Three Fraunhofer institutes have joined forces to develop a modular and flexible solution for direct solar hydrogen generation
While the hydrogen industry continues to invest in “traditional” electrolysis devices, some industry research is trying a second approach for the generation of clean H2. We are talking about the photoelectrochemical split of water (or “PEC”), a branch that has attracted much interest in recent years. The latest progress in this segment comes from the Fraunhofer Institute, the creator of a mini PEC reactor for the production of solar hydrogen.
The developed system is a small self-sufficient tandem module, reliable and capable of producing the vector directly from water by exposure to light alone. In other words, without the need for an external source of electricity. To better understand the scope of innovation, it is necessary to understand how photoelectrochemical cells work.
How do PEC reactors work?
PEC reactors use semiconductor materials to convert solar energy directly into chemical energy. These materials look similar to those used in photovoltaics, with the only big difference being that they are constantly immersed in a water-based electrolyte. The units can be manufactured as electrode systems similar to photovoltaic panels or as suspended particle systems.
In detail, the photoelectrochemical process involves three main stages:
- the generation of charge carriers (electron-spaced pairs) as a result of the absorption of light by a semiconductor with an appropriate bandgap;
- the separation of the charge and its migration to the semiconductor-electrolyte interface;
- the surface reactions of water reduction and oxidation.
The advantage of this approach? On paper, photoelectrochemical splitting offers the potential for high conversion efficiency at low operating temperatures using low-cost materials. In reality, however, technology has to overcome several challenges. Starting with improved solar absorption and longer material life. PEC rectors’ two most significant disadvantages for producing solar hydrogen are the lack of long-term stability of some photocatalysts (due to water corrosion) and the criticality of specific coating and manufacturing processes.
The Fraunhofer Institute’s PEC mini reactor
In the Neo-PEC research project, researchers from three Fraunhofer institutes joined forces and expertise to develop a modular solution allowing flexible hydrogen generation directly from water and sunlight.
The result was a PEC tandem module made by coating a glass plate with semiconductor materials on both sides. “When sunlight hits the glass, one side of the module absorbs short wavelength light. At the same time, long wavelength light passes through the upper layer of the glass and is absorbed on the opposite side. The module releases hydrogen on the opposite side or cathode and oxygen on the upper side, which is the anode side,” explains a press note.
To this result, the scientists studied and developed several optimized photoelectrochemical materials and application techniques to sprinkle very thin semiconductor layers onto the glass. With an active area of half a square meter, the Fraunhofer PEC mini reactor is a modular, flexible and reliable system.
“As for the size of the tandem cell – explains Dr. Arno Görne of Fraunhofer IKTS – we are limited by the fact that our module divides water directly, but electricity is also necessary to pass from one side to the other to this goal. As the area of the module increases, the increasing resistance hurts the system. In the current state of affairs, the existing format has proved optimal. It is stable, robust and significantly larger than any comparable solution.”
But how much hydrogen does the PEC mini reactor produce? According to scientists’ estimates, the system can generate more than 30 kilograms of vector per year on 100 square meters.
