Tuning Mg(OH)2 Structural, Physical, and Morphological Characteristics for Its Optimal Behavior in a Thermochemical Heat-Storage Application.

Elpida Piperopoulos,Emanuela Mastronardo,Maurizio Lanza,Marianna Fazio,Candida Milone

doi:10.3390/ma14051091

Abstract

Thermochemical materials (TCM) are among the most promising systems to store high energy density for long-term energy storage. To be eligible as candidates, the materials have to fit many criteria such as complete reversibility of the reaction and cycling stability, high availability of the material at low cost, environmentally friendliness, and non-toxicity. Among the most promising TCM, the Mg(OH)2/MgO system appears worthy of attention for its properties in line with those required. In the last few decades, research focused its attention on the optimization of attractive hydroxide performance to achieve a better thermochemical response, however, often negatively affecting its energy density per unit of volume and therefore compromising its applicability on an industrial scale. In this study, pure Mg(OH)2 was developed using different synthesis procedures. Reverse deposition precipitation and deposition precipitation methods were used to obtain the investigated samples. By adding a cationic surfactant (cetyl trimethylammonium bromide), deposition precipitation Mg(OH)2 (CTAB-DP-MH) or changing the precipitating precursor (N-DP-MH), the structural, physical and morphological characteristics were tuned, and the results were compared with a commercial Mg(OH)2 sample. We identified a correlation between the TCM properties and the thermochemical behavior. In such a context, it was demonstrated that both CTAB-DP-MH and N-DP-MH improved the thermochemical performances of the storage medium concerning conversion (64 wt.% and 74 wt.% respectively) and stored and released heat (887 and 1041 ). In particular, using the innovative technique not yet investigated for thermal energy storage (TES) materials, with NaOH as precipitating precursor, N-DP-MH reached the highest stored and released heat capacity per volume unit, ~684 MJ/m3.

Highlights

We investigated the influence of metal doping in Mg(OH)2 synthesis, examining the thermochemical comportment, depending on different structural, morphological as well as thermochemical characteristics [32]
N-deposition precipitation (DP)-MH has higher density (660 kg/m3 ) due to the particular morphology formed by globularly shaped hydroxide particles. This morphological characteristic allows the sample to reach a stored heat per volume unit equal to 684 MJ/m3. This value is one of the highest recorded in the literature for pure magnesium hydroxide and represents a promising result toward the aim of thermochemical energy storage
This value method conducts an agglomerated material composed of irregular plate-like morphology is one of the highest recorded in the literature for pure magnesium hydroxide and repreparticles that exhibit less surface area and less pore volume (VPORE )

Summary

Introduction

A technology capable of managing demand peaks with greater efficiency, avoiding supply interruptions, and reducing the load where necessary is required [1,2,3] In such a context, the research and development of the conversion and storage of waste heat are essential to overcome the energy mismatch between supply and demand. As one promising alternative to the storage of sensible [7,8] or latent heat [9,10,11], heat storage through reversible chemical reactions is under investigation [12,13] By this method, the separated components of the thermochemical material (TCM) during the heating are stored in separate vessels to be recombined to generate heat when needed [14,15]. Doped calcium manganites were recently proposed as TES materials, proposing a novel radiative model [19,20]

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