bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Heterogenized Molecular Catalyst Materials for Electrochemical Carbon Dioxide Conversion
Authors: Wang Hailiang
Published: May 2020

Sustainable energy utilization and carbon emission reduction are critical challenges for the world. Solving these challenges requires precise control of many important chemical reactions with sluggish kinetics and myriad possible reaction pathways and associated products. There is a critical need for selective, active, durable and low-cost catalysts. This talk presents our research efforts aimed at bridging the gap between homogenous catalysis and heterogeneous catalysis to realize materials with new or improved electrocatalytic properties for the carbon dioxide reduction reactions. We have developed heterogenized metal-complex electrocatalysts allowing for mechanism-based optimization at the molecular level. We have discovered interesting phenomena including ligand-mediated electron transfer, beyond two-electron reduction via a domino process, and reversible restructuring under reaction conditions. We have also designed reactors to enhance electrochemical performance, study surface/interface phenomena, and perform thermodynamically challenging reactions.
Size-Controlled Synthesis of L10-CoPt Intermetallic Fuel Cell Catalysts on Nitrogen-Doped Mesoporous Graphitized Carbon Support
Authors: Wang Chenyu , Qiao Zhi , Kumar Vijay Bhooshan , Cullen David A. , Li Dongguo , More Karren L. , Wu Gang , Kim Yu Seung , Spendelow Jacob S
Published: May 2020

Ordered intermetallic nanoparticles are promising electrocatalysts with enhanced activity and durability for the oxygen-reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). However, after subjecting to a widely used postsynthesis annealing treatment, the particle size of intermetallic catalysts inevitably increases, leading to a poor performance in practical fuel cell application. In this work, ordered L10-CoPt intermetallic catalyst of small particle size was prepared through using nitrogen-doped mesoporous graphitized carbon (NMGC) support. The porous feature and nitrogen doping of NMGC support immobilized CoPt particles and prevented sintering during annealing treatment. These small and ordered L10-CoPt nanoparticles exhibit outstanding ORR activity (~ 1.18 A/mgPt) and superior high current density in fuel cell testing. Moreover, this L10-CoPt/NMGC catalyst performs remarkably enhanced stability in comparison with L10-CoPt/high surface area carbon (HSC) counterpart and commercial Pt/C catalyst, surpassing the DOE 2020 target. The enhancement in catalyst durability can be attributed to strong particles-support interaction via nitrogen heteroatoms and the strengthened p bonding. To better understand the support effect on particle growth, L10-CoPt particles on NMGC with different porosity/graphitization were prepared and their fuel cell performances were systematically studied. This study demonstrates an effective strategy to control the particle size of intermetallic catalysts with using NMGC support, which achieves excellent practical fuel cell performance.
Microfluidic Zinc-Air Cell
Authors: Ortiz-Ortega Euth , Díaz-Patiño Lucia , Béjar José Eduardo García , Trejo Gabriel , Guerra-Balcázar Minerva , Álvarez-Contreras Lorena , Arriaga Luis G. , Arjona Noé
Published: May 2020

In this work, a microfluidic Zin-Air cell operated with a flow-through concept was constructed electrodepositing zinc on carbon paper electrodes by chronoamperometry. Additionally, chemically obtained α-MnO2 and Mn3O4 spinel were used as cathodes, and the cell performance was also compared with benchmarked Pt/C. Zinc electrodeposition time, flow rate, KOH electrolyte concentration and cathodic material were the variables herein evaluated. Zinc at 60 min was the best anodic material, and the maximum cell performance (~450 mW cm-2) was achieved at 4 M KOH and 3 mL h-1. α-MnO2 and Mn3O4 spinel presented half-wave overpotentials of 92 and 127 mV in contrast with benchmarked Pt/C, and during cell evaluation, these materials displayed power densities of 308 and 317 mW cm-2, respectively.
Surface Treatment of Titanium for Fuel Cell Bipolar Plates
Authors: Sato Haruka , Imamura Junko , Nose Koichi
Published: May 2020

PEFC (polymer electrolyte fuel cell) metallic bipolar plates have attracted much attention because of their thermal and electrical conductivity, gas impermeability, mechanical strength, and ease of manufacturing compared to high-density graphite. Titanium also exhibits these properties but the electrical conductivity is decreased in fuel cell environment due to the growth of surface passive film.

Generally, metal bipolar plate surface is coated by a noble metal, carbon or another material. However, these are high cost due to using expensive materials or process. This study introduces a low cost production method of a high performance titanium bipolar plate. The method consists of pickling and heat treatment and enables to produce bipolar plate with a specific thin film on the surface.

The film formed on the titanium sheet was investigated by transmission electron microscope. The electrical conductivity was measured by contact resistance with carbon paper after endurance test in simulated fuel cell environment.

These results indicate that the material produced by our method exhibits both high conductivity and corrosion resistant. It is expected to be utilized as a bipolar plate for PEFC.
Investigation on Electrochemical Properties of Low-Temperature Ionic Liquid-Based Electrolytes for MET Sensor
Authors: Lin Wendy Jessica , Xu Yifei , MacDonald Shaun , Dai Lenore L.
Published: May 2020

The molecular electronic transducer (MET) sensor that operates based on an electrochemical principle provides an alternative approach for motion sensing applications and seismic investigations. As the liquid state proof mass responds to detected seismic waves, the electroactive species, iodide and triiodide, are brought to the electrodes by the induced fluid motions. At the cathode, the triiodide reduction currents are generated correspondingly and serve as a record of the detected ground activities. Compared to the conventional motion sensor and seismometer with solid state mass-spring system, by utilizing a liquid state electrolyte as the proof mass, the MET sensor presents advantages such as installation angle independence, superior shock tolerance, low mass, and low power consumption. The abovementioned characteristics have made MET sensor an appealing candidate for seismic investigations in space explorations, especially on planetary objects with deployment challenges.

For potential seismic studies on icy ocean worlds, such as Europa, Titanic, and Enceladus where the extremely low temperatures can be challenging for liquid state electrolytes, our group has developed several ionic liquid-based electrolyte systems with broad liquidus range down to -120 ˚C. While enhancements in thermal and transport properties of the electrolyte systems via optimization of intermolecular interactions were validated, we have yet to fully explore their electrochemical properties at low temperatures that are critical for the MET sensor functionality. In this work, we present investigations on electrochemical properties of the developed electrolyte systems over a broad temperature range. Using electrochemical impedance spectroscopy, we observed effects of tailored intermolecular interactions between ionic liquid and incorporated molecular solvents on conductivity evolution from room temperature to -75 ˚C. Specifically, the resulting bulk conductivity of the overall system was governed by an interplay between ion mobility and ion disassociation, and its temperature dependence can be depicted by the Vogel-Fulcher-Tammann model. Furthermore, we also investigated kinetics of the targeted iodide/triiodide redox reactions via cyclic voltammetry for the MET sensing technology. The electrochemical reversibility of triiodide reduction for signal generation was correlated to the employed molecular solvents and their interactions with the electroactive species. Lastly, the electrochemical windows were also identified for respective electrolyte systems at various temperatures as references for future MET sensor operations. Discoveries of the presented work disclose effects of intermolecular interactions on electrochemical properties and contribute to applications of the MET sensing technology at room temperature and low temperatures.
A Raman Spectroscopic Study of Radiation-Grafted Anion-Exchange Membranes Containing Different Anions
Authors: Bance-Soualhi Rachida , Crean Carol , Herman Henryk , Islania Saima , Lai Cheuk Ying , Tencheva Mariya , Varcoe John R. , Whelligan Daniel
Published: May 2020

Anion exchange membranes (AEM) are being developed for use in a variety of electrochemical energy systems, such as alkaline membrane fuel cells, AEM-based electrolysers, reverse electrodialysis (RED), and redox flow batteries (RFB). The AEMs used will contain a variety of anions, depending on the application. For fuel cells and electrolysers (H2 generating or CO2 conversion), then alkaline anions such as OH-, CO3
2-, and HCO3
- are important. For RED cells and RFBs, non-alkali anions such as Cl-, HSO4
-, and SO4
2- are more relevant. If an AEM is synthesised using a methyl iodide reaction, then monitoring the ion-exchange of the resulting "as-synthesised" I- forms to other forms, such as Cl-, is important as it is well known that it can be difficult to completely ion-exchange soft anions such as I- out of AEMs (particularly those containing aromatic cationic groups).

This presentation will highlight some initial results obtained from an on-going Raman spectroscopic study of radiation-grafted AEMs (RG-AEM). This study was initiated to see if Raman spectro-microscopy can be used to identify the anion form of a RG-AEM by looking at the shifts and intensity changes of Raman peaks as a function of anion. The RG-AEMs will be made from either the grafting of vinylbenzyl chloride onto ETFE (followed by reaction with amines such as trimethylamine, imidazole and pyridine) or the grafting of alternative monomers such as vinylpyridine onto ETFE (followed by reaction with methyl iodide).

The below Figure shows Raman spectra (Renishaw inVia Raman microscope: 785 nm laser, 1800 lines mm-1 grating, and x20 objective giving a Airy spot diameter of ca. 3 μm) of a RG-AEM made from the grafting of vinylpyridine onto ETFE films (with a final methyl iodide reaction) in both the I- and Cl- forms (three spectra each):

.

Figure 1
Depth-Profiling Buried Interfaces within Polymer Electrolyte Membranes
Authors: Korzeniewski Carol , Bukola Saheed , Creager Stephen E , Harris Joel M.
Published: May 2020

Confocal Raman microscopy is being adapted to probe interfaces within bipolar membranes and ionomer-graphene composites of interest for use in fuel cell and related electrochemical devices [1-2]. Although versatile and adaptable to in-situ measurements, confocal Raman microscopy depth-profiling has pitfalls when applied to bulk membranes. Optical aberration and sensitivity to light scattering from sample regions outside the probe beam focus limit depth resolution. With these constraints in mind, initial studies focused on detecting single layer graphene (SLG) as a barrier between two Nafion membranes (Nafion 211, 25 µm thickness). These graphene-sandwich membranes have shown high selectivity for proton transport across electrochemical cells [2]. Using a microscope equipped with oil-immersion optics to provide refractive index matching, the graphene layer was easily detected in confocal Raman microscopy depth-profiles. Spectra were sensitive to defects and stress within the buried graphene layer. Building on the ability to probe membrane-supported SLG, SLG adsorbed to a glass microscope coverslip (SLG/SiO2) was adapted as a platform for confocal aperture alignment and probe volume characterization [1]. Using SLG/SiO2to estimate the limiting axial spatial resolution, the junction separating the AEM/CEM (anion exchange membrane / cation exchange membrane) phases of bipolar polymer membrane (Fumasep FBM) was probed and shown to be consistent with roughness at the boundary on the order of a few micrometers (~3 µm). Continuing efforts are aimed at developing 2-dimensional (x-, y-direction) Raman spatial maps of buried polymer membrane interfaces and model AEM/CEM interfaces for high spatial resolution (< 10 nm) neutron reflectometry depth profiling.

1. Korzeniewski, C.; Kitt, J.P.; Bukola, S.; Creager, S.E.; Minteer, S.D.; Harris, J.M. ”Single layer graphene for estimation of axial spatial resolution in confocal Raman microscopy depth profiling” Anal. Chem.2019, 91, 1049 (DOI:10.1021/acs.analchem.8b04390).

2. Bukola, S.; Liang, Y.; Korzeniewski, C.; Harris, J.M.; Creager, S.E. “Selective proton / deuteron transport through Nafion | graphene | Nafion sandwich structures at very high current density” J. Am. Chem. Soc. 2018, 140, 1743. (DOI: 10.1021/jacs.7b10853)
Investigation of Glucose Oxidation on Gold Nanocrystallites Modified Cobalt and Cobalt-Boron Coatings
Authors: Šimkūnaitė Dijana , Upskuvienė Daina , Sukackienė Zita , Balčiūnaitė Aldona , Kepenienė Virginija , Šimkūnaitė-Stanynienė Birutė , Tamašauskaitė-Tamašiūnaitė Loreta , Norkus Eugenijus
Published: May 2020

Herein, the electrochemical oxidation of glucose has been investigated on the Co and CoB alloy coatings, which were deposited on the copper substrate (Cu) and subsequently modified with a small amount of Au nanocrystallites (termed as the AuCo/Cu and AuCoB/Cu catalysts), with the aim to use them as the anode catalysts for direct glucose fuel cells (DGFCs). The catalysts have been prepared via a simple electroless Co deposition method followed by a spontaneous Au galvanic displacement from the Au(III)-containing solution. The activity of the prepared catalysts for the oxidation of glucose in an alkaline medium has been examined by cyclic voltammetry and chrono-techniques.

In conclusion, the Co and CoB alloy coatings, which were modified with a small amount of Au nanocrystallites in the range from 11 to 14 µg Au cm–2, exhibit a significantly higher activity for the oxidation of glucose as compared to that of bare Au, Co and CoB alloy catalysts. Furthermore, the process of glucose oxidation has been significantly shifted to more negative potential domain at the both AuCo/Cu and AuCoB/Cu catalysts, indicating the higher activity of the latter catalysts as compared to that of the unmodified Co/Cu and CoB/Cu catalysts and the bare Au electrode. In addition, approximately 22 and even 67 times higher glucose oxidation current density values have been obtained at the AuCo/Cu and AuCoB/Cu catalysts, respectively, as compared to those for the unmodified CoB/Cu and Co/Cu. The prepared AuCo/Cu and AuCoB/Cu catalysts, which have been prepared with very small amount of Au nanocrystallites, seem to be a promising anode material for DGFCs.
Fuel Cell Durability Study of PGM-Free ORR Catalysts
Authors: Chung Hoon T , Zhang Hanguang , Park Jaehyung , Cullen David A. , More Karren L. , Myers Deborah J. , Alp Esen E. , Zelenay Piotr
Published: May 2020

The focus of LANL’s platinum group metal (PGM)-free catalyst program has been on the improvement and implementation of high-performing and durable cathode catalysts for polymer electrolyte fuel cells (PEFCs). Over the last decade, fuel cell performance of PGM-free catalysts gauged by the current density at 0.9 V
iR-free
in H2-O2 at 1.0 bar has been increased as much as three times (from 12 to 36 mA/cm2). While in durability aspect not much of progress as well as understanding has been achieved.

Fuel cell durability of the catalysts is critical in particular for practical application of the catalysts. Recently ElectroCAT, US DOE supported PGM-free catalyst consortium, proposed the durability test protocol (draft) for PGM-free catalysts. In this presentation, we will report catalyst durability tested following the ElectroCAT-proposed protocol for several catalysts. In conjunction with characterization tools such as cyclic voltammetry, impedance measurement, STEM, x-ray absorption spectroscopy (XAS), and Mössbauer spectroscopy, we will discuss the possible degradation mechanisms as well as pathways to improve the durability of PGM-free catalysts.

Acknowledgements

This research has been supported by DOE Fuel Cell Technologies Office through Electrocatalysis Consortium (ElectroCat). Microscopy was performed as part of a user project supported by Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, a DOE Office of Science User Facility.
Peptide-Controlled Assembly of Anion Exchange Ionomer Thin Films on Electrode Surfaces for Promoting Microphase Separation and Ionic Conductivity
Authors: Su Zihang , Kole Subarna , Arges Christopher George , Renner Julie N.
Published: May 2020

In electrochemical devices such as water electrolyzers and fuel cells, the network and morphology of the conductive ionomers within electrodes are critical for ion delivery and mass transport, significantly influencing the device performance. Most studies investigate these materials as bulk polymer electrolyte membranes and comparatively little attention has been given to their behavior on electrode surfaces as thin films. Anion exchange membrane fuel cells and water electrolyzers (AEMFCs and AEMWEs) would allow the use of non-precious group metals and enable low-cost systems, yet, even less is known about thin films of anion exchange ionomer (AEI). Protein engineering is emerging as a powerful nanomanufacturing tool to control the organization of components on electrodes. In this work, we propose that it can be applied to ionomer control, demonstrating that sequence defined elastin-like peptides assembled on electrode surfaces, and/or solvent vapor annealing processing, alters the microstructure configuration of assembled thin films of anion exchange ionomer. It is observed that peptides form a uniform monolayer on the metal surface, and moderately sized microphase separated ionic domains of the AEI are obtained either by modifying the electrode with peptides or solvent vapor annealing, which correlate with an increased in-plane ionic conductivity of the thin film. Interestingly, the use of peptide-modified electrodes in conjunction with solvent vapor annealing yields excessively large ionic grains that correlates with compromised ionic conductivity. Overall, we show that sequence defined peptides could serve as a tool for controlling electrode architecture, and judicious use of peptides, or solvent vapor annealing, have the potential to control the microstructure of thin AEI films and lead to structure-function understanding.
Performance of Sulfonated Phenylated Polyphenylene Membrane As a Polymer Electrolyte Membrane for Water Electrolysis
Authors: Mutambanengwe Rutendo Leah , Peppley Brant A
Published: May 2020

Traditionally perfluorosulfonic acid (PFSA) membranes such as Nafion are used as membranes for polymer electrolyte membrane water electrolysis (PEMWE) due to their excellent chemical stability, good mechanical strength and high ionic conductivity [1], and low hydrogen permeation. The issue of hydrogen crossover, especially at low current densities or high operating pressures is still of concern since it represents product loss and reduced efficiency. Sulfonated phenylated polyphenylene (sPPP) membranes have been found to be promising electrolyte membranes for electrochemical applications. These sPPPs display significantly less gas crossover compared to Nafion. In addition, they also have high proton conductivity, and are resilient to free radical attack [2]. These properties make them particularly attractive for use in water electrolysis. Tantalum carbide supported iridium based catalysts (IrOx/TaC) have been shown to be potential candidates for use as oxygen evolution reaction (OER) catalysts for water electrolysis [3]. In this study, the use of IrOx/TaC catalyst used in conjunction with sulfonated phenylated polyphenylene membranes as alternative materials for PEMWE to achieve improved performance (utilization and reduced gas crossover) and reduce material costs was investigated. The IrOx/TaC was synthesized in-house using a surfactant mediated method. At low loading, the IrOx/TaC has shown performance comparable to state-of-the-art catalysts. Electrolyser membrane electrode assemblies (MEA)s were fabricated using sPPP membranes, IrOx/TaC (anode) and carbon supported platinum (Pt/C) catalyst (cathode). The electrochemical performance of the MEAs was tested in a single cell electrolyser equipped with an in-situ reference electrode. Current-voltage (I-V) curves were obtained potentiostatically at 80 °C. The I-V performance curves obtained were compared with Nafion based MEAs fabricated using the same IrOx/TaC catalyst. The conductivity of the MEAs was also determined. Scanning electron microscopy (SEM) was used to analyze the morphology and elemental distribution of the electrode surfaces and the cross-section of the MEAs.

References

[1] A. Nikiforov, E. Christensen, I. Petrushina, J. Oluf, and N. J., “Advanced Construction Materials for High Temperature Steam PEM Electrolysers,” in Electrolysis, InTech, 2012, pp. 61–86.

[2] M. Adamski, T. J. G. Skalski, B. Britton, T. J. Peckham, L. Metzler, and S. Holdcroft, “Highly Stable, Low Gas Crossover, Proton-Conducting Phenylated Polyphenylenes,” Angew. Chemie Int. Ed., vol. 56, no. 31, pp. 9058–9061, Jul. 2017.

[3] F. Karimi and B. A. Peppley, “Metal Carbide and Oxide Supports for Iridium-Based Oxygen Evolution Reaction Electrocatalysts for Polymer-Electrolyte-Membrane Water Electrolysis,” Electrochim. Acta, vol. 246, pp. 654–670, Aug. 2017.
Improving Stability and Kinetics of Alkaline HOR Catalysts – Towards Reduced System Cost
Authors: Speck Florian Dominik , Paul Michael T. Y. , Ali S. M. Farhan , Singh Ramesh-Kumar , Böhm Thomas , Kasian Olga , Dekel Dario R. , Kallio Tanja , Cherevko Serhiy
Published: May 2020

Anion exchange membrane fuel cells (AEMFCs) show great promise in overcoming high cost of currently state of the art proton exchange membrane fuel cells, that rely on expensive Pt catalysts for both the hydrogen oxidation reaction (HOR) as well as the oxygen reduction reaction (ORR). With recent advancements in demonstrating high ORR activity and stability of Fe-N-C catalysts in alkaline environments,1 the HOR suddenly became the bottleneck reaction towards high power density platinum group metal (PGM) -low or -free AEMFCs. While application of PGM-free ORR catalysts is an eventual goal, current state of the art NiM nanoparticles show relatively poor performance in terms of both activity and irreversible oxidation and dissolution.2 Hence, at least for some time, one will need to rely on PGM catalysts for alkaline HOR, where the biggest challenge will be lowering the loading and meanwhile increasing the stability in an alkaline environment. To this end, fundamental understanding of surface processes is required.

In this work we investigate model CeOx covered Pt and Pd electrocatalysts as benchmark materials for the HOR reaction3
,
4. To prepare such model electrodes, we use physical vapor deposition for the formation of PGM and atomic layer deposition subsequently, to yield CeOx surface layers of variable thickness. Activity and stability of the CeOx@Pt and CeOx@Pd electrodes are studied in common rotating disk electrode and on-line inductively coupled plasma mass spectrometry setups, respectively. External analytics, e.g. X-ray photoelectron spectroscopy, are used to further characterize the electrodes before and after degradation studies. We show that stability of the electrodes at the higher anodic potentials can be greatly improved by tuning the thickness of the CeOx layer. Interestingly, this can be achieved without sacrificing and even with a significant enhancement in the HOR activity. This unique performance is explained by assuming that the deposited CeOx films form an ion selective semipermeable passivation layer on the surface of Pd and Pt. We anticipate that, as a next logical step, such layers can be used to stabilize PGM-free Ni alloys and reach the goal of having completely PGM-free AEMFCs.

References

1. P. G. Santori, F. D. Speck, J. Li, A. Zitolo, Q. Y. Jia, S. Mukerjee, S. Cherevko and F. Jaouen, J. Electrochem. Soc., 166, F3311 (2019).

2. E. S. Davydova, F. D. Speck, M. T. Y. Paul, D. R. Dekel and S. Cherevko, ACS Catalysis, 6837 (2019).

3. N. M. Markovića, S. T. Sarraf, H. A. Gasteiger and P. N. Ross, J. Chem. Soc., Faraday Trans., 92, 3719 (1996).

4. H. A. Miller, F. Vizza, M. Marelli, A. Zadick, L. Dubau, M. Chatenet, S. Geiger, S. Cherevko, H. Doan, R. K. Pavlicek, S. Mukerjee and D. R. Dekel, Nano Energy, 33, 293 (2017).
Site-Specific Activity of Pt Single Crystal Surfaces for Oxygen Reduction Reaction
Authors: Liu Guangdong , Zeng Zhenhua , Deng Huiqiu , Steinbach Andrew J. , Greeley Jeffrey
Published: May 2020

Development of industrial electrocatalysts with improved performance strongly relies on the fundamental understanding of the model systems. Pt(111) surface is probably the simplest, the most fundamental and thus also the most classic model systems for studying the hydrogen and oxygen electrocatalysis, among others. While the wide terrace has long been taken for granted to be the playground of the electrocatalytic reactions, here we demonstrate that such a hypothesis is far incomplete. By combining DFT calculations with experimental measurements, we unravel a 1-2 nm zone with 50% to 5000% activity enhancement for oxygen reduction reaction, which are induced by intrinsic strain that is generated because of the release of surface stress. We further demonstrate how this mechanistic understanding can be utilized to improve the activity of both model electrocatalysts and industrial electrocatalysts.

References

1. Wang, Z. Zeng, W. Gao, T. Maxson, D. Raciti, M. Giroux, X. Pan, C. Wang, J. Greeley,. Science
363, 870-874 (2019).

2. Zeng, J. Greeley, Nano Energy 29 (2016) 369.
Optimization of Platinum Catalyst Electrode with Different Supporting Electrolytes By a Pulse Electrodeposition Technique
Authors: Wu Wei-Sheng , Yeh Tsung-Kuang , Wang Mei-Ya
Published: May 2020

Due to the low operation temperature and quick start-up, proton exchange membrane fuel cells (PEMFCs) have been investigated nowadays. To improve the power density and short lifetime, much attention has been focused on the catalyst fabrication technique to attain high catalytic activity. Electrodeposition is widely applied using different electrochemical techniques.

With a three-electrode electrochemical cell, Pt catalysts were directly electrodeposited onto the gas diffusion layer. The electrodeposition electrolyte was the hexachloroplatinic acid (H2PtCl6), supporting electrolyte (e.g. Boric acid, perchloric acid or sulfuric acid, etc.) and dispersant (e.g. Ethylene Glycol). The fabrication process of electrodeposited Pt catalyst was conducted under at a specific reduction potential and oxidation potential. By changing the supporting electrolyte, dispersant and applied potentials in fabrication process, the catalytic efficiency of the Pt catalyst electrode was improved.

The Pt dendritic nanostructure was manufactured in an electrolyte containing sulfuric acid or perchloric acid, which was used as a supporting electrolyte. If boric acid was served as the supporting electrolyte, the morphology of the Pt particles were cubic structures instead of dendritic structures. Electrochemical characteristics of catalytic efficiency on the anode and cathode were investigated via cyclic voltammetry analysis in a sulfuric acid solution. Finally, a single cell test was also demonstrated.
(Invited) Ultrathin Bismuth Oxyiodide Nano-Sheets for Photocatalytic Nitrogen Fixation Under Visible Light
Authors: Bao Jiming , Mohebinia Mohammadjavad
Published: May 2020

Artificial photosynthesis of ammonia by using N2 and water under ambient temperature and pressure is an auspicious alternative for the high energy demanding Haber-Bosch process. Among the various photocatalysts, bismuth oxyhalides (BiOX, X = Cl, Br or I) show advantages due to their unique properties: (1) the 2D layered structure, not only enlarges the surface area, but also induces an internal electric field, which accelerates the separation of photo-excited charge carriers; (2) the surface enriched oxygen vacancies on the {001} or {010} facets are essential for the chemical adsorption and activation of N2; (3) the high intrinsic oxygen evolution activity allows an overall reaction without using sacrificial reagents. In this talk, I will show the photocatalytic generation of ammonia from water and nitrogen using ultrathin BiOI Nano-Sheets.
(Invited) Type II Heterojunctions of Inorganic Nanostructures for Efficient Photoelectrochemical Water Splitting
Authors: Jang Ho Won
Published: May 2020

A type II semiconductor heterojunction relies on the transfer of photoexcited electrons from one semiconductor to the other due to the more negative conduction band position of the latter. Holes can travel in the opposite direction from the more positive valence band of the former to the latter, leading to all-round efficient charge separation and enhanced photoelectrochemical (PEC) activity for water splitting. In this talk, we would like to show highly efficient type II BiVO4/MeOx(Me = metal) heterostructure photoanodes on fluorine-doped tin oxide substrate. By combining the photoanodes with perovskite/Si hybrid photovoltaics (PVs), the state-of-the-art PV-PEC performans demonstrated. Efficient charge separation and enhanced PEC performance in transition metal disulfides/p-Si and transition metal oxides/n-Si heterostructures are introduced.
(Invited) Semiconductor Nanomaterials for Photoelectrochemical Solar Fuel Generation
Authors: Wang Lianzhou
Published: May 2020

Semiconducting materials hold the key for efficient photocatalytic and photoelectrochemical water splitting. In this talk, we will give a brief overview of our recent progresses in designing semiconductor metal oxides materials for photoelectrochemical energy conversion including photocatalytic solar fuel generation. In more details, we have been focusing the following a few aspects; 1) band-gap engineering of layered semiconductor compounds including layered titanate, tantalate and niobate-based metal oxide compounds for visible light phtocatalysis, and 2) facet-controlled TiO2, Fe2O3, BiVO4 and perovskites as building blocks for new photoelectrode design，and 3) the combination of a high performance photoelectrode BiVO4 with perovskite solar cells can lead to unassisted solar driven water splitting process with unassisted solar-to-hydrogen conversion efficiency of >6.5%; The resultant material systems exhibited efficient visible light photocatalytic performance and improved power conversion efficiency in solar energy, which underpin important solar-energy conversion applications including solar fuel generation and simultaneous environmental application.
Morphology-Tuned TiO2 Photoelectrodes and Their Charge Transfer Behaviour: From 0- to 2-Dimensional Nanostructure
Authors: Jeong Hye Won , Janáky Csaba
Published: May 2020

Anatase TiO2 photoelectrodes, consist of the different nanoparticle (sphere, sheet, rod) were synthesized using hydrothermal and spray coating method. The surface characterizations of TiO2 films were demonstrated by various analysis tool (TEM, XPS, XRD, DRS), and their photoelectrochemical activities were evaluated by controlling the film parameters (mass loading, surface area, thickness) under sulfite and sulfate solution. The particle size and oxidation state of Ti is nearly identical despite of shape difference; however, the band position estimation from the optical bandgap and valence band maximum (VBM) expects that TiO2 nanorod (TiO2 NR) leads to facilitate the separation of photogenerated electron-hole pair due to the lowest VBM position and narrow bandgap (Eg = 3.22 eV). TiO2 NR film exhibits superiority in the photocurrent generation, achieving ~4 mA cm-2 at 0.2 V vs. Ag/AgCl in all film parameter conditions. The IPCE of TiO2 NR achieved the highest values at 350 nm, and high APCE values indicate that restricted the charge recombination or charge carrier trapping on the surface. The fast charge transfer leads to the improvement of the photoelectrochemical performance of TiO2 NR film, which is demonstrated by Intensity-modulated photocurrent spectroscopy (IMPS) and charge injection efficiency. This study provides a significant insight between the morphology change and the charge transfer phenomena on the surface.
Electrolytic Reduction of Bicarbonate into CO
Authors: Berlinguette Curtis P. , Li Tengfei , Lees Eric W. , Goldman Maxwell , Salvatore Danielle A. , Weekes David M.
Published: May 2020

Electrolyzers designed to convert CO2 into carbon products typically rely on a gaseous CO2 feedstock or CO2-saturated electrolyte. We show herein that aqueous HCO3- solutions can also be electrochemically converted into CO gas at meaningful rates in a flow cell containing a bipolar membrane (BPM) and a silver catalyst on a carbon support. Electrolysis upon a N2-saturated 3.0-M KHCO3 solution yields CO with a faradaic efficiency that is comparable to analogous experiment where the bicarbonate solution is saturated with gaseous CO2. This electrolytic process is made possible by reaction of protons, delivered by the BPM, with bicarbonate to form electrocatalytically active CO2. This reaction pathway offers the potential to use electrolysis to bypass the thermally-intensive step of extracting CO2 from HCO3- solutions generated in carbon capture schemes.
(Invited) 4-NP Reduction As a Reaction-Based Indicator for Quantitatively Assessing the Detrimental Influences of Leaching on Catalysts
Authors: Neretina Svetlana , Hughes Robert A. , Neal Robert D. , Demille Trevor B.
Published: May 2020

The fundamental understanding of liquid-phase catalytic reactions is unavoidably complicated when the catalyst is prone to leaching since questions inevitably arise as to the true nature of the catalyst. While the catalytic reduction of 4-nitrophenol by borohydride is widely accepted as a trusted model reaction, it has faced little scrutiny concerning the potential impact of leached species or the appropriateness of assigning catalytic activity to the inserted nanostructures without rigorous experimental verification. Here, we present results from a spectroscopically monitored split test in which supported silver catalysts are physically separated from the reactants midway through the reaction. It is unambiguously demonstrated that the influence of leaching is far from benign, instead acting to extinguish the catalytic activity of the inserted nanostructures while giving rise to an unsupported species that is the true catalytic entity. With only sub-monolayer quantities of silver leached from the supported structures, the unsupported species must be exceedingly catalytic. Moreover, it is shown that leaching is inherent to aqueous media containing dissolved oxygen, without which the supported nanostructures remain catalytically active. With the same nanomaterial being able to act as either a heterogeneous catalyst or as a reservoir from which leached metal is derived, such influences have undoubtedly compromised prior studies. We, nevertheless, capitalize on the sensitivity of 4-nitrophenol reduction to leached species by using it as a reaction-based indicator able to quantitatively determine the time-dependence of the leaching process and enhancements to oxidative etching when silver, copper, palladium, platinum, and gold are exposed to chloride ions.
(Invited) The Role of Polarons, Interfaces, and Phonons in Photocatalytic Junctions
Authors: Cushing Scott Kevin
Published: May 2020

Femtosecond to picosecond processes are often considered to be a thermalizing bath that has little effect on longer time scale photocatalytic reactions. In this talk, we will discuss when strong electron-phonon interactions can be the rate limiting step in photocatalytic materials and junctions. Specifically, high harmonic generation is used to create X-ray pulses with attosecond pulse widths and energies covering 10-150 eV. The energy range allows for multiple elemental X-ray edges to be measured simultaneously. The XUV pulse is combined with a 3-5 femtosecond excitation pulse and a delay line to allow for transient absorption measurements. The response of the elemental X-ray edges to visible light photoexcitation is separated into electronic and structural components using the Bethe-Salpeter equation with density functional theory. This allows for the heat and charge transfer to be measured as a function of an element. For example, the conversion of photoexcited electrons to polarons is measured in Fe2O3. The time-resolved energy of electrons and holes, as well as their correlation with the acoustic and optical phonon bath, is measured in Si and Ge. Finally, the charge and heat transport is measured between each component of a metal-insulator-semiconductor junction (Ni-TiO2-Si) using the Ni, Ti, and Si X-ray edges.
(Invited) Ferroelectric Photovoltage Enhancement in Chromium-Doped SrTiO3 nanocrystal Photocatalysts for Hydrogen Evolution
Authors: Assavachin Samutre , Nail Benjamin A , Goncalves Renato V , Osterloh Frank E.
Published: May 2020

Chromium-doped SrTiO3 nanocrystals of perovskite structure type and 50 nm edge lengths were obtained by hydrothermal synthesis in water from TiO2, Sr(OH)2, and Cr(NO3)3. According to XPS, chromium is present mainly in the +3 oxidation state, and one third is +6. Optical spectroscopy confirms a broad absorption at 2.3-3.0 eV from the Cr states, in addition to the 3.2 eV absorption of the SrTiO3 host. After modification with Pt nanoparticles, SrTiO3:Cr nanocrystals catalyze photochemical H2 evolution from aqueous methanol under visible light illumination and with a an apparent quantum yield of 0.66% at 435 nm. According to surface photovoltage spectroscopy, SrTiO3:Cr nanocrystals are n-type and have an effective band gap of 2.4 eV. Transient illumination experiments reveal an anomalous photovoltage component of up to 6 V that indicates a ferroelectric dipole in the material. The finding of a ferroelectric polarization in SrTiO3:Cr could be significant for improving its photocatalytic properties.

Figure 1
(Invited) Small Polaron–a Major Factor Limiting Photocatalytic Activity of Meta Oxides
Authors: Wu Nianqiang
Published: May 2020

Our recent studies have shown that small polaron is popular among metal oxides. The presence of small polaron impedes the mobility of electron in metal oxide, which leads to the limited photocatalytic activity and photocurrent in photocatalysts and photoelectrodes.
(Invited) Promoted Nitrogen Photofixation over Periodic WS2@TiO2 Nanoporous Film
Authors: Yang Yang
Published: May 2020

Atmospheric nitrogen fixation using a photocatalytic system is a promising approach to produce ammonia. However, most of the recently explored photocatalysts for N2 fixation are in powders, which suffer from particle agglomeration, difficulty in the collection, and unsatisfied conversion efficiency. To the best of our knowledge, rare research about the N2 photofixation over periodic nanostructured films has been reported. Compared with the powdered photocatalysts, the film materials have the inherent advantages over powders, including but not limited to easy transportation and collection. Moreover, the periodic nanostructured films are beneficial for providing photogenerated charge carriers with short diffusion length and favorable transport pathways, leading to superior photocatalytic performances. In this work, we reported the efficient photofixation of N2 over a periodic WS2@TiO2 nanoporous film, which was fabricated through a facile method combing anodization, E-beam evaporation and chemical vapor deposition (CVD). Oxygen vacancies were introduced into the TiO2 to improve the N2 adsorption and activation. The as-prepared WS2@TiO2 film with an optimized WS2 content shows highly efficient photocatalytic performance for N2 fixation with an NH3 evolution rate of 1.50 mmol g-1 h-1, representing one of the state-of-the-art catalysts. This study aims to explore efficient film materials for not only N2 photofixation but also other solar energy conversion applications.
(Invited) Ultrafast Studies of Plasmonic and Photonic Structures for Energy Conversion Applications
Authors: Wiederrecht Gary P
Published: May 2020

Hybrid materials with plasmonic and/or photonic components are of great interest for enhancing the efficiency of light harvesting and energy conversion processes. Those processes that occur on an ultrafast timescale can be very impactful on overall efficiencies of conversion, and therefore are important to understand. These processes can be, for example, the dynamics of hot plasmonic electron decay or the rate of excitonic migration within materials. In this talk, I describe studies of ultrafast spectroscopy and imaging in several types of plasmonic and photonic structures. These include the ultrafast plasmonic behavior of refractory metals and also gap plasmon metamaterials. Efforts to understand how to create greater numbers of energetic carriers, and how to monitor for their presence spectroscopically, are described. Also described are studies of exciton transport in biomimetic materials, particularly to understand how the concentration and orientation of chromophores impact the efficiency of exciton migration. Also described are metal-organic-frameworks and their relevance to supporting photoinduced exciton transport, with ultrafast photoluminescence used to characterize transport in optically scattering media. Finally I briefly describe the user science capabilities of the Center for Nanoscale Materials. This work was performed, in part, at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
(Invited) Photo-Electrochemical Water and CO2 Reduction Devices Operating Under Concentrated Radiation
Authors: Haussener Sophia
Published: May 2020

Achieving high current densities while maintaining a high energy conversion efficiency is one of the main challenges for enhancing the economic competitiveness of solar fuel producing photo-electrochemical devices [1]. I will discuss two device implementations utilizing concentrated irradiation to achieve high current density operation. The water-splitting device is utilizing thermal integration to sustain high performance while dealing with high current density and the corresponding overpotentials [2]. I will quantify the theoretical increase in the maximum efficiencies at given current densities of photoelectrochemical devices resulting from thermal synergies. I will then discuss device implementation of such an approach and show how more realistic device models (multi-dimensional, multi-scale, multi-physics) can be used to support the device implementation and its operational understanding [3]. I will then show how the design principles developed for water splitting can be translated to CO2 reduction devices and discuss a corresponding device implementation.

References

1. M. Dumortier, S. Tembhurne, S. Haussener, Energy Environmental Science, 8: 3614-3628, 2015.

2. S. Tembhurne, F. Nandjou, S. Haussener, Nature Energy, 4: 399-407, 2019.

3. S. Tembhurne, S. Haussener, Journal of The Electrochemical Society, 163: H1008-H1018, 2016.
(Invited) Engineered Cu Surface for Efficient CO2RR
Authors: Huang Yu
Published: May 2020

Electrochemical CO2 reduction to value-added fuels and feedstocks offers solutions to the shortage of renewable energy sources while remediating CO2 emission from human activity. Copper (Cu) is effective at reducing CO2 to hydrocarbons or oxygenates, but often low product selectivity and short production stability plague practical applications. In this talk I will share our recent efforts in engineering the surfaces of nano-structured Cu for high product selectivity and stability.
(Invited) SnS2 Thin Film and Powder for Artificial Photosynthesis
Authors: Chen Kuei-Hsien , Shown Indrajit , Reta Tadesse Billo , Wu Yu-Kai , Chen Li-Chyong
Published: May 2020

Solar photoreduction of CO2 to produce value added hydrocarbons is highly desirable to tackle environmental and energy issues. [1-2] Despite the great improvement in the efficiency and cost of solar cells, the efficiency in artificial photosynthesis is much lower than the >15% of solar cells. Recent progress in 2D chalcogenides with tunable bandgap and layer numbers offers great opportunity for the investigation in this field. In this work, thin film and powder SnS2 have been synthesized for the study. Hydrothermal synthesis of carbon-containing SnS2 exhibits a highly active photocatalytic conversion of CO2 to selective hydrocarbons under visible-light irradiation. Overall, the carbon doping in the SnS2 nanostructure plays a key role and significantly enhance the visible light photocatalytic activity with a photochemical quantum efficiency above 0.7%. [3-4] Meanwhile, Thin film SnS2 has been grown for the mechanism study. By carbon-ion implantation of the thin film, we observed enhanced CO2 reduction under solar illumination. Other FTIR, Raman, NMR, BET, SECM, and synchrotron based facilities including APXPS and XAS have been used to investigate this issue.

1. Shown, H.C. Hsu, Y.C. Chang, C.H. Lin, P.K. Roy, A. Ganguly, C.H. Wang, J.K. Chang, C.I. Wu, L.C. Chen, K.H. Chen, Nano Letters
14, 6097-6103 (2014).

2. Billo, F.Y. Fu, P. Raghunath, I. Shown, W.F. Chen, H.T. Lien, T.H. Shen, J.F. Lee, M. C. Lin, J.S. Hwang, C.H. Lee, L.C. Chen, and K.H. Chen, Small
14, 1702928 (2018).

3. Shown, S. Samireddi, Y.C. Chang, R. Putikam, P.H. Chang, A. Sabbah, F.Y. Fu, W.F. Chen, C.I. Wu, T.Y. Yu, P.W. Chung, M.C. Lin, L.C. Chen, and K.H. Chen, Nature Comm.
9, 169 (2018).

4. Y. Fu, I. Shown, C.H. Li, P. Raghunath, T.Y. Lin, T. Billo, H.L. Wu, C.I. Wu, P.W. Chung, M.C. Lin, L.C. Chen, and K.H. Chen, ACS Appl. Mater. & Interface
11, 28 (2019).
Employing Non-Noble Metals As Catalysts for CO2 Electroreduction
Authors: Kumawat Adhidesh S.
Published: May 2020

CO2 electroreduction to fuels is one of the most viable solutions for tackling both the issues of global warming and energy crises. It is due to the fact that the products such as formic acid, methanol, etc. which are obtained by electroreduction of CO2 could be employed as hydrogen carriers or directly as fuels. This phenomenon attracts huge research towards the process and its bottlenecks for making it commercial. The major hurdles regarding catalysis of CO2 electroreduction process are low solubility of CO2 in aqueous solutions and low product yields.

In our previous works, we have already demonstrated the employment of gas diffusion electrodes for non – noble metal catalysts such as Pb, Bi and Sn. The usage of gas diffusion electrodes enables us to exploit the three phase contact of CO2 gas – solid catalysts – liquid electrolyte and shows higher product (formate ion) yield.[1] Additionally, we have also shown through another work that the ternary eutectics of these three non – metal catalysts employed exhibits higher activity for CO2 electroreduction than singular pure metals or any other binary or ternary alloyed compositions of the metals.[2]

In this work, we want to exploit the conclusions from both the works and subject ternary alloy composition of Pb – Bi – Sn metals in gas diffusion electrode configuration for the process of CO2 electroreduction. Based on the previous two results, author believes that this would enable us to obtain higher product yield and hence better energy efficiency which would be a step forward towards sustainable development.

Reference:

[1] A. S. Kumawat and A. Sarkar (2017), Comparative study of carbon supported Pb, Bi and Sn catalysts for electroreduction of carbon dioxide in alkaline medium, Journal of Electrochemical Society, 164 (14), H1112 – H1120. doi: 10.1149/2.0991714jes

[2] A. S. Kumawat and A. Sarkar (2019), Electrochemical reduction of CO2 on Pb – Bi – Sn metal mixtures – Importance of Eutectics, SN Applied Sciences 1: 301. doi: 10.1007/s42452-019-0313-y