中村 将志

Abstract Enhancement of the oxygen reduction reaction (ORR) activity is an important subject for the development of fuel cells. In this study, we prepared the n(111)-(111) series of Pt₃Co single crystal electrodes using an induction heating furnace and investigated the ORR in 0.1 M HClO₄ using the rotation disk electrode (RDE). The specific activity of the ORR (j_k) increased monotonously with increasing terrace width n on the n(111)-(111) series of Pt₃Co, showing the highest activity on Pt₃Co(111). The value of j_k of Pt₃Co(111) was 59-fold higher than that of Pt(111) at 0.95 V(RHE). This trend was different from those of the same series of Pt, Pt₃Co, and Pt₃Ni reported previously. Furthermore, the ORR activity was improved on all electrodes by adding melamine to the electrolytic solution. Melamine was preferentially adsorbed at the terrace edge. Pt₃Co(553) n = 5 showed the highest activity. The values of j_k at 0.95 V(RHE) were 23- and 3.3-fold higher than those of Pt(553) n = 5 and Pt₃Co(553) n = 5 without melamine modification, respectively. The durability of Pt₃Co(553) n = 5 with melamine was improved 8.0-fold. Graphical Abstract

Graphene growth on a Pt(111) substrate exposed to benzene was studied at substrate temperatures between 800 K and 1100 K. The effects of the substrate temperature during benzene exposure and post-annealing were examined. It was revealed that the substrate temperature during benzene exposure determined the graphene size, which was measured using scanning tunneling microscopy (STM). Nanographenes (NGs) of ~10 nm in size. were obtained by exposing the substrate to benzene at 800 K and post-annealing at 1100 K. The presence of a C–Pt bond, which may fix the carbon atoms on the Pt(111) surface and suppress any further growth of graphene, was confirmed by the carbon K-edge near-edge X-ray absorption fine structure spectroscopy (C K NEXAFS) and X-ray photoelectron spectroscopy (XPS) for the NG. Angle resolved photoemission spectroscopy (ARPES) performed on the NG has a reduced density of states at the Fermi level.

© 2020 Elsevier Ltd The oxidation of dopamine (DA) on a boron-doped diamond (BDD) electrode was investigated using in situ attenuated total reflection infrared spectroscopy (ATR-IR) and infrared reflection absorption spectroscopy (IRAS). Voltammogram showed multiple anodic/cathodic peaks for the oxidation/reduction of DA and its oxidized derivatives on the BDD electrode. The oxidation/reduction species on the surface and in solution were assigned using ATR-IR and IRAS, respectively. The anodic oxidation of DA promoted polymerization, and the polymerized DA (PDA) was continuously deposited on BDD without being reduced by potential cycles, which resulted in the irreversible behavior of the voltammogram. A decrease in the oxidation current of DA by potential cycles was due to the deposition of PDA. Some intermediate quinone species, such as dopaminequinone and dopaminechrome, were reversibly reduced to hydroquinone.

© 2018 Elsevier B.V. Many time-resolved measurements of electrochemical interface have been developed in conformity with the time scale of various transition. X-ray diffraction using synchrotron radiation is a powerful tool for structural determination of electrical double layer in real time. This short review describes structural dynamics of interfacial ions during the faraday and non-faraday processes in the time scale from microsecond to second.

Carbon-based materials are regarded as an environmentally benign alternative to the conventional metal electrode used in electrochemistry from the viewpoint of sustainable chemistry. Among various carbon electrode materials, boron-doped diamond (BDD) exhibits superior electrochemical properties. However, it is still uncertain how surface chemical species of BDD influence the electrochemical performance, because of the difficulty in characterizing the surface species. Here, we have developed in situ spectroscopic measurement systems on BDD electrodes, i.e., in situ attenuated total reflection infrared spectroscopy (ATR-IR) and electrochemical X-ray photoelectron spectroscopy (EC-XPS). ATR-IR studies at a controlled electrode potential confirmed selective surface hydroxylation. EC-XPS studies confirmed deprotonation of C-OH groups at the BDD/electrolyte interface. These findings should be important not only for better understanding of BDD's fundamentals but also for a variety of applications.

The interfacial structure between aqueous electrolytes and the epitaxial graphene on a SiC(0001) electrode has been determined using X-ray diffraction. The electrolyte and electrode potential dependences are investigated, and it is found that the water bilayer is stabilized on the graphene surface in a similar fashion to icelike structure. There are no specific adsorbed ions and no layer formation of electrolyte ions at the Helmholtz plane, which differs from the double-layer structure found on metal electrodes remarkably. The layer spacing of the water bilayer depends on the electrode potential, indicating that water reorientation occurs. The applied electrode potential is strongly related to the potential drop across the interface induced by the electric dipole field of the bilayer water. A small double-layer current results from non-faradaic charge by the reorientation of the bilayer water.

The presence of a self-assembled monolayer (SAM) of dioctadecyl sulfide (DOS) on a Au(111) electrode affects the underpotential deposition (UPD) of copper in sulfuric acid solution. The first stage of the UPD, i.e., formation of the √3 × √3 R30° lattice comprising the honeycomb structure of copper, is delayed by the DOS SAM of the lower-density phase, in which the chain axis is parallel to the surface. Neutral molecules are preferentially adsorbed on the Au(111) electrode surface at around the potential of zero charge (pzc), which is approximately -0.1 V (vs. Hg|Hg2SO4) in sulfuric acid solution. The adsorption of copper ions at this potential is inhibited by the DOS SAM, which delays the successive Cu-UPD process in the first stage. In contrast, the DOS SAM of the higher-density phase, in which the chain axis is standing upright, inhibits the entire UPD process.

We have studied Pt surfaces for which activity towards the oxygen reduction reaction (ORR) is enhanced by adsorbed amines: octylamine (OA) and an alkyl amine containing a pyrene ring (PA). Adsorbed OA/PA (molar ratio 9/1) enhances activity for ORR on n(111)–(111) surfaces of Pt for terrace atomic rows n greater than 7. The activity on Pt(111), the surface of which is a flat terrace, is particularly enhanced. On Pt(100), which also has a flat terrace, however, the ORR activity is greatly reduced. It is shown that adsorbed OA/PA enhances the ORR on surfaces with a wide (111) terrace, but deactivates the ORR on the (100) terrace.

© 2018 The Electrochemical Society of Japan, All rights reserved. Structural effects on the activity for the oxygen reduction reaction (ORR) have been studied on single crystal electrodes of Pt modified with six aromatic organic molecules (AOMs). The AOMs examined affect the ORR activity slightly. However, the activity of the sites uncovered by AOMs increases after the modification: the ORR activity of uncovered Pt(111) area after the modification of phthalocyanine is 2.5 times as high as that of bare Pt(111). t-BuTAP and iron (II) phthalocyanine also enhance the ORR on Pt(997). These facts show that adsorbed AOMs can enhance the ORR activity of the uncovered active sites on Pt electrodes.

© 2018 The Electrochemical Society of Japan, All rights reserved. This headline article focuses on the oxygen reduction reaction (ORR), cathodic reaction of fuel cells, on well-defined high index planes of Pt and Pd for the elucidation of factors enhancing the activity for the ORR. The surfaces with (111) terrace edge have high activity for the ORR on Pt electrodes. Pt(331) = 3(111)-(111) gives the highest activity for the ORR in the stepped surfaces of Pt. Incorporation of one kink atom among eleven step atoms further enhances the activity of Pt(331). On single crystal electrodes of Pd, however, terrace edge deactivates the ORR and wide (100) terrace enhances the activity. Effects of Pt oxides (PtOH and PtO) on the ORR have been examined using vibrational spectroscopy. Infrared reflection absorption spectroscopy (IRAS) shows that PtOH prevents the ORR on Pt electrodes. Nanoparticle surface enhanced Raman spectroscopy (NPSERS) indicates that PtO also blocks the ORR on Pt(100) of which ORR activity is the lowest. The ORR activity of Pt is also enhanced by the modification of the surfaces by amines with long alkyl chains such as octylamine (OA) and amine with pyrene ring (PA). Modification by OA/PA increases the ORR activity on n(111)-(111) surfaces of Pt with terrace atomic rows more than 7. The activity of flat Pt(111) is enhanced most remarkably by OA/PA. However, the ORR of Pt(100), of which surface is also composed of flat terrace, is deactivated significantly.

Methanol oxidation reaction (MOR) has been studied on the low index planes of Pd (Pd(111), Pd(100) and Pd(110)) in 0.1 M HClO4 using voltammogram. Onset potential of methanol oxidation increases as Pd(110)similar to Pd(100) < Pd(111). The activity for the MOR is estimated using anodic peak current density of the voltammograms. The order of the activity is Pd(111)similar to Pd(110) << Pd(100): (100) surface enhances the activity for the MOR on Pd electrodes. (C) The Electrochemical Society of Japan, All rights reserved.

In situ vibrational spectra of Pt oxides that cannot be measured with IR spectroscopy have been studied on the low index planes of Pt using surface enhanced Raman spectroscopy with bare Au nanoparticles (NPSERS). Two bands appear around 570 and 340 cm(-1) at higher potentials in 0.1 M HClO4 saturated with Ar, which are assigned to the stretching vibration of Pt-O(H) and the libration vibration of Pt-O, respectively. NPSERS spectra are measured in 0 2 saturated solution for the first time. The band intensities of Pt-O(H) and Pt-O in O-2 saturated solution are enhanced significantly compared with those in Ar saturated solution. The onset potentials of Pt-O and Pt-O(H) formation are 1.15 V(RHE) on Pt(100) and 1.2 V(RHE) on Pt (111) and Pt(110). The onset potential of Pt-O and Pt-O(H) and band shape differ from the results obtained using shell isolated surface enhanced Raman spectroscopy (SHINERS). The Pt-O and Pt-O(H) band intensities are normalized using COad as an internal standard. The Pt-O(H) band intensity depends on surface structures as Pt(110) < Pt(111) << Pt(100), whereas the Pt-O band gives a different intensity order for Pt(lll) and Pt(110) as Pt(111) < Pt(110) << Pt(100) in O-2 saturated solution.

The interfacial structure and activity for the oxygen reduction reaction (ORR) were investigated on a PtNi surface alloy on a Pt(111) electrode (PtNi/Pt(111)). The PtNi surface alloy was prepared by thermal annealing of Ni2+ modified on Pt(111) at 573-803 K. After optimizing the alloying temperature and the amount of added Ni, the ORR current density of PtNi/Pt(111) at 0.9 V (reversible hydrogen electrode) is enhanced 9.5 times compared with that of Pt(111), and the activity is decreased by 24% after 1000 potential cycles. The atomic composition and subsurface structure of PtNi/Pt(111) were determined by in situ infrared reflection-absorption spectroscopy and X-ray diffraction. The surface contains a (111)-oriented Pt-skin and the subsurface of the 2nd-5th layers of the PtNi alloy contains less than 11% Ni atoms. The layer spacings of the surface alloy layers are slightly expanded compared with those of bare Pt(111). Homogeneous alloying with a small amount of Ni in the subsurface layers achieves the high ORR activity and durability.

The influence of the preparation method and adsorbed amount of n-tetratetracontane (n-C44H90) on its orientation in a monolayer on the Au(111) surface is studied by near carbon K-edge X-ray absorption fine structure spectroscopy (C K-NEXAFS), scanning tunneling microscopy (STM) under ultrahigh vacuum, and infrared reflection-absorption spectroscopy (IRAS) at the electro-chemical interface in sulfuric acid solution. The n-C44H90 molecules form self-assembled lamellar structures with the chain axis parallel to the surface, as observed by STM. For small amounts adsorbed, the carbon plane is parallel to the surface (flat-on orientation). An increase in the adsorbed amount by similar to 10-20% induces compression of the lamellar structure either along the lamellar axis or alkyl chain axis. The compressed molecular arrangement is observed by STM, and induced conformation and orientation changes are confirmed by in situ IRAS and C K-NEXAFS.

The structural effects of substrates on the incident photon-to-current conversion efficiency (IPCE) of Zn porphyrin (ZnP) dyes (ZnP-ref, YD2, and ZnPBAT) have been studied on well-defined single-crystal surfaces of rutile TiO2 (TiO2(111), TiO2(100), and TiO2(110)). IPCE of ZnP-ref depends on the structure of the substrates remarkably: TiO2(100) &lt TiO2(110) &lt TiO2(111). IPCE of ZnP-ref/TiO2(111) is 13 times as high as that of ZnP-ref/TiO2(100) at 570 nm. YD2 and ZnPBAT also give the highest IPCE on TiO2(111). The relative coverages of the porphyrin dyes give the following order: TiO2(111) &lt TiO2(110) &lt TiO2(100). This order is opposite to that of IPCEs. The orientation of the dyes is predicted using density functional theory calculations on simplified models of TiO2 surfaces. The highest IPCE on TiO2(111) is attributed to the high rate of electron transfer through the space due to the fluctuation of the tilt angle of the adsorbed dyes.