bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis, Characterization and Performance Evaluation of Hybrid Multiblock Copolymers for Proton Exchange Membrane Fuel Cells
Authors: Gaur Bharti , Awasthi Swati
Published: February 2020

Present research has been conducted for a new series of multiblock copolymers based on hydrophobic oligomer poly (arylene ether sulfone) containing 6F-bisphenol A and hydrophilic oligomer sulfonated poly (arylene ether ketone) containing pendant carboxylic acid group with varying hydrophobic block length. The ionic liquid is embedded into the synthesized multiblock copolymers to fabricate the hybrid multiblock membranes via solution casting method. The copolymers are characterized by 1H NMR, FT-IR and gel permeation chromatography (GPC) techniques. The thermal stability of the membranes has been investigated through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) thermograms. The ionic synergism between the I.L and the acidic groups present in the multiblock copolymer provides a free pathway for the protons to travel and the resulting hybrid membranes exhibit proton conductivity in the range of (0.03 - 0.16) S/cm at 80 °C. Compared with pristine membranes, the hybrid membranes exhibit improved oxidative and mechanical stability. Moreover, the scanning electron microscopy (SEM) investigation depicts better phase separation in hybrid membranes than pristine membranes by forming ionic clusters. The membranes have been tested in H2/O2 fuel cell and their performance is compared with the state-of-art Nafion 117 membrane. For hybrid membranes, with the addition of I.L, the voltage and power densities values increased up to 0.59 V and 0.23 Wcm-2, respectively. These investigations suggest that the synthesized multiblock membranes are promising candidate for proton exchange membrane fuel cells.
Understanding the Influence of Porosity on Product Selectivity for Copper CO2 Reduction Electrocatalysts
Authors: Fritz Kevin Eugene , Wiesner Ulrich , Suntivich Jin
Published: February 2020

The carbon dioxide reduction reaction (CO2RR) provides a process for producing valuable chemicals and energy-dense fuels from CO2; however, selectively producing a specific high-value product remains challenging. In this contribution, we present our study on how to harness nanoporous morphologies to address this challenge. Our work is driven by several results in literature which have now established that nanoporous morphologies can affect the CO2RR product distribution on Cu catalysts (1-3). To gain insight into this effect, we use model nanoporous Cu catalysts prepared using a self-assembled block copolymer (BCP) template. The BCP-template approach allows precise control over pore size and geometry as well as thickness. Using these structures and the dependence of the product distribution on pore sizes, pH, and mass transport, we will discuss the influence of nanoporous morphologies on the CO2RR efficacy and the implications for future CO2RR catalyst design, particularly within the context of reaction intermediate trapping for selectivity towards high-value products.

References

(1) A. Dutta, M. Rahaman, N. C. Luedi, M. Mohos, and P. Broekmann, ACS Catal.,
6(6), 3804 (2016).

(2) K. D. Yang, W. R. Ko, J. H. Lee, S. J. Kim, H. Lee, M. H. Lee, and K. T. Nam, Angew. Chem. Int. Ed.,
56(3), 796 (2017).

(3) T. Kim, A. Kargar, Y. Luo, R. Mohammed, E. Martinez-Loran, A. Ganapathi, P. Shah, and D. P. Fenning, ACS Appl. Energy Mater.,
1(5), 1965 (2018).
Developing and Understanding BiFeO3 Photoelectrodes for Solar Water Splitting
Authors: Radmilovic Andjela , Choi Kyoung-Shin
Published: February 2020

Hydrogen production by photoelectrochemical water splitting is a challenging and exciting research topic that continues to receive much attention as it is a promising option for meeting the global energy demand. For this technology to compete with fossil fuels, a solar-to-hydrogen (STH) efficiency above 10% must be achieved using an inexpensive and durable photoelectrochemical cell (PEC). Accordingly, our group has been investigating oxide-based photoelectrodes that can be produced via practical solution-based syntheses using inexpensive raw materials. We are specifically interested in developing ternary oxides, which provide more opportunities to tune the composition and atomic/electronic structures of the photoelectrode materials relative to their corresponding binary oxides.

In this presentation, the synthesis and investigation of BiFeO3 photoelectrodes will be discussed. BiFeO3 has a bandgap of ~2.2 eV and appropriate band positions for water splitting; however, it has not been extensively studied for photoelectrochemical applications. BiFeO3 has previously shown both n-type and p-type behavior, meaning it can serve as either a photoanode for water oxidation or photocathode for water reduction, respectively. Here, we will first introduce electrochemical methods to prepare high-quality n-type and p-type BiFeO3 films. We will then discuss the photoelectrochemical properties of the resulting films and present strategies to further optimize the performance of BiFeO3 as both a photoanode and photocathode for use in a water-splitting PEC.
(Invited) Plasmonic Nanocrystal Composites for Photocatalytic Production of Solar Fuels
Authors: Zamkov Mikhail
Published: February 2020

The visible extinction of noble metal nanoparticles surpasses those of semiconductor and molecular dyes by several orders of magnitude. Such superior light-harvesting characteristics are highly attractive for photocatalytic applications. Of a particular interest is the process of the plasmon near-field energy conversion, which is predicted to yield substantial gains in the photocarrier generation. Here, we employ the sample-transmitted excitation photoluminescence (STEP) spectroscopy to determine the quantum efficiency for the plasmon induced resonant energy transfer (ET) in assemblies of Au nanoparticles and semiconductor quantum dots (CdSe, PbS, etc.). The present technique distinguishes the Au-to-QD ET contribution from metal-induced quenching processes thus enabling accurate estimates of the photon-to-exciton conversion efficiency. We show that in the case of 9.1-nm Au nanoparticles, only 1-2% of the Au absorbed radiation is converted to excitons in the surrounding CdSe nanocrystal matrix. For larger, 21.0-nm Au, the photon-to-exciton conversion efficiency increases to 29.5%. The results of present measurements were used to develop an empirical model for estimating the maximum gain in the plasmon-induced carrier generation versus the mass-fraction of Au.
(Invited) Understanding Photoelectrode/Catalyst Interface for Solar Water Splitting
Authors: Wang Dunwei
Published: February 2020

As a potentially low-cost, high-efficiency solar energy storage solution, solar water splitting faces great challenges. One of the issues is the poor catalytic activity and low stability. Applications of co-catalysts have been shown effective to correct the deficiency by promoting desired chemical reactions so as to minimize charge recombination at the surface and to reduce parasitic corrosion reactions. The detailed behaviors of the light absorber/catalyst interface, however, remain poorly understood. Here we present our recent research in this area. We show that the application of the co-catalysts may greatly influence the charge separation behaviors of the photoelectrode. Detailed thermodynamic and kinetic measurements support our understanding. Furthermore, we show that the photoelectrode substrate also exerts great influences on the co-catalyst behaviors. A strong interaction between the photoelectrode and the catalyst can be beneficial. The combined system may also serve as a new platform to understand heterogeneous catalysis such as water oxidation at a level previously inaccessible. The knowledge generated by our work will likely contribute significantly to the development of solar water splitting technology for a future powered by renewable energies.
(Keynote) Stable Mixed-Anion Photocatalysts for Visible-Light-Induced Water Splitting
Authors: Abe Ryu
Published: February 2020

Photo-induced water splitting using semiconductor photocatalysts has attracted considerable attention for producing H2 as a clean energy carrier, while the effective utilization of visible light is imperative to achieve the desired efficiency for practical applications.[1, 2] Recently, mixed-anion compounds such as oxynitrides have been intensively studied as promising candidates since one can expect that higher energy p orbitals of non-oxide anions (e.g., N-2p) elevate their valence band maximum (VBM) values. Unfortunately, most of them are subject to facile self-oxidation by photogenerated holes, while highly dispersed cocatalyst particles certainly improve the stability of some oxynitrides.[3] We have recently demonstrated that Sillén–Aurivillius type perovskite oxyhalides such as Bi4NbO8Cl can stably and efficiently oxidize water to O2 under visible light without any surface modifications, and also exhibits a stable Z-scheme water splitting when coupled with a H2-evolving photocatalyst.[4] It was revealed that the VBMs of these materials consist mainly of O-2p orbitals, instead of Cl-3p (or Br-4p), but their positions are much more negative than those of conventional oxides. [5, 6] Thus, they possess narrow bandgaps for visible light absorption as well as sufficiently negative CBMs for water reduction. DFT calculation visualized a fairly strong hybridization between the Bi-6s and O-2p orbitals, which can explain why the O-2p orbitals are elevated in energy, combined with the result on Madelung site potential analysis that can rationalize the origin of high energy of O-2p orbital in these materials. Since O– anions are known to be relatively stable, photogenerated holes populated at the O-2p orbitals will not lead to self-decomposition but to oxidize water. These results could provide new strategies for developing durable photocatalytic materials for water splitting under visible light, by manipulating the interaction between post-transition metal s orbitals and O-2p orbitals.

[1] R. Abe, J. Photochem. Photobiol. C: Photochemistry Reviews, 11 (2011) 179.

[2] R. Abe, J. Tang et al., Chem. Rev. 118 (2018) 5201.

[3] R. Abe, M. Higashi, K. Domen, J. Am. Chem. Soc., 132, (2010) 11828.

[4] H. Fujito, H. Kunioku, H. Kageyama, R. Abe et al., J. Am. Chem. Soc., 38 (2016) 2082.

[5] D. Kato, H. Kunioku, R. Abe, H. Kageyama et al. J. Am. Chem. Soc., 139 (2017) 18725.

[6] H. Kunioku, H. Kageyama, R. Abe et al., J. Mater. Chem. A, 6 (2018) 3100.

Key Words: Photocatalyst, Semiconductor, Water splitting, Solar energy
(Invited) Element-Specific Measurement of Hole Transport and Kinetics in a Ni-TiO2-Si Photolectrode Using Transient Extreme Ultraviolet Spectroscopy
Authors: Cushing Scott Kevin
Published: February 2020

A passivating oxide layer is critical for the stability and the performance of solar-fuel photoelectrodes. While the semiconductor surface can be passivated by a few nanometer oxide film, the best performance often correlates with a thicker and defect-rich amorphous TiO2 layer. The defect states are suggested to facilitate hole transport between the semiconductor and metal catalyst. In this presentation, transient extreme ultraviolet (XUV) absorption spectroscopy measures the electron and hole transport between each element of a photoexcited Ni-TiO2-Si photoelectrode. The transient changes in the Ni M2,3 edge, Si L2,3­ edge, and Ti M2,3 edge are quantified using a broad-band, high harmonic XUV continuum that spans 30 to 120 eV. Photoexcitation with a 30 fs, 800 nm optical pulse leads to hole tunneling from the p-type Si to the Ni metal. The transport time and electric field indicate a ballistic tunneling through the TiO2 that originates from a Si hole with mobility of ~400 cm2/Vs. An appreciable transfer of photoexcited electrons is not measured. The quantum yield of the hole tunneling is calculated to be ~50% percent by using the photoexcited carrier density in Si and the measured shift in the Ni M2.3 edge Fermi energy. The holes are measured to back-transfer from the Ni to the Si through the mid-gap states in the TiO2 on a picoseconds time scale. The measured kinetics suggest a hole diffusion constant of ~1 cm2/s. The surface recombination velocity of electrons and holes at the Si-TiO2 interface is also quantified as ~200 cm/s. These results suggest that transient XUV spectroscopy can be used to quantitatively measure electron and hole transport in solar-fuel relevant nanoscale junctions.
(Invited) Structure, Composition, Support, and Electrolyte Effects in CO2 Electroreduction
Authors: Roldan Cuenya Beatriz
Published: February 2020

The efficient electrochemical conversion of CO2 (CO2RR) to valuable fuels and feedstocks is a highly sought process towards the minimization of the carbon footprint. However, higher selectivity towards C2+ products must be achieved before a broad industrial use can be envisioned. Better efficiency can be attained by tuning the morphology (size, shape, dispersion), oxidation state, composition of the catalysts, NP/support interactions, and by a rational selection of the electrolyte. In addition, understanding the changes that a catalyst may experience on its surface during a reaction is crucial in order to stablish structure/composition-reactivity correlations. Here, mechanistic insight into CO2RR will be provided by using as target materials size- and shape-controlled mono and bimetallic NPs including Cu, Cu2O, Zn, Cu-M (M=Zn, Co, Pd, Ag, Au) NPs with spherical and cubic shapes as well as Cu2O cubes decorated with monodispersed M nanoparticles on the surface.

A synergistic combination of spectro-electrochemical methods, in situ microscopy (EC-AFM), operando X-ray absorption spectroscopy (XAS) and quasi in situ X-ray photoelectron spectroscopy (XPS) were used to gain insight into the morphological, structural, and chemical transformations underwent by the NPs during CO2RR. I will illustrate that the as-prepared state of the mono and bimetallic NPs is drastically different from the structure and surface composition of the working catalyst.
(Invited) Ultrafast Studies of Self-Assembled Biomimetic Materials, Metal-Organic-Frameworks, and Plasmonic Metamaterials for Solar Light Harvesting
Authors: Wiederrecht Gary
Published: February 2020

Ultrafast photoprocesses can play important roles in light harvesting, such as picosecond excitonic hopping between chromophores, or femtosecond decays of hot (nonthermal) carriers in plasmonic metamaterials following photoexcitation. In this talk, I focus on ultrafast photoprocesses in nanostructured materials of interest for light harvesting. In particular, ultrafast light harvesting processes in three types of materials are described. I describe the design of new biomimetic nanostructures for light harvesting involving the use of chromophore-doped peptide amphiphiles to create varied and potentially self-healing structures for transporting energy. Through environmental controls, unique opportunities for tuning the structural shape of the self-assembled materials are possible, thereby altering the resultant energy transport properties. The dependence of excitonic transport on chromophore concentration is described. The second topic is that of exploring light harvesting in metal-organic-frameworks using porphyrin building blocks. Efforts to characterize the degree of anisotropy (directionality) in exciton flow as well as distance of exciton migration are described. Finally, I describe the study of plasmonic metamaterials, where nanostructuring and the creation of “gap-plasmons” dramatically increases the number of hot carriers produced under illumination. Our efforts to spectroscopically characterize the production and decay of hot carriers with variations in size, shape, and composition are shown. Physical insights into how to extract the hot carriers before loss of energy to thermalization is given. 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.
Enhanced Electroreduction of Carbon Dioxide to Methanol Using Zinc Dendrites Pulse-deposited on Silver Foam
Authors: Low Qi Hang , Loo Nicholas Wei Xian , Calle-Vallejo Federico , Yeo Boon Siang
Published: February 2020

The electrocatalytic CO2 reduction reaction (CO2RR) can dynamize the carbon cycle by lowering anthropogenic CO2 emissions and sustainably producing valuable fuels and chemical feedstock. Methanol is arguably the most desirable C1 product of CO2RR, although it typically forms in negligible amounts. In our search for efficient methanol-producing CO2RR catalysts, we engineer Ag-Zn catalysts by pulse-depositing Zn dendrites on Ag foams (PD-Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO2 to CH3OH, while their alloys gave CH3OH with Faradaic efficiencies (FE) of ~1%. Interestingly, with nanostructuring, PD-Zn/Ag foam reduces CO2 to CH3OH with FE and current densities reaching as high as 10.5% and -2.7mA/cm2, respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO2RR to CH3OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity.

https://doi.org/10.1002/anie.201810991

Figure 1
(Invited) Atomically Dispersed Eletrocatalysts for High-Efficiency Ambient N2 Fixation
Authors: Han Lili , Liu Xijun , Lin Ruoqian , Liang Zhixiu , Stavitski Eli , Luo Jun , Adzic Radoslav R. , Xin Huolin L.
Published: February 2020

NH3 synthesis by the electrocatalytic N2 reduction reaction (NRR) under ambient conditions is regarded as an appealing alternative to the industrial method that requires high temperature and pressure. Finding a material that can efficiently catalyze electrochemical N2 fixation at ambient condition is a subject of considerable current interest. Atomically dispersed catalysts with mononuclear metal complexes or single metal atoms anchored on supports would be a promising candidate, because of their maximum atom efficiency, unique catalytic performances, and the similarity of the metal coordination environment to the ligand fields in molecular catalysts. A series of cost-effective and optimized atomically-dispersed eletrocatalysts for NRR will be reported. Our results show that the catalysts are featured with high density of single metal atoms supported on hierarchically porous carbon frameworks. They exhibited remarkable selectivity of NH3 formation and high NH3 yield rate at low applied potentials at room temperature. Moreover, the catalysts show negligible activity decay in an NRR electrolysis as long as 50,000 s. On the basis of our results and the previously reported work, a possible mechanism for NRR on the catalyst will be proposed to provide a fundamental insight into the high-efficiency NRR.
Design of Materials for Electroreduction of Nitrogen to Ammonia: A Computational Perspective
Authors: Matanovic Ivana , Garzon Fernando H
Published: February 2020

Theoretical studies and computational modeling play a key role in predicting various properties of catalytic materials, including their activity and selectivity towards a desired electro-catalytic pathway. In the last decade, density functional theory calculations have been used to study the activity and selectivity of various materials for the nitrogen electroreduction, an extremely important aspect in the development of novel technologies for the ammonia synthesis. However, the design of an ideal electro-catalyst that exhibits high activity for nitrogen reduction to ammonia while at the same time suppresses the competing hydrogen evolution reaction is still an ongoing pursuit.

Here we will use the example of molybdenum nitride and molybdenum carbide to illustrate different aspects in the design of materials for nitrogen electroreduction to ammonia and discuss different challenges associated with this effort [1, 2]. We will first present calculations of free energy diagrams and kinetic volcano plots aimed at understanding the activity of different surfaces of the molybdenum nitride (Mo2N) and molybdenum carbides (MoC and Mo2C) towards hydrogen evolution reaction and nitrogen electroreduction to ammonia. Secondly, we will discuss the thermodynamics calculations directed towards understanding the stability of these materials at different cell potentials and pH. Namely, our results show that at the nitrogen reduction potentials the catalytic surface can be covered with the H-adatoms rather than the N-adatoms. In addition, the carbides and nitrides can be converted to oxynitrides or oxides, which can lead to the decrease in the activity and durability of the catalytic material. Molybdenum carbides and nitrides will be used to illustrate how computational modeling can direct the design of the active sites with highest efficiency for nitrogen reduction to ammonia, but also support the optimization of reaction conditions to ensure the catalyst durability.

[1] I. Matanovic, F. H. Garzon, and N. J. Henson, Electro-reduction of Nitrogen on Molybdenum Nitride: Structure, Energetics, and Vibrational Spectra from DFT, Phys. Chem. Chem. Phys. 2014, 16: 3014-3026.

[2] I. Matanovic and F. H. Garzon, Nitrogen Electroreduction and Hydrogen Evolution on Cubic Molybdenum Carbide: A Density Functional Study, Phys. Chem. Chem. Phys. 2018, 20: 14679-14687.
Electrochemical Synthesis of Ammonia Using Origami-like Molybdenum Carbide Nanoflakes As Nitrogen Reduction Reaction Catalyst
Authors: Ramaiyan Kannan Pasupathikovil , Ozden Sehmus , Maurya Sandip , Komini Babu Siddharth , Benavidez Angelica D , Garzon Fernando H , Kim Yu Seung , Mukundan Rangachary , Kreller Cortney R.
Published: February 2020

Ammonia plays a crucial role in feeding the majority of today’s population and its production has increased from a few thousand tons per year in 1908 to above 100 million tons per year today, revolutionizing the fertilizer industry thanks to the Haber-Bosch (HB) process. However, the HB process is highly energy intensive consuming about 1.4 % of the fossil energy generated worldwide and releasing 1.87 tons of the greenhouse gas CO2 into the environment per ton of ammonia synthesized. Hence, finding alternative and energy efficient ways to synthesize ammonia under milder conditions is important from more than one perspective. The challenge associated with NH3 synthesis from its constituent nitrogen and hydrogen gases is breaking the strong N≡N bond (947 kJmol-1). While heterogeneous catalytic synthesis needs high temperature and pressure operation, electrochemical synthesis routes offer a milder approach. However, electrochemical synthesis of ammonia under different temperatures, utilizing different electrolytes and catalysts has not yet reliably produced ammonia at viable rates and efficiencies. We report a Mo2C cathode catalyst for ammonia synthesis that has demonstrated synthesis rates on the order of 2x10-12 molcm-2s-1 for more than 24 hours at 30 °C using Nafion 212 as the electrolyte and Pt/C as the anode. The β-Mo2C has a hexagonal lattice structure with an origami-like morphology containing numerous kinks which may improve its electrocatalytic activity. The maximum synthesis rate was obtained at -0.5 V, however, the faradaic efficiency decreased with increasing over-potential. This catalyst offers a promising alternative for producing ammonia especially with electrolytes that conduct protons under dry conditions. This presentation further covers the utility of Nafion as an electrolyte for electrochemical ammonia synthesis.

References

1. P. Ramaiyan, M. Sandipkumar, A. D. Benavidez, S. K. Nayak, Y. S. Kim, F. H. Garzon, R. Mukundan, C. R. Kreller, Meeting Abstracts 2018, MA2018-01 2012 1.

2. D. Benavidez, S. K. Nayak, E. Coker, F. H. Garzon, Meeting Abstracts
2018, 1.

3. Matanovic, F. H. Garzon, Phys Chem Chem Phys 2018, 20, 14679.
Removal of Nitrate and Ammonia from Wastewater
Authors: Bagheri Hariri Mohiedin , Botte Gerardine G.
Published: February 2020

Ammonia and nitrate contamination of groundwater, surface water, and other water resources is considered a serious environmental and human health issue that causes several problems like algae bloom, fatal illnesses specially for the infant under 6 months. Electrochemical techniques for ammonia oxidation and nitrate reduction reactions are usually straightforward, energy-efficient, environmentally-friendly, and easy to control.

Electrochemical techniques for separate removal of ammonia and nitrate has been extensively studied. However, in this work, we demonstrate a new process that addresses both water pollutants simultaneously in a single cell that leads to a considerable energy saving in the order of 90 % and 35-65 % less energy per grams of ammonia and nitrate removal, respectively. A new flow cell with novel electrode architectures is introduced to perform both ammonia/nitrate removal simultaneously. The concentration of nitrate and ammonia were measured according to the Environmental Protection Agency (EPA) standards which is a UV-vis spectrophotometric based technique, and ammonia Ion Selective Electrode (ISE-THERMO), respectively. Effect of electrode loading and other process variables on the ammonia and nitrate removal rates were evaluated. Findings of this work will be presented at the meeting.
Direct Ammonia-Fueled Solid Oxide Fuel Cells
Authors: Tao Greg
Published: February 2020

Ammonia, as a hydrogen carrier, has a much higher volumetric energy density than hydrogen and can be safely handled and distributed in a liquid form at an ambient temperature with a pressure greater than 1MPa. Similar to hydrogen, a clean-burning ammonia potentially can be used for power generation with zero greenhouse gas emissions. A Solid Oxide Fuel Cell (SOFC), typically operating at a temperature of 700ºC – 900ºC, has been widely acknowledged by the R&D society for a direct conversion of chemical energy of fuels (e.g. hydrocarbon fuels, ammonia, etc.) into electricity at a proven efficiency as high as 60%. Lowering the SOFC operating temperature to 700°C or below potentially enables considerable cost reduction with opportunities of using inexpensive materials for constructing SOFC systems that otherwise could not be considered. However, the corresponding SOFC inevitably faces challenges of higher electrode polarization losses and electrolyte ohmic losses, as well as reduced electrode catalytic activities.

Chemtronergy is actively pursuing the development of the anode-supported SOFC technology capable of operating directly on the ammonia fuel at a temperature below 650ºC for reliable power generation. This talk will cover discussions of cell materials design and ammonia catalyst consideration for the mitigation of the increased polarization losses and ammonia reaction with the nickel-based anode, respectively, caused by lowering operating temperatures. Materials implementation and validation on both button cells (2 cm2) and single cells (100 cm2) over time will also be presented.
(Invited) Probing the Structure and Dynamic Behaviors of Heterogeneous Functional Materials with the Atomic Resolution in Real-Time
Authors: Pan Xiaoqing
Published: February 2020

The recent advancement of aberration-corrected transmission electron microscopy (TEM) and in situ techniques unlocks a door to a new era of discovery in materials science. It allows us to study the local structure, chemical composition, and electronic properties of nanostructures with the atomic resolution, and observe the dynamic evolution of materials in response to applied fields and to changes in environments in real-time. In this talk, I will present our work on the development of in-situTEM techniques for imaging electric polarization, probing the nucleation and growth of ferroelectric domains during electric polarization switching, and observing thedynamic reaction and structural evolution of heterogeneous functional materials under realistic conditions with atomic precisionthrough a MEMS-based, electron-transparent closed cell with a heating stage.
(Invited) How Ti Modifies Oxygen Electro-Adsorption and Oxygen Evolution Reaction on IrO2(110) and RuO2(110) Surfaces
Authors: Kuo Ding-Yuan , Nelson Jocienne N. , Paik Hanjong , Shen Kyle M. , Schlom Darrell G. , Suntivich Jin
Published: February 2020

We present our measurements of the oxygen electro-adsorption and oxygen evolution reaction (OER) on well-defined Ir1-xTixO2(110) and Ru1-xTixO2(110) surfaces grown using molecular-beam epitaxy. The motivation of this contribution is to reveal the role of Ti on the OER electrocatalysis on IrO2 and RuO2. The slow kinetics of the OER is currently the largest source of overpotential (inefficiency) in water-splitting devices. An OER catalyst can reduce this overpotential by stabilizing the OER intermediates via surface electro-adsorption. We study how the Ti addition can impact this capability on IrO2 and RuO2. To understand the effect, we measure the oxygen electro-adsorption and OER on Ir1-xTixO2(110) and Ru1-xTixO2(110) as a function of Ti. Then, using the relationship between the oxygen electro-adsorption, the OER electrocatalysis, and the Ti content, we develop a physical model to explain how Ti affects the OER kinetics from the perspective of the current electrocatalysis theory. We provide possible explanations on why Ti can be sometimes beneficial for the OER and sometimes not. Finally, we will discuss how to design an OER catalyst with distinct cooperative sites to achieve high OER activity in the future.
Triple Conducting Perovskite Oxide Nanocomposites As Oxygen Electrodes for Intermediate-Temperature Protonic Ceramic Cells
Authors: Tong Jianhua "Joshua" , Zhao Zeyu , Mu Shenglong , Zou Minda
Published: February 2020

Protonic ceramic cells (PCCs) based on proton conducting (PC) electrolyte membranes have great potential to be operated at intermediate temperatures of 300-600oC because of the low activation energy for the proton transportation, which allows much more efficient, reliable and cost-effective operation of fuel cells and electrolysis cells. However, the conventional mixed ionic and electronic conducting (MIEC) oxygen electrodes showed sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics because the involvement of water limited the ORR/OER to triple phase boundaries, which resulted in unacceptably poor PCC performance. The triple (proton, oxygen ion, and electron) (TPOE) conducting microcomposite oxygen electrodes comprised of PC and MIEC microphases were studied by mixing well-known phase-pure PC and MIEC powders. Although the ORR/OER performance was improved, the solid-state reactions between PC and MIEC microphases to arrive thermodynamic equilibrium significantly degraded the performance. Furthermore, the microsized distribution of the TPOE conductivities among the microcomposites still is the dominant obstacle for improving ORR/OER performance in the intermediate temperatures range. Recently, the new phase-pure perovskite and perovskite-related oxides with TPOE conductivities were developed as oxygen electrodes for PCCs, which showed significant improvement of the ORR/OER performance because the whole electrode surface area was activated for ORR/OER. However, it is well-known that the adjustment of multiple dopants for achieving proper TPOE conductivities is very difficult. In the current work, we designed a new type of TPOE nanocomposite electrodes comprised of PC and MIEC perovskite nanophases. The dual perovskite nanocomposite (DPNCs) were fabricated using a one-pot polymeric gelation synthesis method starting from solutions of componential metal ions. The resulted DPNCs showed thermodynamically stable nanostructures with the nanosized distribution of TPOE conductivities. The superior ORR/OER performance to the state-of-the-art PCC oxygen electrodes (i.e., phase-pure TPOE perovskite oxide of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ) was demonstrated based on both symmetrical cells and single cells. The architecture of the triple conducting perovskite oxide nanocomposite oxygen electrodes from nanophase basic building blocks (N3Bs) can be extensively used for the development of other components of the energy conversion and storage devices.
Freeze Casting of Tubular Anode Supports for High-Performance Solid Oxide Fuel Cells
Authors: Panthi Dhruba , Woodson Theo , Du Yanhai
Published: February 2020

Freeze casting method has received significant attention in recent years for the fabrication of porous materials with unique pore geometries. A typical freeze casting process involves freezing of a liquid suspension forming solvent crystals that grow in the direction of solidification. When these solvent crystals are removed by sublimation under a reduced pressure, a porous structure with unidirectional and gradient pores is achieved. Such a porous structure is considered ideal for solid oxide fuel cell (SOFC) electrodes because it allows for rapid gaseous diffusion through the bulk of the electrode and a large number of active sites toward the electrolyte–electrode interface for electrochemical reactions. In the present work, we developed a freeze casting and freeze drying process to fabricate tubular SOFC anode supports using an aqueous NiO–yttria-stabilized zirconia (YSZ) slurry. Freeze casting was performed in an aluminum mold that contained peripheral coils for flowing a coolant. After complete freezing of the slurry, the mold was connected to a vacuum chamber for freeze drying. With a proper control of the experimental setup and adjustments in the freeze drying profile, we were able to reduce the total drying time from several days to a few hours. The fabricated anode supports were coated with the thin layers of YSZ electrolyte and strontium-doped lanthanum manganite (LSM)-YSZ cathode to obtain the single cells. The electrochemical performance of the single cells was evaluated by the I–V polarization curves and electrochemical impedance spectra. Owing to the favorable gas transport properties of the freeze-cast anode, the concentration polarization was found to be greatly reduced and thus a high power density was achieved.

Figure 1
Effect of Nanoparticle Impregnation on Ni-YSZ Cermet Electrode Polarization Using YSZ-Supported Cells
Authors: Mo Boshan , Gasper Paul Joseph , Lu Yanchen , Basu Soumendra Nath , Pal Uday Bhanu , Gopalan Srikanth
Published: February 2020

Impregnation of nanoparticles is a solution for increasing the electrocatalytic performance of Ni-yttria stabilized zirconia (YSZ) cermet electrodes in solid oxide fuel cells (SOFCs) and electrolysis cells. The electrocatalytic activity is related to the density of triple phase boundaries (TPBs) within the active layer of the cell. Within the anode active layer (AAL), the TPB density is limited by the feature size of the Ni-YSZ scaffold, which is on the order of microns. Impregnation of nickel nanoparticles with diameters of less than 100 nanometers within the AAL has been shown to improve electrocatalytic activity. However, there is a trade-off between the volume of impregnated nickel particles and the pore volume within the electrode. Infiltration reduces pore volume, slowing gas-phase mass transfer within the AAL and increasing concentration polarization. Another consideration is that impregnated nanoparticles are effective only if they are electrically connected to the Ni-YSZ scaffold. In this work, the impregnation of a second phase is used to fulfill two objectives: anchoring the nickel nanoparticles to prevent coarsening, and providing an electrical path from the nanoparticles to the scaffold. The goal of this study is to find the best electrode performance by comparing cell polarizations while varying nanoparticle impregnation parameters to control nickel loading and nickel particle size. Electrode polarization is measured using EIS on impregnated symmetric cells supported on YSZ substrates in a single atmosphere chamber, at varying gas compositions and temperatures. The microstructure of impregnated electrodes is quantified using analysis of SEM fracture cross-sections. By correlating the morphology of impregnated electrodes with electrode polarization, an optimal procedure for the impregnation of nickel nanoparticles into Ni-YSZ cermet electrodes can be determined for use in anode-supported Ni-YSZ SOFCs.
(Invited) Low Ionic Resistance Radiation-Grafted Cation- and Anion-Exchange Membranes for Reverse Electrodialysis (salinity gradient power) Application: Cross-Linking Is Essential for High Permselectivities.
Authors: Willson Terry , Bance-Soualhi Rachida , Hamerton Ian , Varcoe John R.
Published: February 2020

Reverse electrodialysis (RED) cells are a form of salinity gradient power technology where electrical energy can be recovered from the mixing of waters of differing salinities. RED cells require both cation- and anion-exchange membranes (CEM and AEM, respectively) in order to operate.

This presentation details the development of radiation-grafted (RG) CEMs and AEMs, which were evaluated for ex situ resistances (conductivities) and permselectivities. Trends between ex situ properties will be discussed (e.g. room temperature Na+ conductivities (in water) are higher with RG-CEMs that possess higher gravimetric water uptakes, see Figure).

It is clear that RG-CEMs and RG-AEMs are desirably low resistance. However, non-crosslinked RG-CEMs and RG-AEMs have permselectivities that are too low for application in RED cells. However, the addition of crosslinking (either via the addition of divinyl-monomers, such as BVPE, or through the use of difunctional amination agents, such as N,N,N',N'-tetramethylhexane-1,6-diamine) leads to higher permselectivity types.

Therefore, we conclude that cross-linking is essential for the production of RG-ion-exchange membranes with high permselectivities for such application.

Figure 1
On the Potential of 3D Printed Micro Structured Porous Media to Enhance PEM Fuel Cell Performance
Authors: Schulz Volker Paul , Schmitz Sven , Auvity Bruno , Starke Thomas
Published: February 2020

Over the last years, the additive manufacturing of metals with resolutions down to 50 µm has matured to be used in large-scale production [1]. The Germany-based company 3D MicroPrint uses the selective micro laser sintering (µSLS) together with extremely fine (Ø<5 µm) metal powder to generate micro structured parts.

3D MicroPrint is an industrial partner in a research project where the µSLS is used to manufacture different parts of polymer membrane electrolyte fuel cells (PEM-FC).

PEM-FCs are promising electrochemical devices for zero emission power sources. The transport of hydrogen and oxygen towards the reaction side and the removal of the produced water are essential for the PEM fuel cell performance. This gas transport towards the membrane electrode assembly (MEA) is governed by convection in flow channels of a bipolar plate and by diﬀusion in gas diffusion media (GDL).

In conventional PEM-FCs, the bipolar plates are either punched metal sheets or milled graphite plates. Standard GDLs are based on carbon paper which is treated with Polytetraﬂuoroethylene (PTFE).

In this study, we show a new approach to build up the gas supporting structures of PEM-FCs. Using the µSLS, there is an entirely new design space to build up the micro geometries of flow channels and gas diffusion. Additionally, the bipolar plate and the GDL can be combined and manufactured as a single part a so-called membrane separator.

In this contribution, we present different realizations of homogeneous and heterogeneous µ-3D printed parts used for as transport layers in PEM-FCs together with measured data on the fuel cell performance. One example of a homogeneous periodic structure used as GDL is shown in Fig. 1.

Based on these results, we outline the potential of additive manufactured microporous metal parts for PEM-FC applications.

Figure 1
(Invited) Elucidating Ion Transport Mechanisms in Polymerized Ionic Liquids
Authors: Liu Hongjun , Paddison Stephen J.
Published: February 2020

Poor ionic conductivity typically hinders the utilization of ion containing polymers from functioning as a single ion conductor for energy storage or conversion applications. A provocative sub class of these materials are polymerized ionic liquids (polyILs) which have the potential to combine the desirable ion transport of an ionic liquid with the favorable mechanical properties of a polymer. However, the room temperature conductivity of polyILs is usually 2 or 3 orders of magnitude lower than that of low molecular weight ionic liquids, yet a decoupling of conductivity and structural dynamics in polyILs demonstrates the opposite at the normalized glass transition temperature (T
g/T). This seemingly conflicting observation can be reconciled by the fact that polyILs have higher T
g and lower dielectric permittivity at the same T
g/T than their molecular counterparts. Moreover, ionic conductivity of polyILs is found to be significantly slower than ion diffusion. Inverse Haven ratio shows a strong temperature dependence: saturating at 0.2 at higher temperature and decreasing at lower T. Pronounced reduction in conductivity is attributed to the cross correlation between the mobile ions since the ion pair diffusion is infeasible in polyILs. This speculation remains unverified.

We have recently undertaken atomistic molecular dynamics (MD) simulations to elucidate transport mechanism in polyILs and demonstrate the dynamical heterogeneity and cooperative motion of ion transport in polyILs establishing for the first time quantitative evidence of mobile ion hopping. The hopping of anions is found to be dominantly interchain in nature and is generally facilitated by five associating cations from two different chains. Intrachain hopping was found to be much less significant being mediating with fewer chains. The mobile anions tend to form string-like structures and move cooperatively; and the string length of concerted motion of mobile anions increases with decreasing temperature. Our results reveal the important role of a distance criterion in defining hopping events to correctly elucidate the components of the ion transport mechanism. This molecular-level information will provide an important step in both rationalizing experimental observations and the design of novel ion-containing polymers with superior transport properties.
Characterization of Surface Changes on Molybdenum Nitride Thin Films during the Oxygen Reduction Reaction Using Operando Grazing Incidence X-Ray Absorption Spectroscopy
Authors: Stevens Michaela Burke , Kreider Melissa E. , Gibbons Brenna M. , Gallo Alessandro , Mehta Apurva , Davis Ryan , King Laurie A. , Jaramillo Thomas F.
Published: February 2020

Coupled water electrolysis systems and proton-exchange membrane fuel cells (PEMFC) are a promising technology for clean energy storage and conversion, respectively.1 The efficiency of the hydrogen PEMFC is limited, in part, by the poor performance of catalysts for the oxygen reduction reaction (ORR). Due to problems with low activity and conductivity, the majority of non-platinum group catalysts for the ORR are conductive-carbon-supported nanoparticulate transition metal nitrides and/or carbides. It is difficult to determine the active surface of these catalysts during reaction conditions due to their high surface area, inhomogeneous size and distribution, complicated support-catalysts interactions, and surface oxidation in air. To overcome these complications, our work has focused on the operando structural and compositional characterization of the surface of active molybdenum nitride thin films. These films, prepared via reductive sputtering,2 are an ideal template for study due to their tunable thickness, lack of carbon support, moderate electrical conductivity, and well-defined surface. Using a specifically designed electrochemical cell for grazing incidence x-ray absorption and diffraction, we have been able to characterize changes in our Mo
x
N surface under ORR conditions. These same surface changes are not apparent at similar non-ORR reducing conditions, supporting our hypothesis that we are characterizing the active surface during ORR.
­
This work highlights the role of nitrogen, oxygen vacancies, and electrical conductivity on electrochemical activity and allows us to probe the structure and thickness of the active surface layer as well as the active site geometry. Understanding the role and importance of nitride bulk and the distinct surface structure will allow us to re-think our typical rational design of catalyst materials and help us design more active and stable catalysts in the future.

References

(1) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Combining Theory and Experiment in Electrocatalysis: Insights into Materials Design. Science (80-. ).
2017, 355, 1–12.

(2) Hones, P.; Martin, N.; Regula, M.; Francis, L. Structural and Mechanical Properties of Chromium Structural and Mechanical Properties of Chromium Nitride , Molybdenum Nitride , and Tungsten Nitride Thin Films. J. Phys. D Appl. Phys.
2003, 36, 1023–1029.
Design and Fabrication of Solid Electrolyte for the Prevention of Electrode/Electrolyte Delamination
Authors: Son Min Ji , Lim Hyung-Tae
Published: February 2020

The stability of a solid oxide cell is strongly dependent on the magnitude and profile of internal chemical potential of solid electrolyte. If internal partial pressure is abnormally high, the electrolyte can be delaminated from the electrodes. The formation of high internal pressure is attributed to very low electronic conduction in solid electrolyte. This phenomenon can be significant when the cell is subjected to abnormal operation conditions such as a negative cell voltage. Herein, we suggest a new design of single layer solid electrolyte having local electronic conduction for the prevention of electrode/electrolyte delamination. YSZ and (NiO + YSZ + CeO2) were prepared as electrolyte and anode functional layer, respectively, and these layers were co-sintered at a high temperature, leading to diffusion of cerium ion into YSZ electrolyte. EDS analysis revealed that electronic conduction was locally developed at the anode/electrolyte interface region. The cells were tested under a negative voltage condition using potentiostat. The results indicate that the addition of electronic conduction in the electrolyte can effectively depress internal pressure and prevent anode/electrolyte delamination.
(Invited) Hybrid Li-Ion and Li-O2 battery Enabled By Oxyhalogen-Sulfur Electrochemistry
Authors: Wang Xuefeng , Meng Ying Shirley
Published: February 2020

The large voltage hysteresis between charge and discharge results in significant energy loss which hinders practical application of the high-energy Li-O2 battery. The oxyhalogen-sulfur electrochemistry offers a new hybrid Li ion/Li-O2 battery, where both Li ions and O anions are reversibly stored in the MoS2structure. A new Li2MoO2S2 compound is formed as the main discharge product that has never been observed in the literature before. The reaction mechanism and the structure of the Li2MoO2S2 are probed by the Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), differential electrochemical mass spectrometry (DEMS) and Ultraviolet-visible (UV) spectroscopy. The results show that the MoS2 is oxidized during discharge and is recovered during charge. Theiodine intermediatesplay an important role in triggering the sequence of electrochemical and chemical reactions in the cell. The Li2MoO2S2 is isostructural to the Li2MoO4 rather than adopts structures of other known molybdenum oxysulfides.