Dual-Sensitization of Cocatalysts on Elliptical Metal Oxide Nanofiber to Enhance Sensitivity and Selectivity of Acetylene Gas Sensor

Abstract

Detection of flammable hydrocarbons in power transformer oil has garnered great attention to prevent leakage and explosion, and to maintain safe working environment. Particularly, acetylene which readily dissolves in transformer oil is hazardous for its fast burning property and low explosive limit (2.4 %). Thus, it is of importance to develop highly sensitive chemiresistive materials entailing fast response time. Even if zinc oxide (ZnO) has been recognized as a selective acetylene sensing material [1],it has suffered from several limitations: high resistivity, higher limit of detection and sluggish sensing kinetics. Thus, to overcome such limitations, we designed a novel sensing platform by combining gallium (Ga) doping and co-catalyst decoration.We, herein, introduce highly sensitive and selective acetylene gas sensor through facile morphology tuning with following strategies: 1) Bi-functional Ga doping, 2) morphology control toward elliptical nanofiber, and 3) in-situ coupling of rhodium (Rh) and platinum (Pt) catalysts. The bi-functional Ga dopant does not only lower resistance by forming more free electrons, but also inhibits grain growth. Next, the elliptical nanofiber morphology directed by saponin and H2O-EtOH co-solvent is readily accessible by gas molecules compared to bulk materials, taking advantages of point-to-point contact, a large aspect ratio, a high surface-to-volume ratio, large porosity and high surface area (Fig. 1) [2]. Lastly, the in-situ coupling of Rh and Pt co-catalysts promotes heterogeneous sensitization toward acetylene. The different catalytic behaviors—electronic sensitization of Rh [3] and chemical sensitization of Pt—significantly enhanced the sensitivity and selectivity toward acetylene and achieved a remarkably low limit of detection compared to both bare and mono-metallic catalyst decorated Ga-doped ZnO (Response of bare Ga-doped ZnO to 5 ppm C2H2 > 8). Furthermore, our sodium iodide-templated catalyst synthesis enables small noble metal nanoparticles, facilitating gas penetration and adsorption and numerous p-n heterojunctions, and thereby improving gas sensing performance. These results open a new channel of tailoring highly sensitive and selective acetylene gas sensor. Reference [1] P. Y. Qiao, L. X. Zhang, M. Y. Zhu, Y. Y. Yin, Z. W. Zhao, H. N. Sun, J. Y. Dong, L. J. Bie, Acetylene sensing enhancement of mesoporous ZnO nanosheets with morphology and defect induced structural sensitization, Sensors and Actuators B, 250 (2017) 189-197; doi: 10.1016/j.snb.2017.04.158[2] X. Ren, H. Hou, Z. Liu, F. Gao, J. Zheng, L. Wang, W. Li, P. Ying, W. Yang, T. Wu, Shape‐Enhanced Photocatalytic Activities of Thoroughly Mesoporous ZnO Nanofibers, Small, 12 (2016) 4007-4017; doi: 10.1002/smll.201600991[3] A. Staerz, I. Boehme, D. Degler, M. Bahri, D. E. Doronkin, A. Zimina, H. Brinkmann, S. Herrmann, B. Junker, O. Ersen, J.-D. Grunwaldt, U. Weimar, N. Barsan, Rhodium Oxide Surface-Loaded Gas Sensors, Nanomaterials, 8 (2018) 892; doi:10.3390/nano8110892 Figure 1