Ratandeep S. Kukreja

Solvothermal Synthesis of Platinum Alloy Nanoparticles for Oxygen Reduction Electrocatalysis

Platinum alloy nanoparticles show great promise as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. We report here on the use of N,N-dimethylformamide (DMF) as both solvent and reductant in the solvothermal synthesis of Pt alloy nanoparticles (NPs), with a particular focus on Pt-Ni alloys. Well-faceted alloy nanocrystals were generated with this method, including predominantly cubic and cuboctahedral nanocrystals of Pt(3)Ni, and octahedral and truncated octahedral nanocrystals of PtNi. X-ray diffraction (XRD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), coupled with energy dispersive spectroscopy (EDS), were used to characterize crystallite morphology and composition. ORR activities of the alloy nanoparticles were measured with a rotating disk electrode (RDE) technique. While some Pt(3)Ni alloy nanoparticle catalysts showed specific activities greater than 1000 μA/cm(2)(Pt), alloy catalysts prepared with a nominal composition of PtNi displayed activities close to 3000 μA/cm(2)(Pt), or almost 15 times that of a state-of-the-art Pt/carbon catalyst. XRD and EDS confirmed the presence of two NP compositions in this catalyst. HAADF-STEM examination of the PtNi nanoparticle catalyst after RDE testing revealed the development of hollows in a number of the nanoparticles due to nickel dissolution. Continued voltage cycling caused further nickel dissolution and void formation, but significant activity remained even after 20,000 cycles.

Atomic layer deposition of ultrathin platinum films on tungsten atomic layer deposition adhesion layers: Application to high surface area substrates

Platinum (Pt) atomic layer deposition (ALD) usually yields Pt nanoparticles during initial film growth. In contrast, deposition of continuous and ultrathin Pt films is needed for many important applications, such as the oxygen reduction reaction in polymer electrolyte membrane (PEM) fuel cells. A continuous and high radius of curvature Pt film is more stable and has a higher area-specific activity than the Pt nanoparticles commonly used in PEM fuel cells. However, the Pt film must be ultrathin and have a large surface area to be cost effective. In this paper, a review of earlier Pt ALD studies on flat substrates is presented that demonstrates that tungsten, with a higher surface energy than platinum, can serve as an adhesion layer to achieve Pt ALD films that are continuous at ultrathin thicknesses of ∼1.5 nm. This work utilized MeCpPtMe3 and H2 plasma as the Pt ALD reactants. The deposition of continuous and ultrathin Pt ALD films using MeCpPtMe3 and H2 plasma as the reactants is then studied on two high...

Magnetic Hardening of CeFe11Ti and the Effect of TiC Addition

We report the magnetic hardening of CeFe11Ti by melt spinning and compare ribbons prepared with and without TiC additions for grain refinement. X-ray diffraction indicates that samples melt-spun at surface wheel speeds between vs = 10 and 35 m/s are multiphased. However, CeFe11Ti with a major ThMn12-type phase has been successfully obtained either by directly melt spinning at the optimum wheel speed vs = 10 m/s or by annealing the overquenched ribbons melt spun at vs = 35 m/s. To restrain the grain growth during annealing, 3 and 6 at% TiC have been added to the starting ingots, which were subsequently melt spun in the same range of wheel speed. For as-spun samples, adding TiC leads to much finer grains as well as much greater phase separation compared with samples without TiC. However, upon annealing, multiphased TiC added samples can be fully converted to the desired CeFe11Ti phase with ThMn12type crystal structure together with TiC precipitates. Because of the grain refining effect played by TiC, samples with TiC are subject to less grain growth during the heat treatment, and hence feature an enhanced Hci =1.3

Circumventing Metal Dissolution Induced Degradation of Pt-Alloy Catalysts in Proton Exchange Membrane Fuel Cells: Revealing the Asymmetric Volcano Nature of Redox Catalysis

kOe and energy product (BH)max = 0.87

Spectroscopic in situ Measurements of the Relative Pt Skin Thicknesses and Porosities of Dealloyed PtMn (Ni, Co) Electrocatalysts

MGOe that are 18% and 22% higher, respectively, compared with the best annealed samples without TiC.