Proton exchange membrane fuel cells (PEMFCs) have the potential to become a vital part of sustainable energy systems, provided that cathode catalysts with higher activity and stability are developed. ...A very promising group of materials for the oxygen reduction reaction (ORR) is the group of alloys with platinum and rare earth elements.1, 2.
We have recently showed that sputtered thin films of Pt
3
Y have specific activities for ORR up to seven times higher than polycrystalline Pt in rotating disk measurements, which is similar to that of bulk alloys.3 In addition, sputtered thin films of Pt
3
Y with thicknesses about 3 nm show a mass activity more than an order of magnitude higher than state-of-the-art Pt nanoparticles.
However, in order to become realistic alternative catalysts these materials need to prove an increased activity also under real fuel cell conditions. By sputtering thin films of Pt
3
Y on gas diffusion layers (GDLs) we are able to construct full membrane electrode assemblies (MEAs) and evaluate these in single cell measurements.4 The fuel cell measurements show that Pt
3
Y has a specific activity up to 2.5 times higher than pure Pt. Detailed characterization reveals important materials properties of the thin films and indicates that the catalyst structure of the films on GDL is not optimal. This suggests that even higher activities should be possible in the fuel cell if the electrode and catalyst structure is improved.
References
Escudero-Escribano, M., et al., Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction. Science, 2016. 352(6281): p. 73-76.
Greeley, J., et al., Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nature Chemistry, 2009. 1(7): p. 552-556.
Lindahl, N., et al., High Specific and Mass Activity for the Oxygen Reduction Reaction for Thin Film Catalysts of Sputtered Pt3Y. Advanced Materials Interfaces, 2017. 4(13): p. 1700311.
Lindahl, N., et al., Fuel cell measurements with cathode catalysts of sputtered Pt3Y thin films. ChemSusChem, 2018. http://dx.doi.org/10.1002/cssc.201800023.
Caption. a) Electrochemical single cell characterization of Pt and Pt
3
Y sputtered catalysts in H
2
/O
2
, 80 °C, 1.5 bar absolute pressure, 100% RH, 20 mV s
-1
. Inset shows a schematic image of the atomic stucture of the Pt
3
Y. b) Bright-field TEM micrograph of as-sputtered Pt
3
Y thin film on GDL. The scale-bar is 50 nm.
Figure 1
In\(_2\)O\(_3\)-based catalysts have shown high activity and selectivity for CO\(_2\) hydrogenation to methanol, however the origin of the high performance of In\(_2\)O\(_3\) is still unclear. To ...elucidate the initial steps of CO\(_2\) hydrogenation over In\(_2\)O\(_3\), we have combined X-ray Photoelectron Spectroscopy (XPS) and Density Functional Theory (DFT) calculations to study the adsorption of CO\(_2\) on the In\(_2\)O\(_3\)(111) crystalline surface with different terminations, namely the stoichiometric, the reduced, and the hydroxylated surface, respectively. The combined approach confirms that the reduction of the surface results in the formation of In ad-atoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level-shifts (using methanol and formic acid as benchmark molecules) suggests that CO\(_2\) adsorbs as a carbonate on all surface terminations. We find that CO\(_2\) adsorption is hindered by hydroxyl groups on the hydroxylated surface.
Metal clusters stabilized by a surface ligand shell represent an interesting intermediate state of matter between molecular metal–ligand complexes and bulk metal. Such “metalloid” clusters are ...characterized by the balance between metal–metal bonds in the core and metal–ligand bonds at the exterior of the cluster. In previous studies, the electronic stability for the Al50Cp*12 cluster was not fully understood. We show here that the known cluster Al50Cp*12 can be considered as an analogue to a giant atom (“superatom”) with 138 sp electrons organized in concentric angular momentum shells up to L = 6 symmetry.
Metal clusters stabilized by a surface ligand shell represent an interesting intermediate state of matter between molecular metal–ligand complexes and bulk metal. We show here that the known cluster Al50Cp*12 can be considered as an analogue to a giant atom (“superatom”) with 138 sp electrons organized in concentric angular momentum shells up to L = 6 symmetry.
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NO x storage over hexagonal BaCO3(110) is investigated using first-principles calculations. Special focus is put on the importance of surface decarbonation. Upon decarbonation, supported BaO ...quasi-molecules are formed and a small drive toward (BaO) n cluster formation is predicted. Introduction of NO2 makes the decarbonation energetically relevant, while forming NO2−BaO−NO2 units, on the decarbonated surface. With this configuration, it is possible to replace all surface carbonates with nitrites and nitrates, forming a BaCO3 supported BaNO3NO2 overlayer. Thermodynamic considerations are employed to elaborate on the thermal stability of the formed NO x overlayers.
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