Hierarchical Nano-Electrocatalytic Reactor for High Performance Polysulfides Redox Flow Batteries
Jinji Lan, Ke Li, Le Yang, Qingquan Lin, Jinzhuo Duan, Shu Zhang, Xiang Wang, Jiajia Chen
Abstract
The aqueous polysulfides is an important Earth-abundant and multielectron redox couple to construct high capacity density and low-cost aqueous redox flow batteries (RFB); nevertheless, the sluggish conversion and kinetic behavior of S 2– /S x 2– result in a low power density output and poor active material utilizations. Herein, we present nanoconfined self-assembled ordered hierarchical porous Co and N codoped carbon (OHP-Co/NC) as an electrocatalytic reactor to enhance the mass transfer and redox activity of aqueous polysulfides. Finite element method simulation proves that the OHP-Co/NC with interconnected macropores and mesopores exhibits an enhanced mass transfer and delivers a larger redox electrolyte utilization of 50.1% compared to 23.3% of conventional Co/NC. Notably, the OHP-Co/NC obtained at 850 °C delivers the smallest redox peak potential difference (Δ E = 99 mV). Comparison studies of in operando Raman for aqueous polysulfides in the redox electrolyte and in situ electrochemical Raman on the single OHP-Co/NC particle for the adsorbed polysulfides were carried out. And it confirms that the OHP-Co/NC-850 catalyst has a strong adsorption of S 4 2– and can retard the strong disproportionation and hydrolysis behavior of polysulfides on the electrocatalyst interface. Therefore, the polysulfide/ferrocyanide RFB with an OHP-Co/NC-850 based membrane-electrode assembly (MEA) exhibited a high power density of 110 mW cm –2, as well as a steady capacity retention over 99.7% in 300 cycles.