Facile synthesis of Al–Mg co-doped ZnO nanoparticles and their high hydrogen sensing performances

Abstract

Recently hydrogen has received a great attention as a renewable, clean and high-efficiency source of energy. However, its high explosiveness and leakage increased demand for sensors to monitor hydrogen during production, transport, storage and use. This paper presents a new nanostructured material for hydrogen monitoring. Indeed, to our knowledge, the aluminum/magnesium co-doped ZnO nanoparticles are used in the first time for hydrogen sensing. Al(5%)-Mg(1,3,5%) co-doped ZnO nanoparticles were effectively synthesized by facile sol-gel method in supercritical conditions. The structural, morphological and optical properties have been examined by different techniques. X-ray diffraction data confirmed the hexagonal wurtzite structure and showed a good enhancement of crystallinity with introduction of Al and Mg dopants. Transmission electron microscopy observations showed the nanometric size of the nanoparticles (15–25 nm) and the prismatic like shape of the crystallites. The TGA study proves the stability of the samples and the BET analysis illustrate that the isotherm of the 5A1MZO sample is belong to type II. Ultraviolet–Visible spectroscopy measurements evidenced the narrowing of the band gap energy for the co-doped samples which range between 3.14 and 3.19 eV. Photoluminescence spectra of all samples consist of two major components: a narrow ultraviolet emission band and a broad visible emission band (above 500 nm). Electrical properties were also studied. The synthesized samples have been screen printed and investigated as active layer for conductometric gas sensor devices. Their sensing characteristics towards wide range of hydrogen concentrations (100–30,000 ppm) were tested at various temperatures ranging from 200 to 400 °C in dry air. The Al(5%)-Mg(1%) co-doped ZnO sensor displayed the best sensing performances, showing a fast (3 s) and high (larger than 70) response towards 2000 ppm hydrogen at 250 °C. In addition, it showed low detection limit, good repeatability and high selectivity against various interfering gases. Compared to others recent works, the sensor showed competitive performances and by considering the facile, fast and low cost synthesized method of nanoparticles, it represents a promising material for the selective detection of hydrogen.