Self-healing semiconductor withstands light equal to 160 suns to produce hydrogen

This is a major breakthrough as it is nearly ten times more efficient than previous solar water-splitting experiments.
Baba Tamim
A doctoral student in electrical and computer engineering, operates the molecular beam epitaxy device in which he grew the semiconductor that harnesses sunlight to split water.
A doctoral student in electrical and computer engineering, operates the molecular beam epitaxy device in which he grew the semiconductor that harnesses sunlight to split water.

Brenda Ahearn/University of Michigan 

A new type of solar panel has achieved nine percent efficiency in converting water into hydrogen and oxygen through a process known as artificial photosynthesis

This is a major breakthrough as it is nearly ten times more efficient than previous solar water-splitting experiments, according to a press release by the University of Michigan published on Wednesday. 

"In the end, we believe that artificial photosynthesis devices will be much more efficient than natural photosynthesis, which will provide a path toward carbon neutrality," said Zetian Mi, U-M professor of electrical and computer engineering.

The team behind the study, led by Mi, was able to shrink the size of the semiconductor, typically the most expensive part of the device, and developed a self-healing semiconductor that can withstand concentrated light equivalent to 160 suns. 

Self-healing semiconductor withstands light equal to 160 suns to produce hydrogen
Peng Zhou uses a large lens to concentrate sunlight onto the water-splitting catalyst. Outdoors, the device was ten times more efficient than previous efforts at solar water splitting.

This technology has the potential to significantly decrease the cost of sustainable hydrogen, which is needed for many chemical processes and can be used as a standalone fuel or as a component in sustainable fuels made with recycled carbon dioxide. 

Cheap hydrogen

The exceptional outcome is the product of two developments. The first is the capacity to focus sunlight without damaging the semiconductor used to capture it.

The second method involves splitting water using the higher energy portion of the sun spectrum and heating the reaction by using the lower energy portion of the spectrum. 

A semiconductor catalyst, which powers the magic, becomes better with usage and withstands the deterioration that typically occurs when using sunlight to fuel chemical reactions, claims the press release. 

Self-healing semiconductor withstands light equal to 160 suns to produce hydrogen
A close-up of the panel with the semiconductor catalyst and water inside. Bubbles of hydrogen and oxygen travel up the slope to be separated in the canister.

"We reduced the size of the semiconductor by more than 100 times compared to some semiconductors only working at low light intensity," said Peng Zhou, the first author of the study, a U-M research fellow in electrical and computer engineering. 

"Hydrogen produced by our technology could be very cheap."

The semiconductor can survive high temperatures that are punitive to computer chips in addition to enduring high light intensities.

More heat promotes the hydrogen and oxygen to stay apart rather than re-forming their bonds and splitting the water, which speeds up the water-splitting process. The team was able to gather extra hydrogen because of these.

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The catalyst

On a silicon surface, nanostructures of indium gallium nitride were grown to form the catalyst.

The light is captured by the semiconductor wafer and transformed into free electrons and holes, which are the positively charged spaces left behind when electrons are released by the light.

Nanoscale metal balls that are 1/2000th of a millimeter across are scattered throughout the nanostructures and make use of the electrons and holes in the environment to drive the reaction.

Self-healing semiconductor withstands light equal to 160 suns to produce hydrogen
Peng Zhou, right, and Yuyang Pan, first year PhD student, observe the machine in which the semiconductor nanowires are grown.

The temperature is maintained at a toasty 75 degrees Celsius, or 167 degrees Fahrenheit, by a straightforward insulating layer on top of the screen. This temperature is heated enough to aid in promoting the reaction while remaining cool enough for the semiconductor catalyst to function effectively. 

The effectiveness of converting solar energy into hydrogen fuel in the outside experiment, which had less consistent temperatures and sunlight, was 6.1 percent. However, the system's efficiency indoors was nine percent.

The team plans to continue improving the efficiency of the technology and to produce ultrahigh-purity hydrogen that can be directly used in fuel cells.

The study was first published in Nature journal on January 04, 2022.

Study abstract:

Production of hydrogen fuel from sunlight and water, two of the most abundant natural resources on Earth, offers one of the most promising pathways for carbon neutrality. Some solar hydrogen production approaches, for example, photoelectrochemical water splitting, often require corrosive electrolyte, limiting their performance stability and environmental sustainability. Alternatively, clean hydrogen can be produced directly from sunlight and water by photocatalytic water splitting. The solar-to-hydrogen (STH) efficiency of photocatalytic water splitting, however, has remained very low. Here we have developed a strategy to achieve a high STH efficiency of 9.2 percent using pure water, concentrated solar light and an indium gallium nitride photocatalyst. The success of this strategy originates from the synergistic effects of promoting forward hydrogen–oxygen evolution and inhibiting the reverse hydrogen–oxygen recombination by operating at an optimal reaction temperature (about 70 degrees Celsius), which can be directly achieved by harvesting the previously wasted infrared light in sunlight. Moreover, this temperature-dependent strategy also leads to an STH efficiency of about 7 percent from widely available tap water and sea water and an STH efficiency of 6.2 percent in a large-scale photocatalytic water-splitting system with a natural solar light capacity of 257 watts. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar light and water, overcoming the efficiency bottleneck of solar hydrogen production.