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Intense laser powers used in confocal Raman micro-spectroscopy can photoablate thermally sensitive samples. This has precluded study of the “dark” catalytic layers of hydrogen air fuel cells that consist of carbon supported Pt catalysts embedded in a polymer electrolyte. We now describe how photoablation is mitigated, with retention of z sectioning capability, by lifting the focal point above a transversely homogenous sample surface. This results in a circular conical illumination volume below the focal point. The geometric probability of photons generated in this volume, having pathways to the detector pinhole, is at least two orders of magnitude lower than those emerging from a focal point. However, adequate signal to noise can still be attained by sequestering the laser focal point in an isotropic medium that has no interfering Raman bands. This enables Raman photons from the circular conical illumination volume to dominate the spectra. A finite element model elucidates how incorporation of the isotropic medium for focal point sequestration recovers an order of magnitude in sensitivity. The above methodology provided spectroscopic evidence of the transition of a Nafion exchange site from a protonated sulfonic acid group with no local symmetry, to a dissociated sulfonate exchange site with C 3 v symmetry at the onset of the oxygen reduction reaction in a fully operating fuel cell. [ABSTRACT FROM AUTHOR]

A microkinetic model (MKM), independent from the assumptions of surface coverage or rate determining steps, was developed to understand reactivity trends of several metal and bimetallic catalysts for application as a Solid Oxide Fuel Cell (SOFC) anode at operating conditions ranging from the low (673 K) to high (1273 K) temperatures. A 1:1 composition of H 2 : CO was used as the fuel, which may be obtained from internal or external reforming of a variety of hydrocarbon fuels fed to the SOFC anode. The reactivity of the catalysts was plotted as a volcano plot against two descriptors; the carbon and oxygen binding energies of all the surface intermediates, reactants and products species. While water production rates gave a direct indication of catalyst activity for the oxidation reaction, CO 2 production rates were indirectly interpreted as its ability to oxidize surface adsorbed carbon to provide long-term stable operations. Following the interpolation principle, the volcano plot of the monometallic (Ag, Au, Cu, Pd, Pt, Ni, Co, Rh, Ru, and Re) catalysts dictated opportunities for alloying. A series of bimetallic catalysts containing Ni and other metals were screened for the same oxidation reaction. The results were significant in interpreting previously reported experimental trends on the reactivity of monometallic and bimetallic catalysts as well as in predicting novel compositions of bimetallic catalysts for achieving high catalyst activity and desired stability for a SOFC anode. Additionally, the effect of an applied electrode potential was studied on the activity of transition metal catalysts at SOFC conditions using volcano diagram. The MKM was constructed at an applied potential of U = 1.5 V with respect to a standard oxygen electrode (SOE) and analyzed at T = 873 K and T = 1073 K. Significant decrease in the H 2 oxidation rates were observed, while CO oxidation rates remained unaffected at the applied potential. [ABSTRACT FROM AUTHOR]

• Synthetic current density profiles with renewable power characteristics. • Pressurized alkaline water electrolyzer. • Experimental evaluation of dynamic operating concepts. • Enhancing the part-load operating range by lowering the gas contamination. [Display omitted] Synthetic current density profiles with wind and photovoltaic power characteristics were calculated by autoregressive-moving-average (ARMA) models for the experimental evaluation of dynamic operating concepts for alkaline water electrolyzers powered by renewable energy. The selected operating concepts included switching between mixed and split electrolyte cycles and adapting the liquid electrolyte volume flow rate depending on the current density. All experiments were carried out at a pressure of 7 bar, a temperature of 60 °C and with an aqueous potassium hydroxide solution with 32 wt.% KOH as the electrolyte. The dynamic operating concepts were compared to stationary experiments with mixed electrolyte cycles, and the experimental evaluation showed that the selected operating concepts were able to reduce the gas impurity compared to the reference operating conditions without a noticeable increase of the cell potential. Therefore, the overall system efficiency and process safety could be enhanced by this approach. [ABSTRACT FROM AUTHOR]

A solid oxide fuel cell (SOFC) is an energy converter device that directly converts the fuel's chemical energy into thermal and electrical energies. However, the performance of a SOFC is sensitive to the operating conditions, which indicates the need to control the operating parameters such as the operating temperature and inlet gas physical and chemical properties. In this paper, a three-dimensional (3- D) computational fluid dynamics (CFD) model of a button SOFC has been developed based on fluid flow, mass and heat transfer, and current and potential transport to study the performance of the button SOFC at different operating temperatures and flow rates. The results of all the investigated operating conditions have been validated with an in-house button SOFC. The results showed that the current density of the button SOFC increased significantly, to about 108.5% at average cell voltage 0.6 V and at oxygen flow rate of 1.8 L min−1 and hydrogen flow rate of 0.6 L min−1, when the operating temperature increased from 973 to 1023 K. However, less sensitivity has been found at the same average voltage of 0.6 V and an operating temperature of 973 K, the increase in the current density was about 9.7% when the flow rate of the oxygen increased from 0.4 to 0.6 L min−1, and the hydrogen flow rate increased from 1.2 to 1.8 L min−1, respectively; this was in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]