Formation of an active layer for charge accumulation in NiCo2O4 spinel

Discussion about the mechanism of pseudocapacitance led to the hypothesis that on the surface of pseudocapacitive materials there is an intermediate layer responsible for charge accumulation. Cyclic voltammetry revealed the presence of a hydroxylated layer on the surface of NiCo2O4 film. It was proven that the hydroxylated layer is formed as a result of the interaction of NiCo2O4 with alkali and consists of anionic metal complexes at the phase boundary. The redox switching process is considered as the loss of protons from water molecules or the removal of OH- ions in the environment of a metal ion. The presence of structurally bound hydroxyl groups on the surface was confirmed by TG-DSC, NMR H-1 MAS and XPS. According to the results of ARXPS measurements, the thickness of the surface layer is similar to 0.4 nm.