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Surface-enhanced Raman scattering (SERS) has been a useful sensing technique, in which inelastic light scattering can be significantly enhanced by absorbing molecules onto rough metal surfaces or nanoparticles. Although many methods have been developed to prepare SERS substrates, it is still highly desirable and challenging to design SERS substrates, especially with highly ordered and controlled three-dimensional (3D) structures. In this work, we develop novel SERS substrates with regular volcano-shaped polymer structures using the versatile solvent on-film annealing method. Polystyrene (PS) nanospheres are first synthesized by surfactant-free emulsion polymerization and assembled on poly(methyl methacrylate) (PMMA) films. After annealing in acetic acid vapors, PMMA chains are selectively swollen and wet the surfaces of the PS nanospheres. By selectively removing the PS nanospheres using cyclohexane, volcano-shaped PMMA films can be obtained. Compared with flat PMMA films with water contact angles of ∼74°, volcano-shaped PMMA films exhibit higher water contact angles of ∼110° due to the sharp features and rough surfaces. The volcano-shaped PMMA films are then coated with gold nanoparticles (AuNPs) as SERS substrates. Using rhodamine 6G as the probe molecules, the SERS results show that the Raman signals of the volcano-shaped PMMA/AuNP hybrid substrates are much higher than those of the pristine PMMA films and PMMA films with AuNPs. For the volcano-shaped PMMA/AuNP hybrid substrates using 400 nm PS nanospheres, a high enhancement factor (EF) value of ∼1.12 × 10

This study produces high quality Cu(In,Ga)Se2 (CIGS) solar cells using a two-step process. Stacked In (200 nm)/CuGa (150 ~ 300 nm)/In (500 nm) layers are deposited onto Mo bilayer soda-lime glass by sputtering, using CuGa and In targets, followed by vapor stacking of the elemental Se layers. To produce the CIGS film, the CuGa film is coated in thicknesses of 150, 200, 250 and 300 nm. An appropriate atomic ratio [Cu/(In + Ga), CGI and Ga/(In + Ga), GGI] for the precursors and the CIGS absorption layers composition is easily obtained. Compared to those for the as-deposited precursors, after selenization, the CGI and GGI ratios for CIGS films are almost constant. All CIGS thin films exhibit a peak in the Raman curves at around 173–174 cm−1, which is identified as the CIGS phase. Following sulfurization, the main peaks for CIGS thin films at (112), (220)/(204) and (312)/(116) indicated that the crystalline quaility were improved. The main peaks for the CIGSS films are slightly greater for (112), (220)/(204) and (312)/(116). The band gap energy is increased from 1.19 eV (for the as-grown) to 1.34 eV (for the absorber layer that is sulfurized at 500 °C for 10 min). The performance of the CIGS absorber films is improved by using a proper holding time for sulfurization.

We employ a sequential electrophoresis and electrodeposition approach to fabricate a large-area ordered macroporous Ni foam in 5 × 5 cm 2 via a template route. Images from scanning electron microscope exhibit hierarchical structures with hexagonally-arranged pores and interconnected pore channels. For as-prepared and annealed ordered macroporous Ni foams, the loading-depth profiles from nano indentation show typical elastic and plastic deformation. Upon annealing, moderate growth in grain size is observed, resulting in lower hardness and Young’s modulus. In contrast, for disordered macroporous Ni foam and solid Ni film, nano indentation results reveal larger hardness and undetermined Young’s modulus. The ordered macroporous foam reveals hardness that is 22% of that of solid Ni film, a value close to its theoretic packing density of 24%.

A mixture of polydopamine (PDA) and polyethyleneimine (PEI) are used as the adhesive, wetting, and reducing agent simultaneously to fabricate a conductive silver membrane. The conformal coating of PDA/PEI on individual polypropylene fibers of polypropylene micromembrane (PPMM) renders the latter to be hydrophilic for subsequent electroless silver deposition. The resulting conductive silver membrane demonstrates impressive electric conductivity in both X and Z directions. The thickness of conformal silver overcoat is 250 nm and the effective loading is 2.4 mg/cm2. The mechanical strength of conducive silver membrane is similar to that of pristine PPMM. Both cyclic voltammetry and impedance spectroscopy on the conductive silver membrane reveal a large electrochemical active surface area. To validate its usefulness as a robust soft electrode, the conductive silver membrane is evaluated for the detection of chlorine in aqueous solution in which a low detection limit of 0.07 ppm and a wide detection range of 0.1–20 ppm are validated.

Three-dimensionally ordered macro/mesoporous materials are known to possess a large accessible surface area with impressive permeability. In this work, we combine electrophoresis and electrodeposition to fabricate a hierarchical bi-layered inverse opaline film in which a ZnO sensing layer is stacked with an Au electrode for impressive H2 sensing activities. To enhance its responsiveness, both morphological and crystallographic properties of ZnO inverse opals are optimized using KCl as the porogen. The resulting ZnO inverse opals demonstrate a specific surface area that is three times larger over comparable ZnO inverse opals by the formation of nanoporous skeletons. In addition, the deposition bath was deliberately designed so the predominant crystallographic plane of ZnO is shifted from (10 1 - 0) to (0001) as the latter exhibits superior activity toward reducing gases. Through X-ray photoelectron spectroscopy, we show a significant increase of chemisorbed oxygen on the (0001) plane. Consequently, our hierarchical bi-layered inverse opals reveal a 500 % improvement in the sensitivity toward 15 ppm H2 under 200 °C. In short, this is the first demonstration of a vertically-arranged inverse opaline film incorporating both metal and oxide layers to function as an integrated three-dimensional gas sensor with low detection limit.

We demonstrate the deposition of Pt film on a nickel-based superalloy (CMSX-4) via a combination of galvanic displacement reaction and chemical reduction. The aqueous plating bath contains an optimized mixture of Pt precursor (H2PtCl6), pH adjuster (NaOH), and reducing agent (HCHO). Both time-evolved UV–Vis and X-ray absorption spectra on the plating bath indicate a sequential chemical reduction of Pt4+ → Pt2+ → Pt. In addition, a parasitic galvanic displacement reaction occurs in which Ni, Al, and Co from the CMSX-4 suffer from corrosive dissolution whereas the Pt4+ ions from the plating bath are reduced directly. This surface-mediated galvanic displacement reaction produces numerous Pt nanoparticles serving as the nucleation sites for chemical reduction of Pt4+ from HCHO. Therefore, typical sensitization and activation steps for electroless plating are not necessary in our plating bath. From X-ray diffraction pattern, the Pt film adopts a fcc polycrystalline structure. Images from scanning electron microscope confirm the formation of a dense and continuous Pt film with 1 μm thickness.

We demonstrate a fabrication scheme for the synthesis of conductive core-shell (core@shell) nanoparticles consisting of polystyrene (PS) microspheres in size of 613 nm with consecutive coatings of functionalized polypyrrole (PPy-COOH) and Ag. The PPy-COOH precursors undergo polymerization on PS microspheres forming PS@PPy-COOH microspheres, followed by sensitization and Ag electroless deposition to produce PS@PPy-COOH@Ag microspheres in size of 717 nm. The PPy-COOH serves as the adhesive for intimate bonding of PS and Ag. Images from scanning and transmission electron microscopes confirm a Ag coating of 41–50 nm which is consisted of clustered nanoparticles forming a mono-layered film. From X-ray diffraction pattern, the Ag adopts a polycrystalline fcc structure with grain size of 12 nm. Results from thermal gravimetric analysis indicate a Ag loading of 54 wt%. By four-point-probe, the bulk conductivity for PS@PPy-COOH@Ag is 10,170 S m−1. These microspheres show promising potential for anisotropic conductive paste.

Three-dimensional ordered macroporous Ni films, known as Ni inverse opals, are fabricated via a template approach in which polystyrene (PS) microspheres (820 nm in diameter) are assembled in closely-packed colloidal crystals via a vertical electrophoresis process, followed by electroplating of Ni into the interstitial voids within the colloidal crystals and the selective removal of PS microspheres. To improve its mechanical strength, a conformal Ni-Co layer (45 ∼ 64 nm) is electrodeposited on the skeletons of the Ni inverse opals by cyclic voltammetry. After coating, from nano-indentation tests, the hardness and reduced elastic modulus are enhanced considerably (172 ∼ 220% for hardness; 72 ∼ 79% for reduced elastic modulus), as compared to those of pristine inverse opals. After an annealing treatment for the interdiffusion of Ni and Co, the sample reveals an even stronger hardness. X-ray diffraction patterns indicate that the finite thickness of the inverse opals skeletons induces preferential growth of the (111) plane. In short, a combined effect of solid solution alloying, thickening of inverse opals skeletons for greater load bearing, and a predominant (111) plane is responsible for the improved mechanical strength of the Ni inverse opals.

We explore dopamine (DA) and its mixtures with polyethylene glycol (PEG) or polyethylenimine (PEI) as an adhesion layer for bonding between Cu and SiO2. The DA is oxidized to form polydopamine (PDA) which deposits as aggregates on SiO2 surface with notable surface roughness. After mixing with PEG or PEI, the morphology of PDA aggregates is altered considerably. Electroless Cu deposition in a mild alkaline bath is employed to deposit Cu atop the adhesion layer. The Cu films reveal an fcc lattice with (111) preferred orientation and their thickness was around 650 nm. From measurements of four-point probe, breaking strength, and tape-peeling tests, the PDA/PEG mixture reveals impressive performance serving as a strong adhesive for robust Cu bonding. We attribute the unique adhesive ability of PDA/PEG to the hydrogen bonds established between the catechol and amine groups of DA with PEG that renders desirable film formation on the SiO2 surface for optimized interaction between Cu and SiO2.

aDepartment of Chemical Engineering, National Chung Cheng University, Chia-Yi 62102, Taiwan bDepartment of Chemical Engineering, National Tsing Hua University, Hsin-Chu 30013, Taiwan cDepartment of Materials Science and Engineering, National Chiao Tung University, Hsin-Chu 300, Taiwan dGraduate Institute of Opto-Mechatronics, National Chung Cheng University, Chia-Yi 62102, Taiwan eAdvanced Institute of Manufacturing with High-Tech Innovations, National Chung Cheng University, Chia-Yi 62102, Taiwan

We adopted a displacement reaction in acidic solution that enabled the spontaneous reduction of Pd and Pt cations in conjunction with corrosive dissolution of Ni. The composition for the PdPt was adjusted by varying the concentration of Pd and Pt cations. From SEM images and XRD patterns, the PdPt formed an fcc alloy uniformly deposited on the Ni substrate. Electro-oxidation of ethanol was conducted in alkaline electrolyte for samples of Pd, Pt, and PdPt alloys. In cyclic voltammetric profiles, the Pd 77 Pt 23 revealed the highest electrocatalytic ability in both apparent current and mass activity, followed by Pd 87 Pt 13 , Pd, and Pt. Similar behaviors were observed in life time measurements in which stable performances for ethanol electro-oxidation were obtained.

We fabricated a nanostructured brush by carrying out Ni deposition on a through-channel anodic aluminum oxide (AAO) template, followed by removal of the AAO skeleton. The AAO was prepared by a two-step anodization process resulting in pore diameter and thickness of 350 nm and 40 μm, respectively. Subsequently, the AAO underwent an electroless deposition involving sensitization, activation, and Ni plating, in conjunction with polyethylene glycol used as the inhibitor to prevent premature closing of pore opening. After deliberate control in relevant parameters, we obtained a conformal Ni overcoat along every pore channel leading to a reduced average pore diameter of 78 nm. Afterward, the sample was immersed in a KOH solution to remove the AAO structure, forming freestanding Ni tubules in a brush configuration. The nanostructured brush revealed considerable enhancement for hydrogen evolution reaction in both current-potential polarization and galvanostatic measurements, which were attributed to the increment in apparent surface area.

Hydrogen evolution reaction in 1 M Na 2 SO 4 was investigated using Ni nanowires in diameter of 250 nm with exposed lengths of 20, 35, and 45 μm, respectively. The Ni nanowires were fabricated by a direct-current pulse electrodeposition technique using an anodic aluminum oxide template, followed by selective removal of the supporting pore walls. Scanning Electron Microscope images revealed structural stabilities and X-ray diffraction pattern indicated a polycrystalline fcc phase. In current–potential ( i – V ) polarizations, the Ni nanowires with longer exposed lengths demonstrated larger current responses. Analysis from impedance spectroscopy confirmed increasing double-layer capacitances with longer Ni nanowires. In galvanostatic lifetime experiments, the free-standing Ni nanowires exhibited a reduced overpotential over that of supported ones. Similar procedures were performed for the oxygen evolution reaction in both i – V and lifetime measurements. For the Ni nanowires of 45 μm length, we estimated the energy cost for hydrogen production was 5.24 × 10 5 J/mole.

Eutectic Sn-3.5wt.%Ag alloy is one of the most promising lead-free solders in low temperature processes for wafer bumping. Near eutectic composition of deposited alloy films could be readily acquired by pulse electroplating with a proper combination of active ingredients including K4P2O7, KI, Sn2P2O7, and AgI, as well as polyethylene glycol (PEG), with molecular weights of 200, 600, 2,000, and 4,000, as an inhibitive agent. Pulse electroplating was carried out with current in alternating polarity to conduct electroplating and electropolishing sequentially. As a result, alloy films with grains of less than 1 μm and uniform surface morphology can be obtained. The addition of PEG was necessary for the stabilization of the plating baths to promote a wider process window for the desirable eutectic composition. Electrochemical characterization established that PEG with molecular weight of 4,000 exhibited the strongest inhibition behavior. In contrast, PEG with molecular weight of 200 demonstrated the least interference. Energy dispersive X-ray and differential scanning calorimeter data confirmed the formation of eutectic alloy as a function of deposition current density. X-ray diffraction results indicated that a biphasic structures of β-Sn and e-Ag3Sn was present in the as-deposited film.

Ordered arrays of Ta2O5 nanodots were prepared using anodic aluminum oxide (AAO) as a template to support localized oxidation of TaN. Films of TaN (50 nm) and Al (1.5 μm) were deposited successively on p-type Si wafers and followed by a two-step anodization process at 40 V using oxalic acid as the electrolyte. The first anodization promoted growth of irregular AAO from overlying Al film. After chemical etching, the second anodization was performed to develop well-organized AAO channels and initiate oxidation of underlying TaN film to form tantalum oxide nanodots at the AAO pore bottoms. X-ray photoelectron spectroscopy results confirmed the chemical nature of nanodots as stoichmetric Ta2O5. X-ray diffraction demonstrated the amorphous characteristic of Ta2O5. As shown in field-emission scanning electron microscopy and transmission electron results, the Ta2O5 nanodots exhibited a hillock structure 80 nm in diameter at the bottom and 50 nm in height. We also synthesized 30-nm nanodots by adjusting AAO formation electrochemistry. This demonstrates the general applicability of the AAO template method for nanodot synthesis from nitride to oxide at a desirable size.

The mechanisms responsible for spontaneous silver precipitation in silver-doped sol-gel materials are identified. The chemistry of the solvent phase is found to be the critical factor in controlling this phenomenon. The addition of HCl as catalyst leads to the formation of AgCl and subsequent formation of silver upon light exposure. Another factor leading to silver precipitation is the reducing capability of methanol radicals. Silver precipitation is inhibited by simply washing out the pore solvents by a solvent exchange method.

A vertical electrophoretic deposition method was employed to fabricate polystyrene (PS) colloidal crystals with negligible defects and considerable surface uniformity. Subsequently, the interstitial voids within the colloidal crystals were electroplated with Ni, followed by selective removal of the PS microspheres. With careful adjustment in the processing parameters, we were able to obtain Ni inverse opals at predetermined thickness in relatively short time. The inverse opals revealed superb structural stability and surface uniformity. Because the electrophoresis and electrodeposition were both carried out in a solution state, this fabrication scheme enables facile construction of inverse opals on conductive substrates over conventional approaches.

Cu2O cubes with average edge lengths of 640 nm were prepared by a chemical reduction approach. The as-synthesized Cu2O particles were deposited on carbon clothes for electrochemical characterizations in cyclic voltammetry (CV) and potentiostatic measurements. In 0.5 M NaOH electrolytes saturated with N2 or CO2, both the Cu2O and carbon clothes were stable at the potential range of 0 to − 1.7 V. Comparisons in the current responses from the CV and potentiostatic measurements suggested the Cu2O with notable catalytic abilities for the CO2 reduction. The mass activity was estimated at 0.94 mA/mg. Chemical analysis from gas chromatography confirmed the methanol to be the predominant product.

La 0.6 Ca 0.4 Co 0.8 Ir 0.2 O 3 was prepared by solid state reaction synthesis from mixtures of La(NO 3 ) 3 ·6H 2 O, Ca(NO 3 ) 2 ·4H 2 O, Co(NO 3 ) 3 ·6H 2 O, and IrO 2 at stoichiometric ratio. Images from scanning electron microscopy on the as-synthesized powders exhibited particles in irregular shape at 100–250 nm in size. X-ray diffraction analysis confirmed the formation of perovskite without the rutile signals from IrO 2 , suggesting successful incorporation of Ir 4+ at the Co cation sites. The carbon nanocapsules (CNCs) were used as an electrocatalyst support. Electrodes for electrochemical measurements were fabricated by depositing mixtures of CNCs, La 0.6 Ca 0.4 Co 0.8 Ir 0.2 O 3 , and polymeric binders on commercially available noncatalyzed gas diffusion electrodes. In alkaline electrolyte, the La 0.6 Ca 0.4 Co 0.8 Ir 0.2 O 3 /CNCs demonstrated superior performances than those of La 0.6 Ca 0.4 CoO 3 /CNCs and IrO 2 /CNCs in both charging and discharging current–potential polarization measurements.

Solution processing methods have been used to prepare a solid electrolyte, copper-doped bismuth vanadate, and several different lithium transition metal oxide cathode materials. Dense thin films of the bismuth vanadate were prepared by pyrolysis of metal organic precursors deposited on various oxide substrates. A high degree of crystal orientation was obtained using single crystal MgO substrates. The Pechini process was used to prepare powders of the different materials and a variety of results were obtained. The bismuth vanadate exhibited a second phase of BiVO4 while LiNiO2 and the LiCoxNi1−xO2 solid solution require further efforts at obtaining the proper phase and stoichiometry. The LiCoO2 system formed readily and exhibited good electrochemical performance.

We fabricate cylindrical colloidal crystals (CCCs) via electrophoretic depositions of polystyrene microspheres on a carbon fiber in a concentric arrangement. Images from optical and scanning electron microscope indicate that the CCCs of 460 nm microspheres reveal a semicrystalline structure in close-packed lattice, while the CCCs of 660 exhibit an amorphous arrangement. In optical reflectance spectra, both CCCs demonstrate a dispersive photonic bandgap as compared to that from planar counterparts. The curved contour for the CCCs renders incident light interacting with reflecting planes at slightly different angles, leading to a notable reduction in the reflectance intensity and minor relocation of photonic bandgap contingent on their crystallinity.

We demonstrate a facile fabrication scheme to construct large-area ZnO inverse opals on an indium-tin-oxide substrate with significantly reduced defects and improved stoichiometry. The fabrication steps involve the preparation of colloidal template via vertical electrophoresis of polystyrene (PS) microspheres in 720 nm radius, followed by galvanostatic electrodeposition of ZnO in the interstitial voids among the PS microspheres. Subsequently, the sample undergoes a heat-treatment in air at 500 C for different time to remove the colloidal template, leaving an integral ZnO skeleton with thickness adjusted by the electrodeposition time. Since the colloidal template is deliberately designed with desirable thickness and considerable uniformity, the electroplating of ZnO can be achieved in a reduced ethanol/water ratio that allows faster growth rate and improved ZnO structure. Scanning electron microscope images demonstrate negligible microstructural defects for the ZnO inverse opals. X-ray diffraction reveals a wurtzite hexagonal lattice with (002) preferred orientation. In addition, both X-ray photoelectron spectroscopy and photoluminescence spectra suggest improved crystallinity and stoichiometry with increasing heat-treatment time. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3552604] All rights reserved.

An electroless Ru plating bath is prepared by mixing Ru precursor (K2RuCl5!xH2O), oxidizer (NaClO), stabilizer (NaOH), and reducing agent (NaNO2) simultaneously in deionized water at a molar ratio of 1:1:20:10. Instead of conventional direct reduction route, the RuCl5 2" experiences an oxidative-reductive sequence to form metallic Ru on an activated Si substrate. Spectra from ultraviolet-visible and X-ray absorption spectroscopy indicate that the RuCl5 2" is oxidized to form RuO4 initially, followed by a slight reduction becoming RuO4 2". The RuO4 2" solution is relatively stable and is able to undergo further reduction to render metallic Ru via heterogeneous nucleation and growth. Images from scanning electron microscope demonstrate a solid film of 100 nm with scattered protrusions and cavities after 120 min plating time. Analysis from atomic force microscope determines its surface roughness of 7.8 nm. From X-ray diffraction patterns, the as-deposited film reveals an amorphous structure but turns crystalline after Ar annealing at 400#C for 2 h. Curve-fitting of Ru 3p3/2 signal from X-ray photoelectron spectroscopy suggests a film composition of 92.49 atom % Ru and 7.51 atom % RuO2. The electroless Ru plating bath exhibits impressive life time (137 h) and negligible homogeneous precipitation without involving surfactants and unnecessary chemical additives. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3592996] All rights reserved.

We employed an electrophoretic deposition technique to prepare cylindrical colloidal crystals (CCCs) from polystyrene (PS) microspheres of 460 and 660 nm diameters using a carbon fiber (CF) with 7 μm diameter as the substrate. Measurements on the CCC diameter demonstrated growth rates that slowed down as time progressed. Scanning electron microscope images confirmed that the CCCs of 460 nm microspheres formed a face-centered cubic close-packed lattice, whereas an amorphous structure appeared for the CCCs of 660 nm. Subsequently, both CCCs underwent a potentiostatic electroplating to deposit Ni into the interstitial voids among the PS microspheres. After chemical removal of the PS microspheres, we fabricated cylindrical inverse opals (CIOs) in various diameters. As expected, better crystallinity was found on the CIOs of 460 nm microspheres as opposed to the 660 nm ones. The electrical resistivity for both CIOs exhibited a substantial reduction over that of the CF. Our CCCs and CIOs revealed considerable structure stability with excellent surface uniformity. The fabrication scheme enables rapid preparations of CCCs and CIOs in desirable lengths and diameters.

A vertical electrophoretic deposition technique was employed to prepare polystyrene (PS) colloidal crystals with negligible crystallographic defects. The colloidal crystals were plated with Ni, followed by selective removal of PS microspheres to fabricate inverse opals. With adjustments in relevant processing parameters, we were able to obtain inverse opals in multiple layers with excellent surface uniformities. The inverse opals were used as the electrode material for water electrolysis. Results from current-potential polarizations in 1 M KOH aqueous solution indicated that the catalytic abilities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) increased with the layers of inverse opals. Estimation of the effective current densities determined that the entire area of the inverse opals was available for electrochemical reactions. In galvanostatic measurements for both OER and HER, the inverse opals demonstrated stable voltage profiles without notable degradations for 120 h. Compared with a planar Ni plate, the inverse opals exhibited a significantly reduced overpotential for the water electrolysis.

We employed an amorphous citrate precursor (ACP) method to synthesize stoichiometric La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 powders. Result from X-ray diffraction demonstrated a perovskite La 0.6 Ca 0.4 CoO 3 lattice, indicating the incorporation of Ru 3+ at the Co 3+ sites. Image from the scanning electron microscope revealed a foamlike microstructure with various pores at 0.5-3 μm. La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 exhibited a higher H 2 O 2 decomposition rate in KOH solution as opposed to that of ACP-derived La 0.6 Ca 0.4 CoO 3 , which suggested an improved catalytic ability for oxygen reduction reaction (ORR). A similar behavior was observed during the ORR current-potential polarization using La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 supported on Black Pearl 2000 as a gas diffusion electrode. In addition, impedance spectra at the open-circuit voltage and selective cathodic overpotentials also confirmed a smaller charge-transfer resistance for La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 . In galvanostatic measurements and lifetime evaluation, La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 demonstrated steady voltage profiles with negligible degradation.

Galvanostatic depositions in rectangular pulses and nitrosol precursors were employed to prepare PtRu nanoparticles on carbon clothes in various sizes and compositions. Variables including current on-time Ton, current off-time Toff, and current density were explored to identify the optimized catalytic performances for methanol electro-oxidation. Electrochemical characterizations including cyclic voltammetry and hydrogen desorption were carried out. Images from a transmission electron microscope on the PtRu nanoparticles revealed a moderate size distribution. Signals from X-ray patterns indicated a slight shift of diffraction peaks, suggesting that the Ru was alloyed successfully in the Pt lattice. In addition, the amount of alloyed Ru was found to decrease with reduced duty cycles. Composition determinations from inductively coupled plasma mass spectrometry and analysis on the oxidation states from X-ray photoelectron spectroscopy suggested a displacement reaction in which the Ru was alternately deposited and dissolved during Ton and Toff, while the Pt was deposited continuously. As a result, we observed substantial enrichment of Pt in the PtRu nanoparticles when the duty cycle was shortened.

The types of carbonaceous material and electrocatalyst are the critical components in fabrication of gas diffusion electrodes for fuel cells and metal-air batteries. In this study, carbon nanocapsule (15-30 nm) and Ag-carbon nanocapsule powders were synthesized and characterized for their electrochemical performances as oxygen reduction electrocatalyst in alkaline electrolyte using commercial noncatalyzed gas diffusion electrode as substrate. The i-V polarization response of the carbon nanocapsule demonstrated enhanced electrocatalytic capability over those of XC-72R and vapor growth carbon fiber, delivering 0.80 V at 200 mA/cm 2 . In addition, Ag-carbon nanocapsule powders exhibited a value of 0.99 V at 200 mA/cm 2 , surpassing commercially available Mn-catalyzed, and MnCo-catalyzed gas diffusion electrodes. Galvanostatic discharge of these Ag-carbon nanocapsule powders from 10 to 200 mA/cm 2 confirmed their stability and sustainability. This report identified a class of carbon material that not only exhibits electrocatalytic capability itself but also provides opportunity as substrate for known electrocatalysts.