The world is slowly but surely moving towards relying on clean energy, which we can see in many sustainability efforts and initiatives from both private or public sector.  

Researchers and scientists who have been trying out new ways to make us move faster towards better environment have now turned their attention to photosynthesis. And, a team of researchers at the University of Rochester is on a mission to mimic the natural process of photosynthesis using bacteria to get better hydrogen. 

In a paper published in the journal PNAS, the team demonstrate how the bacteria Shewanella oneidensis can offer an efficient and cheap way to provide electrons to their artificial photosynthesis system. 

By using the properties of the bacteria along with nanomaterials, this discovery has the potential to replace current technology that get hydrogen from fossil fuels and revolutionize the method to produce hydrogen fuel, leading us to a real, powerful, renewable energy. 

“Clean” fuel that is hydrogen 

Despite sounding clean and pure, as it’s usually associated with water and therefore a sense of abundance, pure hydrogen on this planet isn’t available naturally. Hydrogen is almost always bound to other elements like carbon or oxygen, in compounds like hydrocarbons and water. 

If we want to use hydrogen as a fuel source, we must extract it from those compounds. Previously, extracting hydrogen is done from fossil fuel (water extraction came later). 

It’s only recently that there’s been a push to utilize artificial photosynthesis to get the element. 

During natural photosynthesis, plants absorb sunlight in order to power chemical reactions to convert carbon dioxide and water into glucose and oxygen. Basically, plants convert light energy into chemical energy that fuels them. 

In a similar fashion, artificial photosynthesis converts sunlight and an abundant feedstock into chemical fuel. Any systems which employ artificial photosynthesis need three components: a light absorber, a catalyst to make the fuel, and a source of electrons. 

Such systems are typically submerged in water, and a light source provides energy to the light absorber. Then, the energy enables the catalyst to combine electrons with protons from the surrounding water to produce hydrogen gas. 

Unfortunately, most of the current systems rely on fossil fuels during the production process or don’t have an efficient way to transfer electrons. 

One of the researchers, Kara Bren, said, “The way hydrogen fuel is produced now effectively makes it a fossil fuel. We want to get hydrogen from water in a light-driven reaction so we have a truly clean fuel—and do so in a way that we don’t use fossil fuels in the process.” 

 

 

A better alternative to fossil fuels still 

If we disregard the current systems and their reliance on fossil fuels, hydrogen is still the better alternative compared to our current conventional fuel source. 

According to the researchers, this element is the most abundant element in the universe. Although there’s virtually no pure hydrogen in natural settings, we can get it from variety of sources, including water, natural gas, and biomass. And unlike fossil fuels which produce pollutants and greenhouse gases, hydrogen’s byproduct is water vapor. 

Moreover, this element has a high energy density. Compared to fossil fuels, hydrogen contains a lot of energy per unit of weight—which will be more beneficial when we use it in a variety of applications like fuel cells. These fuel cells, be it produced on small or large scales, will be able to provide energy to homes or industrial manufacturing. 

That is why the researchers are keen on perfecting their discovery and system. “If we can figure out a way to efficiently extract hydrogen from water, this could lead to an incredible amount of growth in clean energy,” Bren said. 

Developing the system with bacteria 

For around a decade, the researchers have been working to develop an efficient system which employs artificial photosynthesis and utilizes semiconductor nanocrystals for light absorbers and catalysts. 

Among many challenges, one that the researchers needed to overcome was figuring out a source of electrons and efficiently transferring the electrons from the electron donor to the nanocrystals. 

Per the team, other systems have used vitamin C (ascorbic acid) to deliver electrons back to the system. One of the team, Todd Krauss, stated that although vitamin C might seem cheap, it would need a source of electrons that is almost free or the system becomes too expensive. 

However, the researchers had a eureka moment when they stumbled upon an unlikely electron donor: Shewanella oneidensis. According to the team who gathered the microorganism from Lake Oneida, the bacteria offer an effectively free, yet efficient, way to provide electrons to their system. 

The researchers claim that although other labs have combined nanostructures and bacteria, those systems are taking electrons from the nanocrystals and putting them into the bacteria, then using the bacterial machinery to prepare fuels. 

“As far as we know, ours is the first case to go the opposite way and use the bacteria as an electron source to a nanocrystal catalyst,” Bren said. 

Now, when bacteria grow under conditions where there’s no oxygen, they respire cellular substances as fuel, releasing electrons in the process. Alternatively, Shewanella oneidensis can take electrons generated by its own internal metabolism and donate them to the external catalyst. 

 

 

Will photosynthesis mimicry be an important technology or our planet? 

It seems like artificial photosynthesis is becoming one of the many technologies needed in the greener future. As mentioned, scientists have drawn inspirations from natural photosynthesis and begun utilizing it for many systems. 

Another example of artificial photosynthesis use is a discovery by researchers at TUM Campus Straubing for Biotechnology and Sustainability (TUMCS). By mimicking photosynthesis, they’ve succeeded in producing the amino acid L-alanine from carbon dioxide.  

In the TUMCS research, the team first captured CO2 from the atmosphere and turn it into methanol using green electricity and hydrogen. Their new method converts methanol into L-alanine in a multi-stage process using synthetic enzymes. According to the team, the method is extremely effective and generates very high yields. 

Now, L-alanine is one of the most important components of protein, which is essential to the nutrition of both humans and animals. As we know, protein for conventional animal feed has typically been produced with large-scale agricultural space requirements and negative consequences for biodiversity. 

This new method, if combined with findings from University of Rochester research, might lead us to better, more environment-friendly food production.  

Lead researcher Prof. Volker Sieber of the TUMCS research said, “Compared to growing plants, this method requires far less space to create the same amount of L-alanine, when the energy used comes from solar or wind power sources. 

“The more efficient use of space means a kind of artificial photosynthesis can be used to produce the same amount of foodstuffs on significantly fewer acres. This paves the way for a smaller ecological footprint in agriculture.” 

Hydrogen and better future 

If researchers and scientists continue to refine their discoveries, in this case hydrogen production via artificial photosynthesis, such technology might be within our reach sooner.  

The University of Rochester researchers think the same. Bren has a vision that individual homes would have vats and underground tanks to harness the power of the sun to produce and store small batches of hydrogen in the future. Therefore, people could power their homes and cars with clean-burning and inexpensive fuel.  

It’s just that they still have work to do; there are some vehicles powered by hydrogen fuel cells now, but all the hydrogen that is available to power these systems comes from fossil fuels. 

“The technology’s out there but until the hydrogen’s coming from water in a light-driven reaction—without using fossil fuels—it isn’t really helping the environment,” Bren said. 

 

Sources

https://techxplore.com/news/2023-05-power-photosynthesis-energy-production.html  

https://www.sciencedaily.com/releases/2023/04/230428130805.htm