Nanocolumnar platinum thin films (Pt-TFs) were produced by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction electrocatalysts for polymer electrolyte membrane fuel cells. Conventional high-density Pt-TF prepared by low pressure sputtering was also studied for comparison. Pt-TFs were deposited on a microporous layer (MPL)-like surface composed of carbon particles to mimic catalyst-coated gas diffusion electrodes. Electron microscopy imaging revealed that HIPS Pt-TFs developed a cauliflower-like columnar microstructure, which originated from a shadowing effect during HIPS. This shadowing effect is enhanced on the rough surface of the MPL-like carbon that leads to the nano-cauliflower formation. With this approach, we also aimed to relate the catalyst performance obtained by benchtop tests directly to membrane electrode assembly test results. The electrochemically active surface area of Pt-TFs increased from 10 to 19 m 2 g −1 with increasing sputter pressure. Specific activity of conventional high-density and nanocolumnar films were similar at ∼600 μA cm −2 , which is likely due to their similar crystal grain sizes, >5 nm. On the other hand, mass-specific (MA) activity values increased from ∼0.06 A/mg Pt for conventional Pt-TF to ∼0.13 A/mg Pt for HIPS Pt-TFs, which is consistent with the columnar microstructure of HIPS films providing a better catalyst utilization compared to conventional Pt-TF.

Nanocolumnar platinum thin films (Pt-TFs) with different Pt mass loadings were grown by high pressure sputtering (HIPS) and investigated as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cell applications. Mass loading was controlled by changing the sputter deposition time. A cauliflower-like columnar microstructure was achieved by depositing the Pt-TFs onto a microporous layer (MPL)-like surface composed of carbon particles in order to mimic catalyst-coated gas diffusion electrodes. Microstructural evolution of HIPS Pt-TFs and their ORR activity were investigated. Electrochemical characterization of the nanocolumnar Pt-TFs was performed by cyclic voltammetry and rotating disk electrode measurements on Pt-TF/MPL-like-layer/glassy-carbon samples in an aqueous perchloric acid electrolyte. The electrochemically active surface area increased from 18 to 39 m 2 g −1 as the Pt mass loading was decreased. Specific activity of the films was similar (∼600 μA cm −2 ) for all Pt mass loadings, due to the similar nanoparticle sizes of ∼5 nm as observed by transmission electron microscopy and X-ray diffraction. Mass activity of the films increased from 0.11 to 0.26 A mg −1 as the Pt mass loading was decreased, which is an indication of the effective Pt utilization and better access through the catalyst layer at lower Pt mass loadings.

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The use of zinc oxide (ZnO) nanostructures as a photocatalyst for the degradation of organic pollutants in water has received significant attention over the recent years. However, synthesis methods for producing ZnO nanostructures are generally costly, complicated, and hazardous to the environment. In this work, we demonstrate the synthesis of ZnO nanostructures by a simple hot water treatment (HWT) method and the photocatalytic activity of the hence produced nanostructures. HWT is a one-step, low-cost, eco-friendly, and scalable nanostructure growth method. By HWT, various metal-oxide nanostructures can be produced simply by the interaction of metals with hot water without the need for any chemical additives in the solution. Growth of metal-oxide nanostructures by HWT involves the formation of metal-oxides and their release from the surface of the metal into water, the migration of the metal-oxides in water, and their re-deposition at a different part of the metallic surface, which initiates the growth of nanostructures. In this study, we used zinc powder and plates for producing the ZnO nanostructures by HWT in DI water at 75°C. Scanning electron microscopy and X-ray diffraction were utilized to verify the formation of ZnO nanostructures. Zinc plates produced a suspension of ZnO nanostructures in water, while on the other hand, zinc powder resulted in ZnO nanostructures grown on the powder surface as well as standalone ZnO nanostructures also mixed in water. We used these nanostructures + water suspensions for our photocatalytic degradation studies. Methylene blue (MB) was used as a model organic pollutant. We mixed the ZnO nanostructure suspension with MB and exposed it to UV light. The degradation of MB was observed by measuring its absorbance values using a UV-Visible spectrophotometer over a period of 4 hours. We observed a 20% decrease in the concentration of MB in 4 hours when nanostructured Zn/ZnO powder suspension was used, and a 30% decrease was achieved when ZnO nanostructure-only suspension produced from zinc plates was used. MB alone was also exposed to UV light for the same period as a control experiment, and we did not observe any significant decrease in its concentration. These results indicate that the hot water treatment method presents a very simple, cost-effective, scalable, and eco–friendly alternative for the synthesis of ZnO nanostructures for photocatalytic water treatment applications.

Self-supported nanocolumnar Pt:Ni thin films (TFs) with varying Pt:Ni atomic ratios and Pt mass loadings were produced on a microporous layer (MPL)-like surface composed of carbon particles by high pressure sputtering and examined as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cells. Cauliflower-like microstructures were observed from scanning electron microscopy imaging. Various Pt:Ni atomic ratios were obtained by simply changing the relative deposition power between Pt and Ni source and investigated by X-ray diffraction and quartz crystal microbalance analysis. Electrochemical characterization of the Pt:Ni-TF/MPL-like-layer/glassy-carbon samples was conducted through benchtop cyclic voltammetry and rotating disk electrode measurements. The electrochemically active surface area (ECSA) was found to be between 22-42 m2/g for different Pt:Ni atomic ratios. Lower Pt mass loadings exhibited a higher ECSA and the catalytic activity of all Pt:Ni ratios increased with the increase in Pt mass loading. The ORR activity of the Pt:Ni-TFs increased in the order of 3:1 < 1:1 < 1:3 with exhibiting a specific activity of 1781 µA/cm2 and mass activity of 0.66 A/mg for the Ni-rich film with 1:3 ratio. The catalytic performance of Pt:Ni-TFs were higher than traditional high surface area carbon supported Pt nanoparticles, elemental Pt nanorods, and Pt-Ni nanorods.