Sais de tutton mistos MIMII(SO4)2(H2O)6 (MI = NH4, K; MII = Co, Ni) e suas correspondentes fases langbeinitas como materiais de armazenamento de calor termoquímico

Abstract

In this work, mixed Tutton salts MI

2MII(SO4)2(H2O)6 (where MI = NH4, K and MII = Co, Ni) and their corresponding Langbeinites phases were synthesized and investigated as thermochemical heat storage materials. Individual precursor Tutton salts have also been considered for comparison proposals. Elemental composition, thermal and vibrational properties, and phase transformations/transitions were features examined, along with thermochemical application parameters. The salts (NH4)0,75K1,25Co(SO4)2(H2O)6 ≡ AKCoSH, (NH4)0,85K1,15Ni(SO4)2(H2O)6 ≡ AKNiSH and (NH4)0,93K1,07Co0,31Ni0,69(SO4)2(H2O)6 ≡ AKCoNiSH exhibited charging temperatures between 342-367 K and high energy storage densities (~ 2.3-2.6 GJ/m3 ), The theoretical thermal efficiencies reached 48-53%. Dehydrated AKCoSH and AKNiSH showed complete rehydration and structural reversibility after 18 hours under open system conditions (299 K, atmospheric H2O, and 58% RH). The results support that the introduction of different cations into the monovalent ([NH4] + and K+ ) and divalent (Co2+ and Ni2+) sites in a Tutton-type structure produces intermediate thermal behavior, which may be valuable for tuning thermochemical parameters. K2MII2(SO4)3 type Langbeinites, derived from the mixed Tutton salts AKCoSH and AKNiSH by thermal treatment, also show H2O sorption (incorporated into the structure) during rehydration tests as a function of time. Only partial reversibility was demonstrated after 24 hours, predominantly forming Tutton salts K2MII(SO4)2(H2O)6 and metallic sulfate hydrates MII(SO4)(H2O)6 since the ammonia was lost during heating. On the other hand, AKCoNiSH showed high cyclability, i.e., a high ability to dehydrate and rehydrate for at least 10 cycles without significant degradation. The results obtained here demonstrate that mixed Tutton salts are potential candidates for thermochemical energy storage systems intended for small-scale applications.