Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks

Abstract

Conductive metal–organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu‐CAT‐1 is described.

Catalytic Metal Nanoparticles Embedded in Conductive Metal–Organic Frameworks for Chemiresistors: Highly Active and Conductive Porous Materials

“…The slight increase of lattice spacing to z-axis can reduce the hopping current between C-MOF layers. [44] Moreover, the partially oxidized Pd and Pt (PdO and PtO as confirmed with XPS analysis) can further affect the baseline resistance by creating additional junctions. Since the work functions of PdO and PtO x are 7.90 and 5.65 eV, respectively, [46,47] PtO donates electrons to Cu 3 (HHTP) 2 , whereas PdO deprives Cu 3 (HHTP) 2 of electrons ( Figure S5, Supporting Information).…”

“…This is because H 2 O molecules (hundreds to tens of thousands of ppm levels) in air can be easily adsorbed on the open Cu sites in Cu 3 (HHTP) 2 . [44] The baseline resistances of the samples in dry air were 13 MΩ for pristine Cu 3 (HHTP) 2 , 25 MΩ for Pd@Cu 3 (HHTP) 2 , and 63 MΩ for Pt@Cu 3 (HHTP) 2 (Figure S4, Supporting Information). The increase in baseline resistances was attributed to the creation of multiple junctions between materials of different work functions (5.99 eV for Cu 3 (HHTP) 2 , 5.12 eV for Pd, and 5.65 eV for Pt).…”

“…[22] Analytes are preferentially adsorbed on open metal sites that are coordinatively unsaturated metal centers in MOFs, changing their electrical resistance. [44] Since NO 2 is an electron acceptor at room temperature, the resistance of Cu 3 (HHTP) 2 , a p-type sensing material, decreases when C-MOFs were exposed to NO 2 . The highly porous Cu 3 (HHTP) 2 with MΩ-level resistance and high surface area not only facilitate gas diffusion into sensing layers through a number of pores but also transduce electrical signals from the surface reaction.…”

“…It was noted that the baseline resistance of the sensors in humid atmospheres (relative humidity: ≈95%) continuously increased to the measurement limit (100 MΩ) of our sensing system. This is because H 2 O molecules (hundreds to tens of thousands of ppm levels) in air can be easily adsorbed on the open Cu sites in Cu 3 (HHTP) 2 . The baseline resistances of the samples in dry air were 13 MΩ for pristine Cu 3 (HHTP) 2 , 25 MΩ for Pd@Cu 3 (HHTP) 2 , and 63 MΩ for Pt@Cu 3 (HHTP) 2 (Figure S4, Supporting Information).…”

Solid–solid interface growth of conductive metal–organic framework nanowire arrays and their supercapacitor application

“…Metal-organic frameworks (MOFs) have shown tremendous application potential as active electrodes in field-effect transistors (FETs), supercapacitors, and chemiresistive devices, [1][2][3][4][5][6][7][8][9][10][11] in addition to traditional applications of catalysis, 12 gas storage 13 and drug delivery. 14 These applications are reliant upon new emerging electrically conductive MOFs in general, [15][16][17][18] due to their unique properties of long-range crystallinity, well-established structural tunability, tunable band gaps, and designable charge transport pathways.…”