Mapping the Nexus of Electrical Conductivity and Gas Sensing for Tailored Design of Transition Metal (Cu, Co, Ni)-Based Bimetallic 2D Conjugated MOF

Abstract

Bimetallic 2D π-conjugated HHTP metal–organic frameworks (2D c-HHTP-MOFs), which with improved electrical conductivity, extended active sites, and customizable band gaps, have attracted a greater interest than their monometallic counterparts in electronics. However, there is no study on engineering bimetallic 2D c-HHTP-MOFs containing tunable 3d transition metal units in the field of chemiresistive sensors yet. Here, we present a mapping of electrical conductivity–gas sensing that enables the creation of bimetallic 2D M/Cu-HHTP c-MOFs (M = Co, Ni) with tailored metal nodes. We used crystal structure refinement, density functional theory (DFT) calculations, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT), and conductivity measurements to explore the role of metal nodes in the topology structure, ammonia (NH₃) adsorption capacity, energy band structure, and electrical conductivity. Consequently, we show that designing 2D Co/Cu-HHTP c-MOFs with both enhanced gas sensing and high electrical conductivity (σ ≈ 1.50 × 10^–3 S·cm^–1) can be applied in constructing high-performance room-temperature NH₃ chemiresistor, exhibiting higher sensitivity, better selectivity, reduced baseline resistance drift (<10%), and more superior repeatability and stability, compared with reported monometallic powdered 2D c-HHTP-MOFs. This work paves the way for designing high catalytic activity of bimetallic 2D c-MOFs without compromising their electrical conductivity.