High temperature shape – Stabilized phase change materials obtained using mesoporous silica and NaCl – NaBr – Na2MoO4 salt eutectic

Abstract

Thermal energy storage at temperatures above 400 °C is critical for efficient industrial processes and continuous solar thermal power generation. Phase change materials (PCMs) can be used for both latent heat storage and improved conversion efficiencies, but their use has been prevented by the large, 5–25 % change in molar volume. Herein, shape-stabilized PCMs are prepared using 20% wt. mesoporous silica matrices and NaCl–NaBr–Na2MoO4 salt eutectic. The pristine salt mixture has a total enthalpy of 216 Jg-1 divided into a solid-solid transition at 455 °C and solid – liquid transition at 522 °C. Six mesoporous silica materials of the MCM-41 (Mobil Composition of Matter No. 41), SBA-15 (Santa Barbara Amorphous) and mesocellular foam types were investigated as potential matrices for high temperature, shape-stabilized PCMs. All resulting composites have good thermal stability up to 650 °C. High – temperature optical microscopy shows that all samples retain their macroscopic solid shape above the salt melting point. Electron microscopy revealed a good dispersion of the silica matrix inside the molten salt phases. Both MCM-41 and SBA-15-type matrices yield PCMs with high total heat of fusion values between 169 – 178 Jg-1, in accordance to the 80% wt. salt fraction. The melting point is decreased with 5–10 °C for all composite materials, indicating nanoconfinement effects of the interparticle salt phase. This work therefore provides a new strategy for obtaining shape-stabilized materials useful for high – temperature heat storage.