Effect of bipolar-plates design on corrosion,mass and heat transfer in proton-exchange membrane fuel cells and water electrolyzers:A review

Attaining a decarbonized and sustainable energy system,which is the core solution to global energy issues,is accessible through the development of hydrogen energy.Proton-exchange membrane water electrolyzers(PEMWEs)are promising devices for hydrogen production,given their high efficiency,rapid responsiveness,and compactness.Bipolar plates account for a relatively high percentage of the total cost and weight compared with other components of PEMWEs.Thus,optimization of their design may accelerate the promotion of PEMWEs.This paper reviews the advances in materials and flow-field design for bipolar plates.First,the working conditions of proton-exchange membrane fuel cells(PEMFCs)and PEMWEs are compared,including reaction direction,operating temperature,pressure,input/output,and potential.Then,the current research status of bipolar-plate substrates and surface coatings is summarized,and some typical channel-rib flow fields and porous flow fields are presented.Furthermore,the effects of materials on mass and heat transfer and the possibility of reducing corrosion by improving the flow field structure are explored.Finally,this review discusses the potential directions of the development of bipolar-plate design,including material fabrication,flow-field geometry optimization using threedimensional printing,and surface-coating composition optimization based on computational materials science.

Relationship between elements migration ofα-AlFeMnSi phase and micro-galvanic corrosion sensitivity of Al-Zn-Mg alloy

First principles calculations and scanning Kelvin probe force microscopy(SKPFM)were used to investigate the effect of elements migration ofα-AlFeMnSi phase on micro-galvanic corrosion behavior of Al-Zn-Mg alloy.The simulation results showed that the average work function difference between theα-AlFeMnSi phase and Al matrix decreased from 0.232 to 0.065 eV due to the synchronous migration of elements Fe-Mn-Si.Specifically,as the elements Fe-Si migration during the extrusion process,the average Volta potential difference detected by SKPFM between theα-AlFeMnSi phase and Al matrix dropped down to 432.383 mV from 648.370 mV.Thus,the elements migration reduced the micro-galvanic corrosion sensitivity of Al-Zn-Mg alloy.To reach the calculated low micro-galvanic tendency betweenα-AlFeMnSi phase and Al matrix,the diffusion of Mn should be promoted during extruding process.

Pitting and galvanic corrosion behavior of stainless steel with weld in wet-dry environment containing Cl^-

Accelerated corrosion test of stainless steel with weld was carried out to investigate the corrosion behavior under the wetdry cyclic condition in the atmosphere containing Cl^-. In the surface morphology, corrosion products were analyzed by metallographic observation, scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that the damage to stainless steel with weld in the atmosphere containing Cl^- is due to localized corrosion, especially pitting and galvanic corrosion, Weld acts as the anode, whereas matrix acts as the cathode in the corrosion process. The pitting corrosion, including the nucleation and growth of a stable pit, is promoted by the presence of wet-dry cycles, especially during the drying stage. Pits centralizing in weld are found to be grouped together like colonies, with a number of smaller pits surrounding a larger pit. The composition of the corrosion products is Fe2O3, Cr2O3, Fe3O4, NiCrO4, etc.

Corrosion of Duplex Stainless Steel Manufactured by Laser Powder Bed Fusion: A Critical Review

Laser powder bed fusion (LPBF) is a commonly used additive manufacturing (AM) method for efficiently producing intricate geometric components. This investigation examines factors such as pores, cellular structure, grain size, and inclusions from the manufacturing process that contribute to the corrosion resistance of LPBF DSS. Furthermore, the as-built LPBF duplex stainless steel (DSS) is primarily ferrite due to the rapid cooling process. Therefore, the transformation of ferrite to austenite after various heat treatments in LPBF DSS and its corresponding corrosion resistance are presented. Additionally, a new mixed powder method is proposed to increase the austenite content in the as-built LPBF DSS. This review also focuses on the passivation capability and pitting corrosion performance in LPBF and conventional DSS. This article summarizes the variations in microstructure between as-built and heat-treated LPBF DSS, with their impacts on corrosion resistance, offering insights for manufacturing highly corrosion-resistant LPBF DSS.

定量结构-性质关系(QSPR)中的计算方法研究进展

定量结构-性质关系(QSPR)方法是一种将材料的微观定量结构与其某些性能构建关系的方法.通过构建的关系模型可以对具有其他结构的材料性能进行预测,QSPR已成为材料基因组计划的主要实现途径之一.计算方法是决定QSPR模型准确程度、构建速度的主要因素,选择最佳的计算方法对改善QSPR模型预测精度、计算速度等指标至关重要.本文首先对QSPR模型进行了概述,简单介绍了QSPR方法的计算步骤;重点说明了QSPR中分子描述符计算方法、模型优化算法,并对各个方法进行了优缺点分析;最后总结了近些年QSPR中各类计算方法的应用趋势.

Mechanical properties and corrosion behavior of selective laser melted 316L stainless steel after different heat treatment processes

Irregular grains, high interfacial stresses and anisotropic properties widely exist in 3D-printed metallic materials, and this paper investigated the effects of heat treatment on the microstructural, mechanical and corrosion properties of 316 L stainless steel fabricated by selective laser melting. Sub-grains and low-angle boundaries exist in the as-received selective laser melted(SLMed) 316 L stainless steel. After heat treatment at 1050℃, the sub-grains and low-angle boundaries changed slightly, and the stress state and strength decreased to some extent due to the decrease of dislocation density. After heat treatment at 1200℃, the grains became uniform, and the dislocation cells vanished, which led to a sharp decline in the hardness and strength. However, the ductility was improved after recrystallization heat treatment.The passive film thickness and corrosion potential of the SLMed 316 L stainless steel decreased after heat treatment, and the pitting potential also decreased due to the accelerated transition from metastable to steady-state pitting;this accelerated transition was caused by the presence of weak passive films at the enlarged pores after heat treatment, especially for an adequate solid solution treatment.

Initial formation of corrosion products on pure zinc in simulated body fluid

Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent.The corrosion behavior of pure zinc exposed to r-SBF up to 336 h was investigated by electrochemical measurements and immersion tests. The morphology and chemical composites of the corrosion products were investigated by scanning electron microscope, grazing-incidence X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The results demonstrate that the initial corrosion products on the pure zinc mainly consist of zinc oxide/hydroxide and zinc/calcium phosphate compounds. The pure Zn encounters uniform corrosion with an estimated corrosion rate of 0.02-0.07 mmy;during the immersion, which suggests the suitability of pure Zn for biomedical applications.

Interaction between austein-ferrite phases on passive performance of2205 duplex stainless steel

The passive behavior of 2205 duplex stainless steel（DSS） and its individual phases（α-phase, γ-phase） in neutral 3.5% NaCl solution was investigated by various electrochemical methods. The results indicated that galvanic effect between α and γ phases cannot deteriorate local corrosion, but favors the enhancement of the passive film. Under the galvanic effect, the diffusion of the dissolved passive cations would be promoted in a short distance between α and γ zones, leading to modifications of the chemical composition and semiconductive property of the passive film and therefore the enhancement of the corrosion resistance of DSS 2205.

Effect of Microstructures on Corrosion Behavior of Nickel Coatings:(Ⅱ) Competitive Effect of Grain Size and Twins Density on Corrosion Behavior

Nanocrystalline nickel coatings with grain size of 50 nm were annealed in vacuum at 200 ℃ and 400 ℃ for 10 min, Their microstructures were investigated by transmission electron microscopy （TEM）. And their corrosion behaviors were studied by means of polarization and electrochemical impedance spectroscopy （EIS）, The results showed that their grain size grew up to about 60 nm （200 ℃） and 500 nm （400 ℃）, respectively, The specimen annealed at 200 ℃ possessed higher density of twins in compared with the counterparts of as-deposited and annealed at 400 ℃, The normal grain size effect on the corrosion behavior was not observed, However, it was found that the corrosion resistance of the coating linearly changed with the density of twins.

Multi-action self-healing coatings with simultaneous recovery of corrosion resistance and adhesion strength

In this study, a new self-healing strategy that can simultaneously recover the corrosion resistance and the adhesion strength of coatings was introduced. The coating was based on a shape memory epoxy resin containing ethylene vinyl acetate(EVA) microspheres loaded with Ce(NO_(3))_(3)inhibitors, and was cured at a relatively high temperature to facilitate the fusion of adjacent microspheres for a strengthened self-healing effect. The electrochemical impedance spectroscopy(EIS) and scanning electrochemical microscopy(SECM) results demonstrated that the shape memory effect of epoxy matrix, the filling of molten EVA microspheres as well as the release of Ce(NO_(3))_(3)inhibitors contributed synergistically to suppress the corrosion reaction at the coating damage. After healing, the low frequency impedance modulus of the coatings containing Ce(NO_(3))_(3)-EVA microspheres was three orders of magnitude higher than that of the blank epoxy coating. The adhesion strength of the coatings containing Ce(NO_(3))_(3)-EVA microspheres on the metal substrate was also largely repaired thanks to the strong bonding effect of the EVA microspheres.

Initial formation of corrosion products on pure zinc in saline solution

Corrosion product formed on zinc sample during 2 weeks immersion in saline solution has been investigated.The corrosion layer morphology as well as its chemical composition,was analyzed using scanning electron microscopy(SEM),x-ray diffraction(XRD),x-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FTIR).Electrochemical measurement was used to analyze the corrosion behavior.Zinc oxide,zinc hydroxide and zinc hydroxide chloride were formed on zinc surface in saline solution.The thickness of corrosion layer increased with the time increased.The pure Zn has an estimated corrosion rate of 0.063mmy^−1 after immersion for 336 h.Probable mechanisms of zinc corrosion products formation are presented.

Design materials based on simulation results of silicon induced segregation at AlSi10Mg interface fabricated by selective laser melting

AlSi10Mg fabricated by selective laser melting(SLM)had a unique network-like silicon-rich structure,and the mechanism for its formation was explained by molecular dynamics(MD)simulations.The effects of the silicon-rich phase and Mg-containing structure on corrosion were studied by first-principles methods.According to the simulations,corrosion resistant materials were designed,samples with laser powers of 150 W,200 W and 250 W were fabricated.The results indicated that a local thermal gradient during laser printing caused Si segregation,and the rapid cooling rate lead to a large number of subgrains,which assisted precipitation.The difference in potential caused galvanic corrosion,and a structure with low work function in the molten pool caused pitting.The corrosion resistance of materials processed with a high laser power increased.

Design and fabrication of bipolar plates for PEM water electrolyser

Hydrogen energy,whether in generation plants or utilization facilities,plays a decisive role in the mission to achieve net-zero greenhouse gas emissions,all to minimize pollution.The growing demand for clean energy carrier steadily accelerates the development of hydrogen production processes,and therein proton exchange membrane(PEM)water electrolysis is deemed a promising long-term strategy for hydrogen preparation and collection.This review retrospects recent developments and applications of bipolar plates(BPs)as key components in PEM fuel cells and water electrolysers.The main content includes multifaceted challenges in the R&D or fabrication of BPs and potential future trends have also been proposed.Specific details cover the BPs matrix(metallic materials and carbon composites)and the surface coating types(metal and compound coatings,carbon-based coatings,and polymer coatings),as well as the influence of flow field design for mass transport.Long-term development and feasible researches of BPs are prospected.Especially in the following aspects:(1)Structural and functional integration of components,such as material fabrication and flow field geometry optimization using 3D printing technology;(2)Introduction of environment-friendly renewable energy for hydrogen production;(3)Research on hydrogen energy reversible systems;(4)Composition optimization of surface coatings based on computational materials science and(5)systematic design expected to evolve into the next generation of BPs.

Effect of Microstructures on Corrosion Behavior of Nickel Coatings:(Ⅰ) Abnormal Grain Size Effect on Corrosion Behavior

Nickel coatings with different microstructures were synthesized by pulse jet electrodeposition technique.Their morphology and microstructure were investigated by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The corrosion property of the coatings was studied by using polarization,electrochemical impedance spectroscopy（EIS）,potential of zero free charge（PZFC） measurements and Mott-Schottky（M-S） relationship.The results showed that the coating with grain size of 50 nm possessed higher corrosion resistance than that with grain size of 10 nm.This abnormal behavior may be related to the existence of nanoscale twins in the coatings and the lower concentration of acceptor in the passive films.

Heat treatment effects on the metastable microstructure,mechanical property and corrosion behavior of Al-added CoCrFeMnNi alloys fabricated by laser powder bed fusion

With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex structures.This work investigates Al-added CoCrFeMnNi high-entropy alloys(Al-HEAs)pre-pared by laser powder bed fusion(PBF-LB),adding 4.4 wt.%Al reducing approximately 7%density.The contribution of post-heat-treatment to microstructure,mechanical properties,and corrosion behaviors are explored.Hot cracking along with grain boundaries in the as-built PBF-LB Al-HEAs is determined,which comes from the residual liquid film as a larger solidification temperature range by adding Al.The PBF-LB Al-HEAs mainly consist of a face-centered cubic(FCC)matrix with Al/Ni/Mn decorated dislocation cells therein and a minor body-centered cubic(BCC)phase.Upon 850℃ annealing treatment,massive BCC phases(ordered NiAl and disordered Cr-rich precipitates)generate at the dislocation cell/grain bound-aries and the dislocation cells are still retained.However,the volume fraction of BCC phases and the dislocation cells vanish after 1150℃ solution treatment.As a result,Al-HEA850 shows an over 1000 MPa yield strength with nearly no ductility(<3%);the Al-HEA1150 exhibits considerable strength-ductility properties.Meanwhile,the Al-HEA850 demonstrates the worst pitting corrosion resistance due to the preferential dissolution of the NiAl precipitates in chloride-containing solutions.After comparatively de-liberating the evolution of strength-ductility and localized corrosion,we built a framework about the effects of the heat treatment on the mechanical property and degradation behavior in additively manu-factured Al-added high-strength HEAs.

Recrystallization effect on surface passivation of Hastelloy X alloy fabricated by laser powder bed fusion

Post-heat treatment is generally adopted in the additive manufacturing field due to its alleviation of high residual stress and modification of rapid-solidified multilevel heterogeneous microstructure,and the related performance of the heat-treated counterparts calls for a systemic investigation to build a criterion of the heat treatment procedure.In this work,we focus on the heat treatment effects on the recrystallization of the Hastelloy X alloy produced by the laser powder bed fusion(LPBF)method,and the related surface passivation of the heat-treated counterparts is meticulously assessed as well.Results show that the multilevel heterostructure for LPBF Hastelloy X alloy consists of sub-micro dislocation cell substructures with Cr/Mo elemental segregation,fine columnar grains,and periodically-distributed molten pools.After heat treatment,partially and fully recrystallized structures for LPBF Hastelloy X alloys were achieved at 1100 and 1200℃for 1 h,respectively.Furthermore,the as-built LPBF Hastelloy X alloy shows superior corrosion resistance while the heat-treated one(1100℃)exhibits the worst in the borate buffer solution.The growth of passive film exhibited a highly linear correlation with the nucleation process controlled by diffusion,and high dislocation density and low angle grain boundary decreased the diffusion coefficient of cation vacancies,augmenting the nucleation sites of the passive film and enhancing its growth rate.Moreover,the micro-galvanic effect resulting from the partially recrystallized microstructure actively facilitated the formation of inhomogeneous porous passive films,leading to the worst corrosion resistance.

In-situ observation of asymmetrical deformation around inclusion in a heterogeneous additively manufactured 316L stainless steel

Oxide inclusions widely exist in additively manufactured components due to the native oxide layer on the powder surface,together with gas impurities during the printing process.Using in-situ tensile tests combined with electron backscatter diffraction(EBSD)and electron channeling contrast imaging(ECCI)techniques,we propose an asymmetrical cracking mechanism around the oxide inclusions in a selective laser melted 316L stainless steel.The heterogeneous sub-micro cellular structures lead to different twinning tendencies around the inclusions due to the size-related critical twinning stresses,and the deformation-induced nano-twin clusters can resist the cracking propagation,therefore resulting in the asymmetrical cracking behaviors around the inclusions.