Macroscopic liquid superlubric triboelectric nanogenerator: An in-depth understanding of solid-liquid interfacial charge behavior

Triboelectric nanogenerator (TENG) has been seen as one of the most promising energy harvesting technologies. However, there are an irreconcilable contradiction between low friction and high electrical output performance of the TENG. Here, we have devised a macroscale liquid superlubric triboelectric nanogenerator based on solid-liquid-solid structure, leveraging the concept of liquid superlubricity technology, resulting in a remarkable increase in both the open circuit voltage and short-circuit current by 53.0 % and 58.4 %, respectively. This huge increase in electrical output performance is accompanied by a 99.1 % reduction in friction coefficient (≈ 0.0025) and 99.993 % reduction in wear rate (≈ 0.76×10⁻⁷ mm³/N·m), when compared to those of a lubricant-free triboelectric nanogenerator. This work delves into the lubrication and charge transfer mechanisms. The liquid superlubricity technology achieves friction reduction through a hybrid mechanism combining boundary and hydrodynamic lubrication. And the high outputs arise from the charges transfer at solid-liquid interface. The triboelectric charges generated by the friction pair are transferred from solid to the lubricating liquid. Meanwhile, the lubricating liquid promotes electron transfer and contributes additional electrons. Our work provides profound insights into the lubrication and charge transfer mechanisms at solid-liquid interfaces, and addresses the paradox of high output and low friction in TENGs.