Construction of Metal-Covalent Organic Frameworks with Trinuclear Copper Cluster for Efficient Triboelectric Nanogenerators

Metal-cluster-based covalent organic frameworks (MCOFs), obtained through covalent connections between metal clusters and organic molecules, have shown considerable promise in many applications. However, MCOFs have rarely been employed as triboelectric materials in triboelectric nanogenerators (TENGs), and their corresponding effect on the triboelectric output has not been systematically elucidated. Here, for the first time, a set of MCOFs (Cu₃-S-MCOF, Cu₃-M-MCOF, and Cu₃-L-MCOF) having similar skeletons but different pore spaces (2.1, 3.4, and 4.2 nm) are synthesized using copper-cyclic trinuclear units. All MCOFs are utilized as fillers in the methyl cellulose (MC) matrix to prepare a series of films as triboelectric layers for TENGs. Kelvin probe force microscopy (KPFM) showed that the surface charge density of the fabricated films can be precisely altered based on MCOFs. The mixing ratio between the MCOFs and MC is optimized to boost the triboelectric outputs of TENGs. A very high output current and voltage of up to 54.8 µA and 532.9 V, respectively, at 5 Hz are obtained from TENG with 10wt%Cu₃-M-MCOF@MC, which is further employed as a sensor to monitor human motions. This study provides new insights into the investigation of MCOF materials having tunable functionality to achieve high-performance TENG devices.