# Composite Adsorbent “1-Ethyl-3-methylimidazolium Acetate [EMIM] [Ac] into Mesoporous Silica Gel” for Adsorption Heat Storage

## TL;DR

This paper introduces a new composite material made of an ionic liquid and silica gel that efficiently stores heat through water adsorption.

## Contribution

The novel contribution is the development of a composite adsorbent with high thermal storage capacity and structural stability for heat storage systems.

## Key findings

- The composite achieved an adsorption capacity of up to 0.71 g/g at 50 °C and 80% relative humidity.
- The material showed full process reversibility and minimal hysteresis in adsorption/desorption cycles.
- Thermodynamic analysis confirmed a volumetric heat storage density of 600–920 MJ/m³ at regeneration temperatures below 100 °C.

## Abstract

The aim of this work is to prepare and characterize a composite adsorbent comprising the hydrophilic ionic liquid 1-ethyl-3-methylimidazolium acetate [EMIM-Ac] composite supported on mesoporous silica gel for application in adsorption heat storage systems. Water adsorption/desorption isotherms were measured gravimetrically at T = 40, 50, 70 °C across a relative humidity (RH) range of 0–0.8, demonstrating a high adsorption capacity (up to 0.71 g/g at 50 °C and RH = 0.8, for a 50 wt % [EMIM-Ac] loading). Full process reversibility and negligible ad/desorption hysteresis were also verified. Thermal stability of the prepared silica/[EMIM-Ac] composites was confirmed up to approximately T = 200 °C. Structural stability of samples subjected to repeated ad/desorption aging cycles was verified via FT-IR, High-Resolution Solid-State NMR, and Time-Domain NMR spectroscopy. Finally, the thermodynamic analysis based on adsorption experimental data indicated that the silica/[EMIM-Ac] composite is highly suitable for adsorption heat storage, providing a volumetric density of 600–920 MJ/m3 at regeneration temperatures below 100 °C.