Shamie Jack S, Liu Caihong, Shaw Leon L, Sprenkle Vincent L
Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, Illinois, 60616, USA.
Energy Storage and Conversion Energy Materials, Pacific Northwest National Laboratory, Richland, WA, 99352, USA.
ChemSusChem. 2017 Feb 8;10(3):533-540. doi: 10.1002/cssc.201601126. Epub 2016 Dec 29.
In this study, a new mechanism for the reduction of vanadyl acetylacetonate, VO(acac) , to vanadium acetylacetonate, V(acac) , is introduced. V(acac) has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac) . In previous work, once this transformation occurs, it is no longer reversible because there is a requirement for extreme low potentials for the reduction to occur. Here, we propose that, in the presence of excess acetylacetone (Hacac) and free protons (H ), the reduction can take place between 2.25 and 1.5 V versus Na/Na via a one-electron-transfer reduction. This reduction can take place in situ during discharge in a novel hybrid Na-based flow battery (HNFB) with a molten Na-Cs alloy as the anode. The in situ recovery of V(acac) during discharge is shown to allow the Coulombic efficiency of the HNFB to be ≈100 % with little or no capacity decay over cycles. In addition, utilizing two-electron-transfer redox reactions (i.e., V /V and V /V redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac) during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.
在本研究中，引入了一种将乙酰丙酮氧钒（VO(acac)₂）还原为乙酰丙酮钒（V(acac)₃）的新机制。乙酰丙酮钒（V(acac)₃）用于氧化还原液流电池（RFBs）的研究已有一段时间；然而，水分污染会导致生成乙酰丙酮氧钒（VO(acac)₂）。在之前的工作中，一旦这种转变发生，就不再可逆，因为还原反应需要极低的电位才能发生。在此，我们提出，在存在过量乙酰丙酮（Hacac）和游离质子（H⁺）的情况下，相对于Na/Na⁺，通过单电子转移还原反应，还原可在2.25至1.5 V之间发生。这种还原可以在以熔融Na-Cs合金为阳极的新型混合钠基液流电池（HNFB）放电过程中原位发生。放电过程中V(acac)₃的原位回收表明，HNFB的库仑效率约为100%，且在循环过程中几乎没有容量衰减。此外，由于放电过程中V(acac)₃的原位回收，每个V离子利用双电子转移氧化还原反应（即V³⁺/V²⁺和V²⁺/V⁺氧化还原对）来提高RFBs的能量密度成为可能。材料原位回收的概念可能会在未来维持RFBs循环寿命方面带来更多进展。
