Radiative Cooling Properties of Portlandite and Tobermorite: Two Cementitious Minerals of Great Relevance in Concrete Science and Technology.

Although concrete and cement-based materials are the most engineered materials employed by mankind, their potential for use in daytime radiative cooling applications has yet to be fully explored. Due to its complex structure, which is composed of multiple phases and textural details, fine-tuning of concrete is impossible without first analyzing its most important ingredients. Here, the radiative cooling properties of Portlandite (Ca(OH)2) and Tobermorite (Ca5Si6O16(OH)2·4H2O) are studied due to their crucial relevance in cement and concrete science and technology. Our findings demonstrate that, in contrast to concrete (which is a strong infrared emitter but a poor sun reflector), both Portlandite and Tobermorite exhibit good radiative cooling capabilities. These results provide solid evidence that, with the correct optimization of composition and porosity, concrete can be transformed into a material suitable for daytime radiative cooling.

Cementitious materials as promising radiative coolers for solar cells.

Nowadays, radiative coolers are extensively investigated for the thermal management of solar cells with the aim of improving their performance and lifetime. Current solutions rely on meta-materials with scarce elements or complex fabrication processes, or organic polymers possibly affected by UV degradation. Here, the potential of innovative cement-based solutions as a more sustainable and cost-effective alternative is reported. By combining chemical kinetics, molecular mechanics and electromagnetic simulations, it is shown that the most common cements, i.e., Portland cements, can be equipped with excellent radiative cooling properties, which might enable a reduction of the operating temperature of solar cells by up to 20 K, with outstanding efficiency and lifetime gains. This study represents a first step toward the realization of a novel class of energy-efficient, economically viable and robust radiative coolers, based on cheap and available cementitious materials.

Thermoelectric Performance of IV-VI Compounds with Octahedral-Like Coordination: A Chemical-Bonding Perspective.

Thermoelectric materials provide a challenge for materials design, since they require optimization of apparently conflicting properties. The resulting complexity has favored trial-and-error approaches over the development of simple and predictive design rules. In this work, the thermoelectric performance of IV-VI chalcogenides on the tie line between GeSe and GeTe is investigated. From a combination of optical reflectivity and electrical transport measurements, it is experimentally proved that the outstanding performance of IV-VI compounds with octahedral-like coordination is due to the anisotropy of the effective mass tensor of the relevant charge carriers. Such an anisotropy enables the simultaneous realization of high Seebeck coefficients, due to a large density-of-states effective mass, and high electrical conductivity, caused by a small conductivity effective mass. This behavior is associated to a unique bonding mechanism by means of a tight-binding model, which relates band structure and bond energies; tuning the latter enables tailoring of the effective mass tensor. The model thus provides atomistic design rules for thermoelectric chalcogenides.