Films Of Pt Research Articles

Low-Temperature Wastewater Electrolysis for H2 and Clean Water Generation

Water electrolysis represents a sustainable approach to produce green hydrogen (H2); however, the high energy cost (H2O → 2H+ + 2e- + ½O2, ∆H° = 275 kJ/mol H2, E° = −1.18 V) associated with water electrolysis and electricity cost (>$50/MWh) results in a minimum H2 selling price ≈$4/kg H2. Hence, we need to find alternative process to generate H2 to meet the current U.S. Department of Energy's (DOE's) Energy Earthshots of $1/kg H2 in one decade.Wastewater electrolysis represents an alternative approach to generate H2 with renewable sources by electrochemically oxidizing organic molecules to generate H2 (e.g., CH3COOH + 2H2O → 2CO2 + 8e- + 8H+, ∆H° = 53 kJ/mol, E° = −0.02 V,) which has up to 5 times lower energy requirement than water electrolysis. As opposed to water electrolysis that requires clean water streams, wastewater electrolysis uses readily available waste streams that need cleanup anyway to generate H2; hence, integrating a second application in addition to H2 generation.1-3 In this work, we compare the performance of heterogeneous electrocatalysts for the electrocatalytic oxidation (ECO) of organic molecules present in wastewater as well as electrocatalysts for the H2 evolution reaction (HER) at room temperature. ECO electrocatalysts were developed and tested using real wastewaters derived from several sources including the hydrothermal liquefaction (HTL) of food waste. We synthesized the ECO electrocatalysts using both platinum-group metals (PGM) as well as base-group metals (BGM) with equimolar loadings and tested them as a function of half-cell potential. Our results show that both PGM- and BGM-based bimetallics improve the activity and stability compared to the baseline RuO2-based catalysts4-6. We performed a preliminary techno-economic analysis and showed that the levelized costs of using this technology to process the wastewater alone is equivalent to that of traditional wastewater processing. The sale of the produced H2 co-product will decrease the levelized processing cost below that of current wastewater processing. References Andrews, E.; Lopez-Ruiz, J. A.; Egbert, J. D.; Koh, K.; Sanyal, U.; Song, M.; Li, D.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Gutiérrez, O. Y.; Holladay, J. D., Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds. ACS Sustainable Chemistry & Engineering 2020, 8 (11), 4407-4418.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. Journal of Applied Electrochemistry 2021, 51 (1), 107-118.Lopez-Ruiz, J. A.; Andrews, E.; Akhade, S. A.; Lee, M.-S.; Koh, K.; Sanyal, U.; Yuk, S. F.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Glezakou, V.-A.; Rousseau, R.; Gutiérrez, O. Y.; Holladay, J. D., Understanding the Role of Metal and Molecular Structure on the Electrocatalytic Hydrogenation of Oxygenated Organic Compounds. ACS Catalysis 2019, 9 (11), 9964-9972.Qiu, Y.; Lopez-Ruiz, J. A.; Zhu, G.; Engelhard, M. H.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic decarboxylation of carboxylic acids over RuO2 and Pt nanoparticles. Appl. Catal. B-Environ. 2022, 305, 121060.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2021, 51 (1), 107-118.Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277. Figure 1

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt-Pd Catalytic Films.

Films of titania-supported monometallic Pd, Pt, and bimetallic Pt-Pd catalysts made of metallic nanoparticles were prepared by magnetron sputtering and studied in the oxidative dehydrogenation (ODH) of cyclohexene. Pd/TiOx and Pt-Pd/TiOx were found active at as low temperature as 150 °C and showed high catalytic activity with high conversion (up to 81%) and benzene selectivity exceeding 97% above 200 °C. In turn, the Pt/TiOx catalyst performed poorly with the onset of benzene production at 200 °C only and conversions not exceeding 5%. The activity of bimetallic Pt-Pd catalysts far exceeded all of the other investigated catalysts at temperatures below 250 °C. However, the production of benzene significantly dropped with a further temperature increase due to the enhanced combustion of CO2 at the expense of benzene formation. As in situ NAP-XPS measurement of the Pt-Pd/TiOx catalyst in the reaction conditions of the ODH of cyclohexene revealed Pd surface enrichment during the first temperature ramp, we assume that Pd surface enrichment is responsible for enhanced activity at low temperatures in the bimetallic catalyst. At the same time, the Pt constituent contributes to stronger cyclohexene adsorption and oxygen activation at elevated temperatures, leading to changes in conversion and selectivity with a drop in benzene formation and increased combustion to CO2. Both the monometallic Pd and the Pt-Pd-based catalysts produced a small amount of the second valuable product, cyclohexadiene, and below 250 °C produced only a negligible amount of CO2 (<0.2%). To summarize, Pd- and Pt-Pd-based catalysts were found to be promising candidates for highly selective low-temperature dehydrogenation of cyclic hydrocarbons that showcased reproducibility and stability after the temperature activation. Importantly, these catalysts were fabricated by utilizing proven methods suitable for large-scale production on extended surfaces.

(2022-2023 ECS Toyota Young Investigator Fellowship) Enhanced Water Electrolysis Using Layered Coaxial Nanowire Electrodes

Novel electrocatalytic approaches are urgently needed to increase the energy efficiency and decrease the cost of hydrogen production by PEM water electrolyzers. Recently, we developed a novel catalytic platform, the layered coaxial nanowire electrode (LCANE), which enables PEM water electrolyzers with higher energy efficiency and reduced usage of precious metal catalysts. Electrolyzers based on the LCANE approach use a thin film of IrO2-decorated Pt that is intimately interfaced with an ionomer membrane in the form of vertically-aligned coaxial nanowires. Each nanowire consists of a Pt shell encapsulating an ionomer core, with the Pt shell further decorated by IrO2 clusters. The top region of each nanowire bends to form a layer of in-plane aligned Pt/IrO2 nanowires, providing excellent in-plane electronic conductivity. This unique catalyst/electrode geometry offers several key advantages. By localizing ionomer within the nanowire core, the exterior surface of the catalyst remains free from ionomer, eliminating thin-film transport barriers and preventing catalyst poisoning by ionomer adsorption. The vertically aligned sections of the nanowires provide non-tortuous transport of reactants and products, with abundant pore space for facile access of water and removal of oxygen. Close integration of catalyst and ionomer provides improved proton access and eliminates stranding of catalyst. By incorporating catalyst in the form of a thin film and replacing some of the Ir with Pt, lower Ir loading (as low as 0.1 mg/cm2) is achieved without sacrificing surface area or performance.AcknowledgmentThis work was supported by the ECS-Toyota Young Investigator Fellowship and by the Laboratory Directed Research and Development program at Los Alamos National Laboratory.

(Invited) Extended Thin Film Platinum Group Metal Electrocatalysts with Different Mesoscale Morphologies

The lack of sufficiently active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is a bottleneck to the proliferation of PEM fuel cells and water electrolyzers. Commercially available PGM electrocatalysts fail to attain DOE technical targets due to instabilities and activity losses incurred at low loadings. Morphology control of PGM nanostructures is an enticing route towards activity and stability enhancements of electrocatalysts, but not much is known about the structure-property relationships between PGM mesoscale geometry (5 to 100 nm) and their activity and stability.This talk presents our work on model Pt extended surface electrocatalysts of tunable feature sizes and morphologies prepared from self-assembled block copolymer templates. The morphology, either perpendicular lamellae, cylinders, or perforated cylinders, of the extended surface electrocatalyst was controlled by the block copolymer volume fraction. The periodic lateral feature sizes (10 to 40 nm in this work) were controlled by the block copolymer degree of polymerization. The self-assembled block copolymers were transformed into extended surfaces using sequential infiltration synthesis to prepare aluminum oxide followed by reactive ion etching to remove the block copolymer template. Pt was sputtered onto the aluminum oxide supports. ORR data in a RDE with the new extended nanostructured thin films of Pt showed mass activity values of 0.35 A mgPt-1 to 0.46 A mgPt -1 at 0.9 V vs. RHE. The measured electro-chemically active surface area (ECSA) values obtained from hydrogen underpotential deposition were 64 to 70 m2 gPt -1. The lower values hailed from lamellae morphology while the larger values corresponded to a cylindrical morphology. The measured mass activity values, which have no cobalt or nickel additives and are unoptimized and display competitive mass activity values for ORR. We envision that the block copolymer templated extended surfaces could be an alternative to 3M’s state-of-the-art nanostructured thin film technology.

Low-Temperature Wastewater Electrolysis for H2 and Clean Water Generation

Water electrolysis represents a sustainable approach to produce green hydrogen (H2); however, the high energy cost (H2O → 2H+ + 2e- + ½O2, ∆H° = 275 kJ/mol H2, E° = −1.18 V) associated with water electrolysis and electricity cost (>$50/MWh) results in a minimum H2 selling price ≈$5/kWh. Hence, we need to find alternative process to generate H2 to meet the current U.S. Department of Energy's (DOE's) Energy Earthshots of $1/kg H2 in one decade.Wastewater electrolysis represents an alternative approach to generate H2 with renewable sources by electrochemically oxidizing organic molecules to generate H2 (e.g., CH3COOH + 2H2O → 2CO2 + 8e- + 8H+, ∆H° = 53 kJ/mol, E° = −0.02 V,) which has up to 5 times lower energy requirement than water electrolysis. As opposed to water electrolysis that requires clean water streams, wastewater electrolysis uses readily available waste streams that need cleanup anyway to generate H2; hence, integrating a second application in addition to H2 generation.1-3 In this work, we compare the performance of heterogeneous electrocatalysts for the electrocatalytic oxidation (ECO) of organic molecules present in wastewater as well as electrocatalysts for the H2 evolution reaction (HER) at room temperature. ECO and HER electrocatalysts were developed and tested using real wastewaters derived from the hydrothermal liquefaction (HTL) of food waste. We synthesized the electrocatalysts using both platinum-group metals (PGM) as well as base-group metals (BGM) with equimolar loadings and tested them as a function of potential. Our results show that while PGM-based electrocatalysts were required to perform ECO of HTL-derived wastewater4-6, BGM-based electrocatalysts were able to perform HER similarly to PGM electrocatalysts in HTL-derived wastewater. We performed a preliminary techno-economic analysis to outline a path towards $1/kg H2 via wastewater electrolysis and identified the next research and development areas. References Andrews, E.; Lopez-Ruiz, J. A.; Egbert, J. D.; Koh, K.; Sanyal, U.; Song, M.; Li, D.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Gutiérrez, O. Y.; Holladay, J. D., Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds. ACS Sustainable Chem. Eng. 2020, 8 (11), 4407-4418.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2021, 51 (1), 107-118.Lopez-Ruiz, J. A.; Andrews, E.; Akhade, S. A.; Lee, M.-S.; Koh, K.; Sanyal, U.; Yuk, S. F.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Glezakou, V.-A.; Rousseau, R.; Gutiérrez, O. Y.; Holladay, J. D., Understanding the Role of Metal and Molecular Structure on the Electrocatalytic Hydrogenation of Oxygenated Organic Compounds. ACS Catalysis 2019, 9 (11), 9964-9972.Qiu, Y.; Lopez-Ruiz, J. A.; Zhu, G.; Engelhard, M. H.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic decarboxylation of carboxylic acids over RuO2 and Pt nanoparticles. Appl. Catal. B-Environ. 2022, 305, 121060.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2021, 51 (1), 107-118.Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277. Figure 1

Solid Platinum Nanoprobes for Highly Reliable Conductive Atomic Force Microscopy.

Conductive atomic force microscopy (CAFM) is a powerful technique to investigate electrical and mechanical properties of materials and devices at the nanoscale. However, its main challenge is the reliability of the probe tips and their interaction with the samples. The most common probe tips used in CAFM studies are made of Si coated with a thin (∼20 nm) film of Pt or Pt-rich alloys (such as Pt/Ir), but this can degrade fast due to high current densities (>102A/cm2) and mechanical frictions. Si tips coated with doped diamond and solid doped diamond tips are more durable, but they are significantly more expensive and their high stiffness often damages the surface of most samples. One growing alternative is to use solid Pt tips, which have an intermediate price and are expected to be more durable than metal-coated silicon tips. However, a thorough characterization of the performance of solid Pt probes for CAFM research has never been reported. In this article, we characterize the performance of solid Pt probes for nanoelectronics research by performing various types of experiments and compare them to Pt/Ir-coated Si probes. Our results indicate that solid Pt probes exhibit a lateral resolution that is very similar to that of Pt/Ir-coated Si probes but with the big advantage of a much longer lifetime. Moreover, the probe-to-probe deviation of the electrical data collected is small. The use of solid Pt probes can help researchers to enhance the reliability of their CAFM experiments.

Efficient Near-Infrared Luminescence of Self-Assembled Platinum(II) Complexes: From Fundamentals to Applications.

ConspectusDesigning bright and efficient near-infrared (NIR) emitters has drawn much attention due to numerous applications ranging from biological imaging, medical therapy, optical communication, and night-vision devices. However, polyatomic organic and organometallic molecules with energy gaps close to the deep red and NIR regime are subject to dominant nonradiative internal conversion (IC) processes, which drastically reduces the emission intensity and exciton diffusion length of organic materials and hence hampers the optoelectronic performances. To suppress nonradiative IC rates, we suggested two complementary approaches to solve the issues: exciton delocalization and molecular deuteration. First, exciton delocalization efficiently suppresses the molecular reorganization energy through partitioning to all aggregated molecules. According to the IC theory together with the effect of exciton delocalization, the simulated nonradiative rates with the energy gap ΔE = 104 cm-1 decrease by around 104 fold when the exciton delocalization length equals 5 (promoting vibronic frequency ωl = 1500 cm-1). Second, molecular deuterations reduce Franck-Condon vibrational overlaps and vibrational frequencies of promoting modes, which decreases IC rates by 1 order of magnitude in comparison to the rates of nondeuterated molecules under ΔE of 104 cm-1. Although deuteration of molecules has long been attempted to increase emission intensity, the results have been mixed. Here, we provide a robust derivation of the IC theory to demonstrate its validity, especially to emission in the NIR region.The concepts are experimentally verified by the strategic design and synthesis of a class of square-planar Pt(II) complexes, which form crystalline aggregates in vapor deposited thin films. The packing geometries are well characterized by the grazing angle X-ray diffraction (GIXD), showing domino-like packing arrangements with the short ππ separation of 3.4-3.7 Å. Upon photoexcitation, such closely packed assemblies exhibit intense NIR emission maximized in the 740-970 nm region through metal-metal-to-ligand charge transfer (MMLCT) transition with unprecedented photoluminescent quantum yield (PLQY) of 8-82%. To validate the existence of exciton delocalization, we applied time-resolved step-scan Fourier transform UV-vis spectroscopy to probe the exciton delocalization length of Pt(II) aggregates, which is 5-9 molecules (2.1-4.5 nm) assuming that excitons mainly delocalized along the direction of ππ stacking. According to the dependence of delocalization length vs simulated IC rates, we verify that the observed delocalization lengths contribute to the high NIR PLQY of the aggregated Pt(II) complexes. To probe the isotope effect, both partially and completely deuterated Pt(II) complexes were synthesized. For the case of the 970 nm Pt(II) emitter, the vapor deposited films of per-deuterated Pt(II) complexes exhibit the same emission peak as that of the nondeuterated one, whereas PLQY increases ∼50%. To put the fundamental studies into practice, organic light-emitting diodes (OLEDs) were fabricated with a variety of NIR Pt(II) complexes as the emitting layer, showing the outstanding external quantum efficiencies (EQEs) of 2-25% and the remarkable radiances 10-40 W sr-1 m-2 at 740-1002 nm. The prominent device performances not only successfully prove our designed concept but also reach a new milestone for highly efficient NIR OLED devices.This Account thus summarizes our approaches about how to boost the efficiency of the NIR emission of organic molecules from an in-depth fundamental basis, i.e., molecular design, photophysical characterization, and device fabrication. The concept of the exciton delocalization and molecular deuteration may also be applicable to a single molecular system to achieve efficient NIR radiance, which is worth further investigation in the future.

Nanoparticle Printing for Microfluidic Applications: Bipolar Electrochemistry and Localized Raman Sensing Spots

The local integration of metal nanoparticle films on 3D-structured polydimethylsiloxane (PDMS)-based microfluidic devices is of high importance for applications including electronics, electrochemistry, electrocatalysis, and localized Raman sensing. Conventional processes to locally deposit and pattern metal nanoparticles require multiple steps and shadow masks, or access to cleanroom facilities, and therefore, are relatively imprecise, or time and cost-ineffective. As an alternative, we present an aerosol-based direct-write method, in which patterns of nanoparticles generated via spark ablation are locally printed with sub-mm size and precision inside of microfluidic structures without the use of lithography or other masking methods. As proof of principle, films of Pt or Ag nanoparticles were printed in the chambers of a multiplexed microfluidic device and successfully used for two different applications: Screening electrochemical activity in a high-throughput fashion, and localized sensing of chemicals via surface-enhanced Raman spectroscopy (SERS). The versatility of the approach will enable the generation of functional microfluidic devices for applications that include sensing, high-throughput screening platforms, and microreactors using catalytically driven chemical conversions.

Polarization resistance of Pt/YSZ and ITO/YSZ interfaces in multilayered Pt|YSZ|Pt and ITO|YSZ|ITO thin films

Polarization resistances across Pt/YSZ and ITO/YSZ interfaces were probed on thin film structures with large surface area to volume ratio. High polarization resistance of Pt/YSZ interface responsible for the operating temperature of 873 K is suppressed in ITO/YSZ by atleast three orders of magnitude due to the partial solubility of an electronic conductor ITO in YSZ with the scope for reduction in temperatures to about 673 K. The conductivity of YSZ thin films measured in sandwiched configuration with Pt and ITO electrodes for the temperature interval of 673 – 973 K for multilayers configured as Pt|YSZ|Pt and ITO|YSZ|ITO were compared. Textured thin films of Pt, ITO and 8 mol% of Yttria stabilized zirconia (YSZ) exhibiting columnar growth were deposited on (100) SrTiO3.

A tandem photoelectrochemical cell based on Cu2-xTe nanocrystals for solar energy conversion to hydrogen

In this work we present the design, assembly and characterization of a tandem photoelectrochemical (PEC) cell based on two different crystallographic phases of sub-stoichiometric copper telluride nanocrystals (NCs). The first one, a pseudo-cubic phase, pc-Cu 2-x Te, is characterized by positive photocurrents, while the second one, a hexagonal phase, h-Cu 2-x Te, favors negative ones. Taking advantage of the different optoelectronic properties of the two Cu 2-x Te structures, we prepared a PEC cell composed of a hybrid pc-Cu 2-x Te/TiO 2 photoanode, with TiO 2 acting as a light absorber and electron selective layer, and a h-Cu 2-x Te/CuI photocathode, with CuI behaving as a photo-absorber and hole selective layer. The tandem PEC cell shows a photocurrent density of ∼0.5 mA/cm 2 when measured in a 2-electrode configuration without any co-catalyst. Finally, to test the PEC cell performance for the hydrogen evolution reaction (HER), a thin film of Pt was deposited on top of the photocathode and ∼7 μmol of hydrogen were obtained at 0.6 V in a 1-h experiment, reaching a photocurrent of 1 mA/cm 2 with no losses. • Investigating the optoelectronic properties of different Cu2-XTe crystallographic phases and using them as photoelectrodes for the first time. • Combining Cu2-XTe with TiO2 and CuI to build fully working hybrid photoelectrodes. • Building a functional Tandem PEC cell for hydrogen evolution reaction (HER).

Large imprint in epitaxial 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 thin films for piezoelectric energy harvesting applications

Tuning and stabilizing a large imprint in epitaxial relaxor ferroelectric thin films is one of the key factors for designing micro-electromechanical devices with an enhanced figure of merit (FOM). In this work, epitaxial 500 nm-thick 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN–33PT) films, free from secondary phases and with extremely low rocking curves (FWHM &amp;lt; 0.05°), are grown on ScSmO3 (SSO) and DyScO3 (DSO) substrates buffered with SrRuO3 (SRO). The PMN–33PT is observed to grow coherently on SSO substrates (lattice mismatch of −0.7%), which is c-axis oriented and exhibits large tetragonality compared to bulk PMN–33PT, while on DSO substrates (lattice mismatch of −1.9%), the PMN–33PT film is almost completely relaxed and shows reduced tetragonality. Due to the compressive epitaxial strain, the fully strained PMN–33PT film displays typical ferroelectric P–E hysteresis loops, while the relaxed sample shows relaxor-like P–E loops. Samples present large negative imprints of about −88.50 and −49.25 kV/cm for PMN–33PT/SRO/SSO and PMN–33PT/SRO/DSO, respectively, which is more than threefold higher than the coercive field. The imprint is induced by the alignment of defect dipoles with the polarization and is tuned by the epitaxial strain. It permits the stabilization of a robust positive polarization state (Pr ∼ 20 μC/cm2) and low dielectric permittivity (&amp;lt;700). In addition, the relaxed PMN–33PT film shows improved piezoelectric properties, with a 33% enhancement in d33,eff relative to the fully strained sample. The obtained low dielectric permittivity and the high piezoelectric coefficients at zero electric field in the studied PMN–33PT films hold great promise to maximize the FOM toward applications in piezoelectric devices.

Flexible Energy-Storage Ceramic Thick-Film Structures with High Flexural Fatigue Endurance

When developing flexible electronic devices, trade-offs between desired functional properties and sufficient mechanical flexibility must often be considered. The integration of functional ceramics on flexible materials is a major challenge. However, aerosol deposition (AD), a room-temperature deposition method, has gained a reputation for its ability to combine ceramics with polymers previously considered incompatible with the conventional high-temperature sintering process. In this work, 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN–10PT) thick films were deposited directly on a polyimide substrate using the AD method. As a result, dense and flexible relaxor-ferroelectric thick films were produced by a one-step direct-integration, suitable for large-scale production. After annealing of as-deposited PMN–10PT films at 400 °C, stress-relaxation occurs, which is responsible for the development of a relaxor-ferroelectric character. Achieved high polarization (38 μC·cm–2), high dielectric breakdown strength (∼1000 kV·cm–1), and low hysteresis losses lead to improved recoverable energy density and energy-storage efficiency of the annealed thick films, reaching 10 J·cm–3 and 73% (at 1000 kV·cm–1), respectively. The thick films were subjected to flexural bending tests, which showed high flexibility (1.1% bending strain) and high durability (105 bending cycles). This stable energy-storage operation makes ceramic-polymer layered structures promising for integration into a wide range of flexible electronic devices.

Excimer or aggregate? Near infrared electro- and photoluminescence from multimolecular excited states of N^C^N-coordinated platinum(ii) complexes

Long wavelength (&gt;800 nm) photoluminescence in films of Pt(N^C^N)Cl type complexes originates from aggregates of three to four units. Extremely thin neat emissive layers of 1–2 nm yield a high performance of near infrared OLEDs.

Optical and Electrochemical Effects of Gas Bubbles Generating Passive Convection in Solar Fuels Devices

Photoelectrochemical cells that convert water and/or carbon-dioxide to hydrogen and gaseous hydrocarbons generate bubbles at the surfaces responsible for light absorption and electrocatalysis. Reduced power conversion efficiencies are often ascribed to the presence of large bubbles, but it can be difficult to decouple the optical and electrochemical effects of gas evolution. We have evaluated the effects of gas evolution at macroscopic device areas with microscale features in relevant orientations with respect to the gravitational force vector. Microstructured Si surfaces decorated with thin films of Pt and TiO2/Ni were shown to reduce the departure diameter of H2 and O2 gas bubbles, respectively, relative to a planar surface. The gas coverage was strongly sensitive to the diameter and pitch of microwire arrays. Redox active tracer molecules were used to quantify mass-transfer coefficients in growing bubble films in 0.50 M H2SO4(aq) and 1.0 M KOH (aq). Ray-tracing simulations predicted that bubbles much smaller than the device area do not scatter sunlight away from the absorber surface and were supported direct measurements of the external quantum yield. The results indicate that microstructured electrodes operate acceptably for unassisted solar-driven water splitting regardless of orientation with respect to gravity and that bubbles provide a net benefit to upward-facing photoanodes.

Ab-initio and experimental investigations on Pt:MoS2 for electronic and optical applications

Electronic and optical studies were performed in this work through ab-initio and experimental investigation on MoS2 and Pt:MoS2 thin films. Simulations were performed using PBE-GGA in the Wien2k code. Thin films of MoS2 and Pt:MoS2 were grown with magnetron sputtering technique for experimental investigations. The surface morphology and elemental phase analysis depict the uniform and smooth growth of thin films with expected elemental contents. The simulations and experimental findings have linear correlation in electronic and optical parameters. We observed a sharp increase in absorption and decline in reflectivity of Pt:MoS2 thin films which enables them prominent candidate for photovoltaic applications.

Electrocatalytic Co-Processing of Biomass-Derived Aqueous Waste Streams and Bio-Oils for Renewable Fuel Production at Normal Temperature and Pressure

Electrocatalytic conversion is emerging as a potentially attractive low-cost approach to valorize biomass-derived streams. Conventional upgrading processes require moderate temperatures between 433 and 678 K, pressures of 14,000 kPa, and external sources of dihydrogen; however, the same upgrading reaction can be performed using electrochemical reactors and much lower temperatures and pressures (293 K and 101 kPa) and with no supplied hydrogen (H2).1-4 In this work, we evaluate the electrocatalytic conversion of aqueous waste and bio-oils generated during biomass liquefaction via hydrothermal liquefaction (HTL) and pyrolysis. Our work shows that the main biomass-derived compounds (carboxylic acids, alcohols, ketones, etc.) were successfully converted via electrocatalytic oxidation (ECO) into olefins, paraffins, and alcohols.2, 5 Alternatively, the same compounds could not be upgraded via electrocatalytic hydrogenation (ECH) over a variety of noble and base metals, instead H2 evolution was the preferred reaction.1, 3 Figure 1 shows that the operation (electricity) cost can be offset by the sale of the excess H2 generated (valued at >$2/kgH2) specially when operating at low full cell potentials (<4.5 V) and using low electricity cost (<¢4/kwh).2 Additionally, a preliminary techno-economic analysis shows the capital cost associated with the integrated electrocatalytic process for the aqueous waste treatment and H2 generation can be up to 80% lower than the combined cost for traditional thermal (e.g., gasification) and biological (e.g., anaerobic digestion) wastewater treatment, and H2 generation (via natural gas steam reforming), and can lower the minimum fuel selling price (MFSP) by up to $0.84/GGE. References Andrews, E.; Lopez-Ruiz, J. A.; Egbert, J.; Koh, K.; Sanyal, U.; Miao, S.; Li, D.; Karkamkar, A.; Derewinski, M. A.; Holladay, J.; Gutiérrez, O. Y.; Holladay, J. D., Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds. ACS Sustainable Chem. Eng. 2020, 8 (11), 4407-4418.Lopez-Ruiz, J. A.; Qiu, Y.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Electrocatalytic valorization into H2 and hydrocarbons of an aqueous stream derived from hydrothermal liquefaction. J. Appl. Electrochem. 2020, Accepted.Lopez-Ruiz, J. A.; Andrews, E. A.; Akhade, S. A.; Lee, M.; Koh, K.; Sanyal, U.; Yuk, S. F.; Karkamkar, A. J.; Derewinski, M. A.; Holladay, J.; Glezakou, V. A.; Rousseau, R.; Gutiérrez, O. Y.; Holladay, J. D., Understanding the role of metal and molecular structure on the electrocatalytic hydrogenation of oxygenated organic compounds. ACS Catal. 2019, 9 (11), 9964-9972.Lopez-Ruiz, J. A.; Sanyal, U.; Egbert, J.; Gutiérrez, O. Y.; Holladay, J., Kinetic Investigation of the Sustainable Electrocatalytic Hydrogenation of Benzaldehyde on Pd/C: Effect of Electrolyte Composition and Half-Cell Potentials. ACS Sustainable Chem. Eng. 2018, 6 (12), 16073-16085.Qiu, Y.; Lopez-Ruiz, J. A.; Sanyal, U.; Andrews, E.; Gutiérrez, O. Y.; Holladay, J. D., Anodic electrocatalytic conversion of carboxylic acids on thin films of RuO2, IrO2, and Pt. Appl. Catal. B-Environ. 2020, 277, 119277.Snowden-Swan, L. J.; Hallen, R. T.; Zhu, Y.; Hart, T. R.; Bearden, M. D.; Liu, J.; Seiple, T. E.; Albrecht, K. O.; Jones, S. B.; Fox, S. P.; Schmidt, A. J.; Maupin, G. D.; Billing, J. M.; Elliott, D. C. Conceptual Biorefinery Design and Research Targeted for 2022: Hydrothermal Liquefaction Processing of Wet Waste to Fuels; PNNL-27186. BM0108010; Pacific Northwest National Lab. (PNNL), Richland, WA (United States): 2017. Figure 1

Fully resolved currents from quantum transport calculations

We extract local current distributions from interatomic currents calculated using a fully relativistic quantum mechanical scattering formalism by interpolation onto a three-dimensional grid. The method is illustrated with calculations for Pt$|$Ir and Pt$|$Au multilayers as well as for thin films of Pt and Au that include temperature-dependent lattice disorder. The current flow is studied in the "classical" and "Knudsen" limits determined by the sample thickness relative to the mean free path $\lambda$, introducing current streamlines to visualize the results. For periodic multilayers, our results in the classical limit reveal that transport inside a metal can be described using a single value of resistivity $\rho$ combined with a linear variation of $\rho$ at the interface while the Knudsen limit indicates a strong spatial dependence of $\rho$ inside a metal and an anomalous dip of the current density at the interface which is accentuated in a region where transient shunting persists.

Growth mode and strain effect on relaxor ferroelectric domains in epitaxial 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3/SrRuO3 heterostructures.

Controlling the growth of complex relaxor ferroelectric thin films and understanding the relationship between biaxial strain–structural domain characteristics are desirable for designing materials with a high electromechanical response. For this purpose, epitaxial thin films free of extended defects and secondary phases are urgently needed. Here, we used optimized growth parameters and target compositions to obtain epitaxial (40–45 nm) 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3/(20 nm) SrRuO3 (PMN–33PT/SRO) heterostructures using pulsed-laser deposition (PLD) on singly terminated SrTiO3 (STO) and ReScO3 (RSO) substrates with Re = Dy, Tb, Gd, Sm, and Nd. In situ reflection high-energy electron diffraction (RHEED) and high-resolution X-ray diffraction (HR-XRD) analysis confirmed high-quality and single-phase thin films with smooth 2D surfaces. High-resolution scanning transmission electron microscopy (HR-STEM) revealed sharp interfaces and homogeneous strain further confirming the epitaxial cube-on-cube growth mode of the PMN–33PT/SRO heterostructures. The combined XRD reciprocal space maps (RSMs) and piezoresponse force microscopy (PFM) analysis revealed that the domain structure of the PMN–33PT heterostructures is sensitive to the applied compressive strain. From the RSM patterns, an evolution from a butterfly-shaped diffraction pattern for mildly strained PMN–33PT layers, which is evidence of stabilization of relaxor domains, to disc-shaped diffraction patterns for high compressive strains with a highly distorted tetragonal structure, is observed. The PFM amplitude and phase of the PMN–33PT thin films confirmed the relaxor-like for a strain state below ∼1.13%, while for higher compressive strain (∼1.9%) the irregularly shaped and poled ferroelectric domains were observed. Interestingly, the PFM phase hysteresis loops of the PMN–33PT heterostructures grown on the SSO substrates (strain state of ∼0.8%) exhibited an enhanced coercive field which is about two times larger than that of the thin films grown on GSO and NSO substrates. The obtained results show that epitaxial strain engineering could serve as an effective approach for tailoring and enhancing the functional properties in relaxor ferroelectrics.

Preparation of different thin film catalysts by direct current magnetron sputtering for hydrogen generation.

In this study, thin films of Co, Ni, Pd, and Pt were prepared on Co 3 O 4 support material in pellet form using the direct current (DC) magnetron sputtering method for use as catalysts for hydrogen generation from NaBH 4 .Characterization of the catalysts was carried out using X-ray diffraction (XRD), scanning electronic microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). According to cross-sectional SEM images, catalyst thicknesses were observed in the range of approximately 115.3–495.8 nm. The particle sizes were approximately 25.0, 21.4, 33.9, and 9.5 nm for Ni-Co 3 O 4 , Co-Co 3 O 4 , Pd-Co 3 O 4 , and Pt-Co 3 O 4 catalysts, respectively. The increase in NaOH initial concentration provides an increase in the rate of hydrogen generation for Co, Ni, and Pd catalysts. A maximum hydrogen generation rate of 1653 mL/g cat .min was obtained for the Pt-Co 3 O 4 catalyst.

Electrochemical Evaluation of a Multi-Site Clinical Depth Recording Electrode for Monitoring Cerebral Tissue Oxygen.

The intracranial measurement of local cerebral tissue oxygen levels—PbtO2—has become a useful tool for the critical care unit to investigate severe trauma and ischemia injury in patients. Our preliminary work in animal models supports the hypothesis that multi-site depth electrode recording of PbtO2 may give surgeons and critical care providers needed information about brain viability and the capacity for better recovery. Here, we present a surface morphology characterization and an electrochemical evaluation of the analytical properties toward oxygen detection of an FDA-approved, commercially available, clinical grade depth recording electrode comprising 12 Pt recording contacts. We found that the surface of the recording sites is composed of a thin film of smooth Pt and that the electrochemical behavior evaluated by cyclic voltammetry in acidic and neutral electrolyte is typical of polycrystalline Pt surface. The smoothness of the Pt surface was further corroborated by determination of the electrochemical active surface, confirming a roughness factor of 0.9. At an optimal working potential of −0.6 V vs. Ag/AgCl, the sensor displayed suitable values of sensitivity and limit of detection for in vivo PbtO2 measurements. Based on the reported catalytical properties of Pt toward the electroreduction reaction of O2, we propose that these probes could be repurposed for multisite monitoring of PbtO2 in vivo in the human brain.