Méndez Colberg, Héctor G.

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    Synthesis and characterization of a novel palladium nanostructured ensemble supported on anodized alumina substrates for hydrogen sensing applications
    (2015) Méndez Colberg, Héctor G.; Martínez Iñesta, María M.; College of Engineering; Otaño Rivera, Wilfredo; Padovani Blanco, Agnes; Suleiman Rosado, David; Department of Chemical Engineering; Sundaram, Paul
    Hydrogen is a versatile molecule used in many industrial processes. Hydrogen is flammable at concentrations between 4% to 75% v/v at atmospheric pressure with a tendency to leak. There are a variety of hydrogen sensors, each with its advantages and disadvantages. Resistor type sensors are the most simple and promising sensors since they can readily detect hydrogen at room temperature or higher. Palladium thin film technology can potentially yield selective, small, fast, and energy efficient hydrogen sensors. The principle of this technology is the concurrent electrical and structural changes in the Pd structure upon hydrogen absorption. Synthesis methods for Pd based thin films are often expensive and energy consuming. In this work the solid-state reduction (SSR) synthesis method was established as energy and cost efficient way to obtain Pd, Ag10Pd90 and Pt10Pd90 films that can be used as hydrogen sensors. Film characterization included: X-ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy, Profilemeter, Energy Dispersive X-Ray Spectroscopy and X-Ray Photoelectron Spectroscopy. The hydrogen response was studied at room temperature. The hydrogen sensing conditions were optimized based on the effects of the film morphology, oxidation of the sample, presence of oxygen, working voltage and residence time on the stability, sensitivity and response time. The best synthesis conditions for SSR included liquid phase impregnation with addition of water during reduction. The best sensing results were obtained in a small volume chamber, as it was determined that the response time depends on the residence time. The response of pure Pd films was stable and precise from 0.01% to 2%v/v H2/N2 with sensitivities ranging from 0.6 to 8.3%. However, the signal is affected by structural changes that occur above 2% v/v H2 that are related to the α to ß Pd phase transition. The bimetallic films had an expanded range of detection due to a restriction on the phase transition lattice expansion. The Pt10Pd90 film exhibited the best sensing properties with a stable signal up to 50% v/v H2, a high sensitivity (~10%) that was proportional to the hydrogen concentration up to 8%v/v H2/N2 and a fast response time in the 10 s order of magnitude.