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The production of hydrogen from water via solar energy conversion has attracted immense attention as a potential solution for addressing energy supply issues. We demonstrated a stable and efficient organic-inorganic hybrid photoelectrochemical (H-PEC) cell. Modifying the surface energy and structure of the organic photoactive layer using multi-functional nanomaterials including –OH-modified NiO nanoparticles and reduced graphene oxide (RGO) led to a 2.8-fold enhancement of the water splitting performance in a single junction H-PEC cell. The enhanced performance was attributed to the i) improved water-wettability, ii) enhanced charge extraction property by band-edge alignment, and iii) the catalytic effect of the introduced NiO-OH nanoparticles. In addition, because of the effects of the RGO layer preventing water penetration and photo-corrosion during the oxidation of water, a distinguishable long-term stability was achieved from the H-PEC cell with an RGO capping layer. The best performance was obtained from the organic-inorganic hybrid multi-junction PEC cells consisting of the WO 3 photo-anode (activated under UV irradiation) and the H-PEC cell (activated under visible light irradiation). The H-PEC cell with a WO 3 photo-anode exhibited significantly enhanced stability and performance by a factor of 11.6 higher than photocurrent of the single H-PEC cell.

Advanced Materials Engineering, Korea University of Science and Technology (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113, Korea(Received April 14, 2016 ; revised April 28, 2016 ; accepted April 29, 2016)AbstractThe hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solvefossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has beenthe most attractive technology in a way to produce hydrogen because it does not emit any pollutants comparedto other method such as natural gas steam reforming and coal gasification etc. In order to improve efficiencyand durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalystshave been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) electrocatalysts indicated ahigher activity and stability compared with other transition metals in harsh condition such as acid solution.It is necessary to develop inexpensive non-noble metal catalysts such as transition metal oxides because thePGM catalysts is expensive materials with insufficient it’s reserves. The optimization of operating parameterand the components is also important factor to develop an efficient water electrolysis cell. In this study,we optimized the operating parameter and components such as the type of AEM and density of gas diffusionlayer (GDL) and the temperature/concentration of the electrolyte solution for the anion exchange membranewater electrolysis cell (AEMWEC) with the transition metal oxide alloy anode and cathode electrocatalysts.The maximum current density was 345.8 mA/cm

A chemically etched CuCo-oxide (CE-CCO) electrode prepared by electrodeposition was used for oxygen evolution reaction electrocatalyst. Surface chemical etching of CuCo-oxide (CCO) introduced oxygen vacancies and thus increased electrical conductivity to promote oxygen generation. During practical applicability testing, when CE-CCO was used as the anode of an anion-exchange membrane water electrolyzer, enhanced oxygen evolution performance was observed (current density = 1390 mA/cm2 at 1.8 Vcell), which, among other reactions, was ascribed to the easy removal of O2 from the aerophobic electrode surface. In addition to featuring low mass transfer resistance even at high current density with substantial gas generation, the CE-CCO electrode featured remarkable durability, exhibiting stable performance over 3600 h under the conditions of continuous O2 evolution. Thus, this work shows that the performance of electrodeposited oxide catalysts can be enhanced by introducing oxygen vacancies, while the energy conversion efficiency of the corresponding water electrolysis systems can be increased by lowering mass transfer resistance via efficient gas removal and reactant supply.

We prepare three-dimensional honeycomb-like Cu

The immobilization of Cyt. c (cytochrome c) on C60 (fullerene) nanohybrid TiO2 (titanium dioxide) gel films assembled with C60, Ti(O–nBu)4 and Cyt. c was realized by a surface sol–gel process. Interestingly, C60 was used without any surface modification of the film formation and exhibited good electrochemical performance. Additionally, the surface morphologies of the TiO2 and TiO2/C60 nanocomposite thin films showed remarkable uniformity over a wide area, however, the surface morphology depends on the deposition of Cyt. c, which densely covers the surface with adsorbed Cyt. c molecules. The cyclic voltammetry of the outer-most fullerene films revealed high stability, as well as, a pair of current peaks characteristic of a weak redox system with anodic and cathodic peak potentials at 0.262 V and 0.137 V. The electrochemical properties of thin films can be attributed to the redox system of the C60 layer deposited on the TiO2 gel layer. A pair of well-defined quasi-reversible redox peaks generated by Cyt. c are easily achieved because of the efficient assembly on the C60-modified electrode. In this work, we suggest the efficient introduction of C60 into a TiO2 gel matrix, evaluating the electrochemical characteristics of Cyt. c assembly.

The oxygen reduction reaction, ORR, performances of graphene-supported palladium (Pd) and palladium alloys (Pd3X: X = Ag, Co and Fe) catalysts with highly dispersed catalyst particles are investigated in acidic and alkaline conditions using a rotating disk electrode, RDE. Graphene nanosheet, GNS, supported Pd based catalysts are fabricated without surfactant through the impregnation of Pd and 2nd metal precursors on GNS, leading to small and uniformly dispersed nanoparticles, even when high metal loading of up to 60 wt.% are deposited on supports. The ab-initio density functional theory, DFT, calculations, which are based on the d-band center theory, have been applied to correlate with the results of the ORR performances obtained by half-cell tests. Additionally, the cohesive energy, Ecoh, and dissolution potential, Um, for the Pd nanoparticles have been calculated to understand thermodynamic stability. To elucidate the d-band center shift, the Pd 3d5/2 core-level binding energies for Pd/GNS, Pd3Ag/GNS, Pd3Fe/GNS and Pd3Co/GNS have been investigated by X-ray photoelectron spectroscopy, XPS. The GNS-supported Pd, or Pd-based alloy-nanoparticle catalyst shows good ORR activity under acidic and alkaline conditions, suggesting it may offer potential replacement for Pt for use in cathode electrodes of anion-exchange membrane fuel cell, AEMFC, and acid based polymer electrolyte fuel cell, PEMFC.

A polymer electrolyte membrane water electrolysis system can produce high-purity hydrogen gases in a highly efficient manner. However, the level of hydrogen gas production is still small. In addition, noble-metal catalysts for the reaction in acidic environments, as well as an additional drying step to remove water contained in the hydrogen, are required. Therefore, water electrolysis system with high efficiency and lower cost, an alkaline anion-exchange membrane system that can produce high-purity hydrogen without a noble-metal catalyst, is needed. Nano-size NiCo2O4 powders were prepared by using a sol-gel method to achieve an efficient and economical water electrolysis system. When the powder was calcined at 450 °C, the crystallinity and the cyclic voltammogram measurement showed the best values. In addition, the 15-wt.% polytetrafluoroethylene mixed NiCo2O4 powders exhibited the largest cyclic voltammetry active area and the highest oxygen evolution reaction activity with the appropriate stability.

Solution-processed graphene oxides in their reduced forms are prominent prospective functional materials for organic optoelectronics. For graphene oxide synthesis, several methods have been developed, which induce varying properties in their products. However, the dependence of the graphene oxide properties on their synthesis methods has rarely been studied, hindering the selection of the optimum synthesis route for a target application. In this study, we report our study results on the properties of synthesized graphene oxides and their reduced forms created using several synthesis methods, such as the modified Hummers' method, the improved method, and the Staudenmaier's method as well as from two commercial sources, Angstron Material, Inc. and Graphos, Inc. Focusing on the transparent electrode application, the properties of thin films were investigated using UV–visible spectroscopy, Hall measurements, atomic force microscopy, Raman spectroscopy, work function measurements, and X-ray photoelectron spectroscopy. Our results reveal significant morphological, elemental, structural, and optoelectrical property variations among the as-prepared and reduced thin films of graphene oxides by their synthesis methods. In addition, the results show that the graphene oxides synthesized using the modified Hummers' method and the product from Angstron Material, Inc. are the most suitable materials for the transparent electrode application.

In this report, we demonstrated a reliable switching effect of carbon nanotube (CNT) field-effect transistor (FET) devices integrated with 99% semiconducting CNT as a channel and high-k oxide as the dielectric. CNT FET devices with high-k oxides of Al-ZrHfO2 and Al2O3 were electrically characterized and compared. There was no considerable hysteresis in the Al2O3-based CNT FET device. The Al-ZrHfO2 with a tetragonal phase-based high dielectric constant (~47), designed by an atomic layer deposition process, showed a reliable switching effect as well as low operation voltage (2 was proposed as a primary mechanism to explain a current change of a counterclockwise direction and threshold voltage (Vth) shift for transfer properties. The suggested charge trapping model within bulk oxide was experimentally proven since the hysteresis from the adsorption/desorption of gas molecules to CNT surface was negligible. Endurance characteristics of the CNT switching devices remained stable without any serious current fluctuation during a repetitive cycling test. The memory device with reliable switching properties as well as low operation power would pave a road toward next-generation memory components of portable electronic gadgets.

High metal loaded (60 wt%) binary PdM (M = Ru, Sn, Ir) catalysts were synthesized on reduced graphene oxide (RGO) using the borohydride reduction method, and they were used for the electro-oxidation of simple alcohols, such as methanol, ethanol, and 1-propanol, in alkaline media. Cyclic voltammetry (CV) tests indicated that the Pd-based binary systems could improve electrochemical activities significantly compared to the monometallic Pd/RGO catalyst. Among the prepared catalysts, addition of Ru to Pd (PdRu/RGO) resulted in remarkably improved electrocatalytic activity in terms of larger peak current densities and lower onset potential in all electro-oxidation cases with methanol, ethanol, and 1-propanol. CO-stripping tests also revealed that the onset and peak potentials for the CO oxidation appear to decrease by the addition of Ru to Pd/RGO, indicating that the electro-oxidation of CO can take place more efficiently on the PdRu/RGO catalyst with the assistance of easily formed hydroxyl groups. Such an improvement of electrocatalytic performance can be ascribed to structural and chemical modifications of the Pd catalysts. Physicochemical properties of the PdM/RGO catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS).

Nano-scale Pt particles are often reported to be more electrochemically active and stable in a fuel cell if properly displaced on support materials; however, the factors that affect their activity and stability are not well understood. We applied first-principles calculations and experimental measurements to well-defined model systems of N-doped graphene supports (N-GNS) to reveal the fundamental mechanisms that control the catalytic properties and structural integrity of nano-scale Pt particles. DFT calculations predict thermodynamic and electrochemical interactions between N-GNS and Pt nanoparticles in the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). Moreover, the dissolution potentials of the Pt nanoparticles supported on GNS and N-GNS catalysts are calculated under acidic conditions. Our results provide insight into the design of new support materials for enhanced catalytic efficiency and long-term stability.

Reduced graphene oxide (RGO)-supported bimetallic Pd–Pt nanostructures with core–shell Pd@Pt (Pd@Pt/RGO) and alloyed PdPt (PdPt/RGO) were prepared by a one-pot reduction approach using L-ascorbic acid for the reduction of both the metal precursors and the graphene oxide supports. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and Raman spectroscopy revealed that the three-dimensionally shaped Pd–Pt nanostructures were uniformly deposited onto the reduced graphene oxide surface. The RGO-supported core–shell Pd@Pt and alloyed PdPt catalysts were confirmed and investigated by high-angle annular dark-field scanning TEM (HADDF-STEM) with energy-dispersive X-ray spectroscopy (EDX) in addition to X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and cyclic voltammetry (CV). With the synergetic effects of the binary Pd–Pt system and the RGO support, these catalysts exhibited considerably enhanced catalytic activities and stabilities for the oxidation of methanol in an alkaline solution compared to monometallic Pt/RGO and commercially available carbon-supported Pt (Pt/C) catalysts. The star-shaped core–shell Pd@Pt/RGO catalysts exhibited the greatest improvement in electrocatalytic performance in terms of current density, onset potential, stability, and the charge transfer rate.

N4-chelate macrocycles comprise the foundation for non-precious metal oxygen reduction reaction (ORR) catalyst research, where the main electrochemical process occurs in polymer electrolyte membrane (PEM) fuel cells. Although iron–nitrogen–carbon (M–N–C) complexes are known to be the most active non-precious ORR catalysts to date, a fundamental understanding of the ORR mechanisms of these materials is still in its nascent stage and needs further investigation. In this work, ab initio density functional theory (DFT) calculations have been applied to unveil the underlying principles for the electrocatalytic activity and structural stability of Fe–N4 chelates exposed to acidic media. Therefore, we compared the electronic structures of ferrous phthalocyanine (Fe-Pc) and an in-house developed Fe-Pc modified with diphenylphenthioether substituent species (Fe-SPc). The results of these DFT simulations directly correlate with the results of the half-cell ORR activity and stability electrochemical testing in 0.1 M HClO4. The results indicate that the relative energetic position of the dz2-orbital with respect to the Fermi level can induce an Fe redox couple potential shift and modulate the catalytic activity towards the ORR. Furthermore, our combined DFT calculations and empirical observations highlight that the relative position of the dz2-orbital can be controlled by the incorporation of functional groups, resulting in the ability to tune the ORR activity of these complexes. Structural stability of the materials, as predicted by the DFT-calculated cohesive energies of Fe and FeO, can also be readily tuned by modulating Fe-Pc with the substituent species. This study, coupling rigorous experimental observations with DFT investigations, thereby provides a fundamental insight that can aid in the design of future generations of non-precious ORR catalysts with improved activity and stability.

Perpendicularly attached MoS

Uniformly dispersed Ag nanoparticles were successfully obtained on reduced graphene oxide (RGO) through the simultaneous reduction of Ag and graphene oxide (GO) without surfactant by controlling growth of Ag nanoparticles at low temperatures. Using this method, even a high metal loading of 60 wt.% Ag with a mean diameter of less than 10 nm could be achieved over the RGO sheets. The oxygen reduction reaction activity was investigated using an RGO-supported Ag catalyst (Ag/RGO) in a 0.1 M NaOH solution, and the kinetic parameters were determined using the rotating disk electrode (RDE) technique. For comparison, a commercial carbon-supported Ag catalyst (Ag/C) was investigated under identical experimental conditions. Keywords: Silver-based catalyst, Reduced graphene oxide, Oxygen reaction reduction, Alkaline fuel cell

a b s t r a c t Oxygen reduction and ethanol oxidation reaction (ORR and EOR) have been studied on graphene nanosheet-supported (GNS) pure Pd and Pd3Y nanoscale-alloy (Pd/GNS and Pd3Y/GNS) electrocatalysts. The electrochemical studies were carried out for ORR both in acidic and alkaline solutions employing a rotating disk electrode (RDE), and performed for EOR in alkaline media with cyclic voltammetry method. The structure and composition of the Pd and Pd3Y nanoparticles were verified using TEM, XRD and XPS. We combine the experimental measurements with ab initio density functional theory (DFT) calculations to identify the d-band center position of Pd atom in the pure Pd and Pd3Y alloys as a function of site on near the surface. Both approaches clearly show that alloying the Pd with Y significantly modifies the electronic structures of Pd atoms. Core-level of Pd 3d5/2 shifts to a negative value, which increases the d-band center of Pd atom and enhances the bond strength of Pd O, which implies good catalysts for EOR but ORR. Our results indicate that the electronic structure of the Y-modified bimetallic Pd alloy is a good descriptor for the catalytic activity.

The long-term stability and superior device reliability through the use of delicately designed metal contacts with two-dimensional (2D) atomic-scale semiconductors are considered one of the critical issues related to practical 2D-based electronic components. Here, we investigate the origin of the improved contact properties of alloyed 2D metal-semiconductor heterojunctions. 2D WSe2-based transistors with mixed transition layers containing van der Waals (M-vdW, NbSe2/WxNb1-xSe2/WSe2) junctions realize atomically sharp interfaces, exhibiting long hot-carrier lifetimes of approximately 75,296 s (78 times longer than that of metal-semiconductor, Pd/WSe2 junctions). Such dramatic lifetime enhancement in M-vdW-junctioned devices is attributed to the synergistic effects arising from the significant reduction in the number of defects and the Schottky barrier lowering at the interface. Formation of a controllable mixed-composition alloyed layer on the 2D active channel would be a breakthrough approach to maximize the electrical reliability of 2D nanomaterial-based electronic applications.

The electrocatalytic oxidation of CO was studied using carbon-supported 20 wt% PtRu (PtRu/C) catalysts, which were prepared with different Pt : Ru atomic ratios from 7 : 3 to 3 : 7 using a colloidal method combined with a freeze-drying procedure. The bimetallic PtRu/C catalysts were characterized by various physicochemical analyses, including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). CO stripping voltammetry measurements indicated that the addition of Ru with a Pt catalyst significantly improved the electrocatalytic activity for CO electrooxidation. Among the tested catalysts, the Pt5Ru5/C catalyst had the lowest onset potential (vs.Ag/AgCl) and the largest CO EAS. Structural modification via lattice parameter change and electronic modification in the unfilled d band states for Pt atoms may facilitate the electrooxidation of CO.

In this work, we have probed the shape- and composition-dependent activities of Pt and PtAu catalysts for formic acid electrooxidation. Pt-based hollow nanostructures such as Pt hollow nanospheres (Pt HNSs), Pt nanotubes (Pt NTs), and PtAu alloy nanotubes (PtAu NTs) with controlled Pt:Au compositions are successfully prepared via a galvanic replacement process using sacrificial Ag templates. The physicochemical properties of these Pt and PtAu catalysts are confirmed by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. The electrochemical activities of these hollow structured catalysts are compared for formic acid oxidation by cyclic voltammetry and chronoamperometry methods. Relative to the commercial Pt black and Pt/C nanoparticle catalysts, the hollow nanostructured Pt materials (Pt HNS, Pt NT) exhibit enhanced catalytic activities due to structural effects. Moreover, the bimetallic Pt...

The electrocatalytic oxidation of glycerol was studied using carbon-supported 20 wt.% PtNi (PtNi/C) catalysts, which were prepared with different Pt:Ni atomic ratios from 3:1 to 1:1 using a colloidal method combined with a freeze-drying procedure. The bimetallic PtNi/C catalysts were characterized by various physicochemical analyses, including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) measurements indicated that the addition of Ni with a Pt catalyst significantly improved the electrocatalytic activity for glycerol electrooxidation. Among the tested catalysts, the Pt 2 Ni 1 /C catalyst had approximately 61% higher mass activity than the Pt/C catalyst. Structural modification via lattice parameter change and electronic modification in the unfilled d band states for Pt atoms may kinetically facilitate the electrooxidation of glycerol with an increased exchange current density over the PtNi/C catalysts.

Graphene as a support for various metal nanoparticles was synthesized through a wet-chemical method combined with thermal exfoliation of graphite. The 60 wt% metals (Pt, Pd, Rh, Ru, Sn, and Ni) supported on the graphene materials were prepared by impregnation method with a subsequent heat treatment in H 2 atmosphere. Physicochemical analyses such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were employed to investigate the structural and electronic properties of the deposited metals on the graphene material. The metal nanoparticles were finely dispersed on the graphene support. The graphene-supported Pt, Pd, Rh, and Ru materials appeared to be metallic phase, however, the Sn phase showed an oxide state. The graphene-supported Ni revealed a core/shell-like structure of oxide and metallic phases at the surface and core part, respectively. The graphene-supported Pt and Ni were further heat-treated to investigate structural change of the supported nanoparticles, in which the particle size became larger and their crystallinity of the Pt and Ni was enhanced with increasing treatment temperatures.

Polypyrrole composition over carbon-supported palladium nanoparticles (Pd-PPy/C) is successfully performed as electrocatalysts for acid-based fuel cell. This approach demonstrates that PPy modification on a Pd surface remarkably suppresses the deactivation of Pd under acidic conditions. We attempted to determine the influence of PPy on the Pd surface with respect to stability. For this purpose, a potential cycling test and inductively coupled plasma mass spectrometry (ICP–MS) analysis are applied to this system to investigate how PPy affects Pd surface area loss by dissolution and particle growth/agglomeration. The electronic structure of the catalysts is also analyzed with X-ray absorption-near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The increase in stability upon PPy modification of Pd nanoparticles can be interpreted as a result of the redox properties of PPy polymer itself because the electronic interaction of Pd and PPy doesn’t reveal a shifting of the d-band center (ɛd). Consequently, our work may suggest that conjugated polymer-composited metal catalysts are good potential candidate in the development of efficient electrocatalysts because of the possibility of electrochemical role of the conjugated polymer.

We report very small and highly dispersed PtRu nanoparticles on a graphene support prepared via simple surfactant-free synthesis processes, which demonstrate excellent activity and stability compared with conventional Pt/C and bimetallic PtRu/C for the electrooxidation of biomass-derived glycerol. Keywords: PtRu catalyst, Graphene, Glycerol electrooxidation, Biomass, Fuel cells

Surface-functionalized graphene nanosheets (GNSs) were synthesized from natural graphite via chemical oxidation and subsequent thermal exfoliation. High Pt metal loadings, up to 80 wt.%, were deposited over the synthesized GNS supports and the Pt particle size was maintained at less than 3 nm. The current densities of methanol electrooxidation with these Pt/GNS catalysts were at least twice as large as those observed with conventional Pt/C catalysts. Furthermore, these Pt/GNS catalysts maintained high Pt mass activities with increased Pt loading on the working electrode, ranging from 0.2 to 2.0 mg/cm 2 . This improved mass activity indicates that our electrocatalysts are able to provide more efficient Pt utilization for alcohol electrooxidation compared to conventional catalysts.

The oxygen reduction reaction (ORR) has been studied on graphene-supported electrocatalysts in alkaline media. Uniformly dispersed Pd nanoparticles with a mean diameter of ca. 1.8 nm can be successfully obtained on graphene sheets (GNSs) through chemical synthesis, even at a high metal loading of 60 wt.%. The ORR activity of these catalysts was investigated in a 0.1 M NaOH solution, and the kinetic parameters were determined by the rotating disk electrode (RDE) technique. The GNS-supported Pd catalyst (Pd/GNS) shows significantly high catalytic activity for the ORR. For comparison, the GNS-supported Pt catalyst (Pt/GNS) was also synthesized and investigated under the same experimental conditions. Keywords: Electrocatalyst, Graphene, Palladium, Oxygen reduction reaction, Alkaline fuel cell

Electrocatalytic oxidations of ethylene glycol and glycerol were studied over a carbon-supported PtRuSn catalyst (PtRuSn/C), which was prepared with a Pt:Ru:Sn atomic ratio of 5:4:1 using a colloidal method combined with a freeze-drying procedure at room temperature. The ternary PtRuSn/C catalyst was characterized by various physicochemical analyses such as X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and X-ray absorption-near-edge spectroscopy (XANES). The ternary PtRuSn catalyst showed noticeable modifications on the catalyst phases from Pt or PtRu in regards to structural and electronic features, such as a change in lattice parameter and electronic modification in unfilled d band states of Pt atoms. The structurally and electronically modified PtRuSn/C catalysts substantially enhanced the electrocatalytic activities for ethylene glycol and glycerol oxidations, resulting in larger peak currents and lower onset potentials of the electrooxidations. By incorporating the Ru and Sn elements onto the ternary PtRuSn/C catalyst, efficient oxidative removals of CO or CO-like carbonaceous intermediate species produced during the reaction were also possible, thus preventing poisoning of the active Pt sites. Consequently, significant enhancements of electrocatalytic activity and stability over the ternary PtRuSn/C catalyst could be achieved for the electrooxidations of ethylene glycol and glycerol.

Oxygen evolution reaction (OER) plays a vital role in many energy conversion and storage processes including electrochemical water splitting for the production of hydrogen and carbon dioxide reduction to value-added chemicals. IrO2 and RuO2 , known as the state-of-the-art OER electrocatalysts, are severely limited by the high cost and low earth abundance of these noble metals. Developing noble-metal-free OER electrocatalysts with high performance has been in great demand. In this review, recent advances in the design and synthesis of noble-metal-free OER electrocatalysts including Ni, Co, Fe, Mn-based hydroxides/oxyhydroxides, oxides, chalcogenides, nitrides, phosphides, and metal-free compounds in alkaline, neutral as well as acidic electrolytes are summarized. Perspectives are also provided on the fabrication, evaluation of OER electrocatalysts and correlations between the structures of the electrocatalysts and their OER activities.

Polyoxometalate-deposited Pt/C electrocatalysts are prepared by impregnation with various amounts of polyoxometalate (POM) anions (from 2 to 16.7 wt.% PMo12O403–) on the Pt/C catalyst. The prepared electrocatalysts show a high CO electrooxidation performance over a half-cell system for CO stripping voltammetry, and CO tolerant electrooxidation of H2 is further demonstrated over a proton exchange membrane fuel cell by using CO-containing H2 gas feeds (0, 10, 50, and 100 ppm CO in H2). In the CO stripping voltammograms, the onset and peak potentials for the CO oxidation appear to decrease as the POM deposition is increased, indicating that the electrooxidation of CO undergoes more efficiently on the catalyst surface with the deposited POMs on the Pt/C catalysts. In the single fuel cell tests with the CO-containing H2 gases, the higher current density is also generated with the larger amounts of deposited POMs on the Pt/C catalysts. Importantly, the charge transfer resistance Rp appears to decrease monotonically with the POM amounts, which was measured by electrochemical impedance spectroscopy. Physico-chemical characterizations with electrocatalytic analyses show that the deposited POMs hardly affect the active phase of Pt catalyst itself but can help the electrooxidation of H2 by efficiently oxidizing CO to prevent the Pt catalyst from poisoning. Consequently, this POM-deposited Pt/C catalyst can serve as a promising CO tolerant anode catalyst for the polymer electrolyte fuel cells that are operated with hydrocarbons-reformed H2 fuel gases.

Development of sustainable energy has recalled highly efficient energy storage technology because it generates the electricity stochastically from the sources such as solar and wind. The water electrolysis has been considered as the one of the promising options to convert and store electrical energy as the form of hydrogen. However, relatively large overpotential from anodic half reaction, that is, oxygen evolution reaction (OER) has hindered commercial use of hydropower. The recent studies about OER have focused on finding out non-noble metal catalyst because the RuO2 and IrO2, ideal catalysts for OER, are scarce and expensive. Among the non-noble metal oxides, cobalt (III, IV) oxide has been received great attention since it is anticipated to be second best ideal catalyst for OER from theoretical calculations. With this respect, the number of nano-sized cobalt oxide electrodes with different morphologies have been prepared and utilized as the anode of electrolytic water splitting system. In this work, copper-cobalt oxides nanosheets catalyst layer was electrochemically prepared on the nickel foam substrate. To achieve nano-porous morphology of deposit, cobalt oxide was co-deposited with copper oxide. The structural and spectroscopic analyses revealed that cobalt-copper oxides nanosheet array consists of mixture of Co3O4 and CuxCo3-xO4. As the catalyst for OER, the resulting catalyst showed exceptional catalytic activity thanks to its nano- to micro-porous structure, which allows facile transport of active species. Furthermore, it showed great long-term stability. In this presentation, the catalytic activity of cobalt-copper oxides will be discussed in terms of electrochemical properties. In particular, several electrochemical parameters such as anodic Tafel slopes and overpotentials at different current densities will be suggested and compared to that of other nanostructured catalysts reported in literature. Furthermore, the effect co-deposition of copper and cobalt oxides on growth habit of overall deposit and its OER performance will be discussed.

The increased awareness of low-carbon economy and sustainable energy generation continues to push the development of next-generation of energy conversion and storage systems, which aims to alleviate dependence on fossil fuels and reduce carbon emissions that cause global warming (1). There has been a tremendous interest in pursuing both fundamental and applied research towards developing new types of sustainable energy systems such as fuel cells, metal-air batteries and electrochemical water splitting system (1-3). The significant and share reactions of those applications are oxygen reactions which are oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) (1-3). So far, it is well known that the best catalysts are precious metals like Pt and Pt-based electrocatalysts, which are very expensive (especially in acidic media) because of their critical challenges: i) large overpotentials resulting from insufficient drive for sluggish ORR and OER kinetics, and ii) catalyst degradation by relatively unstable electrochemistry in operating condition. These challenges arise from insufficient activity and durability of the air electrode, which includes electrocatalysts that lower activation energies of the reactions to reduce overpotential in working condition (1-3). Hence recent research efforts in energy materials development have been focused on addressing the above challenges (4, 5). Recent approaches in density functional theory (ab-initio studies, DFT) combining with experimental studies have allowed researchers to precisely simulate catalytic activities and gain fundamental understandings of the bifunctional oxygen reactions (4-6). Especially, it enables designing of efficient non-precious material-based catalysts and effectively minimizing the use of noble metals to render sufficiently active low cost catalysts such as non-precious transition metal-based materials, functionalized carbon-based materials, metal–nitrogen complex and noble metals (7). Particularly in the case of minimizing the use of noble metals, Pt3Ni has been revealed to show enhanced ORR activity due to downward shifted d-band center in electronic structure by Nørskov and associates, which results in a weak adsorption with oxygen intermediates on catalytic surface (6). Understanding eg orbital of valence electrons makes it possible to predict the oxygen reactivity that can be controlled by the number of outer electrons of transition metal in non-precious catalysts (4, 8). In addition, the electrochemical stability has been associated with the dissolution potential and cohesive energy term modelled by changing the morphology and size of the transition metal nanoparticles, as well as support materials (9, 10). Accordingly, a synergetic approach using both experimental and ab initio computational studies with physicochemical analyses is required to efficiently and accurately develop a new catalyst with highly improved activity. To apply energy conversion and storage devices such as fuel cells, metal-air batteries systems, in this work, we have predicted the ORR and OER activity and stability for self-assembled nitrogen-doped fullerenes (N-fullerene), and studied the perovskite oxides for the reaction mechanism in aspect of understanding OER activity. In addition, a highly efficient bifunctional oxygen electrocatalyst, combining Pd and three-dimensionally ordered mesoporous spinel cobalt oxide (3DOM Co3O4), has manly discussed in terms of obtaining a stability. This study provides a way of rationally designing efficient electro-catalyst based on the principle that governs thermodynamic and electrochemical activities and stabilities by applying first principles calculations and state of the art experimental measurements to well-defined model systems. M. E. Scofield, H. Liu and S. S. Wong, Chem. Soc. Rev., 44, 5836 (2015). Z.-L. Wang, D. Xu, J.-J. Xu and X.-B. Zhang, Chem Soc Rev, 43, 7746 (2014). J. K. Norskov and C. H. Christensen, Science 312, 1322 (2006). M. H. Seo, H. W. Park, D. U. Lee, M. G. Park and Z. Chen, Acs Catal, 5, 4337 (2015). M. G. Park, D. U. Lee, M. H. Seo, Z. P. Cano and Z. Chen, Small, 12, 2707 (2016). J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov, Nat. Chem., 1, 552 (2009). Z. Chen, D. Higgins, A. Yu, L. Zhang and J. Zhang, Energy Environ. Sci., 4, 3167 (2011). F. Calle-Vallejo, O. A. Díaz-Morales, M. J. Kolb and M. T. M. Koper, ACS Catal., 5, 869 (2015). M. H. Seo, S. M. Choi, E. J. Lim, I. H. Kwon, J. K. Seo, S. H. Noh, W. B. Kim and B. Han, Chemsuschem, 7, 2609 (2014). D. Higgins, M. A. Hoque, M. H. Seo, R. Wang, F. Hassan, J.-Y. Choi, M. Pritzker, A. Yu, J. Zhang and Z. Chen, Adv. Funct. Mater., 24, 4325 (2014).

In this work, we present a mass production method of nano-sized Ni catalyst using late transition metal oxides La2O3 and CeO2 as promoters on a carbon support. The Ni­­_La0.67Ce0.33O1.67/C catalyst was synthesized by co-precipitation for La0.67Ce0.33O1.67 and solvo-thermal for Ni, which are an easy method and capable of making higher activity and durability catalysts. La0.67Ce0.33O1.67 plays an important role in decreasing the size of the Ni particles and helps to improve the properties of the catalyst in reducing atmosphere by forming a solid solution. The Ni_La0.67Ce0.33O1.67/C catalyst recorded a lower overvoltage of 124 mV at a current density of 10 mA/cm2 and a higher long-term stability in 1 M KOH solution at room temperature compared to the Ni/C catalyst. It is suggested that La0.67Ce0.33O1.67 forms a partial alloy with Ni to prevent the detachment of Ni and acts as a barrier to prevent the migration of Ni. Based on the results of this study, a mechanism of Ni catalyst degradation was proposed.

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen, because it does not emit any pollutants compared to other methods such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) and its oxide catalysts showed a higher activity and stability compared with other non-precious catalysts in operating condition. It is necessary to develop non-precious catalysts with high activity and durability because the PGM catalysts are expensive materials with insufficient it’s reserves. In the water electrolysis field, the numerous researchers have been focused on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) because the OER and HER are a key process (slow kinetics) compared with other resistances such as bubble, electrolyte, diaphragm, membrane, etc. On a point of view of a catalyst, slow kinetics and the use of precious metal (PGM) for high performance should be solved to popularize water electrolysis. The target of this study is the development of non-precious catalysts with high activity via simple and efficient synthesis method that is a wet-chemical based method. The Ni-LaCeO/C (HER catalysts) and CuCoO (OER catalyst) were synthesized through the co-precipitation with oxidation and reduction heat treatment. The catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To investigate electrocatalytic properties of prepared catalysts, we carried out electrooxidation activity measurements such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), long-term stability test, and electrochemical impedance spectroscopy (EIS). The relationship between their physicochemical properties and electrocatalytic activities will be explored and discussed.

Pd catalyst composited with a conducting polymer of polypyrrole is prepared and investigated as a stable H2 electrooxidation catalyst in an acidic condition. A significant stability enhancement of Pd by compositing electropolymerized polypyrrole can be observed and its mechanistic scheme for the stability is discussed through several electrochemical and physicochemical characterizations on the polypyrrole-composited Pd catalysts.

Electrochemical reduction of oxygen is studied over a novel nanowire network catalyst made of highly-dispersed Pt nanoparticles into electrospun Pt nanowire network architecture, which shows an excellent mass activity increase by 50% or higher per equal Pt mass than the conventional cathode electrocatalysts of Pt/C in polymer electrolyte membrane fuel cells. Keywords: Pt electrocatalyst, Nanowire network, Oxygen reduction reaction, Electrospinning, Fuel cells

Electrochemical dehydrogenative oxidation of cyclohexane to benzene was studied over carbon-supported PtNi (PtNi/C) electrocatalysts, which were prepared using a borohydride reduction method combined with a freeze–drying procedure at room temperature. The carbon-supported bimetallic PtNi catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), extended X-ray absorption fine structure (EXAFS) and X-ray absorption-near-edge spectroscopy (XANES). The addition of Ni content to the Pt-based catalysts caused structural and electronic modifications over the PtNi alloy catalyst formation, which could directly affect the electrocatalytic activity of cyclohexane oxidation. The Pt1Ni1/C catalyst as an anode electrocatalyst showed a maximum power density of ca. 30 mW cm−2 mgPt−1, which is 2 times or greater power density than that of Pt/C per Pt milligram. Here, both the structural modification via Pt–Pt bond distance change and the electronic modification through charge transfer from Ni to Pt should be responsible for the activity enhancement in the PtNi/C by facilitating the dehydrogenative electrooxidation of cyclohexane to benzene over the PtNi/C anode of cyclohexane-fueled fuel cell system.

Photosensitive poly(amic acid ester)s (PAEs) with 2-hydroxy-4-oxo-hept-5-enyl side group were simply synthesized from a non-photosensitive polyamic acid (PAA), which was prepared from cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) and 4,4′-diaminodiphenyl ether (DDE) in N-methyl-2-pyrrolidinone (NMP). 1-oxiranyl-pent-3-en-2-one was added to the poly(amic acid) solution to give the photosensitive PAEs by a ring opening esterification of the poly(amic acid). The esterification reaction was conducted with changing a reaction time and amounts of 1-oxiranyl-pent-3-en-2-one. The degree of esterification (DOE) increased with increasing esterification reaction time and amounts of 1-oxiranyl-pent-3-en-2-one. A photo-lithography evaluation for the PAE-D4 with the highest DOE was conducted in the presence of 1-[4-(phenylthio)phenyl]-2-(O-benzoyloxime)-1,2-octanedione (PPBO) as a photoinitiator at a wavelength of 365 nm using a high-pressure mercury lamp. The normalized film thicknesses for PAE-D3 were measured with various post-exposure baking (PEB) temperatures, which showed that the optimum PEB temperature was 120°C. The resolution of the resulting polyimide film cured at 250°C for 60 min was 25 µm. The initial decomposition temperature of the polyimide film was around 354°C and there was no weight loss at the temperature of 250–350°C. Copyright © 2009 John Wiley & Sons, Ltd.

Electrochemical hydrogenation of benzene to cyclohexane was studied over carbon-supported Pt and Pt-based alloy catalysts (e.g., Pt/C, Pt 4 Rh 1 /C, Pt 4 Rh 0.75 W 0.25 /C, Pt 4 Rh 0.75 Mo 0.25 /C, and Pt 4 Rh 0.75 Pd 0.25 /C), which were prepared using a borohydride reduction method combined with a freeze-drying procedure. The Pt 4 Rh 0.75 W 0.25 /C catalyst showed the best performance for the electrochemical hydrogenation of benzene to cyclohexane over a proton exchange membrane fuel cell (PEMFC) system. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate structural modifications on the Pt-based catalysts, in which the carbon-supported Pt-based binary and ternary catalysts indicated effective alloy formation with decreased lattice parameters as compared to Pt/C. X-ray photoelectron spectroscopy (XPS) and X-ray absorption-near-edge spectroscopy (XANES) were also carried out to characterize electronic features of the Pt-based alloy catalysts, in which both the structural and electronic modifications were closely associated with the benzene hydrogenation activities.

Electrochemical dehydrogenative oxidation of cyclohexane to benzene is studied over Pt and Pt1Rh1 nanowire electrocatalysts fabricated by electrospinning method, which shows the higher catalytic activities in a polymer electrolyte membrane fuel cell anode than the conventional Pt nanoparticle catalysts such as carbon-supported Pt or Pt black. The improved performances over the Pt1Rh1 nanowire electrocatalyst can be rationalized by enhanced electrical property and pertinent interface formation with nanowire catalysts in the high Pt-loaded cyclohexane fuel cell system. Keywords: Electrospinning, Bimetallic nanowires, PtRh, Cyclohexane oxidation, Fuel cells

Electrochemical dehydrogenative oxidation of cyclohexane to benzene was studied over carbon-supported PtRh (PtRh/C) electrocatalysts, which were prepared with different Pt:Rh atomic ratios from 4:1 to 1:4 using a borohydride reduction method combined with freeze-drying procedure at room temperature. The bimetallic PtRh/C catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption-near-edge spectroscopy (XANES). The variation of Rh content over the PtRh alloy formation caused significant structural and electronic modifications on the catalyst phase, which could be associated with consistent changes in electrocatalytic activities over a polymer electrolyte membrane (PEM) fuel cell. The Pt 4 Rh 1 /C catalyst as the anode electrocatalyst showed a maximum power density of ca. 8.5 mW cm −2 . Here, both the structural modification via lattice parameter change and the electronic modification through charge transfer from Rh to Pt could kinetically facilitate the sluggish electrode reaction with an increased exchange current density on the dehydrogenative electrooxidation of cyclohexane to benzene over the PtRh/C anodes of cyclohexane fuel cell.

We have synthesized supercapacitor electrodes fashioned of NiO(x)/multiwalled carbon nanotubes (MWNTs), in which the controlled NiO(x) nanoparticles were prepared via a simple colloidal method and supported on the MWNTs. The sizes of the NiO(x) nanoparticles on MWNTs were systematically varied from 4 to 14 nm at a fixed metal loading of 20 wt% by changing sintering temperature in a controlled manner. The maximum specific capacitance of the NiO(x)/MWNTs was measured to be ca. 215 F per unit gram of NiO(x)/MWNTs by cyclic voltammetry (CV) in an aqueous 1 M KOH electrolyte, demonstrating that the specific capacitance of the MWNTs-supported nanosize NiO(x) is strongly dependent on the dispersion and size of the nanoparticles for the supercapacitor performance.

Platinum nanowires were prepared via a template-synthesis method by electrodeposition of platinum within pores of a track-etched polycarbonate (PCTE) membrane, followed by chemical etching to separate the Pt nanowires from the polymer. The structure and morphology of the Pt nanowires were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), revealing a polycrystalline phase with nanowire dimension up to 6 μm long and ca. 47 ± 9.8 nm of diameter. The unsupported Pt nanowires showed the better electrochemical mass activities over the methanol electro-oxidation than supported or unsupported Pt nanoparticles under the high Pt content-loaded conditions that is typically required for direct methanol fuel cells. This enhancement could be rationalized by its unique physicochemical and electrical properties arising from the inherent anisotropic one-dimensional (1D) nanostructure, such as charge transfer facilitation by reducing number of particle interfaces and more efficient use of Pt by alleviating fraction of embedded catalysts.

A series of carbon-supported bimetallic PtSn catalysts for the electrooxidation of C1–C3 alcohols (i.e., methanol (C1), ethanol (C2), and 1-propanol (C3)) were prepared with different Pt:Sn atomic ratios using borohydride reduction method combined with freeze-drying procedure at room temperature. The catalysts were investigated by employing various physicochemical analyses: X-ray diffraction (XRD), transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) to investigate the structural modification, and X-ray photoelectron spectroscopy (XPS) and X-ray absorption-near-edge spectroscopy (XANES) to characterize the change in electronic features. The variation of Sn content by forming PtSn alloys causes significant structural and electronic modifications of Pt crystallites, resulting in increases of lattice parameter and decreases of the Pt 5d band vacancies with Sn content. Cyclic voltammetry (CV) measurements showed that the addition of Sn into the Pt catalyst promotes the electro-catalytic activities for the electrooxidations of C1, C2, and C3 alcohols, in which the maximum activities appeared at different Sn contents for the C1–C3 alcohols. In particular, a shift in optimum Pt:Sn composition was observed in that the Sn content required to reach the maximum peak current density was increased with the increasing number of carbon atoms in the C1–C3 alcohols. Both the geometric and electronic effects with variation of Sn content are in close relationship in the bimetallic PtSn catalysts, consequently affecting the electrocatalytic activities by showing volcano-type behaviors over the electrooxidation of the individual alcohol.

Polyoxometalate anion PMo 12 O 40 3− (POM) is chemically impregnated into a Pt-supported carbon nanotubes (Pt/CNTs) catalyst that is prepared via a colloidal method. The POM-impregnated Pt/CNTs catalyst system (Pt/CNTs-POM) shows at least 50% higher catalytic mass activity with improved stability for the electrooxidation of methanol than Pt/CNTs or POM-impregnated Pt/C (Pt/C-POM) catalyst systems. The enhancement in electrochemical performance of the Pt/CNTs-POM catalyst system can be attributed to the combined beneficial effects of improved electrical conductivity due to the CNTs support, highly dispersed Pt nanoparticles on the CNTs, and increased oxidation power of the polyoxometalate that can assist oxidative removal of reaction intermediates adsorbed on the Pt catalyst surface.

Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1–xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.

Pt-supported reduced graphene oxide (Pt/RGO) catalysts were prepared over the RGO sheets with different sizes for methanol oxidation and oxygen reduction reactions in acidic media. The Pt on the smaller RGO presented higher catalytic activities than the Pt on the larger RGO and the commercial Pt/C catalyst.

A negative-type photosensitive polyamic acid (PAA) was synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride and 2-(methacryloyloxy)ethyl 3,5-diaminobenzoate in N-methyl-2-pyrrolidinone. Glycidyl methacrylate was added into the PAA solution to yield a photosensitive PAA ester (PAE) by the ring-opening esterification reaction of the carboxylic acid group in the PAA and glycidyl methacrylate. Esterification reactions were conducted with varying reaction temperatures and times. The typical PAE (PAE-C3) with a degree of esterification of 20% was used for a photosensitivity study. We investigated the effects of the postexposure baking temperature, amount of photoinitiator, and exposure dose on the photosensitivity of PAE-C3. Furthermore, a photolithography evaluation was conducted on PAE-C3 in the presence of 1-[4-(phenylthio)phenyl]-2-(O-benzoyloxime)-1,2-octanedione as a photoinitiator using a mercury lamp at a 365-nm wavelength. The resolution of the film with 2.0-μm thickness was about 8 μm. PAE-C3 cured at 250°C for 60 min was stable up to around 310°C in a nitrogen atmosphere. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2252–2258, 2006

A series of negative-type photosensitive polyamic acids (PAAs) with various molecular weights was synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 2-(methacryloyloxy)ethyl-3,5-diaminobenzoate, and 2-(methacryloyloxy)ethyl-4-aminobenzoate in N-methyl-2-pyrrolidone. We investigated the degree of planarity, transmittance, and thermal stability for the PAAs after the photoirradiation reaction at an exposure dose of 200 mJ/cm2. The films prepared from the PAA with the lowest molecular weight (PAA-1) exhibited a higher degree of planarity and transmittance compared with those of the film prepared from the PAA with the highest molecular weight (PAA-4). The initial decomposition temperatures of the cured PAAs with different molecular weights were similar and were stable up to around 300°C. Further, the photosensitivity and transmittance of PAA-1 were investigated in the presence of photoinitiators at 365–400 nm with a high-pressure mercury lamp. The resolution of the photocured film was about 50 μm. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2300–2308, 2005