Potassium Storage Performance of UiO-66 Derivatives from First Principles Calculations

The potassium storage performance of UiO-66 derivatives was investigated by density functional theory calculations. The calculation results show that the substitution of all Zr in nodes of UiO-66 by Ti reduces the band gap. During potassiation, UiO-66-Ti and UiO-66-Hf have similar charge transfer processes to UiO-66, in which the charges of Ti and Hf are almost not changed, and the charge transfers from K to C or O near it. Compared with UiO-66, UiO-66-Hf has a lower theoretical capacity (490 mAh/g) with a smaller volume expansion and a slightly higher energy barrier for K-ion diffusion. UiO-66-Ti has a lower diffusion barrier for K ion although it has a larger volume expansion with all sites occupied by K. For the -NH2, -NO2, -Br, -Cl, -OH, -SH, and -CH3 functionalized UiO-66, the substitutions of H in ligands reduce the band gap of UiO-66, with the largest reduction in UiO-66-NH2. The p orbitals of N in the NH2 contribute greatly to the reduction of the band gap. The K intercalated at the K2(L) and K3 sites during the charging process will transfer part of the electrons to the substituents. Between the Zr6O4(OH)(4) nodes, there will be a migration path that crosses the substituent, and the diffusion energy barrier on this path is smaller than that of the original path of UiO-66. The results suggest that proper modification of UiO-66 can improve its electronic conductivity and ionic conductivity as the anode of potassium ion battery.

Automated summary

The potassium storage performance of UiO-66 derivatives was investigated using density functional theory calculations. The results showed that modifying the metal atoms in the UiO-66 nodes can affect the band gap and charge transfer processes. Proper modification can improve the electronic and ionic conductivity of UiO-66 when used as an anode material in potassium ion batteries.