Using the Quadratic Logistic Equation To Analyze Intercalation of Lithium Ions in Layer-by-Layer V2O5 Films

The quadratic logistic equation (QLE) is used to determine the number of electrochemical active sites in V 2 O 5 films, by fitting the absorbance changes resulting from the intervalence transfer V(IV) → V(V) in chronopotentiometry and cyclic voltammetry experiments. Approximately 20% of the V 2 O 5 sites were found to be inactive electrochemically. The absorbance data at 660 nm as a function of the charge injected in layer-by-layer (LBL) films of V 2 O 5 alternated with poly(ethylene oxide)/chitosan blend was fitted with the QLE, from which the polaronic transfer between V 2 O 5 sites could be investigated. The maximum charge injected was 8 mC cm -2 for a 15-bilayer LBL film of V 2 O 5 /blend, with ca. 4.0 × 10 -8 mol cm -2 of electrochemically active V 2 O 5 sites in this film. Departures from the theoretical predictions are interpreted in terms of structural changes in the nanostructured LBL film caused by intercalation of lithium ions. In discussing further applications of the QLE to analyze chemical reactions, it is shown how the number of V(IV) sites is affected by irradiation with a Hg lamp of a 15-bilayer LBL film of V 2 O 5 /blend.