NH2-MIL-125 as a promising material for adsorptive heat transformation and storage

With increasing demand for heating and cooling, the effective utilization of renewable and waste thermal energy becomes a significant challenge. Due to its high energy saving potential AHT (Adsorption Heat Transformation) has gained more and more interest during the last three decades. Large advances in the enhancement of AHT performance can be achieved with the development of new adsorbents. In this paper, the results of a comprehensive study on water adsorption on NH2-MIL-125 and evaluation of the feasibility of the “NH2-MIL-125 - water” working pair for AHT are presented. It is shown that NH2-MIL-125 exchanges 0.39 g H2O g−1 under typical adsorptive chilling cycle conditions, which exceeds the uptake variation for common and innovative adsorbents. NH2-MIL-125 can be regenerated at 348 K which allows use of low-temperature heat sources. The isosteric enthalpy of water adsorption varies from −49.7 ± 1.0 kJ mol−1 to −54.8 ± 2.0 kJ mol−1 at an uptake of 0.03-0.40 g g−1. The adsorption capacity and porosity of NH2-MIL-125 change slightly during the first adsorption cycle and then remain constant. Based on the data obtained, the efficiency and specific power of the chilling cycle utilizing the “NH2-MIL-125 - water” pair were assessed as 0.77-0.80 and 3.2 kW kg−1, respectively, which is of high practical interest.