Nanocatalyst degradation is a serious limiting factor for the commercialization of proton exchange membrane fuel cells. Although the degradation has been extensively studied in the past through various ex situ electrochemical methods, employing an in situ technique can greatly improve our understanding of the mechanisms involved during the electrochemical cycling. In this work, we have employed an in situ liquid cell inside a TEM for a simultaneous investigation of the structural evolution and electrochemical response of Pt–Fe nanocatalysts. We demonstrate that the coarsening processes of these nanocatalyst particles, including the nucleation and growth, are not uniform, both in space and in time scale. The growth rate is found to be both site- and potential-dependent. Furthermore, these particles were found to exhibit considerably different behaviors when attached to an electrode as opposed to when isolated in the electrolyte. With Pt–Fe nanoalloy system as a candidate material, this work demonstrates that the in situ structural characterization of nanocatalysts under electrochemical bias and inside the native electrolyte environment provides much deeper insight into the catalyst degradation mechanisms as compared to the routine ex situ electrochemical studies.

Fine-tuning nanocatalysts to enhance their catalytic activity and durability is crucial to commercialize proton exchange membrane fuel cells. The structural ordering and time evolution of ordered Pt3Fe2 intermetallic core-shell nanocatalysts for the oxygen reduction reaction that exhibit increased mass activity (228%) and an enhanced catalytic activity (155%) compared to Pt/C has been quantified using aberration-corrected scanning transmission electron microscopy. These catalysts were found to exhibit a static core-dynamic shell regime wherein, despite treating over 10,000 cycles, there is negligible decrease (9%) in catalytic activity and the ordered Pt3Fe2 core remained virtually intact while the Pt shell suffered a continuous enrichment. The existence of this regime was further confirmed by X-ray diffraction and the compositional analyses using energy-dispersive spectroscopy. With atomic-scale two-dimensional (2-D) surface relaxation mapping, we demonstrate that the Pt atoms on the surface are slightly relaxed with respect to bulk. The cycled nanocatalysts were found to exhibit a greater surface relaxation compared to noncycled catalysts. With 2-D lattice strain mapping, we show that the particle was about -3% strained with respect to pure Pt. While the observed enhancement in their activity is ascribed to such a strained lattice, our findings on the degradation kinetics establish that their extended catalytic durability is attributable to a sustained atomic order.

Considering the effect of CO emission together with the depletion of fossil fuel resources on future generations, industries in particular the transportation sector are in deep need of a viable solution to follow the environmental regulation to limit the CO emission. Thermoelectrics may be a practical choice for recovering the waste heat, provided their conversion energy can be improved. Here, the high temperature thermoelectric properties of high purity Bi doped Mg(Si,Sn) are presented. The samples MgSiSnBi with x(Sn) ≥ 0.6 and y(Bi) ≥ 0.03 exhibited electrical conductivities and Seebeck coefficients of approximately 1000 Ω cm and -200 μV K at 773 K, respectively, attributable to a combination of band convergence and microstructure engineering through ball mill processing. In addition to the high electrical conductivity and Seebeck coefficient, the thermal conductivity of the solid solutions reached values below 2.5 W m K due to highly efficient phonon scattering from mass fluctuation and grain boundary effects. These properties combined for zT values of 1.4 at 773 K with an average zT of 0.9 between 400 and 773 K. The transport properties were both highly reproducible across several measurement systems and were stable with thermal cycling.

Here we investigate the oxygen reduction reaction electrocatalytic activity and the corrosion stability of several ternary Pt−Au−Co and Pt−Ir−Co alloys, with Pt−Au−Co having never been previously studied for ORR. The addition of Au fine tunes the lattice parameter and the surface electronic structure to enable activity and cycling stability that is unachievable in Pt−25 atom % Co (state-of-the-art binary baseline). The ternary alloys exhibit a volcano-type dependence of catalytic efficacy on the content of Au or Ir. Pt−2.5 atom % Au−25 atom % Co alloy shows a specific activity of 1.41 mA cm −2 at 0.95 V, which is 16% and 404% higher than those of identically synthesized Pt−Co and pure Pt, respectively. This enhancement is promising in comparison to a range of previously published Pt "skeleton" and Pt "skin" alloys and is in fact the most optimum reported for a skeleton-type system. The catalysts exhibit dramatically improved corrosion stability with increasing levels of Au or Ir substitution, with the specific activity of all the ternary alloys being superior to that of Pt−Co after 100,000 potential cycles of 0.6−1.0 V. For instance, postcycled Pt−10 atom % Au−25 atom % Co shows a specific activity of 0.63 mA cm −2 , which is 140% higher than that of Pt−Co and 439% higher than that of Pt. HRTEM and XPS shows that Au alloying promotes the formation of an atomically thin Pt−Au-rich surface layer, which imparts kinetic stabilization against the dissolution of the less noble solute component.