Structure of Atomically Dispersed Pt in a SnO₂ Thin Film under Reaction Conditions: Origin of Its High Performance in Micro Electromechanical System Gas Sensor Catalysis

Abstract

A battery-driven micro electromechanical system (MEMS) gas sensor has been developed for household safety when using natural gas. The heart of the MEMS gas sensor is a 7.5 at % Pt−SnO 2 thin film catalyst deposited on the SnO 2 sensor layer. The catalyst enhances the sensitivity to methane, though its structure under working conditions is unclear. In this study, in situ XAFS was applied to a 7.5 at % Pt−SnO 2 catalyst layer deposited on a Si substrate, and we demonstrated that atomically dispersed Pt maintains its lattice position in SnO 2 with a small loss of surrounding lattice oxygen in the presence of 1% CH 4 and a more reducing gas of 1% H 2 at the reaction temperature (703 K), i.e., no Pt aggregation is observed. The lost oxygen is easily recovered by re-oxidation by air. This work has revealed that the atomically dispersed Pt in the SnO 2 lattice is the active structure and it is stable even under reaction conditions, which guarantees a long lifetime for the gas sensor.

Emerging single-atom catalysts in the detection and purification of contaminated gases

“…Murata et al demonstrated that Pt atoms dispersed randomly in a SnO 2 lattice underwent partial reduction without losing their lattice positions under reducing gases such as 1% CH 4 and 1% H 2 . 117 In situ XAFS measurements showed no formation of Pt nanoparticles even during the reaction ( Fig. 4h ).…”

Tin Oxide Based Hybrid Nanostructures for Efficient Gas Sensing

“…In addition, as the temperature increases, the resistance decreases due to the semiconducting nature of SnO 2 . However, as the temperature is increased to around 160 °C, a small increase in resistance is observed, which is a consequence of the conversion of molecular oxygen (O 2 − ) into atomic oxygen (2O − ) and thus the trapping of more free electrons [ 153 , 154 , 155 , 156 ]. The interaction with the adsorbed oxygen (O − ) by the SO 2 gas molecules on the surface of SnO 2 releases the trapped charge carriers back.…”

Free-Standing Porous and Nonporous Polyethylene Thin Films Using Spin Coating: An Alternate to the Extrusion–Stretching Process

“…Thin films are widely used for various applications, including micro-electromechanical systems, sensors, desalination, filtration, air filters, and integrated circuits . They can be coated on substrates or used as free-standing materials depending on the application.…”