bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Evolution in (Pr1-xNdx)2NiO4+d Cathodes for Intermediate Temperature Solid Oxide Fuel Cell Applications
Authors: Dogdibegovic Emir , Wright Christopher J. , Zhou Xiao-Dong
Published: February 2020

Fast kinetics of Pr2NiO4+δ cathode is counterbalanced by readily occurring phase transitions at operating conditions. Single phase (Pr1-xNdx)2NiO4+δ powders (x=0, 0.25, 0.50, 0.75, 1) were synthesized in an attempt to suppress the phase transitions, and in turn lead to stable long term performance. Rietveld refinement shows linear decrease in unit cell volume with increase in x. This volume contraction is mainly driven by decrease in the c lattice parameter. Thermal annealing on powders and electrodes show reducedphase transitions in a parent nickelate phase with increase in Nd content. Long term thermal annealing shows preserved (Pr0.25Nd0.75)2NiO4+δ and Nd2NiO4+δ phases at 750 °C, as confirmed by x-ray diffraction analysis. Phase transitions in electrochemical cells were also suppressed with increase in Nd content. TEM analysis confirmed multiple phases present in operated Pr2NiO4+δ electrodes, while Nd2NiO4+δ electrodes retained stable phase. SEM analysis showed reduced reaction with ceria buffer layer with increase in Nd content. Diffusion of Pr was decreased by twofold for x=0.25 and by sixfold for x=0.50, while the reaction was fully suppressed with higher Nd content.
Degradation Analysis of SOFC Stack Performance-Durability Test and Verification of Improved SOFCs-
Authors: Yoshikawa Masahiro , Yamamoto Tohru , Yasumoto Kenji , Mugikura Yoshihiro
Published: February 2020

Central Research Institute of Electric power Industry (CRIEPI) has operated six types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG, NGK INSULATORS, and MURATA, to reveal their durability and find dominant degradation factor for each SOFC stack under NEDO’s project. The target of this NEDO durability project is set at 0.11%/1,000hr. In order to evaluate a performance degradation of the SOFC quantitatively and in order to quantify a performance change with time, the performance factor analysis method is required. We have been developed the electrode polarization models which is able to express SOFC performance factors such as Nernst loss (ηne), anode polarization (ηa), cathode polarization (ηc), and internal resistance IR drop (ηiR) with high prediction accuracy for six types of SOFCs. This gives us enable to make detail comparison among different type of SOFCs with the same performance analysis method inside the NEDO project. The MHPS’s stack which was operated until 16,000 hours, showed better stability and no further degradation factor has been identified. On the other hand, peculiar degradation behaviors arising from some impurities in air have been observed in our test for the stacks of Kyocera’s, TOTO’s, NTK’s, NGK’s, and Murata’s. For example, performance test exibited a rapid voltage drop within initial operation period for flattened tubular segment-in-series stack. The factor of this rapid voltage drop was increment of cathode overvoltage from a performance factor analysis result. One of possible reason for the negative effect to cathode overvoltage is sulfur contamination in the supply air from air compressor or thermal insulating foam on furnace.

In this study, we report our recent activities on the durability and the dominant performance factors, and the peculiar degradation behaviors.
Proton Conduction on YSZ Electrolyte Thin Films Prepared by RF Magnetron Sputtering
Authors: Takayanagi Makoto , Tsuchiya Takashi , Minohara Makoto , Kobayashi Masaki , Horiba Koji , Kumigashira Hiroshi , Higuchi Tohru
Published: February 2020

Yttria stabilized zirconia (YSZ) is known as solid electrolyte materials with oxide ion conduction and is used for sensor and solid oxide fuel cells (SOFCs). Recently, Wagner et al. has reported proton conductivity in YSZ single crystals at high temperature. Furthermore, Scherrer et al. has also reported proton conduction in YSZ thin films prepared by various technique. However, the existence of proton conduction of YSZ thin film at intermediate temperature (IMT) region has not been clarified thus far. In this study, we present the structural and electrical properties at IMT region of YSZ thin films prepared by RF magnetron sputtering.

YSZ thin films were deposited on Al2O3 substrates at various temperatures by RF magnetron sputtering using ceramics target. The 8 mol % Y2O3-doped ZrO2 target was prepared by solid phase reaction. The flow rate of Ar gas and the deposition pressure were set at 0.67 sccm, 8.0 × 10-3 Torr. The structural property of the YSZ thin films were characterized as a function of film thickness by powder X-ray diffraction (XRD) analysis. The conductivity of the deposited thin film was measured by AC impedance method at the temperature region of 200-500 ℃. The measurement frequency region was from 0.1 Hz to 32 MHz. In order to probe conducting carriers, the conductivity was measured by changing oxygen gas partial pressure (P
O2). The electronic structure was characterized by photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS).

The lattice constant of the (111)-oriented thin film increases with increasing film thickness due to relaxation of lattice distortion. The 80 nm thick film exhibits the oxide ion conduction with the activation energy of ~ 1.13 eV. Although the conductivity of 160 nm thick film dose not depend on atmosphere during measurement, the 80 nm and 120 nm thick films have higher conductivity in atmosphere than that in dry atmosphere. The activation energy of 80 nm thick film is ~ 0.76 eV and of 120 nm thick film is 0.82 eV. The electrical conductivity depends on film thickness. These results indicate that the thin film has proton conduction at the surface in the temperature region.
(Invited) Origin of the Low Grain Boundary Conductivity in Lithium Ion Conducting Perovskites: Li3xLa0.67-XTiO3
Authors: Guo Xin
Published: February 2020

Although the bulk conductivity of lithium ion conducting Li3xLa0.67-xTiO3 ceramics reaches the level of 10-3 S/cm, the grain boundary conductivity is orders of magnitude lower; the origin of the low grain boundary conductivity should be thoroughly understood as a prerequisite to improve the overall conductivity. According to SEM and TEM investigations, the grain boundaries are free of any second phase; however, the specific grain boundary conductivity is still ~4 orders of magnitude lower than the bulk conductivity. The grain-size-dependent specific grain boundary conductivity indicates that the crystallographic grain boundary does not determine the low grain boundary conductivity. The Li+ ions across the grain boundaries are then determined by the space-charge layer. The grain boundary core in the Li3xLa0.67-xTiO3 is positively charged, causing the depletion of Li+ ions in the adjacent space-charge layers. The very low grain boundary conductivity can be accounted for by the Li+ depletion in the space-charge layers.
(Invited) Concentrated Liquid Electrolytes
Authors: Yamada Atsuo , Yamada Yuki
Published: February 2020

Ever-increasing demand for better batteries has set extraordinarily high standards for electrolyte materials, which are far beyond the realm of a conventional electrolyte design. Superconcentrated (or highly concentrated) solutions are emerging as a new “realistic” class of electrolytes with various unusual functionalities beneficial for advanced battery applications. In this invited contribution, we will introduce our original technical achievements towards (i) versatile salt/solution combination, (ii) ultra high-rate reaction, (iii) high voltage operation over 5 V, iv) corrosion/dissolution prevention, (v) extreme safety, and (vi) advanced high-voltage aqueous energy storage systems, none of which were realized by the conventional electrolytes. Several unique inherent features, as well as the fundamental physicochemical properties, underneath the surprisingly superior battery performance realized by concentrated liquid electrolytes, will be analyzed from the viewpoint of their peculiar solution structure, providing the firm design considerations toward better batteries.
(Invited) Impact of Electrolytes on Li+ Charge Transfer Kinetics at the Electrolyte and Electrode Interface and Rate Performance in Li-Ion Batteries
Authors: Jow Taiguang Richard , Delp Samuel A. , Allen Joshua L. , Borodin Oleg , Allen Jan L.
Published: February 2020

The rate performance of Li-ion batteries remains challenging, especially at temperatures below -20 oC. Apart from engineering improvements, the rate performance of the cell is determined by the rate of Li
+
ion transfer across the interface, so-called charge transfer kinetics and the rate of Li+ ion diffusion within the electrode. In this paper, we will focus on the Li
+
ion charge transfer kinetics as it is still poorly understood and can be improved by modifying the electrolyte. Examination of Li
+
charge transfer kinetics at both a graphite anode and a LiFePO4 cathode, revealed a much higher activation at the graphite anode/electrolyte interface than at the LiFePO4 cathode/electrolyte interface [1]. Values from 50 to 60 kJ mol-1 have been observed for the activation energy at the graphite/electrolyte interface [1-3] whereas, at the LiFePO4 cathode/electrolyte interface, an activation energy of 30 kJ mol-1 has been observed [1]. At either electrode, the solvated Li
+
ion needs to be de-solvated before diffusing into the electrode. The distinct difference between the graphite anode and the intercalating cathode is that there is a distinct presence of a solid electrolyte interphase (SEI) on the graphite anode while there is no SEI or no discretely defined SEI layer on the cathode. What is not clear is why the SEI on the graphite anode leads to a larger Li
+
charge transfer activation energy value. Is this due to diffusion through the SEI itself or the slow de-solvation process in the presence of the SEI?

Recent studies indicate that the electrolyte composition plays a vital role in determining the electrolyte solvation structure and furthermore the nature of the SEI formed on the graphite anode can be modified by changing solvents, salt concentrations and additives [3-5]. This paper will report our recent exploration of how changing the electrolyte composition can improve the Li
+
charge transfer kinetics.

 

References

T. R. Jow, M. B. Marx, J. L. Allen, J. Electrochem. Soc. 2012, 159 (5), A604-A612.

T. Abe, H. Fukuda, Y. Iriyama, Z. Ogumi, J. Electrochem. Soc. 2004, 151(8), A1120-A1123.

Y. Yamada, Y. Iriyama, T. Abe, Z. Ogumi, Langmuir, 2009, 25(21), 12766-12770.

M. Nie, D. P. Abraham, D. M. Seo, Y. Chen, A. Bose, and B. L. Lucht, J. Phys. Chem. C 2013, 117, 25381−25389.

K. Abe, M. Colera, K. Shimamoto, M. Kondo, and K. Miyoshia, J. Electrochem. Soc. 2014, 161 (6) A863-A870.
Carbon Nanostructures for the Electrochemical Conversion of CO2 to Fuels: Defect & Electrocatalytic Activity
Authors: Wu Jingjie , Yadav Ram Manohar , Liu Mingjie , Sharma Pranav P. , Sharma Pranav P. , Wright Christopher J. , Tiwary Chandra , Yakobson Boris I. , Lou Jun , Ajayan Pulickel M , Zhou Xiao-Dong
Published: February 2020

The advantages of the electrochemical conversion of carbon dioxide to fuels using renewable energy sources are twofold: (1) it has the potential to accomplish a carbon-neutral energy cycle and (2) it can provide an approach to tackle the environmental challenges caused by anthropogenic carbon dioxide emissions. Although thermodynamically possible, the kinetics of carbon dioxide reduction to fuels remains challenging and therefore, an efficient and robust electrocatalyst is needed to promote the reaction. The ideal catalyst for the electrochemical CO2 reduction must be capable of mediating multiple proton-coupled electron transfer reactions at low overpotentials, suppressing the concurrent hydrogen evolution reaction, converting CO2 to desired chemicals with high selectivity, and achieving long-term stability. Extensive research has been carried out on metallic electrocatalysts during the past three decades; however, further studies are need to develop materials that are simultaneously efficient and stable for practical purposes.

The focus of this presentation is to report the use of N-doped carbon nanostructures as the electrocatalysts, which are highly efficient, selective and more importantly, stable catalysts to achieve CO2 conversion to CO. The catalytic activity of N-doped carbon nanotubes (NCNTs) was further benchmarked against other metallic catalysts reported in literature. Compared to noble metals Ag & Au, these NCNTs exhibited a lower overpotential to achieve similar selectivity towards CO formation. The dependence of catalytic activity, i.e., the overpotential and selectivity for CO formation on the defect structures (pyridinic, graphitic, pyrrolic-N) inside NCNTs will be discussed. The presence of both pyridinic and graphitic-N was found to significantly decrease the absolute overpotential and increase the selectivity towards CO formation. In addition, the electrocatalytic activity of two-dimensional materials will be presented. Overall, pyridinic-N defects exhibited the highest catalytic activity; thereby suggesting the directions for developing carbon nanostructures as metal-free electrocatalysts for CO2 reduction.
Relating Microstructure to Surface Exchange Kinetics Using in Situ Optical Absorption Relaxation
Authors: Chen Ting , Sasaki Kazunari , Perry Nicola H.
Published: February 2020

Reversible solid oxide cells (R-SOCs) are promising devices, which could directly convert chemical fuels to electrical power (Solid Oxide Fuel Cells, SOFCs) and store energy as chemical fuels (Solid Oxide Electrolysis Cells, SOECs). Nonetheless, the polarization resistance of the oxygen electrode, often originating in sluggish surface oxygen incorporation/ excorporation kinetics, causes large efficiency losses. Seeking to understand and ultimately improve surface exchange kinetics, many previous studies have focused on controlling the bulk defect chemistry (oxygen vacancy and/or electron content) or electronic structure through tailoring chemistry or strain. Fewer studies have focused on understanding the role of microstructural features in controlling both the surface exchange coefficient, k, and its deterioration over time (aging), especially for mixed ionic-electronic conductor (MIEC) electrode materials. SrTi0.65Fe0.35O3-δ (STF35) is a mixed conductor with fast k, which serves as a model system in our studies, to study the impact of microstructure (particularly crystallinity) on k and the aging behavior.

In this work, a series of STF35 thin films were grown by Pulsed Laser Deposition (PLD) using different growth parameters (temperature, time) to vary structural aspects such as crystallinity in a well-defined and controlled manner. Structural characterization of the films’ thickness, orientation, crystal quality, and grain size was performed using X-ray reflectivity and diffraction (coupled scans, rocking curves) plus atomic force microscopy. The surface exchange kinetics (k) of the series of STF35 thin films were measured in situ and continuously using a novel optical transmission relaxation approach, to investigate the impact of the aforementioned structural features on the performance. The approach takes advantage of the different optical absorption signatures of Fe in different valence states. Both XRD and AFM results showed that the STF35 thin films grown on yttria-stabilized zirconia at temperatures up to 400 ºC are amorphous, while the films become crystalline and oriented around 500-550 °C, with larger grains at higher temperatures. There is no obvious optical response to changing gas content for the as-grown amorphous films below 500 °C; however, upon heating these films at 500-550 °C, where they begin to crystallize, rapid oxygen exchange could be observed optically in the same films. Subsequently, the films optically demonstrated an ability to exchange oxygen at temperatures as low as 350 °C. The results indicate that crystalline thin films showed faster oxygen exchange kinetics compared to the amorphous thin films. The aging of STF thin films’ surface exchange kinetics was also studied optically as a function of microstructure, which in every case demonstrated a rapid decline in k during the initial 50 hours of measurement. Implications for electrode design will be discussed.
Electrochemically Fabricated Binary Alloy Catalysts for CO2-C1 Fuel Inter-Conversion
Authors: Hwang Eunkyoung , Kim Hoyoung , Park Hyanjoo , Ahn Sang Hyun , Kim Soo-Kil
Published: February 2020

Electrochemical reduction of carbon dioxide to useful chemical has been studied as a promising method to utilize CO2. This method can selectively produce a variety of useful chemicals (e.g. carbon monoxide, formic acid, methane, and other hydrocarbons) according as reaction condition such as types of electro-catalysts, electrolytes, operation voltage, and so on [1,2]. In this study, we selected formate as a target product because it has various advantages as a feed stock chemical. Formate is produced by the electrochemical reduction of the CO2 and the formate, after treatment to form formic acid, will be used as fuel for Direct Formic Acid Fuel Cell. Particularly in the case of CO2-based unitized re-generative fuel cell, the inter-conversion reaction between CO2-C1 fuels is important. Therefore, we develop a catalyst that can be used in both sides reaction; the electrochemical conversion of CO2 to formate and the oxidation of formic acid [3]. In this case, it is most important to develop bi-functional catalysts that have activities for both reactions. In addition, high selectivity and activity to CO2 reduction as well as reduced amounts of noble metal loading for the formic acid oxidation reaction are also desired.

The catalysts were made by co-electrodeposition of noble metal and post-transition metal to form binary alloy catalysts. Electrodeposition was performed at a constant deposition potential in a 3-electrode cell containing metal precursors, supporting electrolyte, and complexing agent. For some cases, thermal annealing was performed to enhance the characteristics of the fabricated catalysts. The alloy catalysts were characterized with EDS, SEM and XRD. The electrochemical reduction of carbon dioxide was performed and the produced amounts of formate were measured with HPLC. Formic acid oxidation was also performed with CV using the same catalysts. The activities to both reactions were characterized according to the alloy composition, morphologies, and other physic-chemical properties. In conclusion, certain composition of the alloy catalysts exhibited the significant activities to both reactions simultaneously.  

References

1. Journal of The Electrochemical Society, 137 (6) 1772-1777 (1990)

2. Journal of The Electrochemical Society, 159 (7) F353-F359 (2012)

3. Catalysis Today, 244 58-62 (2014)
High Temperature and Pressure Alkaline Electrochemical Reactor for Conversion of Power to Chemicals
Authors: Chatzichristodoulou Christodoulos
Published: February 2020

Moving away from fossil fuels requires harvesting more and more intermittent renewable energy resources and establishing a sustainable system for the production of chemicals. This brings forward the need for efficient large scale energy storage technologies 1-3 and technologies for the conversion of renewable electricity to chemicals. Electrochemical reactors can play a crucial role in this endeavor, since they can efficiently and reversibly transform electricity to high-value chemicals, and thus serve as energy storage and recovery devices for balancing the grid, while offering a means for the sustainable production of chemicals 4-6.

A novel type of alkaline electrochemical cell that can operate at elevated temperature and pressure has been developed that relies on corrosion resistant high temperature diaphragms, based on mesoporous ceramic membranes where aqueous KOH is immobilized by capillary forces. Raising the operating temperature offers a means to boost performance, as both ionic transport and reaction kinetics are exponentially activated with temperature. Indeed, we have demonstrated alkaline electrolysis cells operating at 200-250 °C and 20-50 bar at very high efficiencies and power densities.

This work will provide an overview of our efforts to develop components of such high temperature alkaline electrochemical reactors for different applications. Low-cost large-scale production methods have been successfully employed for the production of ceramic diaphragms and full cells. The influence of composition and microstructure on the long-term chemical stability and mechanical durability of the mesoporous ceramic membranes has been explored. Instrumentation for electrochemical testing at elevated pressures (up to 99 bar) and temperatures (up to 300 °C) with in-line chemical analysis has been established enabling experiments with gaseous or liquids reactants/products at cell sizes of up to 25 cm2. Efforts are currently directed towards the investigation of the intrinsic activity of mixed oxides for the oxygen evolution reaction at elevated temperatures and pressures, and of the intrinsic activity, selectivity and stability of supported metal catalysts towards the electrocatalytic conversion of biomass derivatives to high-value chemicals. Finally, the use of selected electrocatalysts for the production of high performance electrodes will be reported.

References

1. Barton, J. & Gammon, R. J. Power Sources
195, 8222-8235 (2010).

2. Evans, A., Strezov, V. & Evans, T. J. Renew. Sust. Energ. Rev.
16, 4141-4147 (2012).

3. Mansilla, C., Louyrette, J., Albou, S., Bourasseau, C. & Dautremont, S. Energy
55, 996-1001 (2013).

4. Jensen, S. H., Larsen, P. H. & Mogensen, M. Int J Hydrogen Energy
32, 3253-3257 (2007).

5. Zhan, Z. et al. Energy Fuels
23, 3089-3096 (2009).

6. Lebæk, J., Bøgild Hansen, J. & Mogensen, M. GreenSynFuels final project report. (2011).
Characterisation of a Planar Solid Oxide Cell Stack Operated at Elevated Pressure
Authors: Jensen Søren Højgaard , Graves Christopher , Chen Ming , Sun Xiufu , Hansen John Bøgild
Published: February 2020

As the global and local energy production becomes more dependent on intermittent renewable sources like wind and solar, efficient and reversible conversion of electricity to storable fuels becomes increasingly important. Solid oxide cells (SOCs) are interesting in this context since they can be operated either as electrolysers (SOEC) to convert electricity to fuels such as hydrogen or methane, and as fuel cells (SOFC) to convert fuels to electricity. Both productivity and conversion efficiency can be improved if the SOC operation pressure can be increased from ambient pressure to 10-30 bar.

Here we characterize an SOC stack operated at pressures from ambient pressure to 10 bar without fluctuations in the steam supply. The pressure dependency of stack temperature, cell area specific resistance (ASR), current-voltage (iV) curves, stack impedance spectra and pressure drop across the stack and heat exchangers is analyzed and the expected impact of pressurization on the hydrogen production cost is evaluated.

Figure 1
Investigation of Manganese-Cobalt Oxide Nanoparticles As Electrocatalysts for the Oxygen-Evolution Reaction: Influence of Synthesis Conditions on Structure and Activity
Authors: Gliech Manuel , Klingenhof Malte , Spoeri Camillo , Bergmann Arno , Strasser Peter
Published: February 2020

The storage of electric energy has become one of the main challenges in infrastructure development. The development of scalable, cost-efficient and robust synthetic routes toward well-defined solid state structures is a major objective in this field.

Electrocatalytic water splitting is a promising way of chemical energy storage wherein the anodic oxygen evolution reaction (OER) is the determining factor. Manganese based oxides have attracted particular attention as non-noble metal catalysts for the OER. Due to their abundance, low price and ecological harmlessness, those materials are promising candidates for a commercial application. Therefore insights into the relations between synthesis conditions, composition, structure and activity as well as stability are of fundamental interest. 1,2

Here, we present the comparison of different synthesis routes for Mixed Oxide Nanoparticles (NPs) of Manganese and Cobalt to yield Mn3-xCoxOy-NPs in a range from X=0 to 3. The well characterized (TEM, EDX, XRD) catalysts were tested with respect to the relation of crystal structure to electrocatalytic activity and stability for the OER in alkaline media using Rotating Disk Electrode (RDE) measurements.

We report a significant impact of the Cobalt fraction on the morphology, while the crystal structure remains unchanged. Further we found a non-linear relation between composition and activity.

References

(1) Bergmann, A.; Martinez-Moreno, E.; Teschner, D.; Chernev, P.; Gliech, M.; de Araujo, J. F.; Reier, T.; Dau, H.; Strasser, P. Nat Commun
2015, 6.

(2) Gliech, M.; Bergmann, A.; Spöri, C.; Strasser, P. Journal of Energy Chemistry
2016.
Potential Generation Using Salinity Gradients
Authors: Chandran Aishwarya , Khandelwal Ashwini , Amaravati Sivakumar , Chittur Krishnaswamy Subramaniam
Published: February 2020

Salinity gradient power (SGP) is the energy that can be generated from reversible mixing of two kinds of water with different salt contents. A process for generating potential from salinity concentration gradient produced in single cell (25 cm2) and multi-cell assembly is presented. The salinity gradient is created using a fuel cell type cell with a micro-porous ion exchange membrane, both anionic (AEM) and cationic (CEM). The study was performed for various gradients. Salt : Fresh, from 100 : 0 to 16000 : 0 was established using NaCl solution, in the electrode chambers. A potential of about 25 mV/cm can be realized at ambient temperatures and pressures for a bipolar AEM/CEM cell. The achievable potential is still below theoretical value. The performance was optimized for various static and dynamic flow rates of the saline and fresh water. For this purpose the cell flow field was simulated using ANSYS and the flow field design was optimized for maximum coverage of the cell area. The cell performance can further be optimized for various Membrane Electrode System (MES) structure. The thermodynamic, electrochemical and electrical efficiency was discussed for various gradients and flow rates. The higher the salinity gradient the larger is the potential generated. This is limited by the membrane characteristics. There exists a monotonic relation between the number of valence electron/ion/unit time and the potential generated up to about 16000 concentrations. The membrane characteristics have been studied for optimal ion crossover for various gradients and flow.
Hydrogen Production through a Multi-Ion Exchange Membrane Based Electrolysis System
Authors: Nazemi Mohammadreza , Padgett James , Hatzell Marta C.
Published: February 2020

Reverse electrodialysis (RED) is a membrane based electrochemical system used for capturing a portion nearly 2.6 TW of power released through the mixing of sea and river water at global estuaries[1]. This technology encompasses a series of alternating anion and cation exchange membranes (AEM and CEM) which actively separate channels with high and low concentration solutions (0.5 M and 0.011 M NaCl). Creating a concentration gradient across each ion selective membrane, generates a Donnan or Membrane potential. Typically, one cell pair (three membranes, and one high and low concentration chamber) produced an open circuit voltage of 120 mV. As more membranes are added to the system, the generated potential increases and drives faradic reactions at electrodes on either end of the membrane stack.

To date, most RED work has focused on utilizing a large numbers of membranes to produce electrical power through a galvanic cell approach. Due to this focus, traditionally low overpotential reactions are preferred rather than the water splitting reaction (oxygen evolution and hydrogen evolution). Here we investigate the potential for using the RED electrochemical platform for hydrogen production through an electrolysis approach[2, 3]. The use of multiple monopolar membranes and multiple chambers, allows a sustained pH gradient to be maintained across the cell, minimizing the whole cell voltage necessary for hydrogen production. When the cell was operated with a pH gradient equal to 10 pH units, the steady state whole cell onset potential decreased by 700 mV when compared to no pH gradient. This represented a 33% decrease in the energy consumption for the water splitting reaction. Additionally, the steady state current density (11.7 mA/cm2) was achieved using an acidic cathode and basic anode, which was 12 x greater than no pH gradient. We also evaluate the potential tradeoffs between added ohmic resistances, decreased onset potential, and increased membrane potentials within this architecture.

1. Logan, B.E. and M. Elimelech. Nature, 2012. 488(7411): p. 313-319.

2. Hatzell, M.C., I. Ivanov, R.D. Cusick, X. Zhu, and B.E. Logan. Physical Chemistry Chemical Physics, 2014. 16(4): p. 1632-1638.

3. Hatzell, M.C., X. Zhu, and B.E. Logan. ACS Sustainable Chemistry & Engineering, 2014. 2(9): p. 2211-2216.
Improvement of Reverse Electrodialysis Cells for Generating Electrical Power from Salinity Gradient
Authors: Kang Byeong Dong , Kim Dong-Kwon , Kim Hyun Jung , Yoon Baek , Yoo Jaisuk
Published: February 2020

Reverse electrodialysis cells can effectively generate electric power form salinity gradient. Howerver, the power generation densities from the reverse electrodialysis cells are low compared to conventional cells for power generation, and various reserach groups incluidng our group have focused on improving the performance of the reverse electrodialysis cells. In this presentation, the technique for improving the performance of the reverse electrodialysis cells, which have been investigated by our group, is introduced.
Solar Generation of Ion Gradients Using Dye-Sensitized Ion-Exchange Membranes
Authors: White William , Sanborn Christopher D. , Reiter Ronald S. , Ramirez Claudia P. , Ardo Shane
Published: February 2020

Most solar energy conversion technologies generate power through transport of energized electron particles; however, the physics that describes these technologies only requires that the particles be charged and not specifically that they are electrons. My research group studies solar energy conversion technologies that generate power from sunlight through ion transport. In my presentation I will report on my research group’s recent demonstration of ion transport against concentration gradients driven by solar illumination of dye-sensitized ion-exchange materials. Mechanistically, visible light was used to drive endergonic excited-state proton transfer from a covalent photoacid-functionalized polymer membrane. Photoacid molecules convert the energy in light into a change in the chemical potential of protons via a weakening of protic functional groups on the photoacid, i.e. a drop in its pK
a.

As a model system for ion-channels in polymer-electrolyte ion-exchange membranes, dye-sensitized conical nanopores in poly(ethylene terephthalate) (1 – 108 pores/cm2) were investigated. Remarkably, in a region occupied by ~20 zeptoliters (~2 x 10-20 L) of aqueous electrolyte, electrochemistry was used to determine the number of binding groups of the dyes and the ground-state pK
a of the dyes, and fluorescence microscopy was used to determine the conditions where excited-state proton transfer occurred. These data were consistent with a hypothesis that pK
a values of the photoacids in the ground-state and excited-state were significantly smaller than those measured for dye molecules in solution, likely due to incomplete screening of surface charges in the confined nanopores.

Dye-sensitized Nafion monopolar ion-exchange membranes and bipolar ion-exchange membranes were also investigated. Under sunlight-simulated illumination these materials were found to exhibit photovoltaic action, i.e. generation of a photocurrent and a photovoltage. Bipolar membranes are a class of polymeric ion-exchange materials that consist of a monopolar cation-exchange membrane that is in intimate contact with a monopolar anion-exchange membrane. They are unique among the ion-exchange membranes in that they that separate and maintain pH differences across the membrane even during passage of ionic current. Moreover, the physics of ion equilibration processes within these membranes resembles that which occurs during equilibration of semiconductor pn-junctions.

This body of work represents an underexplored solar energy conversion process that is being pioneered by my research group to operate via a mechanism similar to that in semiconductor pn-junctions. The applicability and practicality of these materials as standalone ionic photoelectrochemical devices will also be presented.
Perfluorinated or Hydrocarbon Ionomer-Poly(tetrafluoroethylene) Reinforced Membranes for Renewable Energy Generation
Authors: Lee Chang Hyun
Published: February 2020

Ionomers are polymeric materials containing fixed charged ions (e.g., –SO3
-) to transport their counter ions (e.g., H+, Li+, Na+ and so on) selectively and have been widely used as key materials to make ion exchange membranes for renewable energy generation (e.g., pressure-retarded osmosis, reverse electrodialysis, polymer electrolyte membrane fuel cells, and redox flow batteries). Particularly for effective power generation from salinity gradient, it is necessary to use high flux membranes with excellent ion-selectivity. High water flux can be accomplished by controlling the membrane thickness as thin as possible. However, thin membranes are suffering from high water pressure. This technical trade-off relationship may be overcome by filling ionomers into porous support films with high mechanical strength. It is, however, difficult to prepare the reinforced membranes without defects owing to ionomers solubility and compatibility issues, irrespectively of which ionomers are used. That is, perfluorinated ionomers have low solubility in most of solvents including polar aprotic solvents. The resulting membranes exhibit high brittleness. Much serious problems are observed during reinforced membrane formation using hydrocarbon ionomers. The good solvents to hydrocarbon ionomers dissolve support films, resulting in the breakdown of their pore structures. Moreover, it is important to enhance compatibility between hydrophilic ionomers and hydrophobic support films. Otherwise their interfaces may be converted into defects, which lower ion selectivity. This phenomenon is much easily observed as the pore size become smaller. In this study, a plausible approach, which is called as water-alcohol nanodispersion, was tried to obtain effective ionomers materials for defect-free reinforced membrane formation. Here, microporous poly(tetrafluoroethylene) (PTFE) support films were chosen considering chemical and thermal resistance of resulting reinforced membranes. The appropriate control of the solvent mixture contributed to high compatibility between ionomers and support films, and made spontaneous pore-impregnation possible. Interestingly, the nanodispersed ionomers resulted in much improved ion-selectivity owing to a synergistic effect of well-defined hydrophilic-hydrophobic phase-separated morphologies and high ionic density per hydrated membrane volume.
Development of Cost-Effective Ion-Exchange Membranes for High Performance Reverse Electrodialysis
Authors: Kim Do-Hyeong , Kim So-Eun , Park Jin-Soo , Kang Moon-Sung
Published: February 2020

Reverse electrodialysis (RED) is one of the promising processes for generating electricity from the salt concentration gradient between river and sea water. A RED stack contains alternately arranged anion- and cation-exchange membranes (AEMs and CEMs, respectively) which separate salt solutions of different concentrations. The power generation performance of REDs significantly depends on the characteristics of ion-exchange membranes (IEMs). The important membrane properties dominating the power generation in RED processes are the ion-exchange capacity, water swelling degree, electrical resistance, permselectivity, membrane thickness, and surface morphology etc. Moreover, the cost-effectiveness of IEMs is the most significant factor determining the successful commercialization of the RED process. In recent years, pore-filled IEMs (PFIEMs) in which an inert porous substrate provides excellent mechanical and chemical stabilities while a filling ionomer selectively transports ions through the membrane have been receiving great interests in the application to various energy conversion processes such as fuel cells and redox flow batteries. Simple and cheap mass production by a roll-to-roll process is one of the main advantages of the PFIEMs. In this work, we have investigated the optimum design parameters of the PFIEMs for successful application to a RED process. In addition, we have studied on the surface modification of the PFIEMs through facile methods for the improvement of the membrane properties. (This work was supported in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP) (2015R1A1A1A05001486) and the Technology Innovation Program funded by the Korea government (MOTIE) (No. 10047796).)
Performance Enhancement of Capacitive Deionization By Using Ionomer-Combined Carbon Electrodes and Pore-Filled Ionomer Membranes
Authors: Kim Do-Hyeong , Choi Young-Eun , Kim So-Eun , Park Jin-Soo , Kang Moon-Sung
Published: February 2020

Ion selective polymers (ionomers) are currently widely used in water treatment applications such as the diffusion dialysis, electrodialysis, and capacitive deionization for the desalination of brackish water, production of table salt, recovery of valuable metals from the effluents of metal-plating industry, and recoveries of acid and base from the spent leaching solutions. The functional ionomers are also utilized in various energy devices such as polymer electrolyte membrane fuel cells, redox flow batteries and so on. Especially, capacitive deionization (CDI) is thought to be one of the attractive environmentally-friendly desalination processes. It consumes relatively small energy for operation compared with other competing processes such as reverse osmosis. In addition, it does not produce any secondary regeneration wastes for a re-use. Comparing to the conventional CDI, membrane-CDI (MCDI) and ionomer coated-CDI have gained great interests due to the higher ion selectivity and removal efficiency. In this work, therefore, we have synthesized and characterized functional ionomers for the successful CDI application. The anion-exchange polymer was made from poly(2,6-dimethyl-1,4-phenylene oxide) through the bromination and consecutive amination processes. Meanwhile, the cation-exchange polymer was prepared via the sulfonation of polyetheretherketon. The functionalized ionomers exhibited excellent electrochemical properties of both the low electrical resistance and high ion selectivity. As a result, the functionalized ionomers which were coated on porous carbon electrodes largely improved the current and salt removal efficiencies of the CDI process. We have also developed a pore-filled IEMs (PFIEMs) for the applications to cost and energy efficient CDI processes. The PFIEMs composed of a highly inert and tough porous substrate and a polymer with functional groups that fills the pores can provide both high ion conductivity and excellent mechanical properties. In addition, the PFIEMs could be produced in a cheaper way by a roll-to-roll continuous process. The PFIEMs with a film thickness below 50 μm have been successfully prepared and characterized via various electrochemical analyses. As a result, they were shown to possess excellent electrochemical and mechanical properties. Their electrochemical characteristics have also been optimized for the successful applications to MCDI processes. (This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea (NRF-2015H1C1A1034436) and also by the Technology Innovation Program funded by the Ministry of Trade, industry & Energy (MOTIE) (No. 10047796).)
(Keynote) Skin-Worn Biosensors and Biofuel Cells
Authors: Wang Joseph
Published: February 2020

Wearable sensors have garnered considerable recent interest owing to their tremendous promise for a wide range of healthcare, military, sport and wellness applications. Such sensing platforms provide new avenues to continuously monitor individuals and can thus tender crucial information regarding a wearer’s health and performance in real time. This presentation will discuss recent developments in the field of wearable sensors ad biofuel cells (BFC), integrated directly onto both textile materials and on the epidermis for various non-invasive monitoring and energy-harvesting applications. The preparation and characterization of such textile-based and skin-worn electrochemical sensors and BFC will be described, along with their performance and the influence of the stretching and bending. Such mechanical stress studies indicate that tattoo and textile-based printed electrochemical sensors survive large deformations. Technical challenges and prospects for using textile- and tattoo-based electrochemical sensors for monitoring the wearer’s health, fitness, or surrounding environment will be discussed, along with several demonstrations and prospects for future healthcare and sport applications.
(Invited) Electrical Detection of Biomolecules Using Graphene-Based Devices
Authors: Maehashi Kenzo
Published: February 2020

Label-free electrical monitoring of biorecognition events provides a promising platform, which is simpler, less expensive and requires less energy. Rapid testing of different proteins is required in various applications, including clinical diagnostics, environmental testing, food analysis, bioterrorism detection technologies, etc.

Graphene, a single honeycomb-like sheet of carbon atoms, have been intensively investigated in most recent owing to its extraordinary high mobility even at room temperature [1]. Since graphene has a perfect two-dimensional structure, electrical characteristics in graphene devices are very sensitive for modulation of surface potentials in graphene channels. In this study, we have demonstrated highly sensitive electrical detection of biological molecules based on graphene devices.

A monolayer graphene was obtained by mechanical cleavage of graphite or CVD-based graphene on SiO2 films. Graphene devices were fabricated by conventional lithography and lift-off method. A silicone rubber was placed on the graphene devices so that the graphene channel was immersed in a buffer solution. An Ag/AgCl reference electrode was used as the top-gated electrode to minimize environmental effects.

Solution-gated graphene devices showed good transfer characteristics in buffer solution [2]. To selectively detect targets, receptors were modified on graphene channels [3-7]. For highly sensitive detection of biomolecules, small receptors such as aptamer or antigen-binding fragment (Fab) were utilized. Atomic force microscopy images revealed that receptors were successfully immobilized on the graphene channel. The receptor-modified graphene devices showed electrical detection of targets with concentration from few hundred pM to several hundred nM. Moreover, for development of highly sensitive influenza-virus sensors, glycan-modified graphene devices were also fabricated.

The biological molecules were detected with high sensitivity based on graphene devices. When a different kind of receptor is functionalized on each graphene channel in the graphene-device array, many kinds of biomolecules can be electrically detected simultaneously. Therefore, the graphene-device array can be useful for the fabrication of multiplex hand-held chemical and biological sensors for home medical care.

 

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Electrochemical Transformation of 2,5-Diphenyltellurophene
Authors: Shida Naoki , Komatsuzaki Yusuke , Seferos Dwight , Nishiyama Hiroki , Tomita Ikuyoshi , Inagi Shinsuke
Published: February 2020

Tellurphene-containing materials are attracting great attention in a wide range of chemistry field. Due to the metalloid nature of tellurium, tellurophene shows unique reactivity. Previous report revealed that the 2,5-diphenyltellurophene (PT) reacted with halogen sources to give its dihalogen adducts PT-X2
(Seferos et al., Dalton Trans. 2015, 44, 2092.) (Figure, upper). In this reaction, the oxidation state of tellurium-center changed from Te(II) to Te(IV), in other word, tellurium transformed into the hypervalent state. Interestingly, dehalogenation also occurred by the irradiation of the lights to give an original Te(II)-centered tellurophene.

In this study, we have investigated the electrochemical transformation of PT (Figure, lower). The spectroelectrochemistry measurements have successfully revealed that the oxidation of PT in the presence of halides (F-, Cl-, Br-) gave the corresponding hypervalent tellurium compound, PT-X2
. In addition, the electrochemical reduction of PT-X2
 resulted in the recovery of PT. In the course of Te(II)/Te(IV) redox cycle, there were no trace of side reaction, evidenced by the existence of isobestic points in absorption spectra. The bulk electrolysis of PT was also succeeded to give PT-X2
 in sufficient yield.

Figure 1