Influence of aluminum phosphate on the tribocorrosion performance of chemically bonded phosphate ceramic coatings

In this study, chemically bonded phosphate ceramic coatings (CBPCCs) with different contents of aluminum phosphate (AP) are prepared on stainless steel (AISI 304L). Differential scanning calorimetry, X-ray diffraction, contact angle test, and a tribocorrosion experiment are carried out to clarify the role of AP in the tribocorrosion performance of CBPCCs. The results show that, with the increase in the AP content, the enthalpy of curing increases because of the greater formation of the bonding phase AlPO₄. Both in static corrosion and in tribocorrosion, the corrosion current density of CBPCCs achieves the lowest value when the weight ratio of AP to polytetrafluoroethylene is about 0.78. Additionally, the influence mechanism of AP on tribocorrosion is clarified. AlPO₄ from the reaction between AP and Al₂O₃ has excellent mechanical properties and can enhance the wear resistance of CBPCCs by reducing the mechanical wear and the increased wear due to corrosion. The alumina particles wrapped by AlPO₄ can form a dense and smooth surface and change the direction of electrolyte propagation, which leads to the increase in the tribocorrosion resistance of CBPCCs.     

Experimental investigation on the heat and water transfer enhancement in a membrane-based air-to-air humidifier at insulation condition

In the present study, a membrane-based air-to-air planar humidifier (MAPH) with baffle-blocked flow channels and a common MAPH are fabricated, tested and compared. These MAPHs are well thermal insulated from their surroundings. Polyoxymethylene (POM) plates with some unique properties such as large tensile and flexural strength, high chemical resistance and high stiffness are used to create channels at dry and humid sides of MAPHs. The obtained findings revealed that the higher heat and water transfer rates and smaller dew point approach temperature (DPAT) in entire tested flow rates occurs in baffle-blocked MAPH. To evaluate the MAPH performance with considering the pressure drop, a dimensionless parameter, performance evaluation criteria (PEC), is introduced. At flow rates less than 1 m³/h, PEC is less than 1, indicating a decline in MAPH performance with considering the pressure drop. In baffle-blocked MAPH using water trap in the inlet of dry side leads to the performance deterioration. Additionally, the increased relative humidity (RH) of humid side inlet causes an increase in DPAT, consequently, the performance deterioration.     

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.     

Development of titanium bipolar plates fabricated by additive manufacturing for PEM fuel cells in electric vehicles

Bipolar plates (BPs) are one of the main parts of proton exchange membrane (PEM) fuel cell stacks, which constitute a significant percentage of a PEM fuel cell system in terms of cost, weight, and structural strength. Although frequently used graphite BPs have low density, high conductivity, and high corrosion resistance, machining the desired flow channels on these plates is challenging. On the other hand, BPs made of various materials rather than graphite can be also fabricated by additive manufacturing methods. These methods can be considered as a reasonable alternative to conventional machining for the fabrication of graphite BPs in PEM fuel cells regarding material cost, fabrication of flow channels, and some post-processes in which the large-scale manufacturing of graphite BPs is more complex. This study offers a comparison of formed stainless-steel, additive manufactured titanium and machined composite graphite plates having the same flow-field geometry as a bipolar plate. In addition, titanium BPs are coated with gold and their performances are compared. Among the cells tested, the highest peak power of 639 mWcm^?2 is measured from the cell with 450 nm gold coated titanium BP, whereas those of the cell with conventional graphite and stainless-steel BP are only around 322 mWcm^?2 and 173 mWcm^?2, respectively. Moreover, a new titanium bipolar plate design providing high specific power density is also presented.     

A Ti3C2Tx-carbon black-acrylic epoxy coating for 304SS bipolar plates with enhanced corrosion resistant and conductivity

A conducting and anticorrosive coating is crucial for the application of metal bipolar plates (BP) in proton exchange membrane fuel cell (PEMFC). In this work, a Ti₃C₂T_x (T)-carbon black (C)-acrylic epoxy (AE) coating is prepared on 304 stainless steel (SS) with enhanced corrosion resistance and conductivity. The corrosion resistance of the T-C-AE coating is investigated in a 0.5 M H₂SO₄ solution as compared to the AE, T, and T-AE coatings. The T-C-AE coated 304SS exhibits the strongest corrosion resistance with the most positive corrosion potential and the lowest corrosion current density of 0.00673 μA cm^?2 in all the samples, while retaining intact and compact surface morphology with the lowest metal ion dissolution even after immersed for 720 h. The addition of Ti₃C₂T_x and carbon black into the AE matrix greatly decreases interfacial contact resistance (ICR), and the T-C-AE coating achieves a low ICR of 15.5 mΩ cm^?2 under 140 N cm^?2 compaction force. The excellent anticorrosion performance is mainly attributed to the physical barrier and the cathodic protection provided by the stacked Ti₃C₂T_x (MXene) nanosheets in the T-C-AE coating. This eco-friendly, conducting, and anticorrosive T-C-AE coating has a good application prospect on SS BP of PEMFC.     

Impact of TiO2 nanoparticles and nanowires on corrosion protection performance of chemically bonded phosphate ceramic coatings

The impact of the addition of TiO₂ nanoparticles and nanowires on the morphology, phase characteristics, contact angle, and electrochemical performance of chemically bonded phosphate ceramic coatings (CBPCs) was investigated. The chemical composition and surface morphology of the TiO₂ nanoparticle and nanowire modified with and without (heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane were characterized. Results indicated that the hydrophobic –CF₂– and –CF₃ groups were successfully introduced into the TiO₂ nanoparticles and nanowires after modification. Corrosion resistance of CBPCs with TiO₂ was evidently improved compared with that without TiO₂. Such improvement was mainly due to the combined effects of low surface energy materials and micro/nano structures. In addition, CBPCs with TiO₂ nanowires exhibited higher hydrophobicity and corrosion resistance than those with TiO₂ nanoparticles because of the special columnar structure of the nanowires.     

Additive manufacturing of bipolar plates for hydrogen production in proton exchange membrane water electrolysis cells

Water electrolysis is a process that can produce hydrogen in a clean way when renewable energy sources are used. This allows managing large renewable surpluses and transferring this energy to other sectors, such as industry or transport. Among the electrolytic technologies to produce hydrogen, proton exchange membrane (PEM) electrolysis is a promising alternative. One of the main components of PEM electrolysis cells are the bipolar plates, which are machined with a series of flow distribution channels, largely responsible for their performance and durability. In this work, AISI 316L stainless steel bipolar plates have been built by additive manufacturing (AM), using laser powder bed fusion (PBF-L) technology. These bipolar plates were subjected to ex-situ corrosion tests and assembled in an electrolysis cell to evaluate the polarization curve. Furthermore, the obtained results were compared with bipolar plates manufactured by conventional machining processes (MEC). The obtained experimental results are very similar for both manufacturing methods. This demonstrates the viability of the PBF-L technology to produce metal bipolar plates for PEM electrolyzers and opens the possibilities to design new and more complex flow distribution channels and to test these designs in initial phases before scaling them to larger surfaces.     

Improving tribocorrosion performance of chemically bonded ceramic phosphate coating reinforced by GO-ZnO

To enhance the tribocorrosion properties of chemically bonded phosphate ceramic coating (CBPCC), GO-ZnO was prepared and added into CBPCC. And the tribocorrosion behaviour of CBPCC was investigated. Results show that, with the introduction of GO-ZnO, the open circuit potential of CBPCC shifts in a positive direction and corrosion current density decreases. In addition, the total material loss, the total mechanical wear loss and the total electrochemical corrosion loss of CBPCC all decrease with the increase of GO-ZnO. The wear track of CBPCC after tribocorrosion without GO-ZnO is rough and porous, while the wear track becomes smooth and dense with the incorporation of GO-ZnO. The material in wear track is anchored by GO-ZnO due to the strong bond between GO-ZnO and CBPCC, which decreases the wear loss. Because of the extra force from the tribocorrosion experiment, the material anchored by GO-ZnO forms to a dense structure which prevents electrolyte diffusion into CBPCC. Moreover, GO-ZnO can block the electrolyte diffusion pathway and make it more tortuous. The resistance to the electrolyte diffusion decreases the corrosion current density and the increased wear loss due to electrochemical corrosion.     

Effects of cross rolling on texture,mechanical properties and anisotropy of pure Mo plates

To clarify the influence of the deformation texture on the mechanical properties, pure Mo plates were processed by various cross rolling procedures, and the relation among texture, microstructure and mechanical properties was discussed. The results show that cross rolling of the Mo plates is beneficial for the formation of the rotated cube component, i.e., {001}〈110〉. The corresponding orientation density exhibits a positive correlation with the total rolling deformation and the current-pass deformation. When the total deformation is 96% or greater, the Mo plates form a texture orientation dominated by {001}〈110〉, whereas the γ-fibre texture becomes weaker and the cube texture {100}〈100〉 disappears completely. The presence of {001}〈110〉 has great effects on the properties of cross-rolled Mo plates, which is beneficial for strength enhancement and plasticity reduction in both the rolling direction (RD) and the transverse direction (TD).