bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Activity of Non-Noble Metal Alloy as Catalyst Towards Oxidation of Glycerol in Acidic Media: A Case for the Conceptual Glycerol/Ferric Redox Flow Battery
Authors: Kalu Egwu Eric , Akrasi James , Yeboah Yaw D.
Published: February 2020

Electro-catalytic oxidation of polyols is a very important path towards the production of high value chemicals. The electro-oxidation of glycerol using precious metals such as Au and Pt has been studied and known to be a source of several end products and has also been utilized in the concept of direct glycerol fuel cells to produce electrical energy additionally [1]. Herein an electro-catalyst comprising a non-noble metal alloy composition, namely nickel, copper and tin on carbon support have been fabricated using the electroless deposition method. The electrochemical activity of the prepared catalysts towards the glycerol oxidation reaction in acidic medium have then been evaluated using physical characterization, electrochemical and chromatographic methods. In the current study, the concept is applied to experimentally demonstrate the working principles of a glycerol-fed redox flow battery using an aqueous solution of a Fe2+/Fe3+ couple as cathode [2]. Constant potential electrolysis coupled with high performance liquid chromatography were used to identify the various compounds generated as a result of the electro-catalytic conversion of glycerol.

References

Li W., Xin L., Zhang Z., Wang Z. (2012) Simultaneous Generation of Mesoxalic Acid and Electricity from Glycerol on a Gold Anode Catalyst in Anion-Exchange Membrane Fuel Cells ChemCatChem Vol 4 1105-1114

J, Kalu E. and Yeboah Y. (2017) A Group Additivity based-thermodynamic analysis of a conceptual glycerol/ferric redox flow battery ECS Transactions, 77 (11) 2005-2010
The Physical Characterization of Single-Crystalline Chromium Silicide Nanowires Grown By Chemical Vapor Deposition
Authors: Hsu Han-Fu , Tsai Ping-Chen , Lu Kuo-Chang
Published: February 2020

In this research, chromium disilicide nanowires were synthesized by chemical vapor deposition (CVD) processes on Si (100) substrates with hydrous chromium chloride (CrCl3·6H2O) as precursors. Processing parameters, including the temperature of Si (100) substrates and precursors, the gas flow rate, the heating time and different flow gases of reactions were varied and studied; additionally, the physical properties of the chromium disilicide nanowires were measured. It was found that single-crystal CrSi2 nanowires with an unique morphology were grown at 700°C, while single-crystal Cr5Si3 nanowires were grown at 750°C in reducing gas atmosphere. The crystal structure and growth direction were identified, and the growth mechanism was proposed as well. This study with magnetism, photoluminescence, and field emission measurements demonstrates that CrSi2 nanowires are attractive candidates for future applications in magnetic storage, photovoltaic and field emitters.
Quasi-Two-Dimensional β-Ga2O3 based Hetero-Structure Transistors
Authors: Kim Janghyuk , Kim Suhyun , Kim JiHyun
Published: February 2020

β-Ga2O3 is a wide band gap (4.8 eV) semiconducting material with outstanding chemical and thermal stabilities. As the breakdown voltage of β-Ga2O3 is estimated to be as high as 8 MV/cm, it can be applied to high-power electronics. After β-Ga2O3 thin layers were successfully exfoliated from bulk single crystals by mechanical exfoliation method, the study of high power 2D nano-electronics using β-Ga2O3 received a considerable attention. Though β-Ga2O3 is not a two-dimensional Van der Waals material like graphene and MoS2, a bulk β-Ga2O3 crystal can be easily cleaved into thin nano-flakes in the (100) direction; it has monoclinic structure and the lattice constant is larger along the cleaved plane. Moreover, this ultrathin β-Ga2O3 flakes can be integrated with other 2D materials such as hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDs) to make down-scaled, flexible devices. We demonstrated two types of heterostructure devices (MISFETs and JFETs) based on β-Ga2O3 flakes and 2D materials using PDMS stamp method and photolithography.

β-Ga2O3/h-BN hetero-structure based quasi-two-dimensional metal insulator semiconductor field-effect transistors(MISFETs) are fabricated. The h-BN dielectric, which has an extraordinarily flat and clean surface, provides a minimal density of charged impurities at the interface between β-Ga2O3 and h-BN, resulting in excellent device performances. The fabricated MISFETs showed superior drain current modulation with high on/off ratio and low gate leakage current. The double-gating of the fabricated device was demonstrated by biasing both top and bottom gates, achieving the modulation of the threshold voltage.

N-channel β-Ga2O3/WSe2 heterostructure junction field effect transistors (JFETs) are demonstrated with good gate modulation and negligible hysteresis. Tungsten diselenide (WSe2) is mostly known as a stable p-type 2D layered material. The fabricated heterostructure JFETs also showed excellent ambient stability. The successful JFET operation is attributed to Van der Waals junction interface between β-Ga2O3 and WSe2. These heterostructured wide-band-gap nanodevices show a new route toward stable and high-power nanoelectronic devices. The details of the fabrication procedure and results will be presented.
Development of Self-Powered Mercury Ion Sensor Based on Thermoelectric Effect
Authors: Lin Yu-Jhen , Tsao Yu-Hsiang , Lin Zong-Hong
Published: February 2020

Mercury ion (Hg2+) is a highly toxic matter that can result in serious dangers to human health. Therefore, monitoring the mercury ion concentration in the environment is an extremely important issue. Sensing approaches like atomic absorption spectrometry and inductively coupled plasma mass spectrometry have been applied to detect the mercury ion. However, the heavy and expensive instruments show the difficulty in performing on-site analysis. In our research, we developed a self-powered mercury ion sensor based on thermoelectric effect to overcome the drawback. Tellurium nanowires were synthesized as the probing and thermal energy harvesting materials. The surface of tellurium nanowires is selective for mercury ion binding. Under a temperature difference, the thermoelectric device based on mercury ion binding tellurium nanowires shows a higher electric output than the tellurium nanowires-based thermoelectric device. The electric output of the as-developed self-powered sensor shows a positive correlation with the mercury ion concentration. In addition, we also tested other common metal ions (Na+, K+, Cu2+, Mg2+, Ca2+, Ba2+ and Zn2+) that existed in the environment, confirming that the self-powered sensor is selective for mercury ion detection. Based on those results, we believe that the thermoelectric effect-based self-powered sensor serve as the stepping stone for the development of cost-effective and portable sensors to detect other metal ions and biomolecules in the future.
(Invited) New Thermoelectric Device Architecture Aiming for Low $/W and Wearable Application
Authors: Kim Woochul
Published: February 2020

In this talk, we are going to discuss about modification in thermoelectric device architecture for low $/W and wearable application. We propose a way to lower the $/W value with a decent power output of a thermoelectric device by changing the device architecture. We experimentally demonstrated that more than half reduction in $/W value without increasing the thermoelectric figure of merit, zT. This reduction is equivalent to zT ~ 6, since increasing zT results in low $/W. The device architecture we proposed should be useful to recover low quality waste heat, which is abundant and could be harvested as long as the $/W value is low enough in general. In the second part of the talk, we present two types of wearable thermoelectric devices based on bulk inorganic materials; one is bracelet type and the other is mat style. Utilizing high performance that can be extracted from the bulk inorganic materials, the devices based on the materials are bendable and flexible. Performance of the device attached on a human body is compared with theoretical analysis based on a simplified human thermoregulatory model we developed.
Electrochemical Stability of Closo-Carborane Anions and Their Impact on Cathode Interfacial Properties
Authors: Hahn Nathan T , Seguin Trevor , Carino Emily , Connell Justin Grant , Persson Kristin A , Zavadil Kevin R
Published: February 2020

Electrochemically stable, charge delocalized anions are essential electrolyte constituents for rechargeable, high voltage magnesium batteries. Within this class of anions, magnesium closo-carborane salts were demonstrated to support reversible magnesium electrodeposition/dissolution in tetraethylene glycol dimethyl ether (tetraglyme, G4) highlighting their cathodic stability.1,2 The corresponding anodic stability of these anions remains undetermined due to the lower anodic stability of the glyme solvents preferred for increased salt solubility, ionic conductivity, and stability against magnesium metal. In this paper, we explore the anodic stability of the carba-closo-dodecaborate anion (CB11H12
-) and select functionalized derivatives thereof relative to the more typical battery electrolyte anions bis(trifluoromethylsulfonyl)imide (TFSI) and tetrafluoroborate (BF4). In solvents of higher anodic stability than the glymes, including 3-methylsulfolane and 1,1,3,3-hexafluoroisopropanol, we demonstrate an oxidation potential of 4.5 V vs. Mg/Mg(II) for the base CB11H12
- anion, which is surprisingly lower than that measured for TFSI or BF4. Computational screening of the adiabatic ionization potential and electron affinity of RCB11H11
- (where R is a functional group that replaces the H-C proton) indicates that substitution of the proton at the carbon vertex with an electron withdrawing group can yield a several hundred millivolt increase in oxidative stability without decreasing the cathodic stability. Synthesis and electrochemical evaluation of the fluoro-carba-closo-dodecaborate validates this prediction and offers a rational design strategy for improved electrolyte stability. Oxidation of either the parent or substituted carba-closo-dodecaborate anion is irreversible, resulting in a neutral radical that incorporates within a surface film. The surface film formed inhibits further electron transfer leading to a varying degree of passivation toward further electrolyte decomposition depending on the solvent employed. The composition and structure of this metastable interface and its Mg cation transport properties will be discussed.

O. Tutusaus, R. Mohtadi, T.S. Arthur, F. Mizuno, E.G. Nelson, Y.V. Sevryugina, “An Efficient Halogen-Free Electrolyte for Use in Rechargeable Magnesium Batteries,” Angew. Chem. Int. Ed. 2015, 54, 7900.

S.G. McArthur, R. Jay, L. Geng, J. Guo, V. Lavallo, “Below the 12-vertex: 10-vertex carborane anions as non-corrosive, halide free, electrolytes for rechargeable Mg batteries,” Chem. Comm. 2017, 53, 4453.
Microstructure Evolution in “Li-Free” Thin Film Solid-State Li-Ion Batteries
Authors: Yang Heng , Citrin Michael A , Xia Xiaoxing , Nieh Simon , Greer Julia R
Published: February 2020

Li-ion thin film solid state batteries are capable of battery life of more than 10000 cycles1. “Li-free” anodes in solid-state batteries eliminate lithium metal in the manufacturing stage, which could improve energy density, simplify manufacturing process, and lower cost. Attempts to fabricate “Li-free” cells have been challenging because of the concomitant reduction in cycle stability2, 3. Replacing the Cu current collector with metals like Au and Pt, which alloy with Li, shows improvement in cycle stability, probably because it creates a more stable interface4-6. The microstructural changes associated with such improvement, especially at the interfaces, have not been fully understood, hampering future development of all-solid-state “lithium-free” batteries.

We fabricate LiCoO2 (35 µm)/LiPON (4 µm)/M (~15 nm) thin film solid state cells, where M is Cu, Au, or Pt, and study the electrochemical properties and microstructure changes within each thin film during cycling using an in-situ SEM. Figure 1 shows the nucleation of lithium through Cu, Au and Pt current collectors upon charging the cell for 1.5 µAh. In the case of Cu current collector, lithium penetrates the thin Cu layer and preferentially nucleates along the grain boundaries, which is a result of the LiPON solid electrolyte following the contour of the underneath LiCoO2 layer. Assisted by fast lithium diffusion in the alloy, Li-Au and Li-Pt alloy layers probably homogenize the chemical potential across the surface, leading to well-spaced nucleation sites. We further discuss the growth and stripping of lithium at the solid electrolyte/current collector interface and pay close attention to the interactions of the metals with lithium. Finally, we correlate these microstructural details with coulombic efficiency and cycle stability of the solid state cells. These results provide insights into the fundamental electrochemistry and microstructure evolution that occurs in thin film solid-state Li-ion batteries during cycling and may have significant impact on developing “Li-free” solid-state batteries.

J. Li, C. Ma, M. Chi, C. Liang and N. J. Dudney, Advanced Energy Materials, 2015, 5, 1401408-n/a.

J. B. Bates, N. J. Dudney, B. Neudecker, A. Ueda and C. D. Evans, Solid State Ionics, 2000, 135, 33-45.

B. J. Neudecker, N. J. Dudney and J. B. Bates, J. Electrochem. Soc., 2000, 147, 517-523.

M. Motoyama, M. Ejiri and Y. Iriyama, J. Electrochem. Soc., 2015, 162, A7067-A7071.

A. Kato, A. Hayashi and M. Tatsumisago, J. Power Sources, 2016, 309, 27-32.

K. Okita, K.-i. Ikeda, H. Sano, Y. Iriyama and H. Sakaebe, J. Power Sources, 2011, 196, 2135-2142.

Figure 1
Sodiation Behaviors of 1D Van Der Waals Sb2S3 Nanorods By in-Situ TEM and DFT Calculations
Authors: Yao Shanshan , Cui Jiang , Kim Jang-Kyo
Published: February 2020

Owing to the abundance, low cost and similar electrochemistry of Na to Li, sodium ion batteries (SIBs) are considered an attractive, low-cost alternative to lithium ion batteries (LIBs) for large-scale energy storage [1]. Among various anode materials for SIBs, antimony trisulfide (Sb2S3) has drawn significant attention due its high theoretical capacity of 946 mAh g−1. However, its underlying sodiation behavior is largely unexplored.

This work [2] reports the sodiation kinetics and the evolution of phase transformation in carbon-coated 1D van der Waals Sb2S3 nanorods based on the in-situ TEM, density functional theory (DFT) calculations and molecular dynamic (MD) simulations. Unique two-step reaction mechanisms of Sb2S3 nanorods are revealed, including Na+ ion intercalation and conversion/alloying reactions, during the first sodiation process. Na+ ions are inserted into the voids between the (Sb4S6)n moieties at an ultrafast speed of 146 nm s−1 upon the first sodiation, leading to amorphization of the crystalline Sb2S3 and negligible volume expansion of ~54 %. The in-situ SAED analysis verifies that the generated NaxSb2S3 intermediate phases are transformed into Na2S and Na3Sb with a trace of Sb crystals during the consecutive conversion/alloying reactions. Upon subsequent desodiation, the Na+ ions extracted from the crystalline sodiated composites transform to amorphous desodiated products.

The DFT calculations attribute such anomalous reaction mechanisms to the unexpectedly low sodium diffusion barrier of Sb2S3 nanorods and the largely improved electronic conductivity arising from the amorphous NaxSb2S3 intermediate phases. These findings on phase transformation routes, dynamics and kinetics occurring during the sodiation/desodiation processes in the Sb2S3 nanostructure will offer insights into better understanding of Na+ ion diffusion mechanisms in van der Waals force stacked materials.

References

[1] J. Cui, S. Yao, J.K. Kim, Recent progress in rational design of anode materials for high-performance Na-ion batteries. Energy Storage Mater., 7, 64–114 (2017).

[2] S. Yao, J. Cui, Z. Lu, Z.L. Xu, L. Qin, J. Huang, Z. Sadighi, F. Ciucci, J.K. Kim, Unveiling the unique phase transformation behavior and sodiation kinetics of 1D van der Waals Sb2S3 Anodes for sodium ion batteries, Adv. Energy Mater., 7, 1602149 (2017).
Separator-Free Gel Electrolytes Based on Water-in-Salt Solutions
Authors: Cresce Arthur v. , Eidson Nicolas Thierry , Yang Chongyin , Wang Fei , Wang Chunsheng , Xu Kang
Published: February 2020

Water-in-salt electrolytes (WiSE) are one of a growing family of water-based lithium ion electrolytes that use high concentrations of non-hydrolyzable lithium salts such as LiTFSI. WiSE are non-flammable and have a much wider electrochemical stability window than typical dilute aqueous electrolytes through two anion-based mechanisms: the formation of a passive anode layer through the decomposition of the TFSI- anion and exclusion of water by the anion from the cathode surface. This work details the formation of a polymer gel network containing WiSE as its liquid phase using commercially available polymer and crosslinker components. WiSE gel electrolytes are thought to be a natural evolution of the water-in-salt concept, as a WiSE gel should allow for WiSE-containing batteries to decouple themselves from typical cylindrical and prismatic battery form factors. Cycling performance and mechanical properties of the gel electrolytes will be discussed, along with fundamental investigations into the electrode-electrolyte interface and the minimization of charge-transfer resistance. Additionally, the kinetics of gel reactions in WiSE as a solvent will be discussed.
Highly Stable Sodium Metal Interphase in NaAlCl4-2SO2 Inorganic Electrolyte for Room-Temperature Sodium Rechargeable Battery Anode
Authors: Kim Hyun Jong , Song Juhye , Kim Ayoung , Kim Yeong Eun , Jeong Goojin , Kim Hansu
Published: February 2020

Sodium metal has gain recent attention as a high capacity anode material for sodium rechargeable battery because of its abundance as well as high energy density with low-working potential. Unfortunately, low Coulombic efficiency and dendrite formation of sodium metal anode during cycling are key hurdles to be utilized for practical application. In this work, we have investigated the electrochemical properties of sodium metal interphase with highly concentrated Na+-conductive inorganic electrolyte by various analytical techniques and electrochemical measurements. We found the morphological stability of sodium metal anode with NaAlCl4-2SO2 inorganic electrolyte, forming dendrite-free polygonal sodium deposition. By adopting a highly stable electrolyte for sodium metal, the electrochemical characteristics of sodium metal anode showed significant improvement compared to the conventional Na ion conducting organic electrolyte, encouraging the development of room-temperature sodium metal-based rechargeable batteries. More details of electrochemical performance of sodium metal anode will be discussed on this presentation.
Challenges and Opportunities Involving Electrochemical Processes for the Sustainable Production of Ammonia
Authors: Jaramillo Thomas F
Published: February 2020

The massive scale and vital impact of ammonia-based fertilizer production make sustainable and efficient synthesis of ammonia from nitrogen a key goal. Renewably powered, aqueous electrochemical ammonia production represents an enticing strategy to achieve this goal; however, the hydrogen evolution reaction (HER) often dominates under reductive conditions on known electrocatalyst surfaces. Thus, the ability to selectively and catalytically produce ammonia remains a challenge. Our team of experimental and theoretical researchers are pursuing several promising alternative electrochemical approaches to achieve this goal. One strategy is to limit effective proton availability to at the electrocatalyst surface by reducing the bulk proton concentration using dilute H2O in nonaqueous solutions. A range of electrolyte conditions, including varying N2 pressures, pH levels, solvents, and supporting electrolytes have been explored to understand and minimize the loss of Faradaic efficiency to ammonia due to concurrent hydrogen evolution. In a second strategy, we circumvent the HER entirely by implementing an electrochemical stepwise cycling process. The process comprises three distinct steps of surface preparation, nitrogen activation, and ammonia synthesis which can be combined and cycled for continuous ammonia production. Theoretical considerations elucidate the feasibility and general applicability of this cycle as exemplified by a Li-based cycle that demonstrates an initial current efficiency of 89% toward ammonia production.
(Invited) Ammonia Synthesis Under Mild Condition
Authors: Guo Jianping , Chen Ping
Published: February 2020

With a high hydrogen content (17.6 wt.%), high energy density (4 kWh kg-1), facile storage and transportation, NH3 has been regarded as a potential energy carrier. The key issue for NH3 synthesis and decomposition is the development of non-noble metal based, highly active and stable catalysts that can be operated under mild condition. With the understanding of interactions of hydrides/imides of alkali and alkaline earth metals (AM for short) with 3d metals and their nitrides, the catalyst systems, i. e., AMNH-3d transition metals for NH3 decomposition and AMH-3d transition metals for NH3 synthesis, were developed. The unique chemistry among transition metals, alkali/alkaline earth, N and H creates an energy-favorable pathway allowing NH3 synthesis/decomposition under mild conditions, i.e., detectable NH3 formation rate was obtained at 150 °C over the Mn-, Fe- and Co-LiH composite catalysts, respectively.1.2 The characterization of intermediate phases and surface clusters of catalysts provides interesting information that helps the elucidation of the step-wise reaction pathway and the interpretation of catalytic mechanism.

References

Guo JP, Wang PK, Wu GT, Wu A, Chen P. et al. Angew Chem 2015; 54: 2950-2954

Wang PK, Chang F, Gao WB, Guo JP and Chen P. et al. Nat Chem 2017; 9: 64-70
(Invited) Distributed NH3 Synthesis Via Electrochemical Reduction of N2 on Transition Metal Nitrides in a PEM Electrolyzer
Authors: Xu Bingjun , Yan Yushan , Nash Jared , Yang Xuan , Anibal Jacob
Published: February 2020

With the industrial production of N-based fertilizers from the Haber-Bosch process in the early 20th century, increased crop production has been realized and it is estimated that half of the world’s population is supported by N-based fertilizers. Due to the high temperature, pressure, and feedstocks needed, the Haber-Bosch process consumes approximately 2% of the world energy production and is highly centralized which contributes additional energy and CO2 emissions to transport the ammonia to end users. Electrochemical production of ammonia offers a low temperature, low pressure alternative which can be scaled out and allows for on-site ammonia generation powered by renewable energy sources. With more discussions of carbon taxes for companies that produce CO2, a renewable distributed ammonia production network could become increasingly attractive. However, platinum group metal catalysts show low Faradaic efficiency and low specific ammonia production rates due to the facile hydrogen evolution reaction. In this work, we report the first experimental work of ENRR on metal nitrides. An MEA configuration is employed in the reactivity tests due to the low solubility of N2 in aqueous electrolytes, which poses challenges in product quantification and catalyst characterization. We established a rigorous and reliable procedure to quantify the amount of ammonia produced in ENRR on the catalyst containing N, and thus could be served as a N source. A combination of the Nessler method, UV-Vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) were employed. We show that the bulk remains unchanged and only a thin surface layer of the micro-size particles is participating in ENRR indicating the leaching of N from the catalyst does not contribute to the amount of ammonia detected in the Nessler method in any appreciable degree.
Electrochemical Ammonia Synthesis in Organic Electrolytes
Authors: Schwalbe Jay , Singh Aayush R. , Nielander Adam C. , McEnaney Joshua M , Jaramillo Thomas F , Nørskov Jens , Cargnello Matteo
Published: February 2020

In this talk, we present our experimental efforts to increase selectivity in electrochemical ammonia synthesis with electrolyte engineering. Ammonia synthesis is a vital chemical reaction for the modern world. The Haber-Bosh process is routinely credited with supporting somewhere around half of our current population, at a cost of about 1% of the worlds energy consumption. It also requires hydrogen, typically provided through hydrocarbon reforming and is concomitant with centralized infrastructure and distribution. Clearly, this presents an opportunity to develop a process that is not reliant on large capital infrastructure or hydrocarbon derived hydrogen.

One sought after option is a direct electrochemical process. This would enable ammonia to be produced directly using water and electricity from renewable resources. Unfortunately, faradaic efficiencies for ammonia synthesis in aqueous electrolytes are typically observed to be prohibitively low due to the competing hydrogen evolution reaction. Density functional calculations predict that ammonia synthesis will only proceed at potentials more negative than 1 volt, a potential at which most metal surfaces evolve hydrogen rapidly. While, in principle, it may be possible to find a material that activates nitrogen and not protons, we instead focus on changing the electrolyte to reduce HER. According to our simple kinetic model, reducing the availability of protons at the surface will allow nitrogen binding, the presumed rate limiting step, to compete with proton reduction.[1] While there are a number of possible electrolyte systems that may achieve this, we use aprotic, organic electrolytes with alcohols added as proton donors. By using alcohols as a proton donor, we hope to access an additional degree of freedom when engineering the reactivity of the interface. In preliminary measurements, we see faradaic efficiencies approaching 20%. We use both argon and nitrogen-15 labelled control experiments. We see no ammonia produced under argon purge and only labelled ammonia produced when using nitrogen-15 labelled N2.

[1] Singh, A. R., Rohr, B. A., Schwalbe, J. A., Cargnello, M., Chan, K., Jaramillo, T. F., Nørskov, J. K. (2016). ACS Catalysis, 706–709. doi: 10.1021/acscatal.6b03035
Catalyst-Free, Electrolytic Synthesis of Ammonia from Nitrogen and Water By Plasma-Produced Solvated Electrons
Authors: Hawtof Ryan , Ghosh Souvik , Xu Cheyan , Renner Julie N. , Sankaran R. Mohan
Published: February 2020

Ammonia which is a precursor to fertilizers and food and is one of the most important chemicals in the world is currently synthesized on a large scale by the Haber-Bosch (H-B) process. Recent research has been aimed at developing alternative approaches to synthesizing ammonia to address several issues associated with the H-B process: 1) the very high pressures and high temperatures which lead to enormous capitals costs, 2) the need for hydrogen gas which comes from steam-methane reforming and contributes to high energy costs and environmental impact through greenhouse gas emissions, and 3) the incompatibility with renewable sources of energy that could lower energy costs and environmental impact while also offering more localized, point-of-use sources of ammonia.

Here, we report a hybrid electrochemical system to produce ammonia where one of the metal electrodes is replaced by a plasma (gas discharge). Similar to more typical electrochemical systems, ammonia synthesis is carried out at ambient conditions and only requires electricity. However, the interaction of a plasma and water leads to the formation of solvated electrons, one of the strongest reducing agents known with a reduction potential of ~-2.8 V. Production rates and selectivity (i.e. charge-transfer efficiency) were determined as a function of various process parameters including current, time, and electrolyte composition. We will also discuss a potential reaction mechanism based on the observed results.
Synthesis of Pt-M (M=Ir, Pd) Bimetallic Nanocrystals with Controlled Shape and Composition As a High-Performance Electrocatalyst for Ammonia Electrolysis
Authors: Park Jinho , Hankinson John , Lee Seung Woo , Navaei Milad
Published: February 2020

Ammonia is a promising hydrogen storage carrier owing to its higher hydrogen capacity relative to liquid hydrogen (108 vs 71 g/L), non-flammability, well-developed technologies for synthesis and distribution.1-2 To utilize ammonia as the hydrogen storage carrier, it is essential to develop a highly efficient and durable catalyst that decomposes ammonia into hydrogen and nitrogen. Platinum (Pt) is the most effective catalyst for the electrolysis of ammonia, but it is rapidly deactivated during the reaction due to the strong adsorption of nitrogen on the surface. Thus, it is critical to develop a highly efficient and robust catalyst that surpasses Pt catalyst, enabling the utilization of ammonia as a safe and efficient hydrogen storage carrier. In this work, we synthesized nano-sized Pt-Ir (and Pt-Pd) alloy cubes as a high-performance electrocatalyst for ammonia electrolysis. During the synthesis, both elemental composition and shape of nanocrystals were systemically controlled for improving their electrocatalytic performance (Fig. 1a). Among the as-synthesized catalysts, the Pt-Ir nanocubes exhibited ~7.2 and ~4.6 times higher specific (mA/cm2) and mass (A/mg) activities, respectively, relative to a state-of-the-art commercial Pt/C catalyst (Tanaka) at 0.6 V (vs RHE, Fig. 1b). The significantly enhanced activity can be attributed to reduced adsorption strength of nitrogen, thus mitigating the deactivation of active sites of the catalyst.

Hanada, N.; Hino, S.; Ichikawa, T.; Suzuki, H.; Takai, K.; Kojima, Y., Hydrogen generation by electrolysis of liquid ammonia. Chem Commun
2010,
46 (41), 7775-7777.

Vitse, F.; Cooper, M.; Botte, G. G., On the use of ammonia electrolysis for hydrogen production. Journal of Power Sources
2005,
142 (1), 18-26.

Figure 1
Highly Stereoselective Electrocatalytic Semihydrogenation of Alkynes to Z-Alkenes Using a Proton Exchange Membrane Reactor
Authors: Atobe Mahito , Minoshima Juri , Fukazawa Atsushi , Hashimoto Yasushi , Kobori Yoshihiro , Sato Yasushi
Published: February 2020

Z-alkenes are versatile building blocks in organic synthesis and often found in pharmaceuticals, perfumes, and natural products. Although a number of methods for stereoselective synthesis of Z-alkene have been developed so far, the Lindlar semihydrogeneation of alkynes is a long-standing synthetic transformation and still remains a privileged system. However, it used toxic Pb additive and a large amount of quinolone, and has other limitations such as narrow substrate scope. Therefore, development of a powerful and reliable system for stereoselective semihydrogenation of alkyne to Z-alkene as alternative to the Lindlar catalytic system is still challenging target.

Under these backgrounds, in this work, we have demonstrated electrocatalytic hydrogenation in a proton exchange membrane reactor so called PEM reactor to develop a powerful and reliable stereoselective semihydrogenation system (Figure 1). This system has several merits such as easy separation and recycle use of catalysts, operation under mild and benign conditions, and easy reaction control by applied voltage. Indeed, the use of PEM reactor with Pd catalysts gave Z-alkenes with excellent current efficiencies in our demonstrations.

Figure 1
Paired Electrolysis for Amide Formation Catalyzed By Vitamin B12 Model Complex Under Aerobic Condition
Authors: Shimakoshi Hisashi , Zhongli Luo , Hisaeda Yoshio
Published: February 2020

Electroorganic synthesis is currently expanding into various interdisciplinary fields because of its versatile application to molecular transformations as well as sustainable and economical advantage. Electroorganic synthesis is especially recognized as green process in synthetic organic chemistry since redox process of substrate is progressed by electric current without chemical reagent and waste after the reaction. Among the various methods in electroorganic synthesis, paired electrolysis is excellent method that electrochemical power is used both on the working electrode and the counter electrode to form synthetic useful compounds.1-4 Here we report the paired electrolysis mediated by vitamin B12 derivative,5 cobalt complex, under aerobic condition to form various amide compounds from trichloromethylated organic compounds and tertiary amines.

Reference

A. Paddon, M. Atobe, T. Fuchigami, P. He, P. Watts, S. J. Haswell, G. J. Pritchard, S. D. Bull, F. Marken, J. Applied Electrochem., 2006, 36, 617.

J. Llorente, B. H. Nguyen, C. P. Kubiak, K. D. Moeller, J. Am. Chem. Soc., 2016, 138, 15110.

Senboku, K. Nagakura, T. Fukuhara, S. Hara, Tetrahedron, 2015, 71, 3850.

Kim, R. Uchiyama, Y. Kitano, M. Tada, K. Chiba, J. Electroanal. Chem., 2001, 507, 152.

H. Shimakoshi, Y. Hisaeda, Current Opinion in Electrochemistry, 2018, in press.

Figure 1
Design of Photoredox Systems for Catalytic Fluoroalkylation of Alkenes
Authors: Koike Takashi
Published: February 2020

Radical fluoroalkylation by photoredox catalysis has emerged as a new synthetic methodology over the past several years. In particular, the strategy is useful for introduction of a fluoroalkyl group and a different functional group across a carbon–carbon double bond via a single operation. Step-economical synthesis of diverse organofluorine compounds has been achieved. In this paper, our recent studies on photoredox-catalyzed fluoroalkylation will be discussed

Figure 1
Using the Complementarity of Electrochemistry and Photoelectron Transfer to Probe and Develop the Chemistry of Radical Cations
Authors: Moeller Kevin D , Gonzalez Luisalberto , Feng Ruozhu , Graaf Matthew D.
Published: February 2020

Through the years, we have utilized electrochemistry as a method to explore radical cation intermediates and the oxidative cyclization reactions they trigger. On the mechanistic side of things, we have uncovered a set of empirical rules that govern radical cation reactivity and allow for the design of new reactions. On the synthetic side of things, we have used the ensuing reactions to make heterocycles, fused-, spirocyclic-, and bridged molecules, and highly hindered tetrasubstituted carbons.

Recently, we have found that these initial mechanistic models have to be adjusted to account for not only the initial cyclization reaction, but also the intermediates generated downstream of that step. In particular, the oxidation of a second electron from the molecule (k2
in Scheme 1) frequently plays a key role in the synthetic success of a transformation.

While this observation was clear for cases for slower trapping reactions that might have a reversible first step, it was assumed that our very best trapping reactions that were known to be kinetically fast had no such issues. This assumption has also proven problematic.

Photoelectron transfer reactions that are ideally suited for conducting one-electron oxidation based processes are ideal tools for probing cyclizations that require the loss of a second electron (Scheme 2). Note that all three substrates shown underwent a two electron oxidative cyclization nicely at an anode to give the cyclic products shown. The substrate with the alcohol trapping group also worked well providing a redox neutral complementary product to the electrolysis reaction. The substrate with the sulfonamide trapping group led to no reaction. This was not a surprise since the cyclization with the sulfonamide trapping group is slower than the alcohol trapping reaction. The reaction is dominated by a back electron transfer from the dithioketene acetal derived radical cation to the catalyst. The reaction with the enol ether trapping group led to polymer that showed evidence for consumption of both olefins in the starting material. This was a surprise since the cyclization is known to be very fast (much faster than the alcohol trapping of the radical cation). The reaction clearly required the loss of a second electron to form the desired cyclized product. This was a conclusion that could only be reached by comparing the photochemical and electrochemical reactions.

In the talk to be presented, the historical context and future synthetic ramifications of this and other mechanistic studies that define the nature of the reactive intermediate needed for the initial cyclization will be discussed.

Figure 1
Electrochemical Oxidation/Modification of Lignin Mediated By Aminoxyl Radicals
Authors: Rafiee Mohammad , Stahl Shannon S.
Published: February 2020

Lignin is an abundant biopolymer with an aromatic backbone and offers a bio-based source of aromatic commodity chemicals upon depolymerization.[i] Oxidation methods are widely used for the deconstruction of lignin; successful examples include oxidative delignification in the pulp and paper industry and breakdown of lignin by oxidative fungal enzymes. The hydroxyl functional groups of lignin are particularly susceptible to oxidation. Building on these concepts, our group recently began exploring the controlled oxidation of lignin hydroxyl groups as a means to facilitate lignin depolymerization.[ii] We previously reported an aerobic oxidation method that employs aminoxyl radicals, such as TEMPO, as the catalyst. Acid treatment of the resulting oxidized lignin lead to depolymerization, affording up to 60 wt% yield of low-molecular-weight aromatic compounds.[iii]

Aminoxyl radicals undergo facile electron transfer at the electrode surface to generate an oxoammonium species that is reactive towards hydroxyl oxidation (Figure 1a). This facile electron transfer provides a foundation for selective oxidation of hydroxyl groups under electrochemical conditions.[iv] This talk will highlight some of our advances in the use of aminoxyl radicals as mediators for chemoselective oxidation of hydroxyl groups in the structure of lignin. The beta-O-4 linkage (Figure 1b) is the most prevalent linkage in the structure of lignin that includes hydroxyl functional groups and was used as the model for this study.

Nitroxyl-mediated electrochemical oxidation methods enable selective and quantitative conversion of the primary hydroxyl group of lignin and beta-O-4 model compounds to the corresponding carboxylate under mildly basic conditions. The modified lignin has a high loading of carboxylic acids, which enhance its water solubility relative to native lignin. The sodium salt of the modified lignin behaves as a polyacid polyelectrolyte in aqueous solution. Acid treatment of the oxidized lignin model affords approximately 30 wt% of monomeric aromatic compounds.

[i]. Upton, B. M.; Kasko, A. M. Chem. Rev., 2016, 116, 2275.

[ii]. Rahimi, A.; Azarpira, A.; Kim, H.; Ralph, J.; Stahl, S. S. J. Am. Chem. Soc.
2013, 135, 6415.

[iii]. Rahimi, A.; Ulbrich, A.; Coon, J. J.; Stahl S. S. Nature
2014, 515, 249.

[iv]. Rafiee, M; Miles, K. C.; Stahl, S. S. J. Am. Chem. Soc.
2015, 137, 14751.

Figure 1
Single Nanosheet Photoelectrochemistry
Authors: Sambur Justin
Published: February 2020

Nanoflake thin films made of layered semiconducting transition metal dichalcogenides such as MoSe2 are promising large-area electrodes for photoelectrochemical solar energy conversion applications. However, their energy conversion efficiencies are typically much lower than bulk electrodes. It is unclear to what extent this efficiency gap stems from differences among nanoflakes (e.g., area, thickness, and surface structural features). Moreover, a major unanswered question is whether exfoliated nanoflakes can achieve similar energy conversion efficiencies to bulk crystals. Here we use a single-nanoflake photoelectrochemical approach to show that 7% of MoSe2 nanoflakes in a thin film exhibit larger photocurrents than the parent bulk crystal used for exfoliation. This "champion" population, which is hidden in ensemble average measurements, shows that exfoliated nanoflakes can achieve similar photocurrent collection efficiencies to bulk crystals. However, there is also a large, "spectator" population, which is also hidden in ensemble-average measurements, that is mostly responsible for the overall lower photocurrent efficiency compared to the bulk crystal. Photocurrent mapping showed that photocurrent collection efficiency is lower at perimeter edges than at interior step edges. Our results highlight research opportunities to improve 2D semiconductor thin film photoelectrodes.
Inside the Reaction Layer: Investigation of Electrochemical Reactions By Coupling Electrochemistry and Confocal Fluorescence Microscopy
Authors: Doneux Thomas , de Poulpiquet Anne , Arredondo Imelda Bonifas , Lefrançois Pauline , Vajrala Venkata Suresh Reddy , Goudeau Bertrand , Garrigue Patrick , Sojic Neso , Arbault Stéphane , Bouffier Laurent
Published: February 2020

Electrochemical reactivity studies are usually performed by conventional electrochemical measurements carried out with a single electrode of either macroscopic (∼millimeter) or microscopic (∼micrometer) dimensions. Such kind of measurements provides information which can be time resolved down to very short time scales, but which is typically averaged over the entire electrode area and is thus insensitive to spatial heterogeneities in the x-y plane of the electrode. The measured current also gives access to the transport properties of the involved redox-active species, but this additional information corresponding to the z-direction axial to the electrode is rather indirect. Coupling electrochemistry with confocal fluorescence microscopy (EC-fluorescence) is an expedient way to obtain 3-dimensional spatial information on electrochemical reactions, in-situ and in real time. The optical sectioning enabled by confocal microscopy is particularly useful to map individual chemical species in the diffusion layer, especially for unstable electrogenerated species that further react homogeneously.

The present contribution focuses on the properties of the electroactive, fluorogenic molecule resorufin (see Figure), to illustrate the many potentialities of EC-fluorescence. The highly fluorescent resorufin can be generated electrochemically by the irreversible reduction of its N-oxide parent compound resazurin which is slightly fluorescent. It can also be reduced reversibly to the non-fluorescent dihydroresorufin, whose acetyl derivative is actually the popular Amplex® Red that can be oxidized to generate resorufin. This exhaustive electrochemistry covers several electrochemical reaction mechanisms ranging from simple electron transfers to coupled electrochemical-chemical steps, with different degrees of reversibility. A comproportionation scheme is also evidenced for the first time. Each of these reactions is associated with specific characteristics of the reaction-diffusion layer that can be probed with an appropriate spatial resolution by EC-fluorescence.

Figure 1
Interfacial Electrochemistry of Chemically Modified Electrode Materials, Relevant for Energy Conversion and Storage Systems
Authors: Strmcnik Dusan , Genorio Bostjan , Danilovic Nemanja , Zorko Milena , Martins Pedro F. B. D. , Lopes Pietro Papa , Stamenkovic Vojislav , Markovic Nenad M
Published: February 2020

Electrochemical reactions take place at the electrochemical interface, the region in which the properties change from those in the bulk of the electronic conductor (electrode) to those in the bulk of the ionic conductor (electrolyte). Not surprisingly, then, efficiency of energy conversion and energy storage processes are almost entirely determined by the richness of interfacial processes that control the rate of electron transfer and various types of interactions between the substrate and reactants, intermediates, and products of the reaction. The “interfacial bridge” between two bulk properties is built either by the formation of unique (near)surface atom arrangements (e.g. surface relaxation or reconstruction) and/or by significant differences in electrode composition close to the surface (e.g. segregation profile) and/or via substrate-adsorbates covalent and non-covalent forces and/or ordering of solvent and/or electrolyte molecules observed in the proximity of the surface (up to 10 nm). All of these processes are rather complex, requiring special arsenal of tools that are capable of resolving interfacial properties at atomic and molecular levels.

Despite establishing the structure-function relationships, i.e. correlations between the morphology, composition of the electrode/electrolyte and the physico-chemical properties of the interface such as activity, stability and selectivity, we are still not in a position to provide the fundamental knowledge that is required to control the interfacial processes.

This presentation will give an overview of our recent efforts in predetermining the properties of the electrochemical interface by influencing the delicate interplay between the covalent and non-covalent interactions at or near the electrode surface. Several examples of chemical modification of the interfaces are going to be presented, including the variation in oxygen reduction reaction (ORR) in alkaline solution with the nature of non-covalently adsorbed cation in the double layer, the ORR activity enhancement of PA fuel cell catalyst and hydrogen oxidation reaction selectivity enhancement on PEM fuel cell catalysts. Finally, we will discuss the control of interfacial electrochemical processes through the application of mono- and multi-layer graphene architectures.
(Invited) Effect of the Carbon Matrix Surface Area and Thermal Treatment on the Activity and Durability of Fe-N-C Oxygen Reduction Catalysts
Authors: Lima Fabio H. B. , Galiote Nelson A.
Published: February 2020

The sluggish oxygen reduction reaction (ORR) and the high platinum loading in the cathode are important obstacles that should be overcome for the development of H2/air fuel cells. Thus, studies focused on highly active and cost-effective electrocatalysts have gained attention. Electrocatalysts formed by earth-abundant elements such as those based on iron, nitrogen and carbon (Fe-N-C) have gained considerable attention in research because they allow widespread commercialization of the fuel cells. Previous achievements regarding Fe-N-C oxygen reduction electrocatalysts have been described elsewhere and showed a significant effect of the carbon matrix surface area on the electrocatalytic activity and stability [1,2]. In the present paper, we will focus on the results of the consequence on activity and durability of the thermal treatments on Fe-N-C. The electrocatalyst were synthesized via Fe complexation with phenanthroline, followed by impregnation on carbon powder with different surface areas (Vulcan XC-72R and Black Pearls 2000). The thermal treatments were conducted at different temperatures and on Ar or NH3 atmosphere. The discussion will be focused on the correlation between the results encountered in the characterization by EXAFS, XRD and HR-TEM with those obtained during polarization experiments for the ORR using rotating disk electrode and during fuel cell tests. A strong effect of the thermal treatment temperature and of the surface area of the carbon powder was observed on the activity and durability, mainly for the fuel cell tests with H2/air. We believe that the results from this study may contribute to further understand the parameters that govern the activity and durability of Fe-N-C ORR catalysts.

[1] G.Wu, K.L. More, P. Xu, H-L. Wang, M. Ferrandon, A.J. Kropf, D.J. Myers, S. Ma, C.M. Johnston, P. Zelenay, Chem. Commun., 49 (2013) 3291 – 3293.

[2] L. Yang, N. Larouche, R. Chenitz, G. Zhang, M. Lefevre, J-P. Dodelet, Electrochim. Acta 159 (2015) 184 – 197.

Acknowledgements

The authors gratefully acknowledge financial support from FAPESP (2013/16930-7, and 2016/13323-0) and CNPq.