A Powerful New Solar Cell Produces Both Hydrogen Fuel and Electrical Power
"It's a free lunch."
In a field that’s essentially water-bending meets renewable energy, researchers successfully harnessed photosynthesis to split water to produce hydrogen fuel. Splitting H2O at its molecular level is something scientists have been doing for over 200 years, and could hold the tantalizing key to an emission-free hydrogen economy — if only it could be scaled up.
Fortunately we’ve made progress in bringing down the costs, and researchers have also gotten close to mastering the art of artificial photosynthesis, but low efficiency keeps the process from dreaming big, at least until now.
That’s according to a new a paper released Monday in Nature Materials by the Lawrence Berkeley National Laboratory which presents a simple, elegant hybrid solution that bypasses the current bottleneck for photoelectrochemical cells.
“It’s a free lunch,” lead researcher Gideon Segev tells Inverse.
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Photoelectrochemical Cells Are Science’s Water and Light Bending
Photoelectrochemical cells are usually a stack of different materials that absorb light. Each layer absorbs a different wavelength, building up electric voltages that culminate in a voltage strong enough to split water into oxygen and hydrogen fuel.
This, naturally, sounds like a good use of sunlight. But even when the silicon solar cells work well, issues arise when other materials in the stack can’t match its performance, letting energy go to waste.
“You need two materials, ideally silicon and on top of that some other material that would absorb the more energetic part of the material,” Segev says. “The bottleneck in the system [is] and will always be the other material, so research is mostly in making the other material better.”
How Electrons Present an Elegant Solution
With so much research focusing on that “other material,” Segev and his team decided to take a step back, looking at how they could make the entire system better. And they realized there is an entire other energy source waiting to be tapped: electrons.
“You have this semiconductor material and it absorbs light. Light can be thought of as a particle. So when a photon is absorbed, it gives its energy to the electron, in its excited state,” Segev explains. “You can say the electron has a specific time before it loses its energy, the energy the photons gave it.
Previous research simply allowed the cells to heat up and let the energy dissipate. Segev’s team literally gave the electron’s energy an outlet. While most water-splitting devices usually have two sides, one to produce solar fuels and the other to release the current, this new prototype has two outlets in the back, one for solar fuel generation and one for electrical power. Two types of energy, one cell.
The prototype — which took 19 infuriating iterations over the course of a year to create — has dramatic potential the efficiency rate of solar energy to hydrogen fuel from its current rate, 6.8 percent. With the ideal materials, the group calculated a potential increase to 20.2 percent, tripling the rate of conventional solar hydrogen cells.
Suddenly, solar-hydrogen fueling stations of the future don’t seem hopeless, though additional research is required before we can bring about a hydrogen powered utopia.
“If it would work efficiently and be cost competitive, maybe we can start talking about commercial or hydrogen fueling stations that are powered by the sun,” says Segev. “But I think this is all very premature at this stage, so we’re not at a point where we can talk about making this a technology people would see in their lives tomorrow morning.”
But Segev, we can dream.
Correction: A previous version of the story erroneously printed that the prototype achieved triple efficiency, while this remains a calculation. The story has been updated with additional comment from the study’s author.
