Redox flow batteries (RFBs) are promising energy storage candidates for grid deployment of intermittent renewable energy sources such as wind power and solar energy. Various new redox-active materials have been introduced to develop cost-effective and high-power-density next-generation RFBs. Electrochemical kinetics play critical roles in influencing RFB performance, notably the overpotential and cell power density. Thus, determining the kinetic parameters for the employed redox-active species is essential. In this Perspective, we provide the background, guidelines, and limitations for a proposed electrochemical protocol to define the kinetics of redox-active species in RFBs.

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A water soluble cobalt complex with two redox couples that fall within the water splitting window can be applied as both the posolyte and negolyte in an aqueous symmetric redox flow battery.

Pressure wave transmission attenuation in an air pipe¯ow is investigated both theoretically and experimentally. This investigation is to ensure the viability of remote¯ow measurement in an air pipe¯ow using a new¯uidic pressure-pulse-transmitting¯owmeter. The novel¯owmeter produces self-induced oscillations, whose frequency is proportional to the¯owrate. These pressure waves are transmitted via the¯owing¯uid and can be detected far downstream of the device. Experimental work has been conducted to ascertain how much the pressure waves are attenuated in air¯ow in a pipeline. This was done by using pipes of 0.05 m diameter and both 4.7 and 28.5 m long installed downstream of the¯owmeter. A method of network simulation known as transmission line modelling (TLM), which has been programmed as the Sheeld University Network Analysis Software (SUNAS) code, is described and utilized to predict the wave decay through the air pipe¯ow. The theoretical and experimental results were found to give good agreement, demonstrating both the value of the modelling software and the viability of the remote¯ow measurement concept.

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<div>Aqueous symmetric redox flow batteries (RFB) are of great interest due to the non-flammability and high conductivity of the solvent, and avoidance of irreversible anolyte crossover seen in asymmetric cells. In this work, we introduce a simple octahedral Co(II) complex, termed BCPIP-Co(II), that has 4 appended carboxylic groups on the ligand periphery that render it both water-soluble and pH-sensitive in the range of pH 1.5 - 5.5. The complex has reversible BCPIP-Co(II-III) and BCPIP-Co(II-I) redox couples within the water splitting window, as well as fast kinetics. The overall charge of the complex varies from +3 to -3, resulting from the level of deprotonation of the carboxylic acid moieties and the oxidation state of the cobalt metal center, both of which affect the resulting redox properties. BCPIP-Co(II) was then incorporated, as both the posolyte and negolyte, into a symmetric aqueous RFB, demonstrating Coulombic efficiencies >99% for up to 100 cycles.</div>

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