Mixed tutton salts K2Mn0.15Co0.85(SO4)2(H2O)6 and K2Mn0.16Zn0.84(SO4)2(H2O)6 for applications in thermochemical devices: experimental physicochemical properties combined with first-principles calculations

• Published in: Journal of materials science Vol. 59; no. 31; pp. 14445 - 14464
• Main Authors: de Oliveira Neto, João Gomes, da Silva, Luiz Fernando Lobato, Alves, Tiago Kalil Cortinhas, Neumann, Andreas, de Sousa, Francisco Ferreira, Ayala, Alejandro Pedro, dos Santos, Adenilson Oliveira
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2024; Springer Nature B.V
• Subjects: Band theory; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Cobalt; Computation & Theory; Conduction bands; Crystal lattices; Crystallization; Crystallography and Scattering Methods; Dehydration; Density functional theory; Energy bands; Energy gap; Energy storage; Enthalpy; First principles; Fixed bed reactors; Free energy; Group theory; Heat; Infrared spectra; Insulation; Materials Science; Mathematical analysis; Polymer Sciences; Single crystals; Solid Mechanics; Storage systems; Surface stability; Thermal energy; Thermal stability; Zinc salts
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-024-10049-0

In this paper, two hydrated double salts, whose chemical formulas are K 2 Mn 0.15 Co 0.85 (SO 4 ) 2 (H 2 O) 6 (KMn/Co) and K 2 Mn 0.16 Zn 0.84 (SO 4 ) 2 (H 2 O) 6 (KMn/Zn), were crystallized via solvent slow evaporation. The structural, thermal, and vibrational properties were explored and discussed. Furthermore, a study of geometric, electronic, and thermodynamic (entropy, enthalpy, and free energy) parameters was performed based on computational calculations. Single-crystal X-ray diffraction indicated that the compounds belong to the family of mixed Tutton salts with monoclinic symmetry, space group P 2 1 / c ( C 2 h 5 ), and occupancy factors of Mn 0.15 /Co 0.85 (KMn/Co) and Mn 0.16 /Zn 0.84 (KMn/Zn). Additionally, the intermolecular contacts and total empties in the unit cells were determined by Hirshfeld surfaces and crystal voids, respectively. The two crystals exhibited thermal stability around 333 K (Mn–Co) and 348 K (Mn–Zn). Above these temperatures, endothermic and exothermic events characteristic of dehydration, crystallization, solid–solid transition, and melting are recorded. Furthermore, KMn/Co and KMn/Zn exhibited significant energy densities, making them promising candidates for thermochemical energy storage systems. An energy band gap of 4.13 eV and 4.49 eV was predicted for KMn/Co and KMn/Zn, respectively. These findings are characteristic of insulating materials with major contributions from p orbitals in the valence and conduction bands. Using group theory and density functional theory (DFT), it was suggested that the two compounds have a total of 183 optical modes in the spectral region from 30 to 3600 cm −1 . Furthermore, experimental and calculated Raman and infrared spectra showed a good correlation. Our data suggest that the KMn/Co and KMn/Zn salts present promising thermo-structural results, showing that they can be used in heat-storing thermochemical devices due to their low dehydration temperatures, high dehydration enthalpies, and good energy density. Graphical Abstract