Titanium Nitride Modified Graphite Felt As Negative Electrode For All Vanadium Redox Flow Battery

All vanadium redox flow battery is a new type of green secondary battery with many advantages such as flexible design,independent capacity,high safety,and long service life.Due to the influence of electrode materials and diaphragm,the development of all vanadium redox flow battery has not reached the requirement of ideal large-scale application.In this paper,the titanium nitride modified graphite felt electrodes were papared and used as the negative electrode for all vanadium redox flow battery.Fistly,the commercial titanium nitride was firstly deposited on a glassy carbon electrode?TiN?c?/GCE?for the electrochemical measurement of the V³⁺/V²⁺oxidation-reduction pair,indicating that the titanium nitride has good reversibility and electrocatalytic activity to the V³⁺/V²⁺.After that,the commercial titanium nitride is loaded on graphite felt?TiN?c?/GF?,and used as negative electrode for all vanadium redox flow battery.The results show that the initial charge capacity is 688.1 mAh,which reaches 85.6%of the theoretical capacityand increases 11%than the graphite felt electrode.Secondly,a titanium dioxide was loaded on the surface of graphite felt?TiO₂?s?/GF?by titanium tetrachloride impregnation method.Subsequently,it was converted to titanium nitride?TiN?s?/GF?by ammonia nitrogen reduction at high temperature.The results show that the initial charge capacity of TiN?s?/GF is 699.9mAh,which reches 87.1%of the theoretical capacity and increases 34%than the graphite felt electrode.On basis of previous research work,the titanium dioxide nanowires were prepared by hydrothermal method on the surface of graphite felt.Then,they were converted to titanium nitride nanowires?TiN NWs@GF?by ammonia nitrogen thermal reduction.Experimental optimum conditions were the hydrothermal temperature of 150?,the hydrothermal time of 8 h,the ammonia gas flow between the sample of 90°,and the nitriding temperature of 850?.The composition and structure of the sample were characterized by scanning electron microscope,X ray diffraction and X ray photoelectron spectroscopy.The results show that the TiN NWs grow erect on the surface of graphite felt,with a length of about 4?m,and the width of about 500 nm.The ratio of Ti-O bond and O-Ti-N bond of vertically placed samples is 5.2%and 6.5%lower than that of horizontal placement,while the peak area ratio of Ti-N bond is increased by 11.7%.The prepared TiN NWs@GF is assembled in a cylindrical battery with an initial discharge capacity of 591.1 mAh,reaching 73.5%of the theoretical discharge capacity,20.8%higher than that of the original graphite felt,and the retention rate of 84.6%after cyclic test.