Single-Atom Catalysts\nin Conductive Metal–Organic\nFrameworks: Enabling Reversible Gas Sensing at Room Temperature

Conductive metal–organic frameworks (cMOFs) offer\nhigh porosity\nand electrical conductivity simultaneously, making them ideal for\napplication in chemiresistive sensors. Recently, incorporating foreign\nelements such as catalytic nanoparticles into cMOFs has become a typical\nstrategy to enhance their sensing properties. However, this approach\nhas led to critical challenges, such as pore blockage that impedes\ngas diffusion, as well as limited improvement in reversibility. Herein,\nsingle-atom catalyst (SAC)-functionalized cMOF is presented as a robust\nsolution to the current limitations. Facile functionalization of SACs\nin a cMOF can be achieved through electrochemical deposition of metal\nprecursors. As a proof of concept, a Pd SAC-functionalized cMOF is\nsynthesized. The Pd SACs are stabilized at the interplanar sites of\ncMOF with Pd–N<sub>4</sub> coordination while preserving the\nporosity of the MOF matrix. Notably, the microenvironment created\nby Pd SACs prevents irreversible structural distortion of cMOFs and\nfacilitates a reversible charge transfer with NO<sub>2</sub>. Consequently,\nthe cMOF exhibits a fully recoverable NO<sub>2</sub> response, which\nwas not previously attainable with the nanoparticle functionalization.\nAdditionally, with the combination of preserved porosity for gas diffusion,\nit demonstrates the fastest level of response and recovery speed compared\nto other 2D-cMOFs of this class.