In recent years, triboelectric nanogenerators (TENGs) have garnered significant attention from researchers due to their exceptional performance and cost-effectiveness. However, the limited availability of friction materials, primarily organic polymers, precious metals, and semiconductors, severely hinders the electrical output performance improvement of TENG. In this study, we prepared flexible TENGs using titanium dioxide nanoarrays and four Keplerate-type polyoxometalate (POM) films ({Mo132}, {Mo72Fe30}, {Mo72V30}, and {Mo72Cr30}) as friction materials. POM films were prepared through spin coating on commercial indium tin oxide/poly(ethylene terephthalate) (ITO/PET) substrates using four different types of POMs. The performance test shows that TENG with {Mo132} (3 mg mL–1)-TNF array as friction material has the best electrical output performance, and the output voltage and current are 26.2 V and 125.4 nA, respectively, which is about 5 times of TENG with Ag-TNF array as friction material. In addition, the mechanism of Keplerate-type POMs as friction materials studied in this paper shows that POMs act as electron acceptors in the friction process and can be used as friction materials, effectively improving the electrical output performance of TENGs and expanding the range of available friction materials.