Alkali polyphosphates as new potential materials for thermal energy storage

• Published in: Solar energy Vol. 157; pp. 277 - 283
• Main Authors: Pham Minh, Doan, Sane, Abdoul Razac, Semlal, Nawal, Sharrock, Patrick, Nzihou, Ange
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 15.11.2017; Pergamon Press Inc; Elsevier
• Subjects: Alkali polyphosphate; Dehydration; Energy consumption; Energy storage; Engineering Sciences; Enthalpy; Heat; Heat storage; High temperature; Lithium; Molten salts; Photovoltaic cells; Polyphosphates; Potassium; Salts; Sensible heat; Sensible heat storage; Sodium; Sodium polyphosphate; Solar energy; Temperature effects; Thermal energy; Thermal energy storage; Sensible heat storage; Thermal energy storage; Alkali polyphosphate
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/j.solener.2017.08.030

•For the first time, alkali polyphosphates were investigated as materials for TES.•Monoalkali polyphosphate (MPO3) melts at 628, 657 and 812°C for M=Na, Li, K.•All monoalkali polyphosphates were stable up to 900°C without notable weight loss.•MPO3 may be used as material for sensible heat storage at high temperature. Until now, molten salts (nitrate-based salts) are the main materials for sensible heat storage at industrial scale. The working temperature range of these materials is limited below 500°C. There is not yet a solution for sensible heat storage at high temperature. This paper aimed to investigate alkali polyphosphates ((MPO3)n, with M=Li, Na or K) as new promising materials for sensible heat storage at high temperature. Alkali polyphosphates could be formed by dehydration of monoalkali dihydrogenphosphates (MH2PO4, with M=Li, Na or K), which occurs below 400°C. Alkali polyphosphates resulted from this dehydration melted at 628, 657 and 812°C for sodium, lithium and potassium polyphosphate, respectively. All these liquids evaporated above 900°C but no destruction of their chemical structure was recorded. Sodium polyphosphate seemed to be the most promising material for sensible heat storage at high temperature because of its large potential working temperature (628–900°C), its availability and its low cost compared to lithium and potassium polyphosphates. The results open new prospects for the development of the thermal energy storage field.