Exploring the limits of csq-Zr-MOFs in Adsorption Heat Pumps: a computational study of their potential for cooling and heating applications

Adsorption Heat Pumps (AHPs) promise to play a leading role in achieving targets for decarbonization and reducing worldwide energy consumption. Metal-organic frameworks (MOFs) have been extensively explored in recent years as the medium for AHP due to their outstanding tunability, large surface area, and pore volume. In this work, we computationally design a series of Zr-MOFs with a csq topology using organic linkers of varying lengths to investigate the improvement of the coefficient of performance for heating (COP_H) and cooling (COP_C). Employing DFT methods, we assess the mechanical stability of these csq-Zr-MOFs by analyzing bulk modulus, shear modulus, and Young’s modulus. We set criteria for mechanical stability, requiring hypothetical csq-Zr-MOFs to have superior or at least equal mechanical properties compared to the experimentally obtained reference MOFs: DUT-6, DUT-60, and MOF-399. It is encouraging to observe that mechanically stable, in silico designed csq-Zr-MOF-5T demonstrates superior cooling performance with a COP_C = 0.88. Furthermore, 5T approaches the theoretical COP_H limit with a COP_H = 1.91. This highlights the importance of pore engineering in optimizing MOF properties. In addition to creating new types of MOFs, we advocate for fine-tuning the existing MOFs using molecular simulations as a guidance.