Open circuit voltage (VOC) measured on a TENG operating in contact-separation mode (average power @5 Hz: 79.5 mW m-2, force load 10 N, 5 mm maximum airgap). The electropositive tribomaterial is a polymer film based on a-PVA:Li (w/w, 100:20) and the electronegative tribomaterial is a pre-charged PTFE film.