Chemiresistive gas sensor response based on MOFs

Abstract

The objective of this research is to characterize the chemiresistive gas-sensing properties of the two-dimensional Metal-Organic Framework Ni3(HHTP)2, also referred to as Ni-HHTP. Two different samples were investigated based on the ligand used to make the MOF, which correspond to different oxidation states: Ni-HHTP-red, the semi-oxidized sample, and Ni-HHTP-ox, the fully oxidized sample. Both form ohmic contacts with the electrodes and exhibit semiconducting-like transport (dR/dT < 0). An Arrhenius analysis of Ni-HHTP-ox between 21 and 104 ◦C yields an activation energy of Ea = 71 ± 5 meV, which seems to indicate an extrinsic semiconducting behavior. The material is strongly cross-sensitive to humidity, which is therefore minimized to decouple the gas response. Under low-humidity conditions, the sensors yield reproducible chemiresistive responses to CH4, CO2 and H2 at the ppm level, with sensitivities of ∼0.1–0.3 %/ppm for CH4, ∼10−3 %/ppm for CO2 and up to 1.3 · 10−2 %/ppm for H2.