星 永宏

Abstract The hydrogen evolution reaction (HER) on Au with high chemical stability is activated by alloying it with Ni. We evaluated the HER activity of the AuNi surface alloy prepared at different alloying temperatures on single‐crystal Au electrodes in 0.05 M H₂SO₄. The potential cycle, including the region of Ni oxidative dissolution, further enhanced the HER activity by dealloying Ni, and the activity depended on the surface structure of the Au substrate in the following order: AuNi/Au(100)<AuNi/Au(111)<AuNi/Au(110). The surface structure and atomic composition were investigated using X‐ray photoelectron spectroscopy and surface X‐ray diffraction. Surface structural analysis revealed that the dissolution of Ni from the AuNi surface‐alloy layer resulted in a decrease in the atomic occupancy of the topmost surface layer. Ni dealloying creates low‐coordination Au sites on the AuNi surface alloy, which activates the HER.

Abstract Highly active electrocatalysts for the oxygen evolution reaction (OER) are essential to improve the efficiency of water electrolysis. The properties of OER active sites on single-crystal Pt electrodes were examined herein. The OER is markedly enhanced by repeated oxidative and reductive potential cycles on the Pt(111) surface. The OER activity on Pt(111) is nine times higher in the third cycle than that before the potential cycles. OER activation by potential cycling depends on the (111) terrace width, with wider (111) terraces significantly enhancing the OER. The oxidation/reduction of the Pt(111) surface produces atomic-sized vacancies on the terraces that activate the OER. Structural analysis using X-ray diffraction reveals that the active sites formed by potential cycling are defects in the second subsurface Pt layer. Potential cycling induces the bowl-shaped roughening of the electrode surface, wherein high-coordination number Pt atoms at the bottom of the cavities activate the OER.

An adsorbed hydroxide (OHad) layer is formed on platinum electrodes at positive potentials, which affects many important electrochemical reactions, such as the oxygen reduction reaction. The stability of the OHad layer is strongly governed by the hydrophilicity of the cation interacting with OHad in the electrical double layer (EDL). Therefore, elucidating the detailed hydration structure and role of cations in the EDL is a key research goal. In this study, the structures of H2O, OHad, and Li were investigated using infrared spectroscopy and density functional theory calculations. By optimizing the coverage of OHad (theta(OH)) and Li (theta(Li)), the bending mode of the PtOH (delta(PtOH)) band on the Pt(111) surface under ultrahigh vacuum (UHV) conditions matches with that on the Pt(111) electrode at 0.8-0.9 V versus reversible hydrogen electrode (RHE) in LiOH solution, indicating that a quasi-EDL composed of OHad species interacting with hydrated Li+ on Pt(111) was successfully modeled under UHV conditions. According to the interfacial structure modeled under UHV conditions, theta(OH) = 0.3, and Li interacts directly with OHad at a stoichiometric ratio (theta(OH)/theta(Li)) of 2. Modeling of the EDL, including the outer Helmholtz plane, is beneficial for identifying the microscopic details of the EDL under electrochemical conditions.

© 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.

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.

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.

Helical self-assembly of functional π-conjugated molecules offers unique photochemical and electronic properties in the spectroscopic level, but there are only a few examples that demonstrate their positive impact on the optoelectronic device level. Here, we demonstrate that hydrogen-bonded tapelike supramolecular polymers of a barbiturated oligo(alkylthiophene) show notable improvement in their photovoltaic properties upon organizing into helical nanofibers. A tapelike hydrogen-bonded supramolecular array of barbiturated oligo(butylthiophene) molecules was directly visualized by STM at a liquid-solid interface. TEM, AFM and XRD revealed that the tapelike supramolecular polymers further organize into helical nanofibers in solution and bulk states. Bulk heterojunction solar cells of the helical nanofibers and soluble fullerene showed a power conversion efficiency of 4.5%, which is markedly high compared to that of the regioisomer of butyl chains organizing into 3D lamellar agglomerates.

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.

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.

Infrared spectroscopy of adsorbed hydroxide (OHad) has been performed on the high index planes of Pt: n(111)-(100) and n(111)-(111) series. The bending mode of OHad (delta(ptOH)) appears on these surfaces around 1080 cm(-1), which is similar to the result on the low index planes of Pt. The band intensity of delta(ptOH) depends on surface structure and electrode potential. At 0.9 V vs RHE, the band intensity of delta(ptOH) increases with the decrease of the step atom density: the intensity of delta(ptOH) is higher on the surfaces with lower activity of the oxygen reduction reaction (ORR). These results suggest that the adsorption of OHad is site specific and the deactivating species of the ORR. (C) 2016 Elsevier B.V. All rights reserved.

Hydrogen-bonding oligothiophene bearing octyl chains self-assembles into extended nanorods via the formation of cyclic hexamer. The nanorods can function as an electron-donating materials for electron-accepting PC71BM in bulk-heterojunction solar cells.

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.

Understanding the electrocrystallization mechanisms of metal cations is of importance for many industrial and scientific fields. We have determined the transitional structures during underpotential deposition (upd) of various metal cations on Au(111) electrode using time-resolved surface X-ray diffraction and step-scan IR spectroscopy. At the initial stage of upd, a characteristic intensity transient appears in the time-resolved crystal truncation rod depending on metal cations. Metal cations with relatively high coordination energies of hydration water are deposited in two steps: first, the hydrated metal cations approached the surface and are metastably located at the outer Helmholtz plane, then they are deposited via the destruction of the hydration shell. However, Tl+ and Ag+, which have low hydration energy, are rapidly adsorbed on Au(111) electrode without any metastable states of dehydration. Therefore, the deposition rate is strongly related to the coordination energy of the hydration water. Metal cations strongly interacting with the counter coadsorbed anions such as Cu2+ in sulfuric acid causes the deposition rate to be slower because of the formation of complexes.

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.

The oxygen reduction reaction (ORR) has been studied on kinked stepped surfaces of Pt inside the stereographic triangle with the use of rotating disk electrode (RDE) in 0.1 M HClO4. The kinked stepped surfaces are composed of (331) = 3(111)-(111) structure of which step line contains (100) kink: 3(111) - [m(111) + (100)], where m denotes the number of straight step atoms. The activity for the ORR decreases with increasing the kink atom density d (k) of the surface with m = 1, 3, 6, and 21, whereas the surface with m = 11 has specifically high activity for the ORR. The activity on Pt(16 15 5) = 3(111) - [11(111)-(100)] exceeds that of Pt(331) that gives the highest activity in stepped surfaces. The electricity of Pt oxide formation on Pt(16 15 5) m = 11 is the lowest in the kinked stepped surfaces examined.

Real time dissolution process of shape-controlled Pt nanoparticles (cubic, cuboctahedral, tetrahedral) has been studied using high-speed atomic force microscopy (AFM) during potential cycles in electrochemical environments. The nanoparticles are dissolved above 1.5 V(RHE) when the lower limit of the potential cycle is fixed at 0.05 V(RHE). Edges of cubic nanoparticles are dissolved at first, whereas the tops of cuboctahedral and tetrahedral nanoparticles are dissolved forming pseudo-flat structure at the upper terraces. The order of the durability is cuboctahedral < cubic < tetrahedral. When the upper limit of the potential cycle is fixed at 1.6 V(RHE), the order of the durability depends on the lower limit of the potential cycle: cubic cuboctahedral < tetrahedral between 0.05 and 02 V(RHE), cubic < tetrahedral cuboctahedral between 03 and 0.6 V(RHE). (C) 2016 Elsevier B.V. All rights reserved.

Activities for the oxygen reduction reaction (ORR) were investigated on Ni low index surfaces modified by electrochemical deposition of Pt (Pt/Ni(hkl)) and then thermal annealing. The ORR current density at 0.9 V (RHE) of the Pt/Ni(111) without annealing is three times higher than that of Pt(111). However, the Pt/Ni(111) without annealing has a low durability, with the activity reduction of more than 50% after 1000 potential cycles between 0.6 V and 1.0 V. The catalytic activity and durability are improved by annealing of Pt/Ni(111). The ORR activity of the Pt/Ni(111) with annealing at 650 K is 1.7 times higher than that without annealing and the decrease of the activity is less than 10% after 1000 potential cycles. The annealing process stabilizes the Pt-rich shell on Ni(111). (C) 2016 Elsevier B.V. All rights reserved.

Molecule substrate interactions are sensitively affected by atomic-scale surface structures. Unique activity in heterogeneous catalysts or electrocatalysts is often related with local surface sites with specific structures. We demonstrate that adsorption geometry of a model molecule with an isocyanide anchor is drastically varied among one-fold atop, two-fold bridge, and three-fold hollow configurations with increasing the size of atomic-scale local surface sites of Pd islands on an Au(111) model surface. The vibrational spectroscopic observation of such local information is realized by site-selective and self-assembled formation of hotspots, where Raman scattering intensity is significantly enhanced via excitation of localized surface plasmons.

The effects of alkali meal cation on the surface oxidation and alcohol oxidation reactions on Au(111) have been investigated using surface X-ray diffraction and infrared spectroscopy. It is known that alkali metal cations strongly affect the alcohol oxidation reactions on Pt(111); however, the oxidation reactions on Au(111) do not depend on alkali metal cations. Infrared spectroscopy reveals the formation of adsorbed OH in LiOH and CsOH solutions below the second anodic peak at 1.3 V. This result indicates that surface oxidation processes do not depend on alkali metal cations below 1.3 V. The interfacial structure, including the outer layer, of an Au(111) electrode has been determined using X-ray diffraction in LiOH and CsOH. During the surface oxidation, the Au(111) surface in CsOH gets roughened more remarkably than that in LiOH above 1.3 V. Li+ has a protective effect against surface roughening. Thus, the cationic effect is weaker in the potential region lower than the second anodic peak, which does not affect the lifting of the surface reconstruction and the alcohol oxidation reactions.