Materials and Chemistry for Redox Flow Batteries

Abstract

Vanadium redox reactions have been considered as a key factor affecting the energy efficiency of the all-vanadium redox flow batteries (VRFBs). This redox reaction determines the reaction kinetics of whole cells. However, poor kinetic reversibility and catalytic activity towards of V2+/V3+ and VO2+/VO2+ redox couples on commonly used carbon substrate limit broader applications of VRFBs. Consequently, modified carbon substrates have been extensively investigated to improve vanadium redox reactions. In this Focus Review, recent progress of metal- and carbon-based nanomaterials as an electrocatalyst for VRFBs is discussed in detail, not intending a comprehensive review on whole components of system. The focus is mainly placed on redox chemistry of vanadium ions at a surface of various metals, different dimensional carbons, nitrogen-doped carbon nanostructures, and metal carbon composites. Spatial separation of the electrolyte and electrode is the main characteristic of the redox flow battery technology that liberates them from constraints of overall energy content and energy/power ratio. The concept of flowing electrolyte not only present a cost-effective approach for large-scale energy storage, but recently being embraced to develop a wide range of new hybrid energy storage and conversion systems. The advent of flow based Li-ion, organic redox, metal-air, and photo-electrochemical batteries promise new opportunities for advancing the electrical energy storage technologies. In this review, we present a critical overview of recent progress in conventional aqueous redox flow batteries (RFBs) and next-generation RFB systems, highlighting the latest innovative alternative materials and chemistries. Finally, we outline their technical feasibility for use in long-term and large-scale electrical energy-storage devices as well as the limitations that need to be overcome, providing an overview of future research direction in the field of RFBs.