A bifunctional electrocatalytic graphite felt for stable aqueous zinc-polyiodide flow batteries

Abstract

The appealing features of high safety, environmental friendliness, and flexible layout make the Zn–I2 flow batteries attractive for implementation in long-duration grid-scale energy storage systems. However, the uncontrollable self-transformation of high-soluble polyiodide species often result in the limited reutilization of I3−/I− redox couple and compromise its theoretical energetic potentials. Herein, FeP nanoclusters embedded in N and P co-dopped carbon layer render the functional graphite felt with strong interaction between polyiodides and substrate in combination with the accelerated I−/I3− redox kinetics under working conditions. The heteroatoms and nanoclusters served synergically as strong chemisorption and electrocatalytic hotspots for iodine and its intermediates conversion. The strong interactions between polar matrix and active species facilitated interfacial physicochemical confinement effect mitigates polyiodide crossover and the electrocatalysis effect promises efficient iodine conversion and stable cycling performance. Consequently, the Zn–I2 flow battery delivers excellent rate performance, ultralong cycling life for 1000 cycles with a recorded average Coulombic efficiency of 98.1 %, and substantially enhanced anti-self-discharge capability. The rational modification of carbon felt represents a promising direction to unlock the practical potentials of Zn–I2 flow chemistry.