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Redox flow batteries (RFBs), provide a safe and cost-effective means of storing energy at grid-scale, and will play an important role in the decarbonization of global electricity networks. Several approaches have been explored to improve their efficiency and power density, and recently, cell geometry modification has shown promise in efforts to address mass transport limitations which affect electrochemical and overall system performance. Flow-by electrode configurations have demonstrated significant power density improvements in laboratory testing, however, flow-through designs with conductive felt remain the standard at commercial scale. Concentration gradients exist within these cells, limiting their performance. A new concept of redistributing reactants within the flow frame is introduced in this paper. This research shows a 60% improvement in minimum V 3+ concentration within simulated vanadium redox flow battery (VRB/VRFB) cells through the application of static mixers. The enhanced reactant distribution showed a cell voltage improvement by reducing concentration overpotential, suggesting a pathway forward to increase limiting current density and cycle efficiencies in RFBs.

A vanadium oxygen fuel cell is a modified form of a conventional vanadium redox flow battery (VRFB) where the positive electrolyte (VO2+/VO2+ couple) is replaced by the oxygen reduction (ORR) process. This potentially allows for a significant improvement in energy density and has the added benefit of overcoming the solubility limits of V (V) at elevated temperatures, while also allowing the vanadium negative electrolyte concentration to increase above 3 M. In this paper, a vanadium oxygen fuel cell with vanadium electrolytes with a concentration of up to 3.6 M is reported with preliminary results presented for different electrodes over a range of current densities. Using precipitation inhibitors, the concentration of vanadium can be increased considerably above the commonly used 2 M limit, leading to improved energy density. [ABSTRACT FROM AUTHOR]

A promising approach to improving the energy density of the all-vanadium redox flow battery while also saving on raw materials costs, is to eliminate the positive half-cell electrolyte and replace it with an air electrode to produce a hybrid vanadium-oxygen redox fuel cell (VOFC). This concept was initially proposed by Kaneko et al. in 1992 and first evaluated at the University of New South Wales by Menictas and Skyllas-Kazacos in 1997. In this project the performance of the VOFC over a range of temperatures and using different types of membranes and air electrode assemblies was evaluated. Despite early problems with the membrane electrode assemblies that saw separation of the membrane due to swelling and expansion during hydration, with improved fabrication techniques, this problem was minimized and it was possible to operate a 5-cell VOFC system for a total of over 100 h without any deterioration in its performance. [ABSTRACT FROM AUTHOR]

In recent decades, flow batteries have been rapidly developing for large-scale, low-cost energy storage, yet with concerns about the corrosivity and cost of metal-based electrolytes, such as vanadium. Recent research has shown great interest in seeking alternative redox couples for aqueous organic flow batteries (AOFB) due to their potentially improved safety, relatively lower cost and a wide diversity of tailored molecular structures. While most literature emphasises microscale or cell-scale experiments and modelling for AOFB, very little literature has reported on a detailed stack-level model. To this end, this work proposes an electrochemical stack model for the MV/TEMPTMA system, one of the MV/TEMPO derivatives, which claims high capacity and power density when maintaining excellent stability. The electrochemical stack model is based on the equivalent circuit method, which determines the flow battery's resistances, currents, voltages, efficiencies and capacity fade over multiple cycles, considering shunt currents, ion diffusion, self-discharge and degradation side reactions. The results show that ion diffusion and degradation play a predominant role in the capacity fade of the MV/TEMPTMA AOFB when the accumulation of diffused ions across the membrane suppresses the ion crossover and stabilises the coulombic capacity in the long run. The model uses MV/TEMPTMA as a demonstration but can also be adapted to other non-mixing AOFBs to predict and optimise battery performance. • An electrochemical stack model for the MV/TEMPTMA aqueous organic flow battery is developed. • The stack model is based on the equivalent circuit method to predict the battery performance over multiple cycles. • The effect of current density, ion diffusion across the membrane and degradation on the stack performance is revealed. • The ion diffusion and degradation play a predominant role in the capacity fade of the battery stack. • Diffused ions across the membrane suppress ion crossover and stabilise the capacity but may lead to cell voltage fluctuation. [ABSTRACT FROM AUTHOR]

Human health is a key pillar of modern conceptions of sustainability. Humanity pays a considerable price for its dependence on fossil-fueled energy systems, which must be addressed for sustainable urban development. Public hospitals are focal points for communities and have an opportunity to lead the transition to renewable energy. We have reimagined the healthcare energy ecosystem with sustainable technologies to transform hospitals into networked clean energy hubs. In this concept design, hydrogen is used to couple energy with other on-site medical resource demands, and vanadium flow battery technology is used to engage the public with energy systems. This multi-generation system would reduce harmful emissions while providing reliable services, tackling the linked issues of human and environmental health. [ABSTRACT FROM AUTHOR]

Abstract: The vanadium redox flow battery (VRB) is one of the most promising electrochemical energy storage systems deemed suitable for a wide range of renewable energy applications that are emerging rapidly to reduce the carbon footprint of electricity generation. Though the Generation 1 Vanadium redox flow battery (G1 VRB) has been successfully implemented in a number of field trials and demonstration projects around the world, it suffers from low energy density that limits its use to stationary applications. Extensive research is thus being carried out to improve its energy density and enhance its performance to enable mobile applications while simultaneously trying to minimize the cost by employing cost effective stack materials and effectively controlling the current operating procedures. The vast bulk of this research was conducted at the University of New South Wales (UNSW) in Sydney during the period 1985–2005, with a large number of other research groups contributing to novel membrane and electrode material development since then. This paper presents a historical overview of materials research and development for the VRB at UNSW, highlighting some of the significant findings that have contributed to improving the battery's performance over the years. Relevant work in this field by other research groups in recent times has also been reviewed and discussed. [Copyright &y& Elsevier]