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Among the various fuel cell electrocatalysts studied for the cathodic oxygen reduction reaction and anodic fuel oxidation reaction, platinum-based materials have attracted much attention over the past decade because of their high activity for both reactions. However, Pt-based catalysts suffer from several problems, such as their high cost, low abundance, and low long-term stability. Bimetallic Pt-based nanostructures with a core–shell structure have been considered as candidate cathode catalysts for polymer electrolyte fuel cells. In this study, a Pt/Pd/C catalyst was successfully synthesized by the hydrogen-sacrificial protection method to improve the performance of a membrane electrode assembly. Furthermore, on the basis of electrochemical spectroscopic findings, it was shown that control of the surface structure is an effective strategy to improve the cell performance of the Pt/Pd/C catalyst.

Overpotential for oxygen reduction reaction (ORR) at Au electrode is reported to be reduced by 0.27 V by the modification with boron nitride nanosheet (BNNS) but oxygen is reduced only to H2O2 by 2-electron process at Au electrode. Here we demonstrate that the decoration of BNNS with gold nanoparticles (AuNP) not only reduces the overpotential for ORR further by ca. 50 mV, but also opens a 4-electron reduction route to water. Both rotating disk electrode experiments with Koutecky–Levich analysis and rotating ring disk electrode measurements show that more than 50% of oxygen is reduced to water via 4-electron process at Au–BNNS/Au electrode while less than 20 and 10% of oxygen are reduced to water at the BNNS/Au and bare Au electrodes, respectively. Theoretical analysis of free energy profiles for ORR at the BN monolayer with and without Au8 cluster placed on Au(111) shows significant stabilization of adsorbed oxygen atom by the Au8 cluster, opening a 4-electron reduction pathway. Keywords: Fuel cell, Boron nitride, Oxygen reduction reaction, Gold nanoparticle, Gold electrode

Spectroelectrochemical measurements at indium tin oxide (ITO) electrode modified with viologen monolayer showed two redox peaks corresponding to viologen dication/radical cation (V2+/V+·) and viologen radical cation/neutral form (V+·/V0) in cyclic voltammogram (CV), and stable spectra corresponding to radical cation (V+·) and neutral form (V0) of viologen at potentials between V2+/V+· and V+·/V0 redox peaks and those more negative than V+·/V0 redox peak, respectively. On the other hand, at viologen monolayer modified ITO electrode with Pt complex confined within the monolayer by ion exchange reaction, no redox peaks but large current due to hydrogen evolution reaction (HER) were observed in CV and no absorption peaks corresponding to V+· or V0 were observed in the UV/visible spectra obtained during the potential scan. Time-resolved spectroelectrochemical measurements, however, showed that V+· is formed upon the potential step to the potentials more negative than V2+/V+· redox potential and disappeared within ca. 1 ms, showing that electron is transferred from ITO electrode to proton to form hydrogen via viologen moiety and Pt complex. Keywords: Spectroelectrochemistry, Viologen monolayer, Confined molecular catalyst, Hydrogen evolution reaction

Potential dependent adsorption of oxygen on a gold electrode surface was proved by electrochemical quartz crystal microbalance. The adsorption of oxygen was started to be observed at potentials more positive than the potential where ORR started to take place and the amount of adsorbed oxygen increased and reached the saturated value as potential became more negative. The critical potentials, at which oxygen adsorption was started to be observed, were dependent on anions in solution. The adsorption of oxygen started at more positive potential in perchlorate solution than in sulfate solution, showing the inhibition of the adsorption of oxygen by strongly adsorbed sulfate anion. Keywords: Au electrode, Oxygen adsorption, Electrochemical quartz crystal microbalance

Humidity-dependent water structures at the interfaces between perfluorosulfonate ionomer (PFSI = Nafion) thin film and Pt and HOPG were determined at room temperature by using sum frequency generation (SFG) spectroscopy. At low relative humidity (RH) condition, a peak centered around 3600 cm−1 corresponding to water molecules interacting with sulfonic acid group in proton channel at PFSI surface was observed at both interfaces. However, while this peak increased with RH at PFSI/Pt interface, that at PFSI/HOPG did not increase. These results suggest that the structure of water molecules, especially the water molecules at the proton channel of PFSI surface, is strongly affected by the interaction of PFSI with Pt and HOPG. Keywords: Fuel cell, PEM, Perfluorosulfonated ionomer, Interfacial water, Sum frequency generation spectroscopy