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Plasmonic Au nanoparticle photoelectrodes were fabricated and characterized with ultrafast transient absorption (TA) and photomodulated cyclic voltammetry (CV) to determine whether the plasmonic ph...

Colloidal gold-palladium (Au-Pd) bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) photo-oxidation cycle, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Au-Pd bimetallic alloy and core-shell nanoparticles were prepared to synergistically couple a plasmonic absorber (Au) with a catalytic metal (Pd) with composite optical and catalytic properties tailored towards promoting photocatalytic oxidation. Catalysts utilizing metals that exhibit localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement for small molecule oxidation via augmented photocarrier generation/separation and photothermal conversion. The coupling of Au to Pd in an alloy or core-shell nanostructure maintains SPR-induced charge separation, mitigates the poisoning effects on Pd, and allows for improved EtOH oxidation. The Au-Pd nanoparticles were coupled to semiconducting titanium dioxide photocatalysts to probe their effects on plasmonically-assisted photocatalytic oxidation of EtOH. Complete oxidation of EtOH to CO2 under solar simulated-light irradiation was confirmed by monitoring the yield of gaseous products. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.

Here we present the synthesis of porous platinum–palladium macrobeams templated from high aspect ratio Magnus’ salt needle derivatives. The combination of [PtCl4]2− and/or [PdCl4]2− with [Pt(NH3)4]2+ ions results in salt needles ranging from 15 to 300 µm in length. Electrochemical reduction of the salt templates results in porous macrobeams with a square cross-section. Porous side wall texture and elemental composition was controlled with initial platinum to palladium salt ratio. Macrobeam free-standing films exhibited a specific capacitance up to 11.73 F/g and a solvent accessible surface area of 26.6 m2/g. These salt-templated porous platinum–palladium macrobeams offer a promising material for fuel cell catalysis.

The synthesis of high surface area porous noble metal nanomaterials generally relies on time consuming coalescence of pre-formed nanoparticles, followed by rinsing and supercritical drying steps, often resulting in mechanically fragile materials. Here, a method to synthesize nanostructured porous platinum-based macrotubes and macrobeams with a square cross section from insoluble salt needle templates is presented. The combination of oppositely charged platinum, palladium, and copper square planar ions results in the rapid formation of insoluble salt needles. Depending on the stoichiometric ratio of metal ions present in the salt-template and the choice of chemical reducing agent, either macrotubes or macrobeams form with a porous nanostructure comprised of either fused nanoparticles or nanofibrils. Elemental composition of the macrotubes and macrobeams, determined with x-ray diffractometry and x-ray photoelectron spectroscopy, is controlled by the stoichiometric ratio of metal ions present in the salt-template. Macrotubes and macrobeams may be pressed into free standing films, and the electrochemically active surface area is determined with electrochemical impedance spectroscopy and cyclic voltammetry. This synthesis method demonstrates a simple, relatively fast approach to achieve high-surface area platinum-based macrotubes and macrobeams with tunable nanostructure and elemental composition that may be pressed into free-standing films with no required binding materials.

Titanium dioxide (TiO2) semiconductor photocatalysts were photosensitized to the visible spectrum with gold nanospheres (AuNSs) and gold nanorods (AuNRs) to study the ethanol photo-oxidation cycle, with an emphasis toward driving carbon–carbon (C–C) bond cleavage at low temperatures. The photocatalysts exhibited a localized surface plasmon resonance (SPR) that was harnessed to drive the complete photo-oxidation of formic acid (FA) and ethanol (EtOH) via augmented carrier generation/separation and photothermal conversion. Contributions of transverse and longitudinal localized SPR modes were decoupled by irradiating AuNSs–TiO2 and AuNRs–TiO2 with targeted wavelength ranges to probe their effects on plasmonically assisted photocatalytic oxidation of FA and EtOH. Photocatalytic performance was assessed by monitoring the yield of gaseous products during photo-oxidation experiments using a gas chromatography–mass spectrometry–multiple headspace extraction (GC–MS–MHE) analysis method. The complete oxidation of E...

Photocatalytic assembly of heterometallic nanoarchitectures via plasmonic hot electrons is demonstrated by liquid-phase, reductive photodeposition of platinum (Pt) onto gold nanorods (AuNR) under longitudinal surface plasmon (LSP) excitation. Nucleation of Pt0 from PtCl62– was initiated by plasmonic hot electrons at the Au surface. Sub-5 nm epitaxial overgrowth of Pt followed a core–shell morphology. Measured 6.5 longitudinal:transversal growth aspect ratio revealed longitudinal growth preferentiality that was consistent with the LSP dipole polarity. In situ spectroscopic monitoring of the photocatalytic growth process permitted real-time feedback into Au surface functionalization with PtCl62– according to 16 nm red-shift in its Cl–Pt ligand-to-metal charge-transfer (LπMCT) band involving ligand π orbitals. Subsequent Pt0 growth kinetics were tracked using the LπMCT band. Discrete dipole models elucidated evolving light-matter interactions of Pt-decorated AuNR that were consistent with experimental charac...

The high cost and scarcity of platinum (Pt) materials have considerably hindered their use as catalysts for the oxygen reduction reaction (ORR) and thus wide-scale implementation in fuel cells for practical applications. Here we describe a class of non-noble metal catalysts, i.e., an ordered mesoporous FeNx-doped carbon (OMFeNC) that shows both performance activity and stability approaching or even greater than those of traditional Pt catalysts in acidic and basic solutions, as well as promising performances in operating polymer electrolyte membrane fuel cells (PEMFCs). The OMFeNC was synthesized by pyrolysis of metalloproteins in combination with an ordered mesoporous silica template. The remaining silica from the template in the OMFeNC material was removed during the synthesis process, and required no post-synthesis HF acid treatment. In addition, multiple heat-treatments were explored and it was found that the OMFeNC catalyst obtained after pyrolysis at 800 °C possessed the best catalytic activity and stability for the ORR. The activity and stability of OMFeNC were further evaluated in a single membrane electrode assembled PEMFC, whereby a 355 mW cm−2 peak power was achieved with pure H2/O2 feed streams, the OMFeNC material utilized as the cathode catalyst and a cell operating temperature of 60 °C. After 60 hours of durability testing, 73% of the initial activity remained for the PEMFC, whereas 86% of the initial activity remained after 120 hours of durability testing with a neutralized ionomer binder in the cathode layer.

Plasmonic metal nanoparticles (NPs) extend the overall light absorption of semiconductor materials. However, it is not well understood how coupling metal NPs to semiconductors alters the photo-electrochemical activity of small molecule oxidation (SMO) reactions. Different photo-anode electrodes comprised of Au NPs and α-Fe2O3 are designed to elucidate how the coupling plays not only a role in the water oxidation reaction (WO) but also performs for different SMO reactions. In this regard, Au NPs are inserted at specific regions within and/or on α-Fe2O3 layers created with a sequential electron beam evaporation method and multiple annealing treatments. The SMO and WO reactions are probed with broad-spectrum irradiation experiments with an emphasis on light-driven enhancements above and below the α-Fe2O3 band gap. Thin films of α-Fe2O3 supported on a gold back reflective layer resonantly-traps incident light leading to enhanced SMO/WO conversion efficiencies at high overpotential (η) for above band-gap excitations with no SMO activity observed at low η. In contrast, a substantial increase in the light-driven SMO activity is observed at low η, as well as for below band-gap excitations when sufficiently thin α-Fe2O3 films are decorated with Au NPs at the solution-electrode interface. The enhanced photo-catalytic activity is correlated with increased surface oxygen content (hydroxyl groups) at the Au/α-Fe2O3 interface, as well as simulated volume-integrated near-field enhancements over select regions of the Au/α-Fe2O3 interface providing an important platform for future SMO/WO photo-electrocatalyst development.

Harvesting light to drive water splitting for hydrogen generation is an attractive approach to satisfy the urgent energy demands. The design and fabrication of photoelectrode materials that are able to harvest sunlight is an important scientific undertaking. In this study, a two-quantum-dot (QD) layer is developed to decorate one-dimensional TiO 2 nanorod arrays, which are subsequently utilized as photoanodes to harvest the wide-spectrum sunlight for water splitting. The QD-coated TiO 2 nanorod arrays extend the light absorption range from the UV into the visible region yielding increased solar-to-hydrogen efficiencies. Transient photocurrent decay measurements demonstrate that the multi-layer CdSe-CdS QDs deposited onto the TiO 2 nanorod arrays result in a stepwise band alignment that not only improves the hole extraction but also facilitates electron injection from the QDs to TiO 2 rods. Moreover, the multi-heterojunction photoanode introduces interfacial states that act as recombination centers to trap the photogenerated electrons.

Gold, palladium, and platinum aerogels were prepared by a rapid, direct solution-based reduction synthesis with densities of 0.54, 0.065, and 0.055 g/cm3, respectively. Salt solutions were reduced at 1:1 (v/v) with dimethylamine borane and sodium borohydride to rapidly form gels within seconds to minutes above a threshold salt concentration and were then rinsed and freeze dried. Au, Pd, and Pt aerogels had no presence of oxide phases confirmed by X-ray diffractometry. Specific surface areas determined with gas physisorption were 3.06, 15.43, and 20.56 m2/g for Au, Pd, and Pt. Electrochemically determined specific capacitances using electrochemical impedance spectroscopy and cyclic voltammetry were 2.18, 4.13, and 4.20 F/g, and 2.67, 7.99, and 5.12 F/g for Au, Pd, and Pt, respectively. The rapid synthesis, high solvent accessible specific surface area, conductivity, and capacitance make these noble metal aerogels candidates for many of catalytic, energy, and sensor applications.

This paper highlights experimental and theoretical efforts dedicated to developing plasmonic-enhanced electrodes for the photo-electrochemical ethanol oxidation reaction (EOR) at room temperature in alkaline media. However, decoupling the electrocatalytic dark response from the plasmon-enhanced improvement presents a difficult challenge. To understand the plasmonic-enhancement of the photo-electrochemical EOR, multiple Au-Fe2O3 were fabricated and evaluated in parallel with discrete dipole approximation (DDA) modeling. Different Au-Fe2O3 were synthesized with Au nanoparticles located at variable positions within and/or on the Fe2O3 layer(s). The configurations investigated include thin film, embedded, surface and sandwich layered electrodes to facilitate optimal electrode design considerations for plasmonic-enhancement. The design strategies and configurations were guided by DDA simulations to assess absorption, scattering, and near-field enhancements within or near the semiconductor band edge, as well as the solution/electrode interface. For the different Fe2O3 loadings and Au nanoparticle sizes/distributions considered, it is determined that the Au-Fe2O3 surface configurations significantly enhanced the EOR in terms of a large positive current density enhancement, an increased photo-voltage and a lower onset potential relative to the other electrode designs.

Pd

A protocol is described to photocatalytically guide Pd deposition onto Au nanorods (AuNR) using surface plasmon resonance (SPR). Excited plasmonic hot electrons upon SPR irradiation drive reductive deposition of Pd on colloidal AuNR in the presence of [PdCl4]2-. Plasmon-driven reduction of secondary metals potentiates covalent, sub-wavelength deposition at targeted locations coinciding with electric field "hot-spots" of the plasmonic substrate using an external field (e.g., laser). The process described herein details a solution-phase deposition of a catalytically-active noble metal (Pd) from a transition metal halide salt (H2PdCl4) onto aqueously-suspended, anisotropic plasmonic structures (AuNR). The solution-phase process is amenable to making other bimetallic architectures. Transmission UV-vis monitoring of the photochemical reaction, coupled with ex situ XPS and statistical TEM analysis, provide immediate experimental feedback to evaluate properties of the bimetallic structures as they evolve during the photocatalytic reaction. Resonant plasmon irradiation of AuNR in the presence of [PdCl4]2- creates a thin, covalently-bound Pd0 shell without any significant dampening effect on its plasmonic behavior in this representative experiment/batch. Overall, plasmonic photodeposition offers an alternative route for high-volume, economical synthesis of optoelectronic materials with sub-5 nm features (e.g., heterometallic photocatalysts or optoelectronic interconnects).

Platinum nanomaterials provide an excellent catalytic activity for diverse applications and given its high cost, platinum alloys and bi-metallic nanomaterials with transition metals are appealing for low cost and catalytic specificity. Here the synthesis of hierarchically porous Pt&ndash, Cu macrobeams and macrotubes templated from Magnus&rsquo, s salt derivative needles is demonstrated. The metal composition was controlled through the combination of [PtCl4]2&minus, with [Pt(NH3)4]2+ and [Cu(NH3)4]2+ ions in different ratios to form salt needle templates. Polycrystalline Pt&ndash, Cu porous macrotubes and macrobeams 10&rsquo, s&ndash, 100&rsquo, s &mu, m long with square cross-sections were formed through chemical reduction with dimethylamine borane (DMAB) and NaBH4, respectively. Specific capacitance as high as 20.7 F/g was demonstrated with cyclic voltammetry. For macrotubes and macrobeams synthesized from Pt2&minus, Pt2+:Cu2+ salt ratios of 1:1:0, 2:1:1, 3:1:2, and 1:0:1, DMAB reduced 3:1:2 macrotubes demonstrated the highest ethanol oxidation peak currents of 12.0 A/g at 0.5 mV/s and is attributed to the combination of a highly porous structure and platinum enriched surface. Salt templates with electrochemical reduction are suggested as a rapid, scalable, and tunable platform to achieve a wide range of 3-dimensional porous metal, alloy, and multi-metallic nanomaterials for catalysis, sensor, and energy storage applications.

Pd-containing alloys are promising materials for catalysis. Yet, the relationship of the structure–property performance strongly depends on their chemical composition, which is currently not fully resolved. Herein, we present a physical vapor deposition methodology for developing PdxAu1–x alloys with fine control over the chemical composition. We establish direct correlations between the composition and these materials’ structural and electronic properties with its catalytic activity in an ethanol (EtOH) oxidation reaction. By combining X-ray diffraction (XRD) and X-ray photelectron spectroscopy (XPS) measurements, we validate that the Pd content within both bulk and surface compositions can be finely controlled in an ultrathin-film regime. Catalytic oxidation of EtOH on the PdxAu1–x electrodes presents the largest forward-sweeping current density for x = 0.73 at ∼135 mA cm–2, with the lowest onset potential and largest peak activity of 639 A gPd–1 observed for x = 0.58. Density functional theory (DFT) ca...

Targeted, sequential deposition of metals using localized surface plasmon resonance (LSPR) is a promising fabrication route for solar fuel catalysts and sensors. This work examines liquid-phase, reductive photodeposition of platinum (Pt) nanoparticles onto the longitudinal ends of gold nanorods (AuNR) under surface plasmon excitation. Reductive Pt nucleation is initiated by plasmonic hot electrons at the Au-liquid interface, whose sites are governed by the plasmon polarity. In this work, in situ spectroscopic monitoring of the photodeposition process permitted real-time feedback into AuNR surface functionalization with the Pt precursor, Pt growth kinetics under monochromatic AuNR LSPR excitation, and their evolving light-matter interactions. Energy dispersive spectroscopy (EDS) mappings show Pt deposition was localized toward the AuNR ends. Coordinated X-ray photoelectron spectroscopy (XPS) measurements with density functional theory (DFT) calculations of the Pt-decorated AuNR density of states (DOS) elucidated optoelectronic behavior. Catalytic photodeposition using plasmonic hot electrons provide an economical path towards targeted, hierarchal assembly of multi-metallic nanoarchitectures at ambient conditions with specified optoelectronic activity.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

Plasmonic metal nanoparticles (NPs) extend the overall light absorption of semiconductor materials. However, it is not well understood how coupling metal NPs to semiconductors alters the photo-electrochemical activity of small molecule oxidation (SMO) reactions. Different photo-anode electrodes comprised of Au NPs and α-Fe2O3 are designed to elucidate how the coupling plays not only a role in the water oxidation reaction (WO) but also performs for different SMO reactions. In this regard, Au NPs are inserted at specific regions within and/or on α-Fe2O3 layers created with a sequential electron beam evaporation method and multiple annealing treatments. The SMO and WO reactions are probed with broad-spectrum irradiation experiments with an emphasis on light-driven enhancements above and below the α-Fe2O3 band gap. Thin films of α-Fe2O3 supported on a gold back reflective layer resonantly-traps incident light leading to enhanced SMO/WO conversion efficiencies at high overpotential (η) for above band-gap excitations with no SMO activity observed at low η. In contrast, a substantial increase in the light-driven SMO activity is observed at low η, as well as for below band-gap excitations when sufficiently thin α-Fe2O3 films are decorated with Au NPs at the solution-electrode interface. The enhanced photo-catalytic activity is correlated with increased surface oxygen content (hydroxyl groups) at the Au/α-Fe2O3 interface, as well as simulated volume-integrated near-field enhancements over select regions of the Au/α-Fe2O3 interface providing an important platform for future SMO/WO photo-electrocatalyst development.

In this study we show a method of preparing a high performing catalyst by designing functional nano boundaries in a nanocomposite material. A non-precious nanocomposite material composed of spinel Mn1.5Co1.5O4 nano crystals and FeNx-functioned graphene nano platelets (FeNx/C) was synthesized by an ultrasonic process. The crystal structure and elemental composition of the bimetal oxide were determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The surface morphology of the Mn1.5Co1.5O4–FeNx/C nanocomposite was characterized with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The catalytic activity for the oxygen reduction reaction (ORR) was analyzed by an electrochemical method. The enhancement of activity for the ORR at the nanocomposite material is attributed to double synergistic effects from the bimetal particles and the FeNx/C nano sheets. The nanocomposite material is able to catalyze 4-electron oxygen reduction to generate water in alkaline media with a high kinetic rate constant (7.6 × 10−2 cm s−1 at 0.7 V vs. reversible hydrogen electrode, RHE). Finally, the activity and stability of the nanocomposite material were compared with that of 40% Pt supported on active carbon (40% Pt/C), which reaches 95% activity and a comparable stability of 40% Pt/C at 0.7 V (vs. RHE).

Alkaline and acid-alkaline bipolar membrane electrolytes were prepared from cast and electrospun polymer membranes. The alkaline anion-exchange membrane (AEM) consisted of a polyphenylene oxide (PPO) backbone containing side-chain alkyl amine groups of various lengths. Different AEM membranes were investigated to down-select to a stable chemistry for preparing the acid-alkaline bipolar membrane. Nafion 117 was utilized as the proton-exchange membrane (PEM) component, and the PEM was joined to the AEM to form a PEM-AEM acid-alkaline bipolar membrane electrolyte. Different methods for joining the PEM-AEM were evaluated to determine compatibility matching between layers. In some cases, an electrospun layer junction between the PEM-AEM was created to assist in development. In-plane and through-plane ionic conductivity measurements were performed to evaluate the isolated AEM, PEM and PEM-AEM membranes.

In this study, we demonstrate a non-Pt nanostructured bioinorganic hybrid (BIH) catalyst for catalytic oxygen reduction in alkaline media. This catalyst was synthesized through biomaterial hemin, nanostructured Ag-Co alloy, and graphene nano platelets (GNP) by heat-treatment and ultrasonically processing. This hybrid catalyst has the advantages of the combined features of these bio and inorganic materials. A 10-fold improvement in catalytic activity (at 0.8 V vs RHE) is achieved in comparison of pure Ag nanoparticles (20-40 nm). The hybrid catalyst reaches 80% activity (at 0.8 V vs RHE) of the state-of-the-art catalyst (containing 40% Pt and 60% active carbon). Comparable catalytic stability for the hybrid catalyst with the Pt catalyst is observed by chronoamperometric experiment. The hybrid catalyst catalyzes 4-electron oxygen reduction to produce water with fast kinetic rate. The rate constant obtained from the hybrid catalyst (at 0.6 V vs RHE) is 4 times higher than that of pure Ag/GNP catalyst. A catalytic model is proposed to explain the oxygen reduction reaction at the BIH catalyst.

Non-noble metal-containing electrocatalysts were prepared by an electrospinning method and evaluated as oxygen reduction electrocatalysts. Fe- or Co-containing carbon fibers were prepared by pyrolyzing electrospun polyacrylonitrile (PAN) fibers containing the respective metal precursor and are denoted Fe-PAN and Co-PAN, respectively. The Fe- or Co-PAN carbon fibers were acid-leached and subjected to a second pyrolysis, whereby the final fibers were found to be uniform in diameter with roughened surfaces. Scanning transmission electron microscopy equipped with energy dispersive spectroscopy area-mapping identified Fe or Co nanoparticulates throughout the fiber with a distribution of particulate sizes. X-ray diffractograms (XRD) revealed amorphous Fe-PAN and Co-PAN carbon fibers with no discernible Fe or Co phases, whereas high-resolution XPS scans show a range of potential Fe or Co species. Moreover, the high-resolution X-ray photoelectron spectroscopy (XPS) and peak-fitting analysis provided chemical species information for the C1s, N1s, Fe2p and Co2p regions. The physical characterizations highlighted potential beneficial components for the electrocatalysts that made their use as oxygen reduction reaction (ORR) effective. Rotating disk and ring-disk electrode experiments determined that the best Fe-PAN sample out-performed the best Co-PAN sample and even performed well in comparison to a commercial Pt/C electrocatalyst for the ORR in a high pH media.

A class of Pd–Ni–P electrocatalysts are prepared for the ethanol electrooxidation reaction (EOR). X-ray diffraction and transmission electron microscope reveal that the synthesized Pd–Ni–P catalyst possesses a more amorphous structure with smaller particle sizes when compared with a Pd–Ni sample without P and a control Pd black (Pd-blk) sample. The Pd–Ni–P catalyst contains double the number of electrocatalytically active sites (12.03%) compared with the Pd–Ni (6.04%) and Pd-blk (5.12%) samples. For the EOR, the Pd–Ni–P catalyst has the lowest onset potential (−0.88 V vs SCE), the most negative peak potential (−0.27 V vs SCE), and the highest EOR activity in 0.1 M KOH solution. Moreover, a 110 mV decrease in overpotential is observed for the EOR on the Pd–Ni–P catalyst compared with the Pd-blk catalyst. A Tafel slope of 60 mV/dec at low polarization potentials (

A highly active oxygen reduction reaction (ORR) catalyst was synthesized by supporting Ag nano-particles on graphene nano platelets (Ag/GNP) via ultrasound treatment. The Ag/GNP catalyzes the O2 molecule through a 4-electron reduction to water in 0.1 M KOH electrolyte. The half-wave potential for the ORR on Ag/GNP is similar to a Pt black coated electrode (i.e -0.27 V at Ag/GNP, and -0.18 V at 40% Pt/C vs.SCE). The kinetic rate for the ORR on Ag/GNP is 3.16 × 10−2 cm · s−1 at -0.4 V vs. SCE. The effect of alcohols and other impurities on the ORR catalytic activity for Ag/GNP was examined and found to be highly tolerant to methanol, ethanol and ethylene glycol. The Ag/GNP catalyst is also tolerant to tetraalkyl ammonium hydroxides; i.e. functional groups related to the chemical structure of common alkaline electrolyte membranes.

Proton-exchange membrane fuel cells (PEMFCs) generally contain platinum-group-metal (PGM) electrocatalysts supported on a variety of different carbons. However, the long term durability of PGM electrocatalysts is decreased due to carbon support corrosion and loss of the electrochemically active surface area (ESA) as a result of nanoparticle agglomeration and/or Ostwald ripening. Moreover, the prohibitive expense of PGM materials has forced consideration of non-PGM alternatives. One way to mitigate carbon corrosion and increase long-term operation is by using metal oxide supports. For example, Huang et al. compared PEMFC performance of Pt/TiO2 to Pt/C (TKK) after subjecting both catalysts to an accelerated stress testing (AST) protocol, and found that Pt/TiO2 catalyst essentially retained its ESA and prevented Pt nanoparticle agglomeration. Wu et al. studied the oxygen reduction reaction (ORR) in 0.5 M H2SO4 on Fe-containing carbonized polyaniline supported on TiO2 (PANI-FeTiO2), and found an onset and half-wave (E1/2) potential of 0.98 and 0.83 V vs. RHE, respectively. The authors found that the PANI-Fe-TiO2 catalyst showed better results than Pt/C, and suggested that adding TiO2 not only decreased carbon corrosion but facilitated the ORR. In this study, we focus on developing durable non-PGM electrocatalysts for PEMFCs. We carbonize electrospun polyacrylonitrile (PAN) carbon nanofibers (CNFs) and coat them with TiO2 using atomic layer deposition (ALD). Furthermore, we enhance the surface area and reactive edges of the CNFs by adding nitrogendoped graphene platelets to the surface with a plasmaenhanced chemical vapor deposition (PECVD) process. PAN CNFs are attractive due to their inherent ORR activity and conductivity. Park et al. carbonized electrospun CNFs and reported a ~2x increase in bulk conductivity compared to XC-72R. The addition of TiO2 may act to alleviate carbon corrosion. We plan to study the ORR on TiO2-coated CNF/graphene electrocatalysts with rotating ring disk electrode (RRDE) voltammetry. Additionally, we attempt to compare the ORR activity for TiO2 coatings deposited with different ALD precursors. Physical characterizations such as XRD, XPS, TEM and SEM are performed to understand the electrocatalyst morphology, TiO2 loading and imaging, respectively. Figure 1a and 1b show carbonized PAN CNFs before and after growing graphene platelets onto the nanofiber walls, respectively.

The electro-osmotic drag coefficients (ξ) of water-vapor equilibrated Nafion® 117, a proton conductor, and Tokuyama® A201, a hydroxide conductor were determined from the steady-state voltage of a water concentration cell. The ξ values are reported, along with water uptake, ion-exchange capacity, ionic conductivity, and methanol permeability of these membranes. The room-temperature ξ of Nafion® 117 and Tokuyama® A201 is 0.99 (±0.07) and 0.61 (±0.12), respectively, and is relatively independent of water content over the relative humidity range of 14–96%. The time to steady potential in the water concentration cell was longer for the Tokuyama® A201 membrane than the Nafion® 117 membrane, which is tentatively attributed to the lower mobility of hydrated hydroxide (or carbonate from absorption of adventitious carbon dioxide) in comparison to hydronium ion.

A nano-sized non-noble metal catalyst containing hemin supported on carbon black was synthesized for the oxygen reduction reaction (ORR). The hemin supported on carbon black was heat-treated (HT), and subjected to additional ultrasound treatments to increase the BET surface area and available active sites for the ORR. The HT hemin supported on carbon black was characterized with thermogravimetric analysis (TGA), elemental analysis, transmission electron microscopy (TEM), and BET surface area analysis. The catalytic activity of the synthesized electrocatalysts was analyzed with cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring disk electrode (RRDE). The effect of BET surface area on formal potential, anodic and cathodic peak currents, limiting currents, half wave potentials, and kinetic rate constant for ORR were studied. We found an apparent correlation between catalytic activity and BET surface area for this particular catalyst. Increasing BET surface area, the ORR catalytic activity increases significantly. Our research on HT hemin indicates that the catalytic activity for ORR significantly improves by reducing the particle size and increasing the surface area.

A bio-material, hemin, was heat-treated and used as an oxygen reduction reaction (ORR) electrocatalyst. In addition to heat-treatment, two methods were used to improve the catalysts' electrochemical activity. First, high surface area graphene nanoplatelets (GNP) were chosen as a catalyst support. Second, ultrasound was used to break the catalyst samples into smaller pieces. Hemin supported on GNP and heat-treated at 600 °C showed significantly higher catalytic activity than those without ultrasonic treatment. Furthermore, a single fuel cell fabricated with the synthesized catalyst yielded a power density of 300 mW cm−2. Keywords: Hemin, Graphene, ORR catalysts, Ultrasound, Fuel cell

Targeted, reductive photodeposition of catalytic metals via plasmonic hot electrons excited on an electrode is a promising, economical approach to manufacturing plasmon-sensitized photoelectrodes for catalysis applications. This work examines liquid-phase, anisotropic photodeposition of Pt(0) co-catalysts from chloroplatinic acid, Pt(IV), onto suspended Au nanorods under localized surface plasmon (LSP) excitation. Photochemical Pt(0) nucleation is initiated by plasmonic hot electrons, which migrate to the Au surface according to the plasmon polarity. In situ, time-resolved absorbance monitoring of the photochemical reaction elucidated Au nanorod surface functionalization with Pt(IV), Pt(0) growth kinetics under Au LSP excitation, and the evolving light-matter interactions. Energy dispersive spectroscopy (EDS) mappings show preferential Pt(0) deposition on the Au nanorod ends, consistent with the laser-induced LSP dipoles. Discrete dipole approximation (DDA) of Maxwell’s equations corroborated measured optical responses and allows a priori design of hot electron energetics. Electronic valence band structure of the Pt-functionalized Au nanorod was measured by x-ray photoelectron spectroscopy (XPS) and calculated by density functional theory (DFT) to enumerate the energy distribution of carriers accessible for surface chemistry. Together, these techniques and analyses accelerate development of plasmon-sensitized photoelectrodes for solar fuel generation. Figure 1

The ability to efficiently oxidize small molecules containing C-C bonds (e.g. ethanol and ethylene glycol) is challenging at low temperature (i.e., < 80°C). It was previously shown that bimetallic catalysts (e.g. Pd-Au systems) have enhanced electrocatalytic activities for various organic reactions.1 Moreover, an increased overall selectivity and turnover frequency for primary alcohol conversion to aldehydes has been reported after the addition of Au to Pd nanocrystals.2 However dissociation of the C-C bonds is often incomplete and only undergoes a partial oxidation to intermediate product(s). Therefore, a breakthrough technology is required to overcome this obstacle at low temperature. One strategy is to tailor bimetallic catalysts for photo-electrochemical oxidation reactions by engineering the plasmonic response. For example, bimetallic Pd-Au nanostructures have been tuned to the visible portion of the solar spectrum for use as plasmonic H2 sensors.3 We report the use of nanolithography patterned Pd-Au bimetallic catalysts for the photo-electrochemical oxidation of ethanol and ethylene glycol. We consider the effect of laser and solar-simulated excitations on nanostructured Pd-Au bimetallic electrodes fabricated on atomic layer deposited TiO2 films coupled to a back contact.4-5 The Pd-Au bimetallic electrodes with and without film-coupling are evaluated in parallel with discrete dipole approximation (DDA) modeling derived from doubly-periodic array simulations, which allows assessment of the absorption, scattering, and near-field enhancements. For select bimetallic configurations, we compare the selectivity and kinetics of the photo-electrochemical oxidation reactions and discuss the catalytic response driven by light excitation. Lu, C.L.; Prasad, K. S.; Wu, H.L.; Ho, J.A.; Huang, M.H. JACS 2010, 132 (41), 14546-14553. Enache, D. I.; Edwards, J. K.; Landon, P.; Solsona-Espriu, B.; Carley, A. F.; Herzing, A. A.; Watanabe, M.; Kiely, C. J.; Knight, D. W.; Hutchings, G. J. Science 2006, 311 (5759), 362-365. Nugroho, F. A.; Iandolo, B.; Wagner, J. B.; Langhammer, C. ACS Nano 2016, 10 (2), 2871-9. McClure, J. P.; Grew, K. N.; Das, N. C.; Chu, D.; Baker, D.; Strnad, N.; Gobrogge, E. MRS Advances 2017, 2 (55), 3397-3402. Ciracì, C.; Chen, X.; Mock, J. J.; McGuire, F.; Liu, X.; Oh, S.-H.; Smith, D. R. Applied Physics Letters 2014, 104 (2), 023109.

Small unmanned aerial systems (UASs) have been used for military applications and have additional potential for commercial applications [1-4]. For the military, these systems provide valuable intelligence, surveillance, reconnaissance and target acquisition (ISRTA) capabilities for units at the infantry, battalion, and company levels. The small UASs are light-weight, manportable, can be hand-launched, and are capable of carrying payloads. Currently, most small UASs are powered by lithium-ion or lithium polymer batteries; however, the flight endurance is usually limited less than two hours and requires frequent battery replacement. Long endurance small UAS flights have been demonstrated through the implementation of a fuel cell system. For instance, a propane fueled solid oxide fuel cell (SOFC) stack has been used to power a small UAS and shown to extend mission flight time. The research and development efforts presented here not only apply to small UASs, but also provide merit to the viability of extending mission operations for other unmanned systems applications.

Recently Iron oxide (Fe2O3) nano structure has drawn renewed interest in electrocatalysis process for carbon-carbon (C-C) bond breaking in ethanol. We design and fabricate Fe2O3 plasmonic nanostructures for C-C bond-breaking processes in high density fuels. After patterning Fe2O3 film, we use inductively coupled plasma (ICP) etching equipped with an Argon (Ar) plasma to create the film with nanometer scale dimensions. We used both photoresist mask and hard mask like silicon dioxide film for selecting etching. Fe2O3 film etching process is optimized by using different parameters like ICP power, base electrode power, pressure, temperature, and Ar gas flow etc. We used elliposmetric method as well as UV/Vis reflectance spectroscopy to determine the resonance wavelength of the plasmonic nanostructures suitable for electrocatalysis experiment. Iron oxide (Fe2O3) has recently received much attention among the various semiconductor photo-electrode materials due to its favorable optical band gap (~2.2 eV), excellent chemical stability in high pH media, natural abundance, and low cost [1,2]. However, Fe2O3 exhibits a relatively poor absorptivity of photons near its band-edge due to an indirect band gap, poor electronic conductivity (PEC), and picosecond recombination of excited states, thus leading to a photo-generated hole diffusion length of ~2-4 nm [3]. These non-ideal optoelectronic properties hinder the transport of photo-generated carries and increase the recombination rate, which results in a lowering of the PEC efficiency compared to theoretically predicted values. Controlling the nanostructure of Fe2O3 may provide an effective technology for overcoming the aforementioned problems of Fe2O3 due to the geometry and mechanism-dependent semiconductor structure [4]. The shape of the Fe2O3structures with cone, cylinder, sphere, etc. features alters the electric field dependent absorption and transport processes. We use electron beam evaporation system to deposit thin Fe2o3 film (100-500 nm) on silicon substrate with thin layer of gold (Au) film. We then use an inductively coupled plasma (ICP) etching process to define Fe2O3 nano-structured pillars with various diameters (50nm -5 µm) and heights. We use either e-beam lithography or optical lithography process to define the plasmonic nanostructures. ICP etching process with Ar plasma is used with varying power, pressure and substrate temperature etc. to optimize the Fe2O3 etching process. Scanning electron (SEM) and atomic force (AFM) microscopy tools are used to determine the surface morphology of the nanostructures, whereas ellipsometer and UV-Vis spectrometer elucidate the optical properties. Galvanometeric current-voltage measurement is performed to determine the optimum nano plasmonic structure for carbon-carbon (C-C) bond breaking process in high energy density chemicals. In figure 1, we have shown the etch rate of Fe2O3 film with different substrate temperatures and Ar pressure in the reaction chamber. We find that in order to achieve a smooth surface and reasonable etch rate, the substrate temperature should be between 15-18 ᵒC and the ICP power between 800-1000 W. Detailed deposition, annealing, etching and characterization results of Fe2O3 nano plasmonic structures will be presented in a full paper. References: [1]Wang, G. M.; Ling, Y. C.;Wheeler, D. A.; George, K. E. N.; Horsley, K.; Heske, C.; Zhang, J. Z.; Li, Y. Nano Lett. 2011, 11, 3503 [2] Kay, A.; Cesar, I.; Grätzel, M. J. Am. Chem. Soc. 2006, 128, 15714 [3] Cherepy, N. J.; Liston, D. B.; Lovejoy, J. A.; Deng, H. M.; Zhang, J. Z. J. Phys. Chem. B 1998, 102, 770 [4] Sivula, K.; Zboril, R.; Formal, F. L.; Robert, R.; Weidenkaff, A.; Tucek, J.; Frydrych, J.; Grätzel, M. J. Am. Chem. Soc. 2010, 132, 7436.

The development of technologies which offer efficient and scalable energy conversion and storage is a challenge of considerable importance. Potential applications range from the integration of renewable energy supplies into the domestic power grid to reducing the logistic burden of supplying energy to our military and defense forces. Electrochemical processes are a natural fit for addressing many of these problems; however, system limitations and technical issues confound development efforts. Cost, reliability, scalability, and ease of integration are often among the leading challenges for established domestic technologies, whereas size, weight, storage/transportability, and environmental considerations are of utmost importance for defense applications. Research and development efforts for electrochemical energy conversion and storage technologies are driven by materials requirements. Materials in these electrochemical systems typically have demanding functional requirements (e.g., conductivity, catalyst activity, selectivity, mechanical strength, etc.), which must be met under aggressive operating conditions (e.g., acidic or basic electrolytes, the presence of strong solvents and/or contaminants, highly oxidizing and reducing electrode processes, high temperatures, etc.). All of these functional requirements must be met with expectations for little-to-no degradation during operation and cycling (e.g., loss in active catalyst area, poisoning or chemical degradation, corrosion, fatigue, crack formation, etc.). In many cases the individual constituent materials cannot meet the complex and intertwined functional, environmental, and stability requirements alone, which has driven research and development efforts towards the use of heterogeneous materials. Our own research and development efforts focus on hybrid acidic- and alkaline-membranes for portable fuel cell applications [1-2]. Proton exchange membrane (PEM) electrolytes are relatively well established. Alkaline anion exchange membrane (AEM) electrolytes have more recently come to prevalence. AEMs have been ushered into the fuel cell community based on the prospect of developing cheaper and more compact systems via reductions in noble-metal catalyst content, membrane and packaging materials costs, and water and fuel management requirements [3]. However, development efforts have been hindered by challenges with materials performance and stability [3-5], penalties for anodic processes including hydrogen oxidation [6], and thermodynamic and resistive losses associated with the presence of carbon dioxide [7-8], among others. These challenges have led us to explore the development of hybrid-membrane approaches, such as the bipolar membrane which was shown by Unlu et al [9]. We believe that this type of approach can mitigate some of the catalyst and water/fuel management challenges. However, a suitable AEM and acid-alkaline membrane interface are needed for such an approach. This has led us to study the modification of the underlying AEM materials as well as the introduction of heterogeneity through processing (e.g., via electrospinning processes popularized for fuel cells in the PEM community [10]). In this modeling and theory focused talk, we address the introduction of heterogeneity into membrane electrolyte materials, its influence on key material properties, and the corresponding impact of its integration to bipolar membrane fuel cells. Acknowledgement: The authors gratefully acknowledge the support of the U.S. Department of the Army, Army Materiel Command, and U.S. Army Research Development and Engineering Command. References: [1] K.N. Grew & D. Chu, J. Electrochem. Soc., 161(1), F1037 (2014). [2] J.P McClure, K.N. Grew, D. Chu, ECS Trans., 69#A01-0053, Accepted (2015). [3] J.R. Varcoe & R.C.T. Slade, Fuel Cells, 5(2), 187 (2005). [4] M.A. Hickner, A.M. Herring, E. B. Coughlin, J. Polymer Sci. B, 51(24), 1727 (2013). [5] G. Merle, M. Wessling, K. Nijmeijer, J. Memb. Sci., 377(1-2), 1 (2011). [6] W. Sheng, H.A. Gasteiger, & Y. Shao-Horn, J. Electrochem. Soc., 157(11), B1529 (2010). [7] Y. Wang et al, Electrochem. Comm., 5, 662 (2003). [8] T.D. Myles et al, J. Power Sources, 296, 225 (2015). [9] M. Unlu, J. Zhou, & P.A. Kohl, J. Phys. Chem. C, 113,11416 (2009). [10] J. Choi et al, Macromol., 41, 4569 (2008).

Anion-exchange membranes (AEMs) have received attention for use in alkaline fuel cells and bipolar membrane applications [1] The bipolar membrane concept was recently demonstrated by Unlu et al. as a way to reduce fuel cell costs (i.e., Pt loading) and the overall balance of plant (BOP).[2-3] Bipolar membranes are typically comprised of an H+-conducting membrane adjacent to an OH--conducting membrane with at least one internal acid-alkaline junction. However, most AEMs studied to-date are organic and exhibit low chemical stabilities and low ionic conductivities after prolonged exposure to high pH media and temperatures greater than 60°C.[4] A number of advancements have been made to increase the ion-exchange group stability by using phenyl guanidinium-[5], imidazolium-[6] and other metal-cation exchange groups[7], among others; all of which provide potential routes to circumvent stability issues. In this study, we prepared AEM and PEM precursors which are further developed into bipolar membranes. The combination of our precursors and our electrospinning process proves useful for preparing H+- and OH--conducting membranes. In addition to the aforementioned AEM stability issues, bipolar membranes can suffer from material compatibility issues at the AEM/PEM junction. We demonstrate an approach to create bipolar membranes by, for example, co-electrospinning that allows for short- and long-range fabrication with desirable AEM/PEM interfacial binding. For example, Park et al. recently demonstrated a novel approach for creating AEM membranes by electrospinning, which we extend specifically to develop bipolar membranes.[8] As a proof of concept, we chose PEM and AEM components made primarily of Nafion and modified polysulfone or modified poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) derivatives, respectively. We present 3 different approaches for conjoining the AEM and PEM layers to create the bipolar membranes. Ex-situ ion-transport measurements are presented for bulk in-plane ionic conductivities (σ) of the isolated membranes in OH--, H+- and CO3 2—forms and are compared to the through-plane σ for the bipolar membranes. Physical characterizations such as SEM, BET, and gravimetric swelling measurements are presented for each isolated and combined membranes. For select membranes, we show polarization (i-V) curves for a single MEA operating under H2/O2. Figure 1 shows a schematic of the electrospinning process whereby a rotating roll configuration is utilized for fabricating a co-electrospun bipolar membrane with a typical SEM image shown for an AEM fiber mat. Acknowledgments: We gratefully acknowledge the fuel cell team at the U.S. Army Research Laboratory. We acknowledge the U.S. Department of the Army, AMC and RDECOM for funding and support. References: [1] S. Malkhandi, P. Trinh, A.K. Manohar, K.C. Jayachandrababu, A. Kindler, G.S. Prakash, S.R. Narayanan, Journal of The Electrochemical Society 160 (2013) F943. [2] M. Ünlü, J. Zhou, P.A. Kohl, Angewandte Chemie International Edition 49 (2010) 1299. [3] K.N. Grew, D. Chu, J. Electrochem. Soc., 161(1) F1037 (2014). [4] Y.-J. Wang, J. Qiao, R. Baker, J. Zhang, Chemical Society Reviews 42 (2013) 5768. [5] D.S. Kim, C.H. Fujimoto, M.R. Hibbs, A. Labouriau, Y.-K. Choe, Y.S. Kim, Macromolecules 46 (2013) 7826. [6] F. Gu, H. Dong, Y. Li, Z. Si, F. Yan, Macromolecules 47 (2014) 208. [7] Y. Zha, M.L. Disabb-Miller, Z.D. Johnson, M.A. Hickner, G.N. Tew, Journal of the American Chemical Society 134 (2012) 4493. [8] A.M. Park, P.N. Pintauro, Electrochemical and Solid-State Letters 15 (2011) B27. Figure 1

Improved anion exchange membrane (AEM) materials are needed to develop next generation electrochemical devices including fuel cells. In recent years, largely spurred by some developments with radiation grafted AEM materials out of the laboratories of Robert Slade and John Varcoe, there has been significant attention from within the energy conversion/storage communities [1-3]. In additional to the interest in the use of AEM materials for fuel cells [1-3], the community has given additional consideration to their use for areas including chemical processing and energy storage [3-6], electrolysis and solar-to-fuel production [3,6], desalination and dialysis [3], and purification and separation processes [3]. Many of the interest in these materials is a result of the opportunities that may be presented by a stable, anion-conducting polymer electrolyte materials. In this talk we will highlight our collaborative, simulation-focused efforts to develop and understand high performance AEM materials for electrochemical applications. Among other things, we will discuss our efforts to develop, validate, and apply simulation methodologies that can provide new and fundamental insights into the nature of the membrane(s) cationic stability, anionic conductivity, and the uncertainty in our respective models that range from atomistic to continuum scales. These multiscale modeling approaches include everything from atomistic MD simulations using reactive (ReaxFF) and polarizable force fields, to coarse-grained molecular dynamics simulations with developed using uncertainty quantification (UQ) based methodologies and continuum level modeling approaches. For our initial efforts that we will discuss in this talk, we utilize relatively simple backbone materials such as Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). These backbone materials are effectively used as a model material system. This enables us to develop and validate simulation methods that can predict and resolve the proper structure-property relationships; a key step before moving to more complex materials. Further, the simpler PPO-type backbone materials provide a key advantage at this stage in that they can concurrently be (i) processed, synthesized, and characterized in our labs, and (ii) subjected to unique processing methods/conditions that includes both casting and electro-spinning processes. This last capability is salient because the focus of the model and simulation development efforts are on the application to multi-scale systems. The ability to concurrently process the materials using different methods (i.e., cast, electro-spun, and co-spun with an inert matrix material) and under different conditions can drastically influence the material’s morphologies, structures, ordering, and properties. Acknowledgments: KNG, JPM, and DC gratefully acknowledge the support of the U.S. Department of the Army, Army Materiel Command, and U.S. Army Research Development and Engineering Command. This work was completed, in part, through the U.S. Army Research Laboratory’s Enterprise for the Multiscale Research of Materials (EMRM). This work was completed in conjunction with an Army Research Laboratory EMRM’s Multiscale Modeling of Electronic Materials (MSME) Collaborative Research Alliance (CRA). VM, LCJ, JL, DB, JBH, ZL, AvD, WZ, and RMK gratefully acknowledge the financial support of the MSME CRA. References: 1. J.R. Varcoe and R.C.T. Slade, Fuel Cells, 5(2), 187 (2005). 2. T.N. Danks, R.C.T. Slade, and J.R. Varcoe, J. Mater. Chem., 12, 3371 (2002). 3. J.R. Varcoe et. al., Energy Environ. Sci., 7 ,3135 (2014). 4. W.E. Mustain, J. A. Vega, and N.S. Spinner “Electrochemical Reactor for CO2 Conversion Utilization and Associated Carbonate Electrocatalyst.” U.S. Patent Applications 13/289,508, US20120193222 A1 (2012). 5. N. Spinner and W.E. Mustain, 220’th ECS Meeting, Abs. No. 1501 (2011). 6. J. M. Spurgeon, M. G. Walter, J. Zhou, P. A. Kohl and N. S. Lewis, Energy Environ. Sci., 4, 1772 (2011).

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