Technical Communication A low cost optical hydrogen sensing device using nanocrystalline Pd grating Ritu Gupta, Abhay A. Sagade, Giridhar U. Kulkarni* Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore, Karnatka 560064, India article info Article history: Received 9 December 2011 Received in revised form 2 March 2012 Accepted 4 March 2012 Available online 1 April 2012 Keywords: Optical diffraction Diffraction efficiency Hydrogen sensor Pd grating Micromolding Deflagration abstract A Pd grating of periodicity of 1.5 mm comprising of 1 mm wide nanocrystalline Pd lines has been obtained by a direct micromolding method to serve as Hydrogen sensor element in an optical diffraction set up. The device uses a low power diode laser and a photodetector and works with sensitivity of w20%. The hydrogen sensing action is based on monitoring the changes in the diffraction efficiency (DE) which is defined as the ratio of the first and the zeroth order diffracted beam intensities. The diffraction efficiency undergoes large and sudden changes as the nanocrystalline grating becomes disordered due to PdH x formation, as monitored using in-situ microscopy and optical profilometric measurements. This is truly a low cost, portable hydrogen sensor meant for large installations. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen sensing is important as a safety measure, particu- larly in these times, when its use is on the rise in a variety of applications as a clean, renewable and long lasting energy fuel [1]. The safety aspects apply to both hydrogen storage and transport which by their own merits have grown into giant areas of research in the last two decades. The extensive usage of this flammable gas thus demands for extraordinary detec- tion techniques, and there have been several inventions in this direction in the recent past [2]. Many materials that respond to H 2 sensitively have been tried out for its sensing. Some notable examples are hydrogen uranyl phosphate [3], ZnO nanorods [4], Pt nanoparticles [5], SnO 2 coated carbon nanotubes [6], tungsten nanowires [7] and graphene based materials [8]. Importantly, Pd based nanomaterials have been investigated extensively due to high hydrogen solubility and favourable reaction kinetics [9]. Pd is so selective to H 2 adsorption that it exhibits extremely low sensitivity to other gases such as CO, Cl 2 , SO 2 ,H 2 S, NO x and hydrocarbons. Pd undergoes lattice expansion to form Pd hydride reversibly at room temperature [10]. Exploiting this property, a variety of electrical and optical H 2 sensors have been developed so far. A great deal of literature is available on resistor-based H 2 sensors using Pd nanostructures [11,12]. While electrical devices have been shown to work efficiently, making reliable electrical contacts to individual nanotubes or nanowires is time consuming and cost prohibitive. Importantly, the usage * Corresponding author. E-mail address: kulkarni@jncasr.ac.in (G.U. Kulkarni). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 9443 e9449 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.03.010