bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Mathematical Modeling of Novel Artificial-Photosynthesis Devices
Authors: Bala Chandran Rohini , Weng Lien-Chun , Ardo Shane , Bell Alexis T. , Weber Adam Z
Published: February 2020

An artificial-photosynthesis device is a multicomponent system composed of various components including perhaps light absorbers, electrocatalysts, membranes or separators, and electrolytes in a specific system geometry. The overall solar-to-fuel conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as the design of the system. In this talk, we will cover recent modeling of various motifs of such artificial-synthesis systems. In particular, we will examine modeling and experimental results for particle-based devices for solar-hydrogen production as well as vapor-feed devices for solar water splitting and electrochemical carbon-dioxide reduction. Mathematical modeling is ideally suited to examine the various tradeoffs and determine design targets and feasibility.

Z-scheme particle-suspension reactor designs consisting of freely suspended semiconductor particles in an electrolyte to drive solar water splitting could be cost-effective alternatives to produce renewable hydrogen. In this work, we develop a device-scale model to evaluate the effects of coupled light absorption, electrolyte species transport, and reaction kinetics on overall reactor performance and ability to sustain rector operation via diffusion. We also extend this work by numerically investigating particle-scale and -size effects on colloidal stability, light absorption and scattering, and charge-carrier transport across the semiconductor/cocatalyst/electrolyte interface.

Within the Joint Center for Artificial Photosynthesis (JCAP), we utilize continuum-scale modeling of the various components in order to determine design tradeoffs of vapor-feed or gas-diffusion electrode systems. Such systems can provide routes towards optimizing local reaction conditions and overcoming inherent liquid-phase transport limitations for carbon-dioxide reduction as well as solar water splitting to produce hydrogen. For the latter, integrated architectures can be used that are more stable than those in liquid environments. Overall, the functioning of both vapor feed and particle systems will be explored.
(Invited) Recent Advances in III-V Multijunction Semiconductor Photo-Electrochemical Water Splitting
Authors: Deutsch Todd G , Young James L. , Steiner Myles , Döscher Henning , Turner John A
Published: February 2020

In order to economically generate renewable hydrogen fuel from solar energy using semiconductor-based devices, the U.S. Department of Energy Fuel Cells Technology Office has established technical targets of over 20% solar-to-hydrogen (STH) efficiency with several thousand hours of stability under operating conditions [1]. We have modeled attainable efficiencies of tandem absorbers that, for the first time, considered the absorption of sunlight by water [2]. We used this modeling to identify top and bottom semiconductor bandgap combinations that should be targeted to achieve maximal STH efficiency.

We had to employ several key solid-state technological advances to achieve STH efficiencies exceeding 16%. The first improvement was to increase the device current via a non-lattice-matched 1.2 eV InGaAs grown using the inverted metamorphic multijunction technique developed by NREL’s III-V photovoltaics group. The second modification was to add a thin n-GaInP2 layer to p-GaInP2 to generate a "buried junction", which increased the photocurrent onset or Voc of the device by several hundred mV and enabled 14% STH efficiency. Finally, we increased the top junction photon conversion efficiency by adding an AlInP "window layer", which is commonly used in solid-state PV devices to reduce surface recombination. Through the use of a collimating tube, we measured our devices outdoors under direct solar illumination and verified over 16% STH conversion efficiency. I will also briefly introduce pitfalls of common experimental procedures that can influence the accuracy of measured STH efficiencies, which can be exaggerated for mulitjunction absorbers.

The largest loss in our current system is reflection at the semiconductor/electrolyte interface, so I will address the photon management strategies we use to achieve greater parity between measured efficiency and the theoretical limit. Capturing a significant portion of the ~25% of photons lost to reflection at this interface should allow the realization of devices that exceed 20% STH efficiency.

[1] http://energy.gov/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf

[2] H. Döscher et al., Energy Environ. Sci. 7, 2951 (2016).
(Invited) Fast Detection Method for Analyzing CO2 Electroreduction Products
Authors: Zhang Fen , Co Anne C.
Published: February 2020

Reported herein is a fast electroanalytical method for the qualitative and quantitative identification of CO2 reaction products to reduce the analysis time for catalyst evaluation. This method will enable fast screening of catalyst activity, selectivity and deactivation mechanism.
Theoretical Investigations of Electrochemical CO2 Reduction
Authors: Chan Karen , Liu Xin-Yan , Xiao Jianping , Nørskov Jens
Published: February 2020

The electrochemical reduction of CO2 has the potential to store energy from intermittent renewable sources and to produce carbon-neutral fuels and chemicals1. In recent years, theoretical studies of CO2 reduction have usually applied the computational hydrogen electrode model, which allows for the determination of the energies of reaction intermediates without explicitly treating the potential and the ions in solution2. This thermochemical approach has been shown to correlate well with experimental onset potentials 3,4 and applied to computational screening of new catalysts 5,6. However, an understanding of charge transfer barriers, kinetics, selectivity, and pH effects all require explicit consideration of solvent and charge. In this talk, I will discuss new developments in the explicit treatment of the electrochemical interface, which is based on a simple capacitor model that uses the interfacial charge to obtain barriers at constant potential 7,8. I will then discuss the application of such a scheme to CO2 reduction: the determination of reaction pathways on transition metals, field and solvation effects9,10, the resultant kinetics, and catalyst design criteria.

1 Whipple, D. T. & Kenis, P. J. A. Prospects of CO2 Utilization via Direct Heterogeneous Electrochemical Reduction. The Journal of Physical Chemistry Letters
1, 3451-3458, doi:10.1021/jz1012627 (2010).

2 Nørskov, J. K. et al. Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. J. Phys. Chem. B
108, 17886--17892 (2004).

3 Shi, C., Hansen, H. A., Lausche, A. C. & Nørskov, J. K. Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces. Physical Chemistry Chemical Physics
16, 4720-4727, doi:10.1039/C3CP54822H (2014).

4 Kuhl, K. P. et al. Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces. Journal of the American Chemical Society, doi:10.1021/ja505791r (2014).

5 Chan, K., Tsai, C., Hansen, H. A. & Nørskov, J. K. Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction. ChemCatChem
6, 1899-1905, doi:10.1002/cctc.201402128 (2014).

6 Asadi, M. et al. Robust carbon dioxide reduction on molybdenum disulphide edges. Nature communications
5 (2014).

7 Chan, K. & Nørskov, J. K. Electrochemical Barriers Made Simple. J. Phys. Chem. Lett., 2663--2668 (2015).

8 Chan, K. & Nørskov, J. K. Potential Dependence of Electrochemical Barriers from ab Initio Calculations. The Journal of Physical Chemistry Letters, 1686-1690, doi:10.1021/acs.jpclett.6b00382 (2016).

9 Montoya, J. H., Shi, C., Chan, K. & Norskov, J. K. Theoretical Insights into a CO Dimerization Mechanism in CO2 Electroreduction. The journal of physical chemistry letters
6, 2032--2037 (2015).

10 Chen, L. D., Urushihara, M., Chan, K. & Nørskov, J. Electric Field Effects in Electrochemical CO2 Reduction. ACS Catalysis (2016).

11 Liu, X. et al. Understanding trends in CO2 reductin on transition metals. (2016).
Electrochemical Carbon Dioxide Reduction on Cu-Zn Bimetallic Catalysts with Enhanced Ethanol Selectivity
Authors: Ren Dan , Yeo Boon Siang
Published: February 2020

The electrochemical carbon dioxide (CO2) reduction to ethylene (C2H4) and ethanol (C2H5OH) using renewable energy is a viable method for the production of these commercially vital chemicals. Copper (Cu) based materials are by far the most promising electrocatalysts for this purpose. However, the formation of ethanol using Cu and its oxides is generally less favored as compared to that of ethylene. Here, we demonstrate that the selectivity of CO2 reduction towards ethanol could be systematically tuned by introducing a co-catalyst to generate an in situ source of mobile CO reactant. Cu-based oxides with different amount of Zn dopants (Cu, Cu10Zn, Cu4Zn and Cu2Zn) were prepared via electrodeposition and used as catalysts under ambient pressure in aqueous 0.1 M KHCO3 electrolyte. By varying the concentration of Zn in the bimetallic catalysts, we found that the selectivity of ethanol versus ethylene formation, defined by the ratio of their faradaic efficiencies (FEethanol/FEethylene), could be tuned by a factor of up to ~12.5. Ethanol selectivity was maximized on Cu4Zn at -1.05 V vs. RHE, with a remarkable faradaic efficiency and current density of 29.1% and -8.2 mA/cm2 respectively. The Cu4Zn catalyst was also catalytically stable towards ethanol formation for at least 5 hrs.

Operando Raman spectroscopy revealed that the as-deposited oxides were reduced to the metallic Cu/Zn during CO2 reduction, after which only signals belonging to CO adsorbed on Cu sites were recorded. This indicated that the reduction of CO2 might preferably occur on metallic sites rather than on metal oxides. The importance of Zn as a CO producing site was also demonstrated by performing CO2 reduction on Cu-Ni and Cu-Ag bimetallic catalysts. Thus, the mechanism of ethanol formation was proposed as following: Incoming CO2 molecules could first bind to either Cu or Zn sites, and be reduced to CO. On the Cu sites, CO could be reduced further to CHO or CHx (x=1,2,3) intermediates, while CO adsorbs weakly on Zn sites and is likely to desorb. The desorbed CO could diffuse and spill over onto the Cu sites. The spilled-over CO may then insert itself into the bond between the Cu surface and *CH2, to form *COCH2. Further reduction of *COCH2 will produce acetaldehyde and finally ethanol.

1) Ren, D.; Ang, B. S. H.; Yeo, B. S. ACS Catal.
2016, 8239-8247.

2) Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S. ACS Catal.
2015, 5, 2814-2821.

3) Hori, Y.; Murata, A.; Takahashi, R. J. Chem. Soc., Faraday Trans. 1
1989, 85, 2309-2326.

4) Calle-Vallejo, F.; Koper, M. T. M. Angew. Chem. Int. Ed.
2013, 52, 7282-7285.
Self-sustaining Microbial Photoelectrosynthesis for Hydrogen Generation and Waste Water Cleaning
Authors: Lu Lu , Williams Nicholas , Ren Zhiyong , Gu Jing
Published: February 2020

Sunlight offers an inexhaustible and sustainable source of renewable energy to meet our increasing energy demand. However, direct harvesting of solar energy is still challenging due to the variation of natural sunlight and its intermittent nature. To meet the Terawatt Challenge and harness large quantity of energy, current artificial photosynthesis system is showing great promise for its capability of imitating natural photosynthesis. However, the direct water splitting by artificial photosynthesis requires large energy input. Here we demonstrate GaInP2-TiO2-MoSx photocathode could couple with microbial electrochemical oxidation process, which used to treat wastewater and recover the chemical energy embedded in organics into electricity, to covert water into hydrogen. The self-sustaining system could generate a current of 0.4 mA/cm2 without any external bias and ~10 mA/cm2(with 5 % solar to hydrogen conversion efficiency) at slightly applied bias condition.
(Invited) From in-Situ to in-Operando Evaluation of SOFC Cathodes for Enhanced ORR Activity and Durability
Authors: Wachsman Eric D. , Cohn Gil , Huang Yi-Lin , Pellegrinelli Christopher
Published: February 2020

To study the SOFC cathode oxygen reduction reaction (ORR) mechanism and the effects of ambient gas composition on ORR, we used in-situ
18O isotope exchange techniques to probe the exchange of H2O and CO2 with two of the most common SOFC cathode materials, (La0.8Sr0.2)0.95MnO3-x (LSM) and La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF). A series of temperature programmed isotope exchange measurements were performed to comprehensively study the interaction of H2O and CO2 with the cathode surface as a function of temperature, oxygen partial pressure, and contaminant gas concentration. The experimental data are summarized in a Temperature-PO2 diagram to visualize the dominant reactions at each temperature and PO2 for the two cathode materials.

We further report on the development of a novel in-operando
18O isotope exchange technique by modifying our heterogeneous catalysis system for operation and measurement under electrochemical polarization. The system allows ORR investigations under real time, real life, operating conditions. We will present our studies on the effect of cathodic polarization on LSM and LSCF. The studies show the effects of operating voltage, temperature, and oxygen partial pressure on the oxygen exchange coefficient. We will also present our model for the understanding and analysis of the isotope oxygen exchange profiles under in-operando conditions.
(Invited) The Effect of (La,Sr)MnO3 Cathode Surface Termination on Its Electronic Structure
Authors: Kotomin Eugene , Merkle Rotraut , Mastrikov Yuri , Kuklja Maija , Maier Joachim
Published: February 2020

La1-xSrxMnO3 (LSM) was one of the first perovskites employed as SOFC cathode material and is still used in the form of porous composites with the respective electrolyte [1]. In our previous study [2], we analyzed oxygen adsorption, dissociation and migration on the (001) MnO2-terminated LM surface. In pure LaMnO3, the MnO2 (001) termination was found to be the energetically most stable, however with an increase of Sr doping, the (La,Sr)O termination is predicted to become even more favorable thermodynamically [3].

In this talk, we discuss and compare the results of first principles calculations on the elementary steps (oxygen vacancy formation, O2 molecule and O atom adsorption) of the oxygen reduction reaction on (La,Sr)MnO3 on the two (001) polar terminations – (La,Sr)O and MnO2. The LSM slab calculations were performed using the plane wave VASP computer code with GGA exchange correlation functionals. Properties of oxygen vacancies in different planes from the surface were analyzed. The vacancy formation energy on the MnO2 terminated surface is smaller than that in bulk. In contrast, the vacancy energy on the (La,Sr)O termination is larger, thus strongly reducing the surface vacancy concentration.

Our approach allows for a clear separation of the two distinct effects -- different surface terminations and slab cation stoichiometry (ratio of a number of (La,Sr) ions to Mn that affects the average Mn oxidation state). It is found that oxygen vacancy formation energy in the bulk (slab center) is almost independent of the Mn oxidation state in the region +2.6 to +3.25, whereas it is monotonically decreasing on both surfaces. This surface-to-bulk discrepancy will be discussed. The oxygen atom adsorption energy on the (La,Sr)O termination considerably exceeds that on the MnO2 termination.

As a result, the equilibrium oxygen adsorbate concentration was found to be about two orders of magnitude larger for the (La,Sr)O termination, but on the other hand, the surface oxygen vacancy concentration is smaller by nearly six orders of magnitude. Therefore, the oxygen reduction rate on (La,Sr)O termination is expected to be significantly lower than on the MnO2 termination.

[1]. M. Kuklja, E.A. Kotomin, R. Merkle, Yu.A. Mastrikov, J. Maier, PCCP 15, 5443 (2013).

[2]. Yu.A. Mastrikov, R. Merkle, E. Heifets, E. A. Kotomin, J. Maier, J. Phys. Chem. C 114, 3017 (2010).

[3]. S. Piskunov, E. Heifets, T. Jacob, E. A. Kotomin, E. Spohr, Phys. Rev.B 78, 121406 (2008).
Operando Investigation of the Chemical Interaction of Water Vapor with Ceramic Proton Conductors
Authors: Braun Artur
Published: February 2020

The protons are the key players in ceramic proton conductors. But they are very elusive and had to detect. I will shows a suite of experiments, ex situ, in situ and operando, where the protons are shown as structural elements at low temperatures where they do not yet constitute charge carriers. They actually constitute OH groups in the crystal lattice. With increasing temperature, the protons participate with the lattice vibrations while and OH-bond breaking takes place at some transition temeprature where the protons become charge carriers. We have observed this on the Y-doped BaZrO3 and BaCeO3 model proton conductors with quasi elastic neutron scattering under ambient and under high temperature high pressure conditions. The phonon modes as determined from high presssure Raman spectroscopy propel the protons and cause a net protonic charge transfer via phonons. The changes in the chemical bond environment were observed with ambient pressre x-ray spectroscopy, particular changes in the oxygen core lecvel spectra and the Ce, Y and Zr resonant valence band spectra under humidified high temperature conditions. We are able to sketch the changes in bond breaking at exactly the temperature where the ptoton conductivty sets on.

[1] Q. Chen, F. El Gabaly, F. Aksoy Akgul, Z. Liu, B.S. Mun, S. Yamaguchi, A. Braun, Observation of 8.238 oxygen vacancy filling under water vapor in ceramic proton conductors in-situ with ambient pressure XPS; Chem. Mater., 2013, 25 (23), pp 4690–4696.

[2] Q. Chen, J. Banyte, X. Zhang, J. P. Embs, A. Braun; Proton Diffusivity in Spark Plasma Sintered BaCe0.8Y0.2O3-δ: in-situ combination of quasi-elastic neutron scattering and impedance spectroscopy; Solid State Ionics 252 (2013) 2–6.

[3] Q. Chen, T.-W. Huang, M. Baldini, A. Hushur, A. Pomjakushin, S. Clark, W. Mao, M. Manghnani, A. Braun, T. Graule, The Effect of Compressive Strain on the Raman Modes of the Dry and Hydrated BaCe0.8Y0.2O3 Proton Conductor, J. Phys. Chem. C, 2011, 115 (48), pp 24021–24027.
Understanding the Cathode Reaction Process for Proton Conducting Intermediate Temperature Solid Oxide Fuel Cells Using Comparison Between BSCF and Other Cathode Materials
Authors: Sun Shichen , Cheng Zhe
Published: February 2020

Intermediate temperature (~400-600oC) solid oxide fuel cells (IT-SOFC) have drawn growing attention due to the possibility to use cheaper sealing and interconnect materials and the potential to improve system stability and reliability comparing with conventional SOFC that operate at ≥~750oC. For IT-SOFC, proton conducting oxides such as acceptor-doped Ba(Ce, Zr)O3 are often preferred over oxide ion conductors as the electrolyte materials due to their high ionic conductivities and low electronic leakage at intermediate temperature. In this study, the electrochemical behaviors of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), which is one of the most active cathode materials for SOFC and shows significant hydration to become proton conductive in humidified atmosphere, is studied in comparison with other oxide (e.g., Pr2NiO4+δ) as well as metal (e.g., Ag) cathode materials at intermediate temperatures of ~350-650oC. In particular, the influences of different testing conditions including cell configuration (cathode symmetrical cells versus full cells), proton conducting electrolyte thickness, cathodic bias voltage, oxygen concentration, and the presence of air impurities such as water vapor (H2O) and carbon dioxide (CO2) on the electrochemical performance are systematically investigated. The implication of the experimental observations especially in terms of the similarity and differences in electrochemical behaviors between different electrode materials to the overall cathode reaction mechanism for proton conducting IT-SOFC is discussed. Finally, the directions for further improving the cathode performance for proton conducting IT-SOFC will be pointed out.
Improve Activity and Stability of Ni-Ce0.8Sm0.2O1.9 As the Anode of a Methanol Fuelled Solid Oxide Fuel Cell
Authors: Zhao Yicheng , Li Yongdan
Published: February 2020

Solid oxide fuel cells (SOFCs) are electrochemical devices those convert chemical energy in fuels directly into electricity. Compared with H2, commercial hydrocarbon fuels can be safely stored and are more readily available, which could reduce the overall operation cost. Therefore, direct electrochemical oxidation of hydrocarbons into electricity using SOFCs is appealing. However, there are many operational problems those still need to be solved. The typical NiO-YSZ anode material has excellent catalytic properties for fuel oxidation and good electrical conductivity, while it experiences serious carbon deposition with hydrocarbons as fuels. Therefore, there is a need for developing new kinds of carbon resistant SOFC anode materials for the utilization of hydrocarbon fuels.

In this work, Mo is utilized to modify the Ni-Ce0.8Sm0.2O1.9 (SDC) anode. The NiO-MoO3-SDC anode materials are prepared by impregnation technique, which are reduced to SDC and Ni-Mo alloy phases in H2 atmosphere. SOFCs with Ni-Mo-SDC composite anodes are fabricated and tested with methanol as fuel. The addition of Mo into Ni–SDC anode effectively improves performance and stability of the single cell at 700 oC. The anode with a mole ratio of Mo to Ni of 0.03:1 (Ni-3Mo-SDC) exhibits the lowest polarization resistance. The cell with that anode and SDC-carbonate composite electrolyte exhibits a maximum power density of 680 mW cm-2 at 700 oC. The stability of the cell is enhanced with the increase of the content of Mo in the anode.

In order to further improve the cell performance and stability, rare earth elements (La, Pr and Sm) are introduced into Ni-3Mo-SDC. The effects of La, Pr and Sm addition on the catalytic activity for methanol pyrolysis and coking resistance of the Ni-3Mo-SDC anode are examined. The electrochemical performance of the SOFC is enhanced with introducing La and Sm into the anode. The cell with La addition in the anode shows a maximum power density of 765 mW cm-2 at 700 oC with methanol as fuel. The addition of La, Pr and Sm into Ni-3Mo-SDC anode improves the stability of the cell, which is mainly attributed to the decreased amount of carbon deposition with a high graphitization degree.
(Invited) Phosphoric Acid Migration in Fuel Cells
Authors: Büchi Felix N , Halter Jonathan , Eberhardt Sebastian H. , Schmidt Thomas J.
Published: February 2020

In phosphoric acid (PAFC) and high-temperature polymer electrolyte fuel cells (HT-PEFC) concentrated phosphoric acid is used as the electrolyte. In PAFC the acid is imbibed in an inert silicon carbide matrix while in HT-PEFC polybenzimidazole (PBI) membranes are used. In PAFC, because there is no interaction between the matrix and the acid the phoshate anion has a finite transference number which “results in acid migration toward the anode of an operating cell and results in migration between cells” quote from [1]. In PBI based membranes the phosphoric acid is bound to the PBI and its mobility reduced, so it was expected that acid migration is suppressed. However, in past years it was shown that acid migration is also an issue in HT-PEFC and most probably a life time limiting process. As in PAFC, in HT-PEFC, strategies need to be developed to limit acid migration and thus improve durability. This requires fundamental work to better understand migration and the imbibition of the porous structures at the anode. Therefore the wetting behavior of the anode gas diffusion layers with phosphorc acid is characzterized in ex-situ and operando experiments by X-ray imaging.

Similarities and differences in acid management and it’s characterization in PAFC and HT-PEFC is discussed and the prospects for HT-PEFC in the large co-generation market for small (1 kW) systems is assessed.

[1] H.R. Kunz, ECS Transactions, 11, 1447-1460 (2007)
(Invited) Current Status on Ballard Fuel Cells and Future Catalyst Development
Authors: Ye Siyu , Banham Dustin , Yang Lijun , Knights Shanna
Published: February 2020

Hydrogen and fuel cell technologies offer a pathway to enable the use of clean energy systems to improve air quality, enhance energy security, and stimulate the global economy. Due to the significant advances in fuel cell technology over the last 25 years, fuel cells have become competitive in certain markets. Ballard Power Systems Inc. is recognized as a world leader in proton exchange membrane (PEM) fuel cell development and commercialization. At the heart of each Ballard PEM fuel cell product is a stack of unit cells based on Ballard’s proprietary technology, for unsurpassed performance, durability and versatility. Ballard draws on intellectual property together with unmatched know-how in key areas, including fuel cell MEA/stack development and systems integration. Ballard’s fuel cell products deliver the required functionality at the right scale with optimum performance and low lifecycle costs. This presentation will provide an overview of current status of Ballard fuel cell development.

To enable wide-spread commercialization of fuel cells, particularly automotive applications, further cost reductions and durability improvements are still required. For longer term PEM fuel cell products, the catalyst is still a major cost factor due to the use of platinum group metals (PGMs). In addition to cost, these PGM catalysts have insufficient durability for certain long life applications, particularly at low catalyst loadings. Thus, the most significant remaining challenge for PEMFC catalysts will be to achieve excellent activity at low PGM loadings while also maintaining high durability/stability during operation. The advantages and possible limitations of various types of catalysts, such as Pt alloys (de-alloys), core-shell catalysts and shape-controlled nanocrystal catalysts will be assessed. This presentation will conclude with a discussion of potential future directions for PEMFC catalyst and catalyst layer research to help overcome the last remaining challenges of performance and durability and propel PEMFCs into the wider commercial market.
(Invited) The U.S. Department of Energy’s Energy Materials Network
Authors: Sarkar Reuben , Joost William , Miller Eric L.
Published: February 2020

Affordable, reliable, high performance materials and manufacturing technologies are key for most transformational technology advancements, including those in critical domestic energy applications. However, many materials discoveries in the laboratory either never reach widespread market deployment or spend decades in the development cycle at a cost of many tens or hundreds of millions of dollars. In response, the U.S. Department of Energy (DOE) has established the Energy Materials Network (EMN) to accelerate the materials-to-market process by better integrating the stages from materials discovery through manufacturing. The EMN is a network of national lab-led consortia that support both industry- and government-led research (e.g. CRADAs and FOA awards) on specific energy-related material challenges. The EMN framework facilitates industry stakeholder engagement to ensure that the research is immediately relevant, with high-impact commercial potential. To date, EMN consortia have been set up in the seven technology areas of: light-weight materials for transportation; precious-metal-free catalysts for fuel cells; water-splitting materials for hydrogen production; advanced catalysts for biomass conversion; new materials and designs for photovoltaic modules; advanced solid-state hydrogen storage materials; and advanced caloric materials for refrigeration. This presentation will describe the vision of the EMN as an enduring national resource, and discuss recent technical accomplishments in the current network of EMN consortia.
(Invited) Lightmat: A U.S. Dept. of Energy, Energy Materails Network
Authors: Herling Darrell
Published: February 2020

Accelerating advanced materials development, from discovery through deployment, has the potential to revolutionize whole industries and is critical for the United States to compete globally in manufacturing in the 21st century. However, today only a small fraction of materials innovations make it to widespread commercialization. The goal of the U.S. Department of Energy’s Energy Materials Network (EMN) is to dramatically decrease the time-to-market for advanced materials that are critical to manufacturing many clean energy technologies, enabling manufacturers of all sizes to develop and deliver innovative, made-in-America products to the world market.

The Lightweight Materials National Laboratory Consortium, or LightMAT, is one of, and the first established, node in the EMN, and is comprised of ten national laboratories with technical capabilities highly relevant to lightweight materials development and utilization. LightMAT provides straightforward access to resources and capabilities in this network via a single point of contact and works to match industry research teams with expertise and equipment found only at national laboratories. This presentation will describe some of the unique technical capabilities available through the LightMAT network and how these will be applied to developing materials technologies for future low-carbon energy systems.
Electrochemically Initiated Formation of Sulfonyl Radicals: Synthesis of Oxindoles Via Difunctionalization of Acrylamides Mediated By Bromide Ion
Authors: Zeng Chengchu , Jiang Yangye
Published: February 2020

An efficient electrochemical approach for the synthesis of oxindoles has been developed from electrolysis of a mixture of sodium sulfinate and acrylamide. The chemistry avoids the utilization of additional conducting salt and proceeds in a simple undivided cell employing catalytic amount of NH4Br (10 mmol %) as a redox catalyst. The protocol is practical that is proved by the one-pot, two-step procedure and scaled-up experiments. Mechanical studies reveal that the electrochemical approach involves the formation of sulfonyl radicals via homolytic cleavage of the in-situ generated sulfonyl bromide.

Scheme 1. Oxidative radical coupling for the synthesis of oxindoles

Figure 1
(Keynote) The Nature of the Interaction Between Electrogenerated Anions and Tetraalkylammonium Cations
Authors: Fry Albert Joseph
Published: February 2020

A series of reports from this laboratory have described computational studies defining the first general binding motif yet discovered for ion pairing in conventional electrochemical media (1-4). These studies have shown that tetraalkylammonium cations interact in identical fashion with a variety of organic and inorganic electron donor species. For example, the structures (see image) generated by interaction between tetrabutylammonium cation and nitrobenzene anion radical, dianion, and even neutral nitrobenzene ,are identical. Remarkably similar structures have been found without exception for more than one hundred other species formed by interaction between tetralkylammonium cations where the alkyl group ranges from ethyl through heptyl and electron donors of diverse structural type (polycyclic aromatic hydrocarbon dianions, substituted benzaldehydes, nitrosobenzenes, and even inorganic anions).

 

The uniformity of binding between over a broad range of cationic and anionic structures in these many species is remarkable. Surely electrostatic attractions are important. Yet, in light of the high specificity of structure exhibited by these ion pairs and related species, one may well inquire into the reasons why this is so. Is the explanation simply electrostatic attraction between cations and anions? We will show evidence instead that formation of these structures involves a complex set of phenomena including electrostatics (of course) but also induced charges on each component and electron transfer between the two.

References

Fry, A. J. Tetrahedron
2006, 62, 6558.

Fry, A. J. J. Org. Chem.
2013, 78, 2111.

Fry, A. J. J. Org. Chem.
2013, 78, 5476.

Fry, A. J. J. Org. Chem.
2015, 80, 3758.

Figure 1
Electrosynthesis of Linear PEDOT Fibers By Means of Bipolar Electrochemistry
Authors: Inagi Shinsuke , Ohira Masato , Koizumi Yuki , Nishiyama Hiroki , Tomita Ikuyoshi
Published: February 2020

Recently we reported the electropolymerization of 3,4-ethylenedioxythiophene (EDOT) and its derivatives on a bipolar electrode (BPE) with the sacrificial reduction of benzoquinone (BQ), and found that poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives propagated as a dendritic fiber form (φ = ca. 5 μm) from the ends of Au wires used as BPEs parallel to an external electric field.1

In this study, we demonstrated that the AC-bipolar electopolymerization of EDOT in a micro-space produced the PEDOT fibers with one-dimensional morphology.2 In this situation, the micro-space around the BPEs and generated PEDOT fibers was effective to limit the further access of EDOT monomer from the side of the fibers but allowed it at the terminal of the fibers, which led to the formation of linear PEDOT fibers. This method was found to be useful to connect BPE wires with linear PEDOT fibers, in which the growing direction could be controlled by the external electric field, in a better manner to the previous dendritic growth of PEDOT fibers. The rapid and selective wiring of conductors with organic microfibers would be of potential interest in the application for organic devices.

References

1. Y. Koizumi, N. Shida, M. Ohira, H. Nishiyama, I. Tomita, S. Inagi, Nat. Commun.
2016, 7, 10404.

2. M. Ohira, Y. Koizumi, H. Nishiyama, I. Tomita, S. Inagi, Polym. J. in press.

Figure 1
Impedance of Mediated Electrochemical Processes at Microelectrodes
Authors: Polczynski Piotr , Jurczakowski Rafal Robert
Published: February 2020

Impedance spectroscopy, unlike any other electrochemical method, can provide a full insight into the mechanism and kinetics of electrode processes. However, the interpretation of impedance spectra is possible only for systems having a meaningful mathematical description leading to a proper equivalent circuit.

Recently, we have provided, for the first time, an exact analytical solution in linear diffusion regime for impedance of catalytic processes involving redox mediators [1]. In this process the electrochemical step (E) is followed by a homogeneous chemical reaction regenerating depolarizer (C’). In such systems various electroinactive and quite inert molecules can be catalytically oxidized or reduced by means of redox mediators that carry electrons from or to the electrode surface. Introduced model obtained for general case provide a powerful research tool that can be used in studies of many important catalytic processes. However, in many cases microelectrodes are used and spherical diffusion needs to be taken into account.

In this work, we present an analytical solution for faradaic impedance of the catalytic EC’ processes in spherical diffusion geometry. We provide the range of electrode radius, for which spherical model should be applied. We deliver an equivalent circuit together with potential dependence of all impedance parameters, which allows to rapid and precise determination of all kinetic and thermodynamic parameters of EC’ type reactions on microelectrodes. Similarly as for the solution in linear geometry the resistance of the charge transfer, R
ct tends to a constant value at high overpotentials.

The applicability of the model in characterization of the catalytic processes was confirmed experimentally. It has been shown that all key parameters of catalytic systems may be readily obtained even from a single impedance spectrum.

References:

[1] R. Jurczakowski, P. Połczyński, J. Phys. Chem. 118 (2014) 7980–7988
(Invited) Impedance Characterization of High-Temperature Spinned Fiber Ceramic Materials
Authors: Vanýsek Petr , Novák Vitězslav , Částková Klára , Chladil Ladislav
Published: February 2020

Materials based on cubic ZrO2 stabilized with Y2O3 have good ionic conductivity at higher temperatures, which makes them suitable or promising candidates for use as a membrane in the solid oxide fuel cells (SOFC). The zirconia materials are mainly used as a compact ion conductive membrane, allowing the separation of the positive and negative electrodes while allowing ionic conduction via the oxygen ion. Another possible use in SOFC consists in the idea of creating a highly porous structure coated with a suitable catalyst (e.g., Ni) for the negative electrode. This would lead to a rapid increase in the active surface of the electrode and thereby increase the nominal current density of the fuel cell. The fibrous structure and its large porosity, while ionically bonding, appear to be very suitable for this purpose.

The methods of forming fibers in our laboratory are both the force spinning and electrospinning. From the spinned nanofibrous materials we prepared disc samples (pellets) with opposite flat sides coated with a conductive platinum paste and wee annealed. The prepared samples were contacted using platinum mesh electrodes (a two-electrode connection) to the heated chamber of instrument ProboStat (Dept. of Chemistry, University of Oslo). The whole probe device shrouded in ceramic tube was inserted into a tubular furnace. The sample was held at different temperatures and the impedance spectroscopy data were obtained for a series of temperatures. From this the total impedance of the system, as a function of temperature, was collected. A relative simple equivalent circuit was used to fit the data end extract mostly the conductivity of the sample at each given temperature. Impedance was collected using spectrometer Solartron 1260 at suitable temperature steps (usually 25 ° C) at AC amplitude 100 mV. The equivalent circuit fit was done using ZView (Scribner Associates). Fig. 1 shows an example of impedance plot compared for a bulk (nonfibrous) substrate and one, with prepared from the fibrous material.

The conductivity of ceramic materials is a thermally activated process, and therefore depends on temperature. Thermal conductivity changes are often described using the Arrhenius. In this case, the dependence of the logarithmic conductivity changes upon change of the inverse of the absolute temperature is linear and from the slope of the Arrhenius plot one can calculated the activation energy of the process (Fig. 2). From the figure it is apparent that the bulk and the fibrous material the activation energies are essentially identical, while the actual conductivities are significantly different for each; expectedly lower for the fibrous substrate.

Figure 1
Study of Charge Transfer Dynamics in Spray Deposited Cu2ZnSnS4 (CZTS) Photoelectrodes for Performance Improvement
Authors: Mondal Animesh , Radich James
Published: February 2020

Thin film solar cell based on Cu2ZnSnS4 (CZTS) has the potential for large scale electricity production using solar radiation where the elements are earth abundant, inexpensive and environment friendly. The state of art CZTS solar cell has reached 12.6% efficiency while the commercial production will require at least 15% for economic feasibility. Here, we approach to understand the charge transfer dynamics in CZTS using ultrafast laser spectroscopy and focus on improving the efficiency of CZTS photovoltaics through the incorporation of a mesoscopic hole acceptor, nickel oxide. CZTS photo electrode is prepared using spray deposition of precursor solution, and characterized using SEM, TEM, XRD, XPS and Raman Spectroscopy. The performance of the material is tested in three electrode photo electrochemical cell.
Dependence of Photoelectrochemical Properties on Geometry Factors of ZnO Nanostructured Networks
Authors: Mao Yuanbing
Published: February 2020

The recent surge of alternative clean energy with minimal environmental impact in a cost-effective way requires the exploration of new materials and/or structures as efficient electrodes for industry-level photoelectrochemical (PEC) water splitting into usable H2 fuel. It is well-known that nanomaterials could outperform their bulk counterparts in many aspects because of increased interacting sites, shorter lateral diffusion distance and lower reflectivity. Assembling nano-building blocks into desirable structures is a more advanced intelligent tactic for realizing higher performance and better functionality by exploiting new hierarchy and scaling-up laws. To meet the challenges, hierarchical 3-D nanostructures integrating 1-D conduction trunks and secondary branches, e.g. dendritic nanowires (NWs)/nanofibers (NFs), are particularly desired in light of the greatly improved light-harvesting, the efficient charge separation and short hole diffusion length (L
D) for which the refined secondary structures are responsible. In terms of methodology, a seeding method in solution phase still confronts some engineering obstacles notwithstanding it being regarded as a major avenue to fabricate heterogeneous nanostructures of semiconductors. To elevate the spatial occupancy of one-dimensional ZnO nanostructures and overcome the limitations of multistep seeding method currently widely used, a rational, facile and high-yielding procedure will be presented here for the fabrication of the interconnected three-dimensional “caterpillar-like” ZnO nanostructured networks (CZNs) for photoelectrochemical applications. Moreover, by fine-tuning the synthesis procedure and manipulating their growth process, the dependence of their photoelectrochemical properties on geometry factors of these unique CZNs consisting of branched ZnO nanowires onto ZnO nanofibers with tunable surface-to-volume ratio and roughness factor has been investigated. They offer mechanically and electrically robust interconnected networks with open micrometer-scale structures and short hole diffusion length. The preferential light-material interaction and charge separation to maximize the photo-to-hydrogen conversion efficiency were further studied. When used as photoanode, our CZNs not only favor sunlight harvesting with multireflection ability, but also suppress the recombination of photogenerated charge. Compared to the literature results, our CZN photoanodes with ZnO nanobranches of ~2.2 μm in length and ~25 nm in diameter exhibited the highest photocurrent density of 0.72 mA∙cm-2 at +1.2 V (versus Ag/AgCl) and conversion efficiency of 0.209% at +0.91 V (versus RHE) without being decorated with noble metal cocatalysts or nonmetallic/metallic dopants due to their favorable structural features. Overall, our procedure to obtain the desirable CZN provides great opportunities for facile and efficient fabrication of model photoelectrochemical anodes and would be applied to other materials for sustainable chemistry and engineering applications.
High Performance Bioelectrocatalytic Interconversion Between Formate and Carbon Dioxide
Authors: Kano Kenji , Sakai Kento , Kitazumi Yuki , Shirai Osamu
Published: February 2020

An interconversion of HCOO-/CO2 is one of essential requirements for carbon-based sustainable energy economy. However, when CO2 is reduced and HCOO- is oxidized directly on electrodes, carbon monoxide is generated and quite high overpotential is required. One of the most promising strategies for solving these issues is the utilization of enzymes as catalysts. Enzymes allow the system to function in a specific biological reaction under mild conditions. The electro-enzymatic devices can be used as energy conversion system such as HCOO-/O2 biofuel cells and an efficient bioelectrochemical system of the CO2 reduction.

We focused on the catalytic properties of tungsten-containing formate dehydrogenase (FoDH1; EC 1.2.1.2) from Methylobacterium extorquens AM1 to construct a bioelectrochemical interconversion system of HCOO-/CO2. FoDH1 is a heterodimeric soluble enzyme and catalyzes the oxidation of HCOO- to CO2 in coupled reduction of NAD+ to NADH. In this study, we have found that FoDH1 catalyzes both of the HCOO- oxidation and the HCO3
- reduction with several artificial redox partners (mediators). The bi-molecular reaction rate constants between FoDH1 and mediators and show a linear free energy relationship. The reversible reaction between HCOO- and CO2 through FoDH1 has been realized on cyclic voltammetry by using methyl viologen (MV) as a mediator and by adjusting pH from the thermodynamic viewpoint. The steady-state voltammograms with two-way bioelectrocatalytic properties are interpreted on a simple model by considering the solution equilibrium. Furthermore, we have constructed a light driven HCOO- production system using a spinach thylakoid membrane, MV, and FoDH1.

When the interconversion between HCOO- and CO2 is applied to the construction of efficient bioelectrochemical devices, a large current density should be realized at potentials close to the formal potential of the HCOO-/CO2 couple (E°'CO2). We show a great possibility of MET-type bioelectrocatalysis in the HCOO- oxidation and the CO2 reduction at high current densities and low overpotentials. For the HCOO- oxidation, a high limiting current density (j
lim) of about 24 mA cm-
2 was realized with a half wave potential (E
1/2) of only 0.12 V more positive than E°'CO2 at 30 °C in the presence of MV2+ as a mediator. When a viologen-functionalized polymer was co-immobilized with FoDH1 on the porous electrode, j
lim of about 30 mA cm-
2 was attained at 60 °C with E
1/2 = E°'CO2 + 0.13 V. On the other hand, the CO2 reduction was also realized at j
lim of about 15 mA cm-
2 with E
1/2 = E°'CO2 – 0.04 V at pH 6.6 and at 60 °C in the presence of MV. This is the first report of the enzyme-based bioelectrocatalytic CO2 reduction at such low overpotential and a high j
lim.

The present results are very useful to construct an effective bioelectrochemical reaction for the CO2 reduction and HCOO-/O2 biofuel cells as effective energy conversion systems.