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

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.

MXene Lubricated Tribovoltaic Nanogenerator with High Current Output and Long Lifetime.

Tribovoltaic nanogenerators (TVNGs) have the characteristics of high current density, low matched impedance and continuous output, which is expected to solve the problem of power supply for small electronic devices. However, wear occurrence in friction interface will seriously reduce the performance of TVNGs as well as lifetime. Here, we employ MXene solution as lubricate to improve output current density and lifetime of TVNG simultaneously, where a high value of 754 mA m-2 accompanied with a record durability of 90,000 cycles were achieved. By comparing multiple liquid lubricates with different polarity, we show that conductive polar liquid with MXene as additive plays a crucial role in enhancing the electrical output performance and durability of TVNG. Moreover, the universality of MXene solution is well demonstrated in various TVNGs with Cu and P-type Si, and Cu and N-GaAs as material pairs. This work may guide and accelerates the practical application of TVNG in future.

Wear-Resisting and Stable 4H-SiC/Cu-Based Tribovoltaic Nanogenerators for Self-Powered Sensing in a Harsh Environment.

Tribovoltaic nanogenerators (TVNGs) are an emerging class of devices for high-entropy energy conversion and mechanical sensing that benefit from their outstanding real-time direct current output characteristics. Here, a self-powered TVNG was fabricated using a small-area 4H-SiC semiconductor wafer and a large-area copper foil. Thus, the cost of materials remains low compared to devices employing large-scale semiconductors. The 4H-SiC/metal-TVNGs (SM-TVNGs) presented here are sensitive to vertical force and sliding velocity, making them appropriate for mechanical sensing. Notably, owing to the modulated bindingtons and surface states, these SM-TVNGs performed well in a harsh environment, namely, in high-temperature and high-humidity conditions. In addition, the SM-TVNGs exhibited an excellent wear-resisting property. On these bases, we designed a self-powered and real-time monitoring device able to estimate the number of staff present in various areas of a deep mining site, a high-temperature and high-humidity environment. This work not only discloses basic physics behind the tribovoltaic effect but also sheds light on possible applications of SM-TVNGs for wear-resisting and stable mechanical sensors in harsh environments.