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Researchers led by South Koreas UNIST have developed a new redox flow battery concept that uses iron ore and chromium for redox chemistry. The proposed battery configuration could achieve a stable life of 500 cycles and an energy density of 38.6 Wh L-1.
An international research team has developed a new redox flow battery concept that uses iron ore and chromium for redox chemistry.
“We are in the preliminary phases of exploring the economics of these batteries,” the lead author of the research, Hyun-Wook Lee, told pv magazine . “While we have not yet performed a comprehensive levelized cost of storage (LCOS) estimate, our early results point to potential cost competitiveness, especially given the green nature of our batteries and their promising performance metrics.”
The battery is based on a negative chromium electrolyte, or negolith, and strong-field cyanide ligands, which scientists say can mitigate the Jahn-Teller effect. The latter is a geometric distortion of a nonlinear molecular system that reduces its symmetry and energy and, in redox flow batteries, reduces redox potential, stability, and fast kinetics.
Suppressing the undesirable decomposition of the chromium(II) chloride complex Cr(II) used in the battery is the crucial step to avoid these problems during the electrochemical cycle of redox flow batteries, thus facilitating a stable and fast redox reaction.
The battery also uses a negolith based on hexacyanometalate, an inorganic compound with the formula Cr(CN)6. “The reliable electrochemical properties of Cr(CN)6 are unique due to its low redox potential of -1.15 V,” the group explained. The electrolyte was based on sodium cyanide (NaCN), which is claimed to offer excellent electrochemical stability, especially against very low potentials, combined with high water solubility.
Through a series of density functional theory (DFT) thermodynamic simulations, the researchers found that the negolith coordinates well with the strong-field ligands used for the stack and is able to reduce the Jahn-Teller effect.
The proposed battery configuration can achieve a stable life of 500 cycles and a high energy density of 38.6 Wh L-1, according to the research group.
“This hexacyanometalate-based redox flow battery is capable of relatively high-potential reversible redox reactions as an aqueous system by taking advantage of the low potential of Cr(CN)6 and better cycling performance at high current densities,” he said. "Compared to conventional and other flow batteries, this cell configuration has superior properties in terms of full cell potential and cycling performance."
The new battery concept is presented in the study “ Full-Hexacyanometallate Aqueous Redox Flow Batteries Exceeding 1.5 V in an Aqueous Solution”, published in Advanced Energy Materials . The research group includes scientists from Nanyang Technological University in Singapore and the Ulsan National Institute of Science and Technology (UNIST) in South Korea. |
