Binder-Free Growth of Aluminum-Based Metal-Organic Frameworks on Aluminum Substrate for Enhanced Water Adsorption Capacity

Coating metal-organic frameworks (MOFs) on metal substrates is an important research orientation in the applications of MOFs. However, the existing binder-based coating method needs repetitive operations and unavoidably plugs the pores of MOFs, resulting in a reduction of the adsorption capacity. Herein, a binder-free method is proposed to construct the MOF-on-metal structure. The well-intergrown polycrystalline Al-MOF layer on aluminum substrate is prepared by in situ synthesizing Al-based MOFs (MIL-96 and MIL-100) with aluminum ions from the dissolution of aluminum substrates. The morphology and chemical compositions of the MOF coating layer are systematically characterized, and a pH-controlled strategy is proposed to regulate the relative proportion of the hybrid MOFs. Importantly, the MOF-on-metal structure displays ultrahigh water adsorption capacity of 192.5 g m(-2), which is the highest of all reported desiccant-coated metal structures, and superior cycling stability. Further, the performance of a desiccant heat pump system utilizing MOF-on-metal structure is predicted, demonstrating that the operation period is 80% longer than a system with a binder-based silica gel coating, and the average dehumidification capacity can reach 8.36 g kg(-1) dry air. In conclusion, the new method enables the formation of binder-free, low-cost, and high-performance MOF coating and has a broad prospect in energy-efficient adsorption-based applications.