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- (CrVW)(1-x)(TaTi)x, (x=10 and 20 at.%), high entropy alloys as thermal barriers for nuclear fusion reactorsPublication . Martins, Ricardo; Lara, S. de; Neves, Filipe; Sá, Ana; Luz, Paulo P. da; Pereira Gonçalves, Antonio; Galatanu, Andrei; Sobieraj, Damian; Nguyen-Manh, D.; Dias, MartaABSTRACT: Due to the extreme operating temperatures in nuclear fusion reactors, current divertor monoblock materials, tungsten (plasma-facing material) and CuCrZr (heat sink), exhibit a substantial mismatch in mechanical and thermal properties. Therefore, a thermal barrier interlayer is required to guarantee continuous operation. In this work, (CrVW)(1-x)(TaTi)x alloys (x = 10 and 20 at.%) were studied for application as interlayers in nuclear fusion reactors. Atomistic modeling using Monte Carlo simulations combined with a first-principles-based Cluster Expansion Hamiltonian has been performed as a function of temperature to predict the order-disorder transitions in the investigated high-entropy alloys. Moreover, the experimental alloys were prepared by mechanical alloying followed by spark plasma sintering. Both alloy compositions display strong negative average chemical shortrange ordering below 1500 K for the W-Ta and W-Ti chemical pairs, with an estimated transition temperature around 1300 K. Atomic structures obtained from Monte Carlo simulations for (CrWV)80(TaTi)20 indicate that the ordering observed in this composition is stronger than that for (CrWV)90(TaTi)10. Moreover, both systems exhibit a bcc structure, and heat treated samples show phase growth and a four phase microstructure. The thermal diffusivity increases with temperature, reaching lower values than those of pure W and CuCrZr.
- Cyclopentadienyl vs indenyl control of thermal/photoactivated CO release in cationic molybdenum(II) dicarbonyl-ethylenediamine complexesPublication . Bruno, Sofia M.; Calhau, Isabel B.; Dias, Tiago M.; Santos, Adriana; Silva, Luis Cunha; Nolasco, Mariela M.; Goncalves, Isabel S.; Pillinger, MartynABSTRACT: Molybdenum half-sandwich carbonyl complexes continue to attract attention as potential anticancer agents and prodrugs for therapeutic use of carbon monoxide. Building on the known bioactivity and hydrolytic stability of cyclopentadienyl-based Mo fragments, we report the synthesis, structural characterization, and solution behavior of two cationic half-sandwich complexes, [(eta 5-Cp)Mo(CO)2(en)][BF4] (3) and [(eta 5-Ind)Mo(CO)2(en)][BF4] (4) (Cp = cyclopentadienyl, Ind = indenyl, en = ethylenediamine). Complex 3 is described here for the first time, while 4 was structurally characterized by single-crystal X-ray diffraction, revealing a distorted square-pyramidal geometry with cis-CO ligands and a chelating en ligand positioned beneath the indenyl ring. Both compounds are air-stable in the solid state and exhibit enhanced solubility in polar media due to their ionic nature. UV-vis stability studies under simulated physiological conditions (PBS, pH 7.4, 37 degrees C) show gradual decomposition of both complexes, accelerated by visible-light irradiation and/or the presence of air. CO-release behavior was quantified using the myoglobin assay: the allyl precursors [(eta 5-Cp')Mo(eta 3-C3H5)(CO)2] were inert, whereas complexes 3 and 4 released CO slowly, with 4 exhibiting significantly faster thermal CO liberation (t1/2 approximate to 129 min; 0.74 equiv. CO after 6 h). Complex 3 showed minimal thermal CO release but underwent enhanced and sustained photodecarbonylation under visible-light irradiation, enabling controlled CO delivery. These results identify 3 and 4 as rare examples of Mo-based CO-releasing molecules capable of slow, tunable CO release under biologically relevant conditions, with 3 displaying light-responsive behavior and 4 functioning as a spontaneous thermal CO donor.
- CrFeVWX (X = Ta or Ti) High-Entropy Alloy: A Theoretical and Experimental Comparative Investigation on Phase StabilityPublication . Martins, Ricardo; Valadares, Vasco; Pereira, André; Pereira Gonçalves, Antonio; Neves, Filipe; Sá, Ana; Luz, Paulo P. da; Monteiro, Bernardo; Galatanu, Andrei; Monnier, Judith; Villeroy, Benjamin; Dias, MartaABSTRACT: Materials capable of withstanding extreme environments open promising opportunities for nuclear fusion reactors. In this study, equiatomic CrFeTaVW and CrFeTiVW high-entropy alloys are investigated as interlayer materials between W and CuCrZr. Monte Carlo and Molecular Dynamics simulations predicted a bcc-type structure for both systems. Additionally, the Monte Carlo simulation predicts lower potential energy and a more stable structure for both systems than Molecular Dynamics. For CrFeTaVW, the chemical segregation values are lower in MC than in the MD simulation, whereas for CrFeTiVW, the opposite trend is observed, with MC indicating stronger segregation values. After simulation, the high-entropy alloys were prepared by planetary ball milling, consolidated by spark plasma sintering, and analyzed using X-ray diffraction, scanning electron microscopy, and thermal diffusivity. The experimental results for the milled powders confirmed the formation of a bcc structure in both alloys. The consolidated material revealed a bcc-type structure and an Fe2Ta Laves phase for the CrFeTaVW HEA, while the CrFeTiVW HEA exhibits two different bcc-type structures. The values of CrFeTaVW and CrFeTiVW thermal diffusivity are between 3.5 and 7 mm2/s, which is consistent with the expected values for high-entropy alloys. Overall, the findings indicate that these HEAs have promising properties that can be used in extreme environments.
- Novel fast synthesis route for α-MgAgSb thermoelectric materialsPublication . Santos, Beatriz; Sá, Ana; Luz, Paulo P. da; Neves, Filipe; de Boor, Johannes; Pereira Gonçalves, AntonioABSTRACT: Thermoelectric (TE) materials capable of waste heat recovery in the temperature range of 300-525 K remain relatively underdeveloped compared to conventional Bi2Te3-based systems, which present inherent environmental, health, and cost challenges. Recently, MgAgSb-based compounds have garnered significant research interest for applications in this temperature range owing to their intrinsically low thermal conductivity, high figure of merit and higher abundance. However, synthesis of the desired low-temperature alpha-MgAgSb phase typically requires highly controlled production processes-such as multi-step mechanical alloying, followed by extensive, week-long annealing-to mitigate the formation of or transition to undesirable phases. This study proposes an original, rapid, and scalable synthesis strategy combining induction melting for only six minutes with the subsequent classic hot-pressing method. We investigated the effect of nominal stoichiometry on thermoelectric performance by synthesising three distinct compositions: MgAg0.97Sb0.995, MgAg0.965Sb0.985, and MgAg0.955Sb0.985. The MgAg0.955Sb0.985 composition exhibited optimal performance, achieving an average power factor (PF) of 12.8 mu W K-2 cm-1 in the 300-525 K range. By considerably reducing the thermal budget and processing time, this approach significantly improves the energy payback time (EPBT) and reduces the carbon footprint of production, addressing the critical sustainability-performance trade-off that limits large-scale deployment. This result validates the capacity of the proposed fast synthesis route to yield performant MgAgSb-based samples and suggests that the optimal nominal composition is dependent on the specific production technique employed. Fundamentally, this work demonstrates the rapid and successful preparation of the desired alpha-MgAgSb phase using an easily scalable technique that does not require a perpetually inert atmosphere. This process utilises bulky precursor elements directly, significantly reducing production complexity, associated costs, and health hazards. This advancement provides a simpler and more industrially viable pathway for the transition of MgAgSb materials toward commercial availability.
- Enhanced borohydride oxidation kinetics with Au@MOF-808 nanocomposite electrocatalysts with ultra-low Au loadingPublication . Belhaj, Ines; Becker, J. Alexander; Viana, Alexandre M.; Gusmão, Filipe M. B.; Chaves, Miguel; Pereira, Eulália; Sljukic, Biljana; Balula, Salete S.; Silva, Luis Cunha; Santos, Diogo M. F.ABSTRACT: The highly stable metal-organic framework (MOF) composed of[Zr6O4(mu 3-OH)4(OH)6(H2O)6(BTC)2]& sdot;nH2O units (MOF-808) was modified by incorporating gold (Au) nanoparticles and functional groups to enhance electrocatalytic activity for the borohydride oxidation reaction (BOR). Three composite materials (Au@MOF-808, Au@MOF-808-NH2, and Au@MOF-808-SH) were prepared by the incorporation of Au in structurally related MOFs, MOF-808, MOF-808-NH2, and MOF-808-SH, respectively. These composite materials were evaluated as anodic electrocatalysts for BOR in alkaline media using cyclic voltammetry and chronoamperometry. Among the prepared materials, Au@MOF-808-NH2 exhibited the highest BOR activity, with an apparent activation energy of 15.3 kJ mol-1, a reaction order of 0.6, an anodic charge transfer coefficient of 0.63, and a number of exchanged electrons of 4.4. The latter was significantly below the theoretical eight-electron value, indicating the presence of alternative reaction pathways. Notably, this material achieved a high mass-specific BOR peak current of 4.23 A mu gAu-1, demonstrating outstanding electrocatalytic efficiency despite the ultralow noble metal loading. These results underscore the potential of Au@MOF-808-NH2 as a cost-effective and scalable anodic electrocatalyst for high-performance direct borohydride fuel cells.
- Determination of reflectance of interest from limited state-of-the-art solar reflector field soiling measurementsPublication . Wette, Johannes; Sutter, Florian; Cunha Diamantino, Teresa; Montecchi, Marco; Bern, Gregor; Fernández-García, AránzazuABSTRACT: In concentrated solar thermal technologies, plant operators usually monitor the soiling of their solar field with handheld reflectometers. These measurements can be used for yield calculations and to adapt cleaning strategies: if the reflectometer reading falls below an empirically established threshold, the solar field should be cleaned. There are several commercial reflectometers available for this purpose, but all of them measure at different combinations of wavelength, acceptance angle or incidence angle. It is the purpose of this study to bring the readings from all main commercial reflectometers to the same representative value, enabling their comparison with one another and the translation of these readings into a meaningful reflectance parameter. Thus, different handheld reflectometers are correlated with a laboratory reflectometer, capable of measuring in the whole solar spectral region, covering a wide range of incidence and acceptance angles. The most significant parameter is the near-specular solar-weighted reflectance, measured at the typical incidence and acceptance angles for a given plant, as it is the most precise parameter to describe the reflected energy from the solar field. The correlations for all included reflectometers, show highly linear correlations over a wide range of soiling levels with low deviations. Consequently, the correlations presented herein enable the plant operators at the studied site to compute the near-specular solar-weighted reflectance from their reflectometer readings. and, with that, increase the significance of the measurements without collecting any additional data. The work also establishes a detailed procedure to derive this type of correlations at any site of interest.
- Influence of Cr on the quaternary FeTaTiW medium entropy alloyPublication . Martins, Ricardo; Monteiro, Bernardo; Pereira Gonçalves, Antonio; Correia, Jose B.; Galatanu, Andrei; Alves, Eduardo; Tejado, Elena; Pastor, Jose Ygnacio; Dias, MartaABSTRACT: The search for advanced materials has been growing, and high entropy alloys (HEAs) are emerging as promising candidates for application in the fusion domain. This work investigates the effect of Cr on the FeTaTiW medium entropy alloy to form (CrFeTaTi)70W30 high entropy alloy, comparing the experimental production and characterization with the simulation (molecular dynamics and hybrid molecular dynamics-Monte Carlo) of the phases formed. The alloys were produced by mechanical alloying and sintered by spark plasma sintering. Both simulations have shown that a body-centered cubic structure is formed for both compositions. Monte Carlo simulation provides a more precise prediction of microstructural formation and element segregation. Microstructural examination of the consolidated material revealed the presence of a W-rich phase and a Ti-rich phase, consistent with the phase separation observed in the MC simulations. Moreover, X-ray diffraction analysis of the milled powder for FeTaTiW and (CrFeTaTi)70W30 confirmed the formation of a bcc (body-centered cubic)-type structure with a low fraction of intermetallic phases. Mechanical testing showed ductile behavior at 1000 degrees C where (CrFeTaTi)70W30 showed a stress magnitude almost double that of FeTaTiW. Additionally, the thermal diffusivity between 20 and 1000 degrees C of both alloys increases as the temperature rises. (CrFeTaTi)70W30 exhibits an increase from 3 to 5 mm2/s, while FeTaTiW increases from 4 to 9 mm2/s. Still, both system's thermal diffusivity values are lower than those of CuCrZr and pure tungsten. Despite this, the study underscores the promising attributes of HEAs and highlights areas for further optimization to enhance its suitability for extreme conditions.
- Scale-up of a clean hydrogen production system through the hydrolysis of sodium borohydride for off-grid applicationsPublication . Silva, Diogo; Nunes, Helder Xavier; Rangel, Carmen M.; Pinto, A. M. F. R.ABSTRACT: Hydrogen is considered a promising energy vector with the potential to replace fossil fuels, and sodium borohydride serves as an effective energy carrier capable of releasing hydrogen (H2) for off-grid applications. However, the hydrolysis of sodium borohydride has only matured at laboratory-scale. Therefore, the scale-up of a laboratory reactor was designed and manufactured to study the effect of larger H2 production. For that, the effect of inhibitor NaOH concentration and water quality were studied. Experiments using 3 wt% NaOH showed overall better performance than those using 1 wt%. Additionally, experiments using tap water - scarcely reported in the literature - demonstrated performance equal to or better than that achieved with distilled water. These results are indicative of a possible significant reduction in the H2 production cost through this method.
- Mechanical Performance of Ceria-Coated 3D-Printed Black Zirconia Cellular Structures After Solar Thermochemical CO/H2 Fuel Production CyclesPublication . Oliveira, Fernando; Sardinha, Manuel; Justino Netto, Joaquim Manoel; Leite, Marco; Farinha, Miguel; Barreiros, Maria Alexandra; Abanades, Stéphane; Fernandes, JorgeABSTRACT: Solar fuels production requires developing redox active materials with porous structures able to withstand thermochemical cycles with enhanced thermal stability under concentrated solar irradiation conditions. The mechanical performance of 3D-printed, macroporous black zirconia gyroid structures, coated with redox-active ceria, was assessed for their suitability in solar thermochemical cycles for CO2 and H2O splitting. Experiments were conducted using a 1.5 kW solar furnace to supply the high-temperature concentrated heat to a windowed reaction chamber to carry out thermal redox cycling under realistic on-sun conditions. The ceria coating on ceramic structures improved the thermal stability and redox efficiency while minimizing the quantity of the redox material involved. Crushing strength measurements showed that samples not directly exposed to the concentrated solar flux retained their mechanical performance after thermal cycling (similar to 10 MPa), while those near the concentrated solar beam focus exhibited significant degradation due to thermal stresses and the formation of CexZr1-xO2 solid solutions (similar to 1.5 MPa). A Weibull modulus of 8.5 was estimated, marking the first report of such a parameter for fused filament fabrication (FFF)-manufactured black zirconia with gyroid architecture. Failure occurred via a damage accumulation mechanism at both micro- and macro-scales. These findings support the viability of ceria-coated cellular ceramics for scalable solar fuel production and highlight the need for optimized reactor designs.
- New Modified SPEEK-Based Proton Exchange MembranesPublication . Teixeira, Fatima; Teixeira, António Paulo Silva; Rangel, Carmen M.ABSTRACT: A decarbonized society demands cleaner and sustainable energy sources based on well-established or emerging technologies with the potential to make a significant contribution to energy storage and conversion, such as batteries, fuel cells and water and/or CO2 electrolyzers. The performance of these electrochemical devices relies on key components such as their separators/ion-exchange membranes. The most common commercial membrane, Nafion (R), has several technological limitations. In this study, it is proposed the incorporation of bisphosphonic acid (BP) dopants into membrane matrices to improve their properties. Following this strategy, we prepared new membranes based on sulfonated poly(etheretherketone) (SPEEK) polymer, a reliable and effective alternative membrane polymer, through the incorporation of the BP dopants, to obtain low-cost membranes with improved properties. These membranes were structural, thermal and morphological, characterized by AT-FTIR, TGA and SEM. Their proton conductivity was evaluated over a temperature range between 30 degrees C and 60 degrees C, using Electrochemical Impedance Spectroscopy, and their stability during this process was also observed. The best proton conductivity was observed for the SPEEK membrane doped with BP1 at 2.0 wt% load at 60 degrees C, with a proton conduction of 226 mS cm-1.