Suchen

The development of next generation fuel cell membranes based on aromatic hydrocarbon chemistry calls for a new antioxidant strategy to tackle radical induced membrane degradation. Although damage by radicals cannot be prevented, the formed aromatic intermediates can be repaired by a suitable additive. Fuel cell experiments demonstrate that the approach is viable on the device level and that repair is a catalytic mechanism.

The conversion efficiency for green hydrogen production in a polymer electrolyte water electrolyzer (PEWE) is strongly influenced by the ohmic cell resistance and therefore the thickness of the membrane used. The use of thin membranes (~50 micron or below) is limited by gas crossover of H₂ and O₂, which can lead to the formation of explosive gas mixtures. The incorporation of a recombination catalyst provides remedy and allows a more dynamic operating mode.

PSI researchers have studied the how the electrolyte pH values influence the oxygen evolution reaction (OER) activity and stability of different promising perovskite oxide catalysts for application as anodic electrodes in alkaline water electrolyzers. The OER activity and stability decreased decreasing the electrolyte pH values. By combining electrochemical studies and operando X-ray absorption spectroscopy measurements, it has been suggested that different reaction mechanisms dominate in alkaline and near-neutral electrolyte pH region.

PSI researchers have studied the influence of surface segregation on the oxygen evolution reaction (OER) activity for the, La_0.2Sr_0.8CoO_3-d (LSCO) perovskite, one of the most active perovskite towards the OER in alkaline electrolyte. It has been found that the higher the perovskite synthesis temperature the more strontium segregation occurs on the surface. However, the segregated strontium compounds are soluble in water and they are easily removed when the surface of the electrode is in contact with the electrolyte, leading to the exposure of cobalt enriched layers very active for the OER.

PSI researchers have developed a new methodology for studying the complex transport processes in polymer electrolyte water electrolysis (PEWE). Using advanced operando X-ray tomographic microscopy, we were able to observe for the first time the formation of oxygen pathways in the porous transport layer, in three dimensions. Understanding oxygen transport is crucial for improving PEWE technology and this work provides precious insights for the design of future, better-performing PEWE cells.

Our findings disclose that P-functionalization successfully enhances the oxygen evolution reaction (OER) activity of different cobalt-based catalysts (namely, La_0.2Sr_0.8CoO_3–δ, La_0.2Sr_0.8Co_0.8Fe_0.2O_3–δ, and CoO_x) at near-neutral pHs and that both phosphate ion assistance in the OER mechanism and catalyst Co oxidation state can play a role in the enhanced OER activity.

A vanadium redox flow battery (VRFB) is a grid-scale energy storage device. Its energy conversion unit consists of a cell stack that comprises ion-exchange membranes to separate positive and negative electrode. The projected lifetime of a VRFB is 20 years and 7’000 charge-discharge cycles. Lifetime tests of membranes under application relevant conditions are therefore impractical, and the development of an accelerated stress test (AST) to assess the chemical stability of membranes is crucial.

The role of the oxygen stoichiometry of perovskite catalysts in the oxygen evolution reaction (OER) is systematically studied in the PrBaCo2O5+δ family. The reduced number of physical/chemical variables combined with in-depth characterizations such as neutron diffraction, O K-edge X-ray absorption spectroscopy(XAS), electron energy loss spectroscopy (EELS), magnetization and scanning transmission electron microscopy (STEM) studies, helps investigating the complex correlation between OER activity and a single perovskite property, such as the oxygen content. Larger amount of oxygen vacancies appears to facilitate the OER, possibly contributing to the mechanism involving the oxidation of lattice oxygen, i.e., the lattice oxygen evolution reaction (LOER). Furthermore, not only the number of vacancies but also their local arrangement in the perovskite lattice influences the OER activity, with a clear drop for the more stable, ordered stoichiometry.

The high operational and capital costs of polymer electrolyte water electrolysis technology originate from limited catalyst utilization and the use of thick membrane electrolytes. PSI researchers have developed novel multi-layer porous transport materials, which provide superior electrochemical performance in comparison to conventional single-layer structures.