Innovative Insole Uses Sweat Evaporation to Generate Power

As reported on, researchers from the National University of Singapore have created a 3D printed prototype of a shoe insole that evaporates sweat faster than normal and uses the harvested moisture to generate energy:

“In our new invention, we created a novel film that is extremely effective in evaporating sweat from our skin and then absorbing the moisture from sweat. We also take this one step further—by converting the moisture from sweat into energy that could be used to power small wearable devices,” explained research team leader Assistant Professor Tan Swee Ching, who is from the NUS Department of Material Science and Engineering.

The main components of the novel thin film are two hygroscopic chemicals—cobalt chloride and ethanolamine. Besides being extremely moisture-absorbent, this film can rapidly release water when exposed to sunlight, and it can be ‘regenerated’ and reused for more than 100 times.

To make full use of the absorbed sweat, the NUS team has also designed a wearable energy harvesting device comprising eight electrochemical cells (ECs), using the novel film as the electrolyte. Each EC can generate about 0.57 volts of electricity upon absorbing moisture. The overall energy harvested by the device is sufficient to power a light-emitting diode. This proof-of-concept demonstration illustrates the potential of battery-less wearables powered using human sweat.”

This prototype is certainly interesting and has obvious potential for improving human comfort, confidence, and possibly health. It remains to be seen whether commercialization of the technology will be feasible and whether researchers develop effective ways to recycle the product at the end of its useful life. Conventional electronics are already a waste generation challenge, and wearable technology is notoriously difficult to recycle and a potential contaminant in recycling streams. Further, the incorporation of cobalt chloride in this product could prove problematic and detrimental to sustainable design, as continues to be the case for most electronics. Cobalt mining operations have been supported by child labor, so truly sustainable designs will strive to use reclaimed cobalt from the recycling of existing products for the preparation of cobalt compounds for the manufacture of new devices. It could be the case that innovations such as this one might reduce reliance on batteries, and thus reduce overall demand for cobalt, but any cobalt in a product supply chain must be scrutinized. We can only hope that the same innovativeness that leads to prototypes such as this insole can inspire researchers to continuously improve the overall sustainability of product design and end-of-life management.

Learn more:

Xueping Zhang et al, Super-hygroscopic film for wearables with dual functions of expediting sweat evaporation and energy harvesting, Nano Energy (2020). DOI: 10.1016/j.nanoen.2020.104873

Apple and Google named in US lawsuit over Congolese child cobalt mining deaths

Cavusoglu, AH., Chen, X., Gentine, P. et al. Potential for natural evaporation as a reliable renewable energy resource. Nat Commun 8, 617 (2017).


Reminder: Manuscripts for Special Edition of Challenges Due 12/31/15

challenges-logoManuscripts are still being accepted for the special issue of the journal Challenges, entitled “Electronic Waste–Impact, Policy and Green Design.” 

From the issue’s rationale:

“Electronics are at the heart of an economic system that has brought many out of poverty and enhanced quality of life. In Western society in particular, our livelihoods, health, safety, and well being are positively impacted by electronics. However, there is growing evidence that our disposal of electronics is causing irreparable damage to the planet and to human health, as well as fueling social conflict and violence.

While global demand for these modern gadgets is increasing, policy to handle the increased volumes of electronic waste has not kept pace. International policy governing safe transfer, disposal, reclamation, and reuse of electronic waste is nonexistent or woefully lacking. Where laws do exist about exporting and importing hazardous waste, they are routinely circumvented and enforcement is spotty at best. While European Union countries lead the way in responsible recycling of electronic and electrical devices under various EU directives, most industrialized nations do not have such policies. In the U.S., for example, most electronic waste is still discarded in landfills or ground up for scrap.

It is imperative that we consider how green design practices can address the growing electronic waste problem. This special issue is meant to do just that and spur discussions on how electronic products can become greener and more sustainable.”

If you are interested in submitting a paper for this special issue, please send a title and short abstract (about 100 words) to the Challenges Editorial Office at, indicating the special issue for which it is to be considered. If the proposal is considered appropriate for the issue, you will be asked to submit a full paper. Complete instructions for authors and an online submission form for the completed manuscripts are available on the Challenges web site at The deadline for manuscript submissions is December 31, 2015. Questions may be addressed to co-guest editor Joy Scrogum.