Hydroxide‐exchange membrane fuel cells can potentially utilize platinum‐group‐metal (PGM)‐free electrocatalysts, offering cost and scalability advantages over more developed proton‐exchange membrane fuel cells. However, there is a lack of non‐precious electrocatalysts that are active and stable for the hydrogen oxidation reaction (HOR) relevant to hydroxide‐exchange membrane fuel cells. Here we report the discovery and development of Ni3N as an active and robust HOR catalyst in alkaline medium. A supported version of the catalyst, Ni3N/C, exhibits by far the highest mass activity and break‐down potential for a PGM‐free catalyst. The catalyst also exhibits Pt‐like activity for hydrogen evolution reaction (HER) in alkaline medium. Spectroscopy data reveal a downshift of the Ni d band going from Ni to Ni3N and interfacial charge transfer from Ni3N to the carbon support. These properties weaken the binding energy of hydrogen and oxygen species, resulting in remarkable HOR activity and stability.

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In order to link electrochemical performance degradation of the cathode in a large solid oxide fuel cell (SOFC) to the presence of pollutant species, a spatially-resolved study of contaminants was performed. Distribution maps of pollutants over the cell allowed identifying their sources. Besides chromium and silicon, sulfur was found as a major pollutant species. Its preferential reaction with strontium doped lanthanum cobaltite (LSC), forming strontium sulfate SrSO 4 , compared to strontium doped lanthanum manganite (LSM) is revealed here. When sulfur poisoning arises in combination with chromium, a sulfur-containing strontium chromate compound is formed.

The locally-resolved degradation behavior was studied during 1900 hours in an SOFC repeat-element. In-situ measurements of local electrochemical performance were made on 18 locations over a segmented anode-supported cell. The evolution of local current densities, overpotentials and area-specific resistances was studied, showing a reorganization of the electrochemical reaction with time. The extent and the spatial distribution of degradation were established for different electrochemical reactions steps using impedance spectroscopy. The low-frequency cathode contribution was the mostly altered process, followed by the charge transfer reaction on anode side. Post-experiment analyses allowed to identify three major pollutants on the cathode side (chromium, silicon and sulfur), whose spatial distributions corresponded to the observed local degradation. Sources of pollutants were identified in system components as well as within the stack repeat-element.

Hydroxide‐exchange membrane fuel cells can potentially utilize platinum‐group‐metal (PGM)‐free electrocatalysts, offering cost and scalability advantages over more developed proton‐exchange membrane fuel cells. However, there is a lack of non‐precious electrocatalysts that are active and stable for the hydrogen oxidation reaction (HOR) relevant to hydroxide‐exchange membrane fuel cells. Here we report the discovery and development of Ni3N as an active and robust HOR catalyst in alkaline medium. A supported version of the catalyst, Ni3N/C, exhibits by far the highest mass activity and break‐down potential for a PGM‐free catalyst. The catalyst also exhibits Pt‐like activity for hydrogen evolution reaction (HER) in alkaline medium. Spectroscopy data reveal a downshift of the Ni d band going from Ni to Ni3N and interfacial charge transfer from Ni3N to the carbon support. These properties weaken the binding energy of hydrogen and oxygen species, resulting in remarkable HOR activity and stability.

a b s t r a c t a r t i c l e i n f o (SSZ) were applied by dip-coating in aqueous suspensions. Electrolyte powders had been attrition-milled to decrease their particle size and densification temperature. The quantity of polyacrylic acid (PAA) as dispersant was optimised by ζ-potential measurements. The densification behaviour was studied by dilatometry and SEM-imaging. A sintering temperature of 1250°C was found to densify GDC whereas SSZlayers remained slightly porous.

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Electrocatalytic CO2 to CO conversion is approaching the industrial benchmark. Currently, Au electrodes show the best performance, whereas non-precious metal catalysts exhibit inferior activity. Here we show a densely populated Ni single-atom on nanoparticle catalyst (NiSA/NP) via direct solid-sate pyrolysis, where Ni nanoparticles donate electrons to Ni(i)-N-C sites via carbon nanotubes network, achieves a high CO current of 352 mA cm−2 at -0.55 V vs RHE in an alkaline flow cell. When coupled with a NiFe-based oxygen evolution anode into a zero-gap membrane electrolyser, it delivers an industrial-relevant CO current of 310 mA cm−2 at a low cell voltage of -2.3 V, corresponding to an overall energy efficiency of 57%. The superior CO2 electroreduction performance is attributed to the enhanced adsorption of key intermediate COOH* on electron-rich Ni single atom, together with the dense active sites.