Characterisation of platinum-based fuel cell catalyst materials using 195Pt wideline solid state NMR

Abstract

This study demonstrates the utility of the novel Field Sweep Fourier Transform (FSFT) method for acquiring wideline (195)Pt NMR data from various sized Pt nanoparticles, Pt-Sn intermetallics/bimetallics used to catalyse oxidative processes in fuel cell applications, and various other related Pt3X alloys (X = Al, Sc, Nb, Ti, Hf and Zr) which can facilitate oxygen reduction catalysis. The (195)Pt and (119)Sn NMR lineshapes measured from the PtSn intermetallic and Pt3Sn bimetallic systems suggest that these are more ordered than other closely related bimetallic alloys; this observation is supported by other characterisation techniques such as XRD. From these reconstructed spectra the mean number of atoms in a Pt nanoparticle can be accurately determined, along with detailed information regarding the number of atoms present effectively in each layer from the surface. This can be compared with theoretical predictions of the number of Pt atoms in these various layers for cubo-octahedral nanoparticles, thereby providing an estimate of the particle size. A comparison of the common NMR techniques used to acquire wideline data from the I = 1/2 (195)Pt nucleus illustrates the advantages of the automated FSFT technique over the Spin Echo Height Spectroscopy (SEHS) (or Spin Echo Integration Spectroscopy (SEIS)) approach that dominates the literature in this area of study. This work also presents the first (195)Pt NMR characterisation of novel small Pt13 nanoclusters which are diamagnetic and thus devoid of metallic character. This unique system provides a direct measure of an isotropic chemical shift for these Pt nanoparticles and affords a better basis for determining the actual Knight shift when compared to referencing against the primary IUPAC shift standard (1.2 M Na2PtCl6(aq)) which has a very different local chemical environment.

Direct solid state NMR observation of the105Pd nucleus in inorganic compounds and palladium metal systems

“…see the core-shell cubo-octahedral model in ref. 33). These assertions are supported by the absence of bulk structural components represented by a narrow resonance at K tot B À32 100 ppm (see the 105 Pd static NMR data for the Pd black and Pd sponge in Fig.…”

“…The observation of highly variable static NMR resonance linewidths emanating from particle size effects in metal particles and nanoparticle systems has been previously described in studies on several metal species. 33,34 11,39 A sample of highly polydisperse bio-Pd nanoparticles of average size B2-41000 nm (coarse approximation) was synthesized via the biomineralized reduction of Pd(II) to Pd(0) using E. coli cells and pyrolysed in vacuum. 40 The particle sizes of these Pd metal particle was determined by sampling statistics performed under transmission electron microscopy (TEM) analyses.…”

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid‐State NMR

“…Achieving a uniform broadband excitation for these ultrawide patterns in the current setup of an NMR instrument is sometimes challenging. In a recent report, Rees et al used the field‐sweep Fourier transform (FSFT) method to study Pt and Pt‐alloy nanoparticles. Compared with conventional variable‐offset cumulative frequency‐stepping technique or the spin echo height spectroscopy method, the FSFT method allows a more accurate reconstruction of the 195 Pt NMR pattern with improved resolution and also full automation.…”

Koexistenz von 3d‐Ferromagnetismus und Supraleitung in [(Li1−xFex)OH](Fe1−yLiy)Se

“…Hochaufgelöste 7 Li‐NMR‐Spektren25 zeigen zwei Signale von zwei Li‐Lagen, deren T 1 ‐Relaxationszeiten sich um drei Größenordnungen unterscheiden (Abbildung 6). Ein Anteil ist breit und relaxiert sehr schnell.…”