Electrodepositing Pt on a Nafion-bonded carbon electrode as a catalyzed electrode for oxygen reduction reaction

The research aims to increase the utilization of platinum (Pt) catalysts and thus to lower the catalyst loadings in the electrode for oxygen reduction reaction (ORR). The electrodeposition of Pt was performed on a rotation disk electrode (RDE) of glass carbon (GC), on which a layer of Nafion-bonded carbon of Vulcan XC 72R was dispersed in advance. The behaviors of Pt RDE and GC RDE in an aqueous solution containing HCl and H₂PtCl₆ were firstly studied. It was found that Pt deposition could be achieved if the electrode potential is controlled below −0.20 V versus (saturated-potassium-chloride silver chloride electrode) SSCE. However, quite a high overpotential is necessary if a quick and apparent deposition were required. Unfortunately, at a high overpotential, the hydrogen evolution would be unavoidable and even accelerated by the formation of nanometer size of Pt particles on the RDE. It was found that it is futile to increase platinum deposits just through extending the deposition time. It was also found that too large deposition current is not helpful for increase of platinum deposition because most of the current was consumed on hydrogen evolution in this case. It has been confirmed that it is conducive to richen Pt ions, present in the form of anionic complex in solution, onto the working electrode to be deposited. It is also helpful to eliminate the hydrogen bubbles formed on the working electrode, i.e., uncatalyzed carbon electrode (UCE), by imposing a positive current on the UCE for a length of time in advance of each cathodic deposition. The potential changes during deposition were recorded. Cyclic voltammograms (CV) of electrodes in 0.5 M H₂SO₄ before and after the deposition were used to assess loading of metal catalysts in a wide range of potential from −0.20 to 1.1 V versus SSCE. The results have shown that the performance of such an electrode with loadings estimated to be 50 μg Pt/cm² is much better than those of a conventional electrode with loadings of 100 μg Pt/cm².