Theoretical study of ether group substitution effects on the electrochemical properties of Ti-modified vanadium-oxide...

In this study, the effects of ether group substitution on the electrochemical properties of [Ti₂V₄O₅(OCH₃)₁₄] (Ti2V4) and [Ti₃V₃O₄(OCH₃)₁₅]⁺ (Ti3V3+) were investigated by combining density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The lowest unoccupied molecular orbital energy decreases from Ti2V4 (-1.98 eV) to the ether-substituted derivatives of Ti2V4 (-2.04 eV), and from Ti3V3+ (-2.55 eV) to the ether-substituted derivatives of Ti3V3+ (-2.64 eV). The ether substitution affects the electrochemical window of Ti3V3+ derivatives that increases from 2.69 V for Ti3V3+ to 2.97 V for [Ti₃V₃O₄(OCH₃)₁₂(OCH₂)₃CCH₂OC₂H₄OCH₃]⁺ (Ti3V3TRIOLC+). The ether substitution also affects the interaction between vanadium-oxide clusters and both the solvent CH₃CN and the supporting electrolyte tetrabutylammonium hexafluorophosphate ([NBu₄][PF₆]), leading to a substantial increase in the diffusion coefficient of the Ti3V3+ series: from 5.8 × 10^-6 cm² s^-1 for Ti3V3+ up to 7.8 × 10^-6 cm² s^-1 for [Ti₃V₃O₄(OCH₃)₁₂(OCH₂)₃CCH₂OCH₃]⁺ (Ti3V3TRIOLB+) and 9.2 × 10^-6 cm² s^-1 for Ti3V3TRIOLC+. Radial distribution function (RDF) and electrostatic potential (ESP) analyses further indicate that ether substitution modulates the surface charge density and enhances the hydrogen bonding interactions between CH₃CN and vanadium-oxide clusters. These findings suggest that Ti3V3TRIOLC+ possesses superior electrochemical performance, highlighting its potential as a promising electroactive material for RFBs.