The　addition　of　nanomaterials　to　molten　salts　can　significantly　improve　their　thermal　performance.　To　explore　the　enhancement　mechanisms,　this　work　prepared　carbonate　salt　nanofluids　with　binary　carbonate　as　base　salt　and　20　nm　SiO2　and　20　nm　MgO　nanoparticles　as　additives　by　the　commonly　used　aqueous　solution　method.　Then,　the　key　performance　and　micromorphology　of　the　carbonate　salt　nanofluids　are　characterized　by　differential　scanning　calorimetry,　thermal　gravimetric　analysis,　laser　flash　analysis,　and　micromorphology　analysis.　Results　showed　that　the　20　nm　SiO2　nanomaterials　instead　of　the　20　nm　MgO　nanomaterials　exerted　higher　effects　on　latent　heat　while　the　20　nm　MgO　nanomaterials　instead　of　the　20　nm　SiO2　nanomaterials　exerted　higher　effects　on　the　sensible　heat,　thermal　conductivity,　and　high-temperature　stability　of　carbonated　salt.　In　addition,　different　nanostructures　were　observed　in　SiO2-based　and　MgO-based　molten　salt　nanofluids,　respectively.　Innovatively,　formation　mechanisms　of　molten　salt　nanofluids　were　proposed　based　on　cloud　nuclei　to　explain　the　different　enhancements　in　this　work.　©　2022　Xiong　Yaxuan　et　al.