using the molecular dynamic simulation of debris adhesion. The results indicate that the internal structure of PTFE debris could not be changed easily because of the strong cohesion of PTFE debris. Debris will be adhered on Fe surface by the strong adhesion between Fe surface and debris. With the formation of transfer film, the adhesion between thin debris and Fe surface decreases gradually and will be lower than that of debris and PTFE matrix. The difference of the adhesion between PTFE debris and friction pairs will induce the quite different adsorption behavior of thin debris and thick debris. With the formation of stable transfer film, thin debris tends to be adhered on PTFE matrix and thick debris tends to be adhered on Fe surface. This will reduce the interfacial adhesion of friction pairs. The interactive influence between the adsorption of debris and the evolution of transfer film is beneficial to the decrease of COF and the wear of PTFE.

Shear-driven reactions of organosulfur compounds on ferrous surfaces: A molecular dynamics study

Reactive molecular dynamics simulations were used to investigate reactions between di-tert-butyl disulfide and ferrous surfaces. Tribochemical reactions were characterized with and without a model base oil, n-dodecane, and on either Fe(100) or H-passivated Fe2O3 surfaces. Reaction yield increased with both temperature and pressure for all model systems. The presence of the base oil did not significantly affect the reaction yield or pathway, but the base oil impeded transmission of shear stress to the reactants. Replacing the ideal Fe(100) with H-passivated Fe2O3 surfaces enabled reaction pathways involving oxygen from the surface and decreased the reaction yield. The rate-limiting step of the reactions was analyzed in the context of the Bell model as a step towards better understanding tribochemical reactions.

Theoretical understanding of water adsorption on stepped iron surfaces

Nanoscale zero-valent iron (nZVI) has attracted significant interest due to its high capability in groundwater remediation. Understanding the interaction between water and nZVI is essential to optimizing its performance. While stable stepped surfaces may play a unique role in nZVI during their practical applications due to their higher reactivity, the interactions between water and stepped surfaces are still rarely investigated. Here we applied density functional theory (DFT) to study the adsorption properties of water on stable stepped Fe(210) and Fe(211) surfaces with the consideration of the van der Waals correction. Our results revealed that the adsorption strength of molecular water is enhanced on surface Fe atoms with lower coordination numbers (CN). Accordingly, the water has a stronger interaction on the stepped surface after the dissociation into H and OH. The stepped surface can facilitate water dissociation by greatly reducing dissociation energy barriers. Since water adsorption and dissociation are the first stage of iron oxidation by water, our DFT results demonstrate that the water adsorption on stepped iron surface may determine the lifetime of nZVI. Our findings, therefore, suggests the passivation of stepped surface can be a practical approach to improve the performance of nZVI.

Using first-principles modeling to investigate dehydrogenation of perhydro-dibenzyltoluene on Pt/M surface alloys (M = Fe, Ni, and Cu)

Understanding a dehydrogenation process for a liquid organic hydrogen carrier on catalysts is vital for providing insight into the development of efficient catalysts. This study examined the hydrogen release from perhydro-dibenzyltoluene (H18-DBT) over Pt-doped Pt/M surface alloys with two different Pt surface concentrations: Pt33%/M and Pt67%/M (M = Fe(100), Ni(111), and Cu(111)). The influence of the Pt surface concentrations of each catalyst on the hydrogen release from DBT was analyzed. The effects of the Pt surface concentration differed according to the host catalyst. The dehydrogenation reaction became favorable over Pt67%/Fe(100) surface with increasing Pt surface concentration. By contrast, dehydrogenation on Pt33%/Ni(111) and Pt33%/Cu(111) was more favorable at relatively lower Pt surface concentrations. In addition, the dehydrogenation reaction was tuned by an external electric field provided to the catalyst. The rate-determining step of a dehydrogenation process was the step that first releases hydrogen in the middle ring of H18-DBT over the Pt/M alloys investigated. Overall, the hydrogen adsorption energy was found to be a valid descriptor for assessing promising dehydrogenation catalysts.

Adsorption and dissociation of high-pressure hydrogen on Fe (100) and Fe2O3 (001) surfaces: Combining DFT calculation and statistical thermodynamics

Hydrogen (H2) pipeline systems are fundamentally the same as natural gas pipeline networks, but face a more serious safety challenge due to potential hydrogen embrittlement (HE) risk. At present, H2 transportation and storage are intentionally operated under high-pressure (HP) conditions (i.e., 5–20 MPa for transportation, 35–100 MPa for storage), which make H2 under supercritical state (i.e., supercritical H2, s-H2). In this study, the thermodynamics of H2 at a wide combination of temperatures (300–900 K) and pressures (0.1–100 MPa) has firstly been established based on a lattice-molecule model for predicting the adsorption and dissociation of gaseous and supercritical H2 on the Fe-based steel surface. The configurations of H2 adsorption and dissociation on Fe (100) and Fe2O3 (001) surfaces were investigated through the density functional theory (DFT) calculation, and the corresponding mechanism was elucidated using hybrid orbital theory. By applying the combination of DFT calculation and statistical thermodynamics, the dissociative adsorption of HP H2 on Fe (100) and Fe2O3 (001) surfaces upon varying temperature and pressure was predicted and the results well aligned with previously published experimental studies. Compared to the gaseous H2, s-H2 was likely to be more active on the iron (Fe) and its oxide (Fe2O3) surface in terms of dissociating into H atoms and could cause steels more susceptible to HE. The results also confirmed that the presence of the Fe2O3 scale could protect pipeline steels from environmental hydrogen permeation under the investigated HP conditions.

Friction-induced motion evolution of reduced graphene oxide-Al2O3 at contact interface to achieve superior lubrication performance

Reduced graphene oxide-Al2O3 (rGO-Al2O3) nanoparticle (NP) was synthesized and applied as additive in water-based lubricants. Pin-on-disk tribological experiments indicated that rGO-Al2O3 nanofluid exhibited reinforced lubricity due to the formation of a double-layer tribofilm, contributing to 34.8 % ± 2.3 % and 78.2 % ± 2.5 % reduction in friction coefficient and wear rate. Combined with nonequilibrium molecular dynamics (NEMD) simulation, rGO-Al2O3 NP exerted synergistic effects of interlayer sliding, rolling, polishing and self-mending to obtain higher surface quality. A new parameter (p) was proposed to determine the motion modes of Al2O3. Al2O3 NP exhibited both rolling and sliding motion. The synergy of rGO and Al2O3 NPs increased the rolling motion proportion of Al2O3 from 78 % to 91 % compared to using alone. Similarly, about 12.6 % of the friction force in friction system was shared by the interlayer sliding of rGO monolayers in the presence of Al2O3 than the system with only rGO (9.5 %). Besides, rGO-Al2O3 had higher diffusion coefficient, which was more conducive to the formation of tribofilm. rGO nanosheets with large transverse size adsorbed on the Fe surface to prevent the embedding of high hardness Al2O3 to maintain its rolling effect. Meanwhile, Al2O3 can reversely stimulate the interlaminar sliding of rGO to enhance the lubrication performance of rGO-Al2O3 nanofluid.