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Inexpensive Hydrogen Storage Devised for Solar Energy

Hydrogen fuel cell

Hydrogen fuel cell being tested at the port of Honolulu, Hawaii (Sandia National Lab)

25 August 2016. An engineering team in Switzerland designed a system for producing hydrogen from solar power with abundant available materials, providing an inexpensive and feasible energy storage method. Researchers from Ecole polytechnique fédérale de Lausanne or EPFL and Swiss Center for Electronics and Microtechnology, or CSEM, in Neuchâtel described their system in the 13 August issue of the Journal of the Electrochemical Society (paid subscription required).

The authors, from the Photovoltaics and Thin Film Electronics Laboratory, a joint EPFL-CSEM facility led by engineering professor Christophe Ballif, are seeking to solve a long-standing need for inexpensive storage of intermittent renewable power sources, such as solar and wind energy. Producing hydrogen with electrolysis from solar energy offers a way to store the power for use in hydrogen fuel cells. Current electrolysis methods, however,  require catalysts made from rare earth materials, making them too expensive for widespread use.

The solution devised by Ballif and colleagues proposes increasing the output of solar power produced, as well as redesigning a method for electrolysis that removed the need for expensive catalysts. In both cases, the researchers aimed at using available solutions and materials, emphasizing practicality and affordability.

To generate power, the team combine crystalline-silicon solar cells in alternating layers with amorphous silicon. Crystalline silicon is the most common solar cell in commercial use with high efficiency and long lifetime. Amorphous silicon is the material used in thin-film solar cells, which are inexpensive to produce, but have lower efficiency, and are used to power devices like watches and calculators. The alternating layers of two different materials produce a heterojunction design that combine the advantages of both materials to boost energy output.

The higher-power configuration enables the engineers to use only three solar cells to produce enough power for the electrolysis unit. The electrolysis unit splits water into its hydrogen and oxygen elements, but these devices usually require intensive inputs of energy from existing power grids. In this case, power from the three solar cells produces sufficient energy, which the team estimates would have needed four conventional crystalline-silicon solar cells.

Another drawback of electrolysis units is the high cost of conventional rare earth catalysts that raise the cost of this process, making it infeasible for many applications. For their device, the EPFL-CSEM team uses microstructured nickel catalysts in their proton exchange membrane electrolysis unit.

Tests show the system can convert solar energy to hydrogen at 14.2 percent efficiency, which the authors call unprecedented, and ran for 100 hours, surpassing previous efforts for stability, performance, lifespan, and cost efficiency. In an EPFL statement, Ballif says the system “would allow the generation and storage of enough hydrogen to power a fuel cell car over 10,000 km every year.”

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