 So the next section is on energy conversion technologies. We are going to have two Stanford faculty members, Professor Xiang Hui Fan and Professor Alberto Sileo. Let me get the Xiang Hui onto the stage. Xiang Hui is a professor in electrical engineering at Stanford University. And you have seen over the year, Xiang Hui have this amazing idea using radiated cooling to do energy conversion for more than a decade long right now using the sky for cooling and using the heat exchange between different objects radiation. He has been very, very creative on that front. And this project, I believe, is also funded by our industry partners right here. With that, Xiang Hui, take it away. Okay, all right, so I'll be, let me just give a very brief discussion of some of the work that we're doing. My group actually is a group that is interested generally speaking in photons. And this is, or in electromagnetic field. And fundamentally, photons are described by Maxwell equations. And so all the ability that we have in controlling photon comes from understanding the basic properties of Maxwell equation. So in the case of energy, controlling electromagnetic wave or controlling photon is really very, very important. Certainly our primary source of energy come to us sunlight through photons. And also the way we access energy is largely dominated by use of electromagnetic field. One of the observation here in terms of the detailed form of the technology what you see here, the technology of harvesting sunlight is certainly very, very different from the technology that you use to plug into electric grid because the frequency of the electromagnetic field are drastically different. But the underlying physical idea behind all these technologies as I mentioned come from the same equation. And therefore advances in thinking about some of the basic electromagnetic properties can have very broad implication for wide range of energy technologies. So as you mentioned, in the past 10 years or so we really have been pushing for a variety of different application of advancing electromagnetics for energy applications. I'll be talking about radiator cooling but I'd like to also mention some of the other work that we're very interested in. Electromagnetic energy transfer for example as well as understanding some of the basic theoretical limit of energy conversion process. In fact my student Yubin Park who is sitting there would give a poster about some of our work in really try to push the photovoltaic energy conversion to its ultimate theoretical limit. So with that let me talk a bit about radiator cooling. So the basic argument is to try to harvest the coldness of the universe. And the thermodynamic argument is a relatively straightforward one. This is a sink, heat sink with a very low temperature and the Carnot efficiency limit tells you that it's great to have a heat sink with a temperature that's much lower than the temperature on earth. So the vast majority of the energy harvesting technology at the moment use the earth as a heat sink and being able to use a much colder heat sink can have very broad implication. The photon comes in because we can radiate out the atmosphere is transparent around 10 micron and that happened to be the peak of black body radiation of a 300 Kelvin black body and that happened to be every one of us. So the point here is that every day in fact whenever you see the sky you radiate a heat out and therefore that is a cooling mechanism. And now in spite of what I said about radiated heat out in order to do that as a cooling technology you need to do a little bit more. And the point is that typically if you're in an outdoor environment during the day the sun is gonna heat it up. And so in general in spite of the fact that you are a very good radiator cooler you don't feel any cooling. And so the idea that we proposed about 10 years ago was to develop a material system that strongly reflects sunlight but radiates very strongly in the 8 to 13 micron window. The first material that we did is a multi-layered dielectric thin film placed under silver and when we put it on the roof of our electrical engineering building we get a temperature that about five degree Celsius below ambient with 900 watt per meter square of sunlight directly hitting the sample. So since then there are probably hundreds of material systems that people have explored for radiator cooling purposes and these range from for example textiles that I'm gonna talk about to building materials such as concrete to wood to very wide range of materials. The reason that you can see this radiated cooling from these wide range of materials are basically for two reasons. One of them is that many material in fact most of the material that you encounter are strongly radiatively emitting around the 10 micron wavelength range. So therefore they naturally radiate a heat out. So the engineering that require you to do then is to engineer the solar reflection and there are a huge variety of ways you can do that to enhance the solar reflection. So here's an example, a collaboration with Professor Jia Zhu in Nanjing University where we take silk and then engineer it to make it a radiative cooler. So as I mentioned, like many materials silk are strongly thermally emissive but and also it shines if you look at it and therefore it is actually a pretty good solar reflector. It turned out that it's not reflective enough to you need to reflect sufficient amount of sunlight to get to cooling purposes. So what Professor Zhu did is to attach the silk textile within oxide nanoparticle to enhance the reflection in a UV wave length range. So in the test as you see here again on the roof of the Stanford building you see that with nano process silk you can get to a temperature that is below ambient air temperature again passively without electricity input. So as I mentioned really there are almost any material these days you can probably think about a way to engineer it into a radiative cooler. And so the question is how do you go about using it? Well one of the important application of this is for air conditioning of buildings. And in this case what we do is we couple radiative cooler with standard air conditioning system. We lower for example the water temperature below ambient and use that to drive a water-based cooling tower and this is slowly steadily getting deployed in California through a startup that I co-founded with two of my former postdocs. This is now led by Dr. Eli Ghosting and this is a picture of one of these Skyco systems set up in some of the supermarkets around here. Now the other technology that we are quite interested which is more fundamental is really in trying to harvest energy from the coldness of the universe. And the basic somodynamic argument is that any time you have something cold that's below ambient, any time you have a temperature difference that temperature difference can be harvested. And we have a natural temperature difference between the earth's temperature and the outer space. And that certainly somodynamically can be harvested. Moreover, this is essentially the outgoing thermal radiation from earth and the incoming solar radiation and the outgoing thermal radiation are roughly balanced in order for the earth to be a steady state. And so therefore the amount of energy that's available is in fact quite substantial. So as an initial step towards it, this was an experiment where we take a nighttime radiator cooler and then we put a thermal electric generator on the backside to harvest energy from the ambient to the cooler, the temperature difference. And this allows experimentally, in fact, to generate light from the darkness of the night sky. And as I mentioned, almost any material you can make into a radiator cooler. And so one of these material system that you can do is in fact a solar cell. The encapsulated solar cell has a silica layer on top, which is a very strong radiator cooler. So at night it will actually have temperature for below ambient. And based on this effect, we have recently done an experiment where again we put a thermal electric generator on the backside of the photovoltaic and to show that you could actually get electricity out at night from a solar panel using this kind of technique. The experimentally observed power density that we see here at night in this particular experiment is about 50 milli-watt per meter square, which is a very modest amount of electricity. It's enough to drive a light emitting diode, but it's not that much amount of power. But for these things it's important to understand what the fundamental thermodynamic limit would be. And so as it turned out, for every technology associated with harvesting sunlight, there's a symmetry that map into a technology that harvest the coldness of the universe. And therefore for every theoretical limit for solar energy conversion, you can compute a corresponding power density limit for harvesting the energy from the universe. And the theoretical number actually is quite substantial. These are electricity number. They range from on the order 50 watt per meter square all the way to about 150 watt per meter square depending on the detail scheme that you can see there. The point here is that our experimental number is about quite a few order of magnitude below this. And to me this is a very interesting opportunity, that point to substantial room for further fundamental research in this area. So with that, let me just put out my summary slide. Just want to give an example that advancing fundamental understanding of electromagnetics really has a lot of interesting and important implication in energy technology. And let me stop here. I think Xiang Hui, wait for a second, Xiang Hui. We'll have panel discussion. However, I figure after Alberto's talk, you might forget about your question already. So why don't I take maybe a question for now, Xiang Hui? Sorry about that. I see any questions from the audience? We can, Xiang Hui can answer right away. If you don't have question, we can also wait until the panel. How's that, Xiang Hui? Thank you. Let me invite Professor Alberto Sileo to the stage. He's a professor in materials science engineering. He's the chair of the department. He's literally my boss right here. Well, Alberto will tell you about what happened in the polymer world. Thank you, Alberto. Thank you. Thank you for the introduction and thanks for the invitation. So what we work in my group is materials and in particular a class of materials that are called conjugated polymers. So you know polymers from plastics, sort of the water container bottle. These are polymers that have more functionality than just the structural functionality that you know commodity polymers for. And I will show you how these have multiple uses in energy conversion technologies. So just very quickly, the reason why we like these materials is we think of them almost as Lego building blocks. And the polymers we work with, you can imagine them as having a backbone. So there's a main chain and then there's things sticking from them. And the exciting opportunity for us is that you can sort of mix and match the different functionalities to build almost anything you want. So for example, if you have the backbone, I have two backbones drawn there. One of them is designed to conduct electrons. The other one is designed to conduct holes. They have different energy levels. You can also see they have some carbonyls and nitrogen atoms. So you can also imagine having something that starts looking like a catalyst site, for example. And like I said, you can mix and match them. You can take a certain number of one type and a certain number of the other one and put them all together, essentially making a synthetic designer material that doesn't exist in nature, that chemists are really good at making, essentially anything you want there. And then at the same time, if you want to process these materials, you have to be able to solubilize them in a solvent. And that's where you use the side chains. So those are things that will stick to the side that will grab to solvent. That's sort of the zeroth order functionality. You can add more functionality to the side chains. For example, you can make a side chain hydrophilic so that if you have a liquid electrolyte, the liquid electrolyte will like to get in there. Or you can make them hydrophobic if you want to actually absorb oil, for example. And again, you can mix and match any of these together. So you can have a mix of any percentage of hydrophilic and hydrophobic, essentially designing anything you want with this material and tuning the properties very, very accurately. So here are some examples of energy conversion technologies that we've been working on with polymers. So we've been working on, Shenhui talked a little bit about this, converting photons to electrons. So this would be a solar cell. And solar cells made with polymers have some advantages that are unique compared to conventional solar cells. Lately, we've been interested in sort of a different space, a space, for example, where we convert chemical energy to electrical energy or store chemical energy as electrical energy. This is what you would call a battery. And then the opposite of that would be using electricity to make chemicals. And this is what the function of an electro catalyst would be. So as you can see, a very different variety of functions essentially performed with this one family of very versatile materials. So starting with solar cells. So to make a solar cell with polymers, you actually need two different types of polymers, one that conducts electrons, the other one that conducts holes, so that when a photon strikes a solar cell, the electrons will go one way, the photons will go the other way, and this generates electricity and a potential difference. And the product of current times potential difference is energy. So here's an example of a pair of materials that's been looked at recently in our group. We looked at two. Actually, this pair of materials can reach power conversion efficiencies all the way up to 18%. So now we're talking about numbers that start becoming interesting. The current record for organics is around 20%, and it keeps creeping up. And the reason why these materials are interesting here is that you can design them to essentially match the absorption of the solar spectrum. Remember, you can design them any way you want, so you can figure out their energetics so that they exactly match where the solar spectrum is at its highest intensity, and also make the energetic level so that the electron and the holes are comfortable and can be extracted with high efficiency from the cell. So that's where the backbone design comes into play. The side chains is where the polymers look at each other, and so that controls how soluble they are into each other. And the reason why you want to control that is because you remember, you have one material that conducts electrons, you want it to conducts holes, so you want them to be face separated but at a right length scale so that the charges can get out efficiently. So you see how the advantage of the design of being able to design the backbone and the side chain separately and being able to do it with high accuracy and precision really comes into play in this type of application. And what's unique about organic solar cells or solar cells made with these materials are made with earth abundant elements. The embodied energy is quite low. They can be processed from solvents at low temperature and they can be made different colors because you can design the backbone to have different colors so you can make building integrated photovoltaics. You can even make solar cells that are transparent which seems to be a misnomer if it's transparent. How can it absorb? Well, it absorbs the infrared and the UV and it's transparent in the visible window and there's a company, local company called Ubiquitous Energy that's commercializing these transparent solar cells. You can also optimize the solar cells so that it works in tandem with a greenhouse so that the colors that are best absorbed by plants go through and the colors that plants don't really need get absorbed by the solar cell and essentially make a greenhouse that produces its own energy to run. And there are several companies are exploring this type of application. So as you can see it's sort of a different space in conventional solar cells with some interesting applications nonetheless. Now the applications we've been thinking about more recently involve electrochemistry so there you have to be a little bit more clever with the side chains. So remember the backbone conducts electrons and now if you want to do electrochemistry you need to be able to bring ions into play and that's what you do with the side chains. So you make the side chains such that they like water, they're hydrophilic and if the water contains an electrolyte, salty water, then you can have for example chloride ions or if you have a different type of polymer you can have sodium ions go in. And so now you have the opportunity of combining electricity and chemistry into electrochemistry with these materials. So if you have a material that likes holes and a material that likes electrons their Fermi level or the energy of the electrons and the holes are different in these two materials. And so in this case you have one of the materials what we call the p-type material will have holes in it. The n-type materials would have electrons in it and if you have a potential difference between the two and you connect the potential, the two electrodes to a load you can produce electricity. So you have essentially made depending on who you talk to either a battery or a super capacitor. And this is made with materials that can be completely recycled because it's just a single polymer. If you try to do that conventionally you'll have to have one material that does the ion conduction, one material that does the electron conduction and if you want to recycle you'll have to separate them and that becomes a little bit more complicated. So we've played around a little bit with this type of system and we've shown that in fact you can make an electrode, you can dissolve it in a solvent and then refabricate the new electrode the exact solution that you made the first electrode with. So this is really an example of very nicely taken advantage of properties of polymers that can be easily dissolved and redeposited. And if you look at where this device sits in a ragoni plot it's actually an interesting space between electrochemical capacitors and your lead acid batteries. So the interesting space here is that you can charge and discharge very quickly these type of supercapacitors of batteries depending on how you want to call them. Their power, sorry their energy density is maybe not as high but that's something that can be maybe further optimized through materials design. And like I said, the opposite process of that is taking electricity to chemicals. So the idea there is always the same. So you take a polymer, you deposit it on an electrode. In this case the polymer is designed to have maybe some catalytic sites and then you design it so that if you want to do electro catalysis it conducts electrons. It also have to have the reagents come near it so it has to be sort of the reagents have to be able to dissolve in it and the products have to be able to leave as well. But remember you can design backbone and side chain separately and so you can start entering a design where all these things can happen in one place. The three species that have to be there the electron, the reagent and the product can all be there at the same time and this is an ideal condition to make a beneficent catalyst. Again the advantage compared to how you would do electro catalysis conventionally is there you have to bring these three things together with different materials so if you want to recycle it you'll have to separate them. Well here everything is done very simply in a single material that performs these three functions because we built it with these Lego building blocks that allowed us to you have these three functions in one place. So the example that we worked with we'll choose group is to reduce oxygen to hydrogen peroxide. Hydrogen peroxide is an interesting chemical for several reasons. It's used in multiple industries. It's actually dangerous to transport so maybe you want to produce it locally so being able to produce it locally by electro catalysis is quite an attractive proposition. And you see there with our polymer we're able to, you have the current density there this essentially is a proxy for the production of the hydrogen peroxide and it doesn't have any noble metals. I'm showing there the platinum catalyst because a platinum catalyst or it looks like it performs a lot better, it does but it's performing a different reaction. That one is reducing oxygen to water. So our catalyst actually stops at hydrogen peroxide so it's also chemically selective. It produces the chemical that we wanted to produce. And now remember you can design polymer to different things and so it turns out there is another polymer that can go all the way to water as well. So this polymer is called BBL and you can see that within a certain potential window the current is half, you see it between 0.25 and 0.75 is half than what it is between negative 0.25 and 0.25 and that's half because there it's doing a two electron reaction so that's a hydrogen peroxide at higher potentials is doing a four electron reaction so it's going all the way to water. So this is a nice way to show how the materials design can really give you selectivity and allow you to reach different products depending on how you operate the material which is quite unique. And this is really a brand new area of application for these materials. So in summary, the reason why we like to work in the space is that we like the idea that these materials can be designed and synthesized for different type of energy conversion applications all done with earth abundant elements. Maybe later we can talk about the type of synthesis reactions. We heard later you have to really think sort of holistically about these materials not just about the material itself but also how you make it. There's a very vast design space that's barely explored of how to combine all these different functionalities and also how the material structure plays into its properties. There's so many aspects of different length scales that give very rich fundamental research exploration there. There's a great opportunity to be able to recycle these materials very simply. You just re-dissolve them and then you re-deposit them when they reach your end of life because maybe they've degraded. You re-dissolve them. The part that hasn't degraded, you can reuse it. The part that has degraded, I guess, becomes a waste. And then lastly, because they can be deposited from liquids, you have some unique form factors and applications which is what I showed in the case of the solar cells but that's true for all of other applications. These materials are also used for LEDs for solid state illumination, for example. So with this, I'll be happy to take any question. Thank you for your attention. Thank you, Alberto. Any questions for Alberto? There's one over there, and another one here. Thank you, Professor. Very interesting presentation. I was intrigued by your work on oxygen reduction to form hydrogen peroxide. I believe it's one of the most important things one can do to valorize the oxygen from green hydrogen production. So could you give more detail at what TRL level your current process is? Sorry, what? The oxygen to hydrogen peroxide technology readiness level, is it at a research scale or you have a prototype built to convert oxygen to hydrogen peroxide? It's still at a research scale. We were funded to really understand whether there is a truly electro-catalytic reaction happening there or not. And the conclusion is that for that particular polymer, there isn't, but the other one that I showed actually does. And so now we're at the stage of trying to understand what feature of the molecular structure gives rise to proper electro-catalytic action of the material. Thank you very much. So in regards to the customizability of these polymers that you mentioned, does that usually come with a penalty in scaling or is it relatively easy to scale these very customized processes? Well, so the current chemistry that is used to synthesize them is not scalable, it's sort of a research type chemistry. So it uses pretty nasty chemicals and some reaction conditions that you wouldn't want to scale. But there are well-known alternative syntheses that are scalable. So right now I have a postdoc who's looking into picking one material sort of as an example. Can we design the scalable type synthesis that is also greener that would allow us to make this at scale? So I think the short answer is the way we make them currently for research purposes as we try to hone into the ideal structure, not scalable. But this is a type of thing that a chemical industry is very good at doing, the scaling up with scalable reactions. It's fine in the back. After that one, I'd like to invite also Shanghui to the stage for a short panel discussion. Thank you, Professor Salil for your talk. So I have a question about the recycling of polymers. So the recycling of polymers, do you mean recycling the entire long chain polymer molecule or actually break them down into monomers? No, it's really, so what happens is, let's say the super capacitor, you cycle it for a number of times and after a while its performance drops a little bit because it degrades and that's a separate question, why it degrades and that's interesting per se. There's probably some molecules that react with side reactions in the grade. So then you take that electrode and you dissolve it as is. So the part of the polymer that's non degraded, you can reuse and the part that's degraded you would filter out. So it's not breaking it up and it's not upcycling is really, I would say maybe recycling is not the right word, reusing is maybe a better word. Okay, let me invite also Shanghui to the stage. Alberto, do you want to sit over here and Shanghui over there? Let's have a short panel discussion. I want to ask a few questions. What do I say? Okay, yeah. And I also want to invite audience to ask more questions. Let me start with a couple of questions first. Both of you really presenting several applications. Alberto, for example, you mentioned it could be polymer for solar cells, batteries, electro catalysis. Shanghui, you have radiated cooling. You have also generate electricity as well. For each one of you, what's the most promising application in your build? What's the robot block still ahead of you? Shanghui, do you want to take it first? Okay, yeah, so in the case of radiated cooling, I think it's a general technology that allow you to manage the thermal footprint of object. So you could envision this certainly being quite important in building and that's one of the things we pursue. It may be automobile and in many other situations where cooling is needed. In terms of roadblocks, I think in the case of building cooling, it is a substantial change from the existing technology in doing building cooling and that kind of adoption actually does take substantial amount of time. I will also mention that on the technological side, the availability of these material and systems is not necessarily an issue and the ability to produce them a sufficient skill, but rather is to come up with the right system application and demonstration. For example, in the case of cooling, I think one of the important thing is that the tuneability of the system is going to be very important to be able to adapt to different weather conditions and things like that. How is the cause at this moment? Is cause a big consideration? For example, the rooftop cooling also and retrofit, will people willing to do retrofit, return on investment and so on. Right, so we did quite a bit of analysis in the very beginning and that was part of the reason the company got founded was the fact that in fact, the material cost in the overall cooling system is almost negligible. This is probably in a way not too different. In fact, the value proposition in many way parallel the solar kind of argument that the installation cost, the maintenance cost and the system level cost dominate over the material side of the cost. Yeah, so Alberto, what about for you? Yeah, of the different applications I showed some of are a little bit more mature, some less, so solar cells are more mature, but maybe they're a little bit more of a niche. The one that I think has a lot of potential is the electro catalysis because of the generality of what you can do there. I showed one reaction, but in principle, if once you understand what molecular feature generates a catalytic site, you could generalize that to the synthesis of many different chemicals, but also different types of applications. You could imagine that being part of a fuel cell, for example, is an electrical fuel cell and that helps you reduce the cost by removing the need for noble metals. So I think it has a lot of potential partially because it's completely unexplored. There's very few people looking at that space and for me as a scientist, it's exciting because there's a lot of great scientific questions that haven't been even addressed yet. Yeah, I remember reading your idea first time about using the polymer backbone and so on sidechain for electro catalysis. I thought that's quite creative and now I'm so glad to see you now reduce oxygen to produce hydro peroxide, so looking pretty interesting. Let me ask you a second question that was open to the audience. And Arlund's presentation, he emphasized, how do we go to scale? For energy, we do need scale. We talk about gigaton level, CO2 removal, he talked about 100 kilowatt hour of storage and each application is probably a scaling unit right there. If probably you need it in your mind. Shanghui, I look at your radiated cooling, I was thinking about what's the square footage of the rooftop we can have, how many, what's the gigawatt or terrowatt of radiation can go out of sky to do cooling. So in terms of scaling, do you want to share your thought whether it's Shanghui in your case is radiated power, could you go to the scale or the energy conversion utilizing the universe, the coldness of universe for that. And Alberto for you is this polymer material for the three application you talk about. Is there any thought on scaling you could share? Okay, Shanghui maybe you can go first. Yeah, so in fact, Arlund talked about radiated forcing of carbon dioxide and methane and the unit that he's coating I think is order of watt per meter square scale of radiated forcing meaning the radiative imbalance created by these material. The cooling power of these radiated cooling material can get to about 100 watt per meter square. So it's actually a very substantial radiated forcing. So in other word, if you adopt this at the substantial skill, you will influence the radiated balance both at the local level and at a global level. One of the very interesting thing that we are starting to look at at the modeling skill is for example, to what extent can these things be potentially interesting in mitigating urban heat island if you adopt it at a substantial skill. And I think this is an area that, so in that spirit, radiated cooling is if you do it at that skill is like a geoengineering skill but the interesting part of it is that it's a technology that would be used for other reasons not for geoengineering but has geoengineering implication. And I think that kind of implication is actually very interesting to be studied. Yeah, Alberto. So when we think of scaling, we mostly think of how to scale. Well, not how to, but whether these specialty polymers could be scaled up to the level to the volumes that you would need to make a dent. As I said earlier, right now we make them in the lab with chemistry that if I ask my postdoc to make more than a gram, he would just straight out refuse as just too dangerous and toxic. But that's one type of chemistry and there's well-known chemistry that allow the scale up and we're looking a little bit into that. So the fact that we use earth abundant elements, some of these polymers come probably as byproduct from the oil industry, so there's gonna be plenty of them available and people can develop chemistry that are green and scalable. Not being an expert in that area, but I haven't seen sort of people saying this is a fundamental roadblock. Really the roadblock is to zero in the one polymer that you really want to make at scale and refine the chemistry for that one. And right now that's maybe what's stopping us more is if you were to say what polymer you wanna make in thousands of tons, which one would you pick, we don't know. Once we figured out which one that is, I think there is no fundamental roadblock to scaling it up. Yeah, I guess for plastics for polymer, the scaling question is quite different. Over the years at Preco Institute right here, we have industry partners. I think I've been listening to our partners about scaling. Now it's the new schools are salaried, so scaling is embedded in our mind. Even though Stanford will continue to do excellent research from discovery type of research, this will keep going. And by the same time, I think yesterday for some one of the works I mentioned this style of research is we think about all the way to the end first and back it up and see what technology needed, what science we need to develop. That's another way to do research. Stanford is probably one of the ideal places to get both type of style mingled in to have the best outcome, the best impact. With that comment, let me open this up to the audience for you to ask our panelists questions. I'm Don Wood and I've got a question for a professor fan. You talk about SkyCool, the company that you've created. I was a little confused because you talked about integrating it with photovoltaics, the radiative cooling for the atmosphere. I was wondering also is there cooling for the building? In other words, who's gonna benefit from that product? Who would pay for it and then where do the collection of benefits go? So the SkyCool is a company that's for building cooling. So it's not for photovoltaic, not for energy harvesting, none of those. It's focused on building cooling. There the value proposition is that by lowering the temperature of cooling water that used to drive a water-based cooling tower, you can improve the overall system efficiency and get to electricity saving. So then you can do the calculation on how much saving burns and how much cost and that's the value proposition. To me, I think that is probably one of the area where it's likely to see initial adoption of the radiative cooling technology. There are many other use of it, for example, the energy harvesting that I talked about and I think those are at the much earlier stage compared with building air conditioning. Other questions? A question for Professor Saleh. So you were talking about this polymer supercapacitors or batteries and you showed this plot that they have much lower power density or energy density than lithium ion. So you suggested in your talk that maybe material design would help push this to the higher side. Can you talk more about what type of material design do you envision, whether this is on the cathode, the anode side, the electron light? Do we change these polymers and how does that change the physics and the benefits from this technology? Thank you. Yeah, great question. So from our perspective, you start by changing the design of the polymer, that's sort of what we like about these materials. So what is limiting the energy density here is, for example, a number of charges per unit monomer and that's a stability question. So you can design a monomer to accept two or four charges by looking at the design of the conjugated units you have in there. The other big limitation is I showed you of the side chains that are needed to process these materials. Well, these end up being dead weight once you make your electrode because they don't have any electronic functionality. So you can either think of polymers or what people call microporous. So without those side chains, you can deposit them and the electrolyte can penetrate them. That's the case of that BBL type polymer. It doesn't have any side chains. Another thing you can think about that I think is more clever is you design the polymer with the side chains and then with a simple reaction, the side chains get cleaved off and leave and so you'll have for something that will have a higher energy density. So this is something that people have started looking at. There's other families of materials are not quite conjugated polymers but are similar that are just coming out. There are conjugated networks. There's a group at MIT that's looking at that. So I think there's quite a bit of latitude there to increase the energy density while keeping the important aspect there is you can keep the peak power high because of this rapid insertion and an ejection of ions. So you might be able to sort of move to the right in that ragoni plot and be where, for example, that acid is but we did the advantage of having high power delivery. Alberto, I guess the analog of a different version is actually small molecules, organic molecule, redox. There are quite a large number of libraries. You could probably tap in, like, link together with the side chain real polymer that give you the high potential for cathode, low potential for anode. There's probably very wide space for you to explore. Absolutely, yeah. Question here. I'm curious why you chose hydrogen peroxide as an example to show here and to research. Is there a particular reason why polymers may be better suited for that? Well, the honest reason is that these polymers degrade in oxygen so we figured that they were reactive in oxygen and so this was a good way to look at sort of turning lemons into lemonade. This is not to say that they, our electro catalyst actually does degrade but I would say they reacted with oxygen. I shouldn't say degrade. It was well known that every time you use these polymers in electrochemical applications you'd always see these side reactions with oxygen and so that's sort of where this idea came about. Hi, thank you both for your really inspiring presentations. For Professor Phan, I was really struck by the kind of poetry of using the universe as a heat sink. How do you reach it if it's foggy or I don't really understand how you do that when we have an atmosphere in between us, the universe. Right, so like almost any ambient energy harvesting skin of one kind or the other it depends on the condition of the ambient. So in this case it depends in addition, certainly at a cloudy day the effect largely disappear. In addition the water content of the atmosphere is very important. So typically this favors dry and clear sky. So that I think is unambiguous. Now for humid air there has been quite a bit of work coming out of Asia showing that in summertime even in, there are a lot of work in China showing that as summertime in China you can still see substantial cooling effect. So it's degraded from what we see here in California but you can see it. And in fact there has been a work and I can dig up with you where show you a map of where the cooling power density that you can get as a function of locations and these kind of data actually is available. They are a large enough area in the world near population center to make the radiated cooling to make sense. Steve. Yeah I have a question for both of you. And for both of you you're using highly designed systems in a controlled environment and I'm curious how they behave when they're out in the real world. So whether it's exposed to pollen and dust and rain and so forth for the radiative cooling or for the electro catalysis whether you're easy impurities and other low concentration things and builds up the side products how do they behave out in the wild? Can I take it first? So for radiated cooling panel on the commercial side in fact one of the question and which is related to the adoption is the fact that how long these panel are going to last. So the typical data that many of the we are trying to insert into air conditioning systems and so therefore there are channels and the data that they would like to see is essentially the performance of radiated cooling panel over a period of maybe half a year to a year. And that's the kind of data that's being generated. I will mention that these are largely passive structures. So the degradation can actually be I would say the degradation issue is in fact less severe compared with for example solar cells. The dust also doesn't affect it very strongly because in our case we're trying to scatter away the sunlight and the summer radiation part is not very strongly influenced by the dust. But in spite of what I said which I think fundamentally I think is correct obviously one would need to test this out of a very extensive period for these kind of things. Sean, let me follow up on this and then we'll go to Alberto. Actually one thing have you looked at is actually UV Yes. coupling with the weather condition. Oftentimes outdoor is UV is so serious. So the in the sky course panel is a polymer based panel. There has been in that case we did work with 3M to have the right kind of coating so that the UV won't degrade it. So it is an issue in that way. But they are also inorganic based irradiated cooling set up. For example based on silica and so on where the UV is far less of a issue. Alberto? For us the electrochemical polymers there's too new to really know how they would behave in real environment. Application when there's quite a bit of data is solar cells. People always thought organic solar cells would degrade quickly. It turns out that if they're well encapsulated they last for however long you need them to last with maintaining their efficiency. So then it becomes more an issue of cost. Is the encapsulation cost effective? But there is no fundamental degradation issue that is different from that of all the other solar cells. Thank you for a very interesting presentation. Dr. Fan this is a question for you around the, I love the poetry that somebody said of getting light from the darkness. So that technology seems to me super interesting because it can be employed at scale especially if you can somehow combine it with existing solar panels. It's obviously huge. What are the biggest problems of actually implementing that at scale to a ruins point earlier on? Like what is the, is it technical? Is it money? What is it? So at the moment the demonstrated power density is relatively low. As I mentioned we get to somewhere on the other 50 watt per milli square, milli watt per meter square. We think that with reasonable improvement both on the panel and on the thermal setup one can push it probably towards about a watt per meter square scale. And that's something that we're actually pushing hard on in my lab. As I mentioned there's still a very substantial gap beyond that number to the theoretical limit and that require completely different technology. At the moment we're using some electric for example which the theoretical efficiency is quite low. So at the level of about a watt per meter square this is in fact a power density that's very high for ambient power energy harvesting. If you take out sunlight there's no way that you can compare this to solar. But there are many situations where you care about getting energy from ambient. For example in powering remote sensing, remote sensors in off grid lighting and in off grid cell phone charging and many of these small scale application where I think this kind of technology pushing towards maybe on the order of a watt per meter square kind of power density would make it actually quite attractive. Alberto and Xiang Hui, let me ask you maybe about two questions and then end this panel discussion. The first question is related to the how do we work together with our industry partners. Over the years, if you look at your trajectory you are doing very fundamental science research and Xiang Hui you are certainly you move from a theories become a theory experimental combination. I was very impressed that that migration was so successful and over the years you also work with industry and during the time of global climate energy project GSAP involved in SEA, now the whole political institute. Anything in your wish list you want to speak to our industry partners right here how to be even more effective to engage with industry and the other thoughts other than more money investing and more thoughts. I'll start. I first of all I'm certainly extremely grateful for GSAP and also for the SEA program for supporting my project. I didn't do any energy work before I came to Stanford and GSAP gave me my first grant to work on energy. So and I in many way I think that the fact that the industry can support a long term energy research that address fundamental issues in the technology is extremely valuable and more than the fact of about more money which of course helps is the fact that many of these money go to foundational work that later on can point to new opportunities and that I think it's a very important way that we can engage with industry by looking at longer term issues. But actually similarly to Shanhui I'm very grateful for the support and also I started doing energy research here thanks to GSAP one of my first grants was also a GSAP grant. Also want to add that we're an experimentalist group but I hired a theorist in the group so I'm doing the opposite path as Shanhui and our project on electro catalysis is supported by SEA so it's supported by industry. I would say that for me what the interactions that have been most fruitful is when someone wants to talk to me and sort of explain what the expertise of our group is is then really figuring out what I don't want to say problem but what idea that industry has that our expertise can be useful for has been the best type of interaction. We've developed a very fundamental set of tools to characterize materials and figure out what they do and how they work and it's quite general. So right now we're working on electro catalysis but as you've seen we have quite a broad portfolio of applications cause general material science really can be applied in different areas and so figuring out how to slot into a question that an industrial partner has thanks to our expertise has been a very fruitful way of interacting for me. Yeah, this question is actually for our industry partners right here. We is now a new school starting sustainability accelerator together with Preco Institute and now SEA, our industrial affiliate we are also launching try to launch a net zero alliance. You know it's also a process we want to have a dialogue with our industries how do we work together, deepen the relationship even more and harvest opportunity to help the clean energy transition in a very secure way. My one last question. Any completely new ideas from your lab on energy conversion? Today two of you adding together really cover a big map or energy conversion mechanisms. Any completely new one you are thinking about maybe already working on or is within your wish list you say well it's very exciting to go towards that direction. No pressure, I didn't plan this question so you don't know about this. This is testing your immediate response. Well, let's see. I would say there are always things I dream about. One of the things that I dream about is active cooling rather than passive cooling with light. And that's an area that in fact has quite a bit of theory and very few experiment. But if you look at the potential. You mean you shunt the light onto it instead of heating it up you actually make it cooler? For example, and that's one possibility of course there are laser cooling for it and there I can tell you all the limitations associated with it. The other thing that's related is something called electro luminescent cooling which is to emitting light to cool down the body actively. And those kind of thing I think are very interesting from a technological point of view both in terms of its potential and in terms of the challenge. So I think there's a lot of things that can be done in thinking about the thermodynamic properties of light and a lot of opportunities that one can think about. Very exciting. For us the some of the ideas I showed are so new to our group that what's exciting is really to explore them more deeply. I showed some really initial results and I'm really looking forward to explore both the storage and catalysis more deeply with new materials. So no completely new idea. We generated these recently enough that we wanna stick with them for a while. So with this I encourage all our industry members to talk to Xiang Hui in our portal to find out more. Thank you very much. Thank you for the invitation.