Cementitious composite materials for thermal energy storage applications: a preliminary characterization and theoretical analysis

Abstract

The lack of robust and low-cost sorbent materials still represents a formidable technological barrier for long-term storage of (renewable) thermal energy and more generally for Adsorptive Heat Transformations—AHT. In this work, we introduce a novel approach for synthesizing cement-based composite sorbent materials. In fact, considering the number of available hygrosopic salts that can be accommodated into a cementitious matrix—whose morphological properties can be also fine-tuned—the new proposed in situ synthesis paves the way to the generation of an entire new class of possible sorbents for AHT. Here, solely focusing on magnesium sulfate in a class G cement matrix, we show preliminary morphological, mechanical and calorimetric characterization of sub-optimal material samples. Our analysis enables us to theoretically estimate one of the most important figures of merit for the considered applications, namely the energy density which was found to range within 0.088–0.2 GJ/m 3 (for the best tested sample) under reasonable operating conditions for space heating applications and temperate climate. The above estimates are found to be lower than other composite materials in the literature. Nonetheless, although no special material optimization has been implemented, our samples already compare favourably with most of the known materials in terms of specific cost of stored energy. Finally, an interesting aspect is found in the ageing tests under water sorption-desorption cycling, where a negligible variation in the adsorption capability is demonstrated after over one-hundred cycles.

Minimal set of crystallographic descriptors for sorption properties in hypothetical Metal Organic Frameworks: Role in sequential learning optimization

“…In this study, we assume: T A = 308 K (the minimum temperature on the user side), T C = 353 K (the maximum temperature on the source side), T E = 278 K (the average winter temperature), T F = 303 K (the average summer temperature). Those temperature values are reasonable for space heating applications in temperate climates [58]. Given the Antoine equation, the equilibrium water vapour pressures p E = 866.2 Pa at the evaporator and p F = 4231.6 Pa at the condenser are also uniquely defined considering the average winter and summer temperatures, respectively.…”

“…The most challenging aspect of this task consists in the access to the entire isosteric field of each candidate MOF-water pair for estimating the engineering figure of merit of interest. Clearly, for a large number of MOFs candidates, this is challenging and time consuming both computationally (typically, only the Henry low-coverage regime is reported in literature works [56,57]) and experimentally [58]. In this section, we specifically focus on such challenging aspect.…”

Assessing the suitability of alkali-activated metakaolin geopolymer for thermochemical heat storage

“…In comparison, NS20 has the second highest volumetric energy density as well as the second highest moisture diffusion coefficient, which might be able to provide the best overall energy storage performances, taking into consideration of both energy storage capacity and charging/discharging power. In comparison with other thermochemical energy storage materials, the theoretical energy storage performances of NS20 (350 kW h/m 3 ) is higher than some recently developed porous composite materials impregnated with salt hydrates [6,61] with charging temperature suitable for concentrated solar collectors, as well as for medium temperature waste heat recovery [13,61]. However, it is common that the operational energy storage performances under chosen operation conditions (e.g.…”

Minimal crystallographic descriptors of sorption properties in hypothetical MOFs and role in sequential learning optimization

“…The most challenging aspect of this task consists in the access to the entire isosteric field of each candidate MOFwater pair for estimating the engineering figure of merit of interest. Clearly, for a large number of MOFs candidates, this is challenging and time-consuming both computationally (typically, only the Henry low-coverage regime is reported in literature works 62,63 ) and experimentally 64 . In this section, we specifically focus on such a challenging aspect.…”