Evaluation of Formate Salt PCM’s for Latent Heat Thermal Energy Storage

Samuel Gage, Prashant Sharan, Craig Turchi, Judy Netter

Research output: Contribution to journalArticlepeer-review

3 Scopus Citations


This work examines formate salts as potential phase change materials (PCMs) for middle-high temperature (≤250C) latent heat thermal energy storage applications. The thermophysical properties of three formate salts were characterized: pure sodium formate and binary blends of sodium/potassium formate and sodium/calcium formate. The stability of formate PCM’s was evaluated by thermal cycling using differential scanning calorimetry where sodium formate and sodium/potassium formate appeared stable over 600 cycles, while sodium/calcium formate exhibited a monotonic decrease in heat of fusion over the test period. A longer test with sodium formate led to gas release and decomposition of the salt. FTIR analysis of the PCM showed degradation of formate to oxalate. T-history experiments with 50-g PCM quantities demonstrated a bulk supercooling of only 2–3C for these salts. Thermal conductivity enhancement of over 700% was achieved by embedding aluminum in the solid PCM. Finally, mild carbon steel was immersed in molten sodium formate for up to 2000 h. Sodium formate was found to be non-corrosive, as calculated by mass loss and confirmed by cross-sectional high-resolution microscopy. FTIR analysis of the PCM after 2000 h shows oxidation at the free surface, while the bulk PCM remained unchanged, further indicating a need to protect the formate from atmospheric exposure when used as a PCM.

Original languageAmerican English
Article number765
Number of pages10
Issue number3
StatePublished - 2021

Bibliographical note

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

NREL Publication Number

  • NREL/JA-5700-77957


  • Corrosion
  • Formate salts
  • Latent heat thermal energy storage
  • Phase change materials
  • Supercooling
  • Thermal conductivity enhancement
  • Thermal cycling


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