Novel Photoelectrodes and Noble Metal-Free Catalysts for Light-Driven Water Electrolysis

The generation of fuels from sunlight and water is considered as a task of paramount importance for a sustainable energy supply in the future. Decomposition of water by a photoelectrochemical process is a possibility to harvest solar energy in the form of hydrogen in a large scale. For this purpose, a membrane can be used which -when immersed in an aqueous electrolyte and illuminated by sunlight- will be able to split water into hydrogen and oxygen. Such a device is frequently addressed as artificial leaf. From an eco­nomic and environmental point of view this device should comprise of cheap, abundant and non-toxic elements featuring a Solar-to-Hydro­gen (STH) efficiency > 10% and generating hydrogen at a price of ~3 €/kg H₂.

In our lab two approaches have been pursued to realize artificial leaf type structures:

o  triple junction thin film a-Si/µc-Si solar cells in superstrate geometry with integrated catalysts [1],

o  tandem junction solar cells combined with novel semiconducting ternary metal oxide anodes [2].

As photoanode materials Fe₂WO₆ and BiVO₄ are under investigation. Their performances have shown considerable improvement with respect to their photovoltage and their photocurrent densities when synthesized using sol-gel and spray pyrolysis. To lower the costs of the device, platinum was replaced by carbon supported MoS₂ nanoparticles as hydrogen evolving catalyst. Deposited as a blend with PEDOT:PSS on the backside of the solar cell, a SHE yield of 3.7% was achieved. RuO₂ was replaced by manganese and cobalt oxide thin films, respectively.

References:

[1]      Diana Stellmach, Peter Bogdanoff, Onno Gabriel, Bernd Stannowski, Rutger Schlatmann,

          Roel van de Krol, Sebastian Fiechter; FORMATEX 2013, 880-886.

[2]      Fatwa F. Abdi, Lihao Han, Arno H.M. Smets, Miro Zeman, Bernard Dam, Roel van de Krol,          NATURE COMM. 2013, 4: 2195, DOI: 10.1038/ncomms3195.

[3]      Eric L. Miller, Björn Marsen, Daniela Paluselli, Richard Rocheleau, Electrochemical and Solid-      State Letters 2005, 8: A247.