Review: self-powered

Title: Self-powered materials obtained by interfacing functional assemblies with energy harvesting films

Authors: Wangshu Tong, Zhihao Wang, Xuemei Wang, Xiao Zhang, Yihe Zhang and Qi An

Journal: Materials Chemistry Frontiers (2021) 5: 2623-2648

DOI

Why I read it:

I have had an idea about directly powering my nanostructures for uses like water waste treatment, which is obviously in liquid and need some adjustments regarding power supply. But also, to treat the water, a flow is often necessary, and if one could use the power generated by this flow, it might be sufficient to power the cleaning device itself (self-powered). Even more so, when scaling down materials (nano-world), the properties changes and the energy needs differ. It would be therefore conceivable that nano-shaped materials be powered by attached nano-power generators. It eliminates quite a lot of energy waste (no circuitry, no power circulation for long distances…) and it could be implemented anywhere where things happen.

Summary:

The authors have make a special type of article called a “review”, where they scan and read the literature of the last few years on a specific subject (here: self-powered devices) and give an overview and a summary. These type of articles are extremely useful to “mark” the evolution of scientific achievements in time. It is basically the basics for scientific books, where the more established (reproduced and uncontested) published research is neatly summarize and fundamentally explained. The article is divided into two main sections: the different effects and devices that could provide power directly to functional devices & examples of applied self-powered devices.

The part that interested me more was the first, of course, where basically four type of physical effects can be harnessed with the proper material engineering to create a small amount of power locally. These four effects are called: piezoelectric, triboelectric, pyroelectric and magnetoelectric. The piezoelectric effect occurs in specific materials that are not totally symmetrical in their crystalline structure (most widely use in industry: Lead Zirconate Titanate (PZT)), when they are under mechanical stress. So basically, if these materials are bent, stretched or compressed, they produce charges and an electric potential. The triboelectric effect happens when two very different materials (solid/solid, solid/liquid…) are in contact and friction occurs. In this case, the charges are created by this friction, and it is possible to harvest power from water waves, wind or even human motion. To create this effect it is necessary to have two different type of materials in contact: one that looses easily electrons (i.e. Asbestos, Human skin) & one that takes readily electrons (i.e. Cellophane Tape, Teflon). As for the pyroelectric effect, it is mainly a material of which the crystal structure change drastically with temperature, which can produce an electric field (displacement of charges). Examples of pyroelectric materials: gallium nitride, Tourmaline. Finally, the magnetoelectric devices need to combine magnetostricion (expansion/contraction of a material under magnetic field) and piezoelectricity to generate electric power. Examples of magnetostrictive materials employed in industry are: Cobalt Ferrite, Nickel Ferrite. The authors point out the possibilities of using self-powered devices at nanoscale and macroscale, using ambient power sources (water vapour, light, breath, human motion…) and the usual renewable energy sources (wind, waves, solar…).

The second part of the article takes several examples of applied self-powered devices in different domains: medicine (drug delivery, skin tissue repair, bone growth…), physics (increased resolution in Raman spectroscopy) and engineering (photocatalysis, luminescent films, sensors…). The major challenges to overcome would be the contact between the power-generating part of the device and the power-consuming part of the device – it will be critical to engineer it to have as low-power loss as possible. Evidently, the electric power generated by this small and common phenomenons (friction, temperature change…) are small and at different frequencies from the “normal” grid ones.

Their conclusion:” It is hoped that using electricity to power conventional functional systems will lead to the development of high-performance devices that benefit the society.

My view on the article:

The review is very well-made, with a small explanation of terms and effects at the beginning of each section. The authors try to keep a basic scientific vocabulary, so that the article can be read by a large variety of researchers of different academic background. The choices of examples for potential applications are diverse and give an accurate view of the “state of the art” for each type of devices. An interesting read, mostly for researchers working on device applications and nano-materials.

What to make of it all:

This review sell a nice potential future, where access to a grid/power supply to power a medical equipment or a life-saving sensor is not necessary any more. It could also increase the potential applications in wearable/stretchable devices, as most of the power generator devices could also be made extra thin and mailable – which is not easily achieved with batteries. Of course, this is research, so commercial applications will not be available any time soon, but it could be a surprise and an easy pathway could be found, who knows? Let’s hope so!

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