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.
Structural effects on the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) have been studied on the high index planes of Pt and Pd in 0.1 M HClO4. The exchange current density jo of the HOR increases with the increase of the step atom density dS from n = ∞ to 9 on(n−1)(111)-(110), n(111)-(100), n(100)-(111) and n(100)-(110) surfaces of Pt, where n shows the number of the terrace atomic rows. On the surfaces with n ≤ 9, however, the values of j0 do not depend on dS. These facts support that the step is the active site for the HOR on Pt electrodes, however, only part of the step atoms contributes to the HOR. Pt electrodes of (n−1)(111)-(110) series have the highest activity for the HOR. The activity for the ORR increases with the increase of the terrace atom density dT on Pd electrodes. The step atoms do not affect the ORR. Pd(100) has the highest activity for the ORR. The specific activity of Pd(100) is 4.2 times as high as that of the standard Pt catalyst (TEC10E50E). The mass activity of Pd surfaces covered with monolayer of Pt (Pt/Pd(hkl)) is 7 times as high as that of TEC10E50E.
Pseudomorphic atomic arrangements of the electrochemically deposited Pt monolayer on the Au(111) surface was determined by the resonance surface X-ray scattering (RSXS) measurements. Electro-catalytic activity for oxygen reduction reaction (ORR) of the pseudomorphic Pt monolayer electrochemically prepared on the Au(111) electrode surface was investigated and compared with that of the Pt(111) single crystal electrode.
Drastic reduction in Pt usage is essential for the commercialization of fuel cell vehicles. Improvement of the activity for oxygen reduction reaction (ORR) of the Pt catalyst is a key technology for the reduction of Pt usage. In this report, development of shape-controlled Pt catalysts and Pt monolayer core/shell structured catalysts are described. The enhancement in ORR activity of these catalysts is demonstrated in comparison with a commercially available Pt catalyst.
Electrocatalysts using carbon nanotubes (CNT) show higher catalytic activity as well as higher CO-tolerance in H2-O2 fuel cells. The high performance has been attributed to the interface interaction between Pt (or PtRu) catalyst particles and graphitic carbons based on surface science studies using highly oriented pyrolytic graphite (HOPG).
In order to commercialize polymer electrolyte fuel cells widely, the development of a non-Pt catalyst for oxygen reduction reaction is essentially required. In this article, the necessity of non-Pt catalysts for low temperature fuel cells and our new trials using group 4 and 5 metal compounds are explained.
We have analyzed the electronic structure of carbon alloy cathode catalysts alternative to platinum-based materials for polymer electrolyte fuel cells using synchrotron radiation techniques. A series of X-ray absorption and X-ray photoemission spectra of FePc-based carbon alloy catalysts pyrolyzed at various temperatures clearly show the turnover of chemical species dependent on the pyrolysis temperature. We can feed back the above information to synthesis of advanced catalysts with much higher activity and durability.
In this paper, we tried to evaluate the contact angle for a droplet on the solid surface with ruggedness based on elasticity theory and thermodynamics. In this theory, we assumed that the solid was homogeneous isotropic elastic body. Surface tension was given as function of strain in the imaginary layer which had thin finite thickness τ. By using this function and thermodynamics, cosine of the contact angle of a droplet was given as the function of volume fraction of solid in this imaginary layer. Ando, etc. had announced the experimental data for the porous silicon surface fabricated by anodic etching. For the purpose to confirm the validity of this theory, we compared these experimental data with theoretical calculated data. The theoretical calculated data showed comparatively good agreement with experimental data.
Remote photocatalytic reaction of a Pt-modified TiO2 thin film was investigated by using Ag nanosheet as a marker. The Ag nanosheet is a two-dimensional crystalline film composed of myristate-capped silver nanoparticles (d = 5 nm), which has a strong localized plasmon absorption band at λmax = 470 nm. The Ag nanosheet on a 50 nm gold film was set on a measurement cell at 10 μm distance from the Pt-modified TiO2 film. Then the refractive index change of Ag nanosheet was real-time monitored by a surface plasmon resonance (SPR) technique under UV light irradiation (wavelength: 365 nm) from the back side of the TiO2 film. The plasmon resonance angle shifted to lower angle in consequence of the degradation of Ag nanosheet due to the remote photocatalytic reaction. We found the reaction was continued even after stopping UV irradiation, i.e., a chain reaction in Ag nanosheet was suggested. The chain reaction was influenced by N2 gas purge as well as the ligand exchange of myristate capping molecules to alkyl thiolate.