Ice Formation during PEM Fuel Cell Cold Start: Acceptable or Not?

Proton exchange membrane (PEM) fuel cell faces the inevitable challenge of the cold start at a sub-freezing temperature. Understanding the underlying degradation mechanisms in the cold start and developing a better starting strategy to achieve a quick startup with no degradation are essential for the wide application of PEM fuel cells. In this study, the comprehensive in situ non-accelerated segmented techniques are developed to analyze the icing processes and obtain the degradation mechanisms under the conditions of freeze-thaw cycle, voltage reversal, and ice formation in different components of PEM fuel cells for different freezing time. A detailed degradation mechanism map in the cold start of PEM fuel cells is proposed to demonstrate how much degradation occurs under different conditions, whether the ice formation is acceptable under the actual operating conditions, and how to suppress the ice formation. Moreover, an ideal starting strategy is developed to achieve the cold start of PEM fuel cells without degradation. This map is highly valuable and useful for researchers to understand the underlying degradation mechanisms and develop the cold start strategy, thereby promoting the commercialization of PEM fuel cells.

Boosting the performance and durability of heterogeneous electrodes for solid oxide electrochemical cells utilizing a data-driven powder-to-power framework.

Solid oxide electrochemical cells (SOCs) hold potential as a critical component in the future landscape of renewable energy storage and conversion systems. However, the commercialization of SOCs still requires further breakthroughs in new material development and engineering designs to achieve high performance and durability. In this study, a data-driven powder-to-power framework has been presented, fully digitizing the morphology evolution of heterogeneous electrodes from fabrication to long-term operation. This framework enables accurate performance prediction over the full life cycle. The intrinsic correlation between microstructural parameters and electrode durability is elucidated through parameter analysis. Rational control of the ion-conducting phase volume fraction can effectively suppress Ni coarsening and mitigate the excessive ohmic loss caused by Ni migration. The initial and degraded electrode performances are attributed to the interplay of multiple parameters. A practical optimization strategy to enhance the initial performance and durability of the electrode is proposed through the construction of the surrogate model and the application of the optimization algorithm. The optimal electrode parameters are determined to accommodate various maximum operation time requirements. By implementing the data-driven powder-to-power framework, it is possible to reduce the degradation rate of Ni-based electrodes from 2.132% to 0.703% kh-1 with a required maximum operation time of over 50,000 h.

Structure Design for Ultrahigh Power Density Proton Exchange Membrane Fuel Cell.

Next-generation ultrahigh power density proton exchange membrane fuel cells rely not only on high-performance membrane electrode assembly (MEA) but also on an optimal cell structure. To this end, this work comprehensively investigates the cell performance under various structures, and it is revealed that there is unexploited performance improvement in structure design because its positive effect enhancing gas supply is often inhibited by worse proton/electron conduction. Utilizing fine channel/rib or the porous flow field is feasible to eliminate the gas diffusion layer (GDL) and hence increase the power density significantly due to the decrease of cell thickness and gas/electron transfer resistances. The cell structure combining fine channel/rib, GDL elimination and double-cell structure is believed to increase the power density from 4.4 to 6.52 kW L-1 with the existing MEA, showing nearly equal importance with the new MEA development in achieving the target of 9.0 kW L-1 .

High-consistency proton exchange membrane fuel cells enabled by oxygen-electron mixed-pathway electrodes via digitalization design.

Proton exchange membrane (PEM) fuel cell has been regarded as a promising approach to the decarbonization and diversification of energy sources. In recent years, durability and cost issues of PEM fuel cells are increasingly significant with the rapid increase of power density. However, the failure to maintain the cell consistency, as one major cause of the above issue, has attracted little attention. Therefore, this study intends to figure out the underlying cause of cell inconsistency and provide solutions to it from the perspective of multi-physics transport coupled with electrochemical reactions. The PEM fuel cells with electrodes under two compression modes are firstly discussed to fully explain the relationship of cell performance and consistency to electrode structure and multi-physics transport. The result indicates that one main cause of cell inconsistency is the intrinsic conflict between the separated transport and cooperated consumption of oxygen and electron throughout the active area. Then, a mixed-pathway electrode design is proposed to reduce the cell inconsistency by enhancing the mixed transport of oxygen and electron in the electrode. It is found that the mixing of pathways in electrodes at under-rib region is more effective than that at the under-channel region, and can achieve an up to 40% reduction of the cell inconsistency with little (3.3%) sacrificed performance. In addition, all the investigations are implemented based on a self-developed digitalization platform that reconstructs the complex physical-chemical system of PEM fuel cells. The fully observable physical information of the digitalized cells provides strong support to the related analysis.

Porous Flow Field for Next-Generation Proton Exchange Membrane Fuel Cells: Materials, Characterization, Design, and Challenges.

Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L-1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization.

Alternating Flow Field Design Improves the Performance of Proton Exchange Membrane Fuel Cells.

The flow field structure of a proton exchange membrane fuel cell (PEMFC) is a determining factor for improving the cell power density. In this study, a universal alternating flow field design for the first time is proposed, which arranges structural units with different flow resistances in an alternating way to significantly improve the gas transfer rate into the electrode, with the advantages of easy machining and low pumping loss. Based on the design, it is proposed and tested large-scale fuel cells with three novel flow fields by combining a parallel channel, baffled channel, serpentine channel, and narrowed channel. The results show that the design can significantly enhance the gas supply efficiency and that the novel baffled flow field improves the PEMFC performance by 23% with low pumping loss. The design employed in the study offers additional options for flow field optimization and contributes to the early achievement of next-generation ultrahigh power density fuel cells.

Short-term effects of air pollution on respiratory diseases among young children in Wuhan city, China.

BACKGROUND: The high risks for childhood respiratory diseases are associated with exposure to ambient air pollution. However, there are few studies that have explored the association between air pollution exposure and respiratory diseases among young children (particularly aged 0-2 years) based on the entire population in a megalopolis. METHODS: Daily hospital admission records were obtained from 54 municipal hospitals in Wuhan city, China. We included all children (aged 0-2 years) hospitalized with respiratory diseases between January 2017 and December 2018. Individual air pollution exposure assessment was used in Land Use Regression model and inverse distance weighted. Case-crossover design and conditional logistic regression models were adopted to estimate the hospitalization risk associated with air pollutants. RESULTS: We identified 62,425 hospitalizations due to respiratory diseases, of which 36,295 were pneumonia. Particulate matter with an aerodynamic diameter less than 2.5 µm (PM2.5) and nitrogen dioxide (NO2) were significantly associated with respiratory diseases and pneumonia. ORs of pneumonia were 1.0179 (95% CI 1.0097-1.0260) for PM2.5 and 1.0131 (95% CI 1.0042-1.0220) for NO2 at lag 0-7 days. Subgroup analysis suggested that NO2, Ozone (O3) and sulfur dioxide (SO2) only showed effects on pneumonia hospitalizations on male patients, but PM2.5 had effects on patients of both genders. Except O3, all pollutants were strongly associated with pneumonia in cold season. In addition, children who aged elder months and who were in central urban areas had a higher hospitalization risk. CONCLUSIONS: Air pollution is associated with higher hospitalization risk for respiratory diseases, especially pneumonia, among young children, and the risk is related to gender, month age, season and residential location.

Open-Source CFD Elucidating Mechanism of 3D Pillar Electrode in Improving All-Solid-State Battery Performance.

All-solid-state batteries (ASSBs) have become an important technology because of their high performance and low-risk operation. However, the high interface resistance and low ionic conductivity of ASSBs hinder their application. In this study, a self-developed electrochemical model based on an open-source computational fluid dynamics platform is presented. The effect of contact area reduction at the electrode/solid-state electrolyte interface is investigated. Then, a new conceptual 3D structure is introduced to circumvent the existing barriers. The results demonstrate that the discharge time is shortened by over 20% when the area contact ratio reduces from 1.0 to 0.8 at 1 C-rate, owing to the increased overpotential. By adopting the new 3D pillar design, the energy density of ASSBs can be improved. However, it is only when a 3D current collector is contained in the cathode that the battery energy/power density, capacity, and material utilization can be greatly enhanced without being limited by pillar height issues. Therefore, this work provides important insight into the enhanced performance of 3D structures.

Interlink among catalyst loading, transport and performance of proton exchange membrane fuel cells: a pore-scale study.

An optimum balance between performance and Pt loading is critically important for the commercialization of proton exchange membrane (PEM) fuel cells. This research aims to investigate the interlink among Pt loading, reactive transport, and performance. An advanced pore-scale model is developed to describe the coupled reactive transport in the catalyst layer (CL) with the reactant gas, protons, and electrons all considered. The CL microstructure is stochastically reconstructed as a computational domain, and the physicochemical phenomena inside CLs are resolved by a multi-component lattice Boltzmann (LB) model. The results show that the electronic potential drop is not sensitive to Pt loading, while the ionic potential drop is much higher. The distributions of local overpotential and the reaction rate are similar with peak values near the membrane, indicating the importance of proton conduction. A high Pt loading could decrease the local transport loss for a shorter path to catalyst sites, but increases the overall transport resistance for a thicker structure. Although a larger electrochemical surface area (ECSA) is provided under a high Pt loading, a low Pt loading (0.1 mg cm-2) is suggested for high current conditions (2 A cm-2) where the transport loss is the main factor restricting the performance.

Positive effect of compound amino acid chelated calcium from the shell and skirt of scallop in an ovariectomized rat model of postmenopausal osteoporosis.

BACKGROUND: Osteoporosis has become an important public health issue with the increase of aging population, and afflicts millions of people worldwide, particularly elderly or postmenopausal women. In the present study, we prepared compound amino acid chelated calcium (CAA-Ca) from processing by-products of Chlamys farreri, and evaluated its effect on postmenopausal osteoporosis with an ovariectomized (OVX) rat model. RESULTS: A 60-day treatment of OVX rats with CAA-Ca significantly enhanced the bone mineral density (BMD) and the bone calcium content. Meanwhile, some bone morphometric parameters, trabecular bone number (Tb.N), trabecular bone volume fraction (BV/TV), trabecular bone thickness (Tb.Th) and cortical bone wall thickness (Ct.Th), were also increased by 8.20%, 118.18%, 32.99% and 19.10%, respectively. In addition, the alkaline phosphatase (ALP) levels in serum were significantly reduced after CAA-Ca treatment, while the blood calcium levels were increased. Mechanistically, CAA-Ca down-regulated the levels of receptor activator of nuclear factor-κB (RANK) and receptor activator of nuclear factor-κB ligand (RANKL), and up-regulated osteoprotegerin (OPG) levels in osteoclasts, inhibiting bone resorption and bone loss. Meanwhile, CAA-Ca treatment raised ß-catenin levels and lowered Dickkopf1 (DKK1) levels in the Wnt signaling pathway of osteoblasts, which can promote calcium absorption and bone formation. CONCLUSION: The results suggested that CAA-Ca promoted bone formation, inhibited bone resorption and improved bone microstructure. Therefore, this study contributes to the potential application of CAA-Ca as a functional food resource in the treatment of postmenopausal osteoporosis. © 2021 Society of Chemical Industry.

Designing the next generation of proton-exchange membrane fuel cells.

With the rapid growth and development of proton-exchange membrane fuel cell (PEMFC) technology, there has been increasing demand for clean and sustainable global energy applications. Of the many device-level and infrastructure challenges that need to be overcome before wide commercialization can be realized, one of the most critical ones is increasing the PEMFC power density, and ambitious goals have been proposed globally. For example, the short- and long-term power density goals of Japan's New Energy and Industrial Technology Development Organization are 6 kilowatts per litre by 2030 and 9 kilowatts per litre by 2040, respectively. To this end, here we propose technical development directions for next-generation high-power-density PEMFCs. We present the latest ideas for improvements in the membrane electrode assembly and its components with regard to water and thermal management and materials. These concepts are expected to be implemented in next-generation PEMFCs to achieve high power density.

Oxygen Transport Routes in Ionomer Film on Polyhedral Platinum Nanoparticles.

Understanding the O2 permeation phenomenon in the ionomer thin film on platinum (Pt) nanoparticles is vital to improve the electrocatalyst performance of proton exchange membrane fuel cells at a low Pt loading. In this study, the ionomer film structure, O2 density distribution, transport fluxes, and permeation routes are investigated for carbon-supported polyhedral Pt nanoparticles (cube and tetrahedron) in the facet, edge, and corner regions. The molecular dynamic simulation takes into account the molecular interactions among the ionomer, Pt nanoparticles, carbon support, and O2 molecules. The results show that a dense ionomer ultrathin layer with a tight arrangement of perfluorosulfonic acid is present on the Pt facets (namely region A). In the ionomer near the Pt edges and corners (namely region B), the structure is less dense due to the weaker Pt attraction, resulting in a higher O2 density than that in region A. O2 fluxes in the different regions show that approximately 90% of O2 molecules reach the Pt cube and tetrahedron nanoparticles via their upper corner and edge regions. In the vicinity of Pt nanoparticles, O2 permeation routes are inferred to penetrating region B to the Pt upper corners or edges instead of region A to the Pt facets.

De Novo Design of Covalent Organic Framework Membranes toward Ultrafast Anion Transport.

The emergence of all-organic frameworks is of fundamental significance, and designing such structures for anion conduction holds great promise in energy conversion and storage applications. Herein, inspired by the efficient anion transport within organisms, a de novo design of covalent organic frameworks (COFs) toward ultrafast anion transport is demonstrated. A phase-transfer polymerization process is developed to acquire dense and ordered alignment of quaternary ammonium-functionalized side chains along the channels within the frameworks. The resultant self-standing COFs membranes exhibit one of the highest hydroxide conductivities (212 mS cm-1 at 80 °C) among the reported anion exchange membranes. Meanwhile, it is found that shorter, more hydrophilic side chains are favorable for anion conduction. The present work highlights the prospects of all-organic framework materials as the platform building blocks in designing ion exchange membranes and ion sieving membranes.

Multi-functional anodes boost the transient power and durability of proton exchange membrane fuel cells.

Proton exchange membrane fuel cells have been regarded as the most promising candidate for fuel cell vehicles and tools. Their broader adaption, however, has been impeded by cost and lifetime. By integrating a thin layer of tungsten oxide within the anode, which serves as a rapid-response hydrogen reservoir, oxygen scavenger, sensor for power demand, and regulator for hydrogen-disassociation reaction, we herein report proton exchange membrane fuel cells with significantly enhanced power performance for transient operation and low humidified conditions, as well as improved durability against adverse operating conditions. Meanwhile, the enhanced power performance minimizes the use of auxiliary energy-storage systems and reduces costs. Scale fabrication of such devices can be readily achieved based on the current fabrication techniques with negligible extra expense. This work provides proton exchange membrane fuel cells with enhanced power performance, improved durability, prolonged lifetime, and reduced cost for automotive and other applications.

Mechanism of Water Content on the Electrochemical Surface Area of the Catalyst Layer in the Proton Exchange Membrane Fuel Cell.

Combined molecular dynamics (MD) simulation and experiment are adopted to gain the mechanism of water content on the electrochemical surface area (ECSA) of the catalyst layer in a proton exchange membrane fuel cell. The morphology of water domains in the catalyst layer has a strong impact on the ECSA via MD simulation. The morphology of the water domains is isolated water clusters at low water content, resulting in the poor ECSA due to the lack of proton transport paths. The transport paths of protons tend to be quickly established with increasing water content during the transition process of the morphology of water domains from isolated water clusters to the water channel network, thereby leading to the rapid increase of the ECSA. However, the slight increase of the ECSA at high water content mainly results from the improved contact area between water domains and Pt particle instead of the formation of new transport paths. In addition, the stronger binding of water molecules and the Pt particle at low temperature results in a higher ECSA.

Isolation and purification of a novel antimicrobial peptide from Porphyra yezoensis.

We aimed to isolate antimicrobial peptides from Porphyra yezoensis. Enzymatic hydrolysate of P. yezoensis was purified by ultrafiltration, molecular sieve chromatography, and ion exchange chromatography sequentially. A novel peptide with strong antimicrobial activity against Staphylococcus aureus was isolated and the amino acid sequence was identified to be Thr-Pro-Asp-Ser-Glu-Ala-Leu (TPDSEAL). Physical and chemical properties and antimicrobial activity of the peptide were determined. The antimicrobial mechanism was studied. The antimicrobial activity of TPDSEAL kept stable under acidic or basic conditions, high temperature, and ultraviolet radiation. The antimicrobial mechanism of antimicrobial peptides may damage the cell wall and membrane, and enhance the permeability of cells, which leads to the outflow of intracellular substances and death of bacteria. This study provides novel insight into the preparation of marine-derived antimicrobial peptides. PRACTICAL APPLICATIONS: Antimicrobial peptides, which act as defensive weapons against microbes, have been broadly used as food additives in food industry. Due to the limited amount of natural antimicrobial peptides in organisms and the high cost of chemical synthesis, producing novel natural antimicrobial peptides with bioengineering methods has become an urgent task. In the present study, we prepared a novel antimicrobial peptide from pepsin-digested hydrolysate of Porphyra yezoensis using ultrafiltration, molecular sieve chromatography, ion exchange chromatography, and mass spectrometry analysis. A novel peptide with strong antimicrobial activity against Staphylococcus aureus was isolated and the amino acid sequence was identified to be Thr-Pro-Asp-Ser-Glu-Ala-Leu (TPDSEAL). The identified peptide exhibits great stability under acidic or basic conditions, high temperature, and ultraviolet radiation. Mechanism revealed that TPDSEAL treatment may damage the cell wall and membrane, enhance the permeability of cells, and lead to the death of bacteria. Our study provides the novel insight into the preparation of marine-derived antimicrobial peptides.

Magnetic field alignment of stable proton-conducting channels in an electrolyte membrane.

Proton exchange membranes with short-pathway through-plane orientated proton conductivity are highly desirable for use in proton exchange membrane fuel cells. Magnetic field is utilized to create oriented structure in proton exchange membranes. Previously, this has only been carried out by proton nonconductive metal oxide-based fillers. Here, under a strong magnetic field, a proton-conducting paramagnetic complex based on ferrocyanide-coordinated polymer and phosphotungstic acid is used to prepare composite membranes with highly conductive through-plane-aligned proton channels. Gratifyingly, this strategy simultaneously overcomes the high water-solubility of phosphotungstic acid in composite membranes, thereby preventing its leaching and the subsequent loss of membrane conductivity. The ferrocyanide groups in the coordinated polymer, via redox cycle, can continuously consume free radicals, thus helping to improve the long-term in situ membrane durability. The composite membranes exhibit outstanding proton conductivity, fuel cell performance and durability, compared with other types of hydrocarbon membranes and industry standard Nafion® 212.

Game-Based Memetic Algorithm to the Vertex Cover of Networks.

The minimum vertex cover (MVC) is a well-known combinatorial optimization problem. A game-based memetic algorithm (GMA-MVC) is provided, in which the local search is an asynchronous updating snowdrift game and the global search is an evolutionary algorithm (EA). The game-based local search can implement (k,l)-exchanges for various numbers of k and l to remove k vertices from and add l vertices into the solution set, thus is much better than the previous (1,0)-exchange. Beyond that, the proposed local search is able to deal with the constraint, such that the crossover operator can be very simple and efficient. Degree-based initialization method is also provided which is much better than the previous uniform random initialization. Each individual of the GMA-MVC is designed as a snowdrift game state of the network. Each vertex is treated as an intelligent agent playing the snowdrift game with its neighbors, which is the local refinement process. The game is designed such that its strict Nash equilibrium (SNE) is always a vertex cover of the network. Most of the SNEs are only local optima of the problem. Then an EA is employed to guide the game to escape from those local optimal Nash equilibriums to reach a better Nash equilibrium. From comparison with the state of the art algorithms in experiments on various networks, the proposed algorithm always obtains the best solutions.

Direct Electrochemical Vibrio DNA Sensing Adopting Highly Stable Graphene-Flavin Mononucleotide Aqueous Dispersion Modified Interface.

A biofunctionalized graphene nanohybrid was prepared by simultaneously sonicating graphene and riboflavin 5'-monophosphate sodium salt (FMNS). FMNS, as a biodispersant, showed an efficient stabilization for obtaining highly dispersed graphene nanosheets in an aqueous solution. Due to the superior dispersion of graphene and the excellent electrochemical redox activity of FMNS, a direct electrochemical DNA sensor was fabricated by adopting the inherent electrochemical redox activity of graphene-FMNS (Gr-FMNS). The comparison between using traditional electrochemical indicator ([Fe(CN)6]3-/4-) and using the self-signal of Gr-FMNS was fully conducted to study the DNA-sensing performance. The results indicate that the proposed DNA-sensing platform displays fine selectivity, high sensitivity, good stability, and reproducibility using either [Fe(CN)6]3-/4- probe or the self-signal of Gr-FMNS. The two methods display the same level of detection limit: 7.4 × 10-17 M (using [Fe(CN)6]3-/4-) and 8.3 × 10-17 M (using self-signal), respectively, and the latter exhibits higher sensitivity. Furthermore, the sensing platform also can be applied for the DNA determination in real samples.