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Hexamethyl-p-terphenyl polybenzimidazolium (HMT-PMBI) membranes for the vanadium redox flow battery (VRFB).

Polybenzimidazole Membrane Design Principles for Vanadium Redox Flow Batteries

Energy storage technologies with long storage duration are essential to stabilize electricity grids with a high share of intermittent renewable power. In a redox flow battery, the electrochemical conversion unit, where the charging and discharging reaction takes place, is spatially separated from the energy storage medium. In the all-vanadium redox flow battery (VRFB), a sulfuric acid aqueous electrolyte with dissolved vanadium ions is used as the storage medium. Vanadium is present in 4 different oxidation states, the redox couple vanadium(II) and (III) on the negative side of the cell, and vanadium(IV) and (V) on the positive side. This allows the battery to be repeatedly charged and discharged. A separator or membrane is used between the negative and positive electrode, which should selectively conduct the ions of the supporting electrolyte and minimize the passage of vanadium ions. Fluorinated membranes, such as Nafion™, are often used for this key component, but these ionomers were not originally developed for this application and therefore have functional shortcomings. Furthermore, the production and use of fluorinated materials is to be severely restricted or even banned in Europe. Therefore, the development of hydrocarbon-based membranes for the VRFB is of great importance. The study reported here focuses on polybenzimidazole polymers and membranes, which could be a promising materials class for next generation flow batteries. 

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Outline of the applied methodology of using fast X-ray tomography on a CO2 electrolyzer in operation.

Unraveling degradation processes in a bipolar membrane CO2 electrolyzer by time-resolved X-ray tomographic microscopy

Employing a bipolar ion conducting membrane (BPM) in forward bias is a convenient solution for the biggest issues in the more common anion exchange membrane (AEM) CO2 co-electrolysis: the degradation of the performance caused by carbonate salt precipitation at the cathode and the decrease of net CO2 conversion caused by the crossover of this molecule from cathode to anode also requiring energy for downstream gas separation. However, the performance and stability of this device remain largely insufficient when using such a BPM configuration. To understand the reasons for this, we performed time-resolved X-ray tomographic microscopy of an operating BPM CO2 electrolyzer. The imaging method reveals partly unexpected degradation processes that result in design recommendations for improvement.

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In situ and operando X-ray spectroscopy enables a better understanding of the enhanced oxygen evolution reaction activity of CoOx nanocatalysts coupled with CeO2.

Insights into the superior oxygen evolution reaction activity of CoOx/CeO2 composite electrocatalyst

CeO2 significantly enhances the oxygen evolution reaction (OER) activity of CoOx, although the mechanism behind this synergy is still unclear. Here, operando hard X-ray absorption spectroscopy (hXAS) is applied to monitor the Co-K edge and Ce L3 edge in CoOx/CeO2 to shed light on the evolution of Co and Ce oxidation states during OER. In addition, ex situ soft XAS (sXAS) characterizations provide information on the irreversible surface-specific transformations of the Co L3 edge as well as the O K edge.

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Scheme of the combined SAXS measurement and simulation approach

Quantification of PEFC Catalyst Layer Saturation via Small-Angle X‑ray Scattering

The complex nature of liquid water saturation in polymer electrolyte fuel cell (PEFC) catalyst layers (CLs) greatly affects the device performance. To investigate this problem, a method to quantify the presence of liquid water in a PEFC CL using small-angle X-ray scattering (SAXS) was developed in a collaboration of researchers of the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany), the Photon Science Division and the Electrochemistry Laboratory of PSI. The method leverages the differences in electron densities between the solid catalyst matrix and the CL-pores filled with liquid water under dry and wet conditions, respectively.

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Operando XAS and XRD

Understanding the (de-)lithiation mechanism of nano-sized LiMn2O4 allows achieving long-term cycling stability

We report an in-depth investigation of the local atomic geometry, electronic and crystallographic structure evolution of nano-sized LiMn2O4 using operando XAS and XRD to shed light on (de-)lithiation mechanism when cycled in wide voltage range of 2.0 to 4.3 V vs Li+/Li. Leveraging on these findings, a novel electrochemical cycling protocol, with periodic deep discharge, yields superior electrochemical performance cycled in the range of 3.3 to 4.3 V exhibiting an excellent structure cyclability and an unprecedented increase in the specific capacity upon long cycling.

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Teaser: Bessere Batterien für E-Autos

Améliorer les batteries des voitures électriques

Energie et climat Recherche avec des neutrons Mobilité Meilleures batteries

Des scientifiques du PSI utilisent des neutrons pour visualiser les modifications physiques et chimiques qui se produisent dans l’électrolyte des batteries.

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Left: benzyl-type quaternary ammonium model compounds mimicking the chemistry of anion exchange membranes. All compounds contain perchlorate as counter anion. NBTM = 3-nitro-benzyltrimethylammonium, BTM = bennzyltrimethylammonium, BMP = N-benzyl-N-methyl-piperidiunium, MBTM = 3-methoxy-benzyltrimethylammonium. Degradation of compounds (1 mM) after exposure in the 60Co gamma cell to a dose of 1’200 Gy, corresponding to 0.75 mM of radicals. Comparison between inert atmosphere and air, which leads to different

Insights into radical induced degradation of anion exchange membrane constituents

Electrochemical energy conversion devices, such as fuel cells and electrolyzers, using an anion exchange membrane (AEM) operating in the alkaline regime offer the prospect of the use of non-noble metal electrocatalysts and lower-cost cell construction materials. The wide-spread application of electrochemical cells with AEMs has been largely limited by the low chemical stability of the material. AEM degradation is triggered by i) nucleophilic attack by OH, and ii) by reaction with free radicals formed during cell operation. Whereas the alkaline stability of AEMs has been greatly increased over the last 10 years, the understanding of mechanisms of radical induced degradation is limited. In this study, we have addressed this topic for the first time.

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Comment réduire la quantité de cobalt dans les batteries des voitures électriques?

Energie et climat Transition énergétique Mobilité Meilleures batteries

L'électrification des transports est en augmentation. Cela signifie que davantage de batteries sont nécessaires. Cependant, certaines d'entre elles contiennent une matière première extrêmement problématique : le cobalt. Le PSI recherche des alternatives.

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Crystal structure of the investigated cobalt-based oxides.

Improving the oxygen evolution reaction activity of Co-based oxides by phosphate functionalization

Our findings disclose that P-functionalization successfully enhances the oxygen evolution reaction (OER) activity of different cobalt-based catalysts (namely, La0.2Sr0.8CoO3–δ, La0.2Sr0.8Co0.8Fe0.2O3–δ, and CoOx) 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.


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