Laboratoire Procédés, Matériaux et Energie Solaire

A two-step thermochemical splitting process of doped and undoped neodymium-based manganite perovskites was investigated using thermogravimetric analysis. The samples were synthesized using a modified Pechini method and characterized by XRD, SEM and EDS analysis before redox testing. The results showed that 40% Sr-doped Nd0.6Sr0.4MnO3 outperformed the other samples, achieving 103.7 µmol-O2/g during thermal reduction and 189.2 µmol-CO/g during thermal oxidation, with a re-oxidation yield of 91.2%.

• Thermodynamic and experimental analysis of carbothermal Fe 2 O 3 reduction was achieved. • Carbon resources can derive from CO 2 using solar pyrolysis of biomass or biomethane. • The reaction was studied in TG/MS and tubular reactor coupled with online gas analyzer. • A stepwise reduction pathway was confirmed from analysis of evolved CO/CO 2 gases. • Formation of pure Fe was evidenced at C/Fe 2 O 3 ratio ≥3 for all studied carbon types. The reduction of hematite (Fe 2 O 3 ) to metallic iron via a carbothermal process was investigated with the aim of using carbon derived from captured or recycled CO 2 . This CO 2 -sourced carbon can be obtained by pyrolysis either directly from biomass or methane (issued from biogas or via a synthetic methanation route, through the Sabatier reaction). The carbon can ultimately serve as the reducing agent in a carbon-neutral solar thermal process. A comparative study was conducted to assess the thermodynamic and kinetic behavior of Fe 2 O 3 reduction using four distinct carbon materials: carbon black, activated charcoal, graphite, and biochar. The influence of heating rate and carbon-to-oxide molar ratio (C/Fe 2 O 3 ) was analyzed. Thermogravimetric analysis was employed to examine the reaction kinetics and mechanisms, while independent experiments in a tubular reactor further validated the results. These techniques enabled the synthesis of metallic iron and provided valuable insights into the reaction sequence, gas evolution rates (CO, CO₂), and phase transformations under controlled conditions. The expected phase transformation sequence: Fe 2 O 3 → Fe 3 O 4 → FeO → Fe was evidenced by gas phase analysis. X-ray diffraction analysis of the solid products confirmed nearly complete conversion of Fe 2 O 3 to Fe at a C/Fe 2 O 3 molar ratio of 3.0 or higher. The heating rate did not significantly affect reduction efficiency, whereas a carbon excess promoted near-complete reduction. At a fixed C/Fe 2 O 3 ratio of 4.5, conversion profiles showed slight variations based on the carbon type used. Graphite exhibited a sharp conversion increase at ∼1110 °C, while the other reductants displayed more gradual and similar conversion profiles with stepwise release of CO 2 and CO according to a three-stage mechanism. Notably, a lower onset reduction temperature (∼959 °C) was observed with biochar, indicating the potential of bio-sourced materials conversion for green ironmaking.

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 (~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 (~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.

Past mining activities in the Orbiel Valley pose a significant risk of As contamination to its ecosystems and inhabitants. Approximately 12 million tons of tailings from last century's As and Au mining operations remain on site. Rehabilitation works have been implemented to store mining wastes and treat leaching waters. However recent studies have revealed that contamination is still present in water and sediments (Khaska et al., 2015; Delplace et al., 2022). The complexity of the area and previous findings have shown the importance of a more in-depth study of As sources and fate in the watershed, including 1/ characterizing As contamination levels in the Orbiel River and its tributaries during different hydrological periods, 2/ identifying the main sources of As and 3/ distinguishing the natural geochemical baseline from anthropogenic inputs.Water samples ( 52 %). The anthropogenic origin of this contamination was confirmed by the 87Sr/86Sr ratio, which is less radiogenic than in the upstream pristine area, in relation with lime treatment implemented in the mine waste area. However, some valley limestones exhibit a Ca-arsenate-like isotopic ratio, highlighting the need to use complementary tracers to distinguish between anthropogenic and lithological sources. Finally, the mining-impacted tributaries are identified as significant contributors of As to the Orbiel River.The present study will serve as a reference to interpret the origin, transport, and fate of metal(loid)s during future extreme flood events characteristic of this Mediterranean river. Delplace, G., Viers, J., Schreck, E., Oliva, P., Behra, P., 2022. Pedo-geochemical background and sediment contamination of metal(loid)s in the old mining-district of Salsigne (Orbiel valley, France). Chemosphere 287 (2).Khaska, M., Le Gal La Salle, C., Verdoux, P., Boutin, R., 2015. Tracking natural and anthropogenic origins of dissolved arsenic during surface and groundwater interaction in a post-closure mining context: isotopic constraints. J. Contaminant Hydrol. 177–178, 122–135.

Particle flow structure and associated heat transfer coefficient are examined as a function of temperature in a single-tube fluidized bed solar receiver operating in upward particle flow mode. It is found that temperature has a strong effect on both fluidization regimes and wall-to-bed heat transfer coefficient that varies in the range 800-1200 W/(m2.K). Turbulent fluidization regime results in the most intense heat transfer between the irradiated wall and the fluidized particle.

Compact PV/CSP hybrid systems, based on the integration of both PV and CSP technologies within a single power plant, have been attracting interest in recent years, because of their potential to lower the cost of solar electricity and minimize the land footprint required. However, the objective evaluation of these technologies is complicated by the fact that they involve two separate converters, each delivering a different form of energy (dispatchable for CSP, non-dispatchable for PV). We propose here an original evaluation and optimization approach based on 3 techno-economic indicators quantifying (1) the overall conversion efficiency of these systems compared to their standalone CSP counterparts, (2) the energy production balance between PV and CSP, and (3) the extra manufacturing cost compared to standalone CSP systems. These different indicators are evaluated for two families of hybrid systems (PV Topping and PV Mirror) and for 3 geometries of concentrating optics (Linear Fresnel Lenses, Parabolic Troughs and Solar Towers). One originality of our approach lies in its ability to determine the optoelectronic properties of PV cells likely to lead to the best hybrid performance, taking into account whether or not they are able to reach their own theoretical limits. Another original feature is that the hybrid systems considered in our analysis are compared with CSP equivalents which have been independently optimized. It is shown that the integration of realistic solar cell technologies whose performances deviate significantly from their theoretical limits notably restricts the range of operating conditions for which hybrid systems could outperform their standalone CSP counterparts. We conclude this work by discussing a number of key challenges that need to be overcome in order to develop more competitive and efficient hybrid systems.