Palladium Nanosheet-Based Dual Gas Sensors for Sensitive\nRoom-Temperature Hydrogen and Carbon Monoxide Detection

Abstract

Palladium has long been explored\nfor use in gas sensors because\nof its excellent catalytic properties and its unique property of forming\nhydrides in the presence of H₂. However, pure Pd-based\nsensors usually suffer from low response and a relatively high limit\nof detection. Palladium nanosheets (PdNS) are of particular interest\nfor gas sensing applications due to their high surface area and excellent\nelectrical conductivity. Here, we demonstrate the design and fabrication\nof low-cost PdNS-based dual gas sensors for room-temperature detection\nof H₂ and CO over a wide concentration range. We fabricated\nsensors using multiwalled carbon nanotube@PdNS (MWCNT@PdNS) composites\nand compared their performance against pure PdNS devices for hydrogen\nsensing based on electrical resistive response. Devices using PdNS\nalone had a response and response time of 0.4% and 50 s, respectively,\nto 1% H₂ in air. MWCNT@PdNS (1:5 mass ratio) showed enhanced\nperformance at a lower hydrogen concentration with a limit of detection\n(LOD_H₂) of 5 ppm. Nearly an order of magnitude\nincrease in response was observed on increasing the amount of MWCNT\nto 50 mass % in the nanocomposite, but the response fell off at low\nH₂ concentration. Overall, these PdNS-based sensors were\nfound to show good repeatability, stability, and performance under\nhumid conditions. Their response was selective for H₂ <i>versus</i> CH₄, CO₂, and NH₃; the response to CO was comparable in magnitude but opposite in\nsign to the response to H₂. Upon simultaneous exposure\nto equal concentrations (10 ppm each) of H₂ and CO, the\nresponse to CO was dominant. The PdNS showed high sensitivity to CO,\ndetecting as little as 1 ppm CO in air at room temperature. The sensitivity\nto CO could be used either in a stand-alone room-temperature CO detector,\nwhere H₂ is known not to be present, or in combination\nwith CO and combustible gas detectors to distinguish H₂ from other combustible gases.