Concentrated photosynthesis device promises cheap green hydrogen

We are a solar powered planet. Most of the energy needed for life on Earth comes from the sun, and much of it, including food and fossil fuels, is the result of plant-based photosynthesis, which converts sunlight, water, and carbon dioxide into oxygen and sugars. will be The first chemical step in photosynthesis occurs in chlorophyll, which gives leaves their green color. This step is effectively a hydrosplitting operation that splits H.₂O becomes positively charged hydrogen ions with oxygen released into the air (thanks, plants), driving the rest of the process and ultimately allowing plants to store energy in the form of carbohydrates.

Evolution has given photosynthesis an extraordinary talent. As humanity seeks to free itself from the harmful side effects of fossil fuels, researchers are working to replicate and even improve on this first step, leading some to develop artificial photosynthesis technology. is ultimately the cheapest way to produce green hydrogen for use as an energy storage medium.

“Ultimately, we believe artificial photosynthesis devices will be far more efficient than natural photosynthesis and offer a path to carbon neutrality,” said Zetian Mi, professor of electrical and computer engineering at the University of Michigan. says.

Mi and his team have published a paper. Nature about what they consider to be a giant leap forward in artificial photosynthesis. The team demonstrated a new photocatalytic water-splitting semiconductor that splits water with an efficiency of 9% using the broad spectrum of sunlight, including the infrared spectrum. A relatively affordable device that improves rather than degrades over time.

“Compared to some semiconductors that operate only at low light intensities, we have reduced the size of the semiconductor by more than 100 times,” said Peng Zhou, an electrical and computer engineering researcher and first author of the study. increase. “Hydrogen produced by our technology has the potential to be very cheap.”

This new technology uses concentrated sunlight. This is an option not available in many other artificial photosynthesis devices. Because high intensity light and high temperatures tend to cause them to fail. However, UMich semiconductors, announced by another team last year and made from indium gallium nitride nanostructures grown on silicon surfaces, not only withstand light and heat very well, but also show real hydrogen production efficiency over time. improve to

Where other systems aim to avoid heat, this device relies on heat. This semiconductor powers the process of breaking down water by absorbing higher frequency wavelengths of light and is placed in a chamber with flowing water. Heat the chamber to approximately 70 °C (158 °F) using low-frequency infrared light. This accelerates the water-splitting reaction and reduces the tendency of hydrogen and oxygen molecules to recombine before they become water molecules. collected separately.

The device achieved 9% efficiency in ideal lab tests with purified water. When transitioning to tap water, it achieved about 7%. An outdoor test simulating a large-scale photocatalytic water splitting system with widely varying natural sunlight also returned an efficiency of 6.2%.

These photocatalytic efficiency figures lag behind some of the photoelectrochemical devices we have reported, such as ANU’s cell with 17.6% and the Monash University device with a record-breaking 22%. However, these devices, which use solar cells to power electrochemical water splitting, appear to be more expensive by their nature. The U.S. Department of Energy’s ultimate technology goal for hydrogen production is 25% efficiency for photoelectrochemical systems and 10% efficiency for dual-bed photocatalytic systems. Both represent a competitive hydrogen cost of about US$2.10 (2.2 pounds) per kg calculated in 2011.

Perhaps most interesting is the fact that the UMich device’s 7% efficiency figure for tap water also holds true for seawater decomposition. Freshwater is far from an infinite resource. Already highly scarce in many regions, it is widely expected to become even more scarce and valuable in the coming decades. A photocatalytic device that can do so could be a real game changer in the decarbonization era.

The team says it is working to improve the efficiency of further research and the purity of the hydrogen produced, but some of the intellectual property developed here will be owned by UMich spin-out company NS Nanotech. and NX Fuels.

“The materials we use can also be produced on a large scale with gallium nitride and silicon, allowing us to leverage our current infrastructure to produce low-cost, green hydrogen in the future.” Mr Mi says.

As always, it is commercial viability that will determine the fate of this device. The fuel itself must also be cost competitive. This method relies on rare metals such as gallium and indium, but the small size of the semiconductors required reduces the cost here significantly. I’m looking forward to seeing how it stacks up for industrial use.

Research results published in a journal Nature.

Watch the video below.

Source: University of Michigan