bluuebunny/crossref_metadata_2025 huggingface dataset:
DFT Studies of the Oxygen Reduction Reaction on Pristine and N-Doped Fe3C/Graphene Catalyst
Authors: Reda Mateusz , Hansen Heine A. , Vegge Tejs
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) are considered to be a promising power generation systems for future mobile and stationary applications. One of the main factors that restrain their wide use is the sluggish kinetics of the oxygen reduction reaction (ORR) at the electrode. Platinum-based materials have been so far the most active catalysts for the ORR, but their high cost makes the technology rather exclusive.

In recent years, a number of non-precious ORR catalysts have been reported [1-3]. Among them, a catalyst composed of Fe3C nanoparticles encased in graphitic layers [3] draws an increasing interest due to its high stability and activity, which may be a result of the presence of a new type of active site [4]. To explain this phenomenon, we study possible catalytic sites of Fe3C/graphene interface and its N-doped variant by means of the Density Functional Theory. Additionally we study other potentially interesting systems like Fe3C with multiple graphitic layers and its N-doped variants, as well as FeN4 moieties embedded in the graphitic layers. Free energy diagrams of the 4- and 2-electron associative pathways are calculated. The aqueous environment is modeled by including several explicit water molecules. Catalytic activity and selectivity towards H2O is considered and compared with current state-of-the-art ORR catalysts.

[1] E. Proietti, F. Jaouen, M. Lefèvre, N. Larouche, J. Tian, J. Herranz, J.-P. Dodelet, Nat. Commun., 2011, 2, 416.

[2] G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science, 2011, 332, 443.

[3] Y. Hu, J. O. Jensen, W. Zhang, L. N. Cleemann, W. Xing, N. J. Bjerrum, Q. Li, Angew. Chem. Int. Ed., 2014, 53, 3675.

[4] J.-P. Dodelet, R. Chenitz, L. Yang, M. Lefèvre, ChemCatChem, 2014, 6, 1866.

Figure 1
Transition Metals (Co, Fe, Ni)-N-C Electrocatalysts for Hydrogen Evolution Reaction in Acidic and Alkaline Solutions
Authors: Zhang Lulu , Liu Wen , Shao Minhua
Published: February 2020

Hydrogen is one of the cleanest and most promising energy carriers as an alternative energy source.1, 2 The production of hydrogen from water via a hydrogen evolution reaction (HER) has been widely studied. Platinum is believed to have the highest electrocatalytic activity for HER in both acidic and alkaline solutions. But it is very expensive and rare. Thus, more advanced precious metal free electrocatalysts for HER are required to lower the cost of electrolyzers. 3, 4

In this study, carbon-based non-precious metal catalysts (Me-N-C) were synthesized by impregnating aniline and different metal salts into a carbon matrix and pyrolyzing at 900℃ in N2 atmosphere.5, 6 The structure of obtained composites were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray diffraction. Their hydrogen evolution reaction (HER) activities were investigated in both 0.5 M H2SO4and 1 M KOH. For the first time, these non-precious metal electrocatalysts showed excellent activity for HER and good stability in both acidic and alkaline media. The Ni-C-N catalyst had the lowest onset potential while Co, Fe-C-N catalysts had smaller Tafel slopes than the former (Figure 1a).

Various active sites could contribute to the HER activity in Me-N-C catalysts (Figure 1b). Density functional theory (DFT) calculations were employed to understand the activity enhancement mechanisms and identify the active center. This work paved a new route in the design of cheap, robust and high efficient catalysts to replace Pt.

References

Zhou, W.; Zhou, J.; Zhou, Y.; Lu, J.; Zhou, K.; Yang, L.; Tang, Z.; Li, L.; Chen, S. Chemistry of Materials
2015, 27, (6), 2026-2032.

Fei, H.; Dong, J.; Arellano-Jiménez, M. J.; Ye, G.; Kim, N. D.; Samuel, E. L.; Peng, Z.; Zhu, Z.; Qin, F.; Bao, J. Nature communications
2015, 6.

Deng, J.; Ren, P.; Deng, D.; Yu, L.; Yang, F.; Bao, X. Energy & Environmental Science
2014, 7, (6), 1919-1923.

Zou, X.; Huang, X.; Goswami, A.; Silva, R.; Sathe, B. R.; Mikmeková, E.; Asefa, T. Angewandte Chemie
2014, 126, (17), 4461-4465.

Merzougui, B.; Hachimi, A.; Akinpelu, A.; Bukola, S.; Shao, M. Electrochimica Acta
2013, 107, 126-132.

Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P. Science
2011, 332, (6028), 443-447.

Figure 1
Electrocatalysis at Noble-Metal-Derived Pure Metallic Aerogels
Authors: Cai Bin , Liu Wei , Wen Dan , Eychmüller Alexander
Published: February 2020

Pure metallic aerogels are potentially invaluable electrocatalyst materials due to their combination of the unique properties of both metals and aerogels.[1] For instance, their large specific surface area provides sufficient reactive sites, which is of great importance for the heterogeneous catalysis. Their high porosity and metallic backbones accelerates the mass and electron transfer during the electrocatalysis process. More important, the stability issues from carbon support corrosion are largely overcome based on their self-supportability.

This contribution focuses on our recent progress on the electrocatalytic investigations at a series of pure metallic aerogels. The electrocatalytic ethanol oxidation activities are doubled on the pure Pd aerogels as compared to Pd/C.[2] With the loading of enzyme, the Pd aerogel shows a 3-fold increased bio-electrocatalytic activity for glucose oxidation.[3] The kinetics of the oxygen reduction reaction is improved by a factor of 5 on the bimetallic PdPt aerogels, which also shows a significantly increased stability as compared to Pt/C.[4] Additionally, we employed an alloyed PdNi hollow nanosphere aerogel to further investigate the effects of morphology and alloying on electrocatalysis.[5] The mass and specific activities for alcohol oxidation are improved by a factor of 5.6 and 4.2, respectively, as compared to Pd/C.

References

[1] W. Liu, A. K. Herrmann, N. C. Bigall, P. Rodriguez, D. Wen, M. Oezaslan, T. J. Schmidt, N. Gaponik, A. Eychmüller, Acc. Chem. Res.
2015, 48, 154-162.

[2] W. Liu, A. K. Herrmann, D. Geiger, L. Borchardt, F. Simon, S. Kaskel, N. Gaponik, A. Eychmüller, Angew. Chem. Int. Ed.
2012, 51, 5743-5747.

[3] D. Wen, A. K. Herrmann, L. Borchardt, F. Simon, W. Liu, S. Kaskel, A. Eychmüller, J. Am. Chem. Soc.
2014, 136, 2727-2730.

[4] W. Liu, P. Rodriguez, L. Borchardt, A. Foelske, J. Yuan, A. K. Herrmann, D. Geiger, Z. Zheng, S. Kaskel, N. Gaponik, R. Kotz, T. J. Schmidt, A. Eychmüller, Angew. Chem. Int. Ed.
2013, 52, 9849-9852.

[5] B. Cai, D. Wen, W. Liu, A-K Herrmann, A. Benad and A. Eychmüller, Angew. Chem. Int. Ed.
2015, 54, 13101-13105.

Figure 1
Metallophthalocyanine/C/Nafion Composites for Electrocatalysis of Oxygen Reduction
Authors: Yazar Zuhal , Piskin Mehmet , Odabas Zafer , Ozkaya Ali Riza
Published: February 2020

Oxygen reduction (OR) is a critical reaction occurring at one of the electrodes of both fuel cells and metal-air batteries. However, this reaction has slow electrode kinetics and thus, the catalysis of this reaction has vital importance. The studies in literature showed that some phthalocyanine (Pc) complexes had the ability of displaying high catalytic performance for dioxygen reduction, due to their highly conjugated π-electrons systems and rich redox properties.1 There is a strong relationship between the redox properties of Pc compounds and their efficiency as OR catalyst. Thus, the determination of the electron transfer properties of novel Pc derivatives is highly important.

This work involves the identification of redox properties of various novel mononuclear tetra-2,6-dimethoxy-substituted cobalt(II), iron(II), manganese(II) and nickel(II) Pcs by voltammetry and electrocolorimetry supported in situ spectroelectrochemistry in nonaqueous solution medium. It also includes determination of their suitability for usage as OR catalyst in energy conversion and/or storage devices such as fuel cells and metal-air batteries. In situspectroelectrochemical measurements provided critical support for the complete assignment of the redox processes, i.e., whether the reactions are metal- or ligand-based. The complexes displayed enriched reversible or quasi-reversible ligand and/or central metal-based one-electron redox processes. The electrocatalytic performances of the novel Pc complexes with different metal centers towards OR have been tested and compared by dynamic rotating disk and rotating ring-disk voltammetry measurements of the MPc/C(Vulcan XC-72)/Nafion modified glassy carbon electrodes in aqueous medium. In general, the complexes display different catalytic performances depending on the differences in the interactions of their metal centers with oxygen.

References

[1].  İ. Koç, M. Özer, A.R. Özkaya, Ö. Bekaroğlu, Dalton

Trans.,
32, 6368–6376 (2009).

Acknowledgement: This work was supported by Marmara University, Scientific Research Projects Committee (Project No: FEN-C-YLP-080715-0345).

Fig.1. Molecular structure of mononuclear tetra-beta substituted metal Pc template.

Figure 1
Pd/CNT Catalysts for Electrochemical Oxidation of Small Organic Molecules in Alkaline Media
Authors: Estrada Jose , Flores Jennifer , Nguyen Kelly , Haan John , Muneeb Omar
Published: February 2020

The development of the alkaline anion exchange membrane (AEM) for the direct liquid fuel cell opened up opportunities for the use of new fuels (that oxidized inefficiently in PEM fuel cells) and new catalysts (that corroded easily in PEM fuel cells).  In this work, we explore the effect of a CNT support for Pd catalysts for the oxidation of various alcohol and formate fuels in alkaline media.

We found that the CNT support provided a significant advantage over standard, activated carbon support in several of the fuels.  The increase in oxidation rate in formate, for example, was 5-fold.  However, the oxidation rate of propanol was not significantly enhanced by the CNT support.

We are presently exploring the scientific reason for the enhanced oxidation rates by the CNT support using XRD and XPS analysis.  Masel, et al, suggested that in formic acid the CNT provides enhancement due to its electronic properties, and a shift in Pd 3d5/2­
binding energy supports this.  However, we are presently investigating why the promotion in alkaline media is so much greater than in acidic media, even for the formate (compared with formic acid).
Effect of Water-to-Surfactant Ratio (ωo) in the Ynthesis of Pt/Mwcnts By Inverse Microemulsion for the Oxygen Reduction Reaction
Authors: Silva-Carrillo Carolina , Félix-Navarro Rosa María , Reynoso-Soto Edgar Alonso , Paraguay-Delgado Francisco , Alonso Gabriel
Published: February 2020

Hybrid materials based on platinum nanoparticles deposited on carbon nanotubes (Pt/MWCNTs) have been widely used in recent years as catalysts for oxygen reduction reaction (ORR). RRO is reaction most important for many environmental applications like electric energy generations by fuel cell or hydrogen peroxide production for degradation of pollutants in water. The electrochemical ORR proceeds via two routes, one direct transfer four electrons to produce water; and an indirect route transfer of two electrons producing hydrogen peroxide (H2O2). The electrocatalytic activity and kinetics of Pt/MWCNT catalysts in RRO depends of particle size, the surface atomic structure and the homogeneous distribution of the platinum particles on the carbon support, these three parameters are controlled by the synthesis method used.

Reverse microemulsions it’s a colloidal dispersion of water in oil stabilized by a surfactant film. The aqueous core of the reverse micelles plays a crucial role defining the size of formed particles. The water pool in the microemulsion solubilizes the reactants and provides the stage where the reaction occurs; because of this, the particle size can be controlled varying water concentration. The relation of water core with surfactant concentration is given by ω (ω=[H2O]/[surfactant]). The amount of water within the micelle controls the amount of ions of the metal precursor and reducing agent as well as the lability of Interfas, which dictates the micellar exchange rate.

In this work is presented the effect of W in the activity of the Pt/MWCNT nanomaterial in the oxygen reduction reaction (ORR) and the reaction mechanism. Pt/MWCNT nanomaterials synthesized with a ω=22 and 91 show particles with mean diameters of 1.3 nm and 2.5 nm, respectively. Employing a ω=45 in the synthesis of nanomaterial Pt/MWCNT showed an average nanoparticle diameter of 3.2 nm, also the platinum loading was 2 times that nanomaterials synthesized with a W of 22 and 91. The nanomaterial synthesized with a ω=45 showed greater electrocatalytic activity than the other two nanomaterials, although a decrease in mass transfer was observed in this nanomaterial, besides the mechanism according to the Koutecky-Levich graphs was O2 + 2H + + 2e-→ H2O2.  Pt/MWCNT anomaterials synthesized with a ω=22 and 91 showed the following mechanism : O2 + 4H+ + 4e-→2H2O. High values in the Tafel slopes of Pt/MWCNT nanomaterial synthesized with ω=45 confirm the presence of H2O2 on the surface.

Figure 1
Niobium Oxide/Carbon Supported Platinum and Platinum-Cobalt Nanocomposites As Electrocatalysts for Fuel Cells
Authors: Kepeniene Virginija , Stagniunaite Raminta , Tamasauskaite-Tamasiunaite Loreta , Norkus Eugenijus
Published: February 2020

In the present work, carbon and niobium oxide/carbon supported the Pt and PtCo catalysts (denoted as Pt/C, PtNb2O5/C and PtCoNb2O5/C) were fabricated by means of the rapid microwave heating method. The synthesized catalysts were examined by transmission electron microscopy, X-ray diffraction and inductively coupled optical emission spectroscopy. The electrocatalytic activity of the PtNb2O5/C, PtCoNb2O5/C and Pt/C catalysts towards the oxidation of ethanol and reduction of oxygen was investigated by cyclic voltammetry and chrono-techniques.

It was found that Pt nanoparticles of ca. 1-6 nm in size were successively deposited onto the surface of carbon. Pt nanoparticles were uniform and well dispersed on the surface of carbon.

The PtNb2O5/C, PtCoNb2O5/C and Pt/C catalysts with Pt loadings of 0.114, 0.285 and 0.128 mg Pt cm–2, respectively, were synthesized.

Ethanol oxidation current densities were found to be ca. 6 and 12 times higher at the PtNb2O5/C and PtCoNb2O5/C catalysts, respectively, in comparison with those at the Pt/C catalyst.

In the case of oxygen reduction, the PtCoNb2O5/C catalyst outperforms the PtNb2O5/C and Pt/C catalysts towards oxygen reduction and shows higher onset potential, as well as higher current density towards the oxygen reduction reaction as compared with those at the aforementioned catalysts.
Kinetic Study of the Oxygen Reduction Reaction on Alpha-Ni(OH)2 and Alpha-Ni(OH)2 Supported on Graphene Oxide
Authors: Farjami Elaheh , Deiner L. Jay
Published: February 2020

Development of active non-noble metal catalysts for the oxygen reduction reaction is critical for a range of electrochemical energy storage and conversion technologies.  We have recently discovered that alpha nickel hydroxide supported on graphene oxide (α-Ni(OH)2/GO) displays  surprising activity for the oxygen reduction reaction in alkaline media.  In comparison to α-Ni(OH)2 alone or graphene oxide alone, α-Ni(OH)2/GO possesses a lower onset potential, lower peak current potential, and higher peak current density, suggesting a synergy between the GO support and the α-Ni(OH)2 particles.  To investigate the origin of this synergy, we present a comprehensive kinetic analysis of the supported and unsupported α-Ni(OH)2 catalyst.  Rotating disk electrode linear sweep voltammetry furnishes electron transfer numbers, kinetic rate constants, and reaction orders which provide preliminary evidence for similar elementary steps occurring on supported and unsupported α-Ni(OH)2, but modifications in activity arising from differences in the activation energy for adsorption of O2 and of reaction intermediates.
Bio-Inspired Photoresponsive Regulator for Proton Cross-Membrane Transport
Authors: Li Ying , Tse Edmund C. M. , Barile Christopher J. , Gewirth Andrew A. , Zimmerman Steven C
Published: February 2020

Proton-Coupled Electron Transfer (PCET) is ubiquitous in nature, essential to life but particularly difficult to study because of the complexity of natural systems. We recently developed a new experimental framework to permit fine-tuning of proton-transfer kinetics without perturbing the thermodynamics. The regulation took advantage of the “flip-flop” diffusion of proton carriers inside lipid membranes. Unfortunately, the diffusion happens spontaneously and more precise control could be beneficial. As a result, we designed the first synthetic photoresponsive proton gate incorporated in a lipid layer. The new proton carrier features a boronic acid head-group for proton transfer, a stiff stilbene body for photoresponsiveness, and an alkyl tail for lipid incorporation. The light-induced cross-membrane proton transfer was quantified by the activity of an O2 reduction catalyst buried under the lipid layer by electrochemistry. This molecular switch mimics the natural system to precisely control proton relocation without perturbing the proton thermodynamics (Scheme 1).

Scheme 1.  Illustration of photoresponsive transmembrane proton transfer.

Figure 1
(Invited) Customizing Proteins and Microbes for Biological Fuel Cells
Authors: Ajo-Franklin Caroline Marie , Baruch Moshe , Fukushima Tatsuya
Published: February 2020

Electron transfer between proteins in microorganisms and solid materials underpins many aspects of bioelectrochemical energy research. My laboratory seeks to tailor both new microbes and new proteins for specific bioelectrochemical applications. Here I will first describe how we have customized the industrial microbe Escherichia coli for use in biological fuel cells. By transplanting the Mtr pathway of Shewanella oneidensis MR-1 into Escherichia coli, we can confer upon these cells the ability to reduce metal ions, solid metal oxides, and electrodes. These cells couple current production to a metabolic shift towards more oxidized products, demonstrating that we can electronically control the intracellular state of these engineered E. coli. Additionally, we have shown that these engineered E. coli can accept, as well as donate, electrons from an electrode. Thus, this work provides a blueprint to bi-directionally move energy and information between microbial cells and electrodes, and has direct applications in biosynthesis and bioenergy. I will also describe new studies probing the thermodynamic and structural basis by which Mtr proteins reduce solid metal oxides.  We show that MtrF from S. oneidensis MR-1, which can directly reduce iron oxide, binds to iron oxide, but not structurally similar aluminum oxide. Using protein and X-ray footprinting, we also probe which residues of this extracellular electron transfer protein are potentially involved in binding iron oxide. We find that these residues cluster in the tertiary, rather than primary, structure of the protein, suggesting that these regions form a binding site for their solid substrate.  This new understanding will critically inform efforts to rationally design proteins capable of rapid interfacial electron transfer.
Inverse Spinel NiCo2S4 Nanoparticles Coated on Activated Carbon As an Electrocatalyst Applied in Air Cathode Microbial Fuel Cells
Authors: Pu Liangtao , Li Kexun
Published: February 2020

Here, the hybrid of inverse spinel NiCo2S4 nanoparticles coated on activated carbon (AC) has been first described as an effective nonprecious electrocatalyst for oxygen reduction reaction (ORR) used in air cathode microbial fuel cells (MFCs). MFC with NiCo2S4/AC air cathode obtains the maximum power density of 2000 ± 59 mW/m2, with a value of 125% higher than the control. The combination effect of mixed valence in NiCo2S4/AC composite is favorable for easier electron transfer to make O2 absorbed and reduced. The intensity ratio of Raman D to G band (ID/IG
) decreases from 0.85 (AC) to 0.78 (NiCo2S4/AC), indicating the formation of a partial graphite structure in NiCo2S4/AC.NiCo2S4/AC cathode shows better catalytic activity, lower internal resistance, higher kinetic activity and contains much octahedral catalytic active sites of Co3+, which favors a four electron ORR pathway. The finding shows NiCo2S4/AC will be a novel kind of promising nonprecious catalyst applied in MFC.
Spatially Resolved Confocal Resonant Raman Microscopic Analysis of Anode-Grown Geobacter Sulfurreducens Biofilms
Authors: Lebedev Nikolai , Strycharz-Glaven Sarah , Yates Matthew , Tender Leonard M
Published: February 2020

When grown on the surface of anode electrode, Geobacter sulfurreducens forms a multi-cell thick biofilm in which all cells appear to couple oxidation of acetate with electron transport to the anode which serves as the terminal metabolic electron acceptor. Just how electrons are transported through such a biofilm from cells to the underlying anode surface over distances that can exceed 20 microns remains unresolved. Current evidence suggests it may occur by electron hopping through a proposed network of redox cofactors comprised of immobile outer membrane and/or extracellular multi-heme c-type cytochromes. In the present work we apply spatially resolved Confocal Resonant Raman (CRR) microscopic analysis to investigate anode-grown Geobacter biofilms. The results confirm presence of an intra-biofilm redox gradient whereby the probability that a heme is in the reduced state increases with increasing distance it resides from the anode surface. Such a gradient is required to drive electron transport toward the anode surface by electron hopping via cytochromes. The results also indicate that at open circuit when electrons are expected to accumulate in redox cofactors involved in electron transport due to inability of the anode to accept electrons, nearly all c-type cytochrome hemes detected in the biofilm are oxidized. The same outcome occurs when a comparable potential to that measured at open circuit (-0.30 V vs. SHE) is applied to the anode, whereas nearly all hemes are reduced when an exceedingly negative potential (-0.50 V vs. SHE) is applied to the anode.  These results suggest that nearly all c-type cytochromes hemes detected in the biofilm can be electrochemically accessed by the electrode, but most have oxidation potentials too negative to transport electrons originating from acetate metabolism. The results also reveal lateral heterogeneity (x-y dimensions) in type of c-type cytochromes within the biofilm that may affect electron transport to the electrode.

[1] Lebedev, N., Griva, I. & Blom A. Internal Control of Electron Transfer through a Single Iron Atom by Chelating Porphyrin. J. Phys. Chem. C 117, 6933−6939, 2013.

[2] Lebedev, N., Strycharz-Glaven, S. M. & Tender L. M. Spatially Resolved Confocal Resonant Raman Microscopic Analysis of Electron Transfer in Geobacter sulforreducens Biofilm. ChemPhysChem, 15, 320-327, 2014.

[3] Lebedev, N., Strycharz-Glaven, S. M., & Tender L. M. High resolution AFM and single-cell resonance Raman spectroscopy of Geobacter sulfurreducens biofilms early in growth. Frontiers in Energy Research, 2:34, doi: 10.3389, 2014.
Influence of Anode Configuration on Flow Distribution and Performance in Tubular Microbial Fuel Cells
Authors: Mirhosseini Auvid , Salvacion Michael , Chen Shing , Babanova Sofia , Bretschger Orianna
Published: February 2020

A microbial fuel cell (MFC) is a device that utilizes bacteria to oxidize organic and inorganic matter, and through the process of extracellular electron transfer, generate electricity. When the electron transfer at the bacteria-electrode interface is rapid, the efficiency of a MFC is dependent on the flow distribution and mass transport in the anode, which controls the delivery of reactants and removal of waste products. It has been predicted that diffusion of soluble substrates is fast over the length scale of bacterium, but gets significantly slower over millimeter-scale distances and at the scale of centimeters, advection is required. Electrolyte advection along with optimal flow distribution will bring substrates to anode respiring bacteria and enable substrate utilization at high rates. Therefore, in this study we explored the influence of the anode configuration on flow distribution and MFC performance. The efficiency of the system was determined on the basis of chemical oxygen demand (COD) removal and Columbic Efficiency (CE). 

The MFC used for these studies was a membrane based tubular MFC with a submerged oxygen-reducing cathode. Three anode configurations were explored and included: 1) packed graphite granules (MFC 1); 2) bundles of stacked graphite granules (MFC 2); and 3) a small polypropylene mesh cylinder filled with packed graphite granules, wrapped with pleated carbon cloth (MFC 3). The volume of the anode compartment of each reactor was 1L. The reactors were operated under MFC, semi-batch mode with a downstream flow. The reactors were first inoculated with swine waste and lagoon sediment and subsequently fed with swine waste only 1,300 mg-COD/L.

Key parameters were measured on a weekly basis including COD, pH, dissolved oxygen (DO) and turbidity. Samples for 16S rRNA analysis were also collected on a weekly basis from the effluents of each reactor for the classification and identification of bacterial species present. Voltage data was recorded continuously and polarization curves and cyclic voltammetry were periodically performed to monitor biofilm development and MFCs operation.

The preliminary results indicate that due to the advanced flow distribution, MFC 3 demonstrated the highest performance. It showed a startup time of approximately 4 days and achieved a voltage of 0.40 V. MFC 2 also had a startup time of approximately 4 days and achieved a voltage of 0.15 V. MFC 1 had the slowest startup time of about 11 days with a voltage of ≈ 0.10 V. All MFCs were operated under 560 Ω resistors. Future work will include a comprehensive analysis of microbial dynamics and system performance to determine which anode structure was most correlated to improved wastewater treatment and energy recovery activities.
Development of a Microbiosensor for Acetate Detection in Biofilms
Authors: Atci Erhan , Babauta Jerome T. , Sultana Sujala T. , Beyenal Haluk
Published: February 2020

We developed an amperometric acetate microbiosensor capable of measuring in situ sub-micromolar concentration of acetate inside biofilms. The operating principle of the microbiosensor utilized electrochemically active biofilms (EABs) to convert acetate to electrons on the microelectrode tip. The acetate microbiosensor consisted of a 30 µm glass-covered carbon wire working electrode with G.sulfurreducens biofilm on the tip recessed into a glass outer case approximately 200 μm and a Ag/AgCl reference electrode, as shown in Figure 1. The glass outer case terminated to a 30 µm tip diameter where acetate could flow into and diffuse up to the active tip. Acetate-free G.sulfurreducens growth medium served as electrolyte. The microbiosensor showed a linear response between 50 µM and 1.6 mM acetate concentration with a 79 ± 8 µM limit of detection (S/N=2). The operating potential of the microbiosensor was selected as +300 mVAg/AgCl satisfying the limiting current condition. The microbiosensor also demonstrated a higher specificity to acetate over other possible metabolites that could interfere with acetate measurements.

To test the microbiosensor, we measured local acetate concentration inside G. sulfurreducens biofilms grown on a 1 in2 electrode in a three-electrode bioreactor operated in fed-batch mode. Measuring acetate profiles in G.sulfurreducens biofilms is critical to understand acetate limitations and acetate diffusion and to test the developed microbiosensor in G.sulfurreducens biofilms which utilizes acetate as the electron donor. The microbiosensor was used to measure acetate depth profiles within ~225 µm thick G.sulfurreducens biofilm under no current generation (open circuit potential) and current generation (at +300 mVAg/AgCl) conditions. For depth profile measurements, bulk acetate concentration in the bioreactor was set to 1.5 mM by considering the linear calibration range of the microbiosensor. The acetate concentration remained at bulk values throughout the biofilm at open circuit potential when the biofilm was not respiring. However, the acetate concentration decreased from the bulk values to below the detection limit within 200 μm when current was allowed to pass at +300 mVAg/AgCl. This showed that the biofilm was acetate-limited due to the zero acetate concentration at the bottom of the biofilm.

Figure 1
Ionic Liquid Electrical Double Layer from Large Amplitude Fourier Transformed Ac Voltammetry Data
Authors: Lucio Anthony J , Shaw Scott K , Zhang Jie , Bond Alan M
Published: February 2020

The electrical double layer (EDL) regions in ionic liquid (IL) solvents demonstrate behaviors that are not easily explained by a priori knowledge of aqueous counterparts. Despite previous and ongoing research efforts, debate surrounds the causes and prediction of these behaviors. A possible pitfall is the range of ionicity in IL cation/anion pairs. One relatively new and powerful tool useful for exploring the solid-liquid interface that can address these questions is large-amplitude Fourier transform alternating current (FT-ac) voltammetry. By measuring the FT-ac voltammetry signal in potential windows containing only double-layer charging current, the characteristic morphology of ILs’ EDLs can be revealed. This work will discuss the interfacial capacitance of protic and aprotic ILs systems and develop a relationship to fundamental harmonic components of the FT-ac data across metallic and non-metallic working electrodes. The experimental data will be compared with existing theoretical models to advance a working picture of the IL EDL within the capacitive current regime.
(Invited) How Spatial Heterogeneities Affect Dynamics of Ionic Liquids
Authors: Roy Soham , Zheng Zhuan-ping , Bonn Mischa , Hunger Johannes
Published: February 2020

Despite that the heterogeneous structure of ionic liquids (ILs) has been established, the consequences of the nanoscopic segregation on the dynamics of ILs has remained elusive. In particular, the spatial heterogeneity in ILs may result in inherently different local solute environments when using ILs as solvents. Such different local interactions will affect the ability to re-structure and dissipate excess energy during a chemical reaction, which determines the performance as a solvent.

We study these solvent dynamics using femtosecond infrared spectroscopy for a series of alkylammonium ionic liquids [1, 2]. In these experiments vibrational excitation of the ND or NH stretching vibrations results in an ultrafast, local temperature jump and we monitor the subsequent equilibration as a response to the dissipated energy. Owing to the intrinsic molecular specificity of infrared vibrations we can thus probe specifically the different moieties of the ionic liquid’s ions, providing access to the intrinsic solvation dynamics in the absence of any probe molecules. Our results show that ionic liquids are not only structurally heterogeneous, but exhibit a substantial dynamic heterogeneity, with the equilibration within the hydrophobic domains being two-fold faster than in the ionic domains.

The excitation anisotropy, which provides information on the local rotational mobility of the ionic fragments of the cations, is rather insensitive to the size of the cations: Our results even suggest that increasing the hydrophobic domain size goes along with an acceleration of the restricted rotational motion of the ammonium group of the cationic fragments of the IL’s ions. Such accelerated dynamics are indicative of reduced directional interionic interactions, which in turn signify a more fragile three-dimensional structure as the size of the hydrophobic fragments increases.

Our study shows that local dynamics in these ionic liquids are decoupled from macroscopic properties, like e.g. viscosity. Thus, our findings underline that the structural heterogeneity of ILs makes local dynamics heterogeneous, with substantially different solvation properties within the hydrophobic and the ionic sub-domains.

[1] J. Hunger, T. Sonnleitner, L Liu, R. Buchner, M. Bonn and H.J. Bakker, „Hydrogen-Bond Dynamics in a Protic Ionic Liquid: Evidence of Large-Angle Jumps“ J. Phys. Chem. Lett.
3, 3034 (2012).

[2] Z.P. Zheng, W.H. Fan, S. Roy, K. Mazur, A. Nazet, R. Buchner, M. Bonn, and J. Hunger “Ionic Liquids: Not only Structurally but also Dynamically Heterogeneous”, Angew. Chem. Int. Ed.
54
, 687 (2015).
(Invited) Towards a Molecular Level Understanding of the Electrolyte Choline Chloride / Urea
Authors: Hunt Patricia A , Ashworth Claire , Welton Tom
Published: February 2020

Low melting point deep eutectic solvents (DES), can be formed from quaternary ammonium salts with a variety of neutral species.  Eutectic mixtures of such salts with metal halides are well established, Figure 1a. DES employing an ionic liquid component and hydrogen-bond donor, such as CholineChloride/Urea (ChCl/Urea), Figure 1b, are gaining interest as electrolytes, particularly for clean metal extraction and deposition.  DESs can reduce complex processes, avoid hydrogen evolution and embrittlement, deposit reactive metals and metal-alloys unobtainable from aqueous solutions, provide access to novel coating morphologies and enhanced surface properties (increased hardness, reduced roughness), and may offer advantages for the production of nanoporous and nanostructured metals.

DES have properties that are particularly attractive for  large scale technological applications.  DES  are cheap, non-toxic, potentially biodegradable, they have a good electrochemical window, good thermal stability and reasonable electrical conductivity.  DES can dissolve recalcitrant species such as metal oxides and reduce operating temperatures due to the low melting point.  Additional  advantages of the DES include muti-ton production and a high stability with respect to air and moisture.

For example, direct comparison of DESs with standard aqueous solution processes have shown Ni deposition occurs at comparable rates for the same concentration and temperature conditions.  The increased viscosity and reduced conductivity of ChCl/Urea are not rate limiting factors and it has been suggested that speciation within the electrolyte plays the more significant role.1

            Typically the melting point depression of DES is linked to the formation of a larger more diffuse covalent complexed anion, which has a reduced interaction with associating cations, Figure 1.  However, when the neutral component is an organic species capable of acting as a H-bond donor there are uncertainties with respect to the speciation and bonding within the mixture.  We have employed electronic structure methods to examine the interactions between constituent species of ChCl/Urea.  Within cluster models a subtle interplay of electrostatics and different types of H-bonding are observed and elucidated.  Links can be made between these molecular level interactions and the physico-chemical properties of ChCl/Urea DES.

1Abbott, A. P., Ballantyne, A., Harris, R. C., Juma, J. A., Ryder, K. S., & Forrest, G., Electrochimica Acta, 2015, 176, 718–726. http://doi.org/10.1016/j.electacta.2015.07.051

Figure 1
(Invited) Ionic Liquid-Based Electrolytes for Alkaly Metal Batteries
Authors: Giffin Guinevere , Jeong Sangsik , Passerini Stefano
Published: February 2020

Ionic liquid-based electrolytes are encountering a great interest for the development of alkali metal (Li, Na, Mg, …) batteries. The use of magnesium metal as a negative electrode is of particular interest in post-lithium batteries as it has higher theoretical volumetric capacities and is more abundant in the earth’s crust than lithium. The first prototype system for a magnesium rechargeable battery included electrolytes based on magnesium organohaloaluminate salts, such as Mg(AlCl3R)2 and Mg(AlCl2RR′)2, in organic solvents such as tetrahydrofuran and glymes.1 These systems are based on the combination of a Lewis acid and Lewis base, to produce salts with active Mg species that promote facile and reversible Mg deposition. Recent advances include the development of so-called non-nucleophilic salts, which are less corrosive than the original strongly nucleophilic versions.2 However, these electrolytes are not stable in air and water, thus still present safety risks. Electrolytes containing air and water stable salts, e.g. Mg(TFSI)2, have significant advantages not only in terms of safety, but also in terms of chemical and electrochemical stability. Incorporating air and water stable salts into ionic liquids can result in electrolytes which, unlike those containing organic solvents, have low volatility and flammability.

Understanding Mg2+ solvation in ILs is one key step in the development of stable electrolyte systems which promote facile Mg2+ desolvation at the electrode surface. In this study, the intermolecular interactions between Mg2+ ands the IL anions and the impact of these interactions on the physical properties are examined. Furthermore, the transport mechanism of the Mg2+ in ionic liquid electrolytes is explored.

References

1.         Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature
2000, 407, 724-727.

2.         Zhao-Karger, Z.; Zhao, X.; Wang, D.; Diemant, T.; Behm, R. J.; Fichtner, M. Adv. Energy Mater.
2015, 5, 1401155.
Physical and Chemical Analysis of Three Wide Electrochemical Window Ionic Plastic Crystals As Stable Electrolytes in Li-Ion Batteries
Authors: Stevenson Keith J , Dylla Anthony , O'Mahony Aoife
Published: February 2020

Three ionic plastic crystalline solids were synthesized and analyzed to evaluate their suitability for use as electrolytes in Li-ion batteries: N-propyl-N-methylpiperidinium hexafluorophosphate (PP13PF6), N-propyl-N-methylpiperidinium tetrafluoroborate (PP13BF4) and piperidinium perchlorate (PPClO4). The physical and electro(chemical) properties will be discussed.Voltammetric analysis of the plastic crystals alone showed very wide electrochemical windows (>7.5 V) for PP13PF6 and PP13BF4, and a relatively wide window for PPClO4 (4V). Addition of the analogous lithium salts to each of these species (LiPF6, LiBF4 and LiClO4) in a 50:50 wt% ratio showed sluggish Li+ transport at room temperature, but improved when heated to temperatures greater than 45 °C. However, addition of 20 wt% of EC/DEC solvent increased Li+ transport dramatically, particularly for PP13PF6 and PP13BF4. Overall, a mixture containing LiBF4, PP13BF4 and EC/DEC displayed a stable wide electrochemical window of activity for several cycles and good Li+transport through the electrolyte rendering it a promising mixture for future use in Li-ion batteries.
Multifunctional Carbazole-Based Ionic Liquids
Authors: Kirankumar Rajendranath , Chen Po-Yu
Published: February 2020

In this study, a new class of polymerizable ionic liquids were synthesized and modified upon conductive surfaces to enhance the sensitivity and/or selectivity of the electrodes, or to be electrochromic films. At suitable conditions, the poly-ionic liquids were soluble in some organic solvents.

Ionic liquids (ILs) have shown the advantages on electroanalysis when they were modified on electrode surface. Electropolymerization might be a good approach for the modification of ILs on conductive surface. Various carbazole-based ILs (Figure 1) were synthesized in this study and they were electropolymerized on indium tin oxide (ITO) electrodes by cyclic voltammetry in ILs BMP-TFSI, BMIm-PF6 and etc., as well as in conventional solvents (i.e. acetonitrile, methanol and DMSO)[1]. Electrochemical oxidation of the carbazole pendant units affords a conjugated polymer network (CPN) film of polycarbazole and the polymer is expected to have good conductivity on the conducting surface[2]. The electrode with electropolymerized ILs shows improved activity towards the oxidation of uric acid (UA), compared with that of unmodified electrodes. The polymerized ILs also exhibit electrochromic properties. The ITO electrodes modified with polycarbazole ILs show color change from deep green to pale yellow while the applied potential was scanned from +1.2 V to -0.2 V and vice versa.

On the other hand, bipyridinium (viologen) ionic liquids modified with carbazole via an alkyl spacer were synthesized and their electrochromic behavior in liquid state was studied in various ILs or conventional volatile organic solvents. Viologen is a well-known electroactive material with three different redox states: the dication, the radical cation and the neutral compound. The colors of radical cations depend on the groups substituted on the nitrogen atoms of the viologen moiety[3]. By introducing the carbazole groups, colors different from those observed for the traditional viologen compounds were recorded. This behavior is currently studied.

 

[1] D.-X. Zhuang, P.-Y. Chen, Journal of Electroanalytical Chemistry, 2009, 626: 197–200.

[2] Antonio F. Frau, Nicel C. Estillore and Rigoberto C. Advincula,ACS Appl. Mater. Interfaces, 2010, 2: 3726–3737.

[3] N. Jordao, L. Cabrita, F. Pina and L.C. Branco, Chem.-Eur.J., 2014, 20: 3982–3988.

 

Figure 1
Improvement in Electrochemical Properties of Ionic Liquid PYR14tfsi By Mixing with BMImBF4 As High Safety Electrolyte
Authors: Lee Ching-Feng , Chang Chien-Min , Wang Pin-Han , Chen Hwang-Sheng , Chen-Yang Yui Whei
Published: February 2020

As is known, the characteristics of electrolyte play a significant role in lithium-ion batteries in terms of high conductivity, good compatibility with electrode material and safety. Because of the volatility and flammability of the traditional organic electrolytes, the safety risk has been a big concern for the batteries, especially when it is used in hybrid electric vehicles (HEVs) and electric vehicles (EVs). On the other hand, the room temperature ionic liquids (RTILs) usually are low volatile, non-flammable liquids with wide electrochemical window that benefit to use as electrolytes in high-safety lithium battery. Since the chemical and physical properties are strongly related to combination of the cations and anions composed, unique ionic liquids may be designed for the particular application. Recently, the RTILs formed by imidazolium, pyrrolidinium, piperidinium cations and hexafluorophosphate (PF6
-), tetrafluoroborate (BF4
-), bis(trifluoromethanesulfonyl)imide (TFSI-) anions have been frequently used as the electrolytes for lithium-ion batteries. However, as reported, the organic solvents i.e. ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC) and diethyl carbonate (DEC), which are used for the traditional liquid electrolytes, have often been mixed with the RTIL for reducing the viscosity to increase the conductivity. Yet, the thermal stability can’t be improved essentially. In this study, a solvent-free ternary RTIL-based electrolyte system has been constructed by the RTILs, 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Three different electrolytes with various compositions are prepared and characterized by FTIR, thermogravimetric analysis, differential scanning calorimetry, linear sweep voltammetry, conductivity meter and rheometer. The results show that all three electrolytes are thermally stable up to about 350℃ and have wide electrochemical windows (~5V). Besides, the lowest viscosity and the highest conductivity obtained were 66.2 cP and 2.76 mS, respectively. The highest discharge capacity of the LiFePO4/electrolytes/Li half-cell obtained in the voltage range of 2.5–4.3 V at 0.2C and 55℃ is 158 mAh g-1. This study reveals that the RTIL-based ternary electrolyte is a promising electrolyte candidate for the high-safety lithium-ion battery.

Acknowledgements

The authors gratefully acknowledge the Ministry of Science and Technology, Taiwan, R. O. C. and Chung Yuan Christian University for supporting this research work.
Highly Fractal MoS2 Electrodes Modified By Ammonium Thiomolybdate As Efficient Hydrogen Evolving Electro-Catalysts
Authors: Ramirez-Caro Alejandra , Redeker Frenio A. , Bierwirth Stefanie , Bogdanoff Peter , Ellmer Klaus , Fiechter Sebastian
Published: February 2020

Due to the high energy density of hydrogen it could play an important role as energy storage medium replacing fossil fuels in the future. To produce it in large quantities “artificial leaf”-type structures could be used converting solar light into this fuel by electrochemical decomposition of water. Since this process is most efficient working under acidic conditions in an electrolyzing system semiconducting materials are required on the one hand efficiently absorbing sunlight and generating electron-hole pairs, the energy of which is high enough to split water. To reduce overvoltages on the other hand electro-catalysts are in demand lowering in addition the overvoltages at cathode and anode side.

To replace costly platinum as most efficient HER catalyst for more than a decade attempts were made to replace this noble metal by molybdenum sulfides. It has been shown that nanoparticles of MoS2 are most efficient consisting of three to four S-Mo-S slabs deposited on a suited support, e.g. MoO3-x, multiwalled carbon nanotubes (MWCNT) and activated carbon paper [1, 2].

In this contribution, we report on the deposition of (NH4)2Mo3S13 particles on highly fractal MoS2 layers deposited by reactive magnetron sputtering. Best results were obtained after drop casting a solution of ammonium thiomolybdate on a sputtered MoS2 film as shown in Figure 1. The modified electrode exhibited an overvoltage of -220mV at a current density of 10mAcm-2. Since it is known that the edges of the hexagonal MoS2 crystallites of the sputtered film are containing the highly catalytically active sites this contribution will address the nano-architecture of the modified electrodes.

Figure 1