Triboelectric nanogenerators as a new energy technology
While we are all familiar with solar and wind power, there are other sources of energy yet to be fully explored. If we look at the big picture, we can notice that the combination of SLIPS and TENG technologies, for example, is powerful enough to provide a paradigm shift in the design of blue energy devices, which have more powerful properties and can last long, which in turn makes them adaptable to a wide range of working conditions.
Global energy demand has grown significantly over the past several decades. When we analyze this trend in the context of climate change and its consequences, it’s clear that new solutions, preferably those including renewable energy alternatives, have to be found. Scientists from all over the world are conducting research related to finding new sources of energy and the ways in which such energy can be exploited. While we are all familiar with solar and wind power, for instance, there are other sources of energy yet to be fully explored.
One of them is the way in which mechanical or thermal energy produced by small-scale physical change can be harvested and turned into electricity and scientists and researchers are particularly interested in the potential offered by the water surface. A recent study led by researchers from the City University of Hong Kong has developed a new triboelectric nanogenerator (TENG), using a slippery surface to enhance energy harvesting efficiency. The findings could easily create new ways in which energy harvesting devices are designed, with an aim to provide better stability and durability.
A bit of theory
In case you were wondering, a nanogenerator is a kind of technology that converts mechanical or thermal energy into electricity. It has three typical approaches: piezoelectric, triboelectric, and pyroelectric nanogenerators. While both the piezoelectric and triboelectric nanogenerators can convert mechanical energy into electricity, pyroelectric nanogenerators can be used to harvest thermal energy from time-dependent temperature fluctuation. In this text, we are going to look at the concept of a powerful triboelectric nanogenerator and the ways in which it can be exploited.
TENGs were invented by Professor Wang Zhonglin from the Georgia Institute of Technology, USA, in 2012. This water energy harvesting approach can convert mechanical energy to electrical energy, which is why it has received a lot of attention recently. The mechanism behind TENGs is primarily based on the triboelectric effect and electrostatic induction, which both occur at either solid-solid or solid-liquid interfaces. At the moment, the solid interface of a solid-liquid TENG is designed to be hydrophobic or superhydrophobic, so that water droplets can be timely repelled to allow dry contact areas for continuous power generation.
Still, the physiochemical properties of the solid-liquid interfacial materials of conventional superhydrophobic-based TENGs (SHS-TENGs) are reduced when operating in harsh environments, such as low temperature and high humidity. Namely, the nucleation of water droplets, ice or frost leads to a frozen surface eventually, thus blocking the charge generation. When such a device is submerged in water, biofilms form and limit the longevity and energy efficiency of the device.
Dealing with this obstacle, scientists working at prestigious Chinese and American institutions have developed a new device by combining slippery lubricant-impregnated porous surface (SLIPS) technology with a TENG. What this means is that in low-temperature conditions, the output power of this SLIPS-based TENG (SLIPS-TENG) is at least an order or magnitude higher than that of the conventional SHS-TENG, which is the result the scientist hoped for. Logically, the SLIPS-TENG exhibits better stability at low temperature (-3°C) than the SHS-TENG.
The SLIPS technology was invented by scientists at Harvard University in 2011, who were inspired by pitcher plants. The surface is extremely slippery, which means it can easily repel simple and complex liquids, including water, crude oil and blood. What is more, such a surface can quickly restore its liquid-repellency characteristic following a physical damage, whilst resisting ice adhesion. SLIPS are now fabricated using a perfluorinated liquid as a lubricant on the porous PTFE membrane. The SLIPS are then combined with a TENG to form a liquid–liquid–solid interface. The results are obvious: the SLIPS-TENG offers better optical transparency, configurability, self-cleaning, flexibility and power generation stability than conventional TENGs. The fact that is functions so well at low temperatures, with the same electric output as it does at room temperature, suggests that it can be used in various wearable and flexible devices.
Since experts are continuing their work at providing new options for harvesting energy from renewable sources, we can realistically expect to see new breakthroughs relatively soon. What was quite unimaginable just a decade ago seems like rather plausible and viable today and we will surely be using various devices to convert mechanical and thermal energy into electricity in the near future. If we look at the big picture, we can notice that the combination of SLIPS and TENG technologies, for example, is powerful enough to provide a paradigm shift in the design of blue energy devices, which have more powerful properties and can last long, which in turn makes them adaptable to a wide range of working conditions.