Advanced zinc-cerium redox flow battery（ZCRFB） is a large-scale energy storage system which plays a significant role in the application of new energy sources. The requirement of superior cathode with high acitivity and fast ion diffusion is a hierarchical porous structure, which was synthesized in this work by a method in which both hard template and soft template were used. The structure and the performance of the cathode prepared here were characterized and evaluated by a variety of techniques such as scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray photoelectron spectroscopy（XPS）, cyclic voltammetry（CV）, linear sweep voltammetry（LSV）, and chronoamperometry（CA）. There were mainly three types of pore size within the hierarchical porous carbon： 2 μm, 80 nm, and 10 nm. The charge capacity of the cell using hierarchical porous carbon（HPC） as positive electrode was obviously larger than that using carbon felt; the former was 665.5 mAh with a coulombic efficiency of 89.0% and an energy efficiency of 79.0%, whereas the latter was 611.1 mAh with a coulombic efficiency of 81.5% and an energy efficiency of 68.6%. In addition, performance of the ZCRFB using HPC as positive electrode showed a good stability over 50 cycles.These results showed that the hierarchical porous carbon was superior over the carbon felt for application in ZCRFB.
A green low-cost redox flow battery using Zn/Znredox couple in HAc/NaAc medium and Fe/Feredox couple in HSOmedium was first proposed and investigated for potential stationary energy storage applications. The presence of HAc/NaAc in the negative electrolyte can keep the pH between 2.0 and 6.0even when a large amount of Hions move into negative electrolyte from positive electrolyte through ion exchange membrane. In the pH range of 2.0–6.0, the chemical reaction of Zn species with Hspecies is very insignificant; furthermore, the electroreduction of Hion on the negative electrode is significantly suppressed at this pH range. The zinc-ferrum redox flow battery（Zn/Fe RFB） operated within a voltage window of 0.5–2.0 V with a nearly 90% utilization ratio, and its energy efficiency is around 71.1% at room temperature. These results show that Zn/Fe RFB is a promising option as a stationary energy storage equipment.
Zhipeng XieQi SuAnhong ShiBin YangBaixiong LiuJianchai ChenXiaochun ZhouDingjian CaiLiang Yang
The kinetics of electrode reaction was investigated by cyclic voltammetry,and cyclic voltammograms show that the reversibility of the Fe(bpy)3^2+/Fe(bpy)^3+electrode reaction is better than that of the Zn/Zn^2+electrode reaction on the graphite disc.However,the Fe(bpy)3^2+ion diffusion in electrolyte is subject to greater resistance than that of the Zn^2+ion one.The stability of the Fe(bpy)3Cl2 solution was investigated by UV-vis spectroscopy,and the performance of a mild redox flow battery employing ZnCl2 and Fe(bpy)3Cl2 in the NaCl aqueous solution with various membranes as the separator was also investigated.It was found that the Celgard 3501 membrane cannot effectively prevent Fe(bpy)3^2+ions from leaking into anolyte,leading to the rapid failure of the flow battery.Although the Nafion 115 membrane can be polluted by Fe(bpy)32+ions,it is not invalidated.The Nafion 115 membrane shows good selectivity,which can avoid Fe(bpy)32 ions from leakage into anolyte.The ZnCl2/Fe(bpy)3Cl2 flow battery with the Nafion 115 membrane exhibits the capacity retention of 80%after 200 cycles.
