Measuring the Reaction Heat Between Palladium-Gold Alloy Nanoparticles and Hydrogen Molecules Using MEMS Thermopile Chips

This study presents a method for characterizing the temperature-dependent reactivity of Pd-Au alloy nanoparticles with hydrogen by measuring the microcalorimetric heat released during their interaction using a MEMS-based thermopile differential scanning calorimeter (DSC). The MEMS single-crystal silicon thermopile, which has been integrated into the chip-based DSC, exhibits a high power responsivity of 145.8 V/W. This value is approximately seven times greater than commercially available DSC chips. This high sensitivity enables the detection of minute thermal power changes associated with gas-solid interactions. Using this DSC system, we conducted temperature-programmed measurements of the exothermic reaction between hydrogen and Pd<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>Au<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> nanoparticles supported on Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (Pd<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>Au<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> NPs@Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) over a range from 30°C to 400°C. The results reveal that in a 400 ppm hydrogen atmosphere, the nanoparticles exhibit exothermic behavior above 100°C. The thermal power output increases with rising temperature, though the rate of increase diminishes after 200 °C and approaches a saturation value of 0.28 mW at around 300°C. This observed behavior indicates a positive correlation between temperature and the reactivity of Pd<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>Au<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> NPs@Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> with hydrogen, with a notable saturation effect at higher temperatures. These findings offer valuable insights for determining optimal operating temperatures of hydrogen sensors based on Pd-Au nanoparticles, supporting their application in sensitive and selective gas detection systems.