Green Machines: The natural and artificial photosynthesis powering the planet

What is photosynthesis? Oh, no big deal, just the key to life on Earth as we know it! Join me as I take a deep dive into this amazingly sophisticated chemical process. Hear fascinating details they didn't teach you in school and get a crash course on how natural photosynthesis inspires the development of renewable energy technologies that could someday replace all petroleum products.

Featuring Jan F. Kern, from Berkeley Lab's Biosciences Area; and Joel Ager, from the Energy Sciences Area and an adjunct professor at UC Berkeley.

Produced and hosted by Aliyah Kovner

Chapters

• 0:00 Introduction
• 6:11 Who are the guests?
• 13:28 More photons please!
• 22:38 The not-so-simple splitting of water
• 30:53 Regeneration and repair
• 37:17 Sucking up CO2
• 40:20 Economics of artificial photosynthesis
• 45:13 The Dark Side, aka the Calvin Cycle
• 52:05 The history of photosynthesis collaboration

Transcript

Aliyah (00:02):

Hello, you're listening to a Day in the, Half-Life a podcast all about how science evolves and shapes our lives. And this episode is definitely on a subject that shapes our lives. In fact, it's a chemical process responsible for life as we know it. Yep. Today I'm talking to two scientists about photosynthesis. Now you might think of photosynthesis as just that thing you had to memorize a little bit about in biology class, but it really is one of the most important chemical reactions on earth. And one of the greatest success stories of evolution. Once you take time to stop, zoom in to the atomic level, and appreciate what's going on during the reaction, you'll never look at green growing things the same. You might even devote your life to studying it, like my two guests. One is a bioscientist who studies the proteins involved in photosynthesis. And the other is a material scientist who uses photosynthesis as a reference for designing renewable energy technologies that harvest energy from the sun and create fuel out of carbon dioxide -- a field aptly called artificial photosynthesis. Let's start at the beginning with some quick definitions.

Jan (01:20):

So, photosynthesis is one of the really fundamental processes that enable life on earth. So it developed like 3 billion years ago, give or take a couple hundred millions.

Aliyah (01:33):

That's Jan Kern, a scientist in Berkeley Lab's Biosciences Area, in the bioenergetics department.

Jan (01:41):

And it's really the process that allows life to harvest the energy of the sun that hits earth and convert it into chemical energy. And that way really allowing life to thrive through all parts of earth, all different environments. And so photosynthesis is really using photons from the sun, capturing them, and then converting that energy from these photons; first into, um, separated charges, so like a battery, and then convert this difference in charges into high energy containing chemical compounds.

Joel (02:15):

Artificial photosynthesis is basically exactly what the name implies

Aliyah (02:21):

And that's Joel Ager, a senior scientist in the material science division and an adjunct professor at UC Berkeley.

Joel (02:27):

We are trying to make systems that do exactly what Jan's talking about: harvest, photons from the sun, uh, use their energy to take carbon dioxide and generate not just sugars, but in principle, any chemical that we want. Ambitiously, we'd like to use artificial photosynthetic systems to replace all of chemical manufacturing, which, uh, now relies on sources of carbon that we, uh, dig up from the earth, natural gas and oil and coal being examples of that.

Aliyah (03:03):

Hi Joel, and Yan thank you both for being here. So the first thing I wanna know from both of you is why photosynthesis? Of all the awesome things in science, how did you end up doing what you do now?

Joel (03:15):

Ah,

Jan (03:16):

Okay. Yeah. So I have to admit during normal school, I wasn't that much aware of photosynthesis. So it wasn't like, not like that as a kid, I was curious about green leafs or things like that. But during studying chemistry, so a little bit later in my education, I was lucky to be in an institute in our university, where there were a lot of people interested in photosynthesis and I listened to their physical chemistry lectures. And then suddenly I realized, oh, they, they look at these really cool systems, which can do a lot of stuff, which is very difficult to do synthetically. And then it got really fascinating to me to, to see how in nature, this is done very efficient and very elegantly, and it's still not really understood. And when I started my work in this area, there were even more question marks or different question marks than now, but it was a really fascinating problem for me. And that basically pulled me in, into this field and kept me there since the last 20 years. Roughly.

Aliyah (04:17):

Cool. Yeah. It's, it's really fascinating that biology has like, has built something that's so sophisticated that we're still sort of untangling how it does what it does. And I love that aspect of it. Joel, what about for you?

Joel (04:29):

Yeah. Um, let me clarify that I have no formal training <laugh> in the field of photosynthesis or artificial photosynthesis. Uh, okay. At the, at the relevant time, maybe about a dozen years ago, uh, I was studying semiconductors, which are the heart of solar cells. They do some of the things that we've talked about, uh, that are crucial for artificial photosynthesis. They absorb light, they, uh, separate charges, uh, and what they do with those charges is send them to an external electrical circuit, uh, so that you can have electrical power coming out of the, out of the solar cell. And then you might wonder, well, you know, you have electrical power, you can charge your electrical vehicle and so forth, uh, but you can't store electricity easily. And so you might wonder what the next step beyond that is. As we move to hopefully an economy that's more sustainable.

Joel (05:28):

And it's that point that you realize how beautiful photosynthesis is, or at least I did, because it does some of those same things, but then it actually uses the separated charges to drive specific types of chemistry. And, uh, it also uses, uh, those charges to make biomolecules and is really the heart of life itself. And I realized that no physical laws prevent one from doing that same sort of chemistry with the artificial constructs that I was working on in my photovoltaic work now exactly how to do it, raises some questions. And I've looked for clues in how the natural system works in order to come up with inspirations in that area so that we can have a more sustainable planet.

Aliyah (06:11):

Great. So I'd like to just get a brief overview from both of you about, um, your specific work in this field, just so people have an idea of what your, your day-to-day is and what your focus is in this big picture. So, Jan, would you like to go first and just tell us a little bit about what you study right now?

Jan (06:28):

Yeah. So one of the fascinating parts is how to actually generate oxygen from water. All oxygen we have around us is generated by oxygenic photosynthesis over the last 3 billion years. And so I have been focusing really on, on this question a lot, and there's one specific enzyme in this complex process, which is called photosystem two. And this enzyme, which is found in all plants and algae, and lot of photosynthetic bacteria, this enzyme takes light and takes two molecules of water. And then basically bridges the two oxygens from these two molecules of water together to make one oxygen molecule out of it. And this process is chemically very demanding. So you have a high barrier to bridge these two, um, oxygens together.

Aliyah (07:17):

Cause it doesn't want, it doesn't want to be broken apart, right?

Jan (07:20):

Yeah. The water is perfectly stable. If you have it around you, um, nothing happens with water. Um, so you need to really push it to, to, um, combine two molecules of water together. And you need to have a very strong reactant to actually push this reaction forward. So the center, the heart of this photosystem is a metal cluster where you have four manganese metal ions and one calcium ion. And this combination of metals somehow has the unique property to be able to oxidize water. So this is really very demanding process. So you need to have a very strong oxidant, a very strong oxidative power to, to force water, to get oxidized and the details of how this special arrangement of these metals inside a protein allow this reaction is at the heart of what we try to do. And our daily work, we actually use bacteria, which do photosynthesis.

Jan (08:18):

We grow them in our lab. So one part of the work here is to grow these photosynthetic bacteria. And then we take these bacteria and extract the protein we are interested in from them. So we take solution of the protein and then we crystallize it to have many copies of it, arrange next to each other in a very precise arrangement. And so another step in our work is then to take these crystals of the protein we make and shoot very powerful x-ray beams at these crystals. And look at the pattern that we get when these beams hit the crystals. And from these patterns, we can then deduce atomic detail of the structure of this protein and especially of the metals inside this protein that, um, do this reaction.

Aliyah (09:07):

Cool. So you're, you're zooming in on like the exact moment that the water is split.

Jan (09:12):

Yeah.

Aliyah (09:13):

Great. And Joel, tell us a little bit about your work as well.

Joel (09:16):

Yeah, it it's so interesting. Although we have the same goal, same overarching goal, the set of materials, and some of the approaches are very different in my laboratory. We have living things: the people doing the experiment <laugh> yeah, but everything else is not living. For the starting point for absorbing light, we use, uh, semiconductors, sometimes they're wafers of silicon, uh, shiny little things, other times they're materials that we make ourselves. And a lot of what we do involves testing, whether they are working or not, and how they're working by making cells that are about the size of a small post-it note and shining light on them and seeing if we're actually doing the reaction we want. Now we work both on the reaction that makes oxygen from water. Uh, we call that the oxygen evolution reaction, and we also work on the, for us more challenging reaction of taking carbon dioxide. And electrochemically reducing it to specific products. Where we have, uh, some synergy with Jan is that, that active site when we're doing, uh, what we call water oxidation, we're also using metals, uh, specifically usually metal oxides. Our favorite metals, depending on the pH are, nickel, iron, and in some specific areas, we go a little more expensive <laugh> and use platinum.

Aliyah (10:39):

Nice!

Aliyah (10:40):

And then sometimes even iridium to do, to do the reaction. So that's the, uh, part of the process that takes water and makes oxygen. But we also want to make reduced products of carbon dioxide. And that's where we have a very significant challenge. Uh, the catalysts that we have that do that, these are again, inorganic, uh, materials, often metals, they can make simple products like carbon monoxide, uh, formic acid, but we have difficulties in doing something that nature does so well, which is to make specific more complicated molecules like glucose, for example, we don't have a pathway for doing that.

Joel (11:22):

And so we spend a lot of time trying to control precisely how the electron transfers work from our semiconductor to the catalyst and to the reactive species that are near our active site, so that we can try to get to a specific product. And we use all sorts of experimental techniques to try to interrogate exactly what's going on in that, in that environment. Uh, so those are some of the flavor of what the, the lab looks like. We have little vials of water and bubbling carbon dioxide on the, on the, on the small scale.

Aliyah (11:58):

And how far developed would you say the technology is because, um, I myself and I'm sure others read a lot of really cool stories about, uh, new systems for artificial photosynthesis. Um, would you say that there are sort of like lab-scale prototypes, right now, and it's a scale up thing, or what are kinda the big roadblocks to getting this technology out there?

Joel (12:16):

Yeah. Okay. So I, I can, I can answer specifically, uh, for making carbon monoxide from CO2, it's actually quite a mature technology. You can lease something that will look like a, uh, shipping container that will, if you feed it, CO2 will produce carbon monoxide, and carbon monoxide can actually be used in certain processes to make, uh, diesel fuel.

Aliyah (12:41):

Oh, wow.

Joel (12:42):

So it's a start. Now making other things like say ethanol, which is as, you know, a, a biofuel, we can't quite do that yet. And making a specific, uh, molecule and only that molecule, we can't do that either. So those are, those are at, uh, a substantially lower, uh, position in terms of technological maturity. So some things we can do very well, but we can't do some of the specific things that we would need to do to have the technology really succeed and, and displace, as I said, my goal was, uh, all of petroleum refining and actually all of the use of fossil fuels if, if we're ultimately successful. So we have a ways to do go before we can aspire to do that. Although we have some promising, uh, uh, systems that really do work now.

Aliyah (13:28):

So the reason I brought you both together for this episode is because you each have different, but very complementary expertise on this reaction, which as we've been talking about, is arguably one of the most important chemical reactions on the planet. Um, and for each step of natural photosynthesis, microbes and plants have evolved amazing tools to get the job done. You know, scientists like yourself, Jan, you help to reveal how these work and then material scientists like Joel can use these insights to design these totally new processes that you know, could revolutionize energy. So from what I've learned, sometimes there's a lot of overlap between what happens in natural in artificial photosynthesis. And sometimes each has pretty different challenges and processes involved. So I wanted to go through some of the major steps of photosynthesis and talk about what nature does and then what engineers and material scientists like Joel do. Okay. So the first step here, I think in both systems we could agree, is absorbing photons, right? And turning them into usable chemical energy. Uh, so Jan, how in, how are plants and microbes doing this?

Jan (14:31):

Yeah, so <laugh>, there's the, the really beautiful, um, diversity you can see in nature because life is basically covering all different niches or areas on earth and has to adapt to very different conditions. So, um, and you find photosynthetic organisms basically in every space on earth <laugh>. So there are many different strategies to optimize getting the photons to these reaction centers. So many different, we call these antenna because they collect, um, photons in this case. So many different, um, arrangements of, of proteins that function as an antenna for, for photons. And so they can tune, they can be tuned, um, in terms of the color. So you find very different, um, modifications on these pigments to really be optimized to the wavelengths of the light that is available in this environment where this organism lifts. So you find very deep red ones, you find, um, organisms says absorb more in the blue or more in the green.

Jan (15:33):

So, so nature uses a variety of, of pigments. The most important one, and most widely used one is chlorophyl, which is the green one. We see all around us, but also for example, carotenoids, which we know more orange color, um, they are also used in many of these, um, light collecting antenna systems. One other very important aspect of this light collection is that it is often highly efficient. So these pigments are arranged in, in the organisms in a way that they can easily transfer a photon from one pigment to the next. And they can do that without losing much energy. Another important aspect in the natural system is that the sun intensity can change very rapidly. So you can have cloud cover, you can have shading from other parts of the environment or in the ocean. You can change the depths in which you are that changes to light intensity quite dramatically.

Jan (16:35):

And so the natural systems, many of them spend quite some effort to adapt to these fast changes in the light amount that is available. And so plants, for example, can switch their antenna systems in different states, depending on how much light they have. And so they can avoid getting too much light because photons are pretty energetic. So they carry a lot of energy once you absorb these photons. And if you can't use that energy because you get too much at once, it can actually be quite destructive. So one important --

Aliyah (17:10):

Like a sunburn? <Laugh>.

Jan (17:11):

Like a sunburn, yes. Yeah. And so one important part of the natural systems is that they have kind of safety valves built in,

Aliyah (17:19):

Oh, wow.

Jan (17:19):

That allow it to get rid of this destructive excess energy, because if they, if the sun is too bright, basically the system would burn, but instead they can release this excess energy in form of heat.

Jan (17:33):

So, um, not burning themselves up, but rather than releasing it in form of heat, which can't do as much damage as the, um, absorbed light itself would do these adaptive mechanisms. These are really essential to be for, for these many different organisms to live under often very changing conditions. And one important aspect maybe to, to keep in mind is that for most photosynthetic organisms, light is not the limiting factor. Um, rather these are other parts like water or iron or manganese, for example, so metals that are needed in those reactions. And so light is often not thought of as the limiting factor for, photosynthetic activity. More often, it's rather, um, a problem that there is too much light and the organism has to find a good way to dissipate the access light to avoid getting damaged.

Aliyah (18:26):

Wow. I don't think my poor house plants have that problem. I think they actually might not have enough light, but, uh, that's very cool. It's, it's, it's fascinating that there's not only a complex system, but complex, uh, safeguards involved in the system. Um, yeah. Joel, what about from your perspective?

Joel (18:42):

I guess the main difference that we, we we have is we, uh, tend to use, uh, solid inorganic materials as our absorbers. They're quite stable. In fact, they're the basis of the solar panels that you will see on the rooftops. We have attempted to use some of the enzymatic components that Jan talked about. Uh, they work great for a short period of time, but we don't have <laugh>. We don't have a way of regenerating them. They, uh, they have not yet been successful in our, in our practical systems. Another difference is that we can also change the way that the semiconductors, uh, absorbed by changing their band gaps, the energy that a photon needs to have in order to be absorbed. And the energy of a photon depends on what part of the electromagnetic spectrum that it's in Silicon and other, uh, semiconductors will have a so-called band gap.

Joel (19:38):

And when the photon energy is higher than that band gap, it's absorbed, and some semiconductors have a band gap in the visible [range] when you hold them up to the light, uh, you can see that they absorb some photons and let others through, and that gives them a color. So the idea is to choose various band gaps that are, uh, that are matched to the, to the spectrum of the light coming from the sun, which has many photons in the visible area that we can see, but also has photons that are in the ultraviolet. We can't see those. And also ones that in the infrared, we also can't see those, but we might wanna use the energy from them in our, in our artificial system. So we use, uh, semiconductors that are sensitive to different parts of the spectrum from the sun in order to try to, you know, harvest them all, if we can

Aliyah (20:29):

<laugh> Yes.

Jan (20:30):

Maybe one can compare it a little bit to different colored pigments. Um, so in natural systems you use these combination of different pigments. Yeah. So they, you could say they have a different band gap

Aliyah (20:41):

<laugh>

Joel (20:42):

Yeah.

Aliyah (20:43):

Is there such thing, is there such thing as, um, too many photons, too much light in your systems, Joel, where they get over overburdened?

Joel (20:51):

That's a problem we want to have actually <laugh> um, that that's an area where we actually, um, differ a little bit, you know, since we, since photosynthesis is already on earth and we used to operate our civilization using the products of it only in our, in, in the way we lived, uh, cutting down trees and burning them, for example, and then waiting for new trees to grow. And, uh, mankind, personkind discovered it was possible to dig up fixed carbon from the ground in the form of coal initially, and then oil and gas. Uh, of course this is carbon that was fixed by photosynthesis a long time ago that we're digging up and burning. It was possible to bring a lot more energy to bear in terms of driving our civilization. So in order to rival that or to, to replace the carbon that's used in those activities, we would need something substantially more efficient than current photosynthesis in, in my opinion, which is why, which explains the push that I'm talking about for efficiency. Right? So while it's true that some of our systems are damaged by light. We work to try to engineer around that, uh, cuz we really want every photon we can get, cuz we, we need something that's substantially more efficient than the system we already have in order to meet the energy needs that we've evolved ourselves to have.

Aliyah (22:06):

What about instances of, of low energy or low light? Would that uh, just be, um, like you discussed of having different tune to different band gaps?

Joel (22:14):

Yeah. Okay. We, we wanna make, okay, we try to make use of all of it. Um <laugh> and okay. What you're talking about is cutting-edge thinking on trying to use, uh, some of the lower-energy light that maybe we can't use directly for chemistry, but we wanna use other influence other parts of the system. We are actively working on trying on ways to try to do that. Again, we, we, we want to make use of every single photon if we can.

Aliyah (22:38):

Uh, so let's talk about one of the other big moments, which is splitting water molecules into oxygen, electrons and protons. Uh, Jan, obviously your work has a lot to do with this. So can you tell us a little bit about photosystem II?

Jan (22:49):

Yeah. So these photons having been collected in these antenna systems, um, the next step is really to, to use this energy from the photons. And of course the first step then of several steps there is to, um, separate, um, an electron from a molecule. So basically you use the photon to excite that molecule, so you shine as you would shine light on the, on a pigment and then this excited molecule can give up one electron. And if you have another molecule close by, which is happy to take an electron, you generate a charge separation, we call that. So you have a charge moving from one molecule to another one over a distance and it's basically like a battery. So the work you can perform later depends on how much charge you separate by how much distance. So, okay. Um, in, in the natural system, there's a, the, the systems are designed to move this charge over a distance of about 30 to 40 angstroms or three to four nanometers.

Jan (23:52):

And then use that energy from basically moving an electron over this distance away from its original place to perform specific reactions. So you can, like in a battery, you can use that stored energy to do, um, some work. And in photosystem II, that work is oxidizing a metal. Uh, not one single metal, but an arrangement of five metals together. And these five metals, these are manganese atoms and the calcium atom and these manganese atoms have this very nice property that they are very flexible in terms of how many electrons they want to have. So manganese, um, we call that an oxidation state, has the option to be stable in several different oxidation states. So you can shift it by 1, 2, 3 or four electrons up and down in this oxidation state level. And then a second charge separation event can happen. So a second photo hits the system and can again, extract and electron and oxidize this plus three more, so in the end you can oxidize it four times.

Jan (25:00):

And if you think about, um, four electrons being removed, so that means it's oxidized four times, this is exactly the amount of electrons or the amount of oxidative equivalence you need to oxidize two molecules of water. So if you have two molecules of water and want to form oxygen, you need to remove four electrons from these two molecules of waters. And looking at the basic chemistry, if you take water directly and want to remove all these electrons at once, it's very high barrier. So nature, um, really circumvent this, this big hurdle by, um, basically accumulating, um, these redox steps in this cluster so that you can, um, charge it up like a very highly charged battery and then you have more power to, to perform this reaction. And so then after you charged up this system and you have your manganese cluster, which has, uh, the power to extract four electrons, it can do that by having two waters located very close to each other.

Jan (26:08):

Basically that's the, one of the not, not really understood parts of this reaction, how in the system, the waters are specifically arranged so that they are in the right place to find each other. Um, so you, you want to make sure that you exactly react these two together that you don't, for example, um, loose the partly reacted water, um, to the environment before the reaction is complete. So if you think about water, one intermediate step before reaching oxygen would be peroxide. And hydrogen peroxide, as many know from all daily, um, experience is a highly reactive, um, molecule, which tends to damage every organic matter in its way. So it's basically bleaching, whatever it touches. So in, in the native, in the natural system, it would be very, very difficult if this hydrogen peroxide would be formed and could escape from this active site, because then it would just destroy everything around it. So the, the natural system really is very fine-tuned to avoid any release of these kinds of intermediates in the reaction, which could destroy, um, the catalyst. And only releases the final product, oxygen. And so, so this is some of these very intriguing aspects of how this reaction is performed in nature. And that's different from what is done in artificial, what oxidation systems.

Joel (27:36):

Yeah. I mean, that's that's right. Yeah. And although some of the same chemical principles apply: the number four, for example, yes. We need to take four electrons off two waters in order to complete the reaction, but the way we think about it and do it slightly different. Uh, first I wanna talk about the absorption event inside our semiconductor. Uh, it makes electrons, but if you think about it, we have to, uh, obey the principle of charge conservation. You just can't make a negative charge, you also have to make a positive charge somehow. And we have a special name for the positive charge we make. Uh, when we create an electron, we also make a place where there isn't an electron. We call that a hole and believe it or not, these, these electrons that we make, they can move through our semiconductor; the holes, the absence of electron can also move.

Joel (28:25):

And what we're interested in doing is getting those holes to go to the surface of our semiconductor, where they can take an electron from the water. And, uh, like in the natural system, we don't do that directly. Uh, sometimes we oxidize an element that's on the surface. We tend to use multivalent, uh, metals on the surface, similarly, flexible in their ability to, uh, support different oxidation states. That's why we like iron and, uh, nickel for that purpose. And it's that oxidized surface of our semiconductor, uh, which is actually an interface between a solid material and the water. On the other side, we go after one water at a time. Uh, first we take two electrons off one of the waters with two holes that we made from the absorption of two photons. And then the, uh, entity that we make in that step actually goes out and attacks, a nearby water,

Aliyah (29:21):

Interesting

Joel (29:22):

uh, plus another hole, getting to the next step in the reaction and then one more hole completes it. So we do understand the individual steps of the reaction, which are a little different actually than the ones in natural, uh, photosynthesis. Although they get to the same result, uh, to two oxygen molecules coming off from the, from the waters. Basically the, the, the thing we're trying to do is the same. Uh, but they, it differs in a couple of details. Also. Um, we do sometimes make peroxide, but it's not as destructive in our systems cuz I said they don't have living things in them. Uh, I will observe though, Jan, you may know this, that when we try to mix up natural and artificial systems, that peroxide is a problem actually. Cause it, it it's a great disinfectant. And so the bacteria that you're you and your colleagues have worked so hard to make, okay, we, we just eat them up. Uh, but our inorganic materials are usually not always, but usually untroubled by the hydrogen peroxide. If that's one of the, the things we make, that's an area where we're a little less sensitive to the, uh, making of undesired products. Uh, I believe the natural system is a little more elegant and effective actually, uh, by a few tens of millivolts. Okay. It's a challenge for us to, to do as well as that one. So we're, we continue to be inspired by the natural system and as we design our artificial ones,

Aliyah (30:53):

What about regenerating? The correct, uh, oxidation state to start over? How, um, is that easy in your artificial systems right now, Joel,

Joel (31:01):

Right. Yeah. Okay. Well, when it works, when, when it works, like we draw it on our whiteboards <laugh> yes, we get it's catting gets back, right. It gets back. It gets back to the same, uh, the same point. But, but we have a funny term that's called turnover number. And what does that mean? That means the number of times a catalytic site will work before it doesn't work anymore. You would like that number to be an infinite number. <laugh> like, it will always work, but of course no system lasts forever. And ours don't either. Uh, so that is, that is one of the things that we assess when we, uh, think about how long a system can last, we can regenerate. But mostly that involves regenerating the callous by depositing more of it on the surface, which we can do. Uh, it's not as elegant as the natural system, but it, but it also works <laugh>

Jan (31:48):

Right in the natural system, you have like some sensor. So if, if something goes wrong, like the catalytic site is not performing in the right way anymore, you generate some damage because although it's very, it's very efficient in avoiding side reactions, still these happen. Yeah. And then, uh, this damage is actually sensed by specific other proteins that scan the photosystem. And if they see that damage accumulating in certain parts of the photo system, they actually can chew selectively away some parts of the photosystem and regenerate it. So in, in the, in any plant leaf or whatever photosynthetic system with oxygenic photosynthesis, every 30 minutes, this metal site is disassembled and then replaced by a new site.

Aliyah (32:37):

Wow!

Jan (32:37):

But as this entire, photosystem II complex is pretty big, it would be very wasteful to throw away the entire protein each time. So in the natural system, there's a very not-well-understood cycle that allows to take out only the damaged part, keep the rest, the other 90% of the protein that's not damaged and just reinsert a new piece basically to replace the damaged part. Um, so this is one of the really also fascinating, uh, areas of study at the moment to figure out how this selective replacement and reinsertion of the damaged part works in a natural system. And then, um, very interestingly, once this damage protein is replaced, then the metals need to get back into form this catalytic active metal cluster. And this seems to be a self-assembly process. So once that protein is in the right place and you have right the metal ions or manganese and calcium, which are in the cell, in the cytoplasm of the cell floating around, they can be basically incorporated by itself into the right form. And you just need to have light there. So this reassembly process happens within yeah, very short time in each photosystem. So there's a constant, um, repair process going on. That of course takes a lot of resources from the plant or from the organism, but it allows it to work constantly under light conditions.

Aliyah (34:07):

That is so cool. I mean, not only is it using as many photons as it can, like what it's using them so efficiently it's then fixing itself. And I guess, Joel, you don't have the same efficiency, but at least you don't have to fix the system every 30 minutes.

Joel (34:20):

Well, okay. So efficiency actually. Okay. So efficiency. Okay. We can <laugh> we can run our, okay. What we're talking about, water oxidation. We can run for months, actually. <laugh> seriously.

Aliyah (34:32):

That's great!

Joel (34:32):

Without maintenance. Uh, that's great. We do this, uh, now a single site may not work for, months, but we just put in a lot more sites <laugh> we can just put in more material to compensate, right. Uh, so yeah, we can run for six months, uh, continuously, uh, without a problem now, the way we know and the way we sense there's a problem is of course we're monitoring the products, um, externally by measuring the rate at which we're forming oxygen. So we know by measuring the system, whether there's a problem or not. So that, as I said, we can get several months of lifetime and, and, and be able to, in some, in some cases replace just the part of the system that that's having a problem without having to, uh, throw away the whole thing and start from scratch, which would be inefficient in a practical way, but also in an, in an energy efficiency way, because you'd need the energy to remanufacture your silicon solar cell once, once again. In fact, one of the earlier, or one thing that's guided our thinking in this area is doing life-cycle assessment, where we actually look at how much energy a, uh, uh, artificial photosynthetic system can convert over its useful lifetime versus how much energy it took to manufacture its components. And that's a really interesting analysis to do. You find that they have to last for five to 10 years.

Aliyah (35:55):

Oh wow. Okay.

Joel (35:56):

Maintenance is fine, but complete complete remanufacturing would, would of course require all the energy necessary to make them. So we, we went through that analysis to actually give ourselves bench marks for how long things would have to last to be practical. And, so since we know what that number is, we, we work towards, achieving it. But I have to say there are energy conversion devices operating now on this planet that do last for years. Uh, those would be the photovoltaic panels that, uh, are manufactured now. Uh, you may know that they're warrantied for an amazing period of time, 25 years. Hmm. Yeah. Yeah. Hip replacements are not <laugh>

Aliyah (36:37):

<laugh>

Joel (36:39):

Warrantied for 25 years. I mean, that's, it's ... it's extraordinary that anything, uh, that's in such demanding, cause it's sitting in the sun, uh, think about paint on a house, that does not last for 25 years, but the solar panels have been designed so that they're the, they should actually, uh, be able to last for 25 years. So, uh, we have to make sure that the other things we've added to it, uh, the parts of the system that do the specific chemistry, we want live up to the same, uh, durability requirements. And so we're, that's an area of considerable study now.

Aliyah (37:17):

So let's get forward a little bit in the, in the reaction and talk about, um, a very important step, which is actually getting the CO2 somewhere where you can use it. Right. So I remember from my basic biology class that plants have nice little pores for the CO2, Um, and that's about where my knowledge starts to crumble from, uh, the years that have passed. So let's talk a little bit about this.

Jan (37:41):

So maybe we can start from the natural system again, and this is really one of the big bottlenecks in, in the natural system. So the main enzyme that binds the CO2 and converts it, um, reduces CO2. You can say it's pretty badly designed. <laugh> compared to many other enzymes. It's it doesn't have a very high desire to bind CO2. So if you would put it in a normal air with low level of CO2 that you have to 300, 400 PPM, it's not really not a lot of your enzyme copies would actually bind CO2. And so many photosynthetic organisms came up with different ways to, to work around this flaw. <laugh> So one option is that you push the level of CO2 inside your, um, organism to a higher concentration. So that way this CO2-binding enzyme becomes faster and can work more efficiently. And so that is CO2 concentrating mechanisms used to actively move CO2 from the outside into specific parts of the cell, where then the Rubisco enzyme that, that binds to CO2 and, um, reduces it is sitting, of course they cost also energy. So the plant pays, or the, the organism pays some energy costs to do that, but it helps to actually then push forward the next step.

Joel (39:09):

Yeah, one difference, uh, uh, between the, the, the natural system and the artificial systems that we're making is ours aren't based on cells -- or the word cell means a different thing.

Aliyah (39:22):

<laugh>

Joel (39:22):

Right. A cell is, uh, discreet entity capable of reproducing itself in Jan's world. And a cell to me means a solar cell or something, something that we make. We use that word differently. So we can, we can actually do things that cells would never do when we're, when we're striving for efficiency, we use pure CO2 as our reactant and we essentially blow it at our cell. Uh, we don't yet -- and this is a challenge in the field -- have something that can work well, uh, harvesting CO2 directly from the atmosphere where it's currently at a, a concentration approximately, uh, 400 parts per million. That is a, that is a challenge.

Aliyah (40:04):

So until, um, you know, direct air capture for these systems, um, is enabled. I mean, there it's, like you mentioned, there's other, uh, other scientific fields who are working on direct air capture, carbon capture technology is a big thing. So you could just pair your technologies together and that's pretty cool.

Joel (40:20):

Yeah. So natural photosynthesis does not have to make it economic case for itself.

Jan (40:25):

It did it for the last billion years! Yeah.

Joel (40:28):

It's not competing, is it? You don't have to ask a venture capitalist to plant a seed in your garden. Okay. It's already there. Um, it's, it's proved itself, um, as convincingly as anything that I know! But with artificial photosynthesis and related energy conversion technology, these are new. And in order to operate at the scale that they need to be, to make a difference requires, uh, a change in the way we do things. And I could go on with the additional steps, but of course that would require money and investment and also the human effort to do so. And, uh, of course you have to have a reason to do it. And one way to imagine how you grow something from being a very new technology to something that becomes ubiquitous on earth is you think about initially niche applications where there's a specific need to do this and maybe cost isn't the most, uh, important factor.

Joel (41:23):

Maybe something else is. The classic example is the growth of photovoltaic cells for, uh, solar power conversion. Uh, they were available already from 1950s, uh, close to the efficiencies that we have now, not quite, but, you know, on the order of 10% [as] efficient, they were just like way too <laugh> expensive to manufacture <laugh> to ever imagine that they could used for, uh, power generation on any scale. However, you, you're not gonna build a coal fire power plant in space. There's no oxygen [to burn] the coal. So they found their first application in, um, satellites and spacecraft and so forth. And as a result of the demand that was created for the use of those solar cells in that environment, the, the, uh, companies manufacturing them got better at doing so. And, uh, leading to the point that we are at now 60 years, more or less after the discovery of practical solar cells, where they compete as being the cheapest way to generate electricity in sunny places.

Joel (42:27):

So one can imagine the same trajectory for artificial photosynthesis. So we are trying to look for places where it makes sense, and some of these places are where there's already a pure source of CO2 available for some reason, uh, places that do certain types of biomass processing have these. And so do certain, uh, things in chemical manufacturing. And that will give us a chance to operate at a sort of pilot plant scale, uh, so that we can then go through the learning that's required, to learn a few things along the way -- of course, because that's what a learning curve's about -- so we can get up to this scale that we need to make a difference.

Jan (43:06):

Maybe quickly want to add to <laugh> that. While Joel said that photosynthesis doesn't need to make a case for itself because it, it was successful, but still also in the natural system, there are many opportunities maybe to improve it to some extent. And so for example, some research in UC Berkeley and here [at] LBNL was focused on how to optimize the antenna size in plants. And that, for example, can lead to an increase in the plant productivity by 20%, which is huge. So as we learn more and more about these fine details, how they're regulated, there are also pretty exciting opportunities to, to improve them, either for biofuel, um, production purposes, for example, but also for crop production, things like that. So that's also a fascinating aspect for natural photosynthesis research, not only to feed into artificial system, some ideas or concepts, but also to get some ideas how we could optimize certain aspects of the natural system.

Aliyah (44:07):

Yeah. Has anyone fixed Rubisco? Has anyone kind of souped that up and made like a 2.0 version?

Jan (44:13):

That's one of the big challenges

Joel (44:16):

Is it's unchanged for over 2 billion years or something...

Jan (44:20):

It evolved in a different environment where there was not that high oxygen level and the CO2 level was higher than it is now. So that way, it was at the time it evolved it working well, so --

Aliyah (44:32):

Oh, I see. Okay. Yeah, but now it's just funny that it, it doesn't seem nearly as sophisticated as the enzymes around it, and [photosynthetic organisms] evolved super sophisticated means of, you know, go working around the issue. So that's very interesting.

Jan (44:45):

Yeah. Evolution is not directed, so it's not like the organism says, "oh, I will need to change this part first because then I can do the other ones better." It's really the nature of evolution leads to unpredicted pathways. And so instead of fixing maybe for us, the obvious problem, often there's a work around found by other changes and then [those] prove to be workable. And then there was no pressure to improve the initial problem.

Aliyah (45:13):

So let's skip, yeah. To the next thing I wanted to talk about in the photosynthetic process, which is taking that CO2, taking the energy we've gotten from the light and then actually doing something useful with it, right. Making something. And, uh, the history of this field has a lot to do with Berkeley Lab because Melvin Calvin is the scientist who discovered how, what is now called the Calvin cycle works, which is taking CO2 and making sugars. So let's talk a little bit about this in plants and then how Joel you're doing it to make more fuel-like molecules.

Joel (45:44):

So yeah. You wanna, you wanna walk us through the Calvin cycle?

Jan (45:46):

Yeah. Yeah. So

Joel (45:48):

I think you're more qualified. I mean, I can, you know, <laugh> Ribulose and then I think it's a C5... <laugh> [Joking] And then comes this thing, and it's six and splits into two C threes?

Aliyah (45:58):

Yeah. [Joking] Pyruvate's in there somewhere <laugh>. Yeah,

Joel (46:00):

Yeah, yeah. Pyruvate, yeah. We'd love to be able to make that actually that's a, that's a stretch goal for us actually is making pyruvate

Jan (46:06):

Yeah. So the, the Calvin cycle is really yeah, a fascinating cycle and basically coupling six of these carbons together, in you know, successive reactions. And I always forget how many enzymes are involved, but maybe around 12 <laugh>, something like that in total. So it's a really complex cycle. And as we said at the beginning, one of the major enzymes there is Rubisco, which actually binds the CO2 and um, reduces it. We always, I have to admit from my side, we always say, oh, this is the dark side of the photosynthesis. Cause it's, um, little bit less, um, easy to study with the physical chemistry methods we are doing. So yeah, we have these light-triggered reactions. We can shine a laser flash on it and then see what happens next. But it's basically, yeah, [the Calvin cycle] was discovered with a lot of very ingenious, biochemistry and enzymology using a lot of, um, for example, radioactive labeling of different carbon steps, uh, carbon, um, compounds

Joel (47:11):

Yeah. Made by the synchrotrons here at Lawrence Berkeley Lab. It's brilliant work actually, with carbon-14 labeling.

Jan (47:18):

Yeah, this was essential. And I'm not that qualified to go into a lot of details there except that it's not highly efficient in terms of fixing the carbon dioxide.

Aliyah (47:29):

So these enzymes that are doing a step-by-step conversion, there's, you know, there's a whole big series of them... Are plants, is it, uh, an efficient process where one thing's getting handed off to the next enzyme and it's really smooth and nothing's starting to flow backwards and clogging up the whole machine, you know, does it work well? And, and in a smooth pathway?

Jan (47:47):

Of course it's not as efficient as a simple chemical process in a, in a factory or something because you have these many different steps, but they are tightly coupled. So you basically, um, have all these enzymes spatially co-located and also regulated in a way that they are there in the right amount so that you have no loss of intermediate products. And to ensure that, um, for each step, the product formed can immediately be used in the next step. So this is a basic principle from any of these, these metabolic cycles in biological systems that they are tightly regulated to ensure that there is no waste or loss. Um, but of course, um, each conversion step requires some, um, driving force. So you, you need to put some excess energy in to push that process forward. And the more steps you have, the more of these energy needs you have. And so the Calvin cycle is not optimized to be extremely efficient that way. So basically that CO2 fixation Calvin cycle is the biggest loss in, if you look at the total productivity of a plant, um, in terms how much, how much fixed chemical energy it is producing per photon energy, it is getting. So the efficiency in total depends very much on the conditions of the plant and where it's living, things like that, but it's, um, maybe three, 4% on that level. Um, so it doesn't sound great.

Aliyah (49:31):

<laugh>

Joel (49:31):

Certainly, I don't wanna say anything bad about, I'm glad it survived. Okay. I'm happy for that. Cause otherwise we wouldn't be here having this conversation. But it's also an opportunity for the artificial photosynthesis systems, because we know we can drive the CO2 reduction part much more efficiently and we do. One difference is, uh, we don't, we actually aspire to and actually can go directly after the CO2 molecule. CO2 is actually quite a happy molecule. It's a linear, it has all the electrons it wants, not one more, not one less. In fact, in the gas phase, if you offer an electron -- attempt to reduce it -- it will give the electron back. It's got a negative electron affinity <laugh> however, in the electric chemical environment we create with water around and some electrified surfaces, we find we can bend it and activate it.

Aliyah (50:22):

Ooh, cool.

Joel (50:23):

And get the reaction started and we can do that rather, rather, rather efficiently. Uh, so some of our systems that, um, are light driven can be 10 times as efficient as natural photosynthesis and some, and under some conditions approach the, the efficiency of photovoltaic power conversion. So we've got that part covered, uh, where we need help is making more complicated products like the sugars that the Calvin cycle produces. The advantage we have is we can design systems of different shapes and sizes that so that we can achieve that, where as you know, the Calvin cycle is, you know, you're dealing with molecules and cells and so forth. We can design anything we want and do another thing we're inspired by are actually the methods that <laugh> that Calvin and his coworkers used to figure out the mechanism, isotope labeling and so forth. We do the same thing. Actually, and every time we do it, we're surprised by our results, which is we can be bad or good.

Joel (51:24):

<laugh>, It tells you that your initial thoughts about how things work were perhaps incorrect. Okay. But then it gives you the opportunity to come up with an even better and perhaps more, more scientifically correct explanation of what's going on. So, again, we think that we can do a little better than the natural system in terms of the important money-making reaction, which is the reduction of CO2 by just going about it totally differently. And, uh, I do expect that this type of research will yield some, uh, a very nice and useful results, uh, towards the end of this decade. We can do another podcast at that time. <laugh>

Aliyah (52:05):

That would be great. So it's been so fascinating hearing you both talk about, you know, overlap and, and differences and just how you, the work inspires each other kind of going both directions. And since Berkeley Lab happens to be one of those places where both of these areas of research are, are happening at the, at the same physical location, I'm wondering, do you have like photosynthesis parties where you give the latest updates? Like, how are you guys keeping in touch if those parties aren't happening? Should I start throwing them? I just think it's really cool that, um, you're able to kind of directly work back and forth with each other and what's that dynamic like?

Joel (52:41):

Sure. Yeah. I wanna go to a photosynthesis party. Yeah. <laugh>

Jan (52:46):

So one thing maybe to mention that, uh, um, so we have this, um, Liquid Sunlight Alliance (LiSA) currently at LBL, which is really focused on harnessing solar energy to produce, um, chemicals in this, for example, fuels that can be used. And this was sparked I think a lot by discussions between researchers on natural photosynthesis and artificial photosynthesis talking about, um, these principles and how they could, um, could be used. And so a lot of the initial people pushing this forward were involved in, in both parts [of research] to some extent. So there was this pretty good exchange of ideas over the last 15 years.

Joel (53:31):

Yeah. Let me add a little bit to that. Um, it may seem obvious that a Department of Energy lab, particularly, you know, a nice, one like Lawrence Berkeley lab should be working on energy conversion, but that was not always the case. And the period of time, about 15 years ago that Jan's referring to, actually, at that time there was no photovoltaic research, or very little, at Lawrence Berkeley lab. And I will credit the laboratory director we had at the time, Steven Chu for asking the question, well, shouldn't we be, you know, let's think about what the most important challenges are facing the planet. Shouldn't we be working on those?

Jan (54:05):

<laugh> yeah. <laugh>

Joel (54:07):

It seems simple to say that. Yeah. Uh, but you know, that's a, that's a question that he posed to try to, uh, inspire the scientists to think a little bit beyond their own, uh, area of comfort by, in an area that has it's... Well, it's very important with global significance. And I think it's been a big success story for the lab. Yeah. Yeah. That's why, that's why that building that I have, some of my labs in is called Chu hall. Okay. It's well-deserved name.

Aliyah (54:37):

So that was a fascinating conversation. Thank you both so much for being here.

Jan (54:40):

Yeah. Thank you Aliyah. It was really nice.

Joel (54:41):

Thank you.

Jan (54:42):

Thank you, Joel, as well. It was a really inspiring discussion. I learned a lot as well about things I'm not working with every day, so it's really nice opportunity.

Joel (54:53):

Yeah, it was very nice talking to both of you, until next time

Aliyah (55:09):

As always. Thank you so much for listening. If you like the show, please tell your science-loving friends to also check us out and tweet @BerkeleyLab to tell us about subjects that you want us to dive into next.