An Organofunctionalized Polyoxovanadium Cluster as a Molecular Model of Interfacial Pseudocapacitance

Abstract

To design new materials for efficient and energy-dense electrochemical energy storage, it is critical to understand the interactions between metal oxides and alkali ions. Here, we discuss the solution-phase interactions of lithium, sodium, potassium, and alkylammonium cations with the Lindqvist-type polyoxovanadate alkoxide (POV alkoxide) cluster, [V6O7(OCH3)12]. In all cases, the presence of alkali cations positively shifts the half-wave potentials of the reduction events of the POV alkoxide cluster relative to alkylammonium. In contrast, the two cluster oxidation events are not affected by the presence of alkali ions, indicating that the observed changes in reduction potentials are the result of unique interactions with charge-compensating cations. Further analysis of the shift in reduction potential shows that the energetics of cation binding to the reduced cluster depend both on the charge state of the complex and the charge density of the compensating ion. Single-crystal X-ray diffraction studies indicate that two {Li}+ ions undergo site-selective coordination to opposite faces of the octahedron upon complete reduction, manifesting in sluggish reoxidation of this tightly associated, ion-paired species. Thus, this single molecular complex demonstrates redox behavior that spans the range from nonspecific to highly specific cation binding, which is directly analogous to the transition from double-layer capacitance to pseudocapacitance in bulk energy storage electrodes.

Atomically precise vanadium-oxide clusters

“…This is mainly due to the small ionic radius of vanadium which presents challenges in isolating stable Keggin-and Dawson-type POVs, as well as their corresponding Lacunary derivatives. 51 Seminal contributions into the generation of heteroion-installed polyoxovanadates have been led by Streb [164][165][166][167][168][169][170][171][172][173][174] and others 34,[175][176][177] Fig. 16).…”

Redox-inactive ions control the redox-activity of molecular vanadium oxides

“…[16][17][18] In contrast to these pioneering studies on Mo-and W-POMs, polyoxovanadates [19][20][21][22] have only recently become a focal point for electrochemical reactivity tuning. [23][24][25] Systematic studies have provided critical insights into the effects of heterometalfunctionalization, 22,26,27 organofunctionalization 28 and countercation interactions 29,30 on the electrochemical properties of POVs. This fundamental understanding also enabled POV application in water oxidation catalysis, 31,32 redox-ow batteries, 33 and lithium ion batteries, [34][35][36] and as model catalyst surfaces.…”

Molecular Vanadium Oxides for Energy Conversion and Energy Storage: Current Trends and Emerging Opportunities

“…nBu 4 N + )i nt he supporting electrolyte with Li + or Na + significantly altered the redox potentials of their POV. [29,110] Thes tudies highlight that tuning the electrolyte composition in addition to tuning the POVi sapromising means for controlling POVe lectrochemistry.T hat said, high-enough concentrations of soluble POVs alts or POV-ILs would remove the need for added supporting electrolyte.…”