Thermoelectric hydrogen sensor using Li x Ni1-x O synthesized by molten salt method

Abstract

Li-doped NiO was synthesized by molten salt method. LiNO3-LiOH flux was used as a source for Li doping. NiCl2 was added to the molten Li flux and then processed to make the Li-doped NiO material. Li:Ni ratios were maintained from 5: 1 to 30: 1 during the synthetic procedure and the chemical compositions after characterization were found from Li0.08Ni0.92O to Li0.16Ni0.84O. Li doping did not change the basic cubic structural characteristics of NiO as evidenced by XRD studies; however, the lattice parameter decreased from 0.41769 nm in pure NiO to 0.41271 nm in Li0.16Ni0.84O. Hydrogen gas sensors were fabricated by using these materials as thick films on alumina substrates. The half surface of each sensor was coated with the Pt catalyst. The sensor, when exposed to the hydrogen gas blended in air, heated up the catalytic surface leaving the rest half surface (without catalyst) cold. The thermoelectric voltage thus built up along the hot and cold surface of the Li-doped NiO made the basis for detecting hydrogen gas. The linearity of the voltage signal vs H2 concentration was checked up to 4% of H2 in air (as higher concentrations above 4.65% are explosive in air) using Li0.10Ni0.90O as the sensor material. The response time T90 and the recovery time RT90 were less than 25 sec. H2 concentration from 0.5% to 4% showed a good linearity against voltage. There was minimum interference of other gases and hence H2 gas can easily be detected.