Cu2CoGeS4 nanocrystals for high performance aqueous polysulfide/iodide redox flow batteries: enhanced selectively to the electrocatalytic conversion of polysulfides
Aqueous polysulfide/iodide redox flow battery (RFB) is an attractive candidate for scalable energy storage with highly soluble active materials, which shows great potential to reduce RFB cost. However, their energy efficiency is usually limited by poor kinetics reversibility and electrochemical activity of the redox reaction of polysulfide couples on graphite felt electrode, which hinder its further practical applications. Here, the Cu2XGeS4 (X=Fe, Co, Ni, Cd, Mn) nanocrystals are successfully synthesized through hot injection method, then uniformly coat onto the surface of graphite felt as electrodes. These electrodes can successfully suppress the water splitting side reactions, especially the hydrogen evolution reaction. The ones with Cu2CoGeS4 nanocrystals can significantly boost electrocatalytic activities of S2-/S2-x redox reactions for its proper adsorbability to polysulfide, which inturn improve the charge transfer process and selectively facilitate the electro-conversion reactions of polysulfides. Furthermore, the polysulfide/iodide flow battery with GF-Cu2CoGeS4 generate a high energy efficiency of 77.2% at 20 mA cm-2, a power density of 40.7 mW cm-2 and a stable energy efficiency retention of 92% after approximately 250 continuous cycles.