Hydrogen From Sunlight

A new standard for green hydrogen technology

sunflower with hydrogen molecules
Illustration by Alex Eben Meyer

Fall 2023
Silvia Cernea Clark

Rice engineers have found a way to turn sunlight into hydrogen with record-breaking efficiency with a single durable, cost-effective and scalable device that uses solar energy and next-generation halide perovskite semiconductors to split water into oxygen and hydrogen.

The new technology is a significant step forward for clean energy and could serve as a platform for a wide range of chemical reactions that use solar-harvested electricity to convert materials into fuels.

The lab of chemical and biomolecular engineer Aditya Mohite built the integrated photoreactor using an anticorrosion barrier that insulates the semiconductors from water without impeding the transfer of electrons.
According to a study published in Nature Communications, the device achieved a 20.8% solar-to-hydrogen conversion efficiency.

“Using sunlight as an energy source to manufacture chemicals is one of the largest hurdles to a clean energy economy,” says Austin Fehr, a doctoral student and one of the study’s lead authors. “Our goal is to build economically feasible platforms that can generate solar-derived fuels. Here, we designed a system that absorbs light and completes electrochemical water-splitting chemistry on its surface.”

The device is known as a photoelectrochemical cell because the absorption of light, its conversion into electricity, and the use of the electricity to power a chemical reaction all occur in the same device. Until now, using photoelectrochemical technology to produce green hydrogen was hampered by low efficiencies and the high cost of semiconductors.

“All devices of this type produce green hydrogen using only sunlight and water, but ours is exceptional because it has record-breaking efficiency and it uses a semiconductor that is very cheap,” Fehr says.

The Mohite lab and its collaborators created the device by turning their existing solar cell into a reactor. The challenge they had to overcome was that halide perovskite semiconductors are extremely unstable in water and the coatings used to insulate them ended up either disrupting their function or damaging them.

“Over the last two years, we’ve gone back and forth trying different materials and techniques,” says Michael Wong, a Rice chemical engineer and co-author on the study. After lengthy trials failed to yield the desired result, the researchers finally came across a winning solution.

“Our key insight was that you needed two layers to the barrier: one to block the water and one to make good electrical contact between the perovskite layers and the protective layer,” Fehr says. The researchers showed that their barrier design worked for different reactions and with different semiconductors, making it applicable across many systems.

“With further improvements to stability and scale, this technology could open up the hydrogen economy and change the way humans make things from fossil fuel to solar fuel,” Fehr says. 

Aditya Mohite is faculty director of the Rice Engineering Initiative for Energy Transition and Sustainability and associate professor of chemical and biomolecular engineering, electrical and computer engineering, and materials science and nanoengineering. Michael Wong is the Tina and Sunit Patel Professor in Molecular Nanotechnology; chair and professor of chemical and biomolecular engineering; and professor of chemistry, materials science and nanoengineering, and civil and environmental engineering.