Structural effects on water molecules on the low index planes of Pt modified with alkyl amines and the correlation with the activity of the oxygen reduction reaction

Our previous study shows that the activity of the cathodic reaction (oxygen reduction reaction: ORR) of fuel cells is increased markedly by the adsorption of alkyl amines on a well-defined Pt(111) electrode. On Pt(100) and Pt (110) electrodes, however, the adsorption of alkyl amines deactivates the ORR significantly. We have studied the possible factors of the activation and deactivation by infrared (IR) reflection absorption spectroscopy. An IR band of icelike water is found on all the electrodes after the modification with alkyl amines. The band of the icelike water on Pt(111) is located at a higher wavenumber than those on Pt(100) and Pt(110). These findings indicate that the cluster size of icelike water on Pt(111) is smaller than those on Pt(100) and Pt(110). The cluster size of the ice correlates with the ORR activity on Pt electrodes.