Impurity and valence-dependent solid/solid triboelectric and solid/liquid tribovoltaic effect of CuxO submicron rods for AC and DC generation

Abstract

CuxO is a promising p-type semiconductor, but its triboelectric properties are unexplored. This study investigates both the triboelectric properties of CuxO and the solid–liquid tribovoltaic effects between CuxO and various liquids. CuxO submicron rods are synthesized on Cu foams, doped with Li, and subjected to oxidant reactions. Li doping and valence changes increase CuxO’s work function, as shown by Kelvin probe force microscopy. Solid-solid triboelectric measurements reveal systematic changes in triboelectric voltage and current, with CuxO negatively shifting in the triboelectric series. On the other hand, the CuxO/liquid tribovoltaic effect conducted in an immersion-type device generates a stable direct current. The magnitudes of the tribovoltaic current and voltage systematically vary with the energy level differences between CuxO and the liquids. From the direction of tribovoltaic current and magnitude of tribovoltaic voltage, the relative positions of fermi levels for several liquids are determined. Among all, the best CuxO/NaCl(aq) tribovoltaic nanogenerators exhibit a high-power density of 4900 nW/cm2, and the generated DC is applied for novel rectifier/capacitor-free self-powered electroplating. This work demonstrates a viable method to adjust the triboelectric properties of CuxO and proposes a method to determine the relative energy levels of liquids for the first time.