Search

Recent research into anion exchange membrane fuel cells (AEMFCs) highlights challenges in achieving high performance, primarily due to poor water management. This study delves into how the structure and thickness of the catalyst layer, specifically the pore design, affect AEMFC efficiency. Our study reveals that H 2 /O 2 AEMFC performance is significantly influenced by the distribution and structure of anode porous sizes, which affects water generation and transport kinetics. It has become evident that, instead of oxygen availability at the cathode, the primary factors constraining AEMFC performance are water supply through back-diffusion and water flooding at the anode. Notably, by controlling the carbon content of the anode catalyst layer to create gradient pores, we successfully alleviate mass transport limitations of gases in AEMFCs, while simultaneously improving water transport. Furthermore, insights from surface water transport and detailed phase field model analysis further confirmed that these gradient pores enhance water transportation rates. These results indicate that the fabrication of a porosity-gradient anode catalyst layer using carbon powder significantly increased the limit current density by 24 % (from 4.10 W cm−2 to 5.20 W cm−2) and the power density by 34.6 % (from 1.56 W cm−2 to 2.10 W cm−2), compared to the catalyst layer without carbon powder. • Carbon powder creates a gradient pore structure in the anode layer. • This gradient pore structure markedly boosts AEMFC performance. • Gradient pores boost capillary pressure and water transport in the catalyst layer. • The impact of catalyst layer microstructure on transport processes is deeply analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tuning phases of MIL-100, MIL-110 and MIL-96 by applying formic acid as modulator. • Demonstrating the diversity of various ligands on node sites of MIL-110 and MIL-96. • Illustrating a highly flexible formate bonding site on Al 3 (OH) 3 unit of MIL-96. • Elucidating only a small fraction of node sites contributes to catalysis. Metal oxide cluster MOF nodes are a good platform to understand the reactivities and catalysis. MIL-96, MIL-100 and MIL-110 are drastically different in their node structures. Following our previous reported results for MIL-100, we report the modified synthesis and characterization of the node sites of MIL-110 and MIL-96 and their catalytic sites by using methanol dehydration as probe reaction. We show that these MOFs can be synthesized from the same solution by adding various amounts of formic acid as modulator. Herein, the chemistry of hydroxyl, formate and methoxy groups were used to probe the three MOFs' node sites. IR data show the bonding structures of these ligands are highly diverse, with reactivities and flexibilities depending on node sites. We identified terminal OH group and various µ 2 -OH groups in single, paired or hydrogen bonded modes on the MOF nodes. Formate ligands were introduced to the node sites during the synthesis or by a post treatment in formic acid/DMF solution. Surprisingly, the bonding modes of formate ligands on Al 3 (OH) 3 node structure of MIL-96 can be reversibly switched between monodentate and bidentate through a process induced by water molecules. Further, methoxy ligands—likely to be the intermediate for catalytic reaction—were also observed on the node sites under methanol dehydration conditions at 250 ℃. The activities of MIL-100 and MIL-96 for methanol dehydration determined by TOF per node were similar, both approximately 3-fold higher than that of MIL-110. The data suggests that catalytic sites incorporate adjacent vacancy and defect node sites, which constitute a minority among all observed MOF node sites. We foresee the opportunities in expanding the chemistry and understanding into other MOFs with metal oxide cluster nodes. [ABSTRACT FROM AUTHOR]

• CH 4 and HCl vied for adsorption at the same active sites on the OC surface. • Service life of OC declined to 1136 h due to the formation of crystal islands. • Diffusion resistance of CH 4 into the inner region of HCl-treated OC was reduced. In chemical looping combustion (CLC) of coal, HCl has been demonstrated as the primary gaseous products of the chlorine in coal. Therefore, a comprehensive characterization of Cu-based oxygen carriers (OC) by HCl corrosion was meticulously conducted, including the activity retention, composition distribution and apparent morphology. The experiment consisted of three parts: (I) evaluating of the OC performance for 100 redox cycles with 7.8 vol% CH 4 ; (II) investigating HCl-corrosion of OC by adding 50 ppmv HCl with 7.1 vol% CH 4 for the subsequent 50 cycles; (III) regenerating of OC without HCl addition during the last 50 cycles. The reactivity of OC was attenuating via the HCl addition during the 101st–150th cycles (part II) due to the competition adsorption between HCl and CH 4 , especially for the partly reduced OC. While, in part III, the reactivity performance of OC was partially recovered because of the abundant cracks on the surface of OC particles which ensured the sufficient gas–solid contact. It should be noted that the single particle hardness index and service life were irreversibly decreased for the HCl-treated OC. Moreover, OC particles were fragmented and the inside Al 2 O 3 balls were exposed on the surface of the HCl-treated OC in SEM image. This work will contribute to understanding the mechanism of Cl-corrosive OC and designing the Cl-resistant OC. [ABSTRACT FROM AUTHOR]

Anion exchange membrane fuel cells (AEMFCs) are a promising power source due to zero emissions and high efficiency, and low precious metal loading. However, water management remains a significant issue affecting cell performance and durability. In this study, we develop a multi-physics model to investigate and optimize transport phenomena under various operational conditions and microstructure parameters. The agglomerate model is optimized to consider the influence of anode flooding and cathode drying in electrochemical reactions, and the simulation is validated with experimental results. Our findings indicate that an optimal anode inlet gas relative humidity of 80% achieved a tradeoff between anode flooding and ionic conductivity, resulting in a maximal power density of 758.9 mW/cm2. To alleviate anode flooding, we optimize the microstructure of the anode gas diffusion layer, significantly improving maximal power density to 833.4 mW/cm2 by increasing the contact angle to 130°. The optimal porosity achieves a balance between the transport of liquid water and electron. Large pore diameter and small thickness lead to a slighter anode flooding and higher maximal power density. In summary, our study provides insights into the transport behavior of multi-phase water, reactant gas, ion, and electron to guide the design of high-performance AEMFCs. • AEMFCs model is developed and validated with experimental data. • A modified agglomerate model with a catalyst utilization factor is proposed. • Anode flooding and cathode drying phenomenon are analyzed in detail. • Microstructures of GDL are optimized to enhance liquid water transport. [ABSTRACT FROM AUTHOR]

[Display omitted] • The concept of "metal coverage" is put forward to link with reversal tolerance. • The higher metal coverage causes a longer reversal time and slower degradation rate. • Ir/Pt/C shows more than 50 times longer reversal time than Pt/Ir/C counterparts. • Ir/Pt/C displays two orders of magnitude slower degradation rate than Pt/Ir/C. Anode cell reversal, which is caused by fuel starvation, poses a great threat to the durability of proton exchange membrane fuel cells. Commercially, iridium oxide or iridium is applied to boost oxygen evolution reaction, which alleviates carbon corrosion and protects the catalyst layer structure. However, the key factors that affect the anti-reversal ability and the interaction between Pt, Ir, and carbon support are still unclear. Hence, we systematically studied the performance using three typical carbon supports with three metal contents and different metal deposition orders by experiments and model calculations. A new parameter, "relative metal coverage", is put forward to evaluate and predict the anti-reversal ability, showing higher relative metal coverage results in a longer reversal time and lower polarization performance degradation rate. Typically, only a 15.5% polarization performance loss after 1700 mins reversal time when the relative metal coverage of high metal content Ir/Pt/Super P anode is one. The results suggest that increasing relative metal coverage is a practical approach to improve reversal tolerance and provide new insights into the reversal tolerant anodes design. [ABSTRACT FROM AUTHOR]

• A comprehensive transient axial-symmetric model was developed for the solar thermochemical reactor. • The electrochemical oxygen pump (EOP) with the lowest energy penalty was employed to reduce the oxygen partial pressure. • Reactor performance for EOP scheme and other two traditional schemes (i.e., SG scheme and VP scheme) was compared in detail for different DNI conditions. • Two control strategies were proposed to increase the solar-to-fuel efficiency. Solar thermochemical water splitting provides an efficient route for converting solar energy into renewable fuels. The operation of solar thermochemical reactor under real on-sun condition requires in-depth understanding of its dynamic behaivor under fluctuating direct normal irradiation (DNI). In this work, we developed a 2D axial-symmetric multi-physical model to assess the reactor's dynamic behavior with three oxygen removing technologies electrochemical oxygen pump (EOP), sweep gas (SG), and vacuum pump (VP), under varying solar irradiations. To alleviate the negative effect of decreased DNI, two control strategies (CS) including varying operational conditions for oxygen removing technologies (CS1) and replacing the reduction step with the oxidation step (CS2) were conducted. We found that CS1 was only effective when DNI reduction was larger than 75 % over the whole reduction step (case 2). In general, CS2 can be implemented to alleviate the efficiency decrease for all DNI variations expect for the case 2 in this study. Especially, CS2 significantly increased the solar-to-fuel efficiency compared to the case without control strategy for the reduced DNI from 1000 W/m2 to 500 W/m2 during the whole reduction step. The reactor dynamic behavior in response to the daily DNI variations is also reported which shows that the efficiency profiles are highly in line with the DNI profile. This modeling work as well as proposed control strategies can be used to guide the design and control of solar thermochemical reactors under realistic conditions and hence for better assessing the performance of the reactor in practice. [ABSTRACT FROM AUTHOR]

• A high fidelity and cost-effective 3D model is developed for high-temperature solar cavity receivers. • A novel radiative transfer model based on modified P1 approximation was proposed and implemented. • Effects of material, geometrical, and operational conditions on solar thermal conversion performance are investigated. • The solar-to-thermal efficiency can be improved by 23% with optimized operational conditions. High-temperature solar receivers are core components in concentrated solar energy utilization systems. The rational design of solar receivers relies on the fundamental understanding of coupled physics across various scales. We developed a numerical model to assess the solar thermal conversion behaviour under various porous structure designs, material choices, geometrical designs, as well as operational conditions. The 3D model solves a coupled set of equations accounting for mass, momentum, and energy conservations in the cavity and porous media domains. We have optimized the radiative transfer model to resolve the participating behaviour only in the porous domain and non-participating behaviour only for cavity and window surfaces. This cost-effective model enables fast performance evaluation for various design parameters. The windowless receiver, in general, shows higher solar-to-thermal efficiency compared to the window receiver. This superiority in optical efficiency for the windowless case can be surpassed by the window case at high incident solar power with a fixed outlet temperature. For porous media structure, both window and windowless receivers are optimized by the porosity and pore diameter. The solar-to-thermal efficiency was slightly influenced by the cavity inclination. Large porous layer thickness leads to reduced performance for the windowless receivers, while the efficiency reaches a plateau for the window receiver at large thickness. We have provided a comprehensive modeling framework for the design of solar receivers for high-temperature applications using concentrated solar energy which can be easily adapted for receiver under a wide range of designs and operation conditions. [ABSTRACT FROM AUTHOR]

In plants, Long-chain acyl-CoA synthetases (LACSs) play key roles in activating fatty acids to fatty acyl-CoA thioesters, which are then further involved in lipid synthesis and fatty acid catabolism. LACSs have been intensively studied in Arabidopsis , but its evolutionary relationship in green plants is unexplored. In this study, we performed a comprehensive genome-wide analysis of the LACS gene family across green plants followed by phylogenetic clustering analysis, gene structure determination, detection of conserved motifs, gene expression in tissues and subcellular localization. Our results identified LACS genes in 122 plant species including algae, low land plants (i.e., mosses and lycophytes), monocots, and eudicots. In total, 697 sequences were identified, and 629 sequences were selected because of alignment and some duplication errors. The retrieved amino acid sequences ranged from 271 to 1056 residues and diversified in intron/exon patterns in different LACSs. Phylogenetic clustering grouped LACS gene family into six major clades with distinct potential functions. This classification is well supported by examining gene structure and conserved motifs. Also, gene expression analysis and subcellular localization substantiate with clade division in the phylogeny, indicating that the evolutionary pattern is visible in their functionality. Additionally, experimental analysis of lacs2 mutant validated that LACS2 plays key roles in suberin synthesis. Thus, our study not only provides an evolutionary mechanism underlying functional diversification but also lays the foundation for further elucidation of the LACS gene family. • This is the first genome-wide identification of 629 LACSs genes in 122 plant species. • Phylogenetic analysis of LACSs genes shows six major clades with potential distinct functions. • LACSs genes present specific expression patterns across different tissues with different level. [ABSTRACT FROM AUTHOR]

Scour around a circular monopile in coastal regions has been investigated extensively over the past decades, but the time development of scour depth around an offshore-wind monopile under large current–wave ratio still lacks a predictive model. By considering the conservation of sand volume and adopting the conventional exponential law for temporal variation, a semi-empirical model, which has three parameters, i.e., an equilibrium scour depth, a shape coefficient and a scour characteristic time scale, is developed for predicting the time development of scour depth around a monopile under live-bed conditions of combined wave–current flows. A series of laboratory experiments was conducted in current-only and wave–current flows to obtain data for model calibration and validation. Experimental results indicate that adding weak waves on current accelerates scour development, which is successfully captured by the proposed model through using the far-field bottom shear stress as a key model input. The overall model inaccuracy is within 25%, and the model's applicability is further confirmed by field measurements from an offshore wind farm in east China. This model can help to determine the timing of installing scour protection around offshore monopiles, especially for the circumstances with very strong local sediment transport (live-bed). • A new model for scour time development around a circular pile is proposed. • A set of scour tests was conducted in live-bed conditions for calibration and validation. • A field study was carried out for an offshore monopile wind farm in eastern China. [ABSTRACT FROM AUTHOR]

[Display omitted] • CHSD and lactulose ameliorate STC through different mechanisms. • CHSD has a better effect on community diversity and richness than lactulose. • CHSD and lactulose result in differences in the SCFA composition in faeces. • CHSD and lactulose elevate stimulatory neurotransmitters and reduce VIP in serum. Slow transit constipation (STC) has become an epidemic medical problem. There are several kinds of drugs for constipation; however, each drug has its limitations. The gut microbiota has a close relationship with STC. Lactulose is an effective drug for constipation because it is a kind of bulking laxative and microbioecologic, and it relieves the syndromes of STC. We found that the Chinese Herb Solid Drink (CHSD), which contains medicine food homologous materials such as psyllium husk, sweet almond, semen sesami nigrum, and hemp seed, has a similar effect on relieving constipation as lactulose, although it has different effects on the gut microbiota. We investigated the mechanisms of CHSD in rats with STC, induced by diphenoxylate, via constipation index and enzyme linked immunosorbent assay (ELISA) analyses using serum and 16S rDNA amplicon and gas chromatography-mass spectroscopy (GC–MS). CHSD enhanced the relative abundance of some types of gut microbiota, such as Blautia , Ruminococcus , Roseburia, Coprococcus, Lachnospira, and Phascolarctobacterium , while lactulose enhanced the relative abundance of Blautia, Phascolarctobacterium , Eubacterium , and Akkernansia in diphenoxylate-induced STC rats. Both CHSD and lactulose enhanced the level of short-chain fatty acids in the faeces of rats; however, the composition of those were different between the two drugs. From the perspective of the gut neuroendocrine system, both CHSD and lactulose could elevate neurotransmitters, such as motilin (MTL) and substance P (SP), which promote intestinal peristalsis and reduce the expression of vasoactive intestinal peptide, which inhibits intestinal peristalsis in the serum of STC rats. CHSD could elevate gastrin expression, which also promoted intestinal peristalsis in serum, while lactulose did not have this effect. Our findings suggest that CHSD may be an effective and safe therapeutic choice for STC. [ABSTRACT FROM AUTHOR]