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Solar Water Splitting

The photoelectrochemical generation of hydrogen from water and sunlight utilizing semiconductor devices is a promising and elegant means to store renewable energy. The chemical energy of the hydrogen can be used to generate power either via combustion or in a fuel cell. Alternatively, it can be refined further to liquid hydrocarbons. To split water efficiently into its components hydrogen and oxygen the semiconductor photoelectrode has to meet several requirements:

  1. A high quantum efficiency to utilize the solar spectrum efficiently for the generation of charge carriers;
  2. The generation of a photovoltage at the working point of approx. 1.7 V to sustain the hydrogen and oxygen evolution reactions and to account for additional losses (overpotentials).
  3. Electrochemical stability in a harsh and corrosive environment;
  4. Fast kinetics of the charge transfer at the solid/liquid junction to inhibit unintended side reactions (catalysis).

For this purpose, particularly designed multijunction solar cells on the basis of crystalline, microcrystalline, and amorphous silicon were developed and characterized at the IEK-5. Furthermore, the chemical and electronic surface structure of the solar cells was manipulated by protective coatings and catalysts in order to minimize losses and corrosion damage. The aim of the ongoing research is to enhance the solar-to-hydrogen efficiency of the integrated photoelectrochemical devices and to reduce material and production costs to an economically competitive level.

water splitting

Fig. 1. Schematic energy band diagram and layer sequence of a photoelectrochemical water splitting assembly. The integrated device consists of a silicon multijunction solar cell, a catalyst for the hydrogen evolution reaction (HER) at the solid/liquid junction, an aqueous electrolyte, and a catalytically active anode for the oxygen evolution reaction (OER). Upon illumination, the solar cell generates a photovoltage > ∆E = 1.23 V that is sufficient to both drive the HER and the OER, and to compensate voltage losses (ηHER und ηOER).

Funding:

  1. Priority Programme 1613 of the Deutschen Forschungs¬gemein¬schaft ("Regenerativ erzeugte Brennstoffe durch lichtgetriebene Wasserspaltung: Aufklärung der Elementarprozesse und Umsetzungsperspektiven auf technologische Konzepte", http://www.solarh2.tu-darmstadt.de/)
  2. Sustainable Hydrogen – SusHy, joint project funded by the German Federal Ministry of Education and Research (http://www.matressource.de/projekte/sushy/)

Literature:

F. Urbain, V. Smirnov, J.-P. Becker, U. Rau, F. Finger, J. Ziegler, B. Kaiser, and W. Jaegermann, J. Mater. Res., 2014, 29, 2605–2614.

F. Urbain, K. Wilken, V. Smirnov, O. Astakhov, A. Lambertz, J.-P. Becker, U. Rau, J. Ziegler, B. Kaiser, W. Jaegermann, and F. Finger, Int. J. Photoenergy, 2014, 2014, 1–10.

F. Urbain, V. Smirnov, J.-P. Becker, U. Rau, J. Ziegler, B. Kaiser, W. Jaegermann, and F. Finger, Sol. Energy Mater. Sol. Cells, 2015, 140, 275–280.

J. Ziegler, B. Kaiser, W. Jaegermann, F. Urbain, J.-P. Becker, V. Smirnov, and F. Finger, ChemPhysChem, 2014, 15, 4026–4031.

Multijunction Si photocathodes with tunable photovoltages from 2.0 V to 2.8 V for light induced water splitting
Félix Urbain, Vladimir Smirnov, Jan-Philipp Becker, Andreas Lambertz, Florent Yang, Jürgen Ziegler, Bernhard Kaiser, Wolfram Jaegermann, Uwe Rau, Friedhelm Finger Energy Environ. Sci., 2015 (first published online 05 Oct 2015), DOI: 10.1039/C5EE02393A

Contact:

Dr. Jan Philipp Becker

Felix Urbain

Dr. Vladimir Smirnov

Dr. Friedhelm Finger

Prof. Dr. Uwe Rau


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