Device structure of the blow-driven triboelectric nanogeneratorResults from the Chinese Academy of Sciences suggest that tomorrow’s alcohol breath tests may be self-powered and nano-enhanced.
Small-scale gas sensors are used in countless applications around the word - from monitoring the air quality in tunnels and in labs, to the detection of disease or explosives. Since the 1950’s, they’ve also found widespread use in roadside breath tests for drivers. Despite many changes in design, today’s breathalyzers still operate on the original principle. Based on a chemical reaction between ethyl alcohol (ethanol) and potassium dichromate, these portable sensors produce a color change directly related to the level of alcohol present in the person’s breath. When compared to a known sample of gas, they can also provide a quantitative measure of the alcohol content in the person’s blood.
But work from a team of US and Chinese researchers suggests there may be an even better way to test a person’s breath – a nanowire ‘whistle’ that powers itself. Published in Nano Energy [DOI:10.1016/j.nanoen.2015.06.006], the paper describes the development of a rotating triboelectric generator and gas sensor, that can to detect alcohol at concentrations as low as 10 parts per million (ppm). In its simplest form, the ‘whistle’ is assembled from three main components – a rotator (a rotating acrylic wheel coated with polymer nanowires), a stator (a pair of stationary, copper-coated acrylic disks) and a spacer (soft elastic O-rings to sit between them). It works by the triboelectric effect - blowing into the whistle causes the wheel to rotate. Because copper is an electron-donating material and the fluorinated ethylene propylene (FEP) nanowires are electron-accepting, as the nanowire-coated wheel spins, there is an exchange of electrons between the materials. This produces a large enough current to power a Co3O4 based gas sensor.
The team found that the output voltage of the gas sensor was constant and independent of the user, or the speed at which the user exhaled. Powered by the triboelectric whistle, the sensor could detect a range of different gases at very low concentrations, and connecting a low-cost alarm to it (also powered by blowing into the whistle) minimized the risk of interference by the user.
So, what’s the catch? Well, this system is optimized to operate at 160 °C – not the typical roadside temperature! The next stage of the work is to investigate a series of alternative materials for a system that can operate at ambient temperatures – only then will the system be considered self-powered!
Zhen Wen et al, Nano Energy (2015) Vol 16, 38–46, “Blow-driven triboelectric nanogenerator as an active alcohol breath analyzer.” DOI:10.1016/j.nanoen.2015.06.006