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The limited lifetime and severe degradation after long-term usage of polymer electrolyte membrane fuel cells (PEMFCs) are challenges that have to be overcome, if PEMFCs are to play the anticipated major role in a sustainable energy and transportation system based on green hydrogen. Therefore, analytical scanning methods to precisely characterize and understand the degradation and ageing mechanisms with high spatial resolution are essential. We are using and validating scanning electrochemical microscopy (SECM) as tool for detecting descriptors of the electrochemical performance of PEMFCs treated under different activation and ageing protocols. For this purpose, a pristine Nafion™ membrane, which is typically used as proton exchange membrane (PEM) in low temperature fuel cells, was activated and deactivated after well-defined protocols to demonstrate the fundamental suitability of SECM for investigating PEMFC components. Our results indicate that the impedance associated with the proton conductivity of the Nafion™ membrane as measured by SECM was dependent on the pretreatment of the membrane and increased in the following order: hot water < hydrochloric acid < sulfuric acid. The partial and complete deactivation of the membrane using Fenton’s reagent and barium hydroxide, respectively, could be spatially visualized with SECM as well. In addition, we investigated a PEM as part of a complete membrane electrode assembly in a fully functional PEMFC after accelerated ageing tests and could identify an increased local PEM impedance by SECM. All trends could be confirmed by electrochemical impedance spectroscopy (EIS). Moreover, we investigated a typical gas diffusion layer (GDL) of a PEMFC with SECM. As a result, the microporous side of the GDL showed a much lower impedance than its macroporous side, which is comprehensible since it agrees with the additional carbon black coating on the former side.
In this work, a spatially resolved analytical method based on scanning electrochemical microscopy (SECM) to distinguish different degradation phenomena in polymer electrolyte membranes was developed. SECM was combined with a Franz diffusion cell to distinguish between radical-induced aging of a sulfonated tetrafluoroethylene based fluoropolymer-copolymer due to deactivation of the sulfonic acid groups followed by a decreased proton conductivity, and the radical-induced formation of cracks and holes in the polymer. The experiments were performed with ferrocyanide as redox mediator to detect holes and cracks, and protons (sulfuric acid) to determine the through-plane proton conductivity, respectively. A pristine Nafion™ membrane, a pristine Nafion™ membrane with an artificial pinhole and a Nafion™ membrane aged with Fenton's reagent were investigated to prove the measurement principle. It could be shown that holes and cracks can be reliably detected with this approach and discriminated from a change in proton conductivity. The presence of holes in the investigated aged membranes was confirmed by scanning electron microscopy, whereas the loss of sulfonate groups could be supported by infrared spectroscopy measurements.
A DNS of the turbulent flow and heat transfer in an idealized Czochralski configuration was conducted using a very fine grid. The results show the irregular forming of buoyant thermal plumes as well as the occurrence of a large, stable vortical structure in the bulk of the melt. In the averaged flow field a B´enard-cell-like pattern can be recognized. The DNS data served also as a reference for the validation of the LES method. The LES computations were conducted using different grid sizes, SGS models, and discretization methods. For relatively fine grids and central differences, the results agree very well with the DNS. Using an upwind discretization introduces numerical errors. In combination with coarser grids, this leads to large deviations and even qualitative differences. However, overall the computational effort could be reduced significantly by LES. Thus a compromise between accuracy achieved and effort required has to be found.
In the literature, numerical computations of the Czochralski process for crystal growth are conducted using a quasi-steady state assumption for the crystallization neglecting time-dependent effects. In the present work, an algorithm is developed, which allows to calculate the transient behavior of the crystallization interface including the movement of the three-phase boundary and the free surface of the melt. Thus, in conjunction with the computation of the turbulent melt flow and heat transfer, more realistic predictions of the crystal growth can be achieved. Test cases show that with the algorithm, realistic phenomena like crystal diameter increase and decrease during the growth process could be reproduced.
In the literature, numerical computations of the Czochralski process for crystal growth are conducted using a quasi-steady state assumption for the crystallization neglecting time-dependent effects. In the present work, an algorithm is developed, which allows to calculate the transient behavior of the crystallization interface including the movement of the three-phase boundary and the free surface of the melt. Thus, in conjunction with the computation of the turbulent melt flow and heat transfer, more realistic predictions of the crystal growth can be achieved. Test cases show that with the algorithm, realistic phenomena like crystal diameter increase and decrease during the growth process could be reproduced.
Current crises (i.e., climate crisis, COVID-19 pandemic, Russian invasion of Ukraine, and the resulting energy and food shortages) indicate the need for robust, and sustainable supply chains with regional food production and farmland to secure food supply in the European Union (EU). Recent research shows that organic food is more resilient to supply chain disruptions and price fluctuations. In this context, we examine an approach for the sustainable and resilient transformation of agri-food networks: can an adaptation of value added tax (VAT) levels work as a financial incentive to amplify resilient agricultural practices and sustainable dietary patterns? Within the setting of the amendment of the European framework directive on the use of VAT in 2022, we model the effects of adapting the current German VAT system by (1) reducing VAT on organic vegetarian food to 0% and (2) raising VAT on conventional meat and fish to 19%. Based on historical data on organic sales shares and price elasticities, we project sales shares differentiated by product group for each scenario. Then, we calculate expected tax revenues, changes in consumption patterns, and arising total external climate costs in Germany for both scenarios. Our results show that the overall consumption share of organic food would increase by 21.83% due to the modeled VAT reform compared to the status quo. Despite the VAT reduction to 0% on organic vegetarian products, the measure would yield €2.04 billion in extra tax revenues in Germany per year due to the increased taxation on conventional meat products. We find that annual environmental costs of €5.31 billion can be avoided as a result of lower external climate costs of organic and vegetarian food. Therefore, adjusting VAT rates in the food market can be a political instrument to drive organic food consumption and reduce animal livestock. This supports re-territorialization of agriculture and a more sustainable and resilient European food supply.
Delta-winglet vortex generators (VGs) are known to enhance the heat transfer between the energy-carrying fluid and the heat transfer surfaces in plate-fin-and-tube banks. In this study optimal angles of attack of the delta-winglets are investigated based on the Pareto optimal strategy. The optimization process combines a CFD analysis, genetic algorithms and the response surface methodology. The angle of attack of a pair a delta-winglet-type VGs mounted behind each tube is varied between β = −90° and +90°. Three circular tube rows with inline and staggered tube arrangements are investigated for Reynolds numbers from 200 to 1200 (based on the inlet height and inlet velocity). The flow structure and heat transfer behavior is analyzed in detail for certain cases and the staggered and the inline tube arrangements are compared. Finally, for each of these arrangements the optimal sets of angles of attack for different Reynolds numbers are presented.
Climate change and its damaging consequences for ecology and humanity is advancing. Industry and its metals sector are responsible for most greenhouse gas emissions. Current costs of industrial goods do not reflect the true costs caused by the externalized climate damages of its production and thus offer no competitive incentive to decarbonize. Additionally, regional climate regulation can lead to competitive distortion. We therefore aim to investigate the impact of climate cost internalization on the metals industry. Using true-cost analysis for an exemplary and widely used metal product, the effects of climate true costs depending on production region, technology, and energy mix, CO2e taxation and value chain are examined. Based hereon, the impact of internalizing climate true costs together with the introduction of a carbon-border tax on the carbon leakage problem, climate protection, and the cost situation for companies in global competition are investigated. The results of the study show that steel and wire production is responsible for most CO2e emissions showing significant decarbonization effects by steel recycling whereas production location and logistics play a minor role. On a competitive level, cost internalization has hardly any effect on the product costs because of the currently low CO2e-taxation rates. Thus, almost no incentive to produce or consume in a climate-protective way is generated, incentivizing production in pollution havens versus highly climate regulated regions. Instead, to realize emission efficiency gains and innovations leading to a competitive advantage of decarbonized products and value chains, a significant increase of CO2e-taxation rates together with a carbon-border tax is necessary.
This paper introduces a model predicting the unsteady conditions in vertical pipes of a steam power station during start up of the plant. Knowing the time depending variation in the rate of condensation in the pipe is helpful for optimizing the design of the drainage system, which removes the condensate collected from the pipes. At present this system is designed on the basis of the total amount of condensate produced in a particular pipe during start up of the power plant. The model presented will provide a design based on the true maximum flow rate during said period. The paper describes the mass and energy balances for the gas and the condensate as well as the energy balance for the wall. All equations are transformed into a set of differential and algebraic equations and solved at once. The model was subsequently applied on genuine industrial scenarios. The results obtained from the model are discussed in detail and compared with experimental data. In all situations considered, the maximum condensate flow rate calculated was less than 50% of the estimated value using standard design methods.
The Anthropocene, marked by human-induced climate change, necessitates urgent action to address climate goals and respect planetary boundaries. While sustainability research provides knowledge, the first challenge lies in communicating the findings in an adequate manner to the public and several stakeholders, such as economic and political actors. Therefore, this study explores the significance of science communication in sustainability science, focusing on a case study—the True Cost Accounting (TCA) campaign by the University of Greifswald, Technical Institute of Nuremberg, and German retailer PENNY. TCA herein serves as a transparency tool, economic incentive, and discussion basis for sustainable consumption. This study investigates consumer perceptions of ecological prices of foods through a face-to-face survey during the 2023 PENNY campaign, comparing results to an informational campaign carried out in 2021. Findings indicate a high awareness of the true cost campaign in 2023, with 50.8% of participants hearing about it. Consumers’ willingness to pay true costs and potential behavior changes were explored. In comparison to results from the informational campaign of 2021, customers showed a decrease in this WTP when the true prices would actually impact their spending, indicating an attitude–behavior gap. In addition, a willingness to reduce the consumption of animal foods—if TCA was implemented—of 60.5% was determined, suggests that TCA has the potential for sustainable behavior change. This study highlights factors that influence consumer attitudes and preferences regarding the inclusion of TCAs, such as environmental, social, and animal welfare costs. Customers’ understanding of increased prices like,
in this case, the compensation for environmental and social costs—is an argument in favor of true prices. The results emphasize the need for differentiated scientific communication strategies to bridge knowledge and action gaps in sustainability science.