Corrosion resistant quaternary Al–Cr–Mo–N coating on type 316L stainless steel bipolar plates for proton exchange membrane fuel cells

Insufficient corrosion resistance, electrical conductivity and wettability of bipolar plates are some of the important issues affecting the performance of hydrogen fuel cells. To address these issues, an amorphous Al–Cr–Mo–N coating is deposited on type 316L stainless steel using direct current (DC) magnetron sputtering. The electrochemical corrosion behaviour is investigated under simulated fuel cell anode (H₂-purging) and cathode (air-purging) environment consisting of 0.5 M H₂SO₄ + 2 ppm NaF at 70 ± 2 °C. The corrosion current density is reduced to 0.02 μA cm⁻² comparable to the commercially used Ta/TaN coatings. The polarization resistance increases by two orders of magnitude and the interfacial contact resistance (ICR) reduces significantly due to the application of the coating. Further, the coating shows better water management due to high hydrophobicity than the bare stainless steel.     

Evolution of Ti2Ni precipitations during annealing and their effects on properties of Ti–Nb–Ni foil as PEMFC bipolar plates substrate

In this work, Ti–Nb–Ni foil was cold rolled and different annealing temperatures were conducted. For foils annealed at 600 °C, 650 °C and 700 °C, Ti₂Ni particles were evenly distributed in the matrix. Grain growth was obviously confined during annealing at these temperatures. While more (α+Ti₂Ni) eutectoids along grain boundaries (GBs) formed in the cases of higher temperatures. Plasticity of as-cold rolled foil was obviously improved by annealing and elongations gradually decreased with annealing temperature. Elongations of foil at 600 °C possessed the highest value, viz, 31.6% and 39.8% for RD and TD. For corrosion resistance, 850 °C annealed foil had the lowest i_corr compared with other counterparts. ICR of as-cold rolled and annealed specimens at 1.4 MPa were all lower than 10 mΩ cm⁻², which satisfied the DOE 2025 target.     

Investigation of corrosion properties with Ni–P/TiNO coating on aluminum alloy bipolar plates in proton exchange membrane fuel cell

Aluminum alloy bipolar plates have unique application potential in proton exchange membrane fuel cell (PEMFC) due to the characteristics of lightweight and low cost. However, extreme susceptibility to corrosion in PEMFC operation condition limits the application. To promote the corrosion resistance of aluminum alloy bipolar plates, a Ni–P/TiNO coating was prepared by electroless plating and closed field unbalanced magnetron sputter ion plating (CFUMSIP) technology on the 6061 Al substrate. The research results show that Ni–P interlayer improves the deposition effect of TiNO outer layer and increase the content of TiN and TiO_xN_y phases. Compared to Ni–P and TiNO single-layer coatings, the Ni–P/TiNO coating samples exhibited the lowest current density value of (1.10 ± 0.02) × 10^?6 A·cm^?2 in simulated PEMFC cathode environment. Additionally, potential cyclic polarization measurements were carried out aiming to evaluate the durability of the aluminum alloy bipolar plate during the PEMFC start-up/shut-up process. The results illustrate that the Ni–P/TiNO coating samples exhibit excellent stability and corrosion resistance.     

Comparison of Pt and Pd anode catalysts supported on nanocrystalline Ru–SnO2 for ethanol oxidation in fuel cell applications

The article presents promising catalysts, applicable for direct alcohol fuel cells (DAFC) for portable and mobile applications. The goal of this work is development of Pt and Pd catalysts deposited on interactive nanocrystalline Ru doped SnO₂ support with improved performance. The structure and the morphology of the prepared metal-oxide catalyst support and Pt and Pd based catalysts were examined using XRPD, SEM/EDX and TEM techniques. Electrocatalytic activities of the prepared Pt or Pd based catalysts were evaluated in both alkaline and acidic conditions. The ethanol oxidation reaction (EOR) was studied using conventional electrochemical techniques. The interactive nature of the novel Ru doped SnO₂ catalyst support was confirmed, resulting in the enhancement of the EOR kinetics, in comparison to commercially available catalysts. New and simplified synthetic route applied for preparation of interactive catalyst support was presented with the aim to enable easy scale-up of the catalyst production process. Obtained results on the novel catalysts promise great potential in improving the performance and durability of the DAFC.     

Ce promoting effect on the activity and coke formation of Ni catalysts supported on mesoporous nanocrystalline γ-Al2O3 in autothermal reforming of methane

In this study methane autothermal reforming (ATR) was investigated over Ni/Al₂O₃ and Ni/Al₂O₃–CeO₂ catalysts. The catalyst carriers were prepared through a facile one-step method, which produced mesoporous nanocrystalline carriers for Ni catalysts. The samples were characterized by XRD, TPR, BET, TPO and SEM characterization techniques and the catalytic activity and stability were also studied at different conditions (GHSV and feed ratio) in methane ATR. It was found that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ exhibited higher activity compared to the catalysts supported on the Al₂O₃ and promoted Al₂O₃ with 1 and 6 wt.% Ce. The results also showed that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ possessed the highest resistance against carbon deposition in ATR reaction.     

CuO–CeO2/SiO2 coating on ceramic monolith: Effect of the nature of the catalyst support on CO preferential oxidation in a H2-rich stream

Powder and structured catalysts based on CuO–CeO₂ nanoparticles dispersed on different silica are studied in CO preferential oxidation. Silica of natural origin (Celite) and fumed silica (aerosil), both commercial materials, and synthesized mesoporous SBA-15 with 20, 200 and 650 m²g^-1 respectively, are selected as supports. CuCe/Celite coated on cordierite monolith displays the highest activity, reaching CO conversion above 90% between 140 and 210 °C and more than 99% around 160 °C. The addition of 10% CO₂ and 10% H₂O partially deactivates the monolithic catalyst.The lower surface area of CuCe/Celite favors the contact between CuO and CeO₂ nanoparticles promoting a better interaction of Cu⁺²/Cu⁺ and Ce⁺³/Ce⁺⁴ redox couples. Raman spectroscopy reveals oxygen vacancies and XPS results show high metal lattice surface oxygen concentration and surface enrichment of Cu and Ce which promote the catalytic activity.     

Effect of acid passivation and H2 sputtering pretreatments on the adhesive strength of sol–gel derived Hydroxyapatite coating on titanium surface

In this study, in order to increase the adhesive strength of a Hydroxyapatite (HA) coating, deposited on the surface of commercially pure titanium, acid passivation and hydrogen sputtering pretreatments were used. The pure titanium surfaces were passivized by acid solution and treated by hydrogen sputtering, at a temperature of 300 °C for 1 h. Ca(NO₃)₂·4H₂O and NH₄H₂PO₄ were chosen as starting precursors for Ca and P sources. HA coatings on the titanium surface were deposited using the sol–gel method and sintered in air at the temperatures of 750^oC-900 °C for 1 h. XRD, SEM, EDS and AFM analysis techniques were used for structural and morphological characterization. Scratch test was performed for determining the adhesion of HA coatings. The experimental results indicated that compact and crack free HA coating, which has a Ca/P ratio of 1:6, was formed on pure Titanium (Ti) surface. The adhesive strength values of the HA coating, pretreated with H₂ sputtering and acid passivation were found to be 72.84 MPa and 55.83 MPa at temperature of 900 °C, respectively. It was observed that H₂ plasma sputtering pretreatment, improved the adhesive strength of the HA coatings compared to pretreatment with acid passivation.     

Influence of some metal ions on the structure and properties of doped β-PbO2

The lead dioxide active mass of positive lead-acid battery plates is a gel-crystal system with proton and electron conductivity of the hydrated gel zones. This paper discusses the influence of Sn²⁺, Sb³⁺, Co²⁺, Mg²⁺ and Al³⁺ ions, added to the formation electrolyte, upon the stoichiometry, structure and phase composition of the PbO₂ positive active material (PAM) of lead-acid batteries. PAM samples doped with the above metal ions are characterized by: X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and chemical analysis. The obtained results show that different metal ions are incorporated in different quantities in the PbO₂ particles. Under the influence of dopants, the stoichiometric coefficient of lead dioxide decreases, i.e. dopants increase the non-stoichiometry of PbO₂. The foreign ions in the formation electrolyte exert strong influence on the microstructure of PAM and change the proportion between crystal and hydrated gel zones in the particles.     

The effects of Al2O3–TiO2 coating in a diesel engine on performance and emission of corn oil methyl ester

Today, as a result of increase in oil prices, limited fossil fuel resources, environmental consideration and global warming, the methyl ester fuels have been focused on alternative fuels. Methyl ester fuels can be used more efficiently in low heat rejection engines (LHR), in which the temperature of combustion chamber is increased by creating a thermal barrier. In this study, the piston, cylinder head, exhaust and inlet valves of a diesel engine were coated with the ceramic material Al₂O₃–TiO₂ by the plasma spray method. Thus, a thermal barrier was provided for the parts of the combustion chamber with these coatings. The effects of corn oil methyl ester that produced by the transesterification method, and No. D2 fuels’ performance and exhaust emissions’ rate were studied by using equal in every respect coated and uncoated engines. Tests were performed on the uncoated engine, and then repeated on the coated engine and the results were compared. A decrease in engine power and specific fuel consumption, as well as significant improvements in exhaust gas emissions (except NOx), were observed for all test fuels used in the coated engine compared with that of the uncoated engine.     

Advances in the knowledge of the double perovskites derived from the conformation and substitution of the material Sr2MgMoO6-δ as anode with potential application in SOFC cell

Regardless of the manufacturing process such as solid-state reaction, sol-gel, etc., applied in obtaining anodes in solid oxide fuel cells (SOFCs), Sr₂MgMoO_6-δ (SMMO) double perovskites are recognized worldwide and widely used as anodic material with potential application in SOFC. This is due to several factors such as high electronic conductivity, high electrocatalytic activity, structural stability under reducing atmosphere, high transition temperature, giant magnetoresistance, reasonable tolerance to carbon formation, and its desired ability to reduce sulfur poisoning. In this review article, the advances of the SMMO double perovskite are analyzed.     

Effects of NH＿3 on N＿2O Formation and Destruction in Fluidized Bed Coal Combustion

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The effect of imidazolium ionic liquid on the morphology of Pt nanoparticles deposited on the surface of SrTiO3 and photoactivity of Pt–SrTiO3 composite in the H2 generation reaction

Photocatalytic water splitting has great potential in solar-hydrogen production as a low-cost and environmentally friendly method. Different unique techniques used to obtain photocatalysts with various modifications to improve H₂ generation have been introduced. In the present work, SrTiO₃ was successfully synthesized via the solvothermal method in the presence of ionic liquid (IL) - 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) followed by surface decoration with Pt particles using the photodeposition method. The effect of the noble metal content and presence of IL on the morphology, optical and surface properties of SrTiO₃, thereby the effectiveness of hydrogen generation, has been thoroughly examined and presented. Unexpectedly, the presence of [BMIM][Br] at the SrTiO₃ surface affected the interaction between the semiconductor surface and platinum particles formed throughout photodeposition. Platinum particles at the surface of SrTiO₃_IL were found to be in the form of 2D clusters with a size of 1 nm. In comparison, Pt deposited on SrTiO₃ photocatalyst without application of IL created larger, three-dimensional structures with a diameter exceeding 5 nm. This is the reason why the total amount of platinum deposited on the SrTiO₃_IL sample is smaller than that on SrTiO₃ and justifies a higher efficiency of hydrogen generation of Pt modified SrTiO₃ photocatalyst in comparison to SrTiO₃ prepared in the presence of IL. The mechanism of H₂ generation in the water-splitting reaction in the presence of SrTiO₃_Pt photocatalyst was discussed.     

Influence of polarization on the electrochemical activity of La2–xCaxNiO4+δ electrodes in contact with Ce0.8Sm0.2O1.9 electrolyte

The effect of electrode polarization on the electrochemical activity of La₂NiO_4+δ and La_1.9Ca_0.1NiO_4+δ electrodes in contact with the Ce_0.8Sm_0.2O_1.9 electrolyte is studied by impedance spectroscopy. It is found that anodic polarization facilitates electrode reaction for both electrodes leading to significant decrease in the polarization resistance. The effect of cathodic polarization differs between the electrodes: the polarization resistance of La₂NiO_4+δ electrode slightly increases, while the polarization resistance of La_1.9Ca_0.1NiO_4+δ electrode strongly decreases with the increase in the applied potential. It is established that in all cases the polarization mostly affects the low-frequency stage of the electrode reaction, connected with oxygen surface exchange and diffusion. The surface state of the samples after exposure under polarization is studied by X-ray photoelectron spectroscopy. Correlations between electrochemical activity of the electrodes and the changes in their surface composition under polarization are discussed.     

Electrophoretic deposition of dense anode barrier layers of doped ZrO2 and BaCeO3 on a supporting Ce0.8Sm0.2O2-δ solid electrolyte: Problems and search for solutions in SOFC technology

This work is aimed at the formation of dense anode coatings of yttria-stabilized zirconia (YSZ) and samarium-doped barium cerate BaCe_0.8Sm_0.2O_3-δ (BCS) on the Ce_0.8Sm_0.2O_2-δ electrolyte to increase the performance of a single fuel cell on its base. Materials are obtained by precipitation from a nitrate solution (YSZ-disp), by laser vaporization-condensation (YSZ-lec) and citrate-nitrate method (BCS). YSZ and BCS coatings on SDC substrates were obtained by electrophoretic deposition (EPD) followed by sintering at 1300–1500 °C. Two methods are applied to ensure surface conductivity of the SDC substrates for successful EPD: by synthesizing a conducting polymer - polypyrrole and by depositing a buffer layer of finely dispersed Pt. The main problem of the formation of the dense YSZ layers on the SDC substrates has been revealed, which is associated with their delamination during high-temperature sintering due to thermal expansion mismatch. It is shown that the use of a Pt buffer sublayer makes it possible to avoid delamination during sintering at a temperature of 1500 °C. The BCS barrier layers are shown to be completely compatible with SDC. The influence of the YSZ and BCS barrier layers on the ohmic and polarization resistance values and the open circuit voltage (OCV) values is discussed.     

Investigation on the combustion behaviors of coke and biomass char in quasi-granule with CuO–CeO2 catalysts in iron ore sintering

To thoroughly understand the combustion behaviors of coke and biomass char based on its physiochemical characteristics and distribution states in iron ore sintering, three types of single, composite and pellet quasi-granules of coke and biomass char were prepared carefully, catalytic potential of Cu_0.1Ce_0.9O₂ to increase quasi-granule combustion efficiency defined by the extent of CO destruction in flue gas was investigated. The results showed that biomass char is combusted at relative low temperature in the range of 350–800 °C because it has higher volatiles and porosity, exhibiting high reactivity compared to coke which combusts from 650 °C to 1030 °C. Pellet type has an intrinsic high combustion efficiency due to its fine fuel size and the neighboring compounds effect. Single coarse type granules have a high CO concentration in flue gas and have the highest combustion efficiency improvement by Cu_0.1Ce_0.9O₂ loading among all the types, which is mainly attributed to CO catalytic oxidation following Mars-van Krevelen path rather than the carbon oxidation. Through intentionally producing more coarse single type and composite type granules with 3 wt% Cu_0.1Ce_0.9O₂ in granulation, substitution ratio of biomass for coke can be increased, leading to improved combustion efficiency of ~98% without deterioration of sintering performance.     

Effect of mass transfer on the deactivation model and GPLE parameters of Co/γ-Al2O3 catalysts in the Fischer Tropsch synthesis

The activity of catalysts with various sizes was compared in a fixed-bed Fischer–Tropsch reactor under similar operating conditions by determining the deactivation model. Catalyst size had no impact on the type of deactivation model. The smaller catalyst showed a smaller deactivation constant of catalyst (k_d) and a lower deactivation rate in the initial stage. The decline in the activities of the catalyst with a mesh size of 40 was lower than the other catalysts, suggesting its higher long-term stability (a_ss). Larger catalyst sizes led to the fouling of carbon and heavy hydrocarbons, decreasing the specific surface of the catalyst, thus increasing the pore diffusion resistance and further decrementing the catalyst activities.     

Impacts of nickel loading on properties,catalytic behaviors of Ni/γ–Al2O3 catalysts and the reaction intermediates formed in methanation of CO2

In this study, methanation of CO₂ over Ni/Al₂O₃ with varied nickel loading (from 0 to 50 wt%) was evaluated, striving to explore the effects of nickel loading on catalytic behaviors and the reaction intermediates formed. The results showed that agglomeration of nickel particles were closely related to interaction between nickel and alumina. Increasing nickel loading resulted in the increased proportion of nickel having medium strong interaction with alumina, the reduced reduction degree of NiO, the increase of medium to strong basic sites, the enhanced activity for methanation and the competition between reverse water gas shift (RWGS) reaction and methanation. Lower nickel loading promoted RWGS reaction while methanation of CO₂ dominated at higher nickel loading. The catalyst with a nickel loading around 25% achieved the best activity for methanation. The in–situ DRIFTS studies of methanation of CO₂ showed that CO₂ could be absorbed on surface of metallic Ni, NiO or alumina. More metallic nickel species on alumina suppressed formation of carbonate species while promoted further conversion of HCOO¹ species and ¹CH₃ species, achieving a higher catalytic efficiency. Moreover, more metallic nickel species was crucial for gasifying the carbonaceous intermediates, prevented aggregation of the intermediates to coke and achieving a higher catalytic stability.     

Impact of pre-oxidation on the reactivity and conductivity in H2–H2O atmosphere of a ferritic stainless steel for high temperature water vapour electrolysis

The as-rolled K41X (AISI 441) ferritic stainless steel presents unusual behaviour when exposed in H₂–H₂O atmosphere at 800 °C, with growth of non-protective iron oxides at its surface. The impact of pre-oxidation in air is investigated in this paper. The pre-oxidation induces the formation of a thin chromia layer at the steel surface. The results obtained after subsequent oxidation for 100 h in H₂–H₂O atmosphere evidence a change in the surface reactivity behaviour of the as-rolled alloy: iron oxides formation is avoided and high temperature behaviour (reactivity and conductivity) is improved. Air pre-oxidation seems a promising solution for large scale use of K41X as-rolled steel in H₂–H₂O atmosphere at high temperature.     

Effect of N2O-mediated calcination on nickel species and the catalytic activity of nickel catalysts supported on γ-Al2O3 in the steam reforming of glycerol

The steam reforming of glycerol over supported nickel catalysts is a promising and cost-effective method for producing hydrogen. The activity of nickel catalysts supported on γ-Al₂O₃ is low, primarily due to the formation of inactive nickel species during high temperature calcination in air. In order to address this problem, a Ni/γ-Al₂O₃ catalyst was prepared by calcination at 700 °C in a nitrous oxide (N₂O) environment. The N₂O calcined catalyst showed an enhanced activity for the steam reforming of glycerol. A variety of characterization techniques (XRD, TPR, XPS and H₂ Chemisorption) confirmed that the high temperature N₂O calcination resulted in a significant decrease in the levels of nickel aluminate. The N₂O calcination also led to an enhancement in the amount of NiO as well as nickel ions present on the surface of the catalyst. Interestingly, compared to an air calcined catalyst, the N₂O calcined catalyst contained larger nickel particles after reduction but the N₂O calcined catalyst had a much larger nickel surface area and dispersion, which resulted in higher glycerol conversion and hydrogen yield.     

Pd–Ag thin film membrane for H2 separation. Part 2. Carbon and oxygen diffusion in the presence of CO/CO2 in the feed and effect on the H2 permeability

The effect of CO and CO₂ on the performance and stability of Pd–Ag thin film membranes prepared by electroless plating deposition (EPD) was investigated, observing the presence of dissociation to carbon and oxygen which slowly diffuse in the membrane influencing also H₂ permeability. The effect of the two carbon oxides was investigated both separately and combined in the 400–450 °C temperature range over long-term cumulative experiments (up to over 350 h) on a membrane that already worked for over 350 h in H₂ or H₂–N₂ mixtures. An increase of the H₂ permeation flux was observed feeding only CO₂ in the range 10–20%. This effect was interpreted as deriving from the facilitated H₂ flux caused from oxygen diffusion (deriving from CO₂ dissociation) in the membrane. CO induces instead a partial inhibition on the H₂ flux deriving from the negative effect of CO competitive chemisorption as well as C diffusion in the membrane, which overcome the positive effect associated to oxygen diffusion in the membrane. Carbon and oxygen diffuse through the membrane with a rate two order of magnitude lower than hydrogen, and recombinate at the permeate side forming CO, CO₂ and CH₄ which amount increases with time-on-stream. The effect is reversible and not associated with the creation of cracks or defects in the membrane, as supported by leak tests.