Two-in-one strategy for optimizing chemical and structural properties of carbon felt electrodes for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) have received significant attention for use in large-scale energy storage systems (ESSs) because of their long cycle life, flexible capacity, power design, and safety. However, the poor electrochemical activity of the conventionally used carbon felt electrode results in low energy efficiency of the VRFBs and consequently impedes their commercialization. In this study, a carbon felt (CF) electrode with numerous nanopores and robust oxygen-containing functional groups at its edge sites is designed to improve the electrochemical activity of a carbon felt electrode. To achieve this, Ni metal nanoparticles were initially precipitated on the surface of the CF electrode, followed by etching of the precipitated Ni nanoparticles on the CF electrode using sulfuric acid. The resulting CF electrode had a specific surface area eight times larger than that of the pristine CF electrode. In addition, the oxygen-containing functional groups anchored at the graphite edge sites of the nanopores can act as robust electrocatalysts for VO2+/VO2+ and V2+/V3+ redox reactions. Consequently, the VRFB cell with the resulting carbon felt electrode can deliver a high energy efficiency of 86.2% at the current density of 60 mA cm-2, which is 20% higher than that of the VRFB cell with the conventionally heat-treated CF electrode. Furthermore, the VRFB cell with the resultant carbon felt electrodes showed stable cycling performance with no considerable energy efficiency loss over 200 charge-discharge cycles. In addition, even at a high current density of 160 mA cm-2 , the developed carbon felt electrode can achieve an energy efficiency of 70.1%.

A highly-selective layer-by-layer membrane modified with polyethylenimine and graphene oxide for vanadium redox flow battery

A selective composite membrane for vanadium redox flow battery (VRFB) was successfully prepared by layer-by-layer (LbL) technique using a perfluorosulfonic sulfonic acid or Nafion 117 (N117). The composite membrane referred as N117-(PEI/GO)n, was obtained by depositing alternating layers of positively charged polyethylenimine (PEI) and negatively charged graphene oxide (GO) as polyelectrolytes. The physicochemical properties and performance of the pristine and composite membranes were investigated. The membrane showed an enhancement in proton conductivity and simultaneously exhibited a notable 90% reduction in vanadium permeability. This, in turn, results in a well-balanced ratio of proton conductivity to vanadium permeability, leading to high selectivity. The highest selectivity of the LbL membranes was found to be 19.2 × 104 S.min/cm3, which is 13 times higher than the N117 membrane (n = 0). This was translated into an improvement in the battery performance, with the n = 1 membrane showing a 4-6% improvement in coulombic efficiency and a 7-15% improvement in voltage efficiency at current densities ranging from 40 to 80 mA/cm2. Furthermore, the membrane displays stable operation over a long-term stability at around 88% at a current density of 40 mA/cm2, making it an attractive option for VRFB applications using the LbL technique. The use of PEI/GO bilayers maintains high proton conductivity and VE of the battery, opening up possibilities for further optimization and improvement of VRFBs.

Advanced electrode enabled by lignin-derived carbon for high-performance vanadium redox flow battery

Vanadium redox flow batteries (VRFBs) are promising energy storage systems with the potential to bridge the gap between intermittent renewable electricity generation and continuous supply of reliable electricity. The electrodes found in VRFB cells affect their energy efficiency (EE) and power density. It is important to fabricate electrodes with intriguing properties to enable VRFBs to have high performance. Herein, the abundant and cost-effective lignin is employed as the precursor to produce amorphous carbon particles after undergoing thermal decomposition treatment. The carbon particles cover the surface of carbon felt (CF). The resulting CF modified by lignin-derived carbon particles (Lignin-CF) with increased active sites and improved hydrophilicity displays superior electrochemical activity towards the VO2+/VO2+ pair than both the pristine CF and the heated bare CF. Remarkably, the VRFB consisting of Lignin-CF which acts as the positive electrode shows high performance in terms of the average EE (83.3 %) and average voltage efficiency (VE) (85.0 %) over 1000 cycles (long cycling life) for more than 16 days at 100 mA cm-2, and high power density of 1053.2 mW cm-2. It is noted that the EE and VE are comparable to the highest reported value of CF modified by carbon-based materials, aside having evidently longer cycling life. This study provides a feasible strategy for fabricating an affordable electrode for high-performance VRFBs.

Biomass-derived carbon materials for vanadium redox flow battery: From structure to property

Biomass-derived carbon (BDC) materials are suitable as electrode or catalyst materials for vanadium redox flow battery (VRFB), owing to the characteristics of vast material sources, environmental friendliness, and multifarious structures. A timely and comprehensive review of the structure and property significantly facilitates the development of BDC materials. Here, the paper starts with the preparation of biomass materials, including carbonization and activation. It is designed to summarize the lastest developments in BDC materials of VRFB in four different structural dimensions from zero dimension (0D) to three dimension (3D). Every dimension begins with meticulously selected examples to introduce the structural characteristics of materials and then illustrates the improved performance of the VRFB due to the structure. Simultaneously, challenges, solutions, and prospects are indicated for the further development of BDC materials. Overall, this review will help researchers select excellent strategies for the fabrication of BDC materials, thereby facilitating the use of BDC materials in VRFB design.

Vanadium redox flow battery using activated carbon catalyst produced from low density polyethylene

Carbonized and activated low-density polyethylene (LDPE) is suggested as a carbon catalyst for vanadium redox flow battery (VRFB). This carbon catalyst has many surface oxygen functional groups and a large surface area, while such benefits are achieved through activation of carbonized LDPE. According to electrochemical analysis, this carbon catalyst doped graphite felt (GF) enhances the redox reactivity of vanadium ions. More specifically, peak current density and peak potential separation for redox reaction of vanadium ions are 96.0 and 22.1% more improved than those measured by bare GF, while charge transfer resistance for the redox reactions is also improved by use of the catalyst doped GF. When performance of VRFB using this catalyst doped GF is measured, energy efficiency is 39% more improved than that measured without the catalyst. Based on that, this is revealed that new LDPE-based carbon catalyst is effective for performance improvement of VRFB.

Dataset on performance of large-scale vanadium redox flow batteries with serpentine flow fields

The dataset presented in this article are related to research articles “Effect of electrolyte convection velocity in the electrode on the performance of vanadium redox flow battery cells with serpentine flow fields” [1] and “Effect of channel dimensions of serpentine flow fields on the performance of a vanadium redox flow battery” [2]. The combined dataset on the pressure drop and electrochemical behavior of the vanadium flow battery cells with active areas of 400 cm², 900 cm² and 1500 cm² were obtained using battery life cycler for the circulation of vanadium electrolyte of concentration 1.61 M VOSO₄ dissolved in 5 M H₂SO₄. The cells were designed with various combinations of flow-channel dimensions of serpentine flow field and the electrochemical performance has been obtained at various flow rates and current densities. In addition to the experimental data, computational fluid dynamics simulations have been performed to investigate the electrolyte distribution across the cell. The shared data enables the reader of research articles to delve into the life cycle behavior at various operating conditions and emphasize the importance of flow-channel dimensions, flow rate and uniform distribution of electrolyte in combating the concentration over-potential.

One-step activation of high-graphitization N-doped porous biomass carbon as advanced catalyst for vanadium redox flow battery

In this paper, we reported a one-step activation strategy to prepare highly graphitized N-doped porous carbon materials (KDC-FAC) derived from biomass, and adopted ferric ammonium citrate (FAC) as active agent. At high temperature, FAC was decomposed into Fe- and NH₃-based materials, further increasing graphitization degree, introducing N-containing functional groups and forming porous structure. KDC-FAC has superior electrocatalytic activity and stability towards V²⁺/V³⁺ and VO²⁺/VO₂⁺ redox reactions. High graphitization degree can enhance the conductivity of carbon material, and porous structure is conducive to increase reaction area of vanadium redox couples. Moreover, N-containing functional groups are beneficial to improve the electrode wettability and serve as active sites. The single cell tests demonstrate that KDC-FAC modified cell exhibits good adaptability under high current density and superb stability in cycling test. Compared with pristine cell, the energy efficiency of KDC-FAC modified cell is increased by 9% at 150 mA cm^-2. This biomass-derived carbon-based material proposed in our work is expected to be an excellent catalyst for vanadium redox flow battery.

Application of porous biomass carbon materials in vanadium redox flow battery

Porous nano biomass carbon was synthesized by one-step method using scaphium scaphigerum as carbon source and was employed as negative catalyst for vanadium redox flow battery. Potassium ferrate was used to realize synchronous etching, introducing oxygen-containing groups and graphitization of scaphium scaphigerum to obtain porous, oxygen-rich, high-graphization carbon materials (SS-K/Fe). Compared with traditional two-step method, one-step method has advantages of low-time requirement, high efficiency and no pollution. The prepared SS-K/Fe sample has abundant microporous structure, high degree of graphitization and many oxygen-containing groups. The electrochemical test results show that the prepared carbon-based materials exhibit superior electrocatalytic capability for V²⁺/V³⁺ redox reaction. The electrode process can be accelerated from three steps including ion diffusion, electrochemical reaction and electron transfer processes, which are due to the enhancement of wetting performance and electrical conductivity, and an increase of effective catalytic area. Compared with pristine cell, the SS-K/Fe modified cell can improve the energy efficiency by 6.2% at the current density of 50 mA cm^-2. This method is expected to realize low cost, green and renewable porous carbon materials for future energy storage systems.