bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemically Driven Optical Dynamics of Reflectin Protein
Authors: Lin Yin-Chen , Yang Changxuan , Tochikura Seren , Morse Daniel E , Sepunaru Lior , Gordon Michael J.
Published: August 2024

Neuronally triggered phosphorylation monotonically and cyclably drives the assembly of reflectin proteins, resulting in the fine-tuning of colors reflected from specialized skin cells in squid for camouflage and communication. Reflectin has been found as the primary constituent within stacks of plasma membrane-bounded platelets (iridosomes) found in iridocyte cells. This cellular ‘superstructure’ consisting of alternating layers of high refractive index platelets and low refractive index extracellular space effectively functions as a biological Bragg reflector. In vivo, reflectin assembly triggers osmotic dehydration of the Bragg lamellae, reducing the platelet thickness, and thus dynamically tuning the color of the reflected light. Our previous study has shown that electrochemistry, used as in vitro surrogate for in vivo phosphorylation-mediated charge neutralization, triggers voltage-calibrated and cyclable control of the rate and size of reflectin assembly. This process is highly similar to the observed physiological behavior. Here, we demonstrate for the first time that electrochemical reduction enables tunable and reversible control of refractive index and thickness of a reflectin thin film formed by drop-casting on a conductive substrate to mimic the platelet structures in cephalopod iridophores. Electrochemically driven in situ spectroscopic ellipsometry was developed to trigger and simultaneously analyze the change in optical properties of the reflectin film and thus further elucidate the color-changing mechanisms in squid skin. Our results confirm the hypothesis that the extent of charge neutralization controlled by applied voltage plays a role in calibrating the water volume fraction within platelets and the resulting optical features. This work opens new means for analyzing the biophysical mechanisms regulating color change by reflectin assembly, designing advanced functional materials and devices, and bridging the biotic–abiotic interface.
Electrochemical Monitoring of Respiratory Infectious Disease on Nanostructured Surface Functionalized with Biosynthetic Multimer Aptamers
Authors: Hamidi Seyed Vahid , I. Hosseini Imman , Siavash Moakhar Roozbeh , Khorrami Jahromi Arash , Mahshid Sara
Published: August 2024

Multivalent aptamers have gained substantial interest owing to their enhanced affinity towards target analytes compared to their monomeric counterparts due to their capability to bind simultaneously to diverse regions of a target molecule, fostering more robust and enduring interactions. This study focuses on engineering the surface-based production and modification of multivalent aptamers through room temperature rolling circle amplification technique and chemically modified primers. This process starts with immobilizing modified primers onto an electrode to generate and arrange biosynthesised multivalent aptamers. These bio-engineered multivalent aptamers are utilized as bio-receptors for capturing a specific target (in this case, the SARS-CoV-2 spike protein). The entire surface amplification procedure is extensively characterized using electrochemical, microscopy, and spectroscopy methods, determining the optimal amplification duration for biosensing applications. Impressively, multivalent aptasensors shows substantially increased response signals and affinity compared to monomeric aptasensors. Moreover, the influence of surface structures on response signals is explored by employing both flat screen-printed gold electrodes and nano-/microisland (NMI) electrodes. NMIs-based multimeric aptasensors demonstrate notably heightened sensitivity in detecting SARS-CoV-2 spike protein within the range of 10 to 106 fg/mL in saliva and buffer media. Finally, the signal of the proposed aptasensor has been successfully assessed using several patient samples.
Synthesis of Yolk-Shell CoNi2S4 Spheres Modified Flexible Carbon Cloth Electrode for Highly Sensitive Detection of Neurotransmitter Dopamine
Authors: Pattan-Siddappa Ganesh , Kim Sang-Youn
Published: August 2024

Dopamine (DA) is a neurotransmitter that is connected with transitory information in the mammalian central nervous system; changes in its concentration in the body are directly related to mental activity. The absence and/or low level of DA can cause symptoms of several disorders, including Parkinson’s and schizophrenia. As a result, detecting DA in patients is critical for regulating body function. Many efforts have been made to build electrochemical sensing devices to detect DA in human body or biological fluids due to its inherent advantages of high sensitivity, speed, simplicity, and affordability. However, surface modification with nanomaterials, polymers, pretreatments, or simple functionalization are required to improve the performance of these sensing electrodes. Further, exploration of earth-abundant electro-catalysts with high activity and stability is also important for the development of highly selective and sensitive electrochemical sensing interfaces. With these considerations in mind, our study describes the construction of yolk-shell CoNi2S4 spheres modified flexible carbon cloth (CC) electrode for the sensitive detection of DA. The synthesized material's surface and morphological study were examined, and the successful synthesis was confirmed. The yolk-shell CoNi2S4 spheres shown good electrochemical sensing performance towards DA detection due to their unique surface morphology with large specific surface area and synergistic effects. In comparison to unmodified CC, the yolk-shell CoNi2S4 spheres modified CC demonstrated a low detection limit (5.1 nM), great sensitivity, and a wide linear range (0.01 – 5.2 µM). The detection selectivity was also tested in the presence of a high quantity of the common interference ascorbic acid. Selectivity, stability, and repeatability have also been demonstrated to be satisfactory. Furthermore, the fabricated sensor’s flexibility endows it with significant potential in the fabrication of wearable and soft electronics for human healthcare monitoring.
Strategic Design of Conductive Biopolymer Surface Coatings for Sensing and Remediation Applications
Authors: Sheets Katey M , Murphy Andrew , Jones Andre , Keleher Jason J.
Published: August 2024

Advancement in the utility of conductive polysaccharide-based (i.e., agar, alginate, pectin, cellulose) composite materials for charge transfer applications requires effective surface functionalization and dopant matching to overcome limitations in electron transfer in these dielectric materials. A promising approach is the design of a biomimetic nanocomposite material, coupled with Fe-carboxyl coordination chemistry to photoinitiate the radical polymerization of polyaniline (PANI) in a uniform manner throughout a templated polymer matrix. Results have shown the feasibility of establishing a responsive carbon-based sensor, capable of modulating charge transfer performance in the presence of differing dopants (i.e., hydrochloric acid, sulfuric acid, polyelectrolyte). The aim of this work is to expand upon previous findings by unraveling the dopant-specific charge transport mechanisms as they relate to the polarizability and mobility of the dopant. Additionally, a network-level understanding of how changing the identity of the polymer backbone and the conductive polymer (i.e., aniline, pyrrole, thiophene) alters the charge transfer efficiency and overall stability of the conductive matrix. Current-voltage (I-V) sweeps reveal that these n-doped conductive polymer nanocomposites show enhanced current flow and reduced internal resistance compared to non-functionalized controls. Lastly, once the network reached an equilibrated state, the addition of a model contaminant (mucin) showed a decrease in the potential; however, upon an applied voltage, the contaminant was removed, and the system recovered to its original state. Alternatively, the network was also evaluated for the remediation of model pollutants. Results show that upon an applied voltage in simulated textile wastewater, there was a 10% degradation of methylene blue within 1 hour. Thus, the backbone/dopant/conducting polymer relationship is critical to achieving optimal performance with various applications.
New Electrochemical Channel Flow Cell Design for Electrochemical Studies at Elevated Temperatures and Pressures
Authors: Abdulaziz Muna , Petruk Ariel , Sciaini German , Trevani Liliana
Published: August 2024

Temperature exerts a considerable influence on the efficiency of chemical and electrochemical processes, and it is expected that studies under wide temperature and pressure (T and p) conditions can significantly impact fields of technological interest such as energy storage and conversion, water treatment, waste conversion, metal recovery, and electrosynthesis, among others.1 The electrochemical studies conducted by Bard’s group in near-critical and supercritical aqueous solutions,2 as well as the contributions made by MacDonald’s and Lvov’s3,4 groups on corrosion and pH determination in hydrothermal systems, offer valuable insights into the effects of temperature and pressure on electrochemical reactions under extreme conditions and construction materials and electrode designs. Other studies in the field, though they did not reach such harsh conditions, made valuable contributions by proposing innovative hydrodynamic electrode systems, from channel cells for studies up to 110 oC,5 a rotating disc electrode for temperatures up to 150 oC,6 and even an imping jet electrode able to reach 210 oC.7 Unfortunately, these studies were rarely expanded to more than one or two systems.

In this work, various hydrodynamic electrode configurations have been examined to conclude that the channel flow cell design presents several advantages over other systems for high T and P applications. These cells can provide consistent and reproducible mass transport conditions across a broad range of flow rates and allow channel dimension adjustments to tackle diverse technological challenges. Furthermore, this configuration aligns well with spectroscopic techniques like Raman/SERS (surface-enhanced Raman spectroscopy). COMSOL Multiphysics was used when designing the cell prototype, and validation of the model was carried out using data from previous studies.8 The high T,p cell uses disposable thin-film electrodes (TFEs) patterned onto sapphire wafers through nanofabrication methods; a significant amount of time has been invested in testing the performance of the TFEs up to at least 150°C. These results will also be presented along with experiments conducted with the new channel cell under ambient conditions.

References

(1) Giovanelli, D.; Lawrence, N. S.; Compton, R. G., Electroanalysis (New York, N.Y.)
2004, 16 (10), 789-810.

(2) Liu, C.-y.; Snyder, S. R.; Bard, A. J. J. Phys. Chem.B
1997, 101 (7), 1180-1185.

(3) Macdonald, D. D. Corrosion
2013, 34 (3), 75-84.

(4) Balashov, V. N.; Fedkin, M. V.; Lvov, S. N., J. Electrochem. Soc.
2009, 156 (7), C209.

(5) Wang, H.; Jusys, Z.; Behm, R. J.; Abruña, H. D., J. Electroanal. Chem.
2021, 896, 115251.

(6) Fleige, M. J.; Wiberg, G. K.; Arenz, M., Rev Sci Instrum
2015, 86 (6), 064101.

(7) Trevani, L. N.; Calvo, E.; Corti, H. R., Electrochem. Commun
2000, 2 (5), 312-316.

(8) Moorcroft, M. J.; Lawrence, N. S.; Coles, B. A.; Compton, R. G.; Trevani, L. J. Electroanal. Chem.
2001, 506 (1), 28-33.
Noise Interrogation during an Induced Faradaic Reaction
Authors: Wheeler Kaden , Kajal Kajal , Roehrich Brian , Chung Julia , Gott Joseph , Sepunaru Lior
Published: August 2024

Single-entity electrochemistry has emerged as a potent method that allows for examination of individual responses within a system to comprehend a bulk response. For example, utilizing electrodes on the micrometer scale or smaller provides the requisite sensitivity to discern the impact of a nanoparticle contacting the electrode surface which catalyzes a reaction. Nevertheless, the detection of nanoimpacts is limited by the presence of noise which stems from the inherent non-inert nature of electrodes.

Understanding the noise level under a continuous Faradaic reaction becomes crucial for detecting catalysis at the sub-micron scale. In this presentation, I will describe how we understand and quantify the level of noise under diverse conditions. We measured noise while varying electrode size, sampling frequency, and redox-probe concentration. These results allowed us to formulate a model to predict noise at an electrode. Commonly, noise is thought to scale with the square root of current. However, our measurements reveal that the background noise level shifts from a square root dependence at the macroscale to a linear dependence at the microscale. Moreover, a chemically-coupled reaction (EC’) produces lower noise in comparison with a purely electrochemical reaction that produces the same steady-state current. In combination, these results suggest that diffusion partially dictates the amount of noise, along with the amount of redox-active species exchanging charge with the electrode. By understanding these noise sources, we may begin to control them, yielding more accurate and precise single-entity results.
Elucidating Pathways of Methanol Oxidation on Oxygen-Vacant NiOOH Sites Using a Synergistic in Situ Attenuated Total Reflectance Surface-Enhanced Infrared Absorption Spectroscopy and DFT Study
Authors: Phan Vi T.T. , Nguyen Quy Phu , Wang Bin , Burgess Ian
Published: August 2024

A thorough comprehension of the mechanism underlying the methanol oxidation reaction (MOR) on Ni-based catalysts is critical for electrocatalysis design and development of Ni-based alloys. However, the mechanism of MOR on these materials remains a matter of controversy. There have been few publications on employing surface enhanced spectroscopy to adequately capture the surface chemistry of MOR on NiOOH while the existing theoretical chemistry studies on the reaction mechanism presents a multitude of inconsistent and incomplete results. Here, we combine in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) to determine the mechanism and product distribution of MOR on monometallic Ni-based catalysts in alkaline media. Critically, the DFT calculations include the role of O-vacancy of NiOOH, which is argued to be the active site for methanol oxidation. The SEIRAS results show that two bands corresponding to nas(O=C–O) of HCOO- and nas(C–O) of HCO3
-/CO3
2- appears after the commencement of MOR and varies as a function of potentials. These spectroscopic results are in good agreement with the DFT-based energetics of reaction, suggesting that the MOR mainly proceeds in the following pathway: The early consumption of methanol yields HCOO- as the major product while increasing potentials stimulate further oxidation of adsorbed HCOO* to form HCO3
-/CO3
2-. On the other hand, we show a parallel pathway for the generation of HCO3
-/CO3
2- at high potentials that bypasses the formation of HCOO*. The two main pathways presented in this study are thermodynamically more feasible than the one predominantly reported in literature for MOR on NiOOH. The two former pathways circumvent CHO and/or CO to produce HCO3
-/CO3
2-, whereas the latter involves these species as intermediates. These DFT-based hypotheses are backed up by the spectroscopic evidence that no band associated with CHO and CO can be detected by SEIRAS. This study has the potential to offer invaluable atomic-level insights into MOR on NiOOH as a stepping stone to development of high-performance multi-metallic Ni-based catalysts.

Figure 1
Molecular Solvation Environment Controls the Active Site in Cation-Mediated Electrocatalytic CO2 Reduction to Methanol
Authors: Zhu Quansong , Rooney Conor L. , Shema Hadar , Zeng Christina , Panetier Julien A. , Gross Elad , Wang Hailiang , Baker Lawrence
Published: August 2024

Electrocatalytic synthesis of higher-value products from waste molecules is an emerging technique for sustainable chemical catalysis. Heterogeneous molecular electrocatalysts are an important group of materials where the catalytic activity and selectivity can be controlled using molecularly defined active sites. Despite extensive efforts to synthesize better molecular catalysts, the effects of molecular aggregation, which dominates the interaction of the catalyst with the electrode surface as well as with the electrochemical solvation environment, are not fully understood. Using cobalt phthalocyanine (CoPc) dispersed on carbon nanotubes (CNTs) as a model system, we find that controlling the direct interaction of the molecular catalyst with cations in the electrochemical double layer (EDL) results in significantly enhanced performance for CO2 reduction (CO2RR). Specifically, molecular dispersion of the CoPc onto CNTs yields a 4-fold increase in total current density and 8-fold increase in methanol (MeOH) selectivity compared to aggregated CoPc physically mixed with the same CNT support, enabling CO2 to MeOH conversion with 42.34% Faradaic efficiency (FE). Using surface-selective sum-frequency generation (SFG) vibrational spectroscopy, direct detection of reaction intermediates reveals that the potential-dependent adsorption of two distinct CO intermediates at two types of active sites, one less active and producing mostly CO, the other more active and able to produce methanol. DFT calculations show that the CO intermediate responsible for selective MeOH production results from the direct interaction with cations present in the EDL. This interaction, which is only possible when CoPc is molecularly dispersed on the electrode surface, is responsible for the cation-assisted conversion of CO to MeOH. Control experiments using either strongly hydrated Li+, or chelated K+ by 18-crown-6-ether, which suppress MeOH formation, further confirms the important role of this interaction. Similarly significant enhancement effects are also observed for nitrate reduction reaction (NO3RR) and oxygen reduction reaction (ORR), showing that dispersing molecular catalysts into monomers states is a general design parameter required to enhance activity and selectivity by cation-assisted reaction kinetics inside the EDL.
Toward Sustainable Olefins: Electroreduction of CO2 to Multi-Carbon Olefins Using Trimetallic Cu-Rich Catalysts
Authors: Amouzesh Seyed Parsa , Asadi Mohammad
Published: August 2024

The sustainable conversion of carbon monoxide (CO2) into value-added chemicals via electrochemical methods, powered by renewable electricity, is considered as a promising approach to meet the global energy demand and close the anthropogenic carbon cycle. However, this technology is in the early stage of development, particularly in the production of multi-carbon (C2+) hydrocarbons due to well-studied thermodynamic and kinetic barriers. To overcome these challenges, developing a catalyst with high activity and selectivity is crucial to minimize energy input and maximize the effectiveness of C2+ products formation.

In this work, we will present our recent advancement on developing non-precious tri-metallic catalysts with copper-rich surface synthesized by our developed atomically controllable and environmentally friendly synthesis method. The developed nanostructured tri-metallic electrocatalysts by this method show remarkable selectivity and activity in the electrochemical conversion of CO2 to olefins. In particular, our electrochemical results show an overall C2+ olefine Faradaic efficiency (FE%) of 69% more specifically 58% ethylene and 11% propylene at a current density of -112 mA/cm² under applied potential of -2.8 V in an anion exchange membrane (AEM) electrolyzer. To gain a better understanding of the catalytic performance and find a structural-performance relationships for the developed materials, we performed several physicochemical and electrochemical characterization experiments, including X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS). We will discuss morphology and atomic structure changes of the developed materials under realistic conditions, with a specific focus on understanding how different trimetallic interfaces influence selectivity and activity in the electrochemical CO2 reduction reaction (eCO2RR).
Selective Oxidation of Ethanol on a Nickel Foam Electrode Followed by Aldol Condensation with Furfural to Produce Furan-2-Acrolein
Authors: Manamperi Hemanthi D. , Jackson Michael A.
Published: August 2024

Catalytic conversion of biomass derived molecules into chemicals with energy and industrial applications represents a promising and sustainable route to replace petroleum resources. Therein, furfuraldehyde is among the top 30 biomass derived chemicals defined by the Department of Energy with a wide range of applications. Furfuraldehyde can be easily produced from corncob and straw with an annual production of more than 200000 tons. Furfuraldehyde can be converted into chemicals with high economical value via hydrogenation, oxidation, reductive amination, decarbonylation, nitration, and condensation reactions. Electrosynthesis utilizes a potential or current to replace the redox reagents employed in conventional redox synthesis. In contrast to the tedious reaction and work up conditions required for conventional chemical synthesis, electrosynthesis is often easy and straightforward. Despite these advantages, electrosynthesis represents an under explored area with a vast number of potential applications. The focus of this work is the Aldol condensation of furfural with electrochemically generated acetaldehyde and propanal. Preliminary electrocatalysis experiments conducted in 250 mM KOH with nickel foam working electrode demonstrate 80-95% Faradaic Efficiency for the electrochemical step and nearly 50% conversion of furfuraldehyde. The substrate scope for the oxidative Aldol condensation, optimization of reaction conditions and potential applications of thus formed Aldol products will be discussed in this presentation.
Effect of the EMIM Cation on the CO2 Reduction Reaction on Gold
Authors: Richards Danielle , Percival Stephen J.
Published: August 2024

The electrochemical CO2 reduction reaction (CO2RR) is emerging as a promising method to produce carbon neutral chemical feedstocks. Additives or co-catalysts in the electrolyte can lower the activation barrier for CO2RR, yielding faster conversion rates at lower voltages. Recently, electrocatalytic CO2 reduction mediated by ionic liquids (IL) has been reported but with conflicting accounts to whether the ILs benefit CO2RR or adversely, the competing hydrogen evolution reaction (HER).

We report the effect of added IL EMIM-Cl, specifically EMIM+, in aqueous solutions on the electrochemical CO2RR and competing HER on gold. We show the CO2 reduction current increases by ~1.5x with the highest amount of added EMIM+ relative to the pure electrolyte. Differential pulse voltammetry reveals an additional large change in the reduction current that only appears with both CO2 and EMIM+ present. Lastly, we use advanced electrochemical analysis methods to determine the reaction kinetics and preliminary evidence shows that the standard heterogeneous rate constant increases for the reaction at large overpotentials while the HER is suppressed at low overpotentials with EMIM+ present.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.
Impact of Exposed Crystal Facets on Oxygen Reduction Reaction Activity in Zeolitic Imidazole Frameworks
Authors: Kongpatpanich Kanokwan , Pimu Sorawich , Yodsin Nuttapon , Namuangruk Supawadee
Published: August 2024

Oxygen reduction reactions (ORR) are critical reactions for efficient sustainable and renewable energy storage. However, the limitation of ORR is a slow kinetic reaction due to the multi-step transfer mechanism of electrons. Therefore, electrocatalysts with high ORR activity and stability are needed to overcome the reaction limitations. Zeolitic imidazole framework-67 (ZIF-67) has attracted attention in electrochemical applications due to its multiple redox-active sites and high stability in alkali conditions. The Co-doped porous carbon catalysts derived from ZIF-67 have the potential to be used as ORR catalysts with high performance, while pure phase ZIF-67 electrocatalyst for ORR is rarely studied. The work studies the importance of crystal facets on ORR reactivity. The results show that ZIF-67 nanocube exhibits excellent ORR activity with lower half wave-potential and faster kinetics process compared to its bulk structure. It is proposed that ZIF-67 nanocube provides improvement of selectivity for the four-electron pathway, which is a favorable process with higher reaction efficiency. The density functional theory (DFT) calculations suggest unsaturated Co2+ active sites with enriched (100) facets in the cubic crystal. Therefore, the fast diffusion of oxygen molecules to active sites and strong interaction with intermediate are observed in a cubic structure. The correspondence between experiment and calculation offers enhancement of ORR activity and selectivity from control-specific growth of (100) facet with cubic shape. The work introduces a new strategy for designing highly efficient ORR electrocatalysts with facet-controlled, allowing further study in other electrochemical reactions.
MOF-Derived Selenium-Enriched Hollow NiCo2O4/NiO Nanocages for Enhanced Oxygen Evolution Reaction
Authors: Kale Vaibhav Namdev , T Maiyalagan
Published: August 2024

Finding clean, sustainable, and environmentally friendly technologies is especially crucial in addressing both energy and environmental challenges. Intending to accelerate the oxygen evolution reaction (OER) which happens at the anode and and to decrease the energy consumption for water-splitting at a large scale, exploring high-performing electrocatalysts is an imperative undertaking essential to maximize the practical applicability of water splitting. Developing electrocatalysts through strategic surface modifications represents a significant approach to the deliberate creation of exceptionally active catalytic centers through rational means. Considerable attention has been focused on the advancement of mixed oxides based on transition metals as highly active electrocatalysts. In the present work, we have successfully synthesized electrocatalysts for the OER as elemental selenium incorporated hollowed NiCo2O4/NiO nanocages by employing precise control over the structure and composition of the material. The findings demonstrated that the surface reconstructed hollowed structure with plenty of thin nanocages enhancement of 5 wt% Se-NiCo2O4/NiO resulted in an increased quantity of corresponding edge active sites. This structural achievement further expedited mass transport and due to increased conductivity sped up the charge transfer processes within the system, exhibited remarkable activity for the OER, displaying a low overpotential (η=288 mV) at a current density (j) of 10 mA cm−2 and a Tafel slope (66.7 mV dec−1) including better stability. This work offers a viable and versatile method for fabricating a range of functional coordinated MOF compounds that hold potential for utilization across diverse energy applications including storage, conversion, and environmental purposes.

Figure 1
Investigating the Role of Mixed Oxides for Oxygen Evolution Reaction on Iridium Oxide Electrocatalysts
Authors: Tseng Cindy , Benetti Daniele , Yang Guangmeimei , Rao Reshma R , West Norton , Durrant James , Moore Katie , Stephens Ifan
Published: August 2024

Ongoing concerns over anthropogenic emissions, fossil fuel sustainability, and related geopolitical aspects point to an increasing need for cost-effective renewable fuel sources. A promising solution is the generation of hydrogen via the catalytic splitting of water, which can be achieved with the aid of proton exchange membrane (PEM) electrolyzers. Notably, the anode material in current commercially available PEM electrolyzers is typically iridium oxide. Despite its effectiveness in facilitating the oxygen evolution reaction (OER), the use of iridium oxide poses challenges due to the scarcity and high cost associated with this precious metal. As the quest for sustainable energy intensifies, ongoing research explores innovative approaches, such as the incorporation of alternative materials and catalysts, to enhance efficiency while addressing the economic and environmental concerns associated with iridium oxide. Studies have shown that incorporating mixed oxides and switching the supports for iridium oxide catalysts help lower the iridium loading while enhancing the OER performance.1,2

In this study, we investigate a series of different sputtered, mixed iridium oxides (Ta, Ti, Ir). We use a rotating disk electrode system to benchmark the catalytic activity of different loadings of mixed oxides. To measure the intrinsic activity of each catalytic active site, we use a home-built operando UV-Vis system to quantify the populations of surface species as well as track the kinetics of different redox transitions during OER. We incorporate nanoscale secondary ion mass spectrometry to probe the migration of different mixed oxide species before and after electrochemical cycling and use kelvin probe force microscopy to estimate the conductivity through the different films. In this study, we show the importance of cooperative effects between neighboring iridium oxide species and the coordination of iridium that are responsible for enhanced OER performance. These results indicate that doping modulates coverage dependent interactions at the surface, which affects both the binding energetics and populations of rate limiting intermediates. We believe this study will serve as a steppingstone for future designs of more cost-efficient PEM electrolyzers.

(1) Oh, Hyung-Suk, et al. "Electrochemical catalyst–support effects and their stabilizing role for IrO x nanoparticle catalysts during the oxygen evolution reaction." Journal of the American Chemical Society 138.38 (2016): 12552-12563.

(2) Zheng, Ya-Rong, et al. "Monitoring oxygen production on mass-selected iridium–tantalum oxide electrocatalysts." Nature Energy 7.1 (2022): 55-64.
Electrochemical Nitrogen Fixation at Phosphide Catalyst in Alkaline Medium: Electrocatalytic Approach Toward Validation and Determination of Ammonium Product
Authors: Kulesza Pawel , Rytelewska Beata , Chmielnicka Anna , Siamuk Olena , Rutkowska Iwona A.
Published: August 2024

A catalytic system based on iron phosphide (Fe2P) has exhibited electrocatalytic activity toward N2-reduction reaction in alkaline medium (0.5 mol dm-3 NaOH). Based on voltammetric stripping-type electroanalytical measurements, Raman spectroscopic and spectrophotometric data, it can be stated that the Fe2P catalyst facilitates conversion of N2 to NH3, and the process is fairly selective with respect to the competing hydrogen evolution. A series of diagnostic electrocatalytic experiments (utilizing platinum nanoparticles and HKUST-1) have been proposed and performed to control purity of nitrogen gas and to probe presence of potential contaminants such as ammonia, nitrogen oxo-species and oxygen. On the whole, the results are consistent with the view that the interfacial reduced-iron (Fe0) centers, while existing within the network of P sites, induce activation and reduction of nitrogen, parallel to the water splitting (reduction) to hydrogen. It is apparent from Tafel plots and impedance measurements that mechanism and dynamics of nitrogen reduction depends on the applied electroreduction potential. The catalytic system exhibits certain tolerance with respect to the competitive hydrogen evolution and gives (during electrolysis at -0.4 V vs. RHE) the Faradaic efficiency, namely, the selectivity (molar) efficiency, toward production of NH3 on the level of 60%. Under such conditions, the NH3-yield rate has been found to be equal to 7.5 µmol cm-2 h-1 (21 µmol m-2 s-1). By referring to classic concepts of electrochemical kinetic analysis, the rate constant in heterogeneous units has been found to be on the moderate level of 1-2*10-4 cm s−1 (at -0.4 V). The above mentioned iron-phosphorous active sites, which are generated on surfaces of Fe2P particles, have also been demonstrated to exhibit strong catalytic properties during reductions of other electrochemically inert reactants, such as oxygen, nitrites and nitrates. Supplementary diagnostic experiments have also been carried out to control purity of nitrogen gas and to identify potential contaminants. To comment on general catalytic activity of Fe2P during electroreductions in alkaline medium, we have performed additional comparative measurements using such redox probes as O2, CO2, NO3
- and NO2
-.
Simulation Studies of Interfacial Kinetics of Dye-Sensitized Solar Cells Photoanodes in Scanning Electrochemical Microscopy
Authors: Hamzat Wasiu abidemi , Momontenko Dmitry , Wittstock Gunther
Published: August 2024

Approach curves in the feedback mode of scanning electrochemical microscopy (SECM) were simulated for photoanodes in dye-sensitized solar cells by finite element simulation using COMSOL Multiphysics and compared to experimental data for the sample set with varying the photoanode film thickness (ZnO, cobalt mediator, organic dye). This reveals quantitatively the effect of the mass transport limitation of the mediator diffusion and organic dye regeneration kinetics in the mesoporous photoanode. The simulation of the mesoporous material was made with a pseudo-homogeneous approach in two space dimensions.

The simulation allows to extract the maximum information content from the experimental data. The light adsorption was treated as exponential decay of intensity within the photoanode (Lambert-Beer law), electron injection in the conduction band of ZnO photoanode and loss mechanism was explicitly considered. The light illumination is homogeneous over the entire simulation domain of 1 mm in diameter. Just like in the experiment, the built geometry used for the simulation has a conducting blocking layer (0.6 µm in thickness) to prevent the recombination of electrons with the back contact. The porous dye-sensitized layer has a porosity of 50 - 60% and a thickness of 1- 10 µm. The inner surface holds the dye for absorbing light. The mediator diffuses in the pore of the photoanode (internal solution) and in the bulk of the electrolyte (external diffusion). The transparent conducting glass makes the boundary of the simulation domain. The electrolyte-platinum contact is not modelled. The selected boundary conditions are equivalent to the short-circuit operation of the cell.

Interestingly, the simulation suggests that built meshes which had earlier been used for porous electrode simulation could not adequately describe the electron concentration profile for thinner electrodes despite providing a correct ME electrode current for limiting cases. The mesh convergence analysis studies were made to optimize the mesh to reduce computation time and memory size. The electrons in the conduction band were quantitatively determined because transport in the semiconducting photoanode is primarily driven by a thermally activated trapping-untrapping mechanism that can be described by transport equations similar to Fick's laws.

The unknown parameters (dye absorption coefficient and recombination rate constant) were adjusted to ensure various light intensities in the simulation correspond to the experiment. An accurate description of the electrons within the semiconductor is critical for explaining the time-dependent behavior of the dye-sensitized photoanode in SECM approach curves. After obtaining agreement with experimental approach curves under steady-state conditions, the same parameters are used to study the current transient obtained under intermittent illumination.
Kinetics of Charge Reversal in the Double Layer Studied with an Electrochemical Quartz Crystal Microbalance (EQCM-D)
Authors: Langhoff Arne , Leppin Christian , Johannsmann Diethelm
Published: August 2024

Normal pulse voltammetry on inert electrolytes was combined with a new electrochemical quartz crystal microbalance (EQCM) with millisecond time resolution, which allows to probe the kinetics of charge reversal in the diffuse double layer (DL) after a step in electrode potential. The QCM responds to the charge reversal because the local viscosity-density product depends on the type and the concentration of the ions. The time resolution was improved to 1 ms using multifrequency lockin amplification, which allows to study kinetic effects in dynamic electrochemistry, which were previously not accessible with gravimetry. The noise was lowered to less than 10 mHz by modulating the electrode potential and averaging Δf and ΔΓ over many modulation cycles.

The overtone scaling was found to be the same as in gravimetry (-Δf/n » const. and ΔΓ/n < -Δf/n with n the overtone order), which, however, is not caused by a deposition of a rigid film in the Sauerbrey sense. A Sauerbrey-type QCM response is also caused by changes in Newtonian viscosity inside a layer with a thickness far below the penetration depth of the shear wave (such as the double layer).

The frequency response in the electrolytes studied correlated well with the viscosity B-coefficients of the respective ions as employed in the Dole-Jones equation. The time constants inferred from gravimetry were similar to the time constants (the RC-times) from electrochemical impedance spectroscopy (EIS). There were small differences, which presumably go back to slow rearrangements inside the Helmholtz layer, which are not seen in EIS.

The QCM response to double layer recharging in inert electrolytes is of great importance for the interpretation of QCM results on processes involving Faradayic charge transfer. Such a response is omnipresent as a background and might be misinterpreted as a gravimetric signal.[1]

References

[1] Leppin, C.; Peschel, A.; Meyer, F. S.; Langhoff, A.; Johannsmann, D. Kinetics of Viscoelasticity in the Electric Double Layer Following Steps in the Electrode Potential Studied by a Fast Electrochemical Quartz Crystal Microbalance (EQCM). Analyst
2021, 146 (7), 2160–2171.

Caption: Shifts in frequency and bandwidth in response to potential steps (left). The gravimetric signal followed the steps with a delay of a few milliseconds. The amplitude and the response time depend on cation type (right). The counter ion was NO3
-. Both the amplitude and the response time correlate well with the viscosity B-coefficient.

Figure 1
Protic Ionic Liquids as Electrolytes for Metal-Hydride Batteries
Authors: Kurchavova Ekaterina , Chan Julie , Zhang Junxian , Cuevas Fermin , Mateos Mickael , Monnier Judith , Vivier Vincent , Turmine Mireille
Published: August 2024

Nowadays, the most popular and effective energy storage systems are Li-ion batteries, despite some limitations such as high cost, flammability, temperature restrictions, and use of critical raw material (e.g. Co) [1]. This raises the challenge of the demand for alternative systems. One potential alternative is the Ni-MH battery, which are recognized for their good cyclability, competitive energy density, low memory effect, wide range of operating temperatures, low cost, and environmental friendliness [1]. Their practical use, however, is constrained due to their low specific energy density, high self-discharge rate, and electrode ageing [2,3].

This work is focused on the study of the negative electrode of the Ni-MH battery and its interaction with the electrolyte. The objective aims to improve the performance of the negative electrode of Ni-MH batteries by substituting the conventional water-based KOH 8.7 M electrolyte by a Protic Ionic Liquid (PIL) to overcome aforementioned drawbacks [4]. PILs can exchange a labile proton, thereby supporting the main redox reaction, hydrogenation, at the negative electrode of Ni-MH battery.

Thus, a series of twelve PILs or their combinations were synthesized and tested in a half-cell configuration. The charge/discharge cycle tests were carried out. Results showed that Pyrrolidinium Acetate (PyrrAc), Ethanolammonium Acetate (EOAAc) mixed with g-butyrolactone (GBL), and Diethanolammonium Acetate (DEOAAc) exhibited promising performance in half-cell configuration (Table 1).

PyrrAc was shown to be an optimal electrolyte and has been further studied in terms of long-term performance and system degradation. The morphology of the aged negative electrodes was observed by Scanning Electron Microscopy (SEM) (Fig. 1). For instance, after 7 cycles of charge/discharge, formation of cracks was observed in the electrode (Fig. 1 (right)) due to hydrogen ab/desorption.

The utilization of PyrrAc as electrolyte resulted in no initial capacity loss and, moreover, exhibited an increase in capacity during the first cycles, which can be recognized as an activation of the electrode (similar to the one observed in aqueous electrolytes). In order to obtain a complete understanding of the electrode stability, the electrolytes after cycling as well as calendar corrosion were studied using Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES).

[1] M.A. Hannan, M.M. Hoque, A. Mohamed, and A. Ayob, Renewable and Sustainable Energy Reviews, 69 (2017) 771–789.

[2] B. Puga et al., ChemElectroChem, 2 (2015) 1321–1330.

[3] J. Matsuda, Y. Nakamura, E. Akiba, J Alloys Compd, 509 (2011) 7498–7503.

[4] T. Meng, K. H. Young, D. F. Wong, and J. Nei, Batteries, 3 (2017) 4.

Figure 1
Speciation and Diffusivity of Hydrogen in Molten 2LiF-BeF2 for Nuclear Fission and Fusion Applications
Authors: Williams Haley , Falkowski Zachary , Scarlat Raluca O.
Published: August 2024

The behavior of hydrogen isotopes in molten 2LiF-BeF2 (FLiBe) is of interest to both advanced fission and fusion reactor designs. Tritium (hydrogen-3) is both a fission product and neutron activation product of lithium-6 fluoride in fission reactors which use FLiBe as a heat transfer fluid. In this case, tritium is an undesirable side product. In fusion reactors, FLiBe may be used as a blanket around the plasma which, upon neutron irradiation, generates tritium by the same neutron–Li-6 reaction. Here, tritium is a necessary and desirable product; the tritium is used to continuously fuel the deuterium-tritium fusion reaction. A thorough understanding of tritium’s behavior and residence time is relevant to managing tritium inventories in fission and fusion systems, which is essential for both the safety cases and functional operation of these reactors. Using hydrogen as a non-radioactive surrogate for tritium, we study the speciation and diffusivity of hydrogen in molten FLiBe at various temperatures relevant to reactor operating conditions.

Here we present results of electrochemical investigations of hydrogen in FLiBe using cyclic and square wave voltammetry. We introduce hydrogen to FLiBe through 1) LiH additions and as 2) H2 gas, electrochemically desorbed from graphite. The expected solubility of H2 in FLiBe at 1 atm partial pressure is as low as 1 appm. Previous studies saw a higher apparent solubility of H2 at atmospheric pressure (up to 8000 appm). The possible presence of the postulated quasi-stable intermediate BeH2 is explored to explain the high apparent solubility of H2. The two methods of introducing H (as LiH reacting with BeF2 to form BeH2, which decomposes to H2, and the surface reduction of H2 on graphite) are compared to investigate the different species in which hydrogen may exist in molten FLiBe. Additionally, we attempt to quantify the diffusivity of these hydrogen species in FLiBe at 500ºC and 800ºC and compare findings with predicted diffusivities from computational models of Be and H additions to FLiBe. Overall, these studies seek to elucidate the speciation of hydrogen in FLiBe to aid in the management and operation of fission and fusion systems.
Preparation of Semiconducting Films By Electrooxidation of Naphthalene
Authors: Prus Agnieszka Marta , Leszczyński Piotr Jerzy , Jurczakowski Rafał
Published: August 2024

Due to promising electronic and optical properties, conductive polymers are attracting significant interest. Conductive polymers find applications in electronic devices, e.g. substituted polynaphthalenes are used as blue light sources in OLEDs1. The ability to block the substitution sites where the subsequent polymer unit may be added by functional groups allows the polymer structure to be designed2. Moreover, one of the benefits of conductive polymers is the ability to modify the band gap of these materials by adding substituents to the main chain.

Naphthalene, as the smallest polycyclic hydrocarbon, is an interesting precursor for synthesis semiconducting materials. The anodic oxidation of naphthalene has been described several times in the literature3,4, however, only formation of 1,4-polynaphthalene in the form of a granular product has been reported.

In our research, we performed naphthalene electrooxidation and investigated the impact of the experimental conditions such as naphthalene concentration, water content, and electrode material on the obtained semiconducting materials. We used mass spectrometry to observe mass progression and determine molecular mass of the obtained polymers. The results of electron microscopy imaging showed fine quality coating. We studied the electronic properties of the polymers by cyclic voltammetry and impedance spectroscopy. Based on the results, we discussed the possible mechanism of the reaction.

Samanta, S. K. et al. Synthesis of high molecular weight 1,4-polynaphthalene for solution-processed true color blue light emitting diode. Macromolecules
51, 8324–8329 (2018).

Debad, J. F. & Bard, A. J. Electropolymerization of acenaphtho[1,2-k]fluoranthene derivatives: Formation of a new conductive electroactive electrochromic hydrocarbon ladder polymer. J Am Chem Soc
120, 2476–2477 (1998).

Zecchin, S., Tomat, R., Schiavon, G. & Zotti, G. Polynaphthylene films from anodic coupling of naphthalene. Synthetic Metals vol. 25 (1988).

Huang, Z., Qu, L., Shi, G., Chen, F. & Hong, X. Electrochemical polymerization of naphthalene in the electrolyte of boron trifluoride diethyl etherate containing trifluoroacetic acid and polyethylene glycol oligomer. Journal of Electroanalytical Chemistry
556, 159–165 (2003).
First-Principles Kinetic Monte Carlo Modeling of Passivation in Ni-Based Alloys
Authors: Kaufman Jonas , Xiao Penghao , Wood Brandon C.
Published: August 2024

Corrosion by metal oxidation is a major problem for many structural materials, including Ni-based alloys in high-temperature applications. Passivation can be achieved through various alloying strategies, but common theoretical approaches to understanding key factors such as the critical concentration of the minor element are limited in their predictive capability. In particular, existing models often do not explicitly capture competing metal cation migration mechanisms in the oxide. In this study, we examine passivation kinetics of Ni-Cr and Ni-Al alloys by modeling the evolution of initial NiO oxide films as Cr/Al are incorporated. Surrogate models for the energies of various oxide configurations and the migration barriers of metal cations are parameterized from density functional theory calculations. These inputs are used to drive kinetic Monte Carlo simulations over long time scales. By tracking the time-dependent oxidation behavior across alloy composition, we predict critical concentrations of Cr/Al to form continuous passivation layers. Compositional and structural analyses of the simulated oxides are used to quantify fractions of different phases and provide insight into the nature of passivation in each alloy system. The effect of increasing or decreasing the exchange rate of metal atoms near the alloy-oxide interface, which can be related to alloy processing, is also explored. We discuss the applicability of our method to other systems and its incorporation into an existing open-source software package.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.