This study focuses on voltage cycling induced degradation of cathodes with different loading (0.4 and 0.1 mg Pt /cm 2) when applying square wave or triangular wave based accelerated stress tests (ASTs) between 0.6 and 1.0 V RHE. The degradation of the H 2 /O 2 and H 2 /air performance upon extended voltage cycling (up to 30000 cycles) was analyzed in terms of the voltage loss contributions from ORR kinetics, O 2 mass transport resistances and proton conduction resistances in the cathode. The extent of cathode thinning due to carbon support corrosion was determined by post mortem electrode thickness measurements. Square waves were found to cause a more rapid loss of ECSA and mass activity compared to triangular waves, which was shown to be due to the longer hold periods at high potentials rather than to the rate of the potential transient. The observed increase of the O 2 mass transport resistance with voltage cycling was found to mainly depend on the available Pt surface area, while mass transport resistances due to carbon corrosion were found to be insignificant. Finally, it was shown that by lowering the upper potential limit to 0.85 V RHE , low-loaded catalyst layers can sustain 30000 potential cycles without degradation of the H 2 /air performance.

In this study we report on the direct proportionality between cathode surface area and first discharge capacity of non-aqueous Li-O 2 cells using ether-based electrolytes. Seven different highly structured carbon blacks, characterized by different surface areas and porosities, were used to prepare non-catalyzed cathodes. Surface measurements and porosity analyzes were carried out on both raw materials and electrodes in order to estimate the fraction of cathode surface accessible by the electrolyte. The first specific discharge capacity of different cathodes was then normalized over its specific surface and a strong correlation between the two quantities was found. This result strongly supports a discharge mechanism for Li-O 2 batteries wherein the main factor limiting the capacity is the formation of a passivating layer of products on the surface of the cathode material, impeding ORR at carbon active sites. Also the cyclability of the cells was considered, demonstrating the effect of electrolyte degradation on the increased capacity upon cycling of ethereal electrolytes (e.g. DEGDME). The first discharge specific capacity and cyclability using TEGDME, commonly used in Li-air research, was found similar to reacting or degraded electrolytes, suggesting a much higher reactivity toward superoxide ion radical in comparison to its lighter homologues DEGDME and DME.

Compared to Pt/C, the HOR activity of Pt-Ru alloys in alkaline electrolyte is exceptionally high. Nevertheless, it remains unknown whether this enhancement is due to a bifunctional mechanism involving Pt and Ru as active sites or an electronic effect of Ru on Pt. In this study, we distinguish between those fundamental differences using Ru@Pt core-shell nanoparticles as a model system. Ru@Pt catalysts were prepared from submonolayer to multilayer Pt coverage. The exposure of Ru on the surface of the catalyst was analyzed by cyclic voltammetry, showing that Ru is solely exposed on the surface of Ru@Pt particles with low Pt-coverage. The thickness of the Pt-shell was characterized by CO stripping in H 2 SO 4 , allowing to distinguish between single and bilayered Ru@Pt catalysts. Determining the HOR/HER activity of these catalysts in 0.1 M NaOH revealed that fully Pt-covered Ru is more active than partially covered Ru@Pt nanoparticles. Hence, the participation of Ru as active site in a bifunctional mechanism is of minor importance with respect to the HOR/HER activity compared to its influence on the electronic structure of Pt. Similar to Pt-Ru alloys, the most active Ru@Pt core-shell nanoparticles show a 4 to 5-fold enhancement of the surface-normalized HOR/HER activity compared to Pt/C.

Bimetallic alloys based on Pt and Y are potential cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their high oxygen reduction reaction (ORR) activity. Nevertheless, the synthesis of carbon supported Pt x Y catalysts is challenging due to the low standard reduction potential of yttrium compared to platinum. Hence, extended electrochemical testing in actual PEMFCs remains elusive, especially with respect to catalyst degradation upon voltage-cycling. In this publication, we present the synthesis of a bimetallic Pt x Y/C catalyst via impregnation of commercial Pt/C with an yttrium halide precursor and subsequent heat-treatment in H 2 at 1200 • C. This catalyst showed a high specific ORR activity, at a mass activity similar to Pt/C due to its comparably low electrochemical surface area (ECSA). On the other hand, the large particle size of the here synthesized Pt x Y/C catalyst (≈10 nm) resulted in a significantly enhanced stability versus degradation in an accelerated stress test (AST) based on voltage-cycling between 0.6 and 1.0 V RHE at 50 mV s −1 , showing a superior ECSA, ORR activity and H 2 /air performance after 30000 cycles compared to a standard Pt/C catalyst.

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