MNCL Highlights

The abundance, high energy density, and flexibility of its use, make hydrogen a perfect fuel for future applications. However, despite being abundant, hydrogen does not exist in its elemental form on the earth, and it must be extracted starting from other resources, like hydrocarbons, or, being more environmental friendly, from the most abundant source of hydrogen we have on the earth: water.

The water molecule is composed by one atom of oxygen bound to two atoms of hydrogen, hence, in order to obtain pure hydrogen, one has to break the water molecule into the two elements: 2H₂O -> 2H₂+O₂. In an electrochemical reaction, breaking this molecule requires applying a certain potential between two plates (anode and cathode) in a aqueous solution: the potential between these two plates determines the amount of energy required in order to initiate the water splitting. In the ideal condition, this potential is E₀=1.23 V, however, due to over-potentials associated with cathode and anode reactions, in commercial devices the operating potential is much higher than that (in the order of 1.8-2 V).
A properly designed combinations of materials for anode and cathode can drop significantly the over-potential needed, however, usually, the most effective materials are the expensive noble metals Pt, or Ir, and Ru oxides. Another effective approach is to increase the specific area of the electrodes, and in this paper we have shown that using carbon nanotubes as template to deposit relatively inexpensive Pd, Co, or Ni oxides it is possible to reach state of the art electrochemical water splitting efficiency.

Multi-wall carbon nanotubes (CNTs) are grown by Chemical Vapour Deposition onto Si wafer, and then metals were thermally evaporated on them. Subsequent exposure to the air oxidised almost completely Co and Ni as shown by XPS. The CNTs diameter increased from 25 to 35 nm upon metal deposition as indicate by SEM images.