Room temperature hydrogen gas sensor using candle carbon soot Shivani Dhall a,b , B.R. Mehta b,* a Department of Physics, DAV College, Jalandhar, Punjab, India b Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, India highlights graphical abstract  Fabrication of cost effective H 2 gas sensor at room temperature.  Well controlled functionalization of candle carbon soot at room temperature.  Role of functional groups on the structural property of candle car- bon soot.  Importance of functionalization for carbon soot based H 2 gas sensor. article info Article history: Received 13 January 2020 Received in revised form 16 March 2020 Accepted 18 March 2020 Available online 4 May 2020 Keywords: Candle Carbon Soot Functionalization Raman XRD H 2 sensor abstract In recent years, carbon materials are widely investigated because of they are enormously sensitive to H 2 at room temperature conditions. In the present work, the inexpensive candle carbon soot (CCS) is used to detect 0.5% concentration of H 2 gas at room temper- ature. A simple flame of candle is used to synthesize the layers of carbon soot at room temperature conditions. It is observed that, the acid treatment of CCS drastically improved their structural and sensing properties as compared to as-synthesized CCS. The effect of acid functionalization on the CCS structure were investigated by X-ray diffraction (XRD) and Raman spectroscopy. To the best of our knowledge, detection of low concentrations of H 2 gas is reported here for the first time using economical CCS at room temperature. © 2020 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. * Corresponding author. E-mail addresses: shivani.dhall24@gmail.com (S. Dhall), brmehta@physics.iitd.ac.in (B.R. Mehta). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 45 (2020) 14997 e15002 https://doi.org/10.1016/j.ijhydene.2020.03.142 0360-3199/© 2020 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.