Structural Characterization of Quantum-Crystalline Pt on SiO₂ Aerogels Used for In-a-Chip Catalytic Combustion of Hydrogen

The need to replace fossil fuels with more sustainable energy resources increased the interest in hydrogen as an energy source. In this perspective, catalytic combustion of hydrogen presents advantages when compared to conventional flame combustion, as the last one can result in NO_x production and flashback of the flame.
For an efficient hydrogen oxidation reaction regarding the lowest amount of noble-metal catalyst needed for realization, a homogenous distribution of very small but easy to synthesize catalysts is needed. A good possibility to ensure this is, first, the decoration of the catalyst on a support material enabling a wide distribution. Second, the catalyst consists best of single crystals, avoiding any domain boundaries or particle formation, which reduces the active surface per material mass. Finally, a narrow crystallite size distribution would enable a controlled surface to volume ratio making the use of the catalyst predictable. To realize this, a SiO₂-aerogel support is formed providing high surface area and a certain micro- and meso-porosity for a good distribution and accessibility of the catalyst. Additionally, the catalyst single crystals are realized with a narrow size distribution confirmed using an EnvACS analysis [1]. The morphology of the crystals was refined using real space pair distribution function data obtained from X-ray diffraction data by Fourier transformation, confirming an average of Pt₅₆₁ crystallites. The crystallite size distribution was compared with the particle size distribution obtained from TEM data analysis confirming every particle to be a quantum-crystallite [2]. Finally, both these systems were be combined in a way that a high distribution of the catalyst on the support is realized. In a final step, the nanoparticle/aerogel system is integrated in a silicon chip. Hydrogen catalytic combustion is performed directly in the chip and characterized by measuring the change in resistance of a thermistor placed in a polyimide membrane. The final np@SiO₂ system can enable hydrogen combustion in a chip with different concentration of Pt and hydrogen, with or without preheating, resulting in a temperature change of up to 40 K.
[1] T.M. Gesing, L. Robben, J. Appl. Crystallogr. 57 (2024) S1600576724007362. DOI: 10.1107/S1600576724007362
[2] T.M. Gesing et al. J. Mater. Sci. 57 (2022) 19280-19299. DOI: 10.1007/s10853-022-07854-w