Doping Engineering of M-N-C Electrocatalyst Based Membrane-Electrode Assembly for High-Performance Aqueous Polysulfides Redox Flow Batteries

Polysulfides aqueous redox flow batteries (PS-ARFBs) with large theoretical capacity and low cost are one of the most promising solutions for large-scale energy storage technology. However, sluggish electrochemical redox kinetics and nonnegligible crossover of aqueous polysulfides restrict the battery performances. Herein, it is found that the Co, Zn dual-doped N-C complex have enhanced electrochemical adsorption behaviors for Na₂ S₂ . It exhibits significantly electrochemical redox activity compared to the bare glassy carbon electrode. And the redox reversibility is also improved from ΔV = 210 mV on Zn-doped N-C complex to ΔV = 164 mV on Co, Zn-doped N-C complex. Furthermore, membrane-electrode assembly (MEA) based on Co, Zn-doped N-C complex is firstly proposed to enhance the redox performances and relieve the crossover in PS-ARFBs. Thus, an impressively high and reversible capacity of 157.5 Ah L^-1 for Na₂ S₂ with a high capacity utilization of 97.9% could be achieved. Moreover, a full cell PS-ARFB with Na₂ S₂ anolyte and Na₄ [Fe(CN)₆ ] catholyte exhibits high energy efficiency ≈88.4% at 10 mA cm^-2 . A very low capacity decay rate of 0.0025% per cycle is also achieved at 60 mA cm^-2 over 200 cycles.