Tunable Metal-Organic Frameworks Enable High Efficiency Cascaded Adsorption Heat Pumps

Rising global standards of living coupled with the recent agreement to eliminatehydrofluorocarbon refrigerants are creating intense pressure to develop more sustainable climatecontrol systems. In this vein, the use of water as the refrigerant in adsorption heat pumps is highlyattractive, but such adsorption systems are constrained to large size and poor efficiency by thecharacteristics of currently employed water sorbents. Here we demonstrate control of the relativehumidity of water uptake by modulating the pore size in a family of isoreticular triazolate metalorganicframeworks. Using this method, we identify a pair of materials with stepped, nonoverlappingwater isotherms that can function in tandem to provide continuous cooling with arecord ideal coefficient of performance of 1.63. Additionally, when used in a single-stage heatpump, the microporous Ni2Cl2BBTA has the largest working capacity of any material capable ofgenerating a 25 °C difference between ambient and chiller output.