bluuebunny/crossref_metadata_2025 huggingface dataset:
Promoting Alkaline Hydrogen Evolution Activity Using Ordered Mesoporous Α-MoC1−X
Supported Pt Catalysts
Authors: Baek Du San , Jung Gwan Yeong , Kwak Sang Kyu , Joo Sang Hoon
Published: February 2020

The sluggish reaction kinetics of the alkaline hydrogen evolution reaction (HER) remains to be overcome for the commercialization of water-alkali electrolyzers [1, 2]. In this work, we demonstrate that the metastable face-centered-cubic (fcc) α-MoC1−x
phase shows superior water dissociation capability and alkaline HER activity than thermodynamically stable, hexagonal-close-packed β-Mo2C phase. In order to design high surface area fcc
α-MoC1−x
, an ordered mesoporous α-MoC1−x
(MMC) was synthesized by a nanocasting method. In the MMC structure, the α-MoC1−x
phase facilitates the water dissociation reaction, while the mesoporous structure enables high dispersion of metal nanoparticles (NPs) and efficient mass transport. As a result, Pt NPs supported on the MMC (Pt/MMC) catalyst showed substantially enhanced alkaline HER activity in terms of overpotentials, Tafel slopes, mass and specific activities, and exchange current densities, compared to those of commercial Pt/C and Pt NPs supported on particulate α-MoC1−x
or β-Mo2C. In particular, the Pt/MMC shows a very low Tafel slope of 30 mV dec−1, which is the lowest value among the reported Pt-based alkaline HER catalysts, suggesting the critical role of MMC in enhancing the HER kinetics. Furthermore, Pt/MMC exhibited almost no current decay for after potential cycling test whereas Pt/C underwent a negative shift of polarization curve. The promoting effect of MMC support in the alkaline HER was further demonstrated with an Ir/MMC catalyst.
Electrocatalyst Performance in Acidic Aqueous and Solid Polymer Electrolytes
Authors: Knöppel Julius , Ehelebe Konrad , Escalera López Daniel , Paul Michael T.Y. , Mayrhofer Karl J. J. , Cherevko Serhiy
Published: February 2020

Currently, aqueous electrolytes represent a model system for testing electrocatalyst performance. It is relatively easy to examine activity and stability of electrocatalysts performing simple half-cell electrochemical measurements in such electrolytes. On the other hand, modern electrochemical energy conversion devices such as fuel cells and water electrolysers use solid polymer electrolytes and ionomers in the catalyst layers, while water circulated in the system is deionized. An obvious question arises: "How good are aqueous electrolytes in representing operational conditions of real devices?” This presentation aims to address this question. While electrochemical activity of most catalysts is relatively similar in both environments, stability is not. Both, the extent of catalyst degradation and mechanisms responsible for stability depend on the electrolyte.1,2 Our recent work revealed that dissolution of iridium, as one of the degradation mechanisms, is significantly higher in aqueous acidic electrolytes.3 In order to understand this and other differences, several hybrid systems, i.e. repressing both aqueous and solid electrolytes, have been developed and tested. The main results of these experiments will be shown and discussed in this presentation.

Acknowledgements:

The project CREATE leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 721065.

Literature:

1 Cherevko, S. Current Opinion in Electrochemistry
8, 118-125 (2018).

2 Lafforgue, C. et al.
ACS Catalysis
8, 1278-1286 (2018).

3 Geiger, S. et al. Nature Catalysis
1, 508-515 (2018).
Effect of Substituents on the Activity of Organic Molecular Electrocatalysts for Hydrogen Evolution Reaction
Authors: Yin Xi , Holby Edward F. , Moore Cameron M , Zelenay Piotr
Published: February 2020

The hydrogen evolution reaction (HER) is a fundamental and critical process that enables H2 production through electrochemical water splitting. Conventional HER catalysts are based on metal-containing materials in which the metal atoms function as the catalytic centers. Recently, we demonstrated a metal-free organic molecular electrocatalyst (OMEC) for HER in acidic media with high activity and durability.1, 2 This OMEC is based on a small pyridine-based heterocycle. A density functional theory (DFT) study of the HER mechanism catalyzed by this molecule revealed that the thermodynamic limiting potential is related to the atomic hydrogen adsorption energy at the pyridyl-N site.1, 2 Further, our systematic study of the substituent effects on the proton-coupled electron transfer (PCET) potential at nitrogen-containing heterocycles provided guidance to the rational design of OMECs for HER.3

In this talk, we will present a study on the substituent effects on the activity of the organic molecular electrocatalyst mentioned above.1,2 Several substituents with electron-withdrawing/donating character will be included in this study. The HER activity of these substituted molecules is determined experimentally through electrochemical measurement. Their HER onset potentials are further correlated with the H adsorption energy values at pyridyl-N sites predicted from DFT calculations. Through the combined experimental-computational approach, we demonstrate the structure-activity relationship within this particular type of OMECs, guiding future OMEC research.

Acknowledgments

Financial support for this research by Los Alamos National Laboratory through Laboratory Directed Research and Development (LDRD) Exploratory Research (ER) program is gratefully acknowledged.

References

X. Yin, L. Lin, H. T. Chung, U. Martinez, A.M. Baker, S. Maurya, P. Zelenay. Organic Molecular Catalyst for Hydrogen Evolution Reaction, Meeting Abstracts, The Electrochemical Society, MA2017-02, 1659 (2017).

X. Yin, L. Lin, U. Martinez, H. T. Chung, P. Zelenay. Bifunctional Organic Molecular Electrocatalyst for Hydrogen Evolution Reaction and Hydrogen Peroxide Production, Meeting Abstracts, The Electrochemical Society, MA2018-02, 1609 (2018).

X. Yin, E. F. Holby, P. Zelenay. Structure-Activity Data Mining for Hydrogen Evolution Reaction at Organic Molecular Electrocatalysts, Meeting Abstracts, The Electrochemical Society, MA2019-01, 1429 (2019).
Improvements to Integrate Alkaline Water Electrolyzers for H2 Production from Renewable Sources
Authors: Cho Hyun-Seok , Cho Won Chul , Kim Sang-Kyung , Shimpalee Sirivatch , Kim Chang Hee
Published: February 2020

This presentation provides an overview of the alkaline water electrolysis for hydrogen production and discusses examples of previous and current research activities in KIER, and future opportunities for improvements of this technology. The challenges in material developments including electrodes and a separator to improve the cell performance and durability of alkaline electrolysis as advance designs will be introduced. The compact Unitized Bipolar Electrodes design was applied to evaluate the in situ single cell performance of AWE cells. Porous Ni-Zn-(Fe) electrodes as HER electrodes that were prepared by the electrodeposition method followed by the selective chemical etching of Zn in KOH. For the OER electrodes, Nix-Fe1-x Layered Double Hydroxide(LDH, x=0.5~0.7), which have shown the 100-fold OER activity enhancement over Ni in ex-situ studies was directly grown on metal lath and foams. Electro-activity of the AWE cell with Nix-Fe1-x LDH ＆ Ni-Zn-P electrodes toward HER/ OER has exhibited high-performance at 200 ＆ 600 mA/cm2, as a voltage efficiency of 97 ＆ 80% respectively, which is comparable to that of the well-developed commercial alkaline water electrolyzer.
Elucidating the Catalyst-Ionomer-Membrane Interface in Alkaline Exchange Membrane Electrolysis Cells
Authors: Ghoshal Shraboni , Pivovar Bryan S. , Alia Shaun M
Published: February 2020

In modern day zero gap electrolyzer cells, the fabrication of membrane electrode assembly (MEA) has a pivotal role in determining the performance of a cell. Intricate detail such as choice of membrane and ionomer, ionomer to catalyst ratio and catalyst loadings have been found to affect MEA performances. These factors become more critical in the case of non-precious catalysts where minute modifications can influence the MEA activity to a larger extent than compared to precious group metal catalysts which have high inherent activity. In this work, a combinatorial study using different types of ionomers and alkaline exchange membranes (AEMs) with a variety of supporting electrolytes have been carried out to delineate the effect of membranes and ionomers in an MEA.

References:

1. Leng, L. Wang, M.A. Hickner, C-Y Wang, Electrochim. Acta, 152 93(2015)

2. G-F Li, D. Yang, P-Y. A. Chuang, ACS Catal, 8, 11688 (2018)
Photo-Electric Properties of Polypyrrole Based Gel Electrolyte for Hybrid Photoactive Supercapacitors
Authors: Aljafari Belqasem , Khorramshahi Fatemeh , Ram Manoj K. , Takshi Arash
Published: February 2020

The nature of solar radiation is not steady, therefore having a solar-capacitor device that can simultaneously capture, convert and store solar energy is a considerable device. A self-charging capacitor is designed and fabricated as a functional solar energy storage device, which is accomplished in situ self-assembled storage technique. The solar-capacitor device is assembled on a multilayered photoelectrode combining of cationic dye (i.e. methylene blue, MB) and conducting polymer (i.e. Polypyrrole, Ppy) in contact with a single layer of HCl-Polyvinyl alcohol (PVA) gel electrolyte. Due to the high porosity of the multi-walled carbon nanotube (MWCNT) based counter electrode and the photo-electric properties of Ppy at the working electrode the device is working as photocapacitor. Therefore, the supercapacitor can be charged when the working electrode is illuminated. In this study, a photo-electrochemical device based on two-terminals that combines MWCNT/paper, Ppy/fluorine doped tin oxide conductive substrate (FTO), and a single layer of gel electrolyte is successfully designed and fabricated. This device can work independently as solar cell, supercapacitor, or a solar-capacitor device. Conducting Ppy has been used as a thin film deposited electrochemically on the surface of the FTO. The experiments are carried out in the dark at the beginning and then repeated when the working electrode is under the effect of solar irradiation. The open circuit voltage across the cell in the dark is 52 mV as initial value. Then, the cell voltage is increased gradually from 52 mV to 74 mV in 100 s of illumination. After turning off the light, the voltage is not dropping to the initial dark value immediately, and the slight change is due to the leakage current of the capacitive effect. The results of electrochemical and electrical characterization techniques such as Cyclic Voltammetery (CV), Electrochemical Impedance Spectroscopy (EIS), Open Circuit Voltage (OSV), and Short Circuit Current (SCC) on the hybrid device have been addressed in this study. The results are encouraging for application of Ppy film for solar-capacitor devices to harvest solar energy and store charges in a single device with two-terminals.
Engineering of Sequential-Series Multijunction Dye-Sensitized Solar Cells for Greater Than 10% Solar-to-Electric Efficiency and 2.0 V Photovoltage Output
Authors: Cheema Hammad , Delcamp Jared H.
Published: February 2020

Sequential series multijunction dye-sensitized solar cells (SSM-DSCs) are mechanically stacked single illuminated area DSC devices wired in series to harness photovoltage. SSM-DSCs are strategically designed to optimally utilize the potential energy of photons in each region of the solar spectrum. For this study, strategies to minimize photon reflection losses from glass and glass-air interface and photon management are combined. With a judicious choice of the sensitizer, TiO2 film thickness, solution processable “CYTOP” antireflection coating and immersion oil SSM-DSCs with power conversion efficiency >10% and 2.3 V photovoltage were achieved. Importantly, the SSM-DSC efficiency was substantially higher than any single device in the stack. Furthermore, without external bias this SSM-DSC configuration shows an impressive overall solar-to-fuel conversion efficiency of 6% when powering IrO2 and Au2O3 electrocatalysts for CO2 and H2O to CO and H2 conversion in aqueous solution. Concept of photon management in SSM-DSCs, device engineering, and role of CYTOP will be covered in the talk.
Fabrication of CZTSSe Thin Film Solar Cell By Single Step Sulfo-Selenization of Stacked Metal Precursors
Authors: Son Dae-Ho , Kim Seung-Hyun , Kim Se-Yun , Kim Young-Ill , Knag Jin-Kyu , Yang Kee-Jeong , Kim Dae-Hwan
Published: February 2020

The Cu2ZnSn(S,Se)4 (CZTSSe) thin films are the most promising photovoltaic absorber to replace CIGS, because it is comprised of abundant and inexpensive elements, and have a very high absorption coefficient of over 104 cm−1 with a direct bandgap energy. The theoretical solar conversion efficiency of CZTS-based thin film solar cells is as high as 32.2%. However, the maximum conversion efficiencies reported for electrical characteristics of devices based on these materials are still far from those accomplished more grown CIGS technologies. In order to achieve the efficiency of 20 % or more required for commercial technology, it is necessary to understand the limiting factors of the CZTSSe thin film. A parameter impacting the performance of increasing photovoltaic efficiencies in CZTSSe solar cells is band gap control of absorber through the control of S/(S+Se) ratio of CZTSSe thin films. Most of reported synthesized CZTSSe with high efficiency, the chalcogen composition of the absorption layer was controlled to optimize the characteristics. Most of them explain only the role of S in controlling the band gap in the CZTSSe thin film. It also only describes the characteristics of CZTSSe thin films and devices with different S ratios. However, S element plays another important role in CZTSSe crystal growth process. In this work, we have discussed the different effects of S in the CZTSSe thin film synthesis process. We fabricated CZTSSe thin films using optimized SLG-Mo/Zn/Cu/Sn (MZCT) as a stack structure and described the volatilization phenomenon of Zn element using MZCT stack structure. In addition, we have introduced H2S gas to effectively control the S/(S+Se) of the film in the sulfo-selenization process and to suppress the volatilization of Zn. The S injection process using H2S gas is more uniform and reproducible than any other processes. Unlike the pure selenization process, it was confirmed that a stable ZnSSe thin film was formed on the surface of the precursor during the sulfo-selenization process. The formation of ZnSSe thin film inhibited the volatilization of Zn, which facilitated the control of thin-film stoichiometry and also played an important role in crystal growth. Finally, the characteristics of thin films and devices fabricated through the optimization process are discussed.

Acknowledge: This work was supported by the DGIST R&D Program of the Ministry of Science and ICT (19-BD-05) and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20173010012980).
3D Printed MXene Micro-Supercapacitors with Ultra-High Energy Density
Authors: Orangi Jafar , Beidaghi Majid
Published: February 2020

Small scale energy storage devices are expected to play a significant role in the future advances of portable electronics, wireless sensors, and multifunctional micro/nanosystems. A crucial requirement for the fabrication of energy storage devices with high energy and power densities is using electrode materials with superior electrochemical properties. Another important requirement is the assembly of the electrode materials into structures that promote high ionic and electronic conductivities. In this talk, we report a scalable printing method for fabrication of on-chip three-dimensional (3D) micro-supercapacitors based on a class of 2D transition metal carbides called MXenes as electrode materials. MXenes offer high electronic conductivity and high specific capacitance and therefore, have attracted much interest as high-performance electrode materials for supercapacitors. In our work, the fabrication of MXene electrodes and device assembly is achieved using an extrusion-based 3D printing process that uses viscoelastic water-based MXene ink. A programmable printing machine was used in the printing process which involved layer-by-layer deposition of the MXene ink to fabricate the 3D electrodes. The developed printing method allows rapid fabrication of micro-supercapacitors on a variety of substrates, while electrode height can be controlled by the number of deposited layers. All-solid-state devices printed on flexible substrates showed excellent electrochemical performances under different bending conditions and delivered extremely high areal capacitances (over 1035 mF cm-2). Our study suggests that due to its high electronic conductivity and electrochemical properties, MXene is an excellent electrode material for the fabrication of 3D energy storage devices
(Invited) Keeping It Simple: Anode Free Lithium Metal Cells with Liquid Electrolytes As a Path to Higher Energy Density
Authors: Genovese Matthew , Louli Alex , Weber Rochelle , Martin Cameron , Dahn Jeff R.
Published: February 2020

In the pursuit of higher energy density, both academia and industry are intensely researching many alternative rechargeable battery concepts beyond conventional lithium-ion cells. The most promising alternatives will be those that can achieve cell level energy density larger than that of state-of-the-art lithium ion batteries at a comparable or lower cost. Based on these criteria, anode free lithium metal cells emerge as potentially useful lithium-ion alternatives as their simple cell construction can enable both high energy density and low cost assembly.

In anode free cells, the negative electrode begins as a bare copper current collector and the lithium metal anode is plated in-situ from the lithium inventory in the cathode. These cells can achieve energy density 40-50% greater than lithium-ion at the cell level and have a simpler cell construction that eliminates the need to handle lithium metal foils or coat active materials on the negative current collector. However, the cycling stability of these cells in conventional carbonate liquid electrolytes is often terrible due to the low CE of lithium metal and the lack of an excess lithium reservoir. In this way, anode free cells exaggerate the technical challenges of lithium metal which makes them excellent test vehicles for optimizing lithium metal cycling.

In this presentation we will highlight our progress in improving lithium metal cycling efficiency in liquid electrolytes toward the development of safe, practical, high energy density anode free cells. Much of this work focuses on the development and characterization of anode free LiNi0.5Mn0.3Co0.2O2 (NMC 532)//Cu wound pouch cells. We demonstrate that the cycling stability and safety of these cells is directly correlated to the morphology of the lithium plated during charge. High surface area mossy lithium deposits in conventional liquid electrolytes lead to fast capacity fade and high anode reactivity. We will also show how many different factors including, cycling rate, charge protocol, applied pressure, temperature, and electrolyte composition affect lithium morphology. Our latest results will be highlighted which show that with the appropriate electrolyte chemistry and cycling conditions, smooth lithium morphology with densely packed columns 50 um in diameter can be achieved after cycling in liquid electrolytes. This excellent lithium morphology significantly improves the capacity retention (Figure 1) of anode free cells and limits the reactivity of the deposited lithium. Cell failure mechanisms will also be addressed with insight as to how these failures can be overcome to further improve cycle life. These results demonstrates that stable cycling of dendrite free lithium metal is possible in simple anode free cells with liquid electrolytes which represents a promising and practical avenue for the design of high energy density batteries.

Figure 1
Fabrication of Carbon-Coated 3D Ni Nanomesh and Its Application As a High Surface Area Electrode Material for Li-O2 Battery
Authors: Kee Yongho , Bardé Fanny , Vereecken Philippe M.
Published: February 2020

Over the last two decades, post lithium ion battery chemistries with even higher power and energy density, compared to those of conventional lithium ion batteries with intercalation hosts, have been widely researched for application in large scale energy storage. Among various candidates, Li-O2 battery is one of the most promising alternative chemistries, having a theoretical energy of 3505 Wh kg-1 via plating and stripping of Li2O2 with an average working potential of 3 V vs. Li+/Li. However, Li-O2 battery often shows insufficient areal capacity due to the insulating properties of thick Li2O2 layer.

Previously, our group reported the fabrication of a novel 3.3 μm thick 3D Ni nanomesh current collector, which shows excellent surface area to geometric footprint area ratio (100 cm2/1 cm2) and high theoretical porosity (76 %) with systematically controlled nanowire thickness via anodization of aluminum alloys (Fig. 1) [1, 2]. Thanks to its unique properties, the 3D Ni nanomesh qualifies as an excellent current collector candidate for reversible Li2O2 plating and stripping performance over large surface area with the enhanced areal capacity. In this study, we aimed to introduce amorphous carbon, one of the most studied electrode materials for Li-O2 battery, as a coating material for 3D Ni nanomesh via low temperature PECVD technique. To investigate its potential application as an electrode for Li-O2 battery, the galvanostatic charge and discharge profiles of glassy carbon and carbon-coated 3D Ni nanomesh are recorded with the discharging current rate of 0.1 mA cm-2 and the balanced charging current rate of 0.05 mA cm-2 under pure O2 atmosphere. During the preliminary electrochemical measurement, we observed that the carbon-coated 3D Ni nanomesh showed greatly increased discharge and charge areal capacity than those of glassy carbon (102 and 563 times higher than those of glass carbon). In addition to the above-mentioned findings, the ex-situ STEM images of carbon-coated 3D Ni nanomesh after charging and discharging processes will further be discussed.

References

[1] J. Vanpaemel, A. Abd-Elnaiem, S. De Gendt, and P.M. Vereecken, J. Phys. Chem. C, 2015, 119, 2105-2112.

[2] S.P. Zankowski and P.M. Vereecken, ACS Appl. Mater. Interfaces, 2018, 10, 44634-44644.

Fig. 1. Brief description of 3D Ni nanomesh fabrication process and SEM images of as-prepared 3.3 μm thick 3D Ni nanomesh current collector template.

Figure 1
Improvement of Electrochemical Performance of Thin Film Mixed Ionic Electronic Cathode for Low Temperature Solid Oxide Fuel Cells By Additional Catalytic Current Collecting Layer
Authors: Lee Sanghoon , Cho Gu Young , Ryu Sangbong , Jeong Wonyeop , Cha Suk Won
Published: February 2020

In the present study, catalytic current collecting layer (CCCL) was added to thin film La0.6Sr0.4Co0.8Fe0.2O1-δ (LSCF) cathode for low temperature solid oxide fuel cells (LT SOFCs) to improve both electrical current collection and catalytic activity. By adding CCCL, the maximum power density improved nearly 10-fold compared to the bare LSCF cathode. With thicker Pt or Pd CCCL, ohmic loss in current collection and oxygen reduction reaction (ORR) activity were both improved. Due to smooth oxygen ion conduction of solid oxide electrolytes, a typical range of operating temperature of SOFCs is 800 ~ 1000 ℃, which imposes a number of obstacles for SOFCs to be commercialized. Lots of studies have been carried out to make the operating temperature lower, down to 400 ~ 600 ℃. However, not only ion conduction in electrolytes but also ORR activity in cathode highly depends on temperature. As the operating temperature goes down, the faradaic impedance of SOFCs become severe because of sluggish ORR at a lower temperature. LSCF, one of the widely used cathode material in SOFCs, shows poor ORR activity and electronic conductivity at this temperature range. Therefore, Pt has been mainly used as electrode material for LT SOFCs based on its superior catalytic activity in lower temperature but it suffers from thermal instability, such as agglomeration. In this report, the noble catalysts, Pt and Pd, were investigated as the CCCL for mixed ionic electronic conductor LSCF cathode to enhance both electronic conductivity and catalytic activity at 550 ℃. LSCF cathode was deposited on the single crystal (100) YSZ pellet by using PLD. For the CCCL, Pt and Pd were adopted and deposited via direct current (DC) magnetron sputtering on the LSCF cathode. The thickness of the CCCL was varied from 100 nm to 300 nm. Ni was used as anode and deposited on the other side of the pellet via DC magnetron sputtering for about 300 nm. GDC interlayer with thickness of approximately 250 nm was applied between YSZ pellet and LSCF cathode to block formation of any insulation layer through reaction between YSZ and LSCF. Electrochemical performance was investigated through i-V plot and EIS and long-term stability was measured with Galvanostatic mode. The microstructure of LSCF and CCCL were investigated through FIB-SEM, FE-SEM. Crystal structure of the LSCF cathode CCCL was studied with XRD.
Electrocatalytic Effect of IrO2-Ta2O5|Ti and RuO2-Ta2O5|Ti during the Electrochemical Degradation of Phenol
Authors: León Itzel , Pujol Alberto Alejandro , Cárdenas Jesús , Manríquez Juan , Bustos Erika
Published: February 2020

Titanium electrodes coated by transition metal oxides have shown a large number of applications, thus being the subject of constant research and improvement. One of the most important applications for this type of electrodes is the electro-generation of hydroxyl radicals (•OH) and hydrogen peroxide (H2O2) via catalytic water oxidation to the electrochemical degradation of organic compounds, as phenol (Phen). Looking for improving the electrochemical performance of IrO2-Ta2O5|Ti and RuO2-Ta2O5|Ti electrodes and also provide a better understand about their electrochemical behavior at an interfacial approach, this investigation was focused to compare the electro catalytic removal efficiency of Phen using different Ir:Ta and Ru:Ta ratios at the coating (70:30 and 30:70) by the generation of •OH and H2O2 in acid conditions (H2SO4).
Hydrogen Evolution Reaction on Atomic Layer Deposited Molybdenum Nitride (MoNx) Thin Film on Highly Porous Carbon Cloth-Based Substrate
Authors: Ramesh Rahul , Sawant Sandesh Y. , Nandi Dip K. , Cho Moo Hwan , Kim Soo-Hyun
Published: February 2020

Using the atomic layer deposition (ALD) technique, a uniform, and conformal thin film of molybdenum nitride (MoNx) is successfully coated on to a highly porous carbon cloth-based substrate. The precursor used in ALD-MoNx is molybdenum hexacarbonyl (Mo(Co)6), and ammonia is used as the nitrogen source, while the temperature and number of ALD cycles are set at 225︒C and 700 cycles, respectively. The phase, surface characteristic, thickness, and conformal deposition of the film is established using XRD, XPS and SEM imaging, respectively. A conformal and uniform film with a thickness of 25–30 nm, and with overall composition c.a. Mo0.59N0.41 is observed. The as-deposited film exhibits predominantly amorphous characteristic, with a minor nanocrystalline nature. The film has noticeable oxygen contamination, mainly at the surface. Hydrogen evolution reaction (HER) performance of the as-prepared electrode is evaluated in 0.5 M H2SO4 electrolyte in a conventional three-electrode setup using the Ag/AgCl (3 M KCl) and graphite rod, as reference and counter electrode, respectively. The electrode exhibits good HER performance attributed to the high surface area of the substrate. Further, the porous structure of the electrode is systematically investigated using SEM imaging, and electrochemical impedance spectroscopy (EIS). A direct correlation of pore geometry is established by studying the HER at different overpotential, electrode composition, and nature of the electrolyte.

Acknowledgement

This work was financially supported by the MOTIE (Ministry of Trade, Industry & Energy (#10080651) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device and the Advanced Technology Center Program (#10077265) funded by the MOTIE (Ministry of Trade, Industry & Energy) of the Republic of Korea
Variations of Mass-Transport and Heterogeneous Electron-Transfer Rate with the Temperature in Ionic Liquids
Authors: Lebrun Claire , Turmine Mireille , Vivier Vincent
Published: February 2020

Ionic liquids are molten salts with a melting point under 100°C. They are of growing interest due to their outstanding properties and appear to be good candidates for many electrochemical applications. However, ionic liquids represent a huge category of compounds and an electrochemical reference is needed to be able to make comparison of their behavior. For this purpose, the ferrocene/ferrocenium redox couple is considered as the reference of choice because it has a kinetically facile and rapid process. Moreover, this redox couple usually described as a nearly "solvent independent" formal potential system.1 However, a quick look at the literature shows important discrepancies in the heterogeneous electron-transfer rate constant (k°).1, 2 In this work, we chose to study two ionic liquids (1-butyl-1-methylpyrrolidium bis(trifluoromethanesulfonylimide), C4mpyrTFSI and 1-butyl-3-methyl-midazolium bis(trifluoromethanesulfonylimide), C4mimTFSI) in the temperature range between 20°C to 60°C for which several physicochemical properties (conductivity, density, viscosity) were measured. Then, the electrochemical behavior of ferrocenemethanol was examined by different techniques (linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperommetry) in the same temperature range with a gold and carbon microelectrodes of 25 µm and 11 µm of diameter, respectively. Modifying the temperature leads to a variation of the conductivity and viscosity implying a change in the mass transport of the redox species to the electrode but also in the rate constant k°. From the linear sweep voltammetry, the rate constant of the redox reaction of ferrocenemethanol was determined by the analysis of steady-state voltamogram3 and compared to results obtained from impedance spectroscopy. Additionally, the variations of the diffusion coefficient of the reduced species and the rate constant with the temperature were also analysed in term of viscosity of the solvent.

Bentley, C. L.; Li, J.; Bond, A. M.; Zhang, J., Mass-Transport and Heterogeneous Electron-Transfer Kinetics Associated with the Ferrocene/Ferrocenium Process in Ionic Liquids. J. Phys. Chem. C
2016,
120 (30), 16516-16525.

Siraj, N.; Grampp, G.; Landgraf, S.; Punyain, K., Cyclic Voltammetric Study of Heterogeneous Electron Transfer Rate Constants of Various Organic Compounds in Ionic Liquids: Measurements at Room Temperature. Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics
2013,
227 (1), 105-119.

Mirkin, M. V.; Bard, A. J., Simple analysis of quasi-reversible steady-state voltammograms. Anal. Chem.
1992,
64 (19), 2293-2302.

Figure 1
Catalytic Electrode Membrane and Applications in Fuel Cell Type Reactors for 3 Phases Pollution Control
Authors: Liu Lifen
Published: February 2020

Microbial fuel cell or photocatalytic fuel cell reactors are applicable in removing pollutants from water, air and soils, where catalysts loaded on the electrodes/membranes, can well function that increase cell voltage , power generation and help in degrading /mineralizing pollutants in aqueous or gas phase streams and/or desorbed from soil/solids. The reactors recover energy in pollutants and self biased for simultaneous catalysis over the electrode interface. Examples of catalysts such as Fe/TiO2 /g-C3N4, WO3, BiOCl/BiOI readily function as electrode catalysts, that in PFC , degrade pollutants such as antibiotics, dyes, coking wastewater, in aqueous phase, ethyl acetate, toluene , HCHO in gas phase, and dissolved organics from contaminated soil . Removal Efficiency of organic pollutants can be enhanced by integrating microbial process and bio-electrochemical process, with physiochemical reactions over the electrodes. Filtration through the membrane electrode can enhance further the removal. The electrode reactions can be promoted by using persulfate activation and oxidation, or by compositing with piezoelectric catalysts such as ZnO or other single atom catalysts/or highly dispersed catalyst such as Cu-Co-O. The energy recovered/ generated over the electrode area can reach 11, 22, or 87W/m2. depending on the pollutants concentration and features of pollutant molecule structures.
Simultaneous Detection of Carbamates and Organophosphate Pesticides at Bare Boron-Doped Diamond Electrodes
Authors: Bentin Ella , Foord John S.
Published: February 2020

Carbamate and organophosphate compounds are widely used pesticides because of their high insecticidal activity, and sometimes as nerve agents because of their crippling inhibition of the enzyme acetylcholinesterase (AChE)1. These compounds accumulate in the food chain and can hijack the nervous system of the target organisms indiscriminately. Traditional electrochemical methods of pesticide detection rely on layered structures atop noble metal or carbon electrodes to assist the loading of AChE, which produces currents proportional to its inhibition level. One of the clear advantages of boron-doped diamond (BDD) as an electrode material is its greater potential window in aqueous solutions, compared to conventional electrode materials2. This allows redox behaviour at extended potentials to be observed without damage to the electrode.

Cyclic, differential-pulse, and square-wave voltammetric techniques were used to probe carbaryl (CB), carbofuran (CF), and malathion in Carmody buffers of pH 2–12. Oxidation of CF occurred at the three overpotentials 1.31 V, 1.44 V, and 1.69 V, and a broad reduction peak was observed at 1.10 V, referred against Ag|AgCl. Compared with the oxidation of CB at 1.35 V, these electrochemical differences allowed for simultaneous detection of both compounds. This non-enzymatic sensor demonstrated a linear calibration over a concentration range of 1–100 µM for CB (R=0.9834) and CF (R=0.9938). After exposure to 1 mM malathion, a reduction peak appears that is highly sensitive to pH, attributed to a complex carbon–oxygen adsorbate that is robust to aggressive cleaning methods and only removable by hydrogen plasma etching. This malathion modified surface may be advantageous in future applications such as pH sensing. The oxidised BDD demonstrated failsafe reproducibility, a linear response, and low detection limits at medically relevant concentrations.

References

Kostelnik, P. Kopel, A. Cegan, M. Pohanka, Sensors, 17 (2017) 676.

V. Macpherson, Phys. Chem. Chem. Phys.,
17 (2015) 2935-2949.
Machine-Learning Enabled Search for the Next-Generation Catalyst for Hydrogen Evolution Reaction
Authors: Wei Sichen , Baek Soojung , Reyes Kristofer , Yao Fei
Published: February 2020

As a zero-emission, eco-friendly fuel, hydrogen gas can be generated via electrochemical (EC) water splitting. Achieving high-efficiency water splitting requires the use of a catalyst to minimize the overpotential to drive the hydrogen evolution reaction (HER). Noble metals such as platinum (Pt) can provide an excellent catalytic activity for HER but are too expensive and scarce for broad applications. Therefore, the development of active HER catalysts made from low-cost materials constitutes a crucial challenge in the utilization of hydrogen energy.

Earth-abundant transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), have been discovered recently, which exhibit good activity and stability for electrocatalytic reactions. In order to fully explore the untapped potential of MoS2, the synthesis recipe for MoS2needs to be optimized. Such an optimization process needs scientists to search through a combinatorically large space of experimental parameters, which will be time-consuming and costly if using conventional trial-and-error approaches.

In this report, MoS2 HER catalytic activity optimization is performed by examining different combinations of synthesis parameters during the hydrothermal process. To investigate the structure-activity relationship, scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and various electrochemical characterizations have been conducted. A strong correlation between hydrothermal conditions and HER performance matrix has been observed. In order toaccelerate the search for the best synthesis recipe, machine-learning (ML) techniques have been introduced to help identify the optimal parameter combinations for producing MoS2. The hydrothermal parameters with the corresponding onset potentials and Tafel slopes are adopted as prior knowledge and are incorporated into the Bayesian Optimization model. The model will be able to guide the wet chemical synthesis of MoS2and yield the most effective HER catalyst eventually.
Evaluation of Changes in Bond Parameters in Sulfolane Under the Influence of Electron Donating Substituents
Authors: Yasko Andrey , Khamitov Edward , Kuzmina Elena , Kolosnitsyn Vladimir
Published: February 2020

Sulfolane is a promising solvent for electrolytes in lithium-ion batteries, because it possesses high thermal and oxidative stability, high flash point, well dissolves lithium salts. However, sulfolane has a high melting point (27.5 °C) and viscosity (0.01029 Pa • s at 30 °C). High melting point and viscosity due to the tendency of sulfolane to self-association. To reduce the degree of self-association is possible by introducing various substituents into the sulfolane molecule.

The aim of the work was to investigate how the introduction of substituents into the sulfolane molecule affects its chemical stability. Chemical resistance was judged by changes in bond orders.

Presented work summarizes the results of quantum-chemical calculations of the bond orders in the sulfolane molecule and its substituted analogs, including methyl-, ethyl-, propyl-, vinyl- and allylsulfolanes (Figure 2).

Quantum chemical calculations were performed using the Gaussian09 software package. The optimization procedure was performed using the TPSS/cc-pVTZ method. Analysis of wave functions and calculation of bond orders by “fuzzy” method were performed in MultiWfn software package.

The objects of study were sulfolane and analogs with electron donor substituents. A total of 21 structures. The nature of the change in bond orders shows the influence of the position of substituents on electron density distribution. It has been established that the substitution of hydrogen atoms for this groups has the greatest influence on the order of the C – S and C – C bonds, reducing it, and the smallest on the S = O bond. This is especially clearly observed when hydrogen atoms attached to carbons connected to sulfur are substituted. These data show the possible paths of reduction reactions.

This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7) Russia and was also financially supported by the Russian Science Foundation (project No 17-73-20115).

Figure 1
Ionic Conductivity and Thermal Stability of Polyethylene Glycol Based Polymer Electrolytes Containing Phosphonium Ionic Liquids
Authors: Nomizu Daiki , Tsunashima Katsuhiko , Sakaguchi Yuki , Higashi Toshikazu , Yamada Hirohisa , Matsumiya Masahiko
Published: February 2020

Room-temperature ionic liquids (RTILs), i.e. organic molten salts with melting points below 100 ◦C, have been regarded as potential media in various chemical systems due to the fact that RTILs have unique physicochemical properties such as favorable solubility of organic and inorganic compounds, no measurable vapor pressure, high thermal stability, low flammability, etc. On the other hand, polyethylene glycol (PEG) is widely used as an electrolyte for lithium polymer secondary batteries from the viewpoint of considerable interaction with lithium ions. However, PEG does not show sufficient ionic conductivity because partial crystallization proceeds at temperatures below the melting point.1 In order to solve such a problem, various types of RTILs have been investigated for the PEG based polymer electrolytes; however, RTILs based on quaternary phosphonium cations have rarely been employed for the polymer application despite the fact that the phosphonium RTILs offer both high conductivity and thermal stability.2 In this work, we report the preparation of the PEG-based polymer electrolytes containing phosphonium RTILs, examining their physicochemical properties such as conductivities, thermal decomposition temperatures, etc.

The preparation of the phosphonium RTILs was performed by aqueous ion exchange reaction of the precursor quaternary phosphonium halides with lithium bis(trifluoromethylsulfonly)amide (TFSA). The RTILs and PEG were mixed at a mass ratio of 4:6 to prepare the polymer electrolytes. The conductivities of the polymer electrolytes were evaluated by an ac impedance measurement. The thermal decomposition temperature of the polymer electrolytes obtained was measured by a thermogravimetric analysis.

As shown in Fig. 2, it was found that relatively high conductivities were observed in phosphonium RTIL based polymer electrolytes when compared to those in the polymer electrolytes prepared by using the corresponding ammonium RTILs. This result seems to be due to the relatively high transport property of the phosphonium RTILs. The thermal decomposition behavior of the phosphonium RTIL based polymer electrolytes will be discussed.

References

D. Fauteux, A. Massucco, M. McLin, M. van Buren, J. Shi, Electrochim. Acta, 40, 2185 (1995).

K. Tsunashima, M. Sugiya, Electrochem. Commun., 9, 2353 (2007).

Figure 1
Probing the Influence of Solvation Entropy on Li+/Li Redox in Aprotic Electrolytes
Authors: Leverick Graham , Nienhuis Janet , Crabb Emily , France-Lanord Arthur , Stephens Ryan M. , Grossman Jeffrey C. , Shao-Horn Yang
Published: February 2020

Solvation plays a vital role in determining the thermodynamics1 and kinetics2 of both homogeneous and heterogeneous redox reactions, as well as bulk electrolyte properties such as ionic conductivity. While the enthalpic contribution of aprotic solvents are well understood through empirically measured solvation parameters such as the Gutmann donor and acceptor number3, the contributions of solvation entropy on redox reactions, particularly in nonaqueous solvents, is not well understood. In this work, we consider the effect of solvent, counter anion and salt concentration on the solvation entropy of Li+ ions. Through probing the reaction entropy of the Li+/Li redox couple in a variety of salt and solvent systems, we find in a fully dissociated electrolyte, such as LiTFSI in DMSO, that the solvation entropy depends mostly on the activity and mobility of Li+ ions. Alternatively, in electrolytes with significant ionic association, such as LiTFSI, LiTfO and LiTFA in DME, more complex and non-ideal behavior is observed. The results of this study enable a stronger fundamental understanding of the role of entropy on solvation, promoting rational design of electrolytes in aprotic systems.

References

D. G. Kwabi et al., Angewandte Chemie International Edition, 55, 3129–3134 (2016).

R. A. Marcus, Reviews of Modern Physics, 65, 599–610 (1993).

V. Gutmann, Electrochimica Acta, 21, 661–670 (1976).
Electrodes Modified with Redox Mediators for Improve Charge Transfer in Redox Flow Batteries
Authors: Emmett Robert K , Roberts Mark E.
Published: February 2020

Electrochemical performance of iron redox flow batteries (RFBs) was improved through incorporating iron redox mediators into the electrodes. Unpurified carbon nanotubes electrodes containing ferrocene catalysts, from the carbon nanotubes synthesis, are activated to create “hotspots” for Faradaic charge transfer that reduces losses associated with activation, Ohmic, and mass transfer resistances. This permits higher discharge voltages at elevated discharge currents, which from Ohm’s Law (P = iE) establishes augmented power densities. Carbon nanotube electrodes are activated utilizing cyclic voltammetry, in an acidic environment, to initiate charge transfer interactions between redox electrolytes and iron nanoparticles in the electrode. Modified electrodes exhibited 141% gain in power density and a 56.5% improvement in energy density in coin cell devices. Economic value and ready availability of iron paired with enhanced performance makes iron RFBs a viable option for future RFB research. The highest peak power density reported for all-iron RFBs to the author’s awareness was accomplished at 176 mW cm-2 with iron-modified electrodes under no electrolyte flow.
Free-Standing Carbon Electrodes for the Oxygen Evolution Reaction
Authors: Song Feihong , Ding Yuxiao , Lin Yangming , Heumann Saskia , Schloegl Robert , Mechler Anna Katharina
Published: February 2020

N-functionalized hydrothermal carbon materials (N-HTC) with spherical morphology were prepared by hydrothermal synthesis utilizing glucose and urotropine as starting materials, which makes the synthesis cost-efficient, environmental friendly and allows simple scale-up. The molar ratio of glucose and urotropine has been varied and the powder materials were pelletized, resulting in mechanically stable disc electrodes. By increasing the amount of nitrogen, N-contents from 5 wt% up to maximal 8 wt% were obtained after pyrolysis at 1000 °C. The pellet can then be used as an anode for alkaline water splitting. In literature, there are still no direct evidence of metal-free carbon as electrocatalyst for oxygen evolution reaction. By comparing the N-functionalized sample and without functionalization, we found that the former has superior stability under water splitting condition (relative high potential). Up to one week of stable oxygen production was achieved. The result indicates that nitrogen facilitates oxygen evolution reaction. Besides, the nitrogen species also hinders carbon corrosion, proved by a simple Hoffmann cell measurement. Pellets with different synthesis condition as well as nitrogen content are compared in order to get the optimized synthesis condition.

For better understanding, methylene blue adsorption and mercury intrusion porosimetry are used to characterize the pore structure of the carbon materials. The relative work function and conductivity of the carbon pellet are determined by Kelvin-probe and Van-der-Pauw methods, respectively. A conventional three-electrode assembly is used to characterize the electrochemical performance, including activity, stability as well as mass transport property by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy (EIS). A transmission line equivalent circuit model is used to fit the EIS complex spectra, where the diffusion resistance and reaction resistance can be determined. The two resistances are very important reaction key performance indicator for oxygen evolution reaction, as it can distinguish a diffusion process from a reaction. The gas products as well as electrolyte after electrochemical test can be analysed by mass spectrometry, ESI-MS, UV-VIS spectroscopy, etc. From the mass spectrometry results, the mole fraction of oxygen in the total product gas can be determined, determining the selectivity of the reaction. Besides, water diffusion NMR measurements before and after electrochemical test shows changes in the water interaction, which can be correlated to Nitrogen species changes in the electrode.

This study demonstrates that N-functionalization improves the stability of HTC for oxygen evolution reaction providing a promising pathway for the future energy conversion and storage.