Low-Cost and Durable Bipolar Plates for Proton Exchange Membrane Electrolyzers.
ABSTRACT: Cost reduction and high efficiency are the mayor challenges for sustainable H2 production via proton exchange membrane (PEM) electrolysis. Titanium-based components such as bipolar plates (BPP) have the largest contribution to the capital cost. This work proposes the use of stainless steel BPPs coated with Nb and Ti by magnetron sputtering physical vapor deposition (PVD) and vacuum plasma spraying (VPS), respectively. The physical properties of the coatings are thoroughly characterized by scanning electron, atomic force microscopies (SEM, AFM); and X-ray diffraction, photoelectron spectroscopies (XRD, XPS). The Ti coating (50??m) protects the stainless steel substrate against corrosion, while a 50-fold thinner layer of Nb decreases the contact resistance by almost one order of magnitude. The Nb/Ti-coated stainless steel bipolar BPPs endure the harsh environment of the anode for more than 1000?h of operation under nominal conditions, showing a potential use in PEM electrolyzers for large-scale H2 production from renewables.
Project description:The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P.) grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 10 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK) than Ti alloy.
Project description:Si?N? ceramics and 304 stainless steel were brazed by Ti40Zr25B0.2Cu amorphous solder, and the interfacial microstructure of brazed joint Si?N? ceramics/Ti40Zr25B0.2Cu/Cu/Ti40Zr25B0.2Cu/304 stainless steel was analyzed. The mechanical properties of the brazed joint were overtly affected by the brazing temperature and Cu foil thickness. The results revealed that the interface structure of the brazed joint might be 304 stainless steel/FeTi/Cu-Zr+Cu-Ti+Fe-Ti/Cu(s,s)/Cu-Zr+Cu-Ti+Fe-Ti/Ti-Si+Zr-Si/TiN/Si?N? ceramics. The four-point bending strength of the brazed joint decreased sharply as the brazing temperature increased and reached a maximum of 76 MPa at 1223 K. Furthermore, as the Cu foil thickness was increased from 500 ?m to 1000 ?m, the joint strength rose to 90 MPa at 1223 K.
Project description:Effect of heat-treatment on the pH sensitivity of uncoated stainless-steel electrodes was investigated to comprehend the pH sensitivity of metal-oxide coated stainless-steel electrodes as novel pH sensors. The pH sensitivity of stainless-steel electrodes as-received and heat-treated at 500 °C, 600 °C and 700 °C for 24 h were 91 %, 94 %, 102 % and 91 %, respectively. The pH sensitivity tended to increase with increasing heat-treatment time at a given temperature. Thus, the most suitable heat-treatment condition for the stainless-steel electrodes was 600 °C for 24 h. The austenite phase (fcc) was the main phase on the surface of the heat-treated stainless-steel electrodes. Unexpectedly, the change in the martensite phase (bcc) as the second phase with heat-treatment temperature was similar to the pH sensitivity, with the martensite phase affecting the pH sensitivity. Therefore, it appeared that the pH sensitivity of the metal-oxide coated stainless-steel electrodes was affected by the underlying stainless-steel as well as the outer metal-oxide film coating. A prototype stainless-steel tube electrode was used as a working electrode for demonstrating the depth profiling of pH. The stainless-steel tube electrode showed good performance for measuring pH depth profiles compared to commercially available glass electrodes.
Project description:Bronization and carburization of fine-grain superplastic stainless steel is reviewed, and new experimental results for fine grain Ti88.5Al4.5V₃Fe₂Mo₂ are reported. In superplastic duplex stainless steel, the diffusion of carbon and boron is faster than in non-superplastic duplex stainless steel. Further, diffusion is activated by uniaxial compressive stress. Moreover, non-superplastic duplex stainless steel shows typical grain boundary diffusion; however, inner grain diffusion is confirmed in superplastic stainless steel. The presence of Fe and Cr carbides or borides is confirmed by X-ray diffraction, which indicates that the diffused carbon and boron react with the Fe and Cr in superplastic stainless steel. The Vickers hardness of the carburized and boronized layers is similar to that achieved with other surface treatments such as electro-deposition. Diffusion of boron into the superplastic Ti88.5Al4.5V₃Fe₂Mo₂ alloy was investigated. The hardness of the surface exposed to boron powder can be increased by annealing above the superplastic temperature. However, the Vickers hardness is lower than that of Ti boride.
Project description:A nondestructive study of the internal structure and compositional gradient of dissimilar metal-alloy welds through energy-resolved neutron imaging is described in this paper. The ability of neutrons to penetrate thick metal objects (up to several cm) provides a unique possibility to examine samples which are opaque to other conventional techniques. The presence of Bragg edges in the measured neutron transmission spectra can be used to characterize the internal residual strain within the samples and some microstructural features, e.g. texture within the grains, while neutron resonance absorption provides the possibility to map the degree of uniformity in mixing of the participating alloys and intermetallic formation within the welds. In addition, voids and other defects can be revealed by the variation of neutron attenuation across the samples. This paper demonstrates the potential of neutron energy-resolved imaging to measure all these characteristics simultaneously in a single experiment with sub-mm spatial resolution. Two dissimilar alloy welds are used in this study: Al autogenously laser welded to steel, and Ti gas metal arc welded (GMAW) to stainless steel using Cu as a filler alloy. The cold metal transfer variant of the GMAW process was used in joining the Ti to the stainless steel in order to minimize the heat input. The distributions of the lattice parameter and texture variation in these welds as well as the presence of voids and defects in the melt region are mapped across the welds. The depth of the thermal front in the Al-steel weld is clearly resolved and could be used to optimize the welding process. A highly textured structure is revealed in the Ti to stainless steel joint where copper was used as a filler wire. The limited diffusion of Ti into the weld region is also verified by the resonance absorption.
Project description:Bulk metallic glasses (BMGs) show higher strength and lower Young's modulus than Ti-6Al-4V alloy and SUS 316L stainless steel. This study aimed to perform in vivo evaluations of Zr65Al7.5Ni10Cu17.5 BMGs for osteosynthesis devices. In the study for intramedullary implants, osteotomies of the femoral bones were performed in male Wistar rats and were stabilized with Zr65Al7.5Ni10Cu17.5 BMGs, Ti-6Al-4V alloy, or 316L stainless steel intramedullary nails for 12 weeks. In the study for bone surface implants, Zr65Al7.5Ni10Cu17.5 BMGs ribbons were implanted on the femur surface for 6 weeks. Local effects on the surrounding soft tissues of the implanted BMGs were assessed by histological observation. Implanted materials' surfaces were examined using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDS). In the study for intramedullary implants, bone healing after osteotomy was assessed by peripheral quantitative computed tomography (QCT) and mechanical tests. Histological observation showed no findings of the biological effects. SEM-EDS showed no noticeable change on the surface of BMGs, while Ca and P deposition was seen on the Ti-6Al-4V alloy surface, and irregularities were seen on the 316L stainless steel surface. Mechanical test and peripheral QCT showed that, although there was no significant difference, bone healing of BMGs was more than that of Ti-6Al-4V alloy. The results indicated that Zr-based BMGs can lead to bone healing equal to or greater than Ti-6Al-4V alloy. Zr-based BMGs exhibited the advantage of less bone bonding and easier implant removal compared with Ti-6Al-4V alloy. In conclusion, Zr-based BMGs are promising for osteosynthesis devices that are eventually removed.
Project description:In this study, the tendency and mechanisms by which protein and mechanical loads contribute to corrosion were determined by exposing Ni-Ti and stainless steel arch wires under varying mechanical loads to artificial saliva containing different types of protein (lysozyme, ovalbumin, and bovine serum albumin). The corrosion behavior and in vitro cytotoxicity results show that exposure to both protein and mechanical stress significantly decreased the corrosion resistance of stainless steel and increased the release of toxic corrosion products. Adding protein inhibited the corrosion of Ni-Ti, but the mechanical loads counteracted this effect. Even proteins containing the same types of amino acids had different effects on the corrosion resistance of the same alloy. The effect of protein or stress, or their combination, should be considered in the application of metal medical materials.
Project description:Microneedle patches contain micrometer-scale needles coated with bioactive agents for minimally invasive drug delivery to the skin. In this study, we introduce layer-by-layer approaches to the fabrication of ultrathin DNA- and protein-containing polyelectrolyte films (or "polyelectrolyte multilayers", PEMs) on the surfaces of stainless steel microneedles. DNA-containing PEMs were fabricated on microneedles by the alternating deposition of plasmid DNA and a hydrolytically degradable poly(?-amino ester). Protein-containing PEMs were fabricated using sodium poly(styrene sulfonate) (SPS) and bovine pancreatic ribonuclease A (RNase A) conjugated to a synthetic protein transduction domain. Layer-by-layer assembly resulted in ultrathin, uniform, and defect-free coatings on the surfaces of the microneedles, as characterized by fluorescence microscopy. These films eroded and thereby released DNA or protein when incubated in saline or when inserted into porcine cadaver skin and deposited DNA or protein along the edges of microneedle tracks to depths of ?500 to 600 ?m. We conclude that PEM-coated microneedles offer a novel and useful approach to the transdermal delivery of DNA- and protein-based therapeutics and could also prove useful in other applications.
Project description:Cooling systems remove heat from components and industrial equipment. Water cooling, employing natural waters, is typically used for cooling large industrial facilities, such as power plants, factories or refineries. Due to moderate temperatures, cooling water cycles are susceptible to biofouling, inorganic fouling and scaling, which may reduce heat transfer and enhance corrosion. Hypochlorite treatment or antifouling coatings are used to prevent biological fouling in these systems. In this research, we examine biofouling and materials' degradation in a brackish seawater environment using a range of test materials, both uncoated and coated. The fouling and corrosion resistance of titanium alloy (Ti-6Al-4V), super austenitic stainless steel (254SMO) and epoxy-coated carbon steel (Intershield Inerta160) were studied in the absence and presence of hypochlorite. Our results demonstrate that biological fouling is intensive in cooling systems using brackish seawater in sub-arctic areas. The microfouling comprised a vast diversity of bacteria, archaea, fungi, algae and protozoa. Chlorination was effective against biological fouling: up to a 10-1000-fold decrease in bacterial and archaeal numbers was detected. Chlorination also changed the diversity of the biofilm-forming community. Nevertheless, our results also suggest that chlorination enhances cracking of the epoxy coating.
Project description:A dataset in this report is regarding an article "Ultrathin Effective TiN Protective Films Prepared by Plasma-Enhanced Atomic Layer Deposition for High Performance Metallic Bipolar Plates of Polymer Electrolyte Membrane Fuel Cells" . TiN (Titanium Nitride) thin films were deposited by Plasma-Enhanced Atomic Layer Deposition (PEALD) method using well known two types of precursor: using tetrakis(dimethylamino)titanium (TDMAT) and titanium tetrachloride (TiCl4), and plasma. Summarized reports, growth characteristics (growth rate as a function of each precursor pulse time, plasma power, precursor and plasma purge time, thickness depending on the number of PEALD cycles), each precursor structural information and the atomic force micrographs (AFM) data are herein demonstrated. For TDMAT-TiN, N2 plasma was used as a reactant whereas, H2+N2 plasma was used as TiCl4-TiN reactant. To apply the bipolar plate substrate, two types of TiN thin films were introduced into Stainless steel (SUS) 316L.