Chen Han-Yi, Friedl Jochen, Pan Chun-Jern, Haider Ali, Al-Oweini Rami, Cheah Yan Ling, Lin Ming-Hsien, Kortz Ulrich, Hwang Bing-Joe, Srinivasan Madhavi, Stimming Ulrich
TUM CREATE, 1 CREATE Way, #10-02 CREATE Tower, 138602 Singapore.
Department of Chemical Engineering, National Taiwan University of Science and Technology (NTUST), Taipei 106, Taiwan.
Phys Chem Chem Phys. 2017 Jan 25;19(4):3358-3365. doi: 10.1039/c6cp05768c.
Polyoxometalates (POMs) have been reported as promising electrode materials for energy storage applications due to their ability to undergo fast redox reactions with multiple transferred electrons per polyanion. Here we employ a polyoxovanadate salt, Na[VO], as an electrode material in a lithium-ion containing electrolyte and investigate the electron transfer properties of Na[VO] on long and short timescales. Looking at equilibrated systems, in situ V K-edge X-ray absorption near edge structure (XANES) studies show that all 10 V ions in Na[VO] can be reversibly reduced to V in a potential range of 4-1.75 V vs. Li/Li. Focusing on the dynamic response of the electrode to potential pulses, the kinetics of Na[VO] electrodes and the dependence of the fundamental electron transfer rate k on temperature are investigated. From these measurements we calculate the reorganization energy and compare it with theoretical predictions. The experimentally determined reorganization energy of λ = 184 meV is in line with the theoretical estimate and confirms the hypothesis of small values of λ for POMs due to electrostatic shielding of the redox center from the solvent.
多金属氧酸盐（POMs）因其每个聚阴离子能够进行具有多个转移电子的快速氧化还原反应，已被报道为有前景的用于能量存储应用的电极材料。在此，我们将一种多氧钒酸盐，Na[VO]，用作含锂离子电解质中的电极材料，并研究Na[VO]在长时间和短时间尺度上的电子转移性质。观察平衡体系，原位V K边X射线吸收近边结构（XANES）研究表明，Na[VO]中的所有10个V离子在相对于Li/Li为4 - 1.75 V的电位范围内可被可逆地还原为V。聚焦于电极对电位脉冲的动态响应，研究了Na[VO]电极的动力学以及基本电子转移速率k对温度的依赖性。通过这些测量，我们计算了重组能并将其与理论预测进行比较。实验测定的重组能λ = 184 meV与理论估计相符，并证实了由于氧化还原中心与溶剂之间的静电屏蔽，POMs的λ值较小的假设。
