Phan Ha H, Bell Jon G, Mutch Greg A, McCue Alan J, Phan Anh N, Thomas K Mark
Wolfson Northern Carbon Reduction Laboratories, School of Engineering, Newcastle University Newcastle upon Tyne NE1 7RU UK
School of Engineering, Newcastle University Newcastle upon Tyne NE1 7RU UK.
Mater Adv. 2024 Aug 15;5(18):7170-7198. doi: 10.1039/d4ma00675e. eCollection 2024 Sep 16.
Vanadium redox flow batteries have applications for large-scale electricity storage. This paper reports the influence of carbon structural characteristics of sustainable walnut shell-derived carbons in carbon/polyvinylidene fluoride composite electrodes on vanadium redox reactions. Pyrolysis, gasification, and chemical treatment procedures were used to modify the structural characteristics of carbons. Carbon functional groups were modified by chemical treatment with HNO, heat treatment with KCO, and high-temperature NH treatment. Carbon porous structures were characterized using gas adsorption studies. Raman spectroscopy and X-ray diffraction were used to characterize the carbon molecular structure. Functional groups were characterized using X-ray photoelectron spectroscopy, acid/base titrations, temperature-programmed desorption, and Fourier transform infrared spectroscopy. The influence of carbon structure, porosity, and surface functional groups on the redox reactions of vanadium was investigated using cyclic voltammetry and electrical impedance spectroscopy. The VO/VO and V/V couples had well-defined peaks in cyclic voltammetry, with the former being the most intense, but the V/VO couple was not observed for samples carbonized under nitrogen. The results show that V/V and VO/VO couples observed in cyclic voltammograms were enhanced for carbonization temperatures up to 800 °C. Electrical impedance spectroscopy also showed impedance trends. The electrochemistry results are primarily related to changes in carbon structure and the catalysis of V oxidation by surface functional groups in the carbon structure. The V/VO couple was limited by slow kinetics, but it occurs on specific oxygen and nitrogen sites in the carbon structure. The oxidation of V(iii) to V(iv) only occurs on a limited number of surface sites, and the outer-sphere electron transfer to oxidize V(iii) takes place at much more positive potentials. The coulombic, voltage, and energy efficiency of the carbon electrodes were suitable for batteries.
钒氧化还原液流电池可用于大规模储能。本文报道了碳/聚偏二氟乙烯复合电极中可持续核桃壳衍生碳的碳结构特征对钒氧化还原反应的影响。采用热解、气化和化学处理程序来改变碳的结构特征。通过用HNO进行化学处理、用KCO进行热处理和高温NH处理来改性碳官能团。利用气体吸附研究对碳多孔结构进行了表征。用拉曼光谱和X射线衍射对碳分子结构进行了表征。用X射线光电子能谱、酸碱滴定、程序升温脱附和傅里叶变换红外光谱对官能团进行了表征。利用循环伏安法和电化学阻抗谱研究了碳结构、孔隙率和表面官能团对钒氧化还原反应的影响。VO/VO和V/V电对在循环伏安法中有明确的峰，前者最强，但在氮气气氛下碳化的样品未观察到V/VO电对。结果表明，在高达800℃的碳化温度下，循环伏安图中观察到的V/V和VO/VO电对增强。电化学阻抗谱也显示了阻抗趋势。电化学结果主要与碳结构的变化以及碳结构中表面官能团对V氧化的催化作用有关。V/VO电对受动力学缓慢的限制，但它发生在碳结构中特定的氧和氮位点上。V(iii)氧化为V(iv)仅发生在有限数量的表面位点上，而氧化V(iii)的外层电子转移发生在更正的电位下。碳电极的库仑效率、电压效率和能量效率适用于电池。
