Fabrication and thermal properties of encapsulated reversible thermochromic phase change material for solar thermal energy storage

Reversible thermochromic phase change material (RTPCM) can adaptively adjust the color with temperature and effectively avoid problems such as high surface temperature and uneven temperature distribution in solar thermal utilization. In this paper, the blended solution of sodium alginate and RTPCM with crystal violet lactone as chromogenic agent, bisphenol A as chromogenic agent and tetradecanol as solvent was selected as core material. The encapsulated reversible thermochromic phase change material (E-RTPCM) was successfully prepared by ion exchange reaction between sodium alginate and CaCl 2 . E-RTPCM behaved a good spherical morphology with an average particle size range of 2.0–3.0 mm. E-RTPCM (1:7 water oil ratio, 2 % sodium alginate concentration, and 2 mm needle diameter size) had the best overall performance with phase change enthalpy of 101.4 J/g and 95.01 J/g, respectively, and the thermal conductivity reached 0.5201 W/(m·K) in deionized water . The absorbance of E-RTPCM for solar energy reached 89.0 % in the visible light range. And the heating rates of the three testing points from top to bottom at a light intensity of 300 mW/cm 2 reached 1.5 °C/min, 0.9 °C/min and 0.7 °C/min, respectively, exhibiting excellent photothermal conversion performance. After 200 cycles of heating and cooling, the melting enthalpy and crystallization enthalpy of E-RTPCM only changed by 0.6 J/g and 0.4 J/g, suggesting outstanding cycling thermal stability and reversible phase change behavior. This study provides crucial theoretical guidance for the preparation of E-RTPCM and its application in the field of solar thermal utilization. • A novel E-RTPCM for solar thermal energy storage was developed. • E-RTPCM exhibited outstanding cycling thermal stability and reversible phase change behavior. • The thermochromic and photothermal conversion performance of E-RTPCM were investigated.