Ni-based Surface Research Articles

Deciphering Doping Effects in a V-Doped Ni Catalyst for Hydrogen Electrooxidation.

The improved performance of soluble metal-doped Ni catalysts is perplexed by the evolvable surface structures in the alkaline electrolytes for hydrogen oxidation reaction (HOR). Herein, V-doped Ni nanoparticles, as a proof of concept, were carefully evaluated to explore the intrinsic function of the enthetic V-species in assisting the HOR kinetic improvement. As expected, it exhibits a mass-normalized kinetic current density of 50.34 mA mgNi-1, more than 12 times that of the Ni counterpart without the introduction of V. Systematic investigations prove that the surface V-species, including the V-oxides and the doped V atoms at the outmost layer, would be dissolved into the electrolytes during the alkaline HOR process. The remaining V-dopants inside the nanoparticles would rationally weaken the hydroxyl binding energy (OHBE) of the Ni-based surfaces, thereby accelerating the formation of water molecules. We also uncover that Ni is located at the overstrong branch of the OHBE-described volcano plot through theoretical calculations and alkali-metal cation probe experiments, and weakening the OHBE by internal V-doping can leave the activity to the volcanic apex.

The promotion effect of Ru on catalytic activity and stability of Ni/Co-Al2O3 catalysts for simulated diesel steam reforming

In this work, Ru is incorporated into Ni/Co to synthesize novel Al2O3-supported Ni-Ru/Co-Ru bimetallic catalysts. Tests verify their enhanced catalytic capability and durability and also reveal how each catalyst is deactivated. SEM and EDS results indicate that nanoparticle agglomeration on Ni-based surface triggers deactivation, and TG and XPS results suggest carbon deposition is fatal to Co-based catalysts. Implementing Ru effectively enhances catalytic activity and durability. To gain insight into the promoting effect of Ru, quantum mechanical methods are utilized to investigate the shifts in activation energies (Ea) in CHx* dehydrogenation processes on (111) surfaces. For the Ni catalyst, DFT calculations indicate that adding Ru decreases Ea yet does not change the determining step. In contrast, adding Ru on the Co surface changes the major intermediates from CH* to CH2*, which inhibits further dehydrogenation, and hence mitigates carbon deposition to preserve the catalytic activity of the surface.

Methane Dehydrogenation and Coking Resistance on Ni(111) Surfaces of SOFC Anodes with Different Cu Doping Ratios under a Consistent DFT Framework

Carbon deposition on nickel-based anodes is a key problem for solid oxide fuel cells (SOFCs) using hydrocarbon fuels. One of the solutions is doping with other elements. In this work, DFT calculations were used to systematically study the processes of continuous CH4 dehydrogenation, carbon formation, and carbon elimination on Ni(111) surfaces doped with different amounts of Cu. The Cu doping concentrations on the Ni surface are set as 0, 1/9, 4/9, 5/9, 8/9, and 1 ml, namely Ni(111), NiCu1, NiCu4, NiCu5, NiCu8, and Cu9. The adsorption energies and adsorption sites of the important substances were obtained by calculation. In addition, the kinetics and thermodynamics of the main reactions and potential carbon removal pathways are discussed. Prior studies have shown that the introduction of Cu weakens the interaction between the Ni-based surface and the absorber, thereby enhancing the activity of various species on the surface of Ni-based catalysts. Second, the methane cracking path on the Ni-based surface is CH4 → CH3 → CH2 → CH, and the paths on the other five surfaces are the same. We found that the addition of Cu can weaken the adsorption of C, inhibit the activity of CH4 dehydrogenation, and promote the binding of C to the intermediate medium on the Ni-based surface, thus improving the ability of carbon deposition resistance. Finally, based on our DFT calculations, several potential carbon removal pathways are discussed in detail, and it is believed that the problem of carbon removal on SOFC anodes should focus on the oxidation of CH while preventing its direct cracking.

The effect of microstructure for Ni-based surface finishing thin film on corrosion behavior

Electroless and electroplated single-layer Ni and multilayer Ni/Pd/Au were used as surface finishing materials for automobile device substrates. When the samples were placed in a chamber with various gaseous SO2 concentrations, better corrosion resistance was observed for single-layer electroless Ni and multilayer electroplated Ni/Pd/Au compared with their well-crystalline electroplated and electroless counterparts, respectively. Electrochemical analysis and materials characterization are adopted to investigate the disparate corrosion behaviors. Galvanically displaced Pd(P) and immersion Au with a high grain boundary density provided a large number of diffusion paths for the increased growth of corrosion products on the electroless Ni/Pd/Au surface than on the electroplated surface. Reduced hydrogen gas formed blisters exerting pressure on the grain boundaries and causing defects that may enhance the diffusion of the atoms. These results proved that the microstructure and crystallinity of surface finishing films have a predominant effect on their corrosion behaviors.

Hot corrosion behavior of refractory high entropy alloys in molten chloride salt for concentrating solar power systems

Refractory high entropy alloys have recently attracted widespread attention due to their outstanding mechanical properties at elevated temperatures, making them appealing for concentrating solar power and nuclear energy applications. However, their molten salt corrosion behavior has not been reported, which is critical in evaluating their application merit. Here, the corrosion behavior of two recently developed refractory high entropy alloys, namely TaTiVWZr and HfTaTiVZr, was studied in molten 33NaCl–22KCl–45MgCl2 (wt. %) eutectic salt at 450 °C and 650 °C, using potentiodynamic polarization technique. The results were compared with benchmark alloys, namely 304 stainless steel (SS304) and Inconel 718 (IN718). TaTiVWZr refractory high entropy alloy exhibited an order of magnitude lower corrosion current density (Icorr = 0.7× 10-3 A cm-2) compared to SS304 (Icorr = 9.2 × 10-3 A cm-2) at the higher temperature of 650 °C. The corrosion rate of all the alloys increased with increase in temperature from 450 °C to 650 °C with the exception of TaTiVWZr. The TaTiVWZr alloy showed a corrosion rate of ~ 5 mm/year at 650 °C compared to ~ 110 mm/year for SS304. HfTaTiVZr and IN718 showed comparable corrosion rates in the range of ~ 40 mm/year at 650 °C. The high corrosion resistance of the two refractory high entropy alloys was attributed to a combination of three factors: (i) slower chlorination rate of refractory elements in the molten chloride salt environment driven by thermodynamics, (ii) formation of stable Ta–V and Ta–V–W based complex oxides on their surface, and (iii) Ti/TiCl2 and Zr/ZrCl2 redox couple formation which retarded the depletion of refractory elements. In contrast, the Cr-, Fe-, and Ni-based surface passivation oxides for SS304 and IN718 were less protective in the molten salt environment, particularly at the higher temperature of 650 °C.

On the dynamics of the catalytic surface of a bimetallic mixed-oxide formulation during the oxidative dehydrogenation of ethane

This work aims to evaluate the dynamic performance of a highly selective Ni-based surface during the oxidative dehydrogenation of ethane (ODH-C2). The catalyst comprises an in-house bimetallic mixed-oxide formulation with a Ni/Sn atomic ratio of 10. To corroborate its proper synthesis, it is characterized by TGA, AES, XRD, physisorption of N2 and TEM. The catalytic evaluation of the mixed oxide under dynamic conditions allows the proposition of a redox surface mechanism whose reliability is evaluated through a rigorous analysis, which is based on the development of a kinetic model and a robust experimentation program using a fully-automated micro-reaction unit and registering in-situ surface temperatures and continuous inline monitoring of oxygen and carbon dioxide. Experiments are carried out using a mixture of ethane or ethylene, oxygen and nitrogen as feedstock, at temperatures from 360 to 480 °C, total pressures from 100 to 500 kPa, and space-time values from 8.1 to 133.1 kgcat s molC2H6−1. Oxygen conversion ranges from 5% to 100% while the one for ethane varies from 5% to 60%. Besides, the selectivity and yield to ethylene vary from 30% to 90% and from 2% to 40%, respectively. The suitability of the redox mechanism is here assessed by evaluating statistical and phenomenological foundations, including Boudart’s criteria. Kinetic parameters, estimated by non-linear regression and using the reparametrized form of the Arrhenius and van’t Hoff equations, are phenomenologically well founded, such that changes of entropy and enthalpy of adsorption correctly describe the loss of mobility due to adsorption and the exothermic nature of the adsorption processes. Ethylene formation is the reaction demanding the lowest activation energy (Ea1= 61.94 kJ mol−1), while the total oxidation of ethane is the path requiring the largest activation energy (Ea2= 132.6 kJ mol−1). Concerning the adsorption enthalpy, ethylene exhibits the largest value (−ΔHC2H4° = 123.39 kJ mol−1), while carbon dioxide presents the lowest one (−ΔHCO2° = 42.00 kJ mol−1). Additional findings can be summarized as follows: activity and selectivity are recovered after the dynamic operation under oxidative conditions of the catalytic surface; carbon dioxide is identified as the only no desired byproduct; and hydroxyl surface species lead to the formation of water which affects the selectivity to ethylene, as well as the reaction rates. These findings are of interest for future studies directed at elucidating the performance of the Ni-based catalyst at larger scales, paving the way for the efficient design of the industrial reactor for the ODH-C2.

Effects of alloying on mode-selectivity in H2O dissociation on Cu/Ni bimetallic surfaces.

The influence of alloying on mode-selectivity in H2O dissociation on Cu/Ni bimetallic surfaces has been studied using a fully quantum approach based on reaction path Hamiltonian. Both the metal alloy catalyst surface and the normal modes of H2O impact the chemical reactivity of H2O dissociation. A combination of these two different factors will enhance their influence reasonably. Among all the bimetallic surfaces, one monolayer (Ni4_Cu(111)) and 12 monolayer of Ni on Cu surface (Ni2_Cu(111)) show lowest barrier to the dissociation. Excitation of bending mode and symmetric stretching mode enhances the reactivity remarkably due to a significant decrease in their frequencies near the transition state in the vibrational adiabatic approximation. In the presence of non-adiabatic coupling between the modes, asymmetric stretching also shows similar enhancement in reactivity to that of symmetric stretching for all the systems. Inclusion of lattice motion using a sudden model enhances the dissociation probability at surface temperature 300 K and at lower incident energy, compared to that of the static surface approximation. The mode selective behaviour of H2O molecules is almost similar on all the Cu- and Ni-based surfaces. The excitation of symmetric stretching vibration by one quantum is shown to have largest efficacy for promoting reactions for all the systems. Overall, the dissociation probabilities for all the systems are enhanced by vibrational excitation of normal modes and become more significant with the non-adiabatic coupling effect.

Effects of Cr-doping on the adsorption and dissociation of S, SO, and SO2 on Ni(111) surfaces.

Nickel-based alloys are widely applied materials in high-temperature applications because they exhibit superior corrosion resistance and mechanical properties. The effects of sulfur, which is invariably present in industrial atmospheres, on the early stages of oxidation of Ni-based surfaces are not well understood. Here we use density functional theory to investigate the interactions of sulfur, SO, and SO2 with the Ni(111) and Cr-doped Ni(111) surface and elucidate their electronic interactions and potential energy surfaces. The results show that Cr doping of the Ni(111) surface increases the adsorption energies of sulfur, oxygen on the sulfur pre-adsorbed condition, SO and SO2. Further, this increase positively correlates with Cr concentration on top of the Ni(111) surface, although sulfur does not have any preferential interaction with Cr. This explains why Cr doping has little effect on the activation energy of sulfur for the most preferable diffusion path. Nevertheless, the increase in adsorption energies indicates a strong interaction with Cr-doped surfaces, which is due to the Cr-enhanced charge transfer to sulfur adsorbates. The existence of pre-adsorbed sulfur is shown to have a destabilizing effect on the oxygen interactions with the surfaces. Our results show that Cr doping helps to stabilize the protective oxide scale on Ni(111) surfaces and enhances its corrosion resistance.

Selectivity of Ni-based surface alloys toward hydrazine adsorption: A DFT study with van der Waals interactions

We use dispersion corrected DFT calculations (DFT+D3) to investigate the selectivity of Ni-based surface alloys toward hydrazine adsorption. A series of Ni–M (M=Fe, Pt, Ir, Pd and Rh) alloy films were investigated, namely Ni15/M1/Ni(111), Ni14/M2/Ni(111), Ni12/M4/Ni(111) and Ni8/M8/Ni(111). Our results show that the doped atoms of Ir, Rh and Fe provide stronger adsorption sites than the Ni atom on the Ni(111) surface, while the doped atoms of Pt and Pd provide weaker adsorption sites. By analyzing the most favorable adsorption of hydrazine on Ni–M alloy surfaces we found that Ni8Fe8/Ni(111), Ni8Rh8/Ni(111), Ni15Ir1/Ni(111) and Ni14Ir2/Ni(111) present enhanced adsorption properties if compared to the pure Ni(111) surface, and seem to be better candidates for hydrazine catalysis, which are in agreement with that found by experiments. The correlation between d-band center position and adsorption energies of top modes in the Ni or doped atom has been calculated at DFT+D3 level to provide further insight into the Ni-based surface alloy properties for hydrazine adsorption.

A wirelessly readable and resettable shock recorder through the integration of LC circuits and MEMS devices

This paper presents a passive shock recorder to record shock events for tens of Gs with wireless reading and wireless resetting capabilities through the integration of LC circuits and two MEMS devices. With a micro mechanical-latch shock switch electrically connected to the sensing LC circuit, the shock event that leads to different latching states can be recorded and wirelessly read through the LC resonant frequency. With a micro electro-thermal actuator electrically connected to a wirelessly powered actuating LC circuit, the energy can be wirelessly sent to the micro actuator to provide the necessary unlatched force. By integrating the mechanical-latch shock switch and actuator with LC circuits, the latching state can be reset through the wireless actuation. Therefore, the shock recorder can be used repeatedly. Here, the mechanical-latch shock switch is designed to have a two-level shock recording capability. The fabrication of the shock switch and actuator are achieved by a Ni-based surface micromachining process. When the acceleration reaches 28.06 G, the latching state changes from the original state to the first latching state. The resonant frequency of sensing for the LC circuit is found to switch from 10.14 MHz to 9.16 MHz, correspondingly. By further applying acceleration up to 37.10 G, the latching state changes from the first latching state to the second state, and the resonant frequency shifts to 7.83 MHz. Then, with a current of 2.07 AAC wirelessly induced in the actuating LC circuit, the micro electro-thermal actuator is shown to provide sufficient displacement to reset the shock switch from a latched state back to the original unlatched state, and the resonant frequency is switched back to 10.14 MHz. The fabricated shock recorder is repeatedly tested five times. The wireless reading, resetting and shock recording capabilities are successfully verified.

Origin of synergistic effect over Ni-based bimetallic surfaces: A density functional theory study

Density functional theory calculations have been conducted to explore the physical origin of the synergistic effect over Ni-based surface alloys using methane dissociation as a probe reaction. Some late transition metal atoms (M = Cu, Ru, Rh, Pd, Ag, Pt, and Au) are substituted for surface Ni atoms to examine the variation in electronic structure and adsorption property of Ni(111). Two types of threefold hollow sites, namely, the Ni(2)M and Ni(3) sites, are taken into account. The calculated results indicate that the variation in the CH(x) adsorption energy at the Ni(2)M and Ni(3) sites is dominated by the ensemble and ligand effect, respectively, and the other factors such as surface and adsorbate distortion and electrostatic interaction affect the catalytic properties of the bimetallic surfaces to a smaller extent. Both the Brønsted-Evans-Polanyi relationship and the scaling correlation hold true on the Ni-based bimetallic surfaces. With the combination of these two linear energy relations, the corrected binding energy of atomic C is found to be a good descriptor for representing the catalytic activity of the alloyed surfaces. Considering the compromise between the catalytic activity and catalyst stability, we suggest that the Rh/Ni catalyst is a good candidate for methane dissociation.

Investigation of the doped transition metal promotion effect on CO2 chemisorption on Ni (1 1 1)

The chemisorption of CO2 on the pure Ni (111) and doped Ni (111) by transition metal (Co, Rh, Cr, Ce, La) were investigated by using the generalized gradient approximation (GGA) and the Perdew–Burke–Emzerhof (PBE) functional. The optimized structure of doped metal surface showed that Rh, Cr, Ce, La atoms upward shift from the surface of Ni (111) plane, while the atom radius of Co is the minimum offset which lead to the height is −0.03Å. The ability of CO2 chemisorption follows the order of La/Ni (111)>Ce/Ni (111)>Cr/Ni (111)>Co/Ni (111)>pure Ni (111). It is exothermic when CO2 chemisorbed on Cr/Ni (111) Ce/Ni (111) and La/Ni (111), while it is endothermic on the Co/Ni (111) and pure Ni (111). CO2 molecular chemisorbed on all the metal surfaces are negatively charged, result from the electron transfer between the metal surfaces and the CO2 molecular. The transition metals La, Ce and Cr can promote the transformation of electron and make the CO bonds longer than the pure Ni (111). We also analyzed the dissociation of CO2 on the Ni-based surface and found that the La/Ni (111) surface is the preference surface for the dissociation of CO2, which improved the ability to hinder carbon deposition.

The Microstructure of Ni-Based Surface Infiltrated Layer on Cast Steel Substrate

The Ni-based alloying powder was successfully used as the raw materials for fabricating surface infiltrated layers on cast steel ZG45 substrate through a vacuum infiltration casting technique (VICT). The microstructures of surface Ni-based infiltrated layer, the micro-hardness distribution are investigated. The infiltrated layer includes three areas that are surface part-melting area, melting completely fusion area and diffusion solid solution area. The main composition of surface infiltrated layer was intermetallic compound Cr2B，NiB and solid solution. The main phase of transition layer was solid solution. The micro-hardness of Ni-based infiltrated layer presented gradient change from surface infiltrated layer to substrate. The average micro-hardness was about 550HV.

Microstructure and wear behaviour of Ni-based surface coating on copper substrate

The Ni-based surface coatings were prepared by a vacuum infiltration casting technique on copper substrate. The surface coatings were fabricated through copper melt penetrating into thin preforms whose thickness could change. By optimizing the processing parameters, compact surface coatings were achievable as confirmed through SEM observation. The surface coating was mainly composed of solid solution of Ni, solid solution of Cu and CrB. The macro-hardness of the coating was about HRC 58, and the micro-hardness of the coating shows a gradient distribution. The average micro-hardness of the coating was about HV450. Wear behaviour was investigated by using block-on-ring dry sliding linear contact at several loads (50 N–300 N) and two different sliding speeds (0.424 m/s and 0.848 m/s). Wear rate and friction coefficient were estimated using a method founded upon the PV factor theory. The surface oxidation predominated as the principle wear mechanism at low load. Meanwhile, adhesion and oxidation mechanism were observed when the coatings were tested at higher load more than 200 N. Friction coefficient decreased with increasing load and sliding speed.