Jaak Nerut

Electrochemical and physical characterization of Pt–Ru alloy catalyst deposited onto microporous–mesoporous carbon support derived from Mo2C at 600 °C

The electrochemical reduction of oxygen on binary Pt–Ru alloy deposited onto microporous–mesoporous carbon support was studied in 0.5xa0M H2SO4 solution using cyclic voltammetry, rotating disk electrode (RDE), and impedance method. The microporous–mesoporous carbon support C(Mo2C) with specific surface area of 1,990xa0m2u2009g−1 was prepared from Mo2C at 600xa0°C using the chlorination method. Analysis of X-ray diffraction, photoelectron spectroscopy, and high-resolution transmission electron microscopy data confirms that the Pt–Ru alloy has been formed and the atomic fraction of Ru in the alloy was ∼0.5. High cathodic oxygen reduction current densities (−160xa0Au2009m−2 at 3,000xa0revu2009min−1) have been measured by the RDE method. The O2 diffusion constant (1.9u2009±u20090.3u2009×u200910−5u2009cm2u2009s−1) and the number of electrons transferred per electroreduction of one O2 molecule (∼4), calculated from the Levich and Koutecky–Levich plots, are in agreement with literature data. Similarly to the Ru/RuO2 system in H2SO4 aqueous solution, nearly capacitive behavior was observed from impedance data at very low ac frequencies, explained by slow electrical double-layer formation limited by the adsorption of reaction intermediates and products into microporous–mesoporous Pt–Ru–C(Mo2C) catalyst. All results obtained for C(Mo2C) and Pt–Ru–C(Mo2C) electrodes have been compared with corresponding data for commercial carbon VULCAN® XC72 (C(Vulcan)) and Pt–Ru–C(Vulcan) electrodes processed and measured in the same experimental conditions. Higher activity for C(Mo2C) and Pt–Ru–C(Mo2C) has been demonstrated.

Impact of the Pt catalyst on the oxygen electroreduction reaction kinetics on various carbon supports

Micro- and mesoporous carbide-derived carbons synthesized from molybdenum and tungsten carbides were used as porous supports for a platinum catalyst. Synthesized materials were compared with commercial Vulcan XC72R conducting furnace black. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and low-temperature N2 adsorption methods were applied to characterize the structure of catalysts prepared. The kinetics of oxygen electroreduction in 0.5xa0M H2SO4 solution was studied using cyclic voltammetry and rotating disk electrode methods. The synthesized carbide-derived carbons exhibited high specific surface area and narrow pore size distribution. The platinum catalyst was deposited onto the surface of a carbon support in the form of nanoparticles or agglomerates of nanoparticles. Comparison of carbide-derived carbons and Vulcan XC72R as a support showed that the catalysts prepared using carbide-derived carbons are more active towards oxygen electroreduction. It was shown that the structure of the carbon support has a great influence on the activity of the catalyst towards oxygen electroreduction.

Enhanced stability of symmetrical polymer electrolyte membrane fuel cell single cells based on novel hierarchical microporous-mesoporous carbon supports

Fuel cell electrodes were prepared from Pt nanocluster activated hierarchical microporous-mesoporous carbon powders. The carbon supports were synthesized from molybdenum carbide applying the high-temperature chlorination method. Six different synthesis temperatures within the range from 600 to 1000xa0°C were used for preparation of carbon supports. Thermogravimetric analysis, X-ray diffraction, low-temperature nitrogen sorption, and high-resolution scanning electron microscopy methods were used to characterize the structure of the electrode materials and symmetrical membrane electrode assemblies (MEAs). The MEAs prepared were used to conduct the proton exchange membrane fuel cell (PEMFC)single-cell measurements. The polarization and power density curves for single cells were calculated to evaluate the activity of the catalyst materials synthesized. The electrochemically active surface area (from 2.4 to 11.9xa0m2xa0g−1) was obtained in order to estimate the contact surface areas of platinum and Nafion® electrolyte. The values of the electrolyte resistance, polarization resistance, and cell degradation rate were calculated from electrochemical impedance spectroscopy data. The carbon materials synthesized within temperature range from 600 to 850xa0°C were found to be the most suitable supports for PEMFCs, having higher maximum power density values and better stability (cell potential degradation 240xa0μVxa0h−1) than commercial carbon-based (Vulcan XC72; 670xa0μVxa0h−1) single cells.