A novel liquid-phase exfoliation of layered crystals enables the production of defect-free and high quality 2D-crystal dispersions on a large scale.

The development of high-power density vanadium redox flow batteries (VRFBs) with high energy efficiencies (EEs) is crucial for the widespread dissemination of this energy storage technology. In this work, we report the production of novel hierarchical carbonaceous nanomaterials for VRFB electrodes with high catalytic activity toward the vanadium redox reactions (VO 2+ /VO 2 + and V 2+ /V 3+ ). The electrode materials are produced through a rapid (minute timescale) low-pressure combined gas plasma treatment of graphite felts (GFs) in an inductively coupled radio frequency reactor. By systematically studying the effects of either pure gases (O 2 and N 2 ) or their combination at different gas plasma pressures, the electrodes are optimized to reduce their kinetic polarization for the VRFB redox reactions. To further enhance the catalytic surface area of the electrodes, single-/few-layer graphene, produced by highly scalable wet-jet milling exfoliation of graphite, is incorporated into the GFs through an infiltration method in the presence of a polymeric binder. Depending on the thickness of the proton-exchange membrane (Nafion 115 or Nafion XL), our optimized VRFB configurations can efficiently operate within a wide range of charge/discharge current densities, exhibiting energy efficiencies up to 93.9%, 90.8%, 88.3%, 85.6%, 77.6%, and 69.5% at 25, 50, 75, 100, 200, and 300 mA cm –2 , respectively. Our technology is cost-competitive when compared to commercial ones (additional electrode costs < 100 € m –2 ) and shows EEs rivalling the record-high values reported for efficient systems to date. Our work remarks on the importance to study modified plasma conditions or plasma methods alternative to those reported previously (e.g., atmospheric plasmas) to improve further the electrode performances of the current VRFB systems.

No abstract

In Solid Oxide Fuel Cells (SOFC), interconnects are simultaneously exposed to dual atmosphere conditions in a range of temperature between 600 and 900°C. The presence of dissolved hydrogen in the steel can cause accelerated corrosion on the side exposed to air compared to exposures in air only. Moreover, the interconnect is subject to different humidity levels on the fuel side depending on fuel utilization. It has been already observed that a protective layer of chromia (Cr2O3) at the fuel side can mitigate the dual effect at the airside acting as a barrier for hydrogen permeation into the material. In this work, AISI 441 and Crofer 22 APU samples were exposed to dual atmosphere at 600°C under controlled humidity levels at the fuel side (20% vs. dry). Analysis performed showed how the humidity content on the fuel side largely affects the breakaway corrosion of the samples at the airside.

A novel method that employs electrochemical impedance spectroscopy (EIS) is developed to characterize the oxide scale resistance and thickness of Crofer 22 APU after exposure at 800°C in humidified air. Crofer 22 APU, is one of the most commonly used materials for solid oxide fuel cell interconnects, an application for which oxide scale resistance is of paramount importance. The kinetics of oxide growth were studied for up to 6,000 hours using three different techniques: electron microscopy of cross-sections, gravimetry, and EIS capacitance measurements of the oxide scale. EIS was used to evaluate the scale thickness starting from the material capacitance, and the material resistance at high temperature was estimated using extrapolation of the impedance values at room temperature. The result obtained with this novel EIS method are comparable to those obtained using conventional techniques, and in addition, the new method is cheaper, faster, and more reliable. Moreover, it enables repetitive exposures of the same sample without altering the specimen properties.