Evaluation of mixed Tutton salts (NH4K)MII(SO4)2(H2O)6, (MII = Co or Ni) and their corresponding Langbeinite phases as thermochemical heat storage materials: Dehydration/hydration behavior and reversibility of structural phase transformation

• Published in: Journal of energy storage Vol. 98; p. 113114
• Main Authors: Lopes, Jardel Bruno de O., Oliveira Neto, João G., dos Santos, Adenilson O., Lang, Rossano
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-09-2024
• Subjects: Langbeinites; Phase transformation; Thermochemical heat storage; Tutton salts; Phase transformation; Thermochemical heat storage; Tutton salts; Langbeinites
• ISSN: 2352-152X
• DOI: 10.1016/j.est.2024.113114

In this paper, (NH4K)MII(SO4)2(H2O)6 (MII = Co or Ni) mixed Tutton salts and their corresponding K2MII2(SO4)3 Langbeinite phases are synthesized and investigated as thermochemical heat storage (TCHS) materials. Individual precursor Tutton salts have also been considered for comparison proposals. Elemental composition, thermal and vibrational properties, and phase transformations/transitions are features examined besides thermochemical application parameters. The mixed Tutton salts exhibit charging temperatures between 342 and 367 K, high energy storage densities (∼ 2.3–2.6 GJ/m3), and complete structural reversibilities (full dehydrated samples) after 18 h under open-system conditions (299 K, atmospheric H2O, and 58 % RH). Theoretical thermal efficiencies reach 48–53 %. Putting a mixture of [NH4]+ and K+ in a Tutton-type framework produces intermediate thermal behavior that may be valuable for tailoring thermochemical parameters, giving mixed Tutton salts promising prospects that deserve further attention. Langbeinites, derived from mixed cation Tuttons through thermal annealing, also show H2O sorptions that are incorporated into the structure during rehydration tests. Only a partial reversibility was demonstrated after 24 h to predominantly form K2MII(SO4)2(H2O)6 Tutton salts and metallic sulfate hydrates since the ammonia was lost during the heating.
•Mixed Tutton salts (NH4K)MII(SO4)2(H2O)6 (MII = Co or Ni) exhibit high energy storage densities ∼ 2.3–2.6 GJ/m3•Introducing different monovalent cations in a Tutton-type structure returns intermediate thermal behavior•The mixed Tuttons show complete structural reversibilities after 18 h under 299 K, atmospheric H2O, and 58 % RH conditions•K2MII2(SO4)3 Langbeinites, derived from mixed Tuttons, also show H2O sorptions during rehydration tests over time•After 24 h of rehydration, Langbeinites transform into K2MII(SO4)2(H2O)6 Tuttons and MII(SO4)(H2O)6 metallic sulfate hydrates