Enhanced Ammonia Sorption Performance via NH₄Cl-Impregnated MIL-101(Cr) for Low-Grade Heat Utilization

Efficient ammonia (NH₃) adsorption and desorption under high-pressure conditions are crucial for advancing adsorption-driven thermal energy storage (TES) and heating/cooling systems. In this study, NH₄Cl-impregnated MIL-101(Cr) composites were synthesized to enhance NH₃ sorption performance. The strong NH₄⁺-Cl^- interactions within the metal-organic framework (MOF) scaffold provides abundant active sites, while the porous MIL-101(Cr) matrix ensures rapid NH₃ diffusion and uniform NH₄Cl distribution. This synergistic architecture significantly improves adsorption kinetics, cyclic stability, and desorption efficiency under mild thermal conditions. The optimized composite (MN1.70) exhibits an NH₃ uptake of 0.79 ± 0.02 g/g at 6.2 bar and 25 °C, along with excellent reversibility and a fast sorption rate (∼0.14 mg/g/s). System-level analysis based on these properties indicates a 7% improvement in energy storage capacity compared to the best previously reported sorption-based TES systems. These findings highlight the potential of NH₄Cl-MOF composites as promising candidates for low-temperature NH₃-based thermal energy management, particularly in industrial applications utilizing waste heat and renewable sources.