Infrared reflection absorption spectroscopy of the adsorbed structures of a protic ionic liquid on the low-index planes of Pt

Modification with a protonic ionic liquid containing [7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD)] [bis(pentafluoroethanesulfonyl)imide (beti)] enhanced the activities of the cathodic reactions of fuel cells (oxy-gen reduction reactions (ORR)) on Pt(1 1 1) and Pt(1 1 0), whereas it deactivated Pt(1 0 0). To elucidate the reaction mechanism, the ORR inhibiting species (PtOH) and the adsorption geometries of [MTBD][beti] on the low-index planes of Pt were studied using infrared reflection absorption spectroscopy (IRRAS). After mod-ification with [MTBD][beti], the intensity of the bands representing PtOH decreased in the spectra of all the low-index planes. The adsorbed MTBD was tilted toward Pt(1 1 1) and vertically adsorbed onto Pt(1 1 0). On Pt(1 0 0), MTBD was adsorbed with its molecular plane parallel to the surface. Bands representing adsorbed beti were observed in the spectra of all surfaces. The increased ORR activities of the Pt(1 1 1) and Pt(1 1 0) surfaces were attributed to the decrease in PtOH formation after [MTBD][beti] modification and the low steric hin-drance of the vertically adsorbed MTBD. Meanwhile, the deactivation of Pt(1 0 0) can be attributed to the increased steric hindrance of the parallel adsorption geometry of MTBD.