NH3 has been used in wide applications, such as fertilizers, hydrogen sources, and working fluids, where proper NH3 adsorbents are required to minimize human health risks in daily NH3 exposure as well as to achieve energy efficiency in energy conversion systems. As NH3 operating pressure differs from each usage, the structure and properties of the NH3 adsorbent need to be optimized in each NH3 operating pressure. Metal–organic frameworks (MOFs) have emerged as promising NH3 adsorbents, which would be customizable for different NH3 pressures due to great structural tunability. We introduce up‐to‐date reports with MOFs as NH3 adsorbents and classify them by the NH3 pressure, from high in adsorption heat pumps to extremely low in daily life sensing. MOFs with high NH3 adsorption capacity and durability are suggested in different NH3 pressure ranges, and their structural factors are discussed to help design high‐performance MOFs for NH3 adsorption in different NH3 pressures.

Ammonia has emerged as a potential working fluid in adsorption heat pumps (AHPs) for clean energy conversion. It would be necessary to develop an efficient adsorbent with high-density ammonia uptake under high gas pressures in the low-temperature range for waste heat. Herein, a porous nanocomposite with MIL-101(Cr)-NH 2 (MIL-A) and reduced graphene oxide (rGO) was developed to enhance the ammonia adsorption capacity over high ammonia pressures (3–5 bar) and low working temperatures (20–40 °C). A one-pot hydrothermal reaction could form a two-dimensional sheet-like nanocomposite where MIL-A nanoparticles were well deposited on the surface of rGO. The MIL-A nanoparticles were shown to grow on the rGO surface through chemical bonding between chromium metal centers in MIL-A and oxygen species in rGO. We demonstrated that the nanocomposite with 2% GO showed higher ammonia uptake capacity at 5 bar compared with pure MIL-A and rGO. Our strategy to incorporate rGO with MIL-A nanoparticles would further be generalizable to other metal–organic frameworks for improving the ammonia adsorption capacity in AHPs.

Ammonia has recently emerged as a promising hydrogen carrier for renewable energy conversion. Establishing a better understanding and control of ammonia adsorption and desorption is necessary to improve future energy generation. Metal–organic frameworks (MOFs) have shown improved ammonia capacity and stability over conventional adsorbents such as silica and zeolite. However, ammonia desorption requires high temperature over 150 °C, which is not desirable for energy-efficient ammonia reuse and recycling. Here, we loaded silver nanoparticles from 6.6 to 51.4 wt% in MIL-101 (Ag@MIL-101) using an impregnation method to develop an efficient MOF-based hybrid adsorbent for ammonia uptake. The incorporation of metal nanoparticles into MIL-101 has not been widely explored for ammonia uptake, even though such hybrid nanostructures have significantly enhanced catalytic activities and gas sensing capacities. Structural features of Ag@MIL-101 with different Ag wt% were examined using transmission electron microscopy, X-ray powder diffraction, and infrared spectroscopy, demonstrating successful formation of silver nanoparticles in MIL-101. Ag@MIL-101 (6.6 wt%) showed hysteresis in the N 2 isotherm and an increase in the fraction of larger pores, indicating that mesopores were generated during the impregnation. Temperature-programmed desorption with ammonia was performed to understand the binding affinity of ammonia molecules on Ag@MIL-101. The binding affinity was the lowest with Ag@MIL-101 (6.6 wt%), including the largest relative fraction in the amount of desorbed ammonia molecules. It was presumed that cooperative interaction between the silver nanoparticle and the MIL-101 framework for ammonia molecules could allow such a decrease in the desorption temperature. Our design strategy with metal nanoparticles incorporated into MOFs would contribute to develop hybrid MOFs that reduce energy consumption when reusing ammonia from storage.