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Visualization of the oxygen partial pressures was carried out at the surface of a gas diffusion layer (GDL) for the first time together with the upper part of the gas-flow channel of the cathode of a running polymer electrolyte fuel cell (PEFC) using two different oxygen-sensitive luminescent dye films. The visualized distributions of the oxygen partial pressures at the GDL and the upper gas-flow channel during the PEFC operation were very different in a conventional test cell. The change in the distribution of the oxygen partial pressures was observed by changing the oxygen utilization, which should be connected with the reactive locations in the membrane-electrode assembly (MEA). A numerical calculation was carried out to understand the distributions of water and current density inside the MEA. The water distribution inside the MEA was confirmed to strongly affect the distributions of the current density and the oxygen /partial pressure.

Microscopic proton conductivity at surfaces of a hydrocarbon-type polymer electrolyte membrane of sulfonated poly(arylene ketone) block copolymers (SPK-bl-1) was investigated by current-sensing atomic force microscopy (CS-AFM) under a hydrogen atmosphere. The distributions of proton-conductive regions on the SPK-bl-1 membrane surfaces were different on two surface sides of the membrane: the substrate side and the air side after being cast on a poly(ethylene terephthalate) substrate. After a liquid-water treatment of the membrane at 60 °C, the surface morphology of both sides changed. The proton-conductive area and the “pseudo current density” increased especially on the substrate side, and the difference between two sides of the membrane became very small. The scanning transmission electron microscopy inside the membrane showed no structural change after the hot-water treatment, and the water uptake and conductivity of the membrane were also unchanged. This hot liquid-water treatment activating the membrane surfaces should be related to the conditioning processes of the membrane-electrode assemblies of polymer electrolyte fuel cells.

The R&D of highly active and durable cathode catalysts for the oxygen reduction reaction (ORR) is very important for polymer electrolyte fuel cells (PEFCs). Bimetallic alloys of Pt such as Pt-Co exhibit higher ORR activities than that of pure Pt.1 For polycrystalline Pt alloy electrodes, the kinetically-controlled area-specific current densities (jk ) for the ORR strongly depend on the bulk Co composition.2 It is essential to analyze the mechanism of the increased ORR activity at well-defined Pt-alloys by multilateral techniques. Recently, we have demonstrated the composition dependence of jk at a series of (111), (110), and (100) faces of Pt100−xCox single crystal electrodes, on which well-defined Pt-skin layers were formed by annealing in H2.3 The Pt-skin/Pt73Co27(111) electrode exhibited the highest jk value, which was about 27 times higher than that on pure Pt(111). In the present research, we have examined the effect of layer-by-layer composition, measured under electrochemical conditions, of three different Pt100−xCox(111) electrodes with varying Co bulk content (x = 17, 25, 30 at.%) on the ORR activity. The Pt100−xCox(111) single crystal electrodes (ca. 3.5 mm in diameter and 1.5 mm in thickness) were prepared in the same manner as described in our previous work.3 The Co composition in bulk was evaluated by use of X-ray photoelectron spectroscopy (XPS). Prior to the all measurements, the Pt100−xCox(111) electrodes were heat-treated at 1170 K in 100% H2 to prepare the well-defined surface. In-situ surface X-ray scattering (SXS) measurements were carried out at synchrotron radiation facilities (SPring-8 and the Photon Factory) in the same manner as described previously.4 After filling the electrochemical cell with N2-purged 0.1 M HClO4, the working electrode was polarized at 0.4 V vs. RHE. Structure parameters from the topmost to fourth layers were determined from the least-squares fitting to X-ray reflectivity data [(00) crystal truncation rod (CTR)] with a kinematical calculation based on a specific interfacial model. Figure 1 shows the dependence of jk at 0.9 V vs. RHE on x, together with layer-by-layer composition of Pt and Co analyzed by in situ SXS. The composition of the topmost layer was found to be Pt 98 at.% for all three alloys, regardless of Co content, i.e., a Pt-skin layer was formed on the surface of the Pt-Co(111) single crystal electrodes. In contrast, the Co content in the second layer changed significantly with the Co content in bulk. It is striking that the second layer of Pt75Co25(111) (Pt3Co(111)) was nearly pure Co, 98 at.%, where the jk value was close to the maximum value, ca. 25 times higher than that of pure Pt(111). At Co 30 at.% in bulk, jk decreased, and the Co content in the second layer (32 at.%) was very similar to that in bulk. The Co content in the third layer ranged from ca. 20 at.% to ca. 30 at.% in the three kind electrodes. Thus, the ORR activities of Pt-skin/Pt100−xCox(111) electrodes were strongly correlated with the enrichment of Co in the second layer. It was found by ex-situ angle-resolved, grazing-incidence XPS (ARGI-XPS) for Pt-skin/ Pt73Co27(111) that Co in the subsurface layers was positively charged, which was completely different from the electronic state of Co(II)O.4 Such an electronically positive state of Co is reasonably explained by an electron transfer from Co into the Pt-skin layer, which has been linked to a d-band center downshift. This work was supported by funds for the SPer-FC project from NEDO and a Grant-in-Aid (No. 25410007) for Scientific Research MEXT of Japan. We wish to thank Dr. K. Tamura of the Japan Atomic Energy Agency and Drs. I. Hirosawa and T. Watanabe of SPring-8 for their help with the CTR fitting program and SXS measurements, respectively. The synchrotron radiation experiments were performed as projects approved by the PAC (No. 2016G059) and by JASRI (2016A1184 and 2016B1551). References V. R. Stamenkovic, B. S. Mun, K. J. J. Mayrhofer, P. N. Ross, N. M. Markovic, J. Rossmeisl, J. Greeley, J. K. Nørskov, Angew. Chem. Int. Ed., 45, 2897 (2006). T. Toda, H. Igarashi, H. Uchida, M. Watanabe, J. Electrochem. Soc. 146, 3750 (1999). S. Kobayashi, M. Wakisaka, D. A. Tryk, A. Iiyama, H. Uchida, J. Phys. Chem. C, 121,11234 (2017). S. Kobayashi, M. Aoki, M. Wakisaka, T. Kawamoto, R. Shirasaka, K. Suda, D. A. Tryk, J. Inukai, T. Kondo, H. Uchida, ACS Omega, 3, 154 (2018). Figure 1

Understanding the interfaces in an MEA of a PEFC, or the reaction fields, has become very important, and their structures and properties are intensively studied. Bulk and interfacial structures of polymer electrolyte membranes and binders, as well as the distribution of water inside, are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. Neutron reflectivity (NR) is a powerful method to observe structures of electrolyte polymers on flat substrates with an Angstrom precision in the in-plane direction. NR measurements were carried out on model Nafion films with a thickness of approximately 100 nm formed on a native SiO2 surface and on a Pt layer on Si(100) for understanding the in-plane Nafion and water densities.1) Under N2 humidified with H2O, the temperature was set at 80 ˚C and the relative humidity between 30% and 80% during the NR measurements, simulating the conditions for the power generation. Figure 1 shows the NR profiles of Nafion at 80 °C at different relative humidities on SiO2 and Pt, respectively. Clear NR modulation was obtained under each condition on each specimen. The NR profiles on SiO2 and Pt were very different, showing different film morphologies. The characteristic bump around 0.2 Å-1 observed for Nafion on SiO2 (Fig. 1(a)) could be explained by the existence of a layer with a very different scattering length density (SLD) from that of Nafion, which was not observed for Nafion on Pt (Fig. 1(b)). The analyses of the NR profiles were carried out using the MOTOFIT program. For Nafion on SiO2, the NR data in Fig. 1(a) were fit very well with calculated values applying 4-layer models. Figure 2 shows the layered model of Nafion on SiO2/Si(100). SLD values were converted into Nafion and water densities at each sub-layer. The total thickness of the Nafion film at 80 ºC was 131, 139, 146, and 153 nm at 30, 50, 65, and 80% RH, respectively. The water uptake calculated from the NR data at 80% RH of a 100-nm Nafion on SiO2 was in good agreement with that measured by the mass of a film at 80 ºC.2) In “Topmost Layer” in Fig. 2, the water density was very low, and a hydrophobic conformation at the interface between Nafion and humidified N2 was proposed. The thickness of “Bulk Layer” monotonically increased from 120 to 140 nm as the humidity increased from 30 to 80% RH. The film thickness of “Intermediate Layer” slightly increased from 2.3 to 3.0 nm. The water density in “Intermediate Layer” was two times higher than that in “Bulk Layer”. The thickness of “Water-rich Layer” was 1.3 nm regardless of the humidity, while the water density greatly increased up to 0.97 g cm-3 at 80% RH. As seen in Fig. 1(b), no bump was observed on Nafion on Pt. The Nafion film on Pt/Si(100) was modeled with three layers with no “Water-rich Layer”. The influences of different substrates are clearly observed, which will be discussed in detail. This work was performed under the SPer-FC project of NEDO, Japan. The NR experiments were performed as projects approved by the Japan Proton Accelerator Research Complex under user programs, Nos. 2016A0246, 2016B0036, and 2017B0316. References 1) T. Kawamoto, M. Aoki, T. Kimura, T. Mizusawa, N. L. Yamada, J. Miyake, K. Miyatake, and J. Inukai, accepted to Jpn. J. Appl. Phys. 2) C. Yang, S. Srinivasan, A. B. Bocarsly, S. Tulyani, and J.B. Benziger, J. Membr. Sci. 237, 145, (2004). Figure 1

Pt skin-covered Pt alloy nanoparticles are highly active catalysts for the oxygen reduction reaction (ORR),1 the hydrogen oxidation reaction (HOR),2 and the hydrogen evolution reaction (HER)3 in acid electrolyte. We have sought to understand the effect of the underlying alloying element, usually Fe, Co or Ni, using density functional theory (DFT). The ideal test for the calculations is an electrode that has been characterized at the atomic level, such as a single crystal with known near-surface composition. Recently, we found that a Pt-skin/Pt73Co27(111) electrode exhibited ORR activity that was much higher than that of Pt(111), by a factor of 27.4 Based on in situ surface X-ray scattering measurements, this electrode has a nearly pure Pt surface layer and a nearly pure Co second layer, with the third layer composition close to that of the bulk alloy.5 The objective of the present work is to understand the electrochemical behavior of this type of well-characterized electrode, starting with the cyclic voltammogram (CV) (Fig. 1). Similar to Pt3Ni(111),6 the H adsorption region is shifted negatively, and the OH adsorption region is shifted positively. To model the behavior of the H adsorption region, we carried out DFT calculations on three-layer slab models using DMol3 (Biovia), with geometry optimization with semicore pseudopotentials and energy calculations with all-electron scalar relativistic accuracy.7 This approach has been found to provide realistic adsorption energies. The present work tests its ability to provide realistic trends in the Fermi energy E Fas a function of H coverage alone, since it has been shown by Ishikawa and coworkers that the (111) surface with underpotentially deposited hydrogen HUPD is highly hydrophobic.7 This approach can also accurately model the vacuum experiment, in which the work function change is measured vs. H coverage.8 We also plot the integrated H adsorption charges taken directly from CV, which is the most straightforward way to compare with the calculations. We carried out calculations for a Pt(111)-6x6 3-layer model with sequentially added H atoms, up to unity coverage (36 atoms), with the further addition of 12 H atoms, corresponding to overpotentially deposited H (HOPD). This region is difficult to evaluate with CV, although it is observable spectroscopically.9 The coverage can be converted straightforwardly to a charge, but E F must be empirically transformed to match the electrochemical potential. Interestingly, the calculated curve has a delayed onset, similar to that observed in vacuum.8 Calculations were carried out for a Pt/Pt3Co/Pt3Co model, in which the second and third layers both have the bulk composition (Fig. 1). The curve is shifted downward due to the effect of Co. Finally, calculations were carried out for a realistic Pt/Co/Pt3Co(111) model. Since these are extremely time-consuming, only the bare surface and the unity coverage cases have successfully completed thus far, but these show a further downward shift. The present results show for the first time that the electrochemical behavior of a Pt-Co alloy (111) single crystal can be understood from first principles. Calculations are also in progress to model the OH adsorption region, as well as the catalytic reactions. This work was supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cell” (SPer-FC) project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References 1. T. Toda, H. Igarashi, H. Uchida, and M. Watanabe, J. Electrochem. Soc. 146, 3750 (1999). 2. G. Shi, H. Yano, D. A. Tryk, A. Iiyama and H. Uchida, ACS Catal., 7, 267 (2017). 3. G. Shi, H. Yano, D. A. Tryk, S, Noharaa, and H. Uchida, Phys. Chem. Chem. Phys., 21, 2861 (2019). 4. S. Kobayashi, M. Wakisaka, D. A. Tryk, A. Iiyama, and H. Uchida,J. Phys. Chem. C, 121, 11234 (2017). 5. S. Kobayashi, M. Aoki, M. Wakisaka, T. Kawamoto, R. Shirasaka, K. Suda, D. A. Tryk, J. Inukai, T. Kondo, and H. Uchida, ACS Omega, 3, 154 (2018). 6. V. R. Stamenkovic, B. Fowler, B. S. Mun, G. F. Wang, P. N. Ross, C. A. Lucas, and N. M. Markovic, Science, 315, 493 (2007). 7. Y. Ishikawa, J. J. Mateo, D. A. Tryk, and C. R. Cabrera, J. Electroanal. Chem., 607, 37 (2007). 8. K. Christmann, G. Ertl, and T. Pignet, Surf. Sci., 54, 365 (1976). 9. K. Kunimatsu, H. Uchida, M. Osawa, and M. Watanabe, J. Electroanal. Chem.,587, 299 (2006). Fig. 1. (Upper panel) CV for Pt(111) (black) and Pt-skin/Pt73Co27(111) (blue) electrodes in N2-saturated 0.1 M HClO4 at 50 mV s-1. (Lower panel) Integrated charges (solid lines) based on the CV, with calculated points (open symbols) for Pt/Pt3Co/Pt3Co(111) (red circles) and Pt/Co/Pt3Co (blue squares) models. Figure 1

Central to electrochemistry is the electric double layer (EDL) at the electrode-electrolyte interface where important interfacial phenomena including adsorption and charge transfer occur.1 Understanding the nature of the electric double layer regarding the electronic and structural characteristics has implications relating to bio(chemical) sensors, micro-mechanical actuators and energy storage/conversion devices. Amongst model systems, ferrocene-terminated alkanethiol self-assembled monolayers (Fc SAM) on Au are an attractive model electrochemical interface due to their practical applicability and versatility with structural modifications.2 Within the Fc SAM, a change in the ferrocene/ferrocenium (Fc/Fc+) redox state leads to notable changes to the interfacial structure with respect to the EDL, interactions with the electrolyte, and work function. While existing studies exist on probing the redox-induced Fc SAM structural changes using techniques such as surface plasmon resonance (SPR), Raman, IR and quartz crystal microbalance (EQCM),2 experimental efforts aimed at probing the changes in electronic structure are still limited. Here, we employ X-ray and ultraviolet photoelectron spectroscopy combined with an electrochemical cell (EC-XPS/UPS) which allows us to electrochemically control the Fc SAM redox state and spectroscopically probe the redox-induced electronic and structural changes.3 To perform our experiments, electrochemical (EC) measurements are performed in a separate EC chamber in Ar atmosphere followed by evacuation and then transfer to the XPS/UPS analysis chamber.4 The EC chamber contains a retractable PTFE (polytetrafluorethylene) cell where electrochemical measurements are performed under Ar atmosphere. The cell utilizes a hanging meniscus setup connected via PFA (perfluoroalkoxy alkane) tubing to a syringe containing the electrolyte. This controlled setup permits us to reliably probe the oxidized Fc+ moieties and prevent its decomposition upon exposure to the ambient. Using this approach, following EC and electrode immersion, we can probe changes to the ferrocene/ferrocenium (Fc/Fc+) redox center (Fe oxidation state), deduce the occurrence of ion-pairing, changes in molecular orientation and monolayer thickness (Figure 1). Oxidation to Fc+ is corroborated by UPS, which shows that a shift of the highest occupied molecular orbital (HOMO) towards higher binding energy along with an increase in work function. The reversibility of our observations is confirmed by reproducibly switching between the Fc/Fc+ states. More broadly, our approach is potentially applicable to a variety of electrochemically active systems to assist in the elucidation of redox-related structure-function relationships. Specific details will be provided during the presentation. Figure 1. (a) Schematic and photographs of hanging meniscus inside the EC chamber during EC measurements and following removal from the electrolyte. (b) Molecular structure of Fc SAM used in study and cyclic voltammagram performed in 0.1 M NaClO4. (c) Corresponding XPS Fe 2p, Cl 2p and O 1s spectra of the pristine, oxidized Fc+ and neutral Fc states. Kolb, D. M. Angew. Chem. Int. Ed. 2001, 40, 1162. K. Uosaki, Electrochemistry 1999, 12, 1105. R. A. Wong, Y. Yokota, M. Wakisaka, J. Inukai, Y. Kim, J. Am. Chem Soc. 2018, 140, 13672. M. Wakisaka, S. Mitsui, Y. Hirose, K. Kawashima, H. Uchida, M. Watanabe, J. Phys. Chem. B 2006 , 46, 23489. Figure 1

The understanding of the structural and the chemical properties of Pt catalysts in polymer electrolyte fuel cells (PEFCs) is necessary to improve the activity for the durability of the catalysts. The small-angle X-ray scattering (SAXS) and the X-ray absorption spectroscopy (XAS) measurements are widely used to investigate the properties of Pt catalysts. Recently, Povia et al developed a powerful tool by combining the SAXS and XAS measurements for the characterization of the Pt nanoparticle catalysts [1]. However, this technique is difficult to investigate the chemical states of the low-concentrated catalysts. In this study, we developed the combined SAXS and the fluorescence-yield (FY) XAS measurement systems to investigate the structural and the chemical properties of low-concentrated catalysts. The combined SAXS-FYXAS measurement system was developed at BL19B2 in SPring-8. For the XAS measurements, the Pt LⅢ edge was used. The ionization chamber and a single-element Ge solid state detector were used to obtain the FYXAS spectra. For the SAXS measurements, the X-ray energy was set to 11.5 keV and 11.55 keV, which are below and near to the Pt LⅢ absorption edge, respectively. The scattered X-ray was detected using an area detector (PILATUS 2M). The PtCo alloy nanoparticle for the oxygen reduction reaction was used as the sample in this experiment. As the result, we could demonstrate the combined SAXS-FYXAS measurement systems. We will discuss the degradation mechanism of the PtCo alloy nanoparticle catalyst from both SAXS and FYXAS data. [1] M. Povia et al. ACS. Catal., 8, 7000 (2018).

Structures of polymer electrolyte membranes and binders and the distribution of water inside are important for designing new ion-conductive ionomers for polymer electrolyte fuel cells. Neutron reflectometry (NR) was carried out on a Nafion® film with a thickness of 100 nm formed on native SiO2 surface on Si(100) for understanding the in-plane water distribution. The temperature was set at 80 °C and the relative humidity at 30, 50, 65, and 80% for NR measurements, simulating the conditions for the power generation. Clear NR modulation was obtained under each condition. NR data were fit very well with a 4-layer model parallel to the substrate with different densities of Nafion and water. At the interface between the Nafion film and the Si substrate, a 1 nm water-rich layer was observed under all conditions. The water concentration increased with humidity at all 4 layers, but the thickness increased mainly at the bulk layer.

Cathode catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs) have been investigated toward increasing their activity and durability, which can promote the large-scale commercialization of fuel cell vehicles (FCVs) and residential co-generation systems. In contrast, anode catalysis R&D for the hydrogen oxidation reaction (HOR) has not been so intensive recently. One of the reasons is that the HOR rate is sufficiently fast at Pt/C anode catalysts with a low Pt loading (ca. 0.05 mgPt cm−2) for FCVs with pure H2 as the fuel. For residential PEFCs operated with reformate (H2-rich fuel gas), Pt-Ru anode catalysts have been used predominantly to mitigate the poisoning by CO (below 50 ppm). However, Ru is not only costly (mass activity for the HOR at Pt-Ru/C is low) but is also unstable at high potentials (E > 0.8 V). We demonstrated that both bulk Pt-Co and commercial c-Pt3Co/C exhibited high CO-tolerance in 0.1 M HClO4 solution at temperatures below 70 °C.1 It has been clarified that the Co component leached out into the acidic solution, resulting in the formation of a thin Pt-skin layer on the alloy surface. The excellent CO-tolerance on the Pt-skin layer was ascribed to weaker CO adsorption, which can maintain active sites for the HOR, due to its electronic structure being modified by the underlying alloy.1 However, the CO-tolerance was lost after being heated ≥ 80 °C due to increased dealloying of the Co component, leading to a thick Pt layer. Such dealloying of Co from c-Pt3Co/C catalysts during load-change cycles is also a serious issue. Very recently, we have succeeded in suppressing the dealloying of Co by forming a thin, uniform, stabilized Pt-skin (one to two atomic layers: xAL) on Pt-Co alloy nanoparticles (PtxAL–PtCo), which act as a two-way catalyst for the ORR cathode with high activity and durability2,3 and the HOR anode with high activity, CO tolerance, and robustness at 70 and 90 °C.4 This presentation focuses on the following topics concerning the unique characteristics of the stabilized Pt-skin catalysts, including the analyses of microstructure and electronic structure. 1) Important role of Pt-skin layer and underlying alloy for enhancement of the ORR activity5, 6 The j k value for the ORR at 0.9 V on Pt-skin/Pt100−xCox(111) single crystals reached a maximum at x = 27 atom% that was ca. 27 times higher than that on a pure Pt(111) electrode.5 By the use of in situ STM, in situ SXS, ex situ angle-resolved XPS, and DFT calculations, we have succeeded in correlating this high j k with the specific surface structure and electronic structure.6 2) Potential-cycle induced change in crystal structure of PtxAL–PtCo/C We have found that the crystal structure of PtxAL‒PtCo nanoparticles [face-centered tetragonal (fct) + face-centered cubic (fcc)] was converted to single-phase fcc, which exhibited high ORR activity and durability, surprisingly, only by means of potential cycling from 0.05 V to 1.0 V in 0.1 M HClO4 solution at room temperature. 3) Multilateral analyses of the enhancement of HOR activity and CO-tolerance for the PtxAL‒PtM/C7, 8 It was found by in situ FTIR,7 in situ XAS,8 and DFT calculations8 that the adsorption of CO on terrace sites on the PtxAL skin covering the PtM alloy (M= Fe, Co) was weakened by the modified electronic structure. This work was supported by funds for the ‘‘Superlative, Stable, and Scalable Performance Fuel Cell (SPer-FC)’’ project and “High Performance Fuel Cell (HiPer-FC)” project from NEDO of Japan. References H. Uchida, K. Izumi, K. Aoki, and M. Watanabe, Phys. Chem. Chem. Phys., 11, 1771 (2009). M. Watanabe, H. Yano, D. A. Tryk, and H. Uchida, J. Electrochem. Soc., 163, F455 (2016). M. Chiwata, H. Yano, S. Ogawa, M. Watanabe, A. Iiyama, and H. Uchida, Electrochemistry, 84, 133 (2016). G. Y. Shi, H. Yano, D. A. Tryk, A. Iiyama, and H. Uchida, ACS Catal., 7, 267 (2016). S. Kobayashi, M. Wakisaka, D. A. Tryk, A. Iiyama, and H. Uchida, J. Phys. Chem. C, 121, 11234 (2017). S. Kobayashi, M. Aoki, M. Wakisaka,T. Kawamoto, R. Shirasaka, K. Suda, D. A. Tryk, J. Inukai, T. Kondo, and H. Uchida, ACS Omega, 3, 154 (2018). Y. Ogihara, H. Yano, T. Matsumoto, D. A. Tryk, A. Iiyama, and H. Uchida, Catalysts, 7, 8 (2017). G. Y. Shi, H. Yano, D. A. Tryk, M. Matsumoto, H. Tanida, M. Arao, H. Imai, J. Inukai, A. Iiyama, and H. Uchida, Catal. Sci. Technol., 7, 6124 (2017).

By using a current-sensing atomic force microscope (CS-AFM) under a hydrogen atmosphere, microscopic proton-conductive areas on the membrane surface of sulfonated poly(arylene ether sulfone ketone) block copolymer were investigated. With increasing the bias voltage during the CS-AFM scans, the number and the diameter of proton-conductive spots on the membrane surface continuously increased. Both reversible/irreversible changes in the proton-conductive area on the surface were found. The reversible change indicates that the proton-conductive paths are dynamically rearranged during the power generation in a polymer electrolyte fuel cell. The irreversible change might be related to the enhancement of the performance of the membrane electrode assemblies after being “conditioned” prior to the operation.

The proton-conductive spots on the membrane surface of sulfonated poly(arylene ether) multiblock copolymer were successfully imaged by current-sensing atomic force microscopy under hydrogen atmosphere at various temperatures and humidities. These spots should be connected to the proton-conductive paths inside the membrane. The average diameter of the spots was approximately 12 nm, consistent with the size of hydrophilic domains observed by transmission electron microscopy. The size of the proton-conducting spots was almost unchanged regardless of the temperature and humidity, whereas the number of the spots increased at higher humidity; the total area of the proton-conducting spots increased accordingly on the membrane surface. This increase in the conducting area at high humidity should be related to the bulk ionic conductivity measured by impedance spectroscopy.

Anion conductivity at the surfaces of two anion-exchange membranes (AEMs), quaternized ammonium poly(arylene ether) multiblock copolymer (QPE-bl-3) and quaternized ammonium poly(arylene perfluoro-alkylene) copolymer (QPAF-1), synthesized by our group was investigated using current-sensing atomic force microscopy under purified air at various relative humidities. The anion-conducting spots were distributed inhomogeneously on the surface of QPE-bl-3, and the total areas of the anion-conducting spots and the current at each spot increased with humidity. The anion-conductive areas on QPAF-1 were found on the entire surface even at a low humidity. Distribution of the anion-conducting spots on the membrane was found to directly affect the performance of an AEM fuel cell.

In situ confocal micro-Raman spectroscopy was used to probe the water distribution in an electrolyte membrane in a polymer electrolyte fuel cell (PEFC) under various cell-operating conditions. The water content, λ R (number of water molecules per sulfonic acid group), in a Nafion ® membrane was calculated from the intensity of the O H stretching ( ν (O H)) band. By analyzing the Raman spectra as a function of the membrane depth in an operating PEFC, the λ R distributions in the membrane were obtained under different temperature, humidification, current density and gas-flow rate conditions. The ν (O H) intensity in the electrolyte membrane increased with increasing current density, relative humidity, and gas utilization. The water distribution in the electrolyte membrane can be understood as a balance among back-diffusing water produced from the cathode, electro-osmotic drag, and water removal via the gas diffusion layer (GDL), all of which is information that will be important for the realization of cell operation without humidification in future advanced fuel cell vehicles.

In situ confocal micro-Raman spectroscopy was used to probe the interior of the electrolyte membrane of a polymer electrolyte fuel cell (PEFC) at various temperatures (40–110 °C) and humidities (dry–90% RH). No changes in the Raman spectra for functional groups involved in the polymer were found under humidified and dry conditions, except for the sulfonic acid group. With increasing relative humidity, the band intensity for S–O stretching (ν(S–O)) in the latter increased, and the peak shifted toward lower wavenumber. By analyzing the Raman peaks, water distributions through the Nafion membrane thickness were successfully evaluated in the operating PEFC. It was found that the back-diffusion of water produced at the cathode to the anode, humidifying the membrane, was clearly detectable, and also the rate of water transport in the membrane increased with increasing cell temperature.

Visualization inside polymer electrolyte fuel cells (PEFCs) is important for elucidating reaction distributions to improve the performance and durability of the cells. An O2-sensitive porphyrin luminescent dye film was used to visualize oxygen partial pressures and water blockages simultaneously in triple-serpentine gas flow channels in an operating PEFC. Water droplets formed near the exit of a gas-flow channel lowered the oxygen partial pressure noticeably over the channel by blocking air flow near the entrance. Meanwhile, air was continuously supplied from the other channels through the gas diffusion layer, thus allowing power to be generated in the blocked channel. With water blockages, however, the catalyst layer under the channel became flooded by the water produced during the reaction, and the flooded state continued to exist in the catalyst and/or porous layers, even after blowing the water droplet out, so that the power generation was lowered along the channel.

During start-up/shut-down processes of a polymer electrolyte fuel cell, platinum particles are lost from the catalyst layer at the cathode due to corrosion of the carbon supports. We simulated the start-up/shut-down cycle by exchanging gases at the anode between hydrogen and air. During the gas exchange, the distribution of oxygen partial pressures at the anode was visualized by our real-time/space visualization system, which clearly showed the location of H2- and O2-rich areas along the gas-flow channel from the inlet to the outlet. The gas exchange rate was found to be much slower than that predicted from the simple replacement and to be correlated to the proton transfer derived from carbon corrosion of the cathode catalyst layer. By the visualization results, it was found that the shut-down process gives more serious effect than the start-up process. After the degradation, the oxygen partial pressure at the cathode was visualized during the cell operation. Oxygen was consumed mainly in the middle of the MEA because the MEA was degraded mainly near the inlet and outlet of reactant gases in the cell.

Gas diffusion layer (GDL) is an important component for the performance of polymer electrolyte fuel cells controlling the gas flow and the water transport. In this study, the real-time formation process of water droplets on two GDLs with different pore sizes was imaged using a CCD camera during the cell operation. A porphyrin luminescent dye was coated on the GDLs to clarify the shape of the water droplets. On the GDL with a smaller pore size, the droplets were distributed uniformly on the GDL in the flow channel at the cathode. On the GDL with a larger pore size, the water droplets were larger and formed mainly near the ribs of the flow channel, and the droplets were observed to move slowly towards the gas outlet. The difference in the formation of water droplets were explained by the difference in the partial air flow inside the GDLs along the gas channel.

The development of catalysts with high activity and durability is extremely important for the commercialization of polymer electrolyte fuel cells. The problems to overcome of the present catalysts are discussed with possible solutions in the view of surface science.

For polymer electrolyte fuel cells, Pt-based alloy catalysts have been widely studied. We have developed the nanocapsule method1,2 for the synthesis of PtCo alloy nanoparticles (n-PtCo) with well-controlled size and composition. On n-PtCo subsequently treated in hydrogen gas at high temperature (n-PtCoH2-HT), additional Pt-skin layers were formed (PtxAL-PtCo).3 Figure 1 shows the area-specific activities j k for the oxygen reduction reaction (ORR) at carbon-supported n-PtCoH2-HT and PtxAL-PtCo (n-PtCoH2-HT/C and PtxAL-PtCo/C, respectively) and a commercial carbon-supported Pt catalyst (c-Pt/C) coated with Nafion in O2-saturated 0.1 M HClO4 solution at 65 oC and 0.85 V vs. RHE measured by a multi-channel flow double-electrode cell technique.2 Potential-step cycles were applied to the catalyst electrodes as the accelerated durability tests (ADTs) simulating load-change cycles of fuel cell vehicles4 in N2-saturated solution with no solution flow. Both the initial j k and the durability were the highest at Pt2AL-PtCo/C.3 Figure 2 shows changes in the electrochemically active areas (ECAs) of n-PtCoH2-HT/C and PtxAL-PtCo/C during the ADTs in a constant solution flow at 65 °C so that the re-deposition of Pt became negligible. The ECA values of the catalysts decreased as the number of potential-step cycles increased, and the losses of the ECA of n-PtCo/C and PtxAL-PtCo/C after 5000 cycles were 42% and 26%, respectively. Therefore, the ECA loss was much mitigated by the existence of Pt skins. Figure 3 shows the in-situ X-ray diffraction (XRD) pattern of the (111) peak of Pt-Co alloy of n-PtCo/C and PtxAL-PtCo/C measured during the ADT in a solution flow. For n-PtCo/C, the diffraction peak at ca. 27.6° was close to that for Pt (27.5°), suggesting that Co easily dissolved from n-PtCo into the hot acid electrolyte solution. The peak was small and broad even before the ADT, probably because of a low order of atoms in crystallite. In the XRD pattern of PtxAL-PtCo/C, a significantly large, distinct peak was observed before the potential cycles; the ordering of atoms in PtxAL-PtCo was very high. The peak was almost unchanged after the potential-step cycles, indicating that the crystallite structures of PtxAL-PtCo remained the same. The parameters of the Pt-Co alloy catalysts from the data obtained by the electrochemical measurements, transmission electron microscopy, and in-situ XRD are listed in Table 1. For n-PtCo/C, the crystallite size was approximately 2.3 nm during 5000 cycles. The number of crystallites per area and the metal retention ratio gradually decreased from 14 × 103 to 10 × 103 mm-2 and from 100% to 50%, respectively. Not only the dissolution but the migration/coalescence also played a role. For PtxAL-PtCo/C, the crystallite size was approximately 2.9 nm during 5000 cycles. No change was indicated in the shape and the number of the crystallites per area, as well as the loss of the metals. Interestingly, the ECA of PtxAL-PtCo/C gradually decreased during 5000 cycles by 26%. Therefore, it is assumed that the PtxAL-PtCo crystallites were aggregated into a larger particle consisting of multi-crystallites, while keeping the shape of each crystallite unchanged. The loss of ECA is explained by the loss of surface areas by a contact between crystallites. As shown in Fig. 1, the j k value at PtxAL-PtCo/C remained the same level during the potential-step cycles. The coalescence of alloy crystallites without any dissolution of Pt and Co clearly explains this constant value of j k. Analyzing an EXAFS of Pt in PtxAL-PtCo/C, the Debye-Waller factor for Pt–Pt in PtxAL-PtCo/C was even smaller than that of Pt nanoparticles with a similar size, revealing that the crystallinity of the outer Pt skin was extremely high.6 Thus, the existence of a rigid Pt skin realized the extensively high durability of PtxAL-PtCo/C. Further structural analyses of the Pt-Co catalyst at the atomic level are now in progress. Acknowledgements This work was carried out under the “SPer-FC” project, NEDO, Japan. The synchrotron radiation experiments were performed at BL14B2, BL16B2, BL19B2, and BL46XU of SPring-8 (No. 2015B3388, 2016A1760, 2016A1805, 2016A5390, 2016B1550, and 2016B1856, 2016B5390). References Yano, H.; Kataoka, M.; Yamashita, H.; Uchida, H.; Watanabe M. Langmuir, 2007, 23, 6438. Yano, H.; Song, J. M.; Uchida, H.; Watanabe, M. Phys. Chem. C, 2008, 112, 8372. Watanabe, M.; Yano, H.; Tryk, A.; Uchida, H. J. Electrochem. Soc., 2016, 163, F455. http://fccj.jp/pdf/23_01_kt.pdf in Japanese. Watanabe, M.; Tryk, D. A.; Wakisaka, M.; Yano, H; Uchida, H. Acta, 2012, 84, 187. Shi, G.; Yano, H; Tryk, D. A.; Matsumoto, M.; Tanida, H.; Arao, M.; Imai, H; Inukai, J.; Iiyama A.; Uchida H. Sci. Technol., 2017, 7, 6124. Figure 1

Development of cathode catalysts with high oxygen reduction reaction (ORR) activity and high durability is essential for the large-scale commercialization of polymer electrolyte fuel cells (PEFCs), which are applied to fuel cell vehicles (FCVs) and residential co-generation systems. At the present stage, costly Pt or its alloys have been employed as the cathode catalyst, having appreciable ORR activity and durability in strong acidic electrolyte at low operating temperatures The mass activity MA of Pt-based catalysts is defined as MA (A gPt −1) = j S (A m−2) × ECA (m2 gPt −1). To increase the area-specific activity j S (current density per active surface area), Pt-M alloys (Pt-Fe, Pt-Co, Pt-Ni, Pt-Cr, etc.) have been examined. Assuming spherical catalyst particles, the electrochemically active surface area ECA is inversely proportional to the particle diameter. To increase the ECA, it is effective to disperse Pt or Pt-alloy nanoparticles on high-surface-area carbon supports (Pt/C or Pt-M/C). However, for developing such catalysts having both high ORR activity and high durability, there has been long-standing controversy surrounding important issues such as the crystal structures (ordered and disordered) and the chemical composition of Pt-M alloys, as well as their optimum particle size. Furthermore, because the mechanism of enhancement of the ORR activities at Pt-M alloys is still unclear, the strategy for designing new potential catalysts has not yet been established. This presentation focuses on the following topics for the cathode catalysts from bulk single crystals to practical nanoparticle catalysts. 1) Pt particle-size effect on the durability for an accelerated test, which simulates load-cycles for FCVs So far, much research has suffered from trade-offs in determining the optimal particle-size of the catalysts, due to the different trends of Pt particle-size effects on the MA and durability. However, by the use of our n-Pt/C catalysts with a very narrow size distribution (σd ≤ 10%), the most durable catalyst with the highest MA over the whole test period (65°C, 0.6 ↔ 1.0 V, up to 30,000 cycles) was found to be n-Pt2 nm/C.1 2) Enhanced ORR activities at Pt-M alloys2, 3 2-1) Enormously enhanced ORR activity at Pt-skin layer formed on Pt3Co(111) single crystal electrode Pt-skin/Pt–Co(111) single crystals exhibited extremely high ORR activity, j S. The j S value at 0.9 V reached a maximum at Pt73Co27(111), the value of which is ca. 27 times higher than that on a pure Pt(111) electrode.4 By the use of in situ STM, in situ SXS, ex situ XPS, and DFT calculation, we have succeeded in correlating such a high j S with the specific surface structure. 2-2) ORR activity and durability of ordered- and disordered-Pt3Co/C5 We have recently clarified the effect of the crystal structure of Pt3Co alloy nanoparticles on the ORR activity, H2O2 yield, and durability, for the first time, by the use of the ordered- and disordered-Pt3Co/C catalysts with the nearly identical average particle size, size distribution, and composition.5 3) Enhancement in the ORR activity and durability at stabilized Pt-skin–PtCo alloy catalysts6, 7 We have successfully prepared PtCo alloy nanoparticles, having a stabilized Pt skin (one to two atomic layers: xAL), supported on carbon black or graphitized carbon black (PtxAL–PtCo/C or PtxAL–PtCo/GCB). These new catalysts exhibited high MA for the ORR, together with superlative durability. This work was supported by funds for the ‘‘Superlative, Stable, and Scalable Performance Fuel Cell (SPer-FC)’’ project and “High Performance Fuel Cell (HiPer-FC)” project from the NEDO of Japan. References H. Yano, M. Watanabe, A. Iiyama, and H. Uchida, Nano Energy, 8, 13893 (2016). H. Uchida, H. Yano, M. Wakisaka, and M. Watanabe, Electrochemistry, 79, 303 (2011). M. Watanabe, D. A. Tryk, M. Wakisaka, H. Yano, and H. Uchida, Electrochim. Acta, 84, 187 (2012). S. Kobayashi, M. Wakisaka, D. A. Tryk, A. Iiyama, and H. Uchida, J. Phys. Chem. C. 121, 11234 (2017). H. Yano, I. Arima, M. Watanabe, A. Iiyama, and H. Uchida, J. Electrochem. Soc., 164, F966 (2017). M. Watanabe, H. Yano, D. A. Tryk, and H. Uchida, J. Electrochem. Soc., 163, F455 (2016). M. Chiwata, H. Yano, S. Ogawa, M. Watanabe, A. Iiyama, H. Uchida, Electrochemistry, 84, 133 (2016).

The hydrogen anode in polymer electrolyte fuel cells (PEFCs) is vulnerable to poisoning from traces of carbon monoxide in the reformed hydrogen fuel, due to strong CO adsorption on the platinum surface. Over the past several decades, there have been efforts to develop catalysts for the hydrogen oxidation reaction (HOR) that are CO-tolerant by alloying Pt with other metals, e.g., Fe, Co, Ni and Ru. The latter is a well-known commercial HOR catalyst, but Ru can be replaced with the other, less costly metals. The CO tolerance is expected to be greater for catalysts with decreased CO adsorption strength. Recently, we have found that Pt-Fe and Pt-Co alloys with specially stabilized Pt “skins” with x atomic layers, PtxAL–PtM/C have excellent CO tolerance, HOR activity and durability.1,2 More specifically, the CO tolerance and HOR activity increase in the order Pt < Pt-Ru < Pt-Ni < Pt-Co < Pt-Fe.2 This trend is the same as that for decreasing CO adsorption strength on (110) steps and (111) terraces, as calculated with density functional theory (DFT). It is also the same trend as that for atomic H adsorption on (111) terraces, while the trend is not followed for the (110) steps: the adsorption strengths for H on (110) steps on PtxAL–PtFe(221), PtxAL–PtCo(221), and PtxAL–PtNi(221) are all very similar. Thus, we have proposed a new type of metal-metal spillover mechanism, in which H2 adsorbs dissociatively at the (110) steps and then diffuses to the (111) terraces, from which the 2Had desorb oxidatively to produce 2H+ (Fig. 1). Our understanding of these catalysts has been deepened by in situ Fourier transform infrared (FTIR) spectroscopy3 and X-ray absorption spectroscopy (XAS).4 The FTIR spectra can distinguish between step edge and terrace sites for CO adsorption and can monitor the diffusion of CO from edges to steps in real time. The XAS studies have led to a deep understanding of both the structural and electronic properties of the nanoparticulate PtxAL–PtCo/C catalyst in comparison with Pt/C. When the electrodes are held at low potentials, within the H adsorption region, the Pt particles undergo significant structural (as seen in the EXAFS) and electronic transformations (as seen in the XANES), whereas the PtxAL–PtCo particles are remarkably stable, due to the shorter Pt-Co bond lengths and rigid framework. The same is true of CO adsorption. All of these characteristics are consistent with the DFT calculations, including the weakened H and CO adsorption. We are now extending this work in order to develop even more active, CO tolerant and durable HOR catalysts. References Shi, G.; Yano, H.; Tryk, D. A.; Watanabe, M.; Iiyama, A.; Uchida, H. Nanoscale 2016, 8, 13893-13897. Shi, G.; Yano, H.; Tryk, D. A.; Iiyama, A.; Uchida, H. ACS Catal. 2017, 7, 267-274. Ogihara, Y.; Yano, H.; Matsumoto, T.; Tryk, D.; Iiyama, A.; Uchida, H. Catalysts 2017, 8 (1-13). Shi, G.; Yano, H.; Tryk, D. A.; Matsumoto, M.; Tanida, H.; Arao, M.; Imai, H.; Inukai, J.; Iiyama, A.; Uchida, H. Catal. Sci. Tech. 2017, in press. Figure 1. Atomic models of the PtxAL–PtCo(221) surface, showing (A) non-dissociative H2 adsorption, (B) spontaneously dissociated 2H at the (110) step, and (C) 2H after diffusion to the (111) terraces. Figure 1

Until the mid 1980’s, there had been only few in situ methods available for structural determination of an electrode surface in solution at atomic and monolayer levels. Nowadays, many powerful in situ techniques, such as electrochemical scanning tunneling microscopy (EC-STM), infrared reflection absorption spectroscopy (IRAS), surface-enhanced Raman scattering (SERS), and surface-enhanced infrared reflection absorption spectroscopy (SEIRAS), second harmonic generation (SHG), sum frequency generation (SFG), and surface X-ray scattering (SXS) have been widely employed to characterize the electrode surfaces under potential control with atomic and/or molecular resolution. The object of this review is to highlight some of the progress on in situ methods at solid-liquid interface with atomic and molecular levels. Several selected topics are focused on, specifically adsorbed anions on metal surface, electrocatalysis of the carbon oxide oxidation and dioxygen reduction, and direct observation of single crystal electrode surfaces.

We used in situ Se K-edge X-ray spectroscopy to characterize Ru nanoparticles chemically modified with submonolayers of selenium (Se/Ru) [Cao et al. J. Electrochem. Soc. 2006, 153, A869]. X-ray powder diffraction verified that the Se/Ru catalyst had metallic Ru cores. The in situ X-ray absorption near edge structure taken at the open circuit potential showed that there were both elemental and oxidized selenium on the as-prepared Se/Ru samples. All selenium oxide was reduced to the elemental form of selenium by applying negative potentials. By applying positive potentials, selenium was subsequently reoxidized. The analysis of the extended X-ray absorption fine structure shows the appearance of selenium hydration (Se-OH{sub 2}) in a deaerated solution, which was not observed during the oxygen reduction reaction. We present evidence that Se-free Ru atoms play an important role in the ORR activity of the Se/Ru catalyst studied in this paper.

The adsorption of fullerene malonic acid (C60 malonic acid) adlayer on a Au(111) was carried out by immersing it in a benzene solution containing C60 malonic acid molecules, and the adlayer was transferred into vacuum. The adlayer structure was determined to be (3.1 × 3.1)R5° by using scanning tunneling microscopy and low-energy electron diffraction. It is suggested that there is a strong interaction through hydrogen bonding between C60 malonic acid molecules.

Oxygen reduction Ru/Se and Ru/S fuel cell surface chalcogenide catalysts were prepared via chemical reaction of reduced Ru nanoparticles with selenium and sulfur in xylenes [D. Cao, A. Wieckowski, J. Inukai, N. Alonso-Vante, J. Electrochem. Soc. 153 (2006) A869]. The chalcogenide samples – as well as the starting chalcogens-free Ru nanoparticle material – were immobilized on a gold disk for X-ray Photoelectron Spectroscopy (XPS) characterization. While we found oxygen in most of the samples, predominantly from Ru oxides, we conclude that the oxygen on Ru/S may be located in subsurface sites: the subsurface oxygen. We also found that the transformation of the oxidized Ru black to metallic Ru required intensive electrochemical treatment, including hydrogen evolution. In contrast, five cyclic voltammetric scans in the potential range from 0.00 and 0.75 V versus RHE were sufficient to remove the oxygen forms from Ru/Se and, to a large extent, from Ru/S. We therefore conclude that Ru metal is protected against oxidation to Ru oxides by the chalcogens additives. The voltammetric treatment in the 0.00 and 0.75 V range also removed the SeO 2 or SO x forms leaving anionic/elemental Se or S on the surface. Upon larger amplitude voltammetric cycling, from 0.00 to 1.20 V versus RHE, both Se and S were dissolved and the dissolution process was coincidental with the oxygen growth in/on the Ru samples.

In-situ Se K edge X-ray spectroscopy measurements were carried out for selenium modified ruthenium nanoparticles during oxygen reduction. X-ray powder diffraction verified that the samples had pure Ru cores. In-situ XANES showed that there were significant amounts of oxidized Se in the Ru/Se samples that could be reduced by negative potentials. Selenium in the sample was found to oxidize at electrode potentials of 900 mV and higher (vs. RHE). Analysis of extended x-ray absorption fine structure shows an enhancement of the Se-Ru bonds during oxygen reduction reaction.

The underpotential deposition (UPD) of Bi on Au(1 1 0) was investigated in HClO 4 solution using in situ scanning tunneling microscopy. The UPD of Bi occurred in three steps. A 3 0 1 1 structure, in which Bi atoms formed dimers, was found for the first UPD adlayer. A (1 × 1) image was obtained by STM at the second UPD peak. For the third UPD peak, Bi atoms formed an incommensurate adlayer, and stripes of Bi were observed on terraces. After the third UPD, a structural reconstruction caused by adsorbed Bi was observed.

Hydroquinone molecules were allowed to adsorb on Rh(1 1 1) and Pt(1 1 1) by vapor deposition. The strong interaction between two adjacent hydroxyl groups of neighboring molecules led to the formation of commensurate (√7 × √7)R19.1° and incommensurate (√2.56 × √2.56)R16° adlayer phases on Rh(1 1 1) and Pt(1 1 1), respectively. The formation processes of HQ adlayers on Rh(1 1 1) and Pt(1 1 1) were very different from each other, possibly due to the difference in lattice parameters of the two metal surfaces.

Adlayers of Sb species on Au(100) were investigated in 0.1 M HClO 4 . Using in situ scanning tunneling microscopy, it was found that irreversibly adsorbed oxygenous Sb(III) species formed a quasi (2 x 2) structure on Au(100). These species underwent redox reactions on the surface without desorption. In an HClO 4 solution containing Sb 2 O 3 , two adlayers of Sb, ( 1 - 1 1 2 ) and ( 2 - 2 1 2 ), were found. Comparison between the voltammograms recorded in HClO 4 + Sb 2 O 3 with and without H 2 O 2 showed that the H 2 O 2 reduction reaction is not enhanced on the adlayer of irreversibly adsorbed oxygenous Sb(III) species but it can be enhanced on the submonolayer of Sb(0).

Immersion of an ordered Au( 111) electrode in a 5 ∼ 50 μM haloplatinate solution for 1 min results in spontaneous and irreversible adsorption of a submonolayer to a monolayer Pt complex. In situ STM imaging reveals the formation of highly ordered molecular adlayers of Au(111) - (√7 x √7)R19.1° - PtCl 4 2- and PtBr 4 2- (0 = 0.143) in a solution containing 50 μM of each complex. Dosing in a dilute PtBr 4 2- solution (5 μM) produces another highly ordered structure, identified as Au(111) - (2√19 x 2√19)R23° - 7 PtBr 4 2-+ 6 Br. Atomic resolution STM reveals pinwheel features of the planar PtX 4 2- adsorbates (X = Cl, Br, I). The molecular adlayers of PtI 6 2- are always disordered, irrespective of the dosing conditions. The reduction potentials of these molecular overlayers to produce the deposit of metallic Pt decrease in the order of PtCl 4 2-> PtBr 4 2- > PtI 6 2-. The Pt deposit exists in the form of nanoparticles with an average diameter of 3.0 nm and height of 0.46 nm, and they are uniformly distributed on the Au(111) substrate. The electrocatalysis toward the oxygen reduction of Pt particles on Au(111) is examined with a hanging-meniscus rotating disk technique. The Pt particles prepared with the precursors of chloro- and bromoplatinate are active in catalyzing oxygen reduction, whereas those from iodoplatinate are inert. This result correlates with the strength of surface bond between halide and Au or Pt metal. Iodine adatoms evidently block the active sites on Pt clusters.

Adlayers of sulfur (S) and thiocyanate (SCN) on Cu(1 1 1) were investigated by using in situ scanning tunneling microscopy in alkaline solution. Two different structures of S adlayers, (3/3)R308 and (19/19), were revealed in the double-layer potential region. The (3/3)R308 structure observed at negative potentials was transformed into (19/19) on sweeping the potential in the positive direction. For SCN on Cu(1 1 1), the (3/3)R308 structure was also observed at negative potentials. At positive potentials, a structural change was observed also for the SCN adlayer; however, the adlayer structure was much distorted compared with the (19/19) structure of the S adlayer. # 2003 Elsevier Science B.V. All rights reserved.

Adlayers of toluene, p-xylene, o-xylene, and mesitylene on a Rh(111) electrode in HF solution were investigated by using in situ scanning tunneling microscopy (STM). In situ STM images showed that all molecules were adsorbed with flat-lying orientation on the Rh(111) surface. High-resolution imaging revealed not only the packing arrangement but also the internal structure of each molecule. Methyl functional groups on the benzene ring were clearly discerned. Toluene molecules were arranged nearly hexagonally on Rh(111). The benzene ring of a toluene molecule was assigned to a hollow site on Rh(111). p-Xylene molecules were adsorbed at bridge sites, and a highly ordered c(2√3×4)rect adlayer was formed. The o-xylene adlayer showed a nearly hexagonal arrangement of molecules, and benzene rings were located at bridge sites. Mesitylene molecules appeared triangular in the STM image, which were assigned to hollow sites.

Four topics are presented on the electrode surfaces investigated using an ultrahigh vacuum-electrochemistry combined system: 1) Pt(100) reconstructed electrode, 2) adlayers of halides on electrodes, 3) formation of AgBr in solution, and 4) adlayer of p-xylene on Rh(111).

The structure of a p-xylene adlayer formed on Rh(111) in ultrahigh vacuum (UHV) at room temperature was investigated by using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). STM images revealed that p-xylene formed a highly ordered adlayer on Rh(111) in UHV. From the STM observation and the LEED measurement, the adlayer structure was determined to be c(2√3 × 4)rect, which was reported previously also for the adlayer on Rh(111) in HF solution. Time-dependent STM allowed direct observation of the dynamics of the self-ordering process. Small ordered domains of adsorbed p-xylene molecules appeared and gradually grew in size on terraces. The domain size was found to increase in a few minutes under the exposure to p-xylene. The average domain size was ca. 20 nm.

For polymer electrolyte fuel cells, Pt-based alloy catalysts have been widely studied. We have developed a novel nanocapsule method1,2 for the synthesis of controlled PtCo alloy nanoparticles (PtCo/GCB, graphitized carbon black support to mitigate carbon corrosion), and modified the method3for covering hydrogen-treated PtCo/GCB (H-PtCo/GCB) with Pt-skin layers. Figure 1 shows images obtained with a transmission electron microscope (TEM) of PtCo/GCB, H-PtCo/GCB, and Pt-skin coated PtCo catalyst (PtxAL-PtCo/GCB) with the histograms of the particle-size distributions. Particle sizes were very uniform with the diameters of 2.5±0.2 nm for PtCo/GCB and H-PtCo/GCB, and of 3.0±0.3 nm for PtxAL-PtCo/GCB. By the electron diffraction (Table 1), the lattice of PtCo/GCB was determined as fcc. After the hydrogen treatment at 400 oC,3 the lattice became fct for H-PtCo/GCB. After the addition of a Pt-skin on H-PtCo/GCB, the lattice was mostly (ca. 97%) fct and partially (ca. 3%) fcc, presumably due to the addition of a Pt-skin. By X-ray absorption fine structure (XAFS) measurements, Pt and Co atoms were found to be very uniformly distributed in PtCo/GCB. For H-PtCo/GCB, neither the atomic distances nor the coordination numbers showed a large change, whereas for PtxAL-PtCo/GCB, the Pt-Pt coordination number increased showing the formation of a Pt-skin layer. The effect of the Pt-skin layers was examined in a 0.1-M HClO4 solution at 65 oC with a multi-channel flow double-electrode cell2 on the activity towards the oxygen reduction reaction and the durability examined by the accelerated durability test according to the protocol for load-change cycles4 recommended by the Fuel Cell Commercialization Conference of Japan (FCCJ) (Fig. 2). Both the durability and the mass activity evaluated at 0.85 V vs. the reversible hydrogen electrode were the highest at PtxAL-PtCo/GCB followed by H-PtCo/GCB. By in situ XAFS measurements, the layers of Pt skins were indicated to exist at the surface of the alloy particles in 0.1 M HClO4. After 30,000 cycles, the initial high activity at PtCo/GCB was lost and became almost identical to that at a commercial Pt catalyst supported on carbon black (c-Pt/CB) because of Co leaching out.5,6 The efficiency/usefulness of the atomically-controlled Pt-skin layers was clearly demonstrated. Detailed structural analysis during the durability test is now in progress. Acknowledgements This work was carried out under the “HiPer-FC” and “SPer-FC” projects, NEDO, Japan. The synchrotron radiation experiments were performed at BL14B2 and BL16B2 of SPring-8 (Proposal No. 2015B1851, 2015B1852, 2015B3388, 2015B5390, 2016A5390). References 1) H.Yano, M. Kataoka, H. Yamashita, H. Uchida, M. Watanabe, Langmuir, 23, 6438 (2007). 2) H. Yano, J. M. Song, H. Uchida, M. Watanabe, J. Phys. Chem. C, 112, 8372 (2008). 3) M. Watanabe, H. Yano, D. A. Tryk, H. Uchida, J. Electrochem. Soc., 163, F455 (2016). 4) http://fccj.jp/pdf/23_01_kt.pdf in Japanese. 5) M. Watanabe, D. A. Tryk, M. Wakisaka, H. Yano, H. Uchida, Electrochim. Acta, 84, 187 (2012). 6) K. Okaya, H. Yano, K. Kakinuma, H. Uchida M. Watanabe, ACS Appl. Mater. Interfaces, 4, 6982 (2012). Figure 1

Anion exchange membrane fuel cells (AEMFCs) are attracting much attention because of the potential use of non-platinum catalysts. The hydroxide ion conductivity of the anion exchange membranes (AEMs) is still not sufficient, which is a drawback for the commercialization. To achieve higher performances of AEMFCs, understanding the nano-scale phase separations inside the membranes is essential. So far, only few results have been reported on the anion conducting behavior either inside the bulk or on the surface of AEMs.1,2) In this study, AEMs strategically designed with different chemical structures were systematically investigated by transmission electron microscopy (TEM) in vacuum and small angle X-ray scattering (SAXS) for the structures inside the bulk membranes on the nanometer scale, and by in-situcurrent-sensing atomic force microscopy (CS-AFM) with an environmental chamber for the morphology and the ion conductive region on the membrane surfaces. Fig. 1 shows the chemical structure of the QPE-bl-11 membrane synthesized in our laboratory.3) The membranes with the same chemical component but with different ion exchange capacities (IECs) of 1.23 (X = 4, m: n = 1:2.9) and 1.95 mequiv g−1 (X = 4, m: n = 1:5.4) were prepared in a chloride-ion form. Fig. 2 shows the SAXS profiles of the QPE-bl-11 membrane. For both membranes, the peak intensity increased with increasing humidity, which indicates the development of periodic structures. With 1.23 mequiv g-1 (Fig. 2(a)), weak and broad peaks were observed at the real-space distance (d) of ca. 17 nm. With 1.95 mequiv g-1 (Fig. 2(b), a peak at d = ca. 17 nm first observed at 30% RH became larger and located at d = ca. 18 nm at 90% RH. The peak intensity was larger with IEC =1.95 mequiv g-1 especially at higher humidities. For the CS-AFM measurements at 40 °C, the membrane was pressed on a gas-diffusion electrode (GDE) with a catalyst layer composed of Pt/C and a binder (AS-5, Tokuyama Corp.).2,4) Fig. 3 shows the current images on the two membranes. At 30% RH with IEC =1.23 mequiv g-1 (Fig. 3(a)), the tip current was always less than the detection limit of 0.5 pA in the scanned area of 1 μm x 1 μm. On the membrane with IEC =1.95 mequiv g-1 (Fig. 3(b)), the OH− conductive area covered nearly 100% of the surface. The average current was approximately 10 pA. Fig. 3(c) shows the current image with IEC =1.23 mequiv g-1 obtained at 70% RH. Anion conductive spots were observed over the surface unlike that at 30% RH. Still, the current ranged from 0 to 30 pA. With IEC =1.95 mequiv g-1at 70% RH (Fig. 3(d)), the anion conductive regions were observed over the surface and more homogeneous. The tip current was larger than 5 pA at any location with an average current of 15 pA. The different IECs gave not only quantitative but also qualitative influences on the membrane morphology and properties, and the differences became larger at higher relative humidity. In the presentation, the membranes with other structures will also be discussed. 1) Q. He and X. Ren, J. Power Sources, 220 (2012) 373. 2) M. Hara et al., Langmuir, 32 (2016) 9557. 3) R. Akiyama et al., Macromolecules, 49 (2016) 4480. 4) T. Kimura et al., J. Power Sources, submitted. Figure 1

The reaction distribution inside a PEFC is important for improving the cell performance and durability. Visualization of the oxygen partial pressure (p(O2)) was conducted at the surface of a GDL under the single-serpentine flow channel and the ribs inside a see-through cell during the operation.1) Instrumental setups of the visualization system are reported in detail elsewhere.1, 2) In order to look through a cell with a single-serpentine flow channel (channel length = 1430 mm, rib width = 1 mm, channel width = 1 mm, channel depth = 1 mm) identical to that of the JARI standard cell, a cathode endplate was made of a transparent acrylic resin (Fig. 2(a)). Nine segmented current collectors (14 mm x 15 mm), also serving as ribs for the flow channel, were embedded in the cathode plate (Fig. 2(b)), which made it possible to obtain the current density at each collector. The potentials of the current collectors were controlled to be the same by the external circuit.2) Between the metal ribs plated with gold, the ribs made of acrylic resin were transparent. Therefore, p(O2) was detected not only on the GDL under the flow channel but also under the transparent ribs. The performance of the see-through PEFC with a dye coated on the GDL was reported to be nearly identical to that of the JARI standard cell at current densities lower than 800 mA cm-2.2) Therefore, the influence of the structure of the present see-through PEFC was negligibly small. 407-nm excitation light was irradiated uniformly onto the cell at the cathode. The emission from the dye sprayed on the MEA was filtered (>600 nm) and captured with a CCD camera (500 x 500 pixels, 1 pixel = approximately 120 µm x 120 µm) in a dark room. Stern–Volmer plots for calibration curves were obtained by supplying gas mixtures with various oxygen concentrations (0-25%) inside the cell before the cell operation. The cell was operated at a temperature of 80 °C with the relative humidity of 53% RH. H2 and air were supplied at 300 ml min-1 during the operations. p(O2) was measured at the oxygen utilization (Uo2) from 0 to 78% Fig. 2(a) shows a p(O2) image at Uo2 = 40% with two vertical blue lines in the transparent region. Non-visualized regions, such as the metal ribs, were masked in black.1,2) Along the dashed line on the right rim in Fig. 2(a), p(O2) was plotted in Fig. 2(b) at Uo2 = 0, 20, 40, 60 and 78%. At Uo2 = 0% there is no periodic undulations. During the power generation, 13 undulations appeared (Fig. 2(b)) with the period of 4 mm. The peaks of the undulations seen in Fig. 2(b) are related to the curves in the serpentine flow channel as indicated by red arrows in Fig. 2(a’) (zoomed image of a red rectangle in Fig. 2(a)) and Fig. 2(b), where the gas flow came in in the right direction and went out in the left direction; at the curves, the gas was pushed through the GDL to make p(O2) higher.1) Between the neighboring two curves with high p(O2) pointed at by red arrows in Fig. 2(a’), p(O2) was low as seen in Fig. 2(b). p(O2) was seen to increase from L = 50 to 54 mm. This unexpected increase is thought to have been caused by the side flow through the GDL from a small space between gasket and GDL.1) In Fig. 2(c), along the solid line in Fig. 2(a) across the flow channel and the ribs, periodic undulations in p(O2) are clearly seen; the local maximum and minimum values were observed at the middles of the flow channel and the ribs, respectively. The period of the undulations in Fig. 2(c) was 2 mm, half that in Fig. 2(b). The differences between the neighboring maximum and minimum values became larger with increasing Uo2and smaller along the flow channel from the inlet to the outlet. Details will be discussed at the presentation. With this new method, p(O2) under the flow channels and the ribs was successfully visualized. This technique is expected to be used as a powerful tool for the cell and MEA designs. Acknowledgements This work was carried out under the “HiPer-FC” and “SPer-FC” projects, NEDO, Japan. References 1) K. Takanohashi, M. Uchida, A. Iiyama, J. Inukai, J. Surf. Finish. Soc. Jpn., 68(6), in print. 2) K. Takanohashi, T. Suga, M. Uchida, T. Ueda, Y. Nagumo, J. Inukai, H. Nishide, M. Watanabe, J. Power Sources, 343(1), 135 (2016). Figure 1

International audience; Proton conductive spots on the membrane surface of sulfonated poly(arylene ketone) multiblock copolymer were investigated by current-sensing atomic force microscopy (CS-AFM) under the hydrogen atmosphere with changing relative humidity, temperature, and bias voltage. The bright spots, where the hydrophilic clusters should be effectively connected inside the membrane, were distributed rather inhomogeneously on the surface at low temperature and humidity but became more homogeneous at higher temperature and humidity. The average diameter of the spots was approximately 10 nm at 40% RH, which increased to 13 nm at 70% RH. The total area of the proton conducting spots, as well as current at each spot, on the membrane surface increased at high humidity and temperature. In addition, the diameter of the proton-conductive spots and the ratio of proton-conductive area on the membrane surface continuously increased with increasing the bias voltage. This increase of the conducting area and the current should be related to the change of the bulk ionic conductivity.

The structures of anthracene adlayers on Ag(111), Ag(100), and Ag(110) electrode surfaces in dilute perchloric acid have been investigated in detail by using in situ scanning tunneling microscopy (STM). Anthracene was found to form highly ordered molecular layers with a flat-lying orientation on the Ag single-crystal electrode surfaces in the double-layer region. High-resolution STM images allowed us to reveal packing arrangements of anthracene. Highly ordered anthracene adlayers with (2√3 × 2√3)R30° (θ = 0.08), c(4 × 6) (θ = 0.08), and c(4 × 4) (θ = 0.125) symmetries were observed on Ag(111), Ag(100), and Ag(110) surfaces, respectively.

The underpotential deposition (UPD) of Cu was investigated on a Pd(111) electrode in a H2SO4 solution by using voltammetry and in situ scanning tunneling microscopy (STM). The UPD of Cu yielded a single current peak on Pd(111) in H2SO4 to form a (1 × 1) monolayer. The so-called (√3 × √7) structure of sulfate/bisulfate was consistently observed at potentials negative and positive with respect to the UPD peak. Both the packing arrangement of (√3 × √7) and the internal structure of sulfate/bisulfate were imaged by STM. Bulk deposition of Cu proceeded epitaxially. On the atomically flat surface of the Cu layer, a Moire pattern was observed.

Structure of the adlayer of p-xylene on Rh(111) in HF solution was investigated by the complementary use of in situ scanning tunneling microscopy (STM) and ex situ low-energy electron diffraction (LEED). In situ STM images revealed that p-xylene molecules lie flat on the Rh(111) surface, forming a highly ordered adlayer with a c(2√3 × 4)rect structure. High-resolution imaging revealed not only the packing arrangement but also the internal structure of each molecule. Two methyl functional groups at the para position of benzene were clearly discerned. The adlayer structure obtained by LEED was consistent with that determined by in situ STM.

In situ electrochemical scanning tunneling microscopy (STM) disclosed that highly-ordered adlayers of adsorbed sulfate/bisulfate with atomic features having a (√3×√7) symmetry formed on a well-defined Pd(111) surface in 10 mM H2SO4 in the double layer potential range. Well-defined Pd(111) surfaces were prepared by a flame-annealing-quenching technique. High resolution STM imaging revealed the structure of water molecules in both the first and the second layers of a water-bilayer. Small reversible peaks at 0.45 V versus a reversible hydrogen electrode were found to be due to a disorder–order phase transition. The Pd(111)-(1×1) and (√3×√7) structures were observed at potentials negative and positive with respect to the small peaks, respectively.