Graphite felts modified by vertical two-dimensional WO3 nanowall arrays: high-performance electrode materials for cerium-based redox flow batteries.

Cerium-based redox flow batteries (RFBs) are very attractive for highly efficient energy storage applications with industrial-scale storage capacity. However, the development of active, stable, and earth-abundant catalysts for cerium redox reactions with sluggish kinetics remains a major challenge. Herein, for the first time, two-dimensional (2D) nanostructured architectures were used to design and fabricate efficient and stable electrocatalysts from earth-abundant components toward the Ce(iv)/Ce(iii) redox reaction. A novel WO3/GF hybrid architecture (WGF) built from WO3 nanowall arrays (NWAs) anchored on graphite felt (GF) surfaces was prepared for cerium-based RFBs. This unique hybrid exhibits superior electrocatalytic performance since the vertical nanowall arrays display open and ordered structures that ensure full exposure of the active sites toward electrolytes, which allows direct and full contact of every nanowall with the electrolyte. As an electrode for cerium redox reactions, this WGF electrode exhibits a 42.1% and 32.0% increase in energy efficiency as compared with that of pristine GF and acid-treated GF at a high charge/discharge rate of 30 mA cm-2. Moreover, the long-term cycling performance confirms the superior durability of the as-prepared WGF. This study suggests that the use of 2D nanostructures combined with vertical array microstructures is a promising strategy for efficient electrocatalysts toward cerium redox reactions with scale-up potential.