Overcoming Voltage Losses in Vanadium Redox Flow Batteries Using WO3 as a Positive Electrode

Funding Information: Miguel A. Rodriguez‐Olguin, Han Gardeniers, and Arturo Susarrey‐Arce acknowledge the funding for their research received from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program (Grant agreement No. 742004). C. Flox acknowledges financial support from the Ministery of Science Spain, AEI Severo Ochoa Grant CEX2019‐000917‐S, and the European Commission under the grant MSCA‐IF‐EF‐ST, proposal number 101026162. Publisher Copyright: © 2022 The Authors. ChemCatChem published by Wiley-VCH GmbH.Vanadium redox flow batteries (VRFBs) are appealing large-scale energy storage systems due to their unique properties of independent energy/power design. The VRFBs stack design is crucial for technology deployment in power applications. Besides the design, the stack suffers from high voltage losses caused by the electrodes. The introduction of active sites into the electrode to facilitate the reaction kinetic is crucial in boosting the power rate of the VRFBs. Here, an O-rich layer has been applied onto structured graphite felt (GF) by depositing WO3 to increase the oxygen species content. The oxygen species are the active site during the positive reaction (VO2+/VO2+) in VRFB. The increased electrocatalytic activity is demonstrated by the monoclinic (m)-WO3/GF electrode that minimizes the voltage losses, yielding excellent performance results in terms of power density output and limiting current density (556 mWcm−2@800 mAcm−2). The results confirm that the m-WO3/GF electrode is a promising electrode for high-power in VRFBs, overcoming the performance-limiting issues in a positive half-reaction.Peer reviewe