The PSI Electrochemistry Laboratory studies almost all aspects of electrochemical energy storage and conversion.
Lab News & Scientific Highlights
Hydrogen Electrode for Membrane Water Electrolyzers with Low Gas Crossover
Proton exchange membrane (PEM) water electrolyzer are considered a for the Energy Transition to produce green hydrogen for fuel cell-based mobility, industrial processes, and seasonal storage. Platinum group metals (PGMs) are conventionally used as catalysts for electrode reactions due to their outstanding catalytic activity and chemical stability in the harsh acidic environment of the cell. Commercial carbon-supported platinum (Pt/C) electrocatalysts remains a state-of-the-art choice for the hydrogen evolution reaction (HER) on the cathode side of the cell. While a high Pt loading between 0.5 and 1.0 mgPt/cm2 is commonly used today, a reduction of the Pt loading to below 0.05 mgPt/cm2 is desired to reduce the cost of PGM usage in megawatt-scale PEM water electrolysis systems. In addition, in connection with the trend towards the use of thinner membranes (<0.1 mm), gas crossover through the membrane from the cathode to the anode side can lead to the formation of an explosive gas mixture in the anode product stream. In this study, we varied the design parameters for the cathode catalyst layer to reduce the Pt loading to 0.025 mg/cm2 while at the same time minimizing the rate of hydrogen crossover to the anode.
Real-Time Insights into Sodium-Ion Battery Chemistry
Identification of gaseous decomposition products from irreversible side-reactions enables understanding of inner working of rechargeable batteries. Unlike for Li-ion batteries, the knowledge of the gas-evolution processes in Na-ion batteries is limited. Our study revealed that Na-ion cells develop a less stable solid-electrolyte interphase (SEI) compared to Li-ion cells due to higher solubility of SEI constituents in Na-electrolytes.
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.