Hydrogen is a cornerstone of the energy transition. To harvest hydrogen from solar energy, researchers at LMU have developed new high-performance nanostructures. This material sets a world record for green hydrogen production using solar energy.
When Emiliano Cortés goes in search of sunlight, he doesn't use giant reflectors or sweeping solar farms. On the contrary, the LMU professor of experimental physics and energy conversion devotes himself to studying the nanoscale universe. "Where the high-energy particles (photons) in sunlight meet the atomic structure is where our research starts," Cortez said. "We are working on material solutions to capture and utilize solar energy more efficiently."
His findings have great potential as they could enable new types of solar cells and photocatalysts. The industry has high hopes for photocatalysts because they can harness light energy for chemical reactions - bypassing the need to generate electricity. But Cortes knew that harnessing sunlight presented a major challenge that solar cells also had to deal with: "Sunlight is 'diluted' when it reaches the Earth, so the energy per unit area is relatively low." Solar panels make up for this by covering a large area.
However, Cortés is arguably approaching the problem from another direction: together with his team at the Nano-Institute of the Bavarian State University, funded by the Cluster of Excellence for Electronic Conversion, Solar Technologies go Hybrid (an initiative of the Ministry of Science and Arts of the Bavarian State Government) and the European Research Council, among others, he is developing so-called plasmonic nanostructures that can be used to concentrate solar energy.
Recently, Cortes, together with Dr. Matthias Herland of the Fritz-Haber Institute in Berlin and partners at the Freie Universität Berlin and the University of Hamburg, published an article in the journal Nature Catalysis describing a two-dimensional supercrystal that can generate hydrogen from formic acid with the help of sunlight.
"In fact, this material is so good that it holds the world record for the production of hydrogen from sunlight," Cortes noted. "This is good news both for the production of photocatalysts and for hydrogen as an energy carrier, as they play an important role in a successful energy transition."
For their supercrystals, Cortés and Herrán used two different nanoscale metals, Herrán explains: "We first made particles 10-200 nanometers out of a plasmonic metal - in our case gold. At this scale, protic metals (also silver, copper, aluminum and magnesium) experience a special phenomenon: visible light interacts very strongly with the metal's electrons, causing them to resonate."
This means that the electrons collectively move quickly from one side of the nanoparticle to the other, forming a kind of tiny magnet. Experts call this the dipole moment. "This is a strong change in the incoming light, so it then interacts more strongly with the metal nanoparticles," Cortes explained. "Similarly, we can think of this process as a superlens concentrating energy. Our nanomaterials do this at the molecular scale. This allows the nanoparticles to capture more sunlight and convert it into high-energy electrons. These electrons, in turn, help drive chemical reactions."
But how can this energy be harnessed? To this end, LMU scientists collaborated with researchers from the University of Hamburg. They arranged the gold particles on the surface in an orderly manner based on the principle of self-organization. The particles must be in close proximity, but not touching, to maximize light-matter interaction.
Researchers at TU Berlin, in collaboration with a research group at Freie Universität Berlin, studied the optical properties of this material and found that the absorption of light increased many times. Arrays of gold nanoparticles focus incoming light extremely efficiently, creating highly localized strong electric fields known as hot spots.
These hot spots formed between gold particles, which gave Cortes and Elam the idea of placing platinum nanoparticles, a classic powerful catalyst material, in the gaps between the hot spots. The Hamburg research team has done it again.
"Platinum is not the material of choice for photocatalysis because it absorbs sunlight very poorly. However, we can force platinum in hot spots to enhance this otherwise poor absorption and use light energy to promote a chemical reaction. In our case, the reaction converts formic acid into hydrogen gas," explains Herrán.
This photocatalytic material produces 139 millimoles of hydrogen from formic acid per hour per gram of catalyst and currently holds the world record for hydrogen production using sunlight.
Currently, hydrogen is produced primarily from fossil fuels, primarily natural gas. In an effort to shift to more sustainable production methods, research teams around the world are investigating technologies that use alternative feedstocks, including formic acid, ammonia and water. Research focus also includes the development of photocatalytic reactors suitable for large-scale production. "Smart material solutions like ours are an important cornerstone of technological success," mention the two researchers. "By combining plasmonic and catalytic metals, we are advancing the development of powerful photocatalysts for industrial applications. This is a new way to harness sunlight, offering the potential for other reactions such as converting carbon dioxide into usable substances."
The two researchers have applied for a patent for their material development.
Compiled from /ScitechDaily