Review Article An overview on how Pd on resistive-based nanomaterial gas sensors can enhance response toward hydrogen gas Ali Mirzaei a,b,** , Hamid Reza Yousefi c , Farhad Falsafi c , Maryam Bonyani c , Jae-Hyoung Lee d , Jae-Hun Kim d , Hyoun Woo Kim b,*** , Sang Sub Kim d,* a Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz, Iran b School of Materials Science and Engineering, Hanyang University, Seoul 04763, Republic of Korea c Department of Materials Science and Engineering, Shiraz University, Shiraz, 719646-84759, Iran d Department of Materials Science and Engineering, Inha University, Incheon 22212, Republic of Korea article info Article history: Received 8 March 2019 Received in revised form 29 April 2019 Accepted 22 May 2019 Available online xxx Keywords: H 2 gas Pd-decoration Gas sensor Sensing mechanism abstract Hydrogen has captured a lot of attention in recent years because its abundance, cleanness and one of the most promising sources of green energy. However, hydrogen has an explosive nature. Accordingly, detection of hydrogen leaks is important from a safety point of view. In this review paper, we use numerous examples to explain how Pd-decoration on the surfaces of nanomaterials can lead to enhancements in response and selectivity to- ward hydrogen gas. First, we describe the importance of hydrogen detection, then the properties of Pd and PdH x are reviewed, and metallic Pd hydrogen gas sensors are dis- cussed. Finally, we comprehensively review different semiconducting gas sensors deco- rated with Pd with more emphasis on the sensing mechanism. This review paper provides a simple yet informative background for researchers working in this hot field. © 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. Contents Hydrogen gas and hydrogen gas sensors ...................................................................... 00 Resistive-based semiconducting gas sensors: introduction and working principle ................................. 00 Noble metal-decoration .................................................................................... 00 Palladium and palladium hydride ............................................................................. 00 Metallic Pd-based hydrogen gas sensors ..................................................................... 00 Pd-decorated gas sensors for sensitivity enhancement toward hydrogen gas ..................................... 00 * Corresponding author. ** Corresponding author. Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz, Iran. *** Corresponding author. E-mail addresses: mirzaei@sutech.ac.ir (A. Mirzaei), hyounwoo@hanyang.ac.kr (H.W. Kim), sangsub@inha.ac.kr (S.S. Kim). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2019.05.180 0360-3199/© 2019 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. Please cite this article as: Mirzaei A et al., An overview on how Pd on resistive-based nanomaterial gas sensors can enhance response toward hydrogen gas, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.05.180