Reversal in Output Current Direction of 4H‐SiC/Cu Tribovoltaic Nanogenerator as Controlled by Relative Humidity

Abstract

Tribovoltaic nanogenerators (TVNG) represent a fantastic opportunity for developing low‐frequency energy harvesting and self‐powered sensing, by exploiting their real‐time direct‐current (DC) output. Here, a thorough study of the effect of relative humidity (RH) on a TVNG consisting of 4H‐SiC (n‐type) and metallic copper foil (SM‐TVNG) is presented. The SM‐TVNG shows a remarkable sensitivity to RH and an abnormal RH dependence. When RH increases from ambient humidity up to 80%, an increasing electrical output is observed. However, when RH rises from 80% to 98%, the signal output not only decreases, but its direction reverses as it crosses 90% RH. This behavior differs greatly from that of a Si‐based TVNG, whose output constantly increases with RH. The behavior of the SM‐TVNG might result from the competition between the built‐in electric field induced by metal‐semiconductor contact and a strong triboelectric electric field induced by solid‐liquid triboelectrification under high RH. The authors also demonstrated that both SM‐TVNG and Si‐based TVNG can work effectively as‐is even fully submerged in deionized water. This mechanism can affect other devices and be applied to design self‐powered sensors working under high RH or underwater.