Bismuth nanoparticles anchored on N-doped graphite felts to give stable and efficient iron-chromium redox flow batteries
Iron-chromium redox flow batteries(ICRFBs)use abundant and inexpensive chromium and iron as the active sub-stances in the electrolyte and have great potential as a cost-effective and large-scale energy storage system.However,they are still plagued by several issues,such as the low electrochemical activity of Cr3+/Cr2+and the occurrence of the undesired hydrogen evolu-tion reaction(HER).We report the synthesis of amorphous bismuth(Bi)nanoparticles(NPs)immobilized on N-doped graphite felts(GFs)by a combined self-polymerization and wet-chemistry reduction strategy followed by annealing,which are used as the negat-ive electrodes for ICRFBs.The resulting Bi NPs react with H+to form intermediates and greatly inhibit the parasitic HER.In addi-tion,the combined effect of Bi and N dopants on the surface of GF dramatically increases the electrochemical activity of Fe2+/Fe3+and Cr3+/Cr2+,reduces the charge transfer resistance,and increases the mass transfer rate compared to plain GF.At the optimum Bi/N ratio of 2,a high coulombic efficiency of up to 97.7％is maintained even for 25 cycles at different current densities,the energy effi-ciency reaches 85.8％at 60.0 mA cm-2,exceeding many other reported materials,and the capacity reaches 862.7 mAh L-1after 100 cycles,which is about 5.3 times that of bare GF.
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