Solar Cell Breakthrough: “Artificial Leaf” Beats Photosynthesis At Its Own Game
When a research team from Germany puts a microorganism from Japan to work in a solar cell, you’re either looking at the next iteration of the Godzilla series or a significant solar cell breakthrough. If you guessed solar cell that would be it. The new solar cell is described as an “artificial leaf” that mimics the electron transfer of photosynthesis, at a much faster rate than observed in nature.
The key to the whole thing is a protein complex called photosystem 1 (PS1). If PS1 hasn’t crossed your radar since AP Bio, before we tell you all about that microorganism from Japan let’s get reacquainted with PS1.
Photosystem 1 And The Next Solar Cell Breakthrough
PS1 owes its name to a quirk of history. For some plants and algae there are two sequential protein systems that enable the electron transfer at the heart of photosynthesis. The flow of electrons actually starts at a system called photosystem 2.
The question is why the second system in the series get to be called #1, and the answer is that it was discovered first.
Researchers have been tinkering around with PS1 as a substitute for silicon, as a pathway to leaner, cheaper solar cells. The renewability of the protein is also a plus for reducing the lifecycle footprint of next-generation solar cells.
Putting PS1 To Work Is Harder Than You Think
Back in 2012, CleanTechnica noted that MIT was dipping a toe in the biophotovoltaics (that’s fancyspeak for artificial leaf) field with a “paintable” solar cell using PS1.
That same year a multinational research team from Germany and Israel came up with a way to measure photocurrents in PS1, demonstrating proof of concept for integrating the protein complex into solar cells.
One of the challenges facing researchers is that PS1 is a complex system with both hydrophilic (water-attracting) and hydrophobic (water-resistant) properties, which means that it is not amenable to sitting still.
This is where the new German solar cell breakthrough part comes in. Late last year our sister site Green Building Elements reported that a research team from Ruhr-Universität Bochum (RUB) was developing a “bio-based” solar cell using both PS1 and PS2.
In the latest development, the team has announced that they’ve ramped up the efficiency of the original concept from nanowatts to microwatts. That’s still photovoltaics on the scale of implantable medical devices (the team suggests sensors implanted in contact lenses, in case you’re wondering how sunlight is supposed to get to an implanted medical device). However, the breakthrough was significant enough for the team to foresee application to the next generation of flexible, thin film solar cells.
The progress was accomplished by focusing on PS1. To accommodate the protein’s split hydro-personality, the team developed custom-made redox hydrogels, which are electron-conducting gels that connect enzymes to electrodes.
Like PS1, the tailored hydrogels are both hydrophopic and hydrophilic, but they can be tuned to the hydrophobic aspect of PS1 by shifting the pH.
When the team embedded PS1 in the new hydrogels, the magic happened:
This purpose-built environment provides the optimal conditions for PS1 and overcomes the kinetic limiting steps, which are found in natural leaves. This procedure yields the highest photocurrents observed to date for semi-artificial bio-photoelectrodes while the electron transfer rate exceeds by one order of magnitude the one observed in nature.
Based on their observation of the photocurrents, the team predicts that one order of magnitude is peanuts compared to the potential for even higher electron transfer rates.
About That Bacteria From Japan…
No, we did not forget about that bacteria from Japan. The PS1 used by the German research team came from a type of thermophilic (heat-loving) cyanobacteria found in a hot spring in Japan.
If cyanobacteria rings a bell, you are probably thinking of the stuff commonly referred to as blue-green algae, which has been making a big splash in algae biofuel circles . Cyanobacteria, as its moniker indicates, is not actually an algae as in plant life. It’s a bacteria, but whatevs.
The takeaway is that one of Earth’s most ancient life forms is beginning to play a key role in the high tech, clean tech world of the future.
We’re also beginning to see direct bacteria-to-biofuel action, microbe-based fuel cells, new microbial processes for generating bioplastics, and even a form of self-assembling sustainable ink.
Also, we didn’t forget about that “other” artificial leaf we’ve been following. A project of Harvard (formerly MIT) professor Daniel Nocera, this low-cost photochemical device is designed to use solar power to split water (even dirty water) into hydrogen, which can then be stored and used in a fuel cell to produce electricity.
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If you’re in high school, take every biology class you can. If you’re going to college, but want to go into anything other than science and engineering, take an entry level biology course. If you want to go into science and engineering, take biology, even minor in it. If you want to major in biology, be prepared. You’ll be working along with engineers in joint engineering/biology R&D. For instance, even my hard rock mining school names the original “petroleum refining engineering” department (pre 1950s) “Chemical and Biological Engineering,” or something like that.
This message was not paid for by Americans for Biology Who Are Not Biologists (AFBWANB), because that organization doesn’t exist, yet. However, biology will become integral in everything to do with energy, materials, environmental science/engineering, healthcare (aging baby boomer, yo) and on and on going forward.
So, Tina is right to focus on this. And its neat stuff.
What fraction of the sunlight energy gets converted to electricity? I vaguely recall that photosynthesis captures 1% of incoming energy as chemical potential energy, so an order of magnitude improvement would be around 10%, although these folks are producing electricity instead of sugars.
well, why they call it artificial leaf if the process does not trap carbon dioxide into oxygen and carbon? what’s the point?
About the least informative image I’ve come across, and adds nothing to Tina’s valiant effort to explain in prose. The science is admittedly recherché. Natural photosynhesis is complex enough, mimicking it is even harder – and the researchers are a long way from any usable device, let alone a commercially deployable one. One for the “blue-sky file”.
Photosynthesis in plants is the easiest thing to beat. It’s net efficiency is often a fraction of 1%. Most of the radiant energy that the plant captures is lost by primarily by evaporating the water then via sensible heat transfer, and the minor ones reflection and black body reradiation, the tiny portion is captured for photosynthesis, less than 1%, and if you subtract energy of the plant spent on metabolism, then too little is left for energy storage. Claiming that you beat plant’s photosynthetic efficiency by 100% more is laughable, hey, bump it up by 500% more, it is still laughable.
Good stuff. Shout out to “sensible heat.” I’m too lazy to read the linked information and assume you’re right to claim it’s super salesy. On the other hand, the faster we as a species can figure out the secrets of mother nature, the better. Plant photosynthesis has about the efficiency that’s necessary, pursuant to about a billion years of trial and error. On a mechanistic level all those other physical phenomena (i..e. mass, momentum and energy transfer) are done in concert to produce a most lovely smelling rose. We (us humans) would require a process ten times the size of an oil refinery in Port Arthur, Texas and 100 times the energy input to do the same. Another example is silk from worms versus polyester from petrochemical feed stock.
I completely agree that the plants ultimately is the main producer of food for us, even the animals that we eat has to eat one form of plants or another. We haven’t converted sunlight energy into food through artificial photosynthesis from inorganic compounds, and much more for the unique aromatic compounds and other nutraceutical products that we could not synthesize. But when it comes to harvesting energy from the sun and storing them for our use, not even the best and most efficient plants in the world can come close to the worst performing solar panels sold out there.
Your are correct. Much of the postings by Tina are on technologies at the early stages of research. Maybe development. Tina does a great job shining light on what’s going on out there. Keeps us all on our toes. It’s pretty obvious that the technology being discussed here isn’t anywhere near commercialization. Or too far into development for that matter. If we comment section folks were a feasibility team, photosynthetic power would get screened out in the early stages of technology evaluation. Low marks in effectiveness, implementability and cost. This assumes the time constraints are soon and money is tight.
Nonetheless, the understanding of say photosynthesis and pretty much everything biology, will help us in the pursuit of using less energy to do the things we humans like to do. Which means we would need less PV panels and batteries. Or less tar sands. Etc. There’s a word for this – something like biomimicry engineering or something. For instance, if we understand the switches involved at the molecular level, we may be able to steer the focus away from flower production for reproduction to something else. Maybe simply mass production by intaking more carbon dioxide. Or storing energy in another state. Or not.
I have been excited for the day that solar energy storage became cleaner ever since I saw a lecture by Daniel Nocera. Thank you for the update. Nice article.