Économie circulaire | EPFL Graph Search

L'économie circulaire est un nouveau modèle économique à vision systémique. Les notions d'économie verte, d’économie de l'usage ou de l'économie de la fonctionnalité, de l'économie de la performance et de l'écologie industrielle font partie de l'économie circulaire. Une telle économie fonctionne en boucle, abolissant ainsi la notion de « déchet ». Son objectif est de produire des biens et services tout en limitant fortement la consommation et le gaspillage des matières premières, et des sources d'énergies non renouvelables. Selon la fondation Ellen MacArthur (créée pour promouvoir l'économie circulaire), il s'agit d'une économie industrielle qui est, à dessein, réparatrice et dans laquelle les flux de matières sont de deux types bien séparés : les nutriments biologiques, destinés à ré-entrer dans la biosphère en toute sécurité, et les nutriments techniques (), conçus pour être recyclés en restant à un haut niveau de qualité, sans entrer dans la biosphère

Interfacial engineering for competitive Dye-Sensitized Solar Cells production

Natalie Flores Diaz

Renewable energy deployment and implementation of a circular economy will play a crucial role in decreasing CO2 emissions to meet the target from the Paris agreement. Dye-sensitized solar cells (DSSCs) can be designed in various colors and transparency for building-integrated photovoltaics (BIPV). This emerging technology has gained significant attention for its remarkably high power conversion efficiency (PCE) under indoor lighting up to 34%. To improve the performance of DSSCs, various approaches to study and reduce the interfacial electron recombination from the conduction band of the semiconductor to the electrolyte were implemented in this thesis. One of the approaches was the design of a tandem electrolyte containing two redox species, the radical AZADO (AZ+/0) and the [Co(bpy)3]2+/3+ complex. DSSCs with tandem electrolytes showed increased open-circuit voltage (VOC) up to 1009 mV and enhanced PCE of 9.15%. The VOC enhancement was determined to result from the higher redox potential of (AZ+/0) and the slower electron recombination rate. These findings demonstrate the advantages of employing tandem electrolytes to improve the VOC and overall performance of DSSCs. To decrease the solvent's volatility and the interfacial electron recombination in cobalt-based electrolytes, hyperbranched networks (HB) were designed through a click thiol-ene reaction between a thiol-siloxane and an acrylate monomer. The formed polymers were denoted HB1 (thiol-siloxane and PEGMA) and HB2 (thiol-siloxane and PEGMA). The addition of 20% of HB polymers to a cobalt-based electrolyte retained up to 98% of their initial weight until 150°C. The devices employing 10%(v/v) of HB1 attained the highest PCE under AM1.5 of 8.52%, comparable to 9.36% for the cobalt reference electrolyte. All the HB-electrolytes presented higher VOC values than the cobalt reference due to an upward shift in the CB of TiO2 and longer electron lifetimes. It was determined that the HB-polymers reduce the electron recombination and enhance the photovoltaic performance under low light intensity leading to a PCE of 23.19% under 1000 lux compared to 20.37% for the Co-reference. We then developed a new dye, R7, with a strong electron-donating PAH core and BPT2 as the central building block and a bulkier HF donor to decrease electron recombination at the interface TiO2/electrolyte. We found that in the presence of a copper electrolyte, the dye R7 outperformed devices with R6. EIS revealed that the bulky HF-donor introduction effectively suppressed the electron recombination between the TiO2 surface and the redox shuttle. Additionally, we employed a co-sensitized system of R7+Y123 to reach the outstanding parameters of JSC of 16.15 mAcm-2, VOC of 1035 mV, FF of 0.76 to achieve a top PCE of 12.7%. To the best of our knowledge, this is the highest for copper-based DSSCs using a blue photosensitizer. Lastly, the interfacial phenomena in DSSCs with carbon counter electrodes (CCEs) and copper-based electrolytes were studied to determine the feasibility of the production of monolithic DSSCs with copper-based hole-transporting materials. It was found that the electron transport in devices with CCEs is in the same order of magnitude as those with PEDOT. However, the devices with CCEs presented a decrease of 2 orders of magnitude in the recombination resistance, resulting in decreased VOC and JSC, leading to a PCE of 17% compared to 24.5% for PEDOT devices under 1000 lux illumination.

EPFL2021

Seeking methods for improving sustainability in the extractive sector

Farnaz Eslamishoar

Extractive resources are indisputably a necessary component of international sustainable development. Despite current advancements in the circular economy, world production needs for raw materials are ever increasing, and still a long way remains for it to become rather independent from mineral resources. At the same time, mining has too many negative stories in news headlines about its trade-offs for the environment and human health, which hinders sustainable growth. This thesis deals with this integral dilemma in three chapters. In Chapter 1, I have made an extensive effort to understand the socio-political aspects of the mining business, both internationally and specifically in the context of a developing country, and on the issue of the corporate social responsibility the company requires. I then continued with gathering my primary sources of data for answering my first question: What are the primary social variables contributing to mining sustainability issues? I derived theories from Economic Growth in the Political Economy and Institutional Void from Management Science, trying to place my findings in a broader context. I concluded this chapter with underlying sociopolitical factors interfering with sustainable mining practices. This has led to the shaping of the second chapter of my thesis. Chapter 2 builds on the given that throughout the model of Economic Growth, technological change can happen within a shorter timeline and that new technologies lead to more efficiency in the Process Innovation. The mining industry is no exception. Yet, my quick review at the time revealed that this industry is lagging incumbent mainstream businesses in technological adoption. I therefore made my aim here to discuss conditions for transitions towards a more technologically innovative mining business. I surveyed mining firms internationally and noted the critical criteria for responsible practices. I then made what had been to my knowledge and ability, an exhaustive grouping of innovative technologies for the different sectors of mining firms. These tools granted me the ability to perform different multivariate analyses and decide on the best method for benchmarking different technology groups based on these criteria. In the later part of my thesis (Chapter 3), having these findings in hand and all experiences and observations in place with my assumptions, I decided to take one step back to ask whether the criteria I have for measuring mining sustainability are the correct measures by looking through the question using emerging data science tools. Are the sustainability scopes commonly discussed in the mining community the most crucial sustainability problems of this sector? Having the sustainability reports of all major international mining firms in hand, I evaluated around 3500 documents containing 8 million words discussing current sustainability matters pertaining to mining firms. Through implementing appropriate algorithms of Topic Modeling, I introduced five new main scopes for mining sustainability used to examine the discourse and groupings through this framework to observe any possible differences among the conventional and the generated lists. The results of my thesis are my two conceptual frameworks, technological benchmarking assessment tools, and a data-driven sustainability domains list, as well as the innovation policy recommendations for the mining community.

EPFL2021

Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Anna Minata Cissé

Changing consumption patterns and global population growth lead to ever-increasing waste generation. Human activity and waste generation are irrevocably linked, and the current situation thus calls for a more circular approach to waste management, where wastes become new resources. Industrial ecology offers a variety of waste reduction-favoring concepts. As a first step this project identifies waste-preventing, waste-reducing, end of pipe (EOP) waste management approaches and legislation as classification categories for waste management strategies. Although, according to the waste hierarchy, waste prevention is the most preferable waste management approach, it is the least implemented. To facilitate the identification of waste prevention and reduction potentials, a special waste flow diagram from the waste management perspective is elaborated. The model tends to visualize all waste flows, including by-product valorization along a product's life cycle through the choice of a thematic-geographic system boundary. In a further step the applicability of the waste flow model is tested for concrete-related wastes and phosphorus (P) flows in wastes. The quantification of concrete waste flows for the city of Zurich shows that recycling is well implemented, whereas preferable waste management strategies, prevention and reduction of waste, are hardly put into practice. Scenario modeling is used to show the benefits of these techniques and the comparative LCA for different construction methods and materials identifies waste prevention as most beneficial option. For P, the waste flow model is applied to test its ability to detect P recovery potentials, however no new findings in terms of P-recovery potential are identified. The most compelling result regarding phosphorus is found in the extension to the initial investigation, the mass flow analysis for a wet-chemical and a thermochemical P-recovery procedure from sewage sludge ashes. The analysis shows that for EOP waste technologies, the material output can be bigger than the input due to the extended use of additives. Although all generated by-products can, in this case, be valorized by other industrial activities, this finding highlights the need for more waste prevention-oriented waste management strategies, thus avoiding the necessity to generate high by-product flows in the first place.

2018

Seeking methods for improving sustainability in the extractive sector

Farnaz Eslamishoar

EPFL2021

Interfacial engineering for competitive Dye-Sensitized Solar Cells production

Natalie Flores Diaz

EPFL2021

Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Anna Minata Cissé

2018