Carbon as in-situ coating promoter against molten salts in Lithium/Sodium sulfates intended for high-temperature thermal storage

Lithium/sodium sulfate system shows promising potential for high-temperature solid-state latent heat storage, and recent studies have begun to explore its suitability for thermal storage applications. Despite their advantages, crucial aspects that would allow their jump to the energy market have not yet been solved. Due to the novelty of these materials, their compatibility with the main heat transfer fluid (nitrate-based molten salts such as Hitec XL) has not been addressed to date. The present work addresses this problem through the in-situ formation of protective carbonate coatings. The coating formation process involves an initial carbon film deposition via thermal chemical vapor deposition (T-CVD) catalyzed by nickel (Ni). In the second stage, the carbonate coating is created in-situ through direct contact with the molten salt. This study explores the different stages of this process, including the carbon deposition on sulfates, the interaction between the molten salt and the isolated carbon film, and the overall behavior of the system. • Sulfate-based PCMs request protection when used with nitrate-based molten salts. • Carbon-molten salt interaction forms protective carbonate layers. • Carbon successfully deposited on LNS by T-CVD catalyzed by Ni. • In-situ protective coatings for LNS can be formed during immersion in molten salt.