Advanced Electrodes for Solid Acid Fuel Cells by Platinum Deposition on CsH_(2)PO_4

We demonstrate cathodes for solid acid fuel cells fabricated by vapor deposition of platinum from the metalorganic precursor Pt(acac)_2 on the solid acid CsH_(2)PO_4 at 210 °C. A network of platinum nanoparticles with diameters of 2−4 nm serves as both the oxygen reduction catalyst and the electronic conductor in the electrode. Electrodes with a platinum content of 1.75 mg/cm^2 are more active for oxygen reduction than previously reported electrodes with a platinum content of 7.5 mg/cm^2. Electrodes containing <1.75 mg/cm^2 of platinum show significantly reduced catalytic activity and increased ohmic resistance indicative of a highly discontinuous catalytic-electronic platinum network

Vibrational modes in nanocrystalline iron under high pressure

The phonon density of states (DOS) of nanocrystalline 57Fe was measured using nuclear resonant inelastic x-ray scattering (NRIXS) at pressures up to 28 GPa in a diamond anvil cell. The nanocrystalline material exhibited an enhancement in its DOS at low energies by a factor of 2.2. This enhancement persisted throughout the entire pressure range, although it was reduced to about 1.7 after decompression. The low-energy regions of the spectra were fitted to the function AEn, giving values of n close to 2 for both the bulk control sample and the nanocrystalline material, indicative of nearly three-dimensional vibrational dynamics. At higher energies, the van Hove singularities observed in both samples were coincident in energy and remained so at all pressures, indicating that the forces conjugate to the normal coordinates of the nanocrystalline materials are similar to the interatomic potentials of bulk crystals

Ruthenium-Alloy Electrocatalysts with Tunable Hydrogen Oxidation Kinetics in Alkaline Electrolyte

High-surface-area ruthenium-based Ru_<i>x</i>M_<i>y</i> (M = Pt or Pd) alloy catalysts supported on carbon black were synthesized to investigate the hydrogen oxidation reaction (HOR) in alkaline electrolytes. The exchange current density for hydrogen oxidation on a Pt-rich Ru_0.20Pt_0.80 catalyst is 1.42 mA/cm², nearly 3 times that of Pt (0.490 mA/cm²). Furthermore, Ru_<i>x</i>Pt_<i>y</i> alloy surfaces in 0.1 M KOH yield a Tafel slope of ∼30 mV/dec, in contrast with the ∼125 mV/dec Tafel slope observed for supported Pt, signifying that hydrogen dissociative adsorption is rate-limiting rather than charge-transfer processes. Ru alloying with Pd does not result in modified kinetics. We attribute these disparate results to the interplay of bifunctional and ligand effects. The dependence of the rate-determining step on the choice of alloy element allows for tuning catalyst activity and suggests not only that a low-cost, alkaline anode catalyst is possible but also that it is tantalizingly close to reality

Platinum and Palladium Overlayers Dramatically Enhance the Activity of Ruthenium Nanotubes for Alkaline Hydrogen Oxidation

Templated vapor synthesis and thermal annealing were used to synthesize unsupported metallic Ru nanotubes with Pt or Pd overlayers. By controlling the elemental composition and thickness of these overlayers, we obtain nanostructures with very high alkaline hydrogen oxidation activity. Nanotubes with a nominal atomic composition of Ru_0.90Pt_0.10 display a surface-specific activity (2.4 mA/cm²) that is 35 times greater than that of pure Ru nanotubes at a 50 mV overpotential and ∼2.5 times greater than that of pure Pt nanotubes (0.98 mA/cm²). The surface-segregated structure also confers dramatically increased Pt utilization efficiency. We find a platinum-mass-specific activity of 1240 A/g_Pt for the optimized nanotube versus 280 A/g_Pt for carbon-supported Pt nanoparticles and 109 A/g_Pt for monometallic Pt nanotubes. We attribute the enhancement of both area- and platinum-mass-specific activity to the atomic-scale homeomorphism of the nanotube form factor with adlayer-modified polycrystals. In this case, subsurface ligand and bifunctional effects previously observed on segregated, adlayer-modified polycrystals are translated to nanoscale catalysts

Supportless, Bismuth-Modified Palladium Nanotubes with Improved Activity and Stability for Formic Acid Oxidation

Palladium nanotubes (PdNTs) were synthesized by templated vapor deposition and investigated for formic acid electrooxidation. Annealed PdNTs are 2.4 times more active (2.19 mA/cm²) than commercial carbon-supported palladium (0.91 mA/cm²) at 0.3 V vs RHE. Bismuth modification improved nanotube performance over 4 times (3.75 mA/cm²) vs Pd/C and nearly 2 times vs unmodified PdNTs. A surface Bi coverage of 80% results in optimal site-specific activity by drastically reducing surface-poisoning CO generation during formic acid electrooxidation. The Bi-modified PdNTs are exceptionally stable, maintaining 2 times the area-normalized current density as Pd/C after 24 h at 0.2 V vs RHE. We attribute the enhanced activity and stability of the nanotube catalysts to the presence of highly coordinated surfaces, mimicking a flat polycrystal while retaining high surface area geometry