Porous Stainless Steel Substrate Research Articles

Improved flux and anti-fouling performance of a photocatalytic ZnO membrane on porous stainless steel substrate for microalgae harvesting

Photocatalytic self-cleansing ZnO membranes were developed and used for pre-concentrating microalgae solution prior to harvesting. The inorganic membranes were fabricated via two different methods: (i) direct deposition of ZnO onto a porous stainless steel substrate and (ii) post-growth oxidation of a deposited metallic Zn layer. Systematic surface characterisation revealed a thin layer of homogeneous, crystalline ZnO on the porous membrane. Direct ZnO deposition resulted in a thicker layer with higher UV light absorption capability compared with the post-growth oxidization method. The ZnO coating made the membrane surface highly hydrophilic, resulting in two-fold increase in water permeance compared to the base stainless steel substrate. The high hydrophilicity of the ZnO-coated membrane also led to an increase in the permeate flux of the microalgae solution by up to 100%, making it suitable for microalgae pre-concentration. Upon UV light irradiation, the ZnO membrane demonstrated self-cleansing capability due to the photocatalytic activity of the ZnO coating layer. After 30 min of UV irradiation, the ZnO membrane could achieve 60% permeance recovery after complete fouling. No recovery was observed with the base stainless steel membrane, which was used as the control.

Fabrication of flat stainless steel substrates with improved oxidation behavior for metal-supported solid oxide cells using aqueous tape casting

An aqueous tape casting procedure was developed and optimized to fabricate thick, flat tapes for use as porous stainless-steel substrates for metal-supported solid oxide cells (MS-SOCs). Curling tape is one of the main challenges when using aqueous based slurry formation. This work demonstrated that the sedimentation problem can be solved by increasing solid loading rather than adding excessive binder to raise viscosity. The effect of various casting surfaces on tape curling was also investigated. Materials that allow easy tape release resulted in flatter tapes once the water was evaporated. In addition, substrate oxidation resistance at high temperature was evaluated with respect to starting powder size, sintering extent, and pore former types. High sintering extent that removes or encloses the porosity between steel particles while retaining porosity left by pore formers can effectively prevent breakaway oxidation due to local chromium depletion. Carbon residue in the steel substrates from the slurry organic content can be decreased when formulating the slurry to prevent Cr-rich phase formation in the steel, which severely compromises the substrate oxidation resistance and ductility. By dwelling the substrate in high purity hydrogen, the sensitization can be reversed, but more detailed investigation of the reaction dynamics is needed. By combining the strategies described, this work produced crack-free, flat, 400–500 μm thick stainless steel substrates with 28.7 vol% porosity and improved oxidation resistance compared to previous substrates fabricated by dry pressing of fine powders.

Effect of ceria particle size as intermediate layer for preparation of composite Pd-membranes by electroless pore-plating onto porous stainless-steel supports

The use of H2-selective membranes for ultra-pure H2 production has been assigned as an attractive technology, particularly those based on Pd-films deposited onto porous stainless-steel (PSS) supports. The ability to incorporate thin Pd-films with enough adherence on any internal or external surfaces becomes essential to minimize their complexity and cost while improving their performance. The modification of original PSS substrates with diverse intermediate layers, especially those made of ceria, is presented as a promising alternative. In this context, the current study addresses for the first time the use of different CeO2 particle sizes to generate an intermediate layer and facilitate the subsequent generation of a thin Pd-film by electroless pore-plating (ELP-PP). The membrane containing the smallest CeO2 particle size (membrane S) demonstrated the lowest performance, which was assigned to the high compaction of the material and generation of cracks on its surface during calcination that consequently led to the deposition of a greater amount of Pd. On the other hand, the morphology of membranes M (medium CeO2 particle size) and L (large CeO2 particle size) were very similar, although the first one demonstrated a slightly smaller interparticle porosity, which led to the deposition of a more homogeneous and thinner Pd-film. Therefore, an outstanding performance in terms of H2 permeance (5.98 × 10−4 mol·m−2·s−1·Pa−0.5 at 400 °C) was obtained for this membrane. Permeation tests with binary mixtures (H2-N2, H2-CO2, or H2-CO) revealed a concentration-polarization effect in all cases, as well as a certain inhibition effect in the presence of CO. Finally, it should be highlighted the high stability of the membranes during the entire set of experiments, independently of the considered particle size. Thus, enough mechanical and thermal resistances can be assured for future applications.

Tubular MXene/SS membranes for highly efficient H2/CO2 separation

AbstractAccurately constructing membranes based on two‐dimensional (2D) materials on commercial porous substrates remains a significant challenge for H2 purification. In this work, a series of tubular 2D MXene membranes are prepared on commercial porous stainless steel substrates via fast electrophoretic deposition. Compared with other methods, such as filtration or drop coating, and so on. such preparation route shows the advantages of simple operation, high efficiency for membrane assembly (within 5 min) with attractive reproducibility, and ease for scale‐up. The tubular MXene membranes present excellent gas separation performance with hydrogen permeance of 1290 GPU and H2/CO2 selectivity of 55. Furthermore, the membrane displays extremely stable performance during the long‐term test for more than 1250 h, and about 93% of the membranes from one batch have exceeded the DOE target for CO2 capture. Most importantly, this work provides valuable referential significance for other 2D materials‐based membranes for future application development.

Stimuli-responsive heterojunctions based photo-electrocatalytic membrane reactors for reactive filtration of persistent organic pollutants

The design of semiconducting metal oxide heterojunctions is promising to overcome conventional limitations associated to photocatalysis or electrocatalysis, such as fast recombination of electron-hole pairs and poor long-term stability leading to low catalytic performance. A route to tackle this issue is to design catalysts at the atomic levels by arranging order and controlling nanoscale interfaces to yield catalytic materials with greater response rates and stability to dissolution or corrosion. The present study focuses on the formation of such nanoscale heterojunctions between TiO2 and ZnO via atomic layer deposition across conductive and porous stainless-steel substrates to develop enhanced photo-electro-responsive catalytic membrane reactors. The heterojunction nano-sheet based structures produced higher density of electron and hole pairs and offered efficient separation of charges, longer lifetime of photo-generated electrons compared to single metal oxides, resulting in enhanced photocurrent efficiency. The tailoring of both the nanoscale dimensions of the metal oxide layers and the stacking of these inorganic nano-sheets led to the development of multi-heterojunctions, of a few tens of nanometres, deposited across conductive porous substrates. The high electron mobility across the heterojunction nano-sheets increased the oxygen evolution potential from 1.4 to 1.7 eV, leading to enhanced electrochemical reactions, as well as offered photocurrent densities 2–3 times higher than pristine single metal oxide membranes. The formation of type II heterojunction structures between TiO2 and ZnO leads to band alignment at the interface, yielding an efficient charge separation mechanism and high catalytic performance. A prototype of novel cross-flow filtration module was designed in this study to support the coupling of photo-electrocatalysis on the membrane surface and simultaneous pressure driven membrane processes. The designed 3D printed modules demonstrated highly enhanced degradation of several persistent organic pollutants, leading to reactivity up to 75 × 10−3 min−1 up to 500 % greater compared to single metal oxides generated with the same conditions. The intimate and synergistic interactions across the stacked metal oxide nano-sheets enabled high catalytic efficiency and stability, opening new avenues stimuli-responsive membranes scale up and implementation in wastewater remediation and compact reactors design, where sieving and reactivity are of prime importance.

NaA zeolite membranes on modified porous stainless steel supports: a comparative study of different SiO2 sources

The deposition of a NaA zeolite layer on porous stainless steel substrates was optimized in order to obtain composite membranes for hydrogen separation. The effect of the silica source on NaA zeolite crystallinity and morphology was studied using two synthesis routes: concentrated gel and clear solution. The optimized synthesis conditions were applied for the synthesis of NaA zeolite layers on top of porous stainless steel disks or on the outer surface of tubular supports. SEM and XRD measurements confirmed that the use of rice husk allowed obtaining defect free and pure phase NaA zeolite membranes. Selectivity values similar to those published for NaA zeolite membranes based on ceramic substrates were obtained using zeolite layers deposited on porous stainless steel tubes. From the curve fitting of the experimental data, the contribution of zeolitic and non-zeolitic flux was estimated. For the membranes synthesized from a concentrated gel, H2 showed a predominated contribution of the zeolitic flux.

Skinned carbonaceous composite membrane with pore channels bearing an anchored surfactant layer for nanofiltration

This study finds that a layer of a specific surfactant pair appended to the nanopores in a skinned carbonaceous composite membrane (CnCM) could impact the nanofiltration (NF) capability of the membrane. A CnCM is derived from a methacrylate copolymer coating that composites with a low dose of polymer microspheres. The microspheres have the core-shell structure with polyfurfurylalcohol core and a thin polydopamine shell (PDA@PFA). The polymer coating on a porous stainless-steel substrate is converted to the skinned CnCM through a controlled pyrolysis treatment in a reducing atmosphere. The interface between the microspheres and the carbonaceous matrix prevails the permeation. The functionalities present on the microspheres after pyrolysis thus equip pores with polar group sites, which facilitate growth of a stable binary surfactant layer (CTAC, cationic and Triton-X, nonionic) through adsorption upon the infiltration. An aqueous methylene blue (MB) solution (50 mg/L) was used to assess the membrane for NF. Retention above 98% with an average permeance of 3.5 L/m2⋅h bar could be sustained over 30 h owing to the surfactant layer comprising of cationic and non-ionic types. Softening the internal pore surface of CnCM by the adsorption of a surfactant layer offers a tactic for utilizing porous carbon medium different from the traditional CMS membrane to conduct nanofiltration of liquid solutions.

Preparation of Pd/SAPO-34/PSS composite membranes for hydrogen separation: Effect of crystallization time on the zeolite growth on PSS support

In this study, palladium composite membranes were fabricated on porous stainless steel (PSS) supports using silicoaluminophosphate (SAPO) zeolite (SAPO-34) as a diffusion barrier and substrate modifier. The vacuum-assisted seeding and secondary growth method was used to coat the SAPO-34 zeolite layer on the PSS substrates. The morphologies and microstructures of the membranes were analyzed by AFM, XRD, BET, ICP–AES, FESEM and EDX techniques. The effect of crystallization time (24, 48 and 72h) on the morphology and quality of SAPO-34 modified supports was studied. A continuous palladium layer with a thickness of about 9μm was deposited on the SAPO-34 modified PSS support (72h crystallization time) by electroless plating (ELP) route. The hydrogen permeation tests were carried out in the feed pressures range of 2–4bar and various temperatures (623, 673 and 723K). The values of the hydrogen permeance and ideal selectivity of H2/N2 for the PSM3 membrane were achieved 7.1×10–7molm–2s–1Pa–1 and 866, respectively a feed pressure of 2bar and 723K. In addition, the PSM3 membrane showed perfect stability during 260h hydrogen permeation experiment at a feed pressure of 2bar and 623K.

Development of Metal-Supported Planar SOFCs Fabricated by All Wet Process on Metallurgical Porous Substrates

In this study, metal-supported solid oxide fuel cells (MSCs) are successfully fabricated by all-wet process on the porous stainless-steel substrate. This stainless-steel substrate is made by a powder metallurgy technique which can control its porosity and shrinkage behavior. MSCs were fabricated by co-firing with electrolyte and anode layers with the substrate. This process is similar to that of conventional anode supported cells. Anode and electrolyte layers were coated on the porous metal substrate by screen printing. Then, these layers were sintered by co-firing at 1250 ºC in a reducing atmosphere. The cathode is sintered at 750 ºC in air before electrochemical measurement, keeping the reducing atmosphere on the anode and substrate side. The MSC prepared by the all-wet process on porous stainless-steel substrate showed 1.0 W cm-2 of maximum power output at 750 ºC. This process is expected to contribute the low-cost fabrication of large size MSCs.

Fabrication, characterization, and application of palladium composite membrane on porous stainless steel substrate with NaY zeolite as an intermediate layer for hydrogen purification

Palladium composite membrane with excellent stability was successfully prepared using the electroless plating (ELP) route on a porous stainless steel (PSS) support for hydrogen separation. In order to modify the average pore size of PSS support and to prevent inter-metallic diffusion, the NaY zeolite layer was coated on the PSS support with the seeding and secondary growth method. A high-temperature membrane module was designed by Solid work software and fabricated from 316 L stainless steel with a knife-edge seal. The microstructures and morphologies of the samples were analyzed using XRD, BET, AFM, FESEM and EDX techniques. Permeation experiments were carried out with binary mixtures of H2/N2 with various ratios (90/10, 75/25 and 50/50) and pure H2 and N2 at different temperatures (350, 400 and 450 °C) and feed pressures (200–400 kPa). Hydrogen permeation tests showed that the membrane with a thickness of about 7 μm had a hydrogen permeance of 6.2 × 10−4 mol m−2 s−1 Pa−0.5 with an ideal H2/N2 selectivity of 736, at 450 °C. In addition, the results of stability tests revealed that the membrane could remain stable during a long-term operation by varying temperature and feed gases.

Solvent‐free route for metal–organic framework membranes growth aiming for efficient gas separation

Industrial applications of membranes based on metal–organic frameworks (MOFs) are challenged by their complex fabrication procedures and poor processability, despite their huge potential for efficient gas separation. Especially, the consumption of a large amount of toxic, expensive solvent, and harsh operation by conventional solvothermal growth also make it less attractive for industrial production. Herein, a solvent‐free method is proposed to fabricate continuous defect‐free MOF membranes on commercial porous stainless steel substrates, where the metal precursors are electrodeposited on the support followed by a heat treatment with the ligand powder via solid‐state reaction without using any solvent. This strategy is proven to be applicable for various MOF membranes and it is expected to be a facile, cheap, and environmental friendly way for future large‐scale production. © 2018 American Institute of Chemical Engineers AIChE J, 65: 712–722, 2019

Palladium/ruthenium composite membrane for hydrogen separation from the off-gas of solar cell production via chemical vapor deposition

The potential application of palladium-ruthenium composite membranes to the separation of hydrogen from chlorosilane gases in silicon-based industries was investigated. Palladium and palladium-ruthenium composite membranes were deposited on pretreated porous stainless steel substrates by electroless plating. Hydrogen permeation tests and temperature programmed desorption (TPD) analysis revealed that the addition of a Ru overlayer on Pd changed the hydrogen adsorption characteristics, resulting in improved stability of the membrane at low temperatures. The Ru/Pd/Al2O3/PSS composite membrane had a stable hydrogen permeation flux of 1.8m3m−2h−1 over a period of 1200h at 180°C without suffering hydrogen embrittlement. After exposure to impurities such as HCl and SiHCl3, the hydrogen permeation flux of the Ru/Pd/Al2O3/PSS composite membrane was stable over a period of 9h with feed pressure of 2.0bar at 225°C. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and EDX mapping of the Ru/Pd/Al2O3/PSS membrane after the exposure test showed no surface deposition of Si and Cl.

Porous stainless steel support for hydrogen separation Pd membrane; fabrication by metal injection molding and simple surface modification

We prepared a disc-shaped porous stainless steel (PSS) support for hydrogen separation Pd membrane via metal injection molding (MIM) method to facilitate the mass production of porous substrates. MIMed PSS supports obtained in a batch showed relatively higher apparent porosity (from 32.75% to 39.28%) than that reported for commercially available PSS substrate. In addition, the surface morphologies of the MIMed PSS, surface roughness of 1.119 μm and pore depth of 8.6 μm, indicate its suitability as a membrane support than the commercially available one. Pd membrane prepared over MIMed PSS, which was modified by a simple axial pressing method to control the surface morphologies, had a thinner Pd layer, 2.94 μm, and showed an extremely higher ideal H2/N2 selectivity with a hydrogen permeation flux of 21.3 ml/min/cm2 at del-P = 1 bar and 400 °C, compared with Pd membrane over MIMed PSS modified with conventional surface modification.

Effect of the porous stainless steel substrate shape on the ZrO2 deposition by vacuum assisted dip-coating

The effect of the support shape on the deposition of ZrO2 by the vacuum-assisted dip-coating method was studied. Disc-shaped and tubular porous stainless steel substrates were used to obtain ZrO2 coated supports for the synthesis of PdAu alloy composite membranes. The microstructure of the ZrO2 modified supports was evaluated by scanning electron microscopy and confocal laser microscopy. Besides, a qualitative assessment of the porosity and roughness of the porous substrates was performed by confocal laser microscopy. Dense and continuous palladium-alloy films were deposited on top of the modified tubes after thirteen ZrO2 deposition-calcination cycles. Cross-section EDS mapping and XRD diffraction analysis showed that a complete PdAu alloy formation was obtained even after annealing at 723 K in hydrogen stream during 5 days.

Electroless Pd deposition on a planar porous stainless steel substrate using newly developed plating rig and agitating water bath

A new plating bath was developed to prevent palladium plating in the pores of the porous stainless steel support when using plate-type porous substrate. The plating bath, composed of a holder, a rubber O-ring and a bottom, provides very simple assembly and is very effective in preventing palladium plating in the pores of porous stainless steel. The agitation of the plating solution increases plating rate significantly because the agitation improves the external mass transfer of Pd ion and reducing agent to the membrane surface facilitating ~99.7% plating yield of palladium ion. This new plating method carried out at a temperature range of 293 to 298 K provides a very simple and economic membrane manufacturing process. Using a newly developed plating rig, an 88.9-mm diameter membrane was fabricated, and gas permeation tests showed that the hydrogen permeation flux reached ~0.9 mol s−1 m−2 at 873 K and a pressure difference of 300 kPa and selectivity (H2/N2) was ~1,850 at 873 K with a pressure difference of 100 kPa.

Hydrogen permeation through porous stainless steel for palladium-based composite porous membranes

Surface topography and hydrogen permeation properties of Porous Stainless Steel (PSS) substrates for thin films deposition of Pd-based hydrogen separation membrane were investigated. Hydrogen permeance through the as received PSS substrates demonstrated a wide range, despite a similar average surface pore size of ~15µm determined by SEM and confocal laser microscopy analyses. The surface pores of the PSS substrates were modified by impregnation of varying amounts of tungsten (W) powder. Maximum hydrogen flux reduction of 28% suggested that W has a limited effect on the hydrogen permeation through the PSS substrate. Therefore, it appears that hydrogen transport through PSS substrates is mainly controlled by the substrate geometrical factor (ετ), that is the ratio of the porosity to tortuosity. In addition, tungsten was shown to inhibit the iron inter-diffusion between the PSS substrate and the deposited Pd60Cu40 film at temperature as high as 800°C. Thus, tungsten layer also serves as an effective inter-diffusion barrier. The variation in the permeance between the nominally similar PSS substrates indicates the importance to independently assess the hydrogen transport characteristics of each of the components in a composite membrane.

NaA zeolite membranes synthesized on top of APTES-modified porous stainless steel substrates

NaA zeolite membranes were synthesized on top of both disk and tubular porous stainless steel substrates by the secondary growth method. The support seed stage was optimized, considering the seed synthesis conditions and the deposition method. The formation of the NaA zeolite on both the membrane and the residual powder collected at the bottom of the vessel after synthesis was corroborated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed the formation of a film with well-defined crystals with a cubic morphology characteristic of the NaA zeolite. The support modification with 3-aminopropyltriethoxysilane improved the morphology and stability of the NaA zeolite membranes synthesized on top of porous stainless steel substrates. When vacuum was applied only in the last hydrothermal synthesis stage, a smooth zeolite layer was obtained on top of porous stainless steel supports. The single gas (H2, N2, CO2 and CH4) and mixture (H2/N2 and H2/CH4) perm-selective properties of the tubular membranes were evaluated as a function of temperature and pressure. Separation factors higher than the Knudsen coefficient were obtained in all membranes. The single gas H2 and CO2 permeation flux of the membranes increased with temperature indicating a preponderance of the activated diffusion over the Knudsen diffusion. The higher H2/CO2 ideal separation factors were 7.6 and 5.6 for the more selective tubular membranes, at 453K and 100kPa.

Micro solid oxide fuel cell fabricated on porous stainless steel: a new strategy for enhanced thermal cycling ability.

Miniaturized solid oxide fuel cells (micro-SOFCs) are being extensively studied as a promising alternative to Li batteries for next generation portable power. A new micro-SOFC is designed and fabricated which shows enhanced thermal robustness by employing oxide-based thin-film electrode and porous stainless steel (STS) substrate. To deposit gas-tight thin-film electrolyte on STS, nano-porous composite oxide is proposed and applied as a new contact layer on STS. The micro-SOFC fabricated on composite oxide- STS dual layer substrate shows the peak power density of 560 mW cm−2 at 550 °C and maintains this power density during rapid thermal cycles. This cell may be suitable for portable electronic device that requires high power-density and fast thermal cycling.

Hydrogen Permeation through Porous Stainless Steel for Palladium based Composite Porous Membranes

Surface topography and hydrogen permeation properties of Porous Stainless Steel (PSS) substrates for thin–films deposition of Pd–based hydrogen separation membrane were investigated. Hydrogen permeance through the as–received PSS substrates demonstrated a wide range, despite a similar average surface pore size of 15 micron determined by SEM and confocal laser microscopy analyses. The surface pores of the PSS substrates were modified by impregnation of varying amounts of tungsten (W) powder. Maximum hydrogen flux reduction of only 28% suggested that W has a limited effect on the hydrogen permeation through the PSS substrate. Therefore, it is suggested that hydrogen transport through PSS substrates is mainly controlled by the substrate geometrical factors, particularly the ratio of the porosity to tortuosity (e τ ). The variation in the permeance between the nominally similar PSS substrates indicates the importance to independently assess the hydrogen transport characteristics of each of the components in a composite membrane.

A tailor-made porous stainless steel support for a dense hydrogen separation membrane

A tailor-made DPSS (disc-shaped porous stainless steel substrate) for a thin and dense hydrogen membrane with high performance was fabricated by molding pre-treated metal powder, sintering an ingot and then slicing by electrical discharge machining. The sliced DPSS has a diameter of 50.8 mm and a thickness of 1.6 mm. In comparison with commercially produced support (DPSS-M), the sliced DPSS, having surface roughness of 2.7, maximum surface pore size of about 2 μm, porosity of 33.1% and average pore diameter of 0.58 μm, is more suitable as the support for the thinner Pd membrane. The hydrogen membrane with Pd layer of 4.4 μm was prepared and its performance was evaluated. It was shown that the Pd/DPSS membrane had a higher H2/N2 selectivity (3825) with a hydrogen flux of 24.7 ml/min/cm2, than that of Pd/DPSS-M (1821), at del-P = 1 and 400 °C, even though the surface morphologies of DPSS had been modified with less steps than DPSS-M. For CO2/H2 separation, the Pd/DPSS membrane enriched 40% CO2 to 90.8% and separated 60% H2 to 99.8% at 400 °C and del-P = 20 bar.