‘It Was an Accident’: the Scientists Who Have Turned Humid Air Into Renewable Power
Leo Vermaak
With the effects of climate change becoming more apparent with time, there has been a rush to explore renewable, clean energy sources to replace fossil fuels. Tremendous effort has been put into researching and developing wind, solar, and hydroelectric power to meet these clean energy needs. One field of renewable energy that has been getting recent attention in the past decade is humidity generation. By creating a humidity gradient across a hydrophilic film, a current can be generated, allowing for energy generation. A recently published article from The Guardian compared the humidity generation projects of a team at the University of Massachusetts and the startup CascataChuva.
In the Guardian article, Ned Miles describes how the Yao lab originally discovered humidity generation in 2018 when a humidity detector made of nanotubes/wires was running despite not being plugged in. They describe how water enters a nanotube, bumps into the sides donating a small charge, and after bumping enough times at one end of the tube there would be a charge difference between the two ends. They then describe the current paper, in which they switched from nanowires to punching small holes into materials, and that their current work could produce one µW cm−2. Miles then talks about CascataChuva, who they say discovered humidity generation first in 2015 with a prototype 300,000 times better than the work of the Yao group, which at the time required someone to blow into it. The article states that CascataChuva's current work could power a house with a washing machine-sized device. They then go over current logistic challenges and costs of making these humidity generation devices and mention that while the Yao group uses organic components, CascataChuva uses superior zirconium oxide for their devices.
The original publication from Liu, Gao, and Yao, demonstrates a new type of humidity generator. Previous projects required an external source to maintain a humidity gradient, required an expensive gradient heterogenous film, or only worked for two days before becoming saturated with water. Liu's new humidity generator uses a hydrophilic homogenous film that can maintain a humidity/adsorption gradient without ever wearing out. Liu calls these new generators air generators (air-gens) due to how different they are from previous humidity generators. Their earlier project involved making the film from the protein of a specific bacteria, while the recent paper sought to test various materials and how the depth of the film affects the power generation of an air-gen.
The way the air-gen works is that a film with pores smaller than the mean free path of water is formed on an electrode, with one side open to air. The size of the pores means the water interacts with the surface more than other gas particles, causing the vapor pressure of water to increase with depth in the film. Since pressure equalizes, this creates an inverse water vapor density gradient within the film. The adsorption rate onto the film is correlated with the water vapor density, which means that an adsorption gradient forms as well. The adsorption of the water onto the film's surface generates a charge on the surface, so the adsorption gradient causes a charge gradient in the film, generating a current. Liu tested biological, organic, and inorganic films at thicknesses of 1 µm to 25 µm and pore sizes from sub-nanometer to 200 nanometers, determining the voltage each device generated, along with the average adsorption of the film and adsorption difference between the top and bottom. The paper found that voltage and adsorption difference increased with thickness while average adsorption decreased, while overall adsorption increased with pore size while voltage dropped. Overall, biological films generated the highest voltages, up to 550 mV, due to the hydrophilicity of the protein and the significantly smaller pore sizes. To test the long-term viability the device's weight and relative humidity of a small chamber containing the device were measured to see if the device was collecting water. There was no increase in the device's weight or decrease in relative humidity over several days of runtime. They concluded with other testing that I frankly cannot explain, that the energy produced by the device most likely originated from electrostatic interaction with water molecules rather than from a kinetic effect, using the charges of individual water molecules that diffuse in and out of the device to generate current.
The most important takeaway from this journal article is that humidity generation has been a growing field of study that has until now not been viable for energy generation. With the work of Liu, a breakthrough has been made that could allow for sustainable energy generation through humidity generation using relatively cheap materials, though requiring a large amount of air-gens to create a usable power generation.
Overall, I feel that the online article by Miles and the work published by Liu et al are completely at odds. Miles claims that the air-gens that Liu et al made were nanotubes/wires that water directly entered, while the actual air-gens are a film made out of protein nanowires that form nanopores that the water enters. Also, Miles insinuates that the tubes are open-ended, while the whole reason why the air-gens work is that only one side of the film is open to air. Another problem with the physical description of the devices Miles uses is that Liu's current project was punching nanopores directly into materials to create the devices when this is not mentioned anywhere in the journal article. Miles undermined the work of Liu by saying CascataChuva's devices produce 300,000 times more power when the point of Liu's work is that it does not need an external source of water density like the CascataChuva devices. Miles also claims that Liu only used organic material to make the air-gens while CascataChuva uses superior inorganic zirconium oxide. The point of the paper was to test different biological, organic, and inorganic films that form nanopores of the desired sizes. Even then, Liu found that biological films work best for air-gens while inorganic worked the worst. My score for the Guardian article is a 3/10 due to the sheer amount of inaccuracies present in the article.
Good job explaining this complex research. Like you said, the misleading way Miles described the synthesis of the films as “punching materials” with holes and the lack of description of the actual research in the Advanced Materials paper makes it seem like not much thought was put into the science behind this technology and makes me skeptical of the claims this article makes. I like how many quotes from scientists were used and it discussed other aspects about the feasibility of hygroelectricity as an energy source, but the focus on CascataChuva really lowered my opinion of the article. It sounded like this article was publicity for the startup and I wonder if Miles could have been more critical of CascataChuva. How do you think the startup should have been discussed? And do you think the Guardian article is overstating the promise of humidity gradient based power generators?
ReplyDeleteI didn't want to come off too argumentative in my post, but I am pretty sure this was a puff piece for CascataChuva. One of the big issues with humidity generation is that it requires a humidity gradient. CascataChuva's devices as describe in the article require an external source to generate this, which is briefly mentioned when talking about having to breath into their devices. This makes CascataChuva's devices infeasible for home use, as you would both need to power a machine to pump water vapor through it constantly, constantly supply water to it, and constantly dehumidify the home to prevent mold growth. If they were critical on the feasibility of CascataChuva's devices, it would have made for a better articles, as well as not taking talking points directly from CascataChuva and the Catcher Group's website, such as fulfilling the dreams of Tesla. I don't think humidity gradient based power works as a replacement for current power sources. Even Liu's air-gen that works indepedently would need 10 cubic meters to power a home, and would need to be outside with constant access to air.
DeleteYou did a great job on the research article summary, and I agree that the Guardian article could have been a lot better. The first thing I noticed when reading Yao et al's work (and that you also touched on) was that a variety of materials were used, not just organics like the news article claimed. Because of this, I felt like Miles was trying to contextualize CascataChuva's research as an improvement upon Yao et al's work. If Yao et al's work was not mentioned in the beginning, I feel like the article would have been more or less the same. The article would have even been more cohesive if Miles had just focused on CascataChuva.
ReplyDeleteMiles focused a lot on the setbacks and drawbacks of hygroelectricity. Manufacturing these devices is costly, and it may not be as environmentally friendly due to the raw materials and energy required. The choice of quotes was odd to me as well. Mentioning that the technology was made by accident, that it could only be feasible provided there is no contamination of the devices, and that the process is time consuming does not make me optimistic. If the goal of the article was to convince people that this new form of energy could be the new primary form of generating electricity it definitely didn't work on me. The Guardian made it seem like hydroelectricity was on the verge of being implemented because CascataChuva has a prototype. However, there is a long way to go in terms of hygroelectricity optimization and scale-up. The title is a little misleading in this sense, because researchers haven't completely turned humid air into renewable power. One device is only capable of producing 1.5 volts and 10 milliamps. If they can stack the devices they will hopefully produce more, but will it be the 10 kilowatt hours they predict? No one can know until they accomplish this. According to experts it will be no small feat.
I also feel that the Yao's work was mentioned to make the CascataChuva's work seem more impressive and competent. The microbial contamination does not make sense to me. The pores on these devices are 200 nm at maximum, just barely big enough to worry about contamination, while most devices will have pores significantly smaller. I agree that this technology is no where near ready enough to become a reliable renewable energy source, without an even more impressive breakthrough than the work of the Yao group. The main draw for why this could become a replacement for other renewable energy sources is that they can be stacked on top of each other, allowing for a large amount of energy generation in an area, but the amount is still very little and the cost to build them in a large scale would be immense.
DeleteI agree with what you and the previous comments have expressed about the Guardian article. It feels as though Miles has the endpoint and message of the piece in mind before he even engages with the research, with the CascataChuva work obviously being the centerpiece here. The near omission of discussion about costs in an article whose motive so clearly seems to be promotional fluff for a start-up definitely rings some alarms. The paper feels neither conclusive in its discovery nor intending to be so, as evidenced by their experimenting with several different materials, including the decidedly *not* organic Au nanowires. An ongoing trend with many of the news articles we've encountered thus far is a tendency towards linearization, where research is turned into simplified trajectories of discovery. Not only can this be misleading, offering a skewed picture of the process of research, but in cases like this it can feel downright insidious, as it simultaneously exaggerates and downplays the value of the study in service of leading one to a congealed answer to the problem posed at the beginning of the article. Good for narrative pace, perhaps, but not particularly respectful of the study!
ReplyDeleteI agree with what you are saying about linearity of news narratives versus the branching paths of research. Even when talking about humidity generation, the work by Liu et al is just another branch of this research field, not some sum total of all the work that has come before it. It is also not declaring itself as the be-all and end-all of this field of research, that more research needs to be done, that the current work is just a promising prospect. I also agree with you that it feels like the paper was written with an end goal in mind. CascataChuva almost certainly hired him to write a puff piece and he just filled in the blanks to create a good narrative. I just check out Miles' website and this is something he expressly advertises his writing services for.
DeleteGreat job on the blog post, Leo! I really enjoyed reading it, especially the way you summarized the workings behind electricity capture using humidity detectors.
ReplyDeleteStarting with the title, I found it quite “clickbaity” for referring to it as an accident. I do think so that the news article could work better on providing the basics behind how these devices actually work so that balanced view should be presented to the public that are non-scientific readers. I think a better job could be done in comparing it with other renewable energy sources in terms of the efficiency and how challenging it can be when it comes to scalability so that readers can understand the technical difficulties behind the process. I totally agree with your point of punching nanopores into material - news article should provide correct information to the public. I think Miles was not able to understand the science behind it and providing misleading information was the result of that.
On a positive note, I appreciated some of the quotes included in the article, such as “You have a positive pull and a negative pull, and when you connect them, the charge is going to flow.” That really caught my attention.
Overall, good job on the blog post. I would rate the news article 5/10.
Hey Anika, I agree that the title is quite clickbaity and that they did a good job quoting the authors. An interesting thing about that renewable energy comparison is that the original paper (in the SI) includes a table comparing many renewable energy sources in terms of their efficiency and challenges with scalability. It is not just the punching nanopores that is an issue, outside of the quotes, all but one piece of information, the one µW cm−2 of their devices, is incorrect. That is why I gave them suck a low score, not just because it was a puff piece, but because it couldn't explain any of the science and when it tried it did it wrong.
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