Self-driven electrochemical system using solvent-regulated structural diversity of cadmium(II) metal-organic frameworks.

Optimizing friction materials based on molecular diversity in a molecular framework system is an effective method to improve the output performance of triboelectric nanogenerators (TENGs). In this study, three cadmium(II) metal-organic frameworks (Cd-MOFs) with different cavities were synthesized solvothermally by the assembly of cadmium nitrate (Cd(NO3)2·4H2O), 4',4'''-carbonylbis(([1,1'-biphenyl]-3,5-dicarboxylic acid)) (H4CBBD), and trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe) via a solvent-regulated strategy. The topology and porosity of Cd-MOFs could be controlled effectively by the solvent constituents and were demonstrated to be closely related to their triboelectric behaviors. Theoretical calculations and experimental characterizations revealed that the TENGs fabricated by the Cd-MOF with maximum porosity exhibited the best triboelectric performance owing to the enhanced specific surface area and surface potential. In the applications, the high-output TENGs can be successfully used as an efficient power supply for electrochemical systems, enabling the direct bromination of aromatic compounds in high yields with good regioselectivity. This study provides a simple and feasible method to optimize positive friction materials at the molecular level and develops the practical applications of TENGs in electrochemical systems.