Tiva Sharifi, Hans-Martin Berends, Johannes Messinger, Thomas Wagberg: Novel hierarchical nanostructure based on nitrogen doped carbon nanotubes and maghemite for electrochemical water oxidation

We have developed a new type of nanostructured anode material and studied its performance for catalyzing the oxygen evolving half reaction (OER) associated with electrolysis of water. The hybrid material, comprising a hierarchical iron oxide/nitrogen doped carbon nanotube structure, was used as a direct electrode for electrochemical water splitting without any further modification. The electrode is prepared in a bottom up process by CVD growth of NCNTs on the fibers of a conductive carbon paper, followed by a hydrothermal growth of iron hydroxide nanorods on the surface of the nitrogen doped carbon nanotubes (NCNTs). The iron hydroxide nanorods are then transformed to maghemite. The resulting hierarchical nanostructure exhibit large surface area, and ideal attachment of maghemite nanorods to NCNTs which are further well attached to the carbon paper. The hybrid electrode demonstrates very good electrochemical water oxidation activities in 0.1 M KOH. For a current density of 1 mA cm-2 (geometric surface) an overpotential of only 392 mV is needed. By combining electrochemical water oxidation with isotope ratio mass spectrometry we show that only water is oxidized.