Breakthrough Research on Trimodal Thermal Energy Storage Materials for Renewable Energy Applications

Academic Background

With the global reduction in dependence on fossil fuels, the widespread application of renewable energy has become a key focus for future energy development. However, the intermittency and instability of renewable energy make efficient, low-cost, and sustainable energy storage technologies an urgent need. The combination of thermal energy storage materials (TESMs) with Carnot batteries is believed to revolutionize the energy storage sector. However, the lack of stable, low-cost, and high-energy-density thermal energy storage materials has hindered the further development of this technology.

Thermal energy storage materials primarily store energy through three modes: sensible heat storage, latent heat storage, and thermochemical storage. Sensible heat storage relies on the heat capacity of materials, latent heat storage stores energy through the phase transition of phase change materials (PCMs), and thermochemical storage stores energy through reversible chemical reactions or adsorption processes. In recent years, the concept of combining these three modes in a single system has gained attention due to its potential to unlock extremely high thermal energy storage capacities.

Source of the Paper

This paper was co-authored by Saliha Saher, Sam Johnston, Ratu Esther-Kelvin, Jennifer M. Pringle, Douglas R. MacFarlane, and Karolina Matuszek, affiliated with Monash University and Deakin University in Australia. The paper was published in Nature from December 19 to 26, 2024, under the title Trimodal Thermal Energy Storage Material for Renewable Energy Applications.

Research Process and Results

Research Process

1. Material Screening and Preparation
   The research team first screened a series of binary mixtures of boric acid with different organic acids, ultimately selecting the eutectic mixture of boric acid and succinic acid as the research subject. The mixture was prepared using a grinding method to ensure uniformity.

2. Thermal Performance Testing
   The thermal properties of the material were tested in detail using differential scanning calorimetry (DSC). DSC tests showed that the eutectic mixture of boric acid and succinic acid undergoes a phase transition at 148°C, accompanied by a reversible thermal energy uptake of 380 J/g.

3. Raman Spectroscopy Analysis
   Through Raman spectroscopy analysis, the research team confirmed the chemical reaction of boric acid dehydrating to form metaboric acid during the phase transition. Raman spectra showed characteristic peaks of metaboric acid in the liquid mixture, indicating that the chemical reaction occurs simultaneously with the phase transition.

4. Long-Term Stability Testing
   To verify the long-term stability of the material, the research team subjected the eutectic mixture to 1,000 heating-cooling cycles. The results showed that the material maintained stable thermal performance throughout the cycles, with no significant chemical changes.

5. Cost and Sustainability Analysis
   The research team also evaluated the cost and sustainability of the material. Both boric acid and succinic acid are low-cost, environmentally friendly materials, and the preparation process is solvent-free, making it suitable for large-scale production.

Key Results

1. High Thermal Energy Uptake and Release
   The eutectic mixture of boric acid and succinic acid exhibited a thermal energy uptake of 380 J/g at 148°C, and this energy was fully released during cooling. Considering sensible heat storage in practical applications, the total thermal energy storage capacity reached 394 J/g.

2. Synergistic Effect of Chemical Reaction and Phase Transition
   The study revealed for the first time that boric acid undergoes dehydration during the phase transition, forming metaboric acid and water. The water in the liquid mixture rapidly participates in the rehydration of metaboric acid, making the entire process highly reversible.

3. Long-Term Stability
   After 1,000 heating-cooling cycles, the material’s thermal performance showed no significant changes, indicating excellent long-term stability.

4. Low Cost and Sustainability
   Both boric acid and succinic acid are low-cost materials, and the preparation process is solvent-free, making it suitable for large-scale production. The material’s global warming potential (GWP) is low, and its environmental impact can be further reduced by using renewable energy sources.

Conclusions and Significance

This study reports for the first time a “trimodal” thermal energy storage material that integrates sensible, latent, and thermochemical storage modes to achieve extremely high thermal energy storage capacity. The eutectic mixture of boric acid and succinic acid exhibited a thermal energy storage capacity of 394 J/g at 148°C, with high reversibility and long-term stability. The development of this material provides a new solution for renewable energy storage, with broad application prospects.

Research Highlights

1. High Thermal Energy Storage Capacity
   The material exhibited a thermal energy storage capacity of up to 394 J/g at 148°C, far exceeding existing phase change materials.

2. Synergistic Effect of Chemical Reaction and Phase Transition
   The study revealed for the first time that boric acid undergoes dehydration during the phase transition, and the rapid rehydration through water in the liquid mixture addresses the reversibility challenges of thermochemical storage materials.

3. Long-Term Stability
   The material maintained stable thermal performance after 1,000 heating-cooling cycles, demonstrating excellent long-term stability.

4. Low Cost and Sustainability
   The material is composed of low-cost, environmentally friendly boric acid and succinic acid, and the preparation process is solvent-free, making it suitable for large-scale production.

Other Valuable Information

The research team further verified that the material undergoes no irreversible chemical changes during heating-cooling cycles through nuclear magnetic resonance (NMR) and powder X-ray diffraction (PXRD) analysis. Additionally, the team developed a solvent-free preparation method, making the production process more environmentally friendly and sustainable.

This study provides an efficient, low-cost, and sustainable thermal energy storage material for the renewable energy storage sector, with significant scientific value and application prospects.