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We investigated the mismatched kinetics of electrode reactions in VRFB, RuO2, and Bi nanoparticles as the functional components electrodeposited on graphene porous gelatum-graphite bipolar plate (ERGO-GBP) integrated electrode and serving as anode and cathode, respectively. Benefitting from the unique structure and specific functionality, the novel integrated electrodes exhibit excellent electrochemical properties and functionality. The asymmetric VRFB with an RuO2-ERGO-GBP anode and a Bi-ERGOGBP cathode shows better performance compared to the symmetric VRFB with ERGO-GBP as both anode and cathode, suggesting a feasible strategy to construct asymmetric VRFB with various functionalized ERGO-GBP integrated electrodes. [ABSTRACT FROM AUTHOR]

Carbon nanofibers with multi-scale pores have been easily constructed by synchronous water etching during the carbonization process of PAN nanofibers, reducing the additional consumption of energy and time. After etching by high-temperature water vapor, the fiber surface becomes more coarse, and large amounts of etched pits are formed, effectively increasing the electrode's specific surface area and hydrophilicity. Oxygen content is also significantly increased, which may effectively increase the electrocatalytic active sites of the electrode. Electrochemical tests verified the improved electrocatalytic activity and increased effective surface area. As a result, the VRFB single cell with water vapor etched carbon nanofibers as its electrode shows higher battery efficiencies than that with pristine carbon nanofibers; the energy efficiency improves by nearly 9.4% at 200 mA·cm-2. After 100 charge/discharge cycles, the battery efficiency has no obvious attenuation, and the capacity attenuation rate of single cycle is nearly 0.26%, suggesting a satisfactory cycling stability. This green and simple method for constructing multi-scale porous carbon nanofibers electrode is expected to achieve large-scale production of high-performance electrode materials, and can be applied in various electrochemical energy storage systems. [ABSTRACT FROM AUTHOR]

Electrochemical performance of the electrospun carbon nanofibers (ECNFs) electrode for all vanadium redox flow battery (VRFB) is significantly enhanced by introducing urea into the precursor solution and the subsequent thermal treatment. A novel N, O dualdoped carbon nanofibers with a series of micronanometer multiscale pores on the surface can be easily obtained by the in situ thermolysis processes of urea, which endows the electrode larger surface area, better wettability and improved electroactive sites. The electrochemical results demonstrate that the N, O co-doping ECNFs with multiscale pores shows reduced charge transfer resistance and diffusion resistance for vanadium ions redox reactions, which should be attributed to the synergy of the larger effective surface area and better electrocatalytic activity. The VRFB equipped with the novel carbon nanofibers electrode delivers a 84.6% increase of the discharge capacity and 17% amplification of the energy efficiency compared with the pristine ECNFs at 150 mA cm-2. This simple method to construct electrodes with N, O dual-doped and micronanometer multiscale pores also paves the way to finely regulating the internal microstructure and composition of the electrodes in a variety of energy storage systems. [ABSTRACT FROM AUTHOR]

Aiming at the shortcoming of low specific surface area of the most commonly used carbon felt (CF) electrodes in vanadium flow battery (VFB), there are mainly two approaches to enhancing its specific surface area: anchoring effect and digging effect. Based on the digging effect, the CO2-etched CF has been fabricated by a simple heat treatment under the CO2 atmosphere. As expected, lots of etch pits are formed and evenly distribute on the fiber surface, indicating a greatly enhanced surface area. Meanwhile, the content of O in the CO2-etched CF increases obviously, meaning the formation of more oxygen-containing groups, which are conducive to the improvement of hydrophilicity and electrochemical surface area. Furthermore, the oxygen-containing groups newly generated during the CO2 etching process not only improve the hydrophilicity, but also enhance the electrocatalytic activity toward to the V3+/V2+ redox couples. Consequently, VFB with CO2-etched CF as its electrodes presents significantly improved energy conversion efficiencies, discharge capacity and cycling stability. This work supplies a convenient and efficient way to improve the VFB performance by enhancing the specific surface area of CF electrodes through digging effect. [ABSTRACT FROM AUTHOR]