Understanding the respective morphology changes with compression of the gas diffusion layer (GDL) and microporous layer (MPL) in unitized gas diffusion media (GDM) is critical for polymer electrolyte fuel cell (PEFC) high-power performance, as the compression affects the ohmic resistance and the porosity that influences masstransport resistance. We present a comprehensive study of morphology of two types of GDM (paper-type SGL 29BC and felt-type Freudenberg H2315 C2) under varied levels of compression using X-ray computed tomography (CT) to link GDM microstructure to fuel cell performance. The SGL 29BC morphology evolves more significantly with compression in ways that we expect to occlude oxygen diffusivity, while transitions in the Freudenberg H2315 C2 are more gradual. Upon compression by 0− 34% its initial thickness, the 29BC pore-size distribution (PSD) shifts from bimodal (12.6 and 34.9 μm average pore radii) to unimodal (9.67 μm), extensive MPL surface cracks decrease in surface area and depth (5−2.2% crack surface area), and void volume fraction decreases from 0.45 to 0.18. Freudenberg H2315 C2 GDM maintains a unimodal PSD (10.5 to 8.33 μm average pore radii), has minimal surface cracking in its discrete MPL layer, and maintains a larger void volume (0.54 to 0.35) upon compression from 0 to 28% its initial thickness. As a result, PEFCs operated in hot and humid conditions (80 °C, 100% RH) with SGL 29BC applied as cathode GDM lose performance beyond 14% compression; the current density at 0.6 V decreases from 827.8 to 795.9 mA cm −2 as 29BC compression increases from 14 to 28% the uncompressed GDM thickness. Alternatively, PEFCs with Freudenberg H2315 C2 GDM at the cathode increase in current density at 0.6 V as compression increases from 14 to 28% (1007 to 1098 mA cm −2 ).

High-surface-area ruthenium-based Ru x M y (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 Ru0.20Pt0.80 catalyst is 1.42 mA/cm2, nearly 3 times that of Pt (0.490 mA/cm2). Furthermore, Ru x Pt y 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.

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/cm 2 ) than commercial carbon-supported palladium (0.91 mA/cm 2 ) at 0.3 V vs.RHE. Bismuth modification improved nanotube performance over 4 times (3.75 mA/cm 2 ) 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 hours 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.

We detail the relationships between operating environment and performance of a thin and lightweight open-cathode fuel cell based on flexible circuits that may be advantageous for unmanned air vehicle (UAV) propulsion. The open-cathode fuel cell performance is studied in a broad range of realistic atmospheric flight conditions by mounting it in a wind tunnel within an environmental chamber. The relationships between the operating environment and performance are quantitated in terms of polarization behavior and the underlying loss mechanisms are discussed qualitatively in the context of electrochemical impedance spectroscopy (EIS), DC resistance and infrared temperature measurements. The wind tunnel experiments demonstrate that open cathode operation is possible over wide ranges of ambient temperature (5–55°C), relative humidity (22–90% RH), air speed (0–15.4 m s−1) and altitude (240–3240 m). Forced airflow is shown to improve mass transport, waste heat rejection, and water management, broadening the effective operating envelope of this open-cathode fuel cell over others that rely on free convection. Sacrificing air preconditioning renders open-cathode fuel cell performance sensitive to the conditions of the surrounding environment. The lightweight open-cathode fuel cell in this study has high specific power, exceeding 1.3 kW/kgcell in favorable ambient conditions of 5°C, 50% RH at sea level.

Supportless platinum nanotubes (PtNTs) were synthesized by the decomposition of platinum acetylacetonate vapor within anodic alumina templates at 210 • C. As synthesized, the nanotubes are nanoparticulate aggregates composed of Pt crystallites approximately 3 nm in diameter and with a range of lengths from 1 μm to 20 μm. Annealing treatments result in crystallite growth and morphological evolution of the tubular nanostructures including the development of nanoscale porosity. In rotating disk electrode measurements carried out in 0.1 M HClO 4 , porous PtNTs annealed at 500 • C exhibited a specific activity for oxygen reduction of 2390 ± 423 μA/cm 2 Pt at 0.9 V, comparable to bulk polycrystalline Pt. The electrochemical surface area of the annealed structures was a relatively low 10 m 2 /g, resulting in a moderate overall mass activity of 240 ± 41 mA/mg Pt .