•Reviewed the degradation mechanisms for PEM fuel cells.•Summarized the steady-state durability test results and experimental conditions.•Evaluated the in-situ accelerated stress test results and ...protocols.•Scrutinized the ex-situ accelerated stress test results and experimental techniques.
Durability is one of the most significant technical barriers to successful commercialization of polymer electrolyte membrane (PEM) fuel cells for practical vehicular applications. It is determined by the aging (degradation) and malfunction of various components during the long-term operation. Therefore, understanding the mechanisms of degradation modes in different components is crucial to the development of high-performing and long-lasting PEM fuel cells. In this review article, the critical degradation modes in major cell components, including membranes, catalyst layers, gas diffusion layers, and distribution plates, are comprehensively reviewed and analyzed, and the potential causes are described. Advanced experimental techniques to investigate the PEM fuel cell degradation modes reported in literature include steady-state durability tests and accelerated stress tests (ASTs). The steady-state durability test is straightforward but time-consuming and costly; therefore, ASTs are often applied to accelerate durability testing. For comparable results among different research studies, the experimental protocols and conditions have to be consistent, and the details of these experimental techniques are systematically reviewed in this article. The experimental results with a focus on the degradation modes, degradation rate, and test time of the PEM fuel cells have been reported. Finally, in order to understand the root causes of degradation modes and to develop the mitigation strategies, ex-situ ASTs in literature have been reviewed, including the effects of cyclic temperature, humidity, water wet-dry, freeze-thaw, clamping stress, and vibration operations.
•Durability of concrete with different types of carbon nanotubes (CNTs) was analysed.•Mechanical strength and durability properties could be improved as much as 25%.•CNTs were more efficient in ...tested properties under cracking conditions.•Oxidized CNTs showed lower to similar behaviour of pristine CNTs.•Nucleation and microcrack bridging of CNTs were shown by SEM and TG analysis.
In this study the durability of concrete reinforced with different types of multi-walled carbon nanotubes (CNTs) is analysed. One type of acid treated CNTs and two types of pristine CNTs with distinct aspect ratios were analysed. Common structural concrete with various w/c ratios were produced and characterized regarding immersion and capillary water absorption and carbonation and chloride penetration resistance. Results show the potential of CNTs contribution to the enhancement of mechanical and durability properties of concrete, regardless of the type of CNTs and w/c ratio. The incorporation of 0.05–0.1% CNTs, by weight of cement, improved mechanical strength and durability properties up to 21% and 25%, respectively. The incorporation of CNTs was more effective when concrete was subjected to cracking conditions. In general, the best performance was found in concrete with higher amounts of CNTs of lower aspect ratio. Functionalized CNTs showed lower to similar behaviour to pristine CNTs of identical aspect ratio. The crack bridging and nucleation effect provided by CNTs was confirmed by SEM and thermogravimetric analysis.
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•La0.5Ba0.5CuxFe1−xO3−δ is used as a cathode for H-SOFC on BZCY electrolyte.•Thermal expansion, oxide-ion and proton conductivity varies with the Cu/Fe ratio.•An initial power density ...exceeding 820 mW cm−2 is obtained at 700 °C.•Increase in the ohmic rather than polarization resistance dominates the degradation.
La0.5Ba0.5CuxFe1−xO3−δ (0 ≤ x ≤ 1) perovskite was investigated as a cathode for a protonic solid oxide fuel cell (H-SOFC) using BaZr0.1Ce0.7Y0.2Oδ (BZCY) electrolyte. A maximum electric conductivity (76.84 S cm−1 at 700 °C) was achieved in the air at the composition of La0.5Ba0.5Cu0.4Fe0.6O3−δ. Comparing to La0.5Ba0.5CuO3−δ (LBC), the increase in Fe content increased the Dchem (1.07x10−5 to 1.74x10−5 cm2 S−1) and Kchem (1.12x10−10 to 3.01x10−10 cm2 S−1) at La0.5Ba0.5Cu0.2Fe0.8O3−δ (LBCF28) but decreased the proton conductivity from 7.5 to 4.3 mS cm−1. Either Fe doping in LBC or Cu doping in La0.5Ba0.5FeO3−δ increased the thermal expansion coefficient (TEC), but a low TEC among samples with mixed cations was achieved at La0.5Ba0.5Cu0.5Fe0.5O3−δ (LBCF55) (16.12 ppm K−1). LBC suffered from superficial decomposition in the ambient air, causing an ohmic resistance loss of the full cell on Ni(O)-BZCY support. A high initial cell performance (820 mW cm−2) can be achieved for the cell with LBCF55 and LBCF28 cathode but the latter was unstable under a cathodic bias owing to the increase in ohmic resistance owing to the production of intermediate layer between electrode and electrolyte. With better stability than LBCF28 and higher performance than LBC, LBCF55 was regarded as a viable cathode material for H-SOFC. This work explores systematically the behavior of a perovskite with mixed Cu and Fe cations as a cathode for H-SOFCs.
Research into the extreme feats of endurance that humans and some animals achieve has uncovered a range of metabolic and physiological adaptations along with their evolutionary origins.
This study explores the novel production dependent characteristics of ready-to-eat whole pulse flakes from desi chickpea splits. The research investigates a three-stage process: minimal live steam ...conditioning, precise rolling, and rapid fluidised bed drying. Effects of steam time (1, 3, 5 min), roller gap (0.5–0.8 mm, 0.8–1.3 mm), and drying temperature (150 °C, 200 °C) on flake quality were examined. These conditions altered flake appearance, with optimal roller settings maintaining the aspect ratio within 10% of the original split. Steam time increased starch gelatinisation by 21–31%, while longer steaming and wider roller gaps decreased water absorption, improving bowl life. Drying at 200 °C accelerated moisture loss, reducing durability of 5-min steamed flakes. The study demonstrates that tailored processing can yield viable chickpea flakes comparable to whole grain cereals. These findings have significant implications for the food processing industry, offering a pathway to develop nutritious, pulse-based ready-to-eat products.
•Pilot scale production of pulse flakes from Desi Chickpeas.•Chickpea flakes produced from direct steam heat, rolling and fluid bed drying treatments.•Treatments changed the flake shape, puffing, Pfost durability and bowl life.•Treatments controlled gelatinisation level and pasting viscosity.
As luxury fashion brands need to address the environmental impact of their products (both internally and externally), a framework to achieve a common and accessible language becomes paramount to ...avoid confusing claims. Tools, such as Life Cycle Assessment and Eco-Design, help companies assess and reduce the negative effects of their products on the environment; nonetheless, more work is needed. The desire to create durable goods is a direct reaction to the current throw-away culture perpetuated by planned obsolescence during the production phase of many fast-fashion brands. However, without a proper understanding of the term ‘durability’ and its different dimensions, a common language cannot be adopted by the various actors in the value chain (both up- and down-stream). Particularly, the characteristics of terms such as ‘resilience’ are mistakenly confused with those of ‘durability.’ Here, we review the literature from 2011 to date for determining clear definitions for both terms. A self-developed analysis framework was used for the systematic review of the literature, slightly adapting the methodology from an established process. The different levels (A, B, and C) of the framework reveal, in a structured manner, what a ‘durable’ or ‘resilient’ product is (at every stage of its lifecycle). We show that two dimensions should be considered for both concepts: ‘intrinsic’ (also referred to as ‘physical’ in the existing literature) and ‘extrinsic’ (often referred to as ‘emotional’). Most authors fail to acknowledge the existence of both terms or use them inconsistently. Consequently, a thorough assessment of product durability and resilience is lacking, as studies have focused solely on one of the two dimensions or on a single lifecycle stage (most often the design phase) of a product. Thus, beyond its original aim, our model analysis framework can also help evaluate the environmental impact of luxury fashion products at each stage of their lifecycle.
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•The use of an intrinsic and extrinsic dimension is preferred over physical and emotional.•Resilience differs from durability and enables products to bounce back from environmental changes.•All the lifetime stages should be considered to assess a product's durability and resilience.•The analysis framework can serve as a working tool for environmental impact assessment.
The degradation mechanisms of natural fiber in the alkaline and mineral-rich environment of cement matrix are investigated. Cement hydration is presented to be a crucial factor in understanding fiber ...degradation behavior by designing a contrast test to embed sisal fibers in pure and metakaolin modified cement matrices. In addition to durability of sisal fiber-reinforced cement composites determined by means of flexural properties, degradation degree of the embedded fibers is directly evaluated by proposing a novel separation approach. The results indicate that, by reducing alkalinity of pore solution, metakaolin effectively mitigates the deterioration of natural fiber. By combining results of thermogravimetric analysis and microstructure, the alkali degradation process of natural fiber, which consists of hydrolysis of lignin and hemicellulose, stripping of cellulose microfibrils and deterioration of amorphous regions in cellulose chains, is visually presented. Two new concepts of mineralization mechanism, calcium hydroxide (CH)-mineralization and self-mineralization, are also proposed and quantitatively characterized.
3D printed concrete (3DPC) creates opportunities, including a reduction in construction waste and time and increased design freedom. However, because of the differences in the construction technique ...compared to traditional concrete casting, the structures also perform differently; namely, the micro- and meso-structure and durability are shown to be different. For the 3DP technology to find its way to the market, one needs to be aware of these differences and needs to know how to quantify the above-mentioned properties, as differences in the testing methodologies impose themselves when characterizing printed instead of cast concrete. In this paper, we elaborate on the test methods to investigate the micro- and meso-structure and the durability of 3DPC. We start with a discussion on the micro- and meso-structure of the 3D printed concrete and how it is different from conventional mold-cast concrete. An in-depth discussion of the test methods to assess the durability of 3D printed concrete is outlined. Reported findings related to the two aforementioned properties are discussed. In addition, we report on the technologies proposed to improve the durability performance of 3DPC, and we highlight the remaining challenges and opportunities related to 3DPC.
Geopolymer (GP) binders are an appealing alternative to Portland cement (PC) binders as they have the potential to reduce the CO2 emissions associated with the cement and concrete industry. However, ...their durability in aggressive environments needs thorough examination if they are to become a viable alternative to traditional PC materials. This study investigated the effect of increasing slag content and activator dosage on the sulfuric acid resistance of fly ash GP binders. Their performance was also compared with that of neat PC mixes using various physical and microstructural techniques. The results show that increasing the slag content of fly ash GPs decreases porosity, but makes the reaction products more susceptible to sulfuric acid attack. It was also found that increasing the alkaline activator dosage of fly ash GPs has little impact on sulfuric acid resistance. Finally, GP binders displayed superior sulfuric acid resistance than their PC counterparts.
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