bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Oxygen Reduction Reaction Performance of Fe-N-C Catalyst
Authors: Nakamura Genki , Tanaka Hirohisa
Published: February 2024

Fuel cells are gaining worldwide attention as an acceptable technology for achieving carbon neutrality. However, existing fuel cells use large amounts of precious metals, which limits their widespread adoption. Precious metal-free fuel cells have been studied in our laboratory. The oxidation-reduction reaction (ORR) at the cathode of the fuel cell must start at a higher potential and proceed smoothly in a four-electron reduction reaction without producing hydrogen peroxide1,2. We have synthesized iron-based complex catalysts using the method reported by Plamen Atanassov3 et al. Iron nitrate dihydrate is mixed in aqueous solution with glucose, 2-methylimidazole, and zinc nitrate hexahydrate, followed by hydrothermal synthesis at 200°C for 24 hours. It is then acid-treated with nitric acid to dissolve excess metallic iron, and the process is repeated twice at 950°C to complete the Fe-N-C catalyst. However, SEM and XRD analysis confirmed the presence of large amounts of metallic iron. In response to these results, the synthetic process of the Fe-N-C catalyst was repeatedly improved, and the prepared catalyst was subjected to in-situ XAFS (X-ray absorption fine structure) analysis using synchrotron radiation at SPring-8 (Fig. 1). The peak around 7110 eV is significantly different from that of metallic iron (Fe foil), indicating that iron complex, iron phthalocyanine (II), and it is like the peak of iron phthalocyanine (II), confirming that the prepared Fe-N-C catalyst forms a good complex. The performance of the Fe-N-C catalyst with the confirmed complexation was then investigated, and a cathode that exhibited ORR performance comparable to that of the Pt catalyst was successfully synthesized (Fig. 2). In the future, further improvement of the catalyst preparation process will be discussed to develop a catalyst with much better performance than Pt.

Reference

1N. Yamamoto, D.Matsumura, Y. Hagihara, K.Tanaka, Y. Hasegawa, K. Ishii, H. Tanaka, “Investigation of hydrogen superoxide adsorption during ORR on Pt/C catalyst in acidic solution for PEFC by in-situ high energy resolution XAFS”, Jounal of Power Sources, 557, 15, (2023), 232508

2S. Kusano, D. Matsumura, K. Ishii, H. Tanaka, J. Mizuki, “Electrochemical Absorption on Pt Nanoparticles in alkaline Solution Observed Using in-situ High Energy Resolution X-ray Absorption Spectroscopy”, Nanomaterials, 9, 4, (2019), 642

3 R. Gokhale, L-K. Tsui, K. Roach, Y. Chen, M. M. Hossen, K. Artyushkova, F. Garzon, p. Atanassov, “Hydrothermal synthesis of platinum-Group-Metal-Free Catalysts: Structural Elucidation and Oxygen Reduction Catalysis”, ChemElectroChem, 5, 14, (2017), 1848-1853

Figure 1
Synthesis of Ir Nanoparticles As Promoters for the Stabilization of Fenc-Catalysts Under Ssc Conditions
Authors: Sondershausen Lars , Gridin Vladislav , Segura Salas Nicole , Hofmann Kathrin , Kramm Ulrike I.
Published: February 2024

Fuel cells are promising devices for implementation in automotive propulsion. While the standard operation seems feasible, during start-up and shutdown high potentials occur on the cathodic site induced by the reverse current mode. In consequence, the carbon oxidation reaction (COR) occurs and limits the lifetime of PEMFCs. One approach suppressing carbon corrosion is the introduction of small amounts of an oxygen evolution reaction (OER) catalyst, as e.g. iridium. In our recent work we showed that in relative manner the durability was improved, however, the initial performance was less compared to the non-modified FeNC catalyst.[1
] These NP had been prepared by a polyol approach.[2
] However, capping agents (CA) could eventually still be present in these systems, blocking the particles in their performance.

Herein, we present our results using an alternative surfactant free synthesis of Ir nanoparticles, adapted from literature,[3
] that are then used for the modification of an FeNC catalysts. The performance of the newly prepared FeNC+Ir vs the FeNC+Ir+CA reference was evaluated employing accelerated stress tests mimicking the start-up and shut down conditions in RDE and PEMFC. It is shown that with this new approach the amount of NP on the surface can be better controlled. Beside the electrochemical testing structural characterization by X-ray-diffraction, thermogravimetric analysis and transmission-electron-microscopy was performed.

It will be shown that by surfactant free synthesis Ir nanoparticles with high purity can be obtained. Due to the higher purity, an improvement of the OER activity can be achieved with the same Ir loading. In the RDE, an improvement in stability was observed by loading an FeNC catalyst with Ir nanoparticles. However, under fuel cell conditions, no improvement in stability was observed by loading Ir nanoparticles onto a FeNC catalyst.

List of references

[1] Prössl, C., Kübler, M., Paul, S., Ni, L., Kinkelin, S. J., Heppe, N., Eberhardt, K., Geppert, C., Jaegermann, W., Stark, R. W., Bron, M. & Kramm, U. I. (2022). Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions. Journal of Materials Chemistry A, 10(11), 6038-6053.

[2] Prössl, C., Kübler, M., Nowroozi, M. A., Paul, S., Clemens, O., & Kramm, U. I. (2021). Investigation of the thermal removal steps of capping agents in the synthesis of bimetallic iridium-based catalysts for the ethanol oxidation reaction. Physical Chemistry Chemical Physics, 23(1), 563-573.

[3] Bizzotto, F., Quinson, J., Schröder, J., Zana, A., & Arenz, M. (2021). Surfactant-free colloidal strategies for highly dispersed and active supported IrO2 catalysts: Synthesis and performance evaluation for the oxygen evolution reaction. Journal of catalysis, 401, 54-62.
Causes and Effects of Unintended Cation Crossover in CO2 Reduction Cells
Authors: El-Nagar Gumaa , Haun Flora , Gupta Siddharth , Stojkovikj Sasho , Mayer Matthew T.
Published: February 2024

Electrochemically converting carbon dioxide into useful products is a promising approach to combat climate change by reducing our reliance on fossil fuels and promoting a sustainable carbon cycle.

The operation of membrane electrode assemblies within gas diffusion cells facilitates the efficient reduction of CO2 at rates relevant to industrial applications. However, their long-term stability is often limited by formation of solid precipitates in the cathode pores. This is a consequence of a combination of 1) local alkalization due to the electrochemical reaction, 2) generation of (bi)carbonate by chemical reaction of CO2 with the alkaline electrolyte, and 3) the presence of alkali metal cations. In catholyte-free, zero-gap cells using anion exchange membranes, the presence of electrolyte cations at the cathode is the result of unintended crossover from the anolyte, and a detailed understanding of the factors enabling this crossover is lacking. Here we show that the anolyte concentration governs the flux of cation migration through the membrane, and this substantially influences the behaviours of copper catalysts in catholyte-free CO2 electrolyzers.

Our findings highlight the substantial impact of cation effects, including unintended crossover, even in catholyte-free cells, on reaction pathways. This aspect should be considered in the future development of catalysts and devices. As an outlook a more in-depth knowledge with the help of operando measurements could help to understand and manage cation crossover for optimizing the performance, selectivity, and durability of these electrochemical systems.
Ultra-Low Loading IrO2 on Porous Transport Layer for Catalysis of Proton Exchange Membrane Water Electrolysis
Authors: Shen Jie , Bens Frennie , van Dijk Bas , Ripepi Davide , Diaz-Morales Oscar
Published: February 2024

Proton Exchange Membrane Water Electrolysis (PEMWE) is a commercial technology with specific advantages such as high-power density and rapid start-up times, which makes it a perfect match to produce hydrogen from intermittent renewable energy sources (green H2). [1] However, very scarce materials, such as iridium and platinum, are currently used as catalysts and protection coatings to withstand the harsh operating conditions in PEMWE. Iridium is the anode catalyst in the state-of-the-art PEMWE, with loadings in the range 1-2 mg/cm2. This metric translates into using 200-500 kg of iridium per GW, which accounts for roughly 10% of the global iridium production per year. Reducing iridium usage in PEMWE is critical to realize the 10-100 GW/year growth in green H2 power. [2,3]

To significantly reduce the Ir loading, while maintaining the lateral conductivity, we coated the iridium catalyst by atmospheric spatial Atomic Layer Deposition (sALD) on titanium porous transport layer (PTL), which acts as the electrically conductive substrate. The coating renders ultra-low iridium loadings, which is 100-200 times less iridium than the state-of-the-art catalyst coated membrane technology, while retaining ca. 60-80% of the performance (in terms of current density), with durability demonstrated up to 100 h (see Figure 1). We will also show here that protection coatings on the titanium PTL are beneficial to yield good durability with these ultra-low loadings of iridium and demonstrated that sALD has the potential to produce non-PGM based protection coatings.

[1] Barbir, F. Solar Energy 78 (2005) 661-669.

[2] Gavrilova, A., Wieclawska, S.M. “Towards a green future. Part 2” (2021). TNO report 21-12158.

[3] Minke, C., Suermann, M., Bensmann, B., & Hanke-Rauschenbach, R. J. Hydrogen Energy 46 (2021) 23581-23590.

Figure 1
Tailoring Binding Abilities By Incorporating Oxophilic Transition Metals on 3D Nanostructured Ni Arrays for Accelerated Alkaline Hydrogen Evolution Reaction
Authors: Kim Jaerim , Jung Hyeonjung , Jung Sang-Mun , Kim Yong-Tae , Han Jeong Woo , Kim Jong Kyu
Published: February 2024

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water electrolysis plays a key role for renewable hydrogen energy technology. The slow reaction kinetics of HER in alkaline solutions, however, has hampered advances in high-performance hydrogen production. Herein, we investigated the trends in HER activity with respect to the binding energies of Ni-based thin film catalysts by incorporating a series of oxophilic transition metal atoms. It was found that the doping of oxophilic atoms enables the modulation of binding abilities of hydrogen and hydroxyl ions on the Ni surfaces, leading to the first establishment of a volcano relation between OH-binding energies and alkaline HER activities. In particular, Cr-incorporated Ni catalyst shows optimized OH-binding as well as H-binding energies for facilitating water dissociation and improving HER activity in alkaline media. Further enhancement of catalytic performance was achieved by introducing an array of three-dimensional (3D) Ni nanohelixes (NHs) that provide abundant surface active sites and effective channels for charge transfer and mass transport. The Cr dopants incorporated into the Ni NHs accelerate the dissociative adsorption process of water, resulting in remarkably enhanced catalytic activities in alkaline medium. Our approach can provide a rational design strategy and experimental methodology toward efficient bimetallic electrocatalysts for alkaline HER using earth-abundant elements.

Reference

Journal of the American Chemical Society 3, 1399-1408 (2021) [Front Cover]
LiMn2O4 as a Model System to Understand the Mn Dissolution Mechanism during Water Oxidation
Authors: Bisen Omeshwari Yadorao , Baumung Max , Schönewald Florian , Volkert C. a. , Risch Marcel
Published: February 2024

LiMn2O4 as a model system to understand the Mn dissolution mechanism during water oxidation

Omeshwari Bisen1,2, M. Baumung1,2, F. Schönewald2, C. A. Volkert2, M. Risch1,2

1

Nachwuchsgruppe Gestaltung des Sauerstoffentwicklungsmechanismus,
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1,14109 Berlin, Germany

2

Institut für Materialphysik, Georg-August-Universität Göttingen, Germany

Email: omeshwari.bisen@helmholtz-berlin.de

The water splitting provides an attractive avenue for chemical energy storage by producing the green hydrogen, but it suffers from the inefficiency of the oxygen evolution reaction (OER) and the degradation of the electrocatalyst under the harsh oxidizing conditions of the reaction. Manganese oxides are attractive due to their abundance and as a non-critical raw material, but they are known to degrade quickly during the OER, which hinders their usage severely. [1] Therefore, it is equivalently important to focus on the understanding of degradation processes during the OER. [2]

In this study and our previous studies, we used the battery material LiMn2O4 as a model system for the OER in alkaline media where the Mn valence can be tuned with little effect on structure. [3, 4] LiMn2O4 exhibits a core-shell cubic-spinel structure with tetrahedral antisite Mn2+ defects in the shell. [5] We have used the rotating ring-disk electrode (RRDE) setup to obtain the product current of manganese corrosion and oxygen evolution by applying the desired potential at the Pt ring (Fig. 1a). We monitored the dissolution of Mn from the LiMn2O4 (Fig. 1b) and found two onsets of exponential currents, indicating the two distinct Mn loss processes; one independent of the OER and one associated to it, which is further investigated by Tafel slopes. The ex-situ X-ray absorption spectroscopy (Fig. 1c) and X-ray photoelectron spectroscopy (Fig. 1d) represents the oxidation of Mn moieties after voltage cycling including the OER, and loss of Mn2+
and Li+. We correlate near-surface oxidation with the charge attributed to dissolved Mn, which demonstrates increasing Mn dissolution with the formation of surface Mn4+ species under anodic potential and observed the distinct atomistic origin before and after OER onset.[6] It is highly desirable to understand the atomistic insights into the Mn dissolution processes for the knowledge-guided mitigation of electrocatalyst degradation during water oxidation, which can be broadly extended to manganese-based oxide systems.

References:

[1] M. Rabe et al., Phys. Chem. Chem. Phys., 2019, 21, 10457

[2]M. Risch,Current Opinion in Electrochemistry2023, 38:101247

[3] M. Baumung et al., ChemPhysChem 2019, 20, 2981-2988

[4] M. Baumung et al., Sustain. Energy Fuels 2019, 3, 2218-2226

[5] F. Schönewald et al. arXiv:2007.04217v1 [6] O. Bisen et al. arXiv preprint arXiv:2309.00101

Figure 1
SrAl12O19:Eu,Cr As Luminescence Thermometers
Authors: Zeler Justyna , Zych Eugeniusz , Kwiatkowski Mateusz
Published: February 2024

Luminescent nanothermometers offer several approaches to determine the absolute temperature. Mostly, temperature-stimulated changes in the intensity ratio of emission bands, emission kinetics, band/emission line width, or luminescence band/line peak position are explored. The list is longer and is still growing. In our project, the Cr3+, Eu2+-based aluminates materials were designed taking into account the possibility to work as non-contact luminescent thermometers using mentioned above approaches. In Figure 1 the luminescence spectra of SrAl12O19:Eu,Cr phosphor are shown in the temperature range of 15-500 K. The emission comes from both the directly excited ions, Eu2+ and Cr3+. Particularly strong changes with temperature can be seen in the Eu2+ emission around 350 - 470 nm and Cr3+ above 670 nm. Luminescent mechanisms of energy transfer between specific activators of the aluminates lattice will be presented, the consequence of which is obtaining by the material sophisticated thermometric properties in a wide range of measured temperature, from cryogenic to around 500 K.

The research finances by the Polish National Science Centre under grant #UMO2018/31/B/ST4/00924 and partially by program “Excellence Initiative – Research University” (IDUB) for years 2020-2026 for University of Wrocław (grant # BPIDUB.4610.678.2021)

Figure 1
Crystal Structure–Photoluminescence Correlations in Ce3+-Doped Ca2ZnSi2O7phosphors
Authors: Park Kyeongsoon , Gwon S.Y. , Kim S.H.
Published: February 2024

In this work, Ce3+-doped Ca2-x
ZnSi2O7:xCe3+ phosphors were prepared by the solid-state reaction in air. The crystal structure and photoluminescence properties of the prepared phosphors were investigated. All the prepared samples formed the tetragonal crystal structure. XRD Rietveld refinement was performed to retrieve a detailed crystal structure of the Ca2-x
ZnSi2O7:xCe3+ phosphors. The lattice parameters a and c increased with increasing Ce3+concentration. The lattice parameters a and c of the Ca1.996ZnSi2O7: 0.004Ce3+ phosphor were 7.825 Å and 5.015 Å, respectively. The Ca2-x
ZnSi2O7:xCe3+ phosphors showed strong and asymmetric bands covering the 415 to 650 nm range, which were attributed to the transitions of Ce3+ ions from the 5d excited state to the 2F5/2 and 2F7/2 ground states. The emission intensity increased with increasing Ce3+concentration up to x = 0.012. The dipole-dipole interaction was responsible for the concentration quenching. The CIE coordinate (x, y) was located in the blue spectral region. These results indicate that the prepared Ca2-x
ZnSi2O7:xCe3+ phosphors can serve as an efficient blue phosphor in the white light emitting diodes.
Prediction of Emission Level Energy of Mn4+ in Oxides Based on the Local Structure Using First-Principles Calculations and Machine Learning
Authors: Tanaka Shuma , Ogasawara Kazuyoshi
Published: February 2024

The white LED is an important next-generation light source. Most of the high color rendering white LEDs that have become popular in recent years consist of blue LEDs combined with green and red phosphors. For example, Eu2+:SrxCa1-xAlSiN3 (SCASN) and Mn4+:K2SiF6 (KSF) are used as red phosphors. However, considering the production cost and the stability against high temperature and high humidity, novel red phosphors obtained by adding Mn4+ to oxide crystals are still desired. To realize a Mn-doped oxide red phosphor for white LEDs, it is indispensable to clarify the relationship between the multiplet energies and the local structures. Semi-empirical methods based on experimental data are generally used to analyze luminescent materials, but these methods cannot be applied to unknown or hypothetical materials. In this work, we analyzed the relationship between the local structure and the energy levels of hypothetical Mn4+-doped oxides by performing first-principles electronic structure calculations using the discrete-variational multi-electron (DVME) method. The local structures around Mn4+ were systematically changed by changing the bond distances and angles and the multiplet energies corresponding to each local structure were calculated non-empirically. Then the relationship between the energy and the local structure was visually represented by creating energy-structure maps. Using these systematic theoretical values as the training data, a machine learning model for the prediction of the first-principles calculation results based only on the structural parameters was also created. The results of this study would provide guidelines for the development of novel phosphors based on oxide crystals doped with Mn4+.
Prediction of 4f-5d Transition Energy of Ce3+ in Oxides By First-Principles Calculations and Machine Learning
Authors: Honda Mamoru , Ogasawara Kazuyoshi
Published: February 2024

A Ce3+ ion has only one electron in the 4f orbitals and its 4f-5d transition energy is strongly influenced by the width of the crystal field splitting of the 5d orbitals. In other words, the absorption and emission wavelengths of Ce3+ in crystals can be widely controlled by changing the ligand field environment. As an example of Ce3+-doped phosphor, Ce:YAG (Y3Al5O12) is widely used as an yellow phosphor for standard white LEDs. Therefore, novel phosphors with desired emission colors can be developed by adding Ce3+ to appropriate host crystals.

In this work, we aimed to construct an efficient prediction model for the transition energy of Ce3+ in oxide crystals. Small clusters consisting of the substituted Ce3+ ion and the first-neighbor anions were constructed and molecular orbital calculations were performed using the relativistic discrete-variational Xα (DV-Xα) method. Then machine learning based on structural and electronic state parameters was performed to create a predictive model for the 4f-5d transition energy of Ce3+ in crystals. By creating the correlation diagrams, the influence of each parameter on the transition energy was analyzed in detail.
Optimization of the First-Principles Calculation Conditions of d3 Ions in SrTiO3
Authors: Okada Sayaka , Tanaka Shuma , Ogasawara Kazuyoshi
Published: February 2024

Since transition metal ions are generally more stable in supply than rare earth ions and are inexpensive, researches on alternative materials based on transition metal elements to those based on rare earth elements are actively conducted. As phosphors using transition metal ions, Cr3+ and Mn4+ with d3 configuration are used for red emission while Mn2+ with d5 configuration is used for green emission. For theoretical search of novel phosphor materials, first-principles calculations of the transition energies based on the cluster approach are useful. However, in order to establish an efficient and effective method for prediction, optimization of computational conditions is indispensable.

In this study, first-principles calculations of the d-d transition energies of d3 ions such as Cr3+ and Mn4+ in SrTiO3 were performed using the discrete-variational multi-electron (DVME) method. The clusters with Ti4+ at the center were constructed based on the crystal structure data of SrTiO3, and then Ti4+ was replaced with Cr3+ or Mn4+. In order to determine an appropriate cluster size, model clusters consisting of 7, 15, 63, 89, 143, 199, and 391 atoms were constructed. In order to improve the accuracy, the first-principles calculations were carried out considering the configuration-dependent correction (CDC) and the correlation correction (CC), which correct the overestimation of the multiplet energies. The effect of the lattice relaxation was also considered based on the structural optimization using the CASTEP code. Then the cluster size dependence and the effect of the lattice relaxation were clarified based on the detailed comparison of the first-principles calculation results.
(Digital Presentation) One-Step Hydrothermal Preparation of Chiral Carbon Quantum Dots and Its Chiral Recognition of Glutamine Enantiomers
Authors: Zhu Xiashi , Li Xiang
Published: February 2024

Abstract: A novel method for chiral recognition of glutamine enantiomers using fluorescence intensity changes of chiral carbon quantum dots(CCQDs) is proposed. CCQDs was prepared by one-step hydrothermal method with L-tryptophan as carbon source and chiral source, which are spherical nanoparticles exhibiting blue color luminescence for fluorescence probe to recognize glutamine enantiomeric isomers[1] . Fluorescence intensity(∆Fe )enhanced by addition of L-glutamine to CCQDs solution and ∆Fe was well linear with L-glutamine concentration in the range 0.01-5.0 mM and the limit of detection was 0.22 mM. Fluorescence quenching(∆Fq) by D-glutamine addition to CCQDs solution and ∆Fq was well linear with D-glutamine concentration in the range of 0.01-5.0 mM with a detection limit of 0.28 mM. Calculation of the binding energy between L/D-glutamine and CCQDs by molecular modelling to explain the chiral recognition mechanism[2,3]. The method was applied to the determination of L-glutamine content in real sample and the results showed good recoveries, indicating the feasibility of the method.

References:

[1] F. Copur, N. Bekar, E. Zor, S. Alpaydin, H. Bingol, Nanopaper-based photoluminescent enantioselective sensing of L-Lysine by L-Cysteine modified carbon quantum dots, Sensors and Actuators B: Chemical. 279 (2019) 305–312. https://doi.org/10.1016/j.snb.2018.10.026.

[2] O. Xu, S. Wan, Y. Zhang, J. Li, X. Zhu, A unique dual-excitation carbon quantum dots: Facile synthesis and application as a dual-“on-off-on” fluorescent probe, Sensors and Actuators B: Chemical. 340 (2021) 129904. https://doi.org/10.1016/j.snb.2021.129904.

[3] X. Hou, J. Song, Q. Wu, H. Lv, Chiral carbon quantum dots as fluorescent probe for rapid chiral recognition of isoleucine enantiomers, Analytica Chimica Acta. 1184 (2021) 339012. https://doi.org/10.1016/j.aca.2021.339012.
Anodic Chlorination of Poly(3-(2-ethylhexyl)Thiophene) Films Facilitated by Constructing Ordered Structures
Authors: Kurioka Tomoyuki , Tomita Ikuyoshi , Inagi Shinsuke
Published: February 2024

π-Conjugated polymer (CP) is known to show unique optoelectronic properties due to their extended π-conjugation moieties along with their main chains.[1] To control these properties, post-functionalization methods are powerful approaches. Among post-functionalization methods, electrochemical post-functionalization (ePF) is a useful and promising approach to manipulate the optoelectronic properties of the film-state CPs.[2] Considering their optoelectronic properties in the film state, these properties are often affected by their structures. On the basis of this idea, the structure of CP films is expected to serve a crucial role in the efficacy of ePF; however, the relationship between their structures and ePF methods remains unexplored.

In this work, we report the relationship between the structures of CP films and the efficacy of ePF by performing anodic chlorination of poly(3-(2-ethylhexyl)thiophene) (P3EHT) films (Figure 1).[3] Changing solvents used in preparing P3EHT films is found to result in P3EHT films with different structures (i.e., amorphous and crystalline structures). The amorphous P3EHT films are not electrochemically chlorinated, whereas P3EHT films possessing crystalline domains are successfully chlorinated in the same reaction conditions. In situ conductance measurements of P3EHT films evidence that the reactivity difference in the anodic chlorination between both P3EHT films is because of their electrical conductivity.

References

[1] X. Guo, M. Baumgarten, K. Müllen, Prog. Polym. Sci.
2013, 38, 1832–1908.

[2] T. Kurioka, S. Inagi, Chem. Rec.
2021, 21, 2107–2119.

[3] T. Kurioka, T. Komamura, N. Shida, T. Hayakawa, I. Tomita, S. Inagi, Macromol. Chem. Phys.
2022, 223, 2100435.

Figure 1
Single Benzene Yellow Fluorophore: Anodic Synthesis of Tetrahydrobenzodifuran
Authors: Okada Yohei , Wang Zimo , Horiguchi Genki , Kamiya Hihidero
Published: February 2024

Fluorophores have proven to be indispensable tools in fields ranging from physics, chemistry, and biology. Organic fluorophores have high degrees of freedom in their molecular designs, which is essential for fundamental applications such as imaging probes. The strategies to produce organic fluorophores with improved physicochemical properties are two-fold, including an extension of aryl systems and a construction of push-pull motifs, where electron-donating and -withdrawing groups are conjugated. When used in bio-related research fields, the construction of push-pull motifs is preferred in terms of water solubility and molecular size, since the extension of aryl systems produces relatively large hydrophobic, planar, and thus highly crystalline, structures.

The early work by Shimizu in 2009 triggered explosive growth in the development of new single-benzene fluorophores. From the viewpoints of synthetic practicality and unique and tunable photophysical properties, installing diagonally symmetrical substitution patterns with the same electron-donating and -withdrawing groups is the simplest strategy to create new single-benzene fluorophores.

During the course of our studies focusing on electrochemical cycloadditions, we found that dihydrobenzofuran derivatives armed with electron-donating and -withdrawing groups exhibited bright fluorescence. In order to suppress molecular motions that cause non-radiative transitions, formation of a furan ring is effective in restricting bond rotation. Furthermore, we found that symmetrically substituted dialkoxy-dicarbonylbenzenes exhibited unique bright fluorescence. In this study, we successfully demonstrate that constructing symmetrical push-pull motifs in combination with restricting bond rotations is the key to creating small yet brightly emitting fluorophores. The anodically constructed tetrahydrobenzodifuran moiety has proven to be an effective core architecture to realize unique and powerful single-benzene fluorophores with high quantum yields and large Stokes shifts.
A Molecular Copper Catalyst for Electrochemical Conversion of CO2 to C2+ Products
Authors: Liu Na , Liang Hong Qing , Wohlrab Sebastian , Francke Robert
Published: February 2024

Electrochemical carbon dioxide reduction (CO2RR) is a promising route to address the excessive emission of CO2 and the depletion of fossil fuels.[1] Metallic Cu and Cu-based materials have attracted increased attention, as Cu is the only metal that can reliably convert CO2 into hydrocarbons and oxygenates, such as ethanol, ethylene, and n-propanol.[2] To optimize CO2-to-C2+ conversion, considerable efforts were made to modify the catalyst composition and structure, adjusting the electrolyte, and optimizing the electrochemical setup.[3] In this context, molecular catalysts (i.e. transition metal complexes) are interesting alternatives, since the performance can be precisely tuned via ligand modification and due to the possibility for mechanistic studies at well-defined and uniform active sites.[4]

Herein, a catalytic system based on an immobilized dinuclear Cu phenanthroline complex is reported that can be prepared with a straightforward synthetic method. The catalyst exhibits excellent CO2RR selectivity toward C-C coupling in aqueous electrolytes with only small production of H2. The highest Faradaic efficiency (FE) for C2+ products achieved was 62% at -1.85 V vs. Ag/AgCl with less than 10% FE for H2. Furthermore, a steady current density and a stable FE(C2H4) over 10 h continuous operation indicate a good stability of the Cu complex. In this contribution, both the electrolysis results and the relationship between structural aspects and product selectivity will be discussed, the latter based on scanning/transmission electron microscopy, X-ray photoelectron/absorption spectroscopy, and further analytical techniques.

Literature:

[1] X. Su, Z. Jiang, J. Zhou, H. Liu, D. Zhou, H. Shang, X. Ni, Z. Peng, F. Yang, W. Chen, Z. Qi, D. Wang, Y. Wang, Nat. Commun.
2022, 13, 1322. [2] W. Quan, Y. Lin, Y. Luo, Y. Huang, Adv. Sci.
2021, 8, e2101597. [3] J. Yu, J. Wang, Y. Ma, J. Zhou, Y. Wang, P. Lu, J. Yin, R. Ye, Z. Zhu, Z. Fan, Adv. Funct. Mater.
2021, 31. [4] D. H. Nam, P. De Luna, A. Rosas-Hernandez, A. Thevenon, F. Li, T. Agapie, J. C. Peters, O. Shekhah, M. Eddaoudi, E. H. Sargent, Nat. Mater.
2020, 19, 266.
Genetic Code Expansion in the Service of Bioelectrochemistry
Authors: Alfonta Lital , Algov Itay , Boyarski Anastasya , Zhou Lu , Cohen Yael , Moshel Itay , Shaferman Michael , Meijler Michael
Published: February 2024

Genetic code expansion is a method that enables the inclusion of unnatural amino acids (UAAs) into proteins by expanding the genetic code beyond the 20 canonical amino acids. This can be accomplished by introducing new codons (triplet sequences that encode specific amino acids) into the genetic code via orthogonal tRNA/synthetase pairs.

Orthogonal tRNA/synthetase pairs are comprised of aminoacyl-tRNA synthetases (aaRSs) and tRNAs that are not present in nature. These pairs can recognize and charge UAAs with tRNAs that possess non-natural codons, allowing for the integration of these amino acids into proteins in response to non-sense codons.

In our laboratory, we utilize this approach to incorporate various UAAs, some of which serve as orthogonal chemical handles for "clicking" them with redox-active molecules or biomolecules (via click chemistry) or for attaching them to electrodes to enable site-specific orientation of enzymes. Some UAAs are redox-active on their own, which imparts new properties to the proteins and enzymes into which they are incorporated for biosensing and catalysis. In my presentation, I will outline a simple straightforward technique developed in our lab for selecting new UAAs-compatible aaRSs and provide examples and electrochemical characterizations from our recent investigations. Genetic code expansion is a method that enables the inclusion of unnatural amino acids (UAAs) into proteins by expanding the genetic code beyond the 20 canonical amino acids. This can be accomplished by introducing new codons (triplet sequences that encode specific amino acids) into the genetic code via orthogonal tRNA/synthetase pairs.

Orthogonal tRNA/synthetase pairs are comprised of aminoacyl-tRNA synthetases (aaRSs) and tRNAs that are not present in nature. These pairs can recognize and charge UAAs with tRNAs that possess non-natural codons, allowing for the integration of these amino acids into proteins in response to non-sense codons.

In our laboratory, we utilize this approach to incorporate various UAAs, some of which serve as orthogonal chemical handles for "clicking" them with redox-active molecules or biomolecules (via click chemistry) or for attaching them to electrodes to enable site-specific orientation of enzymes. Some UAAs are redox-active on their own, which imparts new properties to the proteins and enzymes into which they are incorporated for biosensing and catalysis. In my presentation, I will outline a simple straightforward technique developed in our lab for selecting new UAAs-compatible aaRSs and provide examples and electrochemical characterizations from our recent investigations.
A Low-Cost, Safe and Anion-Flexible Method for the Electrosynthesis of Diaryl Iodonium Salts
Authors: Scherkus Anton , Müller Bernd H. , Francke Robert
Published: February 2024

Hypervalent iodine compounds have been studied extensively in the past. They are considered to be non-toxic and mild oxidants which represent useful alternatives to toxic heavy-metal based reagents.[1] Hypervalent iodine(III) and iodine(V) species such as (diacetoxy)iodobenzene (PIDA) and the Dess-Martin periodinane are commercially available and routinely employed in oxidation reactions.[2] For synthesis of both iodine(III) and iodine(V) species, electrochemical approaches have been developed.[3] The electrochemistry of diaryl iodonium salts (see Figure, compound 3), however, is much less explored. Such compounds are typically employed as versatile arylation reagents.[4] Their conventional synthesis starts from a iodoarene that undergoes a reaction with a chemical oxidizer, followed by subsequent treatment with aryl-boron, aryl-silicon or aryl-tin reagents to yield the diaryl iodonium salt.[4] A more practical approach that does not require activated arenes is based on the use of meta-chloroperbenzoic acid (mCPBA) in presence of a strong acid (e.g. triflic acid) for oxidative C-I coupling.[5]

Using electric current as an oxidizer constitutes a further advancement for synthesis of diaryl iodonium salts. In a recent example, the electrolytic transformation of iodoarenes has been carried out in a HFIP-MeCN solvent mixture using excess triflic acid as the supporting electrolyte and anion source, rendering aryliodonium triflates in medium to high yields.[6]

However, the dependence on the hazardous and costly HFIP and triflic acid still represents a major limitation. In this work, the development of a cheaper, greener, and acid-free synthesis of diaryl iodonium salts is presented.[7] The method uses MeCN as the sole solvent as well as lithium salts as supporting electrolyte/anion source. Since many lithium salts with weakly coordinating anions are commercially available and well soluble in MeCN, the approach provides flexibility regarding the choice of the anion.

[1] a) A. Yoshimura, V. V. Zhdankin, Chem. Rev.
2016, 116, 3328-3435; b) B. Olofsson, I. Marek, Z. Rappoport, PATAI's Chemistry of Functional Groups, John Wiley & Sons, 2018.

[2] a) C. H. Willgerodt, J. Prakt. Chem.
1886, 33, 154-160; b) D. B. Dess, J. C. Martin, J. Org. Chem.
1983, 48, 4155-4156.

[3] a) R. Francke, Curr. Opin. Electrochem.
2019, 15, 83-88; b) R. Francke, Curr. Opin. Electrochem.
2021, 28

[4] E. A. Merritt, B. Olofsson, Angew. Chem. Int. Ed.
2009, 48, 9052-9070.

[5] M. Bielawski, M. Zhu, B. Olofsson, Adv. Synth. Catal.
2007, 349, 2610-2618.

[6] M. Elsherbini, W. J. Moran, Org. Biomol. Chem.
2021, 19, 4706-4711.

[7] A. Scherkus, B. H. Müller, R. Francke, 2023; manuscript in preparation.

Figure 1
Tools to Simulate Resonance Raman Spectra for in-Situ Studies of Electron Transport Mediators and Bioelectrocatalysts
Authors: Ozuguzel Umut , Aquino Adelia , Minteer Shelley , Korzeniewski Carol
Published: February 2024

Raman spectroscopy is widely applied as an in-situ probe of electrochemical processes. When the excitation light is resonant with an electronic transition, the detected signal can be enhanced by more than 1,000-fold. Resonance Raman (RR) spectroscopy has broad application in the study of common organic electron transport mediators (i.e., viologens, phenazines, photosynthetic pigments) and active sites of redox proteins (i.e., laccases, peroxidases, flavin-containing enzymes). To support investigations of bioelectrocatalytic membranes, we have been adapting RR spectroscopy to gain insights into the properties of immobilized redox mediators and biocatalyst active sites.1,2 Computational methods can be useful for guiding spectral interpretation. This poster reports on applications of recently advanced time-dependent density functional theory (TDDFT) codes that enable the simulation of RR spectra for small electron transport mediators (e.g., methyl viologen radical anion) and redox protein active site models (e.g., laccase T1 site mimics). The ORCA program suite3 was adapted. A series of Cu-centered compounds that model the T1 active site in laccases was studied along with the methyl viologen radical cation. The T1 site in laccases facilitates direct electron transport to an electrode and is a target for in-situ RR measurements. The reported work demonstrates careful selection of the functional (B3-LYP versus the long-range corrected hybrid exchange functional, ωB97X-D3) results in TDDFT-calculated electronic absorption and RR spectra that have features in excellent agreement with experiment. The results provide a foundation to build from in advancing models of small redox mediators and laccase catalytic active sites in support of sustainable technologies.

Ozuguzel, U.; Aquino, A.J.A.; Nieman, R.; Minteer, S.D.; Korzeniewski, C. “Calculation of Resonance Raman Spectra and Excited State Properties for Blue Copper Protein Model Complexes” ACS Sustainable Chem. Eng. 2022, 10, 14614.

Xu, J.; Koh, M.; Minteer, S. D.; Korzeniewski, C. “In Situ Confocal Raman Microscopy of Redox Polymer Films on Bulk Electrode Supports” ACS Measurement Science Au
2023 (DOI: 10.1021/acsmeasuresciau.2c00064).

Neese, F.; Wennmohs, F.; Becker, U.; Riplinger, C. “ORCA Quantum Chemistry Program Package” J. Chem. Phys.
2020, 152, 224108.
Synthetic Chemistry and Microelectrode Arrays: Building Stable Platforms for Point of Care Diagnostics
Authors: Moeller Kevin D , Chang Yu-Chia , Huang Albert
Published: February 2024

Molecular diagnostics typically require three main components. A molecular interaction that identifies a specific target, a device that detects, quantifies, and records that interaction, and an interface between the two. The interface is critical because it provides a means to fix molecular recognition elements to the surface of the device. For a "point-of-care" application, the interface must be stable both in terms of chemistry and time while still allowing the signal from the molecular interaction to be sensed and recorded by the device. For the use of a microelectrode array as the detection device, construction of the interface must also allow for individual molecular recognition elements to be placed by individual, addressable electrodes in the array.

Because of the need for stability and synthetic flexibility, we made the choice to move away from the use of self-assembled monolayers as the interface for developing microelectrode arrays as point-of-care devices. To that end, we have employed diblock copolymers to coat the surface of microelectrode arrays, a change that has offered increased stability of the surface and enabled the use of a broad array of synthetic methods for functionalizing the electrodes in the array. In this talk, we show how the use of a diblock copolymer in conjunction with Cu(I)- and Cu(II)-mediated reactions can be used to functionalize a microelectrode array with multiple DNA-aptamers for the multiplex detection of metabolites. The resulting surface is stable for over 30 weeks (and counting), allows for the detection of multiple metabolites in the same experiment, and retains the detection sensitivity obtained with a self-assembled monolayer.

One of the goals of the talk will also be to illustrate for the synthetic community the role that it can play in developing new tools for molecular diagnostics. After all, it is the surface on a microelectrode array that in the long-run defines what an array can be used for and the quality of the resulting analytical experiments. The construction of those surfaces is a synthetic chemistry challenge that moving forward will require both new synthetic methods and new approaches for characterization of the products generated from the new methods. One approach for characterization will be discussed in the context of the Cu(I)- and Cu(II)-mediated reactions employed in the current study.
(Invited) Electrochemical Multi-Electron Oxidation of Thiophene-Derivatives Promoted by Coordination of Electrolytes
Authors: Shida Naoki
Published: February 2024

Supporting electrolyte is an essential component of the electrochemical systems, although its effect on the reactivity of electrochemically generated cation/anion species has been rarely discussed.[1][2] Our recent study on the electrochemical behavior of tellurium-containing π-conjugated molecule revealed that the coordination of anion species toward the electrochemically generated radical cation species determines the number of electrons, where 1e/2e oxidation were switched depending on the donor number of electrolyte-derived anion species as well as solvents.[3]

In the present study, we expanded this idea to thiophene-derivatives to explore the synthetic applicability of electrolyte-coordination. As expected, electrolyte-dependent oxidation behavior of π-expanded thiophene derivatives was confirmed. Especially, the use of coordinating anion promoted multi-electron oxidation of thiophene derivatives, which enabled facile C-C coupling chemistry and oxidative intramolecular cyclization to give rare thiophenium motif in a single step. This study implies the importance of a rational design of the electrolyte to develop novel electrosynthetic reactions.

[1] N. Shida, Electrochemistry, 2022, 90, 101004

[2] S. Yoshinaga, M. Atobe, N. Shida, Electrochemistry, in press (DOI: 10.5796/electrochemistry.23-67013)

[3] N. Shida, H. Nishiyama, F. Zheng, S. Ye, D. S. Seferos, I. Tomita, S. Inagi, Commun. Chem.
2019, 2, 124.

Figure 1
(Keynote) Enabling Continuous Molecular Monitoring in vivo via Implantable and Wearable Aptamer-Based Sensors
Authors: Arroyo Netz
Published: February 2024

The ability to continuously monitor fluctuating concentrations of specific molecules in the body can drastically improve precision medicine by allowing the real-time correlation of dynamic molecular processes with health and disease. While this ability has been pursued from multiple directions, electrochemical strategies have been successful and commercializable platforms. For example, continuous glucose monitors have dramatically improved the therapeutic management and quality of life for Type 1 diabetics. Unfortunately, the enzymatic sensing used in glucose monitors is not applicable to a large number of clinically relevant biomarkers. This limitation significantly reduces the scope of dynamic biochemical processes we can probe to study healthy human physiology and disease. In response, my laboratory is developing in vivo electrochemical aptamer-based sensors, a platform that is generalizable to the highly specific sensing of arbitrary molecular targets and supports continuous molecular monitoring in the body. In this presentation I will discuss the current state-of-the-art of these sensors, and the challenges we are addressing to enable preclinical and clinical applications.
(Invited) Increasing the Reproducibility and Stability of Temperature-Responsive Elastin-like Polymer Surfaces
Authors: Halpern Jeffrey M , Feeney Stanley , Higgins Grace , Sims Myranda , Albeshir Zahraa , Arnold Galen , Waters Jeffery , Balog Eva Rose M
Published: February 2024

The coacervation versus solubility of Elastin-Like Polymers (ELPs) in solution can be triggered by different factors including ionic strength and temperature. Therefore, the Lower Critical Solution Temperature (LCST) response of ELPs is relatively well understood. However, tethered or surface-bound ELPs are less understood, and the surface reproducibility and stability still needs to be characterized.

Recently our group studied the electrochemical impedance spectroscopy (EIS) response of ELP-modified surfaces associated with changes in ionic strength, and we observed intermediate states of ELP surface collapse.1 Within this work, we present our progress on monitoring the thermal response of surface-bound ELP. Using EIS, We will examine the localized temperature-triggered collapse for I40 ELP (AGCAG(VPGIG)40VPASW). We aim to better understand the way charge transfer changes within a range of temperature and intermediate states. We will report on observed changes in charge transfer resistance from 5 to 40 degrees Celsius. We will discuss protocols we developed to increase the reproducibility of these surfaces. We will also discuss our progress in making these surfaces more stable by looking at the longevity of these surfaces over time.

Support was provided by a National Science Foundation EPSCoR award (#2119237).

[1] Morales, M.A., Paiva, W.A., Marvin, L., Balog, E.R.M. and Halpern, J.M., 2019. Electrochemical characterization of the stimuli-response of surface-immobilized elastin-like polymers. Soft matter, 15(47), pp.9640-9646.