Grain-boundary-rich Pt nanoparticle assembly for catalytic hydrogen sensing at room temperature

We report a facile method of synthesizing grain-boundary(GB)-rich platinum nanoparticle assembly. GBs are formed between platinum nanoparticles during their random collision and attachment in solution driven by water electrolysis. The GB-rich nanoparticle assembly exhibits ~400-fold higher catalytic hydrogen oxidation rate than platinum nanoparticles before assembly, enabling catalytic hydrogen sensing at room temperature without external heating. Our sensor also demonstrates fast response/recovery (~7 s at >1% H2), nearly no signal variation during a 280-hour-long stability test, and high selectivity toward hydrogen over 36 interference gases. Furthermore, this sensor can be easily fabricated from commercial thermometers at a low cost (< $5 per unit). Theoretical calculation results reveal that the high performance of GB-rich platinum nanoparticle assembly arises from tensile strain at the GBs.

Deconvolution of Ferromagnetic Resonance Spectrum of Magnetic Nanoparticle Assembly Using Genetic Algorithm

The ferromagnetic resonance (FMR) spectra of dilute random assemblies of magnetite nanoparticles with cubic magnetic anisotropy and various aspect ratios are calculated using the stochastic Landau-Lifshitz equation at a finite temperature, T = 300 K, taking into account the thermal fluctuations of the particle magnetic moments. Particles of non-spherical shape in the first approximation are described as elongated spheroids with a given semiaxes ratio a/b, where a and b are the long and transverse semiaxes of a spheroid, respectively. A representative database of FMR spectra is created for assemblies of randomly oriented spheroidal magnetite nanoparticles with various transverse diameters D = 5 - 25 nm, moderate aspect ratios a/b = 1.0 - 1.8, and magnetic damping constants k = 0.1, 0.2. The basic FMR spectra of assemblies with D = 25 nm at different aspect ratios can be considered as representatives of assemblies of single-domain magnetite nanoparticles with transverse diameters D > 25 nm. The database is calculated at exciting frequency f = 4.9 GHz (S-band) to clarify clearly the details of the FMR spectrum that depend on the nature of the particle magnetic anisotropy. The data obtained make it possible to analyze arbitrary combined FMR spectra constructed as weighted linear combinations of FMR spectra of the base assemblies. In addition, using a genetic algorithm, the corresponding inverse problem is solved. The latter consists in determining the volume fractions of the base assemblies in some arbitrary nanoparticle assembly, which is represented by its FMR spectrum.PACS: 75.20.-g; 75.50.Tt; 75.40.Mg