bluuebunny/crossref_metadata_2025 huggingface dataset:
Understanding and Optimizing Aqueous Viologen Bromide Redox-Enhanced Electrochemical Capacitors
Authors: Evanko Brian , Yoo Seung Joon , Chun Sang-Eun , Vonlanthen David , Wang Xingfeng , Ji Xiulei , Boettcher Shannon Wachter , Stucky Galen
Published: February 2020

Research in electric double layer capacitors (EDLCs) and rechargeable batteries is converging, producing devices known as pseudocapacitors. Pseudocapacitors store energy electrochemically, utilizing fast and reversible faradaic redox reactions at the interface between high surface area electrodes and an electrolyte. The result is a technology that delivers a long cycle life, high specific power, and moderate specific energy. One frontier in pseudocapacitor research is redox-active electrolytes, which replace the traditional solid redox-active materials with soluble redox couples.

Here we have identified viologen bromide salts as promising aqueous redox-active electrolytes for redox-EDLCs.[i] During charging, Br- is oxidized to Br3
- at the positive electrode and the viologen dication (V2+) is reduced to the stable monocation radical (V+•) at the negative electrode (Figure 1). The system shows unusually high coulombic efficiency and low self-discharge rates for an aqueous redox-supercapacitor. This was initially attributed to strong adsorption of the Br3
- and V+• to the activated carbon electrodes, but we now present a more detailed analysis that confirms the behavior is attributable to two electroprecipitation mechanisms. In these mechanisms, each ion acts as a charge-storing redox couple at one electrode an as a complexing agent at the other electrode. The processes are highly reversible and cells show negligible capacity fade even after 20,000 cycles. The devices use conventional activated carbon electrodes, and because crossover is not a concern and self-discharge is suppressed, a simple cellulose separator is sufficient and ion-selective membranes are not required.

Heptyl viologen devices achieve specific energy densities of 11 Wh/kg (normalized to the mass of both electrodes and electrolyte), significantly higher than commercially available EDLCs (Figure 2). Using methyl viologen increased specific energy to 14 Wh/kg, but at the expense of cycling stability. By studying the operating mechanisms and synthesizing a large series of viologens with different alky substituents we have now identified viologens that deliver both the stability of heptyl viologen and the specific energy of methyl viologen. Finally, a simple electrochemical device model was developed to understand the behavior of the system and predict the maximum theoretically achievable performance (Figure 3). The results model experimental data well and suggest that significant performance improvement is possible, making this technology an exciting candidate for applications like automotive engine start-stop and grid-scale energy storage.

[i] S.-E. Chun, B. Evanko, X. Wang, D. Vonlanthen, X. Ji, G. D. Stucky, and S. W. Boettcher, “Design of aqueous redox-enhanced electrochemical capacitors with high specific energies and slow self-discharge,” Nat. Commun., vol. 6, p. 7818, 2015.

Figure 1
Cobalt-Nickel Sulfide and Graphite-Coated Iron Carbide As Potential Materials for High-Performance Asymmetric Supercapacitors
Authors: Khani Hadi , Wipf David O
Published: February 2020

Nanostructured metal sulfides and carbides have recently attracted much attention in many energy storage and conversion applications. In this study, we report the fabrication of an asymmetric supercapacitor with high energy and power density based on carbon fiber@CoNi2S4 nanosheets as a positive electrode and nickel foam@graphite-coated Fe3C nanocomposite as a negative electrode in aqueous KOH electrolyte. CoNi2S4 nanosheets were electrochemically deposited on the carbon fiber cloth via a one-step square-wave pulsed potential technique from a dilute solution of metal ions and thiourea as an ion complexing agent and sulfur source. The high conductivity, surface area, and redox reversibility of the self-support CoNi2S4 nanosheets on carbon fiber make it a promising pseudo-supercapacitor positive electrode. Graphite-coated iron carbide (Fe3C) nanocomposites have been synthesized via a facile two-step heating procedure from the aqueous solution of Fe(III)-citric acid complex. The formation mechanism of Fe3C from the Fe(III)-citric acid complex is investigated by characterizing the starting, intermediate, and final materials by thermogravimetric analysis, X-ray diffraction spectroscopy (XRD), and IR spectroscopy techniques. The morphology and nanostructure of each electrode material are systematically investigated by scanning electron microscopy, transmission electron microscopy, XRD, Raman spectroscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry was carried out on each individual electrode in the asymmetric supercapacitor assembly to study the charge transfer mechanism. All CVs show two well-defined redox peaks, corresponding to the reversible Faradaic redox reactions of Fe(III)/Fe(II) and CoNi2S4 /CoS2xOH-Ni2S4-2x at the negative and positive supercapacitor electrodes, respectively. The result of galvanostatic charge-discharge tests in a three-electrode system exhibit a high specific capacitance of 582 F g-1 and 2302 F g-1 at 1 A g-1 and 1026 F g-1 and 2180 F g-1 at 20 A g-1 at the negative and positive supercapacitor electrodes, respectively. The optimized asymmetric supercapacitor was reversibly cycled in the high-voltage region of 0-1.6 V and displayed intriguing performances with a specific capacitance of 262 F g−1, high energy density of 94 Wh kg−1, and high power density of 16.1 kW kg−1. Moreover, the supercapacitor exhibits excellent rate capability and retains a high capacity after the hundreds of cycles. These fascinating performances can be attributed to the positive synergistic effects of the two electrodes. These results suggest that carbon fiber@CoNi2S4 nanosheets and nickel foam@graphite-coated Fe3C nanocomposite are very promising for next generation high-performance supercapacitors.
(Invited) Pyrrole-Based Polycyclic Pi-Electron Systems with Various Redox States
Authors: Takase Masayoshi
Published: February 2020

We have recently reported a series of pyrrole-fused azacoronenes. Due to the interior nitrogen atoms and various resonance forms, all azacoronenes showed multiple oxidation states with different electronic properties. On the basis of these results, a pyrrole-fused azacoronene functionalized with carbonyl groups was designed and synthesized. From the ESR and crystal structure analyses, the azacoronenes revealed spin-delocalized diradical nature in the neutral state. The CV results showed multistep oxidation and reduction peaks. The band gap is very small and the absorption spectra tailed near-infrared region. Pi-extended systems over the previous azacoronenes were also obtained using a similar synthetic strategy. Some crystal structure analyses revealed highly contorted structures. In the presentation, we will report the synthesis, structures, and basic physical properties.
(Invited) Supramolecular Porphyrin Copolymer Directed By Host-Guest Interactions and Metal Coordination
Authors: Haino Takeharu
Published: February 2020

A bisporphyrin cleft molecule with a trinitrofluorenone moiety assembled to form supramolecular polymers through a head-to-tail host-guest interaction. Bispyridine derivatives work as interchain cross-linkers among the supramolecular polymer chains. The supramolecular networked polymers showed characteristic solution viscosity that revealed the formation of the entangled supramolecular polymers. Viscoelastic spectroscopy established that the supramolecular polymers resulted in well-entangled solutions with associating and networking polymers. Morphological transition of the supramolecular polymers was given by AFM images. The non-cross-linked polymer gave rise to wide-spread thin networks while the cross-linked networks resulted in thicker worm-like nanostructures. The supramolecular networks gelled in 1,1,2,2-tetrachloroethane, and an elastic free-standing film was fabricated with a Young's modulus of 1 GPa.

In this presentation, I will describe the synthesis and characterization of newly developed supramolecular porphyrin polymer, and macroscopic features.

1)    Kinjo, K.; Hirao, T.; Kihara, S.-i.; Katsumoto, Y.; Haino, T. Angew. Chem. Int. Ed.
2015, 54, DOI: 10.1002/anie.201508475.

Figure 1
Simple and Economic Paper Based Graphitic Touch-Pad for Multipurpose Applications
Authors: Bhattacharjee Mitradip , Bandyopadhyay Dipankar
Published: February 2020

Most of the electronic gadgets need a human intervention for interaction, for example, a keyboard for a computer or a keypad for an ipad or mobile phone. The presently available technologies are expensive and extensive research effort is directed towards developing devices that are radically economic. The present innovation employs economic materials to compose a high sensitivity touchpad, which possesses the potential to replace existing non-economic keyboards or keypads. The resistive touchpad reported here is based on paper, graphite, and polymer PDMS. While the graphite coated layers act as conductive layers in the touchpad, PDMS acts as a protective and transparent coating on the proposed device. This transparent coating also applied as dielectric spacer between two graphite coated papers. In the proposed touchpad, the location of ‘touch’ is determined from the output electrical resistance of a particular place because the output resistance differentiates the particular location to be determined. The proposed touchpad is consists of two flexible resistive sheets made of paper, which eventually enables the making of a touchpad with flexible sides. Since the touchpad is composed of a pair of resistive sheets in which, at any time, at least one of the sides is free for user to ‘touch’ in such a manner that the pad brings a portion of one of the resistive surface in contact with the other resistive surface. The paper based resistive sheets contain conductive graphite coating and a copper connect. Further, each resistive sheet including the contacts is electrically isolated from adjacent sheet by an insulator. The resistive sheets composed of paper are protected by a PDMS film in the side where the graphite layer is absent. Further, the resistive layers are also patterned in such a manner that each touch zone is separated from other by a thin PDMS layer. The proposed proof-ofprinciple prototype have shown very high sensitivity towards human touch and can be integrated with state-of-art touchscreen devices in future.

Figure 1
Pressure Swing Recovery from Cyclic Delamination of Freestanding Carbon Nanofiber for Li-Air Battery Cathodes
Authors: Kim Jangwoo , Joo Yong Lak
Published: February 2020

Lithium air or lithium oxygen batteries draw keen attention for its high energy density even with the fact that considerable obstacles must be overcome in order to achieve reasonably stable discharge-charge cycles. Limiting the formation of insulating discharge products on the surface of air cathodes by cutting off the cell operation at a certain capacity instead of using a voltage window is a widely-accepted way of enhancing the rechargeability, along with methods preventing the formation of electrochemically irreversible products due to parasitic reactions by manipulating the composition of electrolyte and modifying carbon surface with metallic catalysts or organic functional groups. In this study, we propose a novel process of operating the cell based on our finding that the accumulation and subsequent removal of reaction products during discharge-charge cycles cause severe delamination of freestanding carbon nanofiber cathode structure. It is demonstrated that rebinding the multiple carbon layers of the cycled air cathodes via heavy metal press results in the enhanced cycle performance and reduces the discharge overpotential at the same time. The results stress the importance of maintaining physical structure of the air cathode from volume expansion during cell operation, and provide a new insight towards pulling out full capacity retention of the system by better utilization of the available carbon surface in the air cathode.

Figure 1
(Invited) 2D Van Der Waals Crystals and Heterostructures for Smart Life
Authors: Banerjee Kaustav
Published: February 2020

The experimental demonstration of graphene in 2004, a truly one-atom thick layer of carbon atoms, has opened up a window to the two-dimensional (2D) world of materials. This has subsequently triggered a surge of research activities on various 2D crystals including single layers of hexagonal-boron nitride (h-BN), several dichalcogenides (such as MoS2 and WSe2), and complex oxides. Atomic scale thicknesses (few Å/layer) of 2D semiconducting crystals and their controllable precise band gaps as a function of number of layers also enable the scaling of electronic devices without inducing performance variations. Moreover, seamless planar synthesis and stacking of various 2D crystals can be exploited to build novel lateral and vertical heterostructures, respectively. This talk will highlight and discuss the prospects of such 2D crystals for designing ultra-low power, low-loss, and ultra-energy-efficient active and passive devices targeted for designing next-generation green electronics needed to support the emerging paradigm of Internet of Things. More specifically, this talk will examine the genesis of the power dissipation challenge in conventional MOSFETs, and provide an overview of the recently demonstrated 2D-channel tunnel-FET from my group that overcomes this challenge and is a fundamentally different transistor employing several innovations. This talk will also bring forward some applications uniquely enabled by 2D crystals, including sensors and flexible high-frequency electronics for improving quality of life, and discuss related challenges and opportunities.
(Invited) Two-Dimensional Layers: The Synthesis and Properties of Graphene and Beyond
Authors: Robinson Joshua A
Published: February 2020

The isolation of graphene constituted a new paradigm in next generation electronic technologies. In this work, I will discuss recent works in graphene and beyond for novel device applications. This includes a focus on epitaxial graphene materials and device properties, as well as “beyond graphene” opportunities that could lead to new areas of research.  Transition metal dichalcogenides (TMDs) and their heterostructures could have an even greater impact on next generation technologies. Molybdenum disulfide (MoS2) is currently a leading TMD for scientific exploration, but there are a variety of other suitable, less explored, TMDs and heterostructures that exhibit very attractive bandgaps, charge carrier effective masses, and mobilities for electronic applications. Transition-metal dichalcogenides (TMDs) in the form of MeX2 (where Me = a transition metal such as Mo, W, Ti, Nb, etc. and X = S, Se, or Te) also exhibit extreme flexibility, possession of tunable band gaps, modest electron mobilities, and wide variety of band-offsets. Additionally, monochalcogenides (i.e. GaSe) have the potential to provide routes toward alternative wide bandgap 2D materials suitable for high power and UV optoelectronics. Furthermore, synthesizing and heterogeneously combining these atomic layered materials to form van der Waals (vdW) solids, where each layer may be different from the previous, is a powerful way to develop novel nanoscale materials.  This talk will elaborate on recent breakthroughs for direct growth of two-dimensional atomic heterostructures (MoS2, WSe2, and hBN) on a graphene template, discuss recent breakthroughs in the synthesis of 2D nitrides beyond hBN, and elucidate mechanisms for achieving selective area growth of 2D materials.
Use of Patterned Metal Anodes for Studying Hydrogen Electrochemical Oxidation Reaction in Proton-Conducting SOFCs
Authors: Sun Shichen , Awadallah Osama , Cheng Zhe
Published: February 2020

Despite the great potential for proton-conducting solid oxide fuel cells (SOFCs) for clean power generation at intermediate temperature (e.g., 400-700 oC), there are significant knowledge gaps about fundamental aspects for such cells.  In particular, very little is known about the kinetics and reaction mechanism for the hydrogen electrochemical oxidation reaction in proton-conducting SOFCs.  Here, we will report the preliminary results of our study using patterned metal anode over acceptor-doped Ba(Ce,Zr)O3 proton-conducting electrolyte.  The effects of various factors such as choice of anode metal (e.g., nickel versus copper), anodic bias voltage, gas atmosphere, temperature, and electrode geometry (e.g., triple phase boundary TPB length and electrode area) on the electrochemical behaviors of proton-conducting SOFC will be studied.  The results will be correlated to previous studies for hydrogen electrode reaction in conventional oxide-ion conducting SOFCs, and the implications on the fundamental reaction mechanism for the hydrogen electrode reaction involving proton-conducting oxides will be discussed.
Transition Metal Chalcogenide Based Elelctrocatalysts for Facile Water Oxidation/Reduction
Authors: Swesi Abdurazag T , Masud Jahangir , Nath Manashi
Published: February 2020

Transition metal chalcogenides has been a heartthrob of solid state chemists owing to the richness of properties they exhibit as well as their structure-property correlation. In addition to their viable optoelectronic properties, it has been recently observed that some of these transition metal chalcogenide (especially selenides) show high electrocatalytic activities for oxygen evolution/reduction reactions (OER/ORR respectively) and hydrogen evolution reaction (HER). Recently we have formulated some new transition metal chalcogenide based compositions which show an enhanced catalytic activity for OER based on their d-electron occupancy and structural parameters.1 Among these the Ni-based selenide thin films and nanostructures show much better catalyst activity along with lower onset potential for O2 evolution outperforming the state-of-the-art precious metal based catalysts. It was also observed that doping other transitional metals in the Nickel selenide matrix led to enhancing catalyst efficiency. The catalysts were synthesized mainly through electrodeposition on different substrates like Au-coated glass, Au-coated Si as well as glassy carbon (GC). The nanostructured catalysts were made through chemical vapor deposition (CVD) and solvothermal reaction. In a separate approach nanorod and nanotube arrays of these electrocatalysts were grown through electrodeposition on lithographically patterned nanoelectrodes. Nanostructuring typically led to much better efficiency with low catalyst volume, with the nanorod/nanotube pattern producing the highest activity with lowest electrode coverage with the active material. The catalytic activities for OER, ORR and HER were investigated through detailed electrochemical measurements including linear scale voltammetry, chronoamperometry, Tafel slope analysis as well as determination of Faradaic efficiency through rotating ring disk electrode studies. Interestingly some of these selenides showed bifunctional or trifunctional nature showing efficient catalytic activity for OER-HER and OER-HER-ORR processes, respectively. In this talk we will present a systematic study of the selenide based electrocatalysts including binary (NixSey, CoxSey) as well as ternary chalcogenides, Ni
xMy
Sen (M = Fe, Co, Mn, Al) and investigating their catalytic activities for OER, HER, and ORR reactions. We will also discuss the effect of d-electron counts, electronic structure and morphology on the catalytic efficiency.  

References

Swesi, A.; Masud, J.; Nath, M. Energy Environ. Sci.
2015 doi: 10.1039/C5EE02463C.
Structure-Activity Relationships in Ni-Fe Oxyhydroxide Oxygen Evolution Electrocatalysts
Authors: Batchellor Adam S. , Burke Michaela S. , Enman Lisa J. , Boettcher Shannon Wachter
Published: February 2020

The oxygen evolution reaction (OER) is kinetically slow and hence a significant efficiency loss in electricity-driven water electrolysis.  Understanding the relationships between architecture, composition, and activity in high-performing catalyst systems are critical for the development of better catalysts.1

To reach the relevant operating conditions of industrial electrolyzers, high mass loadings are required even when current state of the art catalysts are employed.  Several challenges arise when studying high loading films which complicate determination of intrinsic OER activity.  For example, to accurately report turnover frequencies the number of metal centers participating in the OER must be known.  Furthermore, diminished electronic and mass transport through a thick catalyst film could result in active sites located in different parts of the film generating oxygen at different rates.  We compare several methods of determining the number of electrochemically active metal centers, and report the loading dependent behavior of Ni-Fe oxyhydroxide films, the fastest known water oxidation catalyst in alkaline media.2We find that commonly employed methods used to determine the electrochemically active surface area could result in errors of several orders of magnitude due to the potential dependent conductivity of many transition metal-based catalyst systems. 

We discovered that the method of electrodeposition strongly affects the intrinsic Ni(Fe)OOH activity, as well as the practical electrode performance.3Pulse electrodeposited films increase in turnover frequency with loading, while continuously deposited films decrease in activity with loading.  The improvements stemming from this pulsed deposition method are wide reaching, affecting both the architecture and the composition of the catalyst film. The role of these effects on intrinsic and geometric OER activities will be discussed in the context of the design principles for high-performance electrode architectures.

(1)  Burke, M. S.; Enman, L. J.; Batchellor, A. S.; Zou, S.; Boettcher, S. W. Oxygen Evolution Reaction Electrocatalysis on Transition Metal Oxides and (Oxy)hydroxides: Activity Trends and Design Principles. Chem. Mater.
2015, 27, 7549-7558.

(2)  Trotochaud, L.; Ranney, J. K.; Williams, K. N.; Boettcher, S. W. Solution-Cast Metal Oxide Thin Film Electrocatalysts for Oxygen Evolution. J. Am. Chem. Soc.
2012, 134, 17253-17261.

(3)  Batchellor, A. S.; Boettcher, S. W. Pulse-Electrodeposited Ni–Fe (Oxy)hydroxide Oxygen Evolution Electrocatalysts with High Geometric and Intrinsic Activities at Large Mass Loadings. ACS Catalysis
2015, 5, 6680-6689.
Hydrogen Production Using Different Graphene/Au@TiO2 Composites Under Visible and Ultraviolet Light
Authors: Machín Abniel , Márquez Francisco
Published: February 2020

In order to avoid serious environmental and economic damages from energy use, humans must stop using fossil fuels altogether, as soon as possible. One possible strategy to cut the dependence of fossil fuels and, at the same time create a new economic force, is to develop a hydrogen based energy economy. A potentially viable way forward is to produce H2 from water by combining solar energy and heterogeneous photocatalysts. For these reasons the objectives of this investigation were: 1) synthesize a high surface area TiO2 nanowires (NWs) catalyst in the rutile phase, 2) incorporate different amount of gold nanoparticles into the as-synthesized catalyst and into the commercial form of TiO2 (P-25) using a chemical reduction method, 3) incorporate graphene to the Au@TiO2 composites, 4) produce hydrogen via water splitting using visible and ultraviolet light. The hypotheses of the study were: a) The catalyst with the higher surface area will produce the highest amount of hydrogen, b) The gold nanoparticles will enhance the hydrogen production and will allow the use of visible light due to the surface plasmon resonance of the gold nanoparticles, c) The incorporation of graphene will enhance the hydrogen production since it will reduce the electron/hole recombination in all the Au@TiO2 composites. Interestingly, the incorporation of gold nanoparticles into the titania surface enhanced the surface area in both P25 and TiO2 NWs. The hydrogen production obtained by using Au@P25 catalysts was measured to be 800 μmolg-1h-1 under irradiation at 400 nm and 1,436 μmolg-1h-1 using Au@TiO2 NWs at the same wavelength. The incorporation of graphene enhanced the hydrogen production in both P25 and TiO2 NWs. A maximum hydrogen production of 978 μmolg-1h-1 and 1,689 μmolg-1h-1 was obtained for P25 and TiO2 NWs, respectively, after the incorporation of graphene. All the hypotheses were correct and all the objectives achieved. The characterization of the synthetized compounds were performed with: 1) X-ray diffraction (XRD), 2) Field emission Scanning Electron Microscopy (FESEM), 3) Brunauer, Emmett and Teller (BET), 4) Gas Chromatographer with a Thermal Conductive detector (GC-TCD) and 5) Ultra Violet Visible spectroscopy (UV-VIS). Future works will be focused on producing hydrogen via water splitting by incorporating gold nanoparticles and graphene on synthesized zinc oxide nanowires and nanoparticles. The results with the zinc oxide composites will be compared with those obtained by the TiO2 composites. The contribution of this investigation relies in finding new and clean ways to produce hydrogen via water splitting.
(Invited) Electrochemistry on 4d and 5d Transition Metal-Oxide Films Epitaxially Grown on Single Crystal Substrates: Implications for Electrocatalysis
Authors: Kuo Ding-Yuan , Eom Chuhyon , Paik Hanjong , Kawasaki Jason , Hautier Geoffroy , Shen Kyle , Schlom Darrell G. , Suntivich Jin
Published: February 2020

We present our electrochemical studies of epitaxial ruthenate and iridate films grown on single crystal substrates. Iridates and ruthenates are among the most studied oxygen evolution reaction (OER) electrocatalysts for water splitting applications. In the past decade, advances in deposition technologies and substrate availabilities have enabled the growth of single-crystal transition-metal oxides with high structural perfection. We use these advances, specifically Molecular-Beam Epitaxy (MBE), to prepare epitaxial ruthenate and iridate films on single crystal substrates. The use of epitaxial, single-crystal films allow us to link the features from our electrochemical characterizations to the physical adsorptions, which we will compare to the first-principle calculations. We further discuss the alloying effect on the surface adsorption process. We use this information to reveal insights into how to tune the surface physicochemical properties on the ruthenates and iridates and discuss the implications on the OER electrocatalysis.
Abrupt Mechanistic Variation of Hydrogen Evolution Reaction on Metal Electrode Surfaces in the Potential-pH Space
Authors: Haghighat Shima , Dawlaty Jahan
Published: February 2020

Understanding the mechanisms of multi-electron and multi-proton electrochemical reactions, particularly in the context of renewable electrochemical energy conversion, is an outstanding challenge. The electrocatalytic hydrogen evolution (2H+ + 2e-...> H2) is the half reaction of water splitting and is heavily studied. However, the kinetic variation of this reaction under various pH conditions has not been fully understood.

In this work, we studied hydrogen evolution reaction on different electrodes (Pt, Cu, FeS2, Ni, and Ti) over a wide range of neutral (pH=6.5) to acidic (pH=1.5) solutions. Despite variations in the properties of these electrodes, we observe a discontinuous change in the onset potential as a function of current in the pH range of 2.5 to 3.5 in all the electrodes. We also represent two fundamental kinetic parameters, empirical electron transfer coefficient α and the reaction order with respect to proton ρ, as a function of pH and potential. An important observation is that α is constant (α≈0.2) at pH values higher than the discontinuous jump, while at lower pH values alpha increases with decreasing pH. The maximum value of alpha varies for different electrodes and is increasing from Ti < Ni< Cu < FeS2 < Pt. The proton reaction order is non-zero in the acidic side, whereas it is zero in the neutral limit and this trend is common for all the electrodes.

To our knowledge, for the first time, we are presenting the kinetic parameters in two-dimensional plots as a function of both pH and potential. This representation allows us to clearly see global trends in the kinetics of the reaction. We will propose possible explanations for such common behavior based on a kinetic model that accounts for both concerted and step-wise electron and proton transfer. We hope that this study sheds light on the fundamentals of electron-proton transfer during hydrogen evolution.

Figure 1
Hematite Nanostructures for High Efficient Solar Water Splitting
Authors: Sun Xuhui , Deng Jiujun , Zhong Jun
Published: February 2020

Hematite has emerged as a good photocatalyst for efficient solar water splitting due to its favorable optical band gap (2.1–2.2 eV), extraordinary chemical stability in oxidative environment, abundance, and low cost. According to theoretical prediction, the solar-to-hydrogen efficiency of hematite can be 16.8% and the water splitting photocurrent can be 12.6 mA cm-2. However, the practical performance of hematite for solar water splitting is far from the ideal case which has been limited by several factors such as poor conductivity, short lifetime of the excited-state carrier (10-12s), poor oxygen evolution reaction (OER) kinetics, short hole diffusion length (2–4 nm), and improper band position for unassisted water splitting. In our recent work, enormous efforts have been focused on improving the performance of hematite nanostructure photoelectrode. Different methods such as morphology control, elemental doping, and improvement of the charge transport of hematite have been developed to improve the performance of hematite photoelectrode in solar water splitting. We present the preparation of Ti-doped and H2-treated hematite nanostructures. The H2-treated hematite photoelectrode showed a high photocurrent of 2.28 mA/cm2 at 1.23 V vs. RHE, which was over 2.5 times than that for pristine hematite. Moreover, when compared to hematite photoelectrode with oxygen vacancies but treated by controlling the oxygen content in the sintering process, a cathodic shift of the onset potential was observed by about 120 mV (from 0.99 to 0.87 V vs. RHE). The cathodic shift of the onset potential was attributed to the surface effect of H2-treatment. The Ti-doped hematite nanostructures with optimized oxygen vacancies achieved a remarkable maximum photocurrent value of of 4.56 mA/cm2at 1.6 V vs. RHE. Moreover, Ti-doping can expand the applicative partial oxygen pressure to a wide range compared to that for undoped hematite. The expansion of partial oxygen pressure range might be useful for the practical application. The coupling of extrinsic Ti-doping and intrinsic oxygen vacancies stands for an effective strategy to design oxide-based photoanodes for efficient solar water oxidation. 

Reference:
 

J. Deng, X. Lv, J. Liu, H. Zhang, K. Nie, C. Hong, J. Wang, X. H. Sun, J. Zhong, S. T. Lee, ACS Nano, 9, 5348 (2015).

M. Li, J. J. Deng, A. W. Pu, P. P. Zhang, H. Zhang, J. Gao, Y. Y. Hao, J. Zhong and X. H. Sun, "Hydrogen-Treated Hematite Nanostructures with Low Onset Potential for Highly Efficient Solar Water Oxidation", Journal of Materials Chemistry A, 2, 6727 (2014)

A.W. Pu, J.J. Deng, M. Li, J. Gao, H. Zhang, Y.Y. Hao, J. Zhong and X.H. Sun, “Coupling Ti-doping and Oxygen Vacancies in Hematite Nanostructures for Solar Water Oxidation with High Efficiency”, Journal of Materials Chemistry A, 2, 2491(2013)

J.J. Deng, X.X. Lv, J. Gao, A.W. Pu, M. Li, X.H. Sun and J. Zhong “Facile synthesis of carbon-coated hematite nanostructures for solar water splitting”, Energy & Environmental Science, 6, 1965 (2013).
The ARPA-E CHARGES Program: How to Get Paid for Grid Storage, and the Duty Cycles Needed to Prove Your Technology
Authors: Albertus Paul S. , Heffner Reid R.
Published: February 2020

The Advanced Research Projects Agency-Energy (ARPA-E) has invested a significant amount of funding in novel, electrochemical-based electrical energy storage technologies for stationary applications. However, widespread adoption of new storage technologies has been hindered by a lack of proven economic benefit, performance, and long term reliability.  This presentation will focus on the economic modeling of the value of grid energy storage conducted in the Cycling Hardware to Analyze and Ready Grid-Scale Electricity Storage (CHARGES) program, including the revenue that can be captured under both existing and potential future utility rate structures and markets for applications such as day ahead, real time, demand charge reduction, ancillary services, and others.  In addition to the revenue that can be captured by participation in single applications, the revenue available by stacking applications will also be assessed.  The CHARGES program has also sought to translate the operation of a battery to maximize revenue into duty cycles that researchers can run on the electrochemical technologies they are developing, to move beyond the typical constant-current cycling to duty cycles linked to economic valuation in an actual grid context.  At the end of this presentation, battery developers should have a clear understanding of value-driven performance requirements that allow for evaluation of their technology early in the development cycle.
Determination of Mass and Charge Transport of La2Ni0.95Al0.05O4.025+
d
at Isothermal Condition
Authors: Im Ha-Ni , Jeon Sang-Yun , Yoo Young-Sung , Song Sun-Ju
Published: February 2020

Mixed oxide-ion and electron conducting ceramic material La2NiO4+
d (LNO) have been reported to exhibit impressive oxide ion and p-type electronic conductivity, and high catalytic activity which makes them an excellent component of some electrochemical devices such as fuel cell cathode, oxygen permeation membrane and sensors. The structure of hyper-stoichiometric LNO is consists of alternating LaNiO3 perovskite and LaO rock salt layers. The oxygen excess in LNO is associated with the incorporation of interstitial oxygen into the rock salt layers and holes are simultaneously created in the perovskite layers to maintain the charge neutrality of the system. Given the oxygen activity difference across an oxide, its electrochemistry is determined by its ambipolar conductivity or the product of its oxide ionic conductivity and electronic transference number or vice versa. The partial ionic and electronic conductivities which govern the mass transport in an electric field are thus the most important properties of an electrochemical device material to characterize and understand. However, there are very few reports on the study of transport properties of mixed conducting oxide material. In this work we have analyzed the partial conductivity of La2Ni0.95Al0.05O4.025+
d
in relation with the thermoelectric power and calculate diffusion coefficient and surface exchange coefficient in order to analyze the oxygen exchange kinetics of La2Ni0.95Al0.05O4.025+
d.
Quantitative one-Dot Differential Electrochemical Mass Spectrometry Study on Electro-Oxidation of Ethanol at Carbon-Supported Pt and Ir-Containing Catalysts
Authors: Qu Yunteng , Gao Yunzhi , Wang Long , Li Can , Yin Geping
Published: February 2020

“One-dot” differential electrochemistry mass spectrometry (ODEMS) system was constructed by using a pin-hole covered with a Teflon film as gas inlet, thus leading to a high signal-to-noise ratio. The electrocatalytic activity of Pt/C and Pt-Ir/C electrocatalysts for the ethanol oxidation reaction (EOR) was investigated by potentiostatic techniques by ODEMS system. The 20 wt% electrocatalysts were synthesized by a modified polyol method and physically characterized by different techniques, including X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The chronoamperometry study shows that, although the ethanol oxidation starts at lower potential on Pt-Ir/C, the kinetics of the reaction is faster on Pt/C. The CO2 current efficiency (CCE) was also determined on both electrocatalysts after calibration of the m/z= 44 signal: the CCE value can reach up to 21% on Pt-Ir/C at room temperature, compared to ca. 6% on Pt/C.

Figure 1
Evaluation and Comparison of the Electric Field in the Physicochemical Properties of a Vertisol Type Soil and Sodium Bentonite
Authors: Pérez Maribel , Rodríguez José Miguel , Gómez César , Bustos Erika
Published: February 2020

Soil electro-remediation is a technique that allows the removal of organic and inorganic compounds [1-4]. Changes in the soil matrix during application of the electric field affects desorption and/or absorption, and even the mobilization process of pollutants [5].

Changes caused by the potential gradient in a model soil (sodium bentonite) and the results of pH and contaminant transport of a model designed in Visual Basic were compared to evaluate the process of electro-migration which was simulated through the transport number.

When we compared the behavior of the model soil with a Vertisol soil, the parameters evaluated throughout the cell were: pH, electrical conductivity and z potential. The behavior between the model soil and the Versitol type soil pH is similar in the area near the anode where there is a decrease in pH attributed to the generation of H+ and the cathode pH was slightly increased by the presence of –OH (Figure 1).

However, the behaviors of the electrical conductivity and z potential are not similar due to the presence of organic matter, microorganisms and the diversity of ions contained in the Versitol type soil. The observed changes in these parameters promote the removal of pollutants. In the case of Vertisol type soil the observed changes in the soil matrix are minimal, which is an advantage of electro-remediation in comparison of another treatments of soil, as biological and chemical procedures.

References.

[1] K. R. Reddy, Technical challenges to in-situ remediation of polluted sites. Geotech. Geol. Eng., 28(3), 211-221 (2010).

[2] M. Pérez-Corona, A. Corona, E. D. Beltrán, J. Cárdenas and E. Bustos, Evaluation of IrO2 – Ta2O5|Ti electrodes during the electroremediation of hydrocarbon – contaminated soil. Sustain. Environ. Res., 23 (4), 279 – 284 (2013).

[3] A. Medel, D. Patiño, E. Méndez, Y. Meas, L. Godínez, J. Manríquez, F. Rodríguez, A. Rodríguez and E. Bustos, Novel electrokinetic remediation system – boron doped diamond (EKR-BDD) process for the destruction of polyaromatic hydrocarbons (PAHs) in liquid phase. Environ. Engin. Manag. J., 14 (4) 879 – 886 (2015).

[4] I. Robles, M. J. Lozano, S. Solís, G. Hernández, M. V. Paz, M. G. Olvera and E. Bustos, Electrokinetic treatment of mercury – polluted soil facilitated by ethylenediaminetetraacetic acid coupled with a reactor with a permeable reactive barrier of iron to recover mercury (II) from wáter. Electrochimica Acta 181, 68 – 72 (2015).

[5] I. Robles, E. Bustos and J. Lakatos, Comparison of the sorption behavior of mercury (II) on inorganic, organic and biomass substrates in the presence of different counter-ions. Sustain. Environ. Res., 25 (5), 255- 260 (2015).

Figure 1
Advanced Modeling of New Batteries
Authors: Wang Yun
Published: February 2020

Flow batteries, capable of storing large quantity of energy, have great potential to increase the flexibility of power systems and improve dynamic response to energy demand. Flow batteries are a rechargeable electrochemical energy system, in which electrolytes contain one or more dissolved electroactive species, and the chemical energy in electrolytes is reversibly converted to electricity. The fuel electrolyte is stored externally in a tank, and delivered to the reactor. Batteries can be recharged by replacing electrolytes, similar to conventional vehicles, or by external electric power that is similar to secondary batteries. Flow battery technology offers advantages in energy storage and conversion, including: 1.) large capacity (determined by the external tank volume); 2.) negligible degradation when left completely discharged for long periods; 3.) charge/recharge through electrolyte replacement or external power source; and 4.) no permanent damage when electrolytes are accidentally mixed. Among the major types of flow batteries, the vanadium redox flow battery is a type of rechargeable flow battery that employs vanadium ions at different oxidation states to store chemical potential energy.

Lithium-based batteries have received a great deal of research attention in recent years owing to their relatively high efficiency and energy density. A major hurdle to their development, however, is the insufficient low energy capability as opposed to fossil fuels. The gasoline’s specific energy is about 13,000 Wh/kg, an order-of-magnitude higher than that of Li-ion batteries. Li-air batteries are an emerging area with a great promise of high specific energy storage. Their theoretical specific energy reaches around 11,680 Wh/kg, comparable to gasoline and higher than methanol. Their unique feature is that the cathode active material--oxygen is obtained from the ambient environment, and the anode uses lithium metal, rather than Li intercalated graphite (LiC6) as that in Li-ion batteries. Air cathodes are a major area of study in non-aqueous Li-air battery. In cathodes, Li compounds such as Li2O2 or Li2CO3 are produced during discharging. These substances in general have low solubility in major non-aqueous electrolytes, therefore precipitate at the reaction surface. They are also poor electric conductor, causing electrode passivation. As discharging proceeds, the precipitates accumulate inside the pore network, deteriorating voltage drop.

In this talk, I will discuss the ongoing work of modeling development on RFBs and Li-air batteries at UCI. The models are formulated by rigorously accounting for the conservation of mass, momentum, species, charges, and energy, in conjunction with the electrochemical reaction kinetics of vanadium RFBs and Li-air batteries. I will emphasize the similarity and difference in modeling the two types of new battery systems. The models are validated against experimental data.
(Invited) Luminescent Rare-Earth Doped Thin Film Nanostructures As Building Blocks for Nanophotonic and Lighting Applications
Authors: Camps Ivan , Mariscal Antonio , Serna Rosalia
Published: February 2020

Active light emitting nanostructured materials are essential elements for the development of compact and efficient devices in applications such as photonics, lighting, safety, sensing and biotechnology. These nanostructured materials require a suitable design and specific choice of wavelength depending on the targeted application. Rare-earth(RE) ions are known for providing a robust and high purity light emission Within this context we aim to design and fabricate nanostructured efficient emitters that will be used as building blocks for the development of the next generation of complex photonic devices that will have integrated functionalities such as emission, switching, processing and detection of light, operating in a wide wavelength range covering the visible-infrared spectrum.

 In this talk we will present the recent results obtained by our group using the methodology of embedding nanolayers of rare-earth ions into thin film oxides and oxinitrides with the aim to build efficient nanoemitters. By suitably choosing the nature, composition and crystallinity of the matrix, and the oxidation state of the RE-ion and its concentration and distribution in the nanolayers we will show several examples of functionalized emission. The examples will include the demonstration of narrow emission from pure europium oxide thin films in which fine tuning of the emission is shown by exploiting crystal field effects triggered by stress, the development of efficient wide band emitters in the visible based on Eu2+ doped oxide and oxinitride films, and the demonstration of RGB emission based on a combined doping of RE-ions.
(Invited) Ionophore-Doped Ion-Selective Electrode Membranes
Authors: Buhlmann Philippe , Zhen Xue V , Hu Jinbo
Published: February 2020

Ion-selective electrodes with ionophore-doped sensing membranes are are highly sensitive and selective analytical tools that offer a variety of advantages, such as simplicity of measurement, high analysis throughput, rapid detection, and low cost of analysis. While such sensors are used in clinical laboratories for billions of measurements every year, applications in biomedical sciences, the food industry, and environmental monitoring are hindered by biofouling and the frequent need for recalibration. With prolonged exposure to biological samples, solid contact polymeric-membrane ISEs exhibit a breakdown of selectivity and response due to biofouling and changes in the phase boundary potential at the interface of the ion-selective membrane and the underlying electron conductor. Therefore, frequent recalibrations are needed for many clinical and biological applications. This talk will discuss experimental techniques such as impedance spectroscopy and hydrodynamic methods to characterize sensor aging, and it will address the use of hydrophobic redox buffers incorporated into the sensing membranes to stabilize the phase boundary potential at the interface to the underlying electron conductor. These redox buffers permit a high electrode-to-electrode reproducibility of the emf response, which is needed for the development of ion-selective potentiometric devices that can be used in a calibration-free manner [1].

[1] Calibration-Free Ionophore-Based Ion-Selective Electrodes With a Co(II)/Co(III) Redox Couple-Based Solid Contact, Zou, X. U.; Zhen, X. V.; Cheong, J. H.; Bühlmann, P. Anal. Chem.,
2014, 86, 8687–8692.