DIFFER: Publications
Not a member yet
3526 research outputs found
Sort by
Spark Ablation for the Fabrication of PEM Water Electrolysis Catalyst-Coated Membranes
No full textProton-exchange-membrane (PEM) electrolyzers represent a promising technology for sustainable hydrogen production, owing to their efficiency and load flexibility. However, the acidic nature of PEM demands the use of platinum-group metal-electrocatalysts. Apart from the associated high capital costs, the scarcity of Ir hinders the large-scale implementation of the technology. Since low-cost replacements for Ir are not available at present, there is an urgent need to engineer catalyst-coated membranes (CCMs) with homogeneous catalyst layers at low Ir loadings. Efforts to realize this mainly rely on the development of advanced Ir nanostructures with maximized dispersion via wet chemistry routes. This study demonstrates the potential of an alternative vapor-based process, based on spark ablation and impaction, to fabricate efficient and durable Ir- and Pt-coated membranes. Our results indicate that spark-ablation CCMs can reduce the Ir demand by up to five times compared to commercial CCMs, without a compromise in activity. The durability of spark-ablation CCMs has been investigated by applying constant and dynamic load profiles for 150 h, indicating different degradation mechanisms for each case without major pitfalls. At constant load, an initial degradation in performance was observed during the first 30 h, but a stable degradation rate of 0.05 mV h-1 was sustained during the rest of the test. The present results, together with manufacturing aspects related to simplicity, costs and environmental footprint, suggest the high potential of spark ablation having practical applications in CCM manufacturing.</p
ODS steels for nuclear applications: thermal stability of the microstructure and evolution of defects
No full textInfluence of porosity and blistering on the thermal fatigue behavior of tungsten
No full textTungsten is the leading plasma-facing material (PFM) for nuclear fusion applications. It faces severe operating conditions, including intense hydrogen plasma exposure and high-cycle transient heat loading, which create various defects in tungsten. Additionally, defects have often already been introduced during manufacturing. Little is understood regarding the synergistic effect of such defects on the lifetime of tungsten so far. Here, we investigate the influence of porosity and blistering on the thermal fatigue behavior of tungsten. The pores resulted from powder metallurgy whereas the blistering was induced by hydrogen plasma exposure. Both conditions were subjected to transient heat loading by a high-power pulsed laser. The exposure was performed in the linear plasma generator Magnum-PSI, which closely mimics the expected particle and heat flux in the world\u27s largest fusion experiment, ITER. Both porosity and blistering degraded the fatigue resistance of tungsten. Pores tended to aggregate at high-angle grain boundaries (HAGBs) and assisted crack initiation therein, as revealed by focused ion beam (FIB) cross-sectioning and electron backscatter diffraction (EBSD) analysis. The blisters were characteristic of subsurface cavities, which were located at a depth close to the surface roughness induced by transient heat loading. The stress concentration at the tip of the cavities is considered to promote crack initiation. The results highlight the necessity of a \u27life cycle assessment\u27 of the tungsten PFM for nuclear fusion reactors.</p
Carbon bed post-plasma to enhance the CO2 conversion and remove O2 from the product stream
No full textCO2 conversion by plasma technology is gaining increasing interest. We present a carbon (charcoal) bed placed after a Gliding Arc Plasmatron (GAP) reactor, to enhance the CO2 conversion, promote O/O2 removal and increase the CO fraction in the exhaust mixture. By means of an innovative (silo) system, the carbon is constantly supplied, to avoid carbon depletion upon reaction with O/O2. Using this carbon bed, the CO2 conversion is enhanced by almost a factor of two (from 7.6 to 12.6%), while the CO concentration even increases by a factor of three (from 7.2 to 21.9%), and O2 is completely removed from the exhaust mixture. Moreover, the energy efficiency of the conversion process drastically increases from 27.9 to 45.4%, and the energy cost significantly drops from 41.9 to 25.4 kJ.L−1. We also present the temperature as a function of distance from the reactor outlet, as well as the CO2, CO and O2 concentrations and the temperature in the carbon bed as a function of time, which is important for understanding the underlying mechanisms. Indeed, these time-resolved measurements reveal that the initial enhancements in CO2 conversion and in CO concentration are not maintained in our current setup. Therefore, we present a model to study the gasification of carbon with different feed gases (i.e., O2, CO and CO2 separately), from which we can conclude that the oxygen coverage at the surface plays a key role in determining the product composition and the rate of carbon consumption. Indeed, our model insights indicate that the drop in CO2 conversion and in CO concentration after a few minutes is attributed to deactivation of the carbon bed, due to rapid formation of oxygen complexes at the surface.</p
Anisotropic cosmic-ray diffusion in isotropic Kolmogorov turbulence
No full textUnderstanding the time scales for diffusive processes and their degree of anisotropy is essential for modelling cosmic-ray transport in turbulent magnetic fields. We show that the diffusion time scales are isotropic over a large range of energy and turbulence levels, notwithstanding the high degree of anisotropy exhibited by the components of the diffusion tensor for cases with an ordered magnetic field component. The predictive power of the classical scattering relation as a description for the relation between the parallel and perpendicular diffusion coefficients is discussed and compared to numerical simulations. Very good agreement for a large parameter space is found, transforming classical scattering relation predictions into a computational prescription for the perpendicular component. We discuss and compare these findings and, in particular, the time scales to become diffusive with the time scales that particles reside in astronomical environments, the so-called escape time scales. The results show that, especially at high energies, the escape times obtained from diffusion coefficients may exceed the time scales required for diffusion. In these cases, the escape time cannot be determined by the diffusion coefficients
Implementation of high-resolution spectroscopy for ion (and electron) temperature measurements of the divertor plasma in the Tokamak à configuration variable
No full textHigh resolution spectroscopy on the Tokamak à Configuration Variable (TCV) divertor plasma provided Doppler broadening measurements to infer the ion and neutral temperature of injected helium gas. This paper presents the Divertor Spectroscopy System’s (DSS) access to He II ion temperature measurements over a broad range, ≈0.5–15 eV, with an uncertainty of <10% for most of the studied plasma discharges. TCV’s shaping flexibility was employed to validate these measurements against Thomson scattering across the DSS lines of sight. In detachment-related experiments, T i(He II) ≃ T e, making this diagnostic a reliable thermometer along the divertor leg plasma over the wide range of magnetic equilibria and divertor configurations achievable in TCV. A detailed description of the diagnostic hardware, data analysis, and sources of uncertainty is presented.</p
Introduction Special Issue on European Programme towards DEMO: Outcome of the Pre-Conceptual Design Phase
No full textOne of the main EU fusion roadmap objectives [1] is to develop a Demonstration Fusion Power Plant (DEMO), following ITER and due to come into operation after the middle of this century. This is currently viewed as one of the final crucial steps towards the exploitation of fusion power, not only in Europe but also by many of the nations engaged in the ITER construction.<br/
Microstructural engineering of high-power redox flow battery electrodes via non-solvent induced phase separation
No full textRedDB, a computational database of electroactive molecules for aqueous redox flow batteries
No full textAn increasing number of electroactive compounds have recently been explored for their use in high-performance redox flow batteries for grid-scale energy storage. Given the vast and highly diverse chemical space of the candidate compounds, it is alluring to access their physicochemical properties in a speedy way. High-throughput virtual screening approaches, which use powerful combinatorial techniques for systematic enumerations of large virtual chemical libraries and respective property evaluations, are indispensable tools for an agile exploration of the designated chemical space. Herein, RedDB: a computational database that contains 31,618 molecules from two prominent classes of organic electroactive compounds, quinones and aza-aromatics, has been presented. RedDB incorporates miscellaneous physicochemical property information of the compounds that can potentially be employed as battery performance descriptors. RedDB’s development steps, including: (i) chemical library generation, (ii) molecular property prediction based on quantum chemical calculations, (iii) aqueous solubility prediction using machine learning, and (iv) data processing and database creation, have been described