Doping effects on magnesium hydroxide: Enhancing dehydration and hydration performance for thermochemical energy storage applications

Abstract

Thermochemical energy storage (TCES) holds significant promise owing to its remarkable energy storage density and extended storage capabilities. One of the most extensively studied systems in TCES involves the reversible hydration/dehydration reaction of magnesium hydroxide (Mg(OH)2) to magnesium oxide (MgO). This system suffers from several challenges such as the dehydration temperature of 360 °C, which is considered higher for some applications, low kinetics, and conversion fraction, in addition to the conversion decay after cycles. Nonetheless, it is essential to recognize that each material within thermochemical systems has distinct operational requirements, including temperature and pressure conditions, making them suitable for specific applications. Consequently, the development of materials is a pivotal factor in expanding the effectiveness of sustainable technologies. This research addresses challenges associated with the reversible reaction by partially substituting Mg with transition metal elements like Zn, Ni, Mn, Co, and Cu, leading to the development of new materials Mg1-xMx(OH)2 with x = 0.05. The results indicate successful synthesis of hydroxide systems through coprecipitation. Morphological analysis reveals that material morphology plays a significant role in the performance of thermochemical systems. Additionally, the developed materials demonstrate a reduction in dehydration temperature, reaching 295 °C with cobalt doping. There is also an increase in the conversion reaction, with a 10 % improvement in energy density recorded for the material doped with 5 % Zn. Lastly, the developed materials exhibit good cyclability performance for up to 6 cycles.