bluuebunny/crossref_metadata_2025 huggingface dataset:
Demonstrating the Activity and Stability of Conformal RuO2 "Nanoskins" on Technologically-Relevant, 3D Electrode Suports for Water Oxidation in Acid Electrolyte
Authors: DeSario Paul A. , Chervin Christopher N. , Nelson Eric S. , Sassin Megan B. , Rolison Debra R.
Published: February 2020

The commercial viability of many energy-storage and energy conversion devices is compromised by limited efficiency in oxidizing water to generate molecular oxygen (OER). Current state-of-the-art OER anodes fail to meet device-relevant rates of water oxidation at reasonable potentials and suffer from poor stability at the high oxidizing potentials they must adopt to sustain device-relevant O2 generation. Additionally, the high cost and scarcity of the most promising OER catalysts―RuO2 and IrO2―have motivated the search for electrode designs that deploy a nanoscopic amount of the active material while maintaining activity and stability. Most thin film preparations of IrO2 and RuO2 are not amenable with insulating supports and/or non–line of sight geometries. We leverage our solution-based electroless synthetic protocol to deposit conformal, ultrathin films of RuO2 (“nanoskins”) on three-dimensional supports and benchmark their activity under device-relevant conditions. When a self-wired RuO2 thin film is expressed as a nanoshell around the fibers in commercially available SiO2 paper, RuO2@SiO2 electrodes exhibit current densities (10 mA cm–2 @ η=280) 25-times higher than when expressed on planar, conductive supports. By wrapping the fibers with conductive graphitic carbon before nanoskin deposition, we retain the high specific activity of RuO2 nanoskins (40–60 mA mg–1 @ η=330 mV) and preserve the desirable macroscale properties of SiO2 fiber paper: porous, lightweight, flexible, and inexpensive. By efficiently expressing the electrocatalyst, we innately restrict the oxidizing potentials needed to meet a given rate of water oxidation, which diminishes dissolution of the catalyst and corrosion of its underlying current collector, thereby extending anode lifetime.
On the Evaluation of Charge Transport and Reaction Kinetics in Z-Scheme Semiconductor Particles for Solar Water Splitting
Authors: Bala Chandran Rohini , Ardo Shane , Weber Adam Z.
Published: February 2020

Solar water splitting is a promising approach to convert and store solar energy in the form of stable chemical bonds. A tandem particle-suspension reactor design1 (shown in Figure 1), comprising semiconductor particles (photocatalysts) suspended in an aqueous solution to effect Z-scheme water splitting in the presence of soluble redox shuttles, is considered here. Using a device-scale numerical model1, we identified reactor designs and concentration of photocatalysts and redox shuttles to yield up to 3.8% solar-to-hydrogen conversion efficiency with diffusion-driven species transport. Higher energy conversion efficiencies are predicted with natural convection facilitated species mixing. In this design, each semiconductor particle is wetted by electrolyte that contains at least four chemical species that can be involved in redox reactions on the particle surface. Therefore, selective surface catalysis becomes crucial to achieve high solar-to-hydrogen conversion efficiencies. In the present study, we develop a numerical model to evaluate the transport and kinetics of photogenerated charge-carriers inside a spherical semiconductor particle and across the semiconductor–electrolyte interface. The potential distribution within the particle is obtained by solving the Poisson-Boltzmann equation self consistently with the charge-carrier transport equations. The fluxes of the majority and minority charge-carriers across the semiconductor–electrolyte interface take into account all plausible redox reactions at the interface. Modeling results elucidate the dependence of the reaction selectivity on not only the kinetic parameters, but also on variables such as irradiance, operating temperature, particle size, recombination pathways and the electrolyte electrochemical potential. Results are further interpreted to identify strategies to boost the energy conversion efficiency for Z-scheme water splitting systems.

References

(1) Chandran, R. B.; Breen, S.; Shao, Y.; Ardo, S.; Weber, A. Z. Meet. Abstr.
2016, MA2016-01 (38), 1919–1919.

Figure 1
Small Polaron Formation Leads to Intrinsic Photoexcited Charge Trapping in α-Fe2O3
Authors: Cushing Scott Kevin , Carneiro Lucas M. , Zuerch Michael , Chang Hung-Tzu , Leone Stephen R.
Published: February 2020

The diminished carrier mobility in the ground-state of metal oxide photocatalysts is known to depend on polaron formation and hopping. Photo-excited dynamics and short carrier lifetimes, however, are usually associated with trap states. In this presentation, we investigate the role that small polaron formation plays in the ultrafast localization and trapping of photoexcited carriers in hematite (α-Fe2O3), potentially bridging these two pictures. Ultrafast transient extreme ultraviolet (XUV) spectroscopy on the Fe M2,3 edge measures a sub-5 fs shift in charge density from the oxygen to the iron atom following optical excitation. Small polaron localization of the photoexcited electrons begins on a 100 fs time scale, as measured by a splitting of the Fe M2,3 edge. The subsequent kinetics reproduce the lifetimes typically associated with trap or mid-gap states in hematite. The splitting of the Fe M2,3 edge, however, only matches predictions of polaron localization, and not the pre-edge absorption or bleach expected for mid-gap trap states. The measured polaron formation efficiency also matches the discrepancy between the incident photoconversion efficiency and the visible light absorption of hematite with varying excitation wavelength. These results suggest that sub-100 fs small polaron formation is responsible for the intrinsic recombination and transport issues that limit hematite’s performance, even when techniques such as nanostructuring or trap-state passivation are employed. The role of small-polaron localization in metal oxide photocatalysts, as well as possible materials routes to overcome this effect, will be discussed.
Simulations of Non-Monolithic Tandem Solar Cell Configurations for Electrolytic Fuel Generation
Authors: White Robert Turner , Kumar Bijandra , Kumari Sudesh , Spurgeon Joshua M
Published: February 2020

The efficient conversion of solar energy to fuels through electrochemical processes requires optimizing the photovoltage and current for an ideal coupling with the electrolysis reaction. A modular architecture for tandem photovoltaics is explored and modeled as a strategy to drive an arbitrary electrolysis reaction from sunlight to produce the maximum fuel product in a day. Non-monolithic tandem solar cells based on Si and organometal halide perovskites are simulated in two-terminal and four-terminal arrangements and coupled with experimental data on water-splitting and CO2 reduction to predict the performance of an integrated solar fuels system. An appropriately designed four-terminal system is modeled to match or exceed the output of a two-terminal system. The four-terminal configuration leads to a 15.8% increase in daily H2 production with a 1.5 eV/1.12 eV system, and a 5.3% increase with a more ideal 1.74 eV/1.12 eV combination. The four-terminal system is also simulated to match the production of formic acid and increase the production of ethylene by 20.4% in a Cu-catalyzed CO2 reduction process compared to a two-terminal tandem arrangement. The effects of series resistance in non-monolithic tandem devices are modeled as well, showing a much greater tolerance to cell width in the four-terminal systems.
Integrated Photoelectrochemical Solar Energy Conversion and Redox Flow Battery Devices
Authors: Li Wenjie , Fu Hui-Chun , Li Linsen , Cabán-Acevedo Miguel , He Jr-Hau , Jin Song
Published: February 2020

The practical utilization of solar energy demands not only efficient energy conversion but also inexpensive large scale energy storage. Building on mature regenerative photoelectrochemical solar cells and emerging electrochemical redox flow batteries (RFBs), more efficient, scalable, compact and cost-effective hybrid energy conversion and storage devices could be realized. Here we present an integrated PEC solar energy conversion and electrochemical storage device by integrating regenerative photoelectrochemical solar cells in aqueous electrolytes with RFBs using the same pair of organic redox couples. In such an integrated PEC-RFB device, solar energy is absorbed by semiconductor electrodes and photoexcited caries are collected at the semiconductor-liquid electrolyte interface and used to convert the redox couples in the RFB to fully charge up the battery (i.e. store the solar energy into the redox couples). When electricity is needed, the charged up redox couples will be discharged on the surface of carbon felt electrodes as one would do in the discharge of a RFB to generate the electricity. We demonstrated that such an integrated PEC-RFB device can be charged under solar illumination without external electric bias and deliver a high discharge capacity comparable with state of the art RFBs over many cycles. This integrated device can utilize solar energy efficiently -- an overall direct solar-to-output electricity efficiency (SOEE) of 1.7% have been achieved without significant performance optimization.

Figure 1
Multiphysics Modeling of Gas Diffusion Electrodes for CO2 Reduction
Authors: Weng Lien-Chun , Bell Alexis T. , Weber Adam Z.
Published: February 2020

One of the main challenges towards achieving high efficiency solar fuel generators performing carbon dioxide reduction is the mass transport limitations in traditional aqueous systems. Typically, the current density for liquid phase carbon dioxide reduction is limited to approximately 10 mA/cm2 due to concentration polarization near the cathode surface.1This can be overcome by introducing a gas diffusion electrode, which allows vapor phase carbon dioxide to be fed directly to the catalyst, significantly decreasing the diffusion length.

Experiments have shown almost two orders of magnitude improvement in efficiency for vapor-fed devices compared to traditional aqueous systems.2,3 This improvement is most likely due to a higher surface area in the porous electrode and an increased diffusivity of gas phase CO2. For this work, we have developed a multiphysics model for gas diffusion electrodes that simulates species transport in gas phase, liquid phase and solid phase, charge transport, and (electro)chemical reaction kinetics. The model will focus on understanding transport of species in and out of the catalyst layer, and investigate the effects of gas diffusion electrode properties such as thickness, porosity and hydrophobicity on cell performance.

Acknowledgements

This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

References

Singh, M. R.; Clark, E. L.; Bell, A. T., Physical Chemistry Chemical Physics, 2015, 17(29), 18924-36.

Verma, S.; Lu, X.; Ma, S.; Masel, R. I.; Kenis, P. J. A., Physical Chemistry Chemical Physics, 2015, 18, 7075-7084.

Kim, B.; Hillman, F.; Ariyoshi, M.; Fujikawa, S.; Kenis, P. J. A., Journal of Power Sources, 2016, 312, 192-198.
Boosting Photocatalytic Performance of Inactive Rutile TiO2 Nanorods for Degradation of Orange (II) Dye Under Solar Light Irradiation: Synergistic Effect of Acid Treatment and Metal Oxide Co-Catalysts
Authors: Dhandole Love Kumar , Mahadik Mahadeo A , Kim Su-Gyeong , Chung Hee-Suk , Cho Min , Ryu Jung Ho , Jang Jum Suk
Published: February 2020

Fast charge separation and availability of surface hydroxyl groups are important aspects for photocatalysis. Fast charge separation could be achieved by forming interface between the catalysts and transition metal oxides. In the present work we accomplish charge separation by controllably forming interface between acid treated molten salt rutile TiO2 nanorods and transition metal oxide co-catalysts. FT-IR and XPS (oxygen deconvolution) results confirmed that hydroxyl groups were enhanced on the surface of rutile TiO2 nanorods after acid treatment. Transition metal oxide (MnO, NiO, Co2O3, and CuO) co-catalysts were successfully loaded on the surface of acid treated TiO2 nanorods (ATO-NRs) by conventional wet impregnation method. HR-TEM analysis revealed fine dispersion of metal oxide nanoparticles on the surface of ATO-NRs. The photocatalytic activities of as-prepared (TO-NRs), acid treated (ATO-NRs), metal oxide loaded (MTO-NRs), and both acid treated and metal oxide loaded (MATO-NRs) nanorods were compared based on the rate kinetics and dye degradation efficiency was also determined. Cobalt oxide (1 wt%) loaded on 1.0 M acid treated TiO2 nanorods (Co/ATO-NR), exhibited the higher photocatalytic degradation efficiency of 98.57% within 120 min compared to other photo-catalysts under solar irradiation. The synergistic effect of acid treatment and co-catalyst for improved photocatalytic activity of TO-NRs might be due to fast charge transfer of finely dispersed metal oxides on the OH rich surface of acid treated TiO2 nanorods. Photoelectrochemical analysis demonstrated that the charge transfer process in Co/ATO-NR is significantly higher than the untreated samples. Charge transfer mechanism involved in such co-catalyst loaded photocatalyst was studied in detailed.

KEYWORDS: Synergistic effect; co-catalyst; Acid treatment; Transition metal oxides; Dye degradation

Acknowledgments

This research was supported by the BK21 plus and Basic Science Research Programs (2012R1A6A3A04038530) funded by the Korean National Research Foundation (NRF).
Microwave-Assisted Hydrothermal Synthesis of Co Doped ZnO Nanocrystals
Authors: Nishiumi Nobuyuki , Sun He , Yasuhara Taichi , Mastushima Yuta , Furis Madalina , White Matthew Schuette , Stadler Philipp , Shiroishi Hidenobu , Khosla Ajit , Yoshida Tsukasa
Published: February 2020

Spintronic devices employing both semiconducting and ferromagnetic properties of materials are to be realized by doping of high spin transition metal ions to semiconductors such as ZnO. Transition metal oxides are also interesting as electrocatalysts for electrochemical conversion of renewable electricity to chemical energy for its storage. In this study, we have attempted microwave (MW)-assisted hydrothermal synthesis of Co, Mn-doped ZnO nanoparticles.

Aqueous precursor solutions containing ZnCl2 and CoCl2 or MnCl2 at various ratios in a total concentration of 0.2 M were basified with NaOH to ca. pH 13, and subjected to a 2.45 GHz MW[1,2] to promote reaction at 160°C for 30 min. The products were characterized by FE-SEM, XRD and UV-Vis. Mesoporous electrodes of ZnO and Zn0.92Co0.08O were fabricated by doctor blading method.

The green-colored Co-doped samples exhibit characteristic absorption peaks at around 560, 610 and 650 nm due to d-d transition of Co(II) and a red shift of the bandgap absorption onset. Phase separation of Co(OH)2 has also been suggested by XRD and FE-SEM images for x > 0.1, so that doping up to about 10% was apparently possible. Systematic shift of the three major XRD peaks of Wurtzite ZnO towards low angles was recognized upon increasing x, suggesting substitution of the lattice Zn2+ ions with Co2+. Lattice constants were calculated as a = b = 3.252 Å, c = 5.204 Å for ZnO, whereas they were enlarged to 3.277, 5.244 Å, respectively, for x = 0.20.

CVs of ZnO and Zn0.92Co0.08O electrodes in a neutral electrolyte are compared in Fig. 1. Besides the clear decrease of cathodic charging and discharging currents, Co-doping results in an anodic wave at around + 1 V due to Co2+ → Co3+, followed by a large increase of irreversible anodic current, as compared to the non-doped sample. Chronoamperograms for a few minutes confirmed this current enhancement and gas bubble evolution from the anode due to catalytic oxidation of water (2H2O → O2 + 4H+ + 4e-).

 

[1] Y. Hirai, K. Furukawa, H. Sun, Y. Matsushima, K. Shito, A. Masuhara, R. Ono, Y. Shimbori, H. Shiroishi, M. S. White & T. Yoshida, “Microwave-assisted hydrothermal synthesis of ZnO and Zn-terephthalate hybrid nanoparticles employing benzene dicarboxylic acids” Microsyst Technol (2017). doi: 10.1007/s00542-017-3392-y

[2] H. Sun, L. Sun, T. Sugiura, M. S. White, P. Stadler, N. S. Sariciftci, A. Masuhara & T. Yoshida, “Microwave-assisted hydrothermal synthesis of struture-controlled ZnO nanocrystals and their properties in dye-sensitized solar cells” Electrochemistry, in press.

Figure 1
Fabrication of Cu3BiS3 Photocathode for Photoelectrochemical Hydrogen Evolution
Authors: Kamimura Sunao
Published: February 2020

Hydrogen production from water using abundant solar light is now an important research subject from viewpoints of usage of renewable energy and environmental issues. Photoelectrochemical (PEC) water splitting utilizing semiconductor electrodes has been studied extensively as a potential means of converting solar energy into chemical energy in the form of H2.

Chalcogenide compounds have emerged as a leading class of thin films for photocathodes due to their suitable band gap for solar energy absorption, high photo-absorption coefficients, and usability in the polycrystalline state. Although Cu-chalcogenide photocathodes such as CuInS2,CuGaSe2, CuGa3Se5,(Ag,Cu)GaSe2,

and Cu(In,Ga)Se2, show excellent solar-to-hydrogen conversion efficiency, there are many difficulties in largescale production from the viewpoints of low throughput and material utilization because of the limited availably of elements (i.e., In, Ga and Se). It is therefore evident that more research is required to search for alternative inexpensive and earth-abundant materials.

Cu3BiS3 is one of the promising chalcogenide compounds for a photovoltaic device due to its ability to absorb visible light (Eg
≈ 1.4–1.7 eV), a high absorption coefficient (>105 cm-1) compared to that of CuInSe2 and Cu2ZnSnS4, and p-type conductivity with a carrier concentration of ~ 2×1016 cm-3

. Moreover, it is made of cheap, non-toxic, earth-abundant elements and can be easily produced on a large scale.

We fabricated a Cu3BiS3 thin film by a simple electrodeposition technique on a molybdenum-coated glass substrate to utilize it as a photocathode for PEC hydrogen evolution. The Cu3BiS3 film was composed of dense crystallites with thicknesses of ca. 0.65 μm, and the optical bandgap was estimated to be ca. 1.6 eV. Photoelectrochemical characterization revealed that the Cu3BiS3 film was a p-type semiconductor with a flat band potential of ca. +0.1 V (vs Ag/AgCl at pH 6), which is suitable for water reduction but cannot be used for water oxidation. Deposition of an In2S3 buffer layer, by which effective contact between p-type Cu3BiS3 and n-type In2S3 was formed, resulted in a significant increase in the photocurrent and a large shift of the photocurrent onset to the positive region. H2 evolution under AM 1.5G simulated solar light was demonstrated using the Pt-In2S3/Cu3BiS3 electrode combined with a Pt electrode under an applied bias (0 V vs. RHE).
Unbiased Photoelectrochemical Solar Hydrogen Generation on Highly Stable, Ultrathin Organic Linker/Metal Ions-Treated InGaN Nanorods on Metal
Authors: Ebaid Mohamed , Priante Davide , Liu Guangyu , Zhao Chao , Alias Mohd Sharizal , Buttner Ulrich , Ng Tien Khee , Isimjan Tayirjan Taylor , Idriss Hicham , Ooi Boon S
Published: February 2020

InGaN-based nanostructures have recently been recognized as promising materials for efficient solar hydrogen generation. This is due to their chemical stability, adjustable optoelectronic properties, suitable band edge alignment, and large surface-to-volume ratio. The inherent high density of surface trapping states and the lack of compatible conductive substrates, however, hindered their use as stable photo-catalysts. We have designed, synthesized and tested an efficient photocatalytic system using stable InGaN-based nanorods (NRs) grown on an all-metal stack substrate (Ti-Mo) for a better electron transfer process. In addition, we have applied a bifunctional ultrathin thiol-based organic surface treatment using 1,2-ethanedithiol (EDT), in which sulfur atoms protected the surface from oxidation. This treatment has dual functions, it passivates the surface (by the removal of dangling bonds) and creates ligands for linking Ir-metal ions as oxygen evolution centers on top of the semiconductor. This treatment when applied to InGaN NRs resulted in a photo-catalyst that achieved 3.5% solar-to-hydrogen (STH) efficiency, in pure water (pH~7, buffer solution) under simulated one-sun (AM1.5G) illumination and without electrical bias. Over the tested period, a steady increase of the gas evolution rate was observed from which a turnover frequency of 0.23 s-1 was calculated. The novel growth of InGaN-based NRs on a metal as well as the versatile surface functionalization techniques (EDT-Ir) have a high potential for making stable photo-catalysts with adjustable band gaps and band edges to harvest sun light.
(Invited) Redox Reaction of Proteins in Hydrated Cholinium Dihydrogen Phosphate
Authors: Fujita Kyoko
Published: February 2020

Ionic liquids (ILs) have attracted attention as solvents because of their fascinating features, such as negligible vapor pressure and high thermal, chemical, and electrochemical activity. ILs have been widely studied as green, multi-use media for electrochemistry and chemisry even in bio-applications. Generally, however, most proteins are not soluble in ILs. Surface modification on the proteins, e.g. poly(ethylene oxide) (PEO) modification is one of the way to dissolve biomolecules in ILs [1]. PEO modified cytchrome c dissolved and showed the redox activity in ILs.

As another way, hydrated IL have been studied to realize the dissolution of proteins without chemical modification. Hydrated ILs maintain the basic properties of ILs, but a small amount of water was added. However, it is difficult to dissolve proteins in most hydrated ILs. Selection of component ion is essential to realize the dissolution and maintaining the higher ordered structure of proteins in hydrated IL. Hydration state of ILs which could be estimated on kosmotropicity was suggested one of the key factor to control the protein compatibility [2]. Hydrated cholinium dihydrogen phosphate ([ch][dhp]) acts as an excellent solvent to dissolve and preserve proteins for long term [3]. Furthermore, the original reactions such as enzymatic reactions and electron transfer reactions were observed in hydrated ILs, when the higher ordered structures were remained [4]. However, when the biocatalytic reaction was detected as an electrochemical response, the observed redox current was smaller than that in buffer solution. The redox reaction rate between a fixed protein and electrode was investigated to clarify the reason for the depression of the redox response of biocatalytic reactions in hydrated [ch][dhp] [5]. It was revealed that the electron transfer rate between protein and electrode was fast in hydrated [ch][dhp] as same that in buffer. Fast electron transfer reaction in hydrated ILs is expected to be more stable over a wider temperature range and longer period of time than general aqueous system.

 

References

[1] H. Ohno, C. Suzuki, K. Fukumoto, M. Yoshizawa, K. Fujita, Electron Transfer Process of Poly(ethylene oxide)-Modified Cytochrome c in Imidazolium Type Ionic Liquid, Chem. Lett., 32 (2003) 450-451.

[2] Y. Nikawa, K. Fujita, H. Ohno, Quantitative Assessment of Kosmotropicity of Hydrated Ionic Liquids by Nuclear Magnetic Resonance, Phys. Chem. Chem. Phys., 19 (2017) 8148-8151.

[3] K. Fujita, D. R. MacFarlene, M. Forsyth, Protein solubilising and stabilising ionic liquids, Chem. Commun. (2005) 4804-4806.

[4] K. Fujita, N. Nakamura, K. Igarashi, M. Samejima, H. Ohno, Biocatalytic oxidation of cellobiose in an hydrated ionic liquid, Green Chem., 11 (2009) 351-354.

[5] K. Fujita, J. Kuwahara, N. Nakamura, H. Ohno, Fast Electron Transfer Reaction of Azurin Fixed on the Modified Electrode in Hydrated Ionic Liquids, J. Electrochem. Soc., 163 (2016) G79-G81.
Ab Initio Studies of Ultrathin Ionic Liquid Films on Au (111) Surface
Authors: Liu Mingjie , Sitaputra Wattaka , Stacchiola Dario J , Wishart James F. , Wang Feng , Sadowski Jerzy T. , Wu Qin
Published: February 2020

Room-temperature ionic liquids (RTILs) as alternative electrolytes are of great interest to electrochemical energy storage devices, such as supercapacitors. A key to understanding the performance of these systems is to know the ion arrangement near the electrode surface and the ion-electrode interaction. In this work, we will present our ab initio studies of a few layers of 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (EMMIM TFSI) ionic liquid on gold (111) surface, a system that was recently studied in a novel experiment using low-energy electron and photoemission electron microscopy (LEEM/PEEM). [1] Our work probes different ion arrangements on Au (111) and the corresponding work function change. We further investigate the most stable ion arrangement at different electrode charge densities and identify their out-of-plane layering structure. The dynamics of the ions with reordering and drifting under electric field can be inferred as well. We then use our findings to explain the observed changes in electron reflectivity/photoemission yield in LEEM/PEEM. Together, our results provide important understanding towards the structures and responses of ionic liquids on an electrified metal surface.

This research was carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-SC0012704.

[1] Wattaka Sitaputra, Dario Stacchiola, James F. Wishart, Feng Wang, and Jerzy T. Sadowsk, In situ Probing of Ion Ordering at Electrified Ionic Liquid/Au Interface, Adv. Mater. DOI:10.1002/adma.201606357
Influence of Mesoscale Organization on Charge Transport and Dynamics in Ionic Liquids
Authors: Cosby James Tyler , Tsunashima Katsuhiko , Liu Hongjun , Paddison Stephen J. , Sangoro Joshua R
Published: February 2020

Mesoscale aggregates arising from the separation of ionic and alkyl groups into polar and nonpolar regions have been observed for a variety of ionic liquids (ILs). The existence of these distinct regions provides ILs with the ability to solvate both polar and nonpolar molecules and has important implications for applications such as energy storage, nanoparticle growth, biomass processing, and organic synthesis. It has been found by computational studies and x-ray scattering that the morphology of the mesoscopic structure is highly sensitive to the alkyl chain length, however, the influence of aggregate formation and morphology on physicochemical properties, such as ionic conductivity and dynamics, is not yet well understood. In this study, a homologous series of imidazolium, quaternary ammonium and phosphonium-based ionic liquids are investigated by broadband dielectric and shear-mechanical spectroscopy as well as molecular dynamics simulations to elucidate the impact of alkyl chain length and hydrophobic aggregation on charge transport and dynamics. It is observed that systematic ordering of ionic liquids into complex polar and nonpolar domains results in the emergence of slow, sub-α dynamics in both the dielectric and shear-mechanical spectra. These findings confirm the existence of long-lived nanoscale aggregates in neat ionic liquids and provide a new avenue to elucidate the interplay of morphology, ion transport and dynamics in these nanostructured fluids.
(Invited) Role of Organic Solvents in Immobilizing Fungus Laccase on Single-Walled Carbon Nanotubes for Improved Current Response in Direct Bioelectrocatalysis
Authors: Wu Fei , Mao Lanqun
Published: February 2020

Tuning interactions between proteins and solid surfaces is important for rationalizing molecular orientation of redox enzymes immobilized on the electrode to favor an efficient direct bioelectrocatalysis. Supramolecular docking calls for specific “linker” molecules to direct the position of enzyme redox active sites on surfaces of electrodes or conductive nanomaterials, for example, carbon nanotubes (CNTs). In this work we focus on a high-potential fungus laccase, a multi-copper oxidase that catalyzes electroreduction of oxygen, and investigate the regulative effects of organic solvents on laccase immobilization on single-walled CNTs (SWCNTs) and its direct bioelectrocatalytic activity. Herein the maximum reductive current response is dramatically improved by 600% through ethanol-assisted enzyme immobilization, which is a result of ethanol-promoted laccase-SWCNT contact and favorable enzyme orientation on SWCNTs from conformation analysis. Extended investigation on more organic solvents with distinct physiochemical properties show that organic solvents with lower polarity, weaker denaturing capacity and higher vapor pressure are well-suited for assisting DET. This study reveals that organic solvents regulate laccase immobilization for direct bioelectrocatalysis by balancing surface wetting and protein denaturing. It further solidifies our fundamental knowledge of bioelectrochemistry of laccase and may inspire the design of electrode-enzyme interfaces with tunable surface wettabilities.

Figure 1
(Invited) Electrochemical Studies of Zinc/Cysteine Interactions in Aqueous Buffers
Authors: Cheek Graham T. , Worosz Matthew A. , Doan Michelle Y
Published: February 2020

Introduction

The naturally occurring amino acid L-cysteine is involved in many important biochemical processes, including the formation of “zinc finger” proteins (1). The electroactive thiol group in cysteine allows electrochemical investigation of its properties and interactions with other substances. The present contribution deals with the complexation of L-cysteine with zinc(II) ions in various buffered aqueous media and is a continuation of work previously presented (2).

Experimental

L-Cysteine was obtained from Sigma-Aldrich Corporation. Electrochemical experiments were carried out under nitrogen using a Gamry Instruments Interface 1000 potentiostat and Framework software. Working electrodes were obtained from BASi (Glassy carbon, 3.0 mm diameter; platinum 1.6 mm) and eDAQ (gold, 1.0 mm diameter). Potentials were measured with respect to a silver/silver chloride saturated KCl reference electrode (BASi).

Results and Discussion

 Recent work from this laboratory has shown that the interaction of zinc(II) ions, added as ZnSO4 heptahydrate, with L-cysteine can be followed by cyclic voltammetry (Figure 1). This work is intended as a model for the formation of “zinc finger” proteins, which involve interactions between zinc(II) and cysteine and histidine units in the protein structure (1). Figure 1 (a) shows the voltammogram for 8.6 mM L-cysteine in 0.1 M pH 7.4 phosphate buffer at glassy carbon. Upon addition of ZnSO4 to L-cysteine in a 1:2 Zn2+: Cysteine mole ratio [Figure 1(b)], the broad oxidation process underwent a significant shift to a more positive potential. This observation is consistent with the complexation of Zn(II) by L-cysteine. Upon sweeping to more negative potentials, reduction of the complex was found to occur near the solvent reduction limit, followed by zinc stripping at approximately -1.0 V vs Ag/AgCl. Interesting comparisons with results at gold electrodes (2) can also be made. Further details for the complexation process are also planned for presentation. Other investigations have involved electrochemical impedance spectroscopy (EIS) to determine the extent to which L-cysteine interacts with various electrode surfaces.

References

C.K. Mathews, K.E. Van Holde, D.R. Appling, and S. J. Anthony-Cahill, Biochemistry, 4th Edition, Pearson Canada, Toronto, 2013.

G. T. Cheek and M. A. Worosz, ECS Transactions, 2016, 72(27), 1-8.

Figure 1. Cyclic voltammograms at glassy carbon in aqueous pH 7.4 phosphate buffer, 100 mV/s scan rate.

Solid black line : L-Cysteine 8.6 mM, initial positive-going sweep

Dashed red line : ZnSO4 . 7 H2O 4.3 mM addition, to previous solution, initial positive-going sweep

Figure 1
(Invited) Tunable CNT Fiber and Yarn Microelectrodes for Measurements of Different Neurochemicals
Authors: Yang Cheng , Venton B. Jill
Published: February 2020

Traditionally, in vivo analysis of neurotransmitters has concentrated on the molecule dopamine and much of the surface characterization of new electrodes has been focused on the kinetics of dopamine detection. However, the field of in vivo electrochemistry is expanding to many new molecules and electrode design should follow suit to examine the extent to which it is possible to design new electrodes that have surface chemistry that is advantageous for different neurochemicals. Beyond dopamine, other small neurotransmitters that are often targeted include serotonin, norepinephrine and epinephrine. Serotonin and it’s metabolite 5-HIAA are known to foul the electrode surface of carbon fibers, but recently developed carbon nanotube-polyethyleneimine (PEI/CNT) fiber microelectrodes show reduced susceptibility for fouling. PEI/CNT fiber microelectrodes are more selective to DOPAC, and CNT yarn microelectrodes show significantly higher selectivity to serotonin than other fibers. Chlorosulfonice acid (CA)/CNT fiber microelectrodes have the highest selectivity of dopamine to ascorbic acid and uric acid, because of the negative charge carried by CA. Our lab has also investigated CNT yarn microelectrodes for adenosine detection and found that CNT yarns may be advantageous for detecting all three oxidation peaks for adenosine. In addition, we have explored surface treatments of microelectrodes, including laser treatment, oxygen plasma treatment, and antistatic gun treatment. These treatments increase the sensitivity and change the selectivity of the sensors, allowing the properties to be tuned. Thus, electrode materials, design, and surface materials are important considerations for designing in vivo microelectrodes that are sensitive to a variety of different analytes.
Ultrasensitive Electrochemical Detection of miRNA-21 Using a Zincfinger Protein Specific to DNA−RNA Hybrids and Redox Cycling
Authors: Fang Chiew San , Kwon Junguk , Yang Haesik
Published: February 2020

Both high sensitivity and high specificity are crucial for detection of miRNAs that have emerged as important clinical biomarkers. Just Another Zinc finger proteins (JAZ, ZNF346) bind preferably (but nonsequence-specifically) to DNA−RNA hybrids over single-stranded RNAs, single-stranded DNAs, and double-stranded DNAs. We present an ultrasensitive and highly specific electrochemical method for miRNA-21 detection based on the selective binding of JAZ to the DNA−RNA hybrid formed between a DNA capture probe and a target miRNA-21. This enables us to use chemically stable DNA as a capture probe instead of RNA as well as to apply a standard sandwich-type assay format to miRNA detection. High signal amplification is obtained by (i) enzymatic amplification by alkaline phosphatase (ALP) coupled with (ii) electrochemical-chemical-chemical (ECC) redox cycling involving an ALP product (hydroquinone). Low nonspecific adsorption of ALP-conjugated JAZ is obtained using a polymeric self-assembled-monolayer-modified and casein-treated indium−tin oxide electrode. The detection method can discriminate between target miRNA-21 and nontarget nucleic acids (DNA−DNA hybrid, single-stranded DNA, miRNA-125b, miRNA-155, single-base mismatched miRNA, and three-base mismatched miRNA). The detection limits for miRNA-21 in buffer and 10-fold diluted serum are approximately 2 and 30 fM, respectively, dicating that the detection method is ultrasensitive. This detection method can be readily extended to multiplex detection of miRNAs with only one ALP-conjugated JAZ probe due to its nonsequence-specific binding character. We also believe that the method could offer a promising solution for point-of-care testing of miRNAs in body fluids.
(Invited) Enhancing Electron Transfer Rates on Ultra-Thin Graphene Electrodes Using a Sub-Surface Patterning Approach
Authors: Rodriguez-Lopez Joaquin
Published: February 2020

We will discuss the potential of mono- and few-layer graphene electrodes as versatile platforms for the exploration of new electrocatalyst design principles. By transferring cm2 layers of CVD-grown graphene over metal deposits patterned on insulating substrates, and following passivation of pinholes and grain boundaries, we have measured enhanced rates of outer-sphere and inner-sphere electron transfer on sites modified with the sub-surface metal. Reactive imaging of these electrodes using scanning electrochemical microscopy was used to confirm our modification strategy and to highlight the possibility of using this strategy to spatially encode reactivity on surfaces. These electrodes enable a unique opportunity to modify the reactivity and mechanism of electrochemical reactions by means of electronic interactions that operate at scales coincident with their limiting thickness.

In a first study,[1] we deposited bi-layer graphene on SiO2 chips modified with thin deposits of Au and Pt. SECM imaging using reversible outer-sphere mediators (ferri/ferrocyanide and ferrocenemethanol) showed a five-fold increase in the heterogeneous electron transfer constant on sub-surface modified sites. These enhancements are likely a consequence of increased electronic density of states due to a donating effect from the substrate. Following this principle, we explored the impact on an inner-sphere process, the oxygen reduction reaction. Our results indicate that both the kinetics and mechanism of the reaction are sensitive to sub-surface modification, with the kinetics largely driven by the identity of the metal and the reaction mechanism dominated by graphene or adsorbed molecular catalysts.[2] SECM imaging in the redox competition mode and in the H2O2 collection mode confirmed observations done on macro-electrode interfaces. The design principles derived from these experiments open new opportunities in the coupling of materials with different electrocatalytic properties using graphene as a mediating surface. We will discuss our recent progress expanding this toolbox for mitigating problems associated with several electrocatalytic reactions and exploring other reactions of interest, including the electrochemical reduction of CO2.

[1] Hui, J.; Zhou, X.; Bhargava, R.; Chinderle, A.; Zhang, J.; Rodríguez-López, J. Electrochim. Acta 2016, 211, 1016-1023.

[2] Hui, J., et al., Rodríguez-López, J. In Preparation.

Figure 1
Electrochemical Investigation of CO2 Conversion Utilizing Nanoporous Polystyrene-Polyvinylpyridine Catalyst
Authors: Ghebremichael Habte , Sidorenko Alexander
Published: February 2020

The threat of climate change proves to be one of mankind’s most daunting challenges. Carbon dioxide emissions are believed to be a leading contributor to climate change. The development of nontoxic and abundant catalysts for the reduction of CO2 is critical in enabling this much needed technology. A method of reverse combustion would be prove to be advantageous in mitigating climate change and providing for a carbon neutral fuel source. Pyridine has shown to be electrocatalytically active at reducing carbon dioxide at low overpotentials to hydrocarbons.The development of nanoporous polymer thin films have exhibited many useful properties that have yet to be exploited. Taking advantage of the microphase separation phenomenon of poly(styrene)poly(4vinylpyridine), PSP4VP, block copolymers allows for pyridine moieties to assemble onto the cylindrical interior of these nanoporous surfaces. These moieties we've shown to be both electrocatalytically active in conjunction with conductive cocatalyst via a radical mechanism.
Grain Boundary Effect in Electroreduction Catalysis for Renewable Energy Conversion
Authors: Feng Xiaofeng
Published: February 2020

Electrocatalysis plays a key role in the energy conversion processes that are central to renewable energy technologies such as fuel cells and artificial photosynthesis. A rational design of catalyst relies on our understanding of structure-activity relationships and identification of catalytically active sites. So far, numerous efforts have been made to optimize nanostructured catalysts by tuning their size, composition, and shape, while new design principles are essential for electroreduction catalysis such as CO2 recycling using renewable electricity. Here we show that grain boundaries (GBs) in metal nanoparticles create new active sites for electroreduction catalysis. Through a careful design of metal nanoparticle catalysts with different GB densities, extensive TEM characterization, and electrochemical measurements, we found that the catalytic activity for CO2 reduction on Au and CO reduction on Cu is directly correlated with GB density in the catalysts [1, 2]. The quantitative GB-activity relationships indicate that GBs in metal nanoparticles create new active sites for electroreduction catalysis and lead to highly active and stable catalysts for a two-step electrochemical conversion of CO2 to liquid fuels such as ethanol and acetate. In addition, we found that GBs in Au enhance its activity for oxygen reduction reaction, which suggests that GB engineering is a general strategy for improving electrocatalytic activity for renewable energy conversion.

References:

(1) Feng, X.; Jiang, K.; Fan, S.; Kanan, M. W. J. Am. Chem. Soc.
2015, 137, 4606–4609.

(2) Feng, X.; Jiang, K.; Fan, S.; Kanan, M. W. ACS Cent. Sci.
2016, 2, 169−174.
Understanding Electrochemical Reduction of CO2 Using Quantum Chemistry Modeling
Authors: Saravanan Karthikeyan , Keith John A.
Published: February 2020

Electrochemical reduction of CO2 into usable hydrocarbons by multiple proton and electron transfers is hindered by slow kinetics and unfavorable thermodynamics. Experiments have reported a wide range of compounds from organic molecules to metal oxides to be suitable homogenous catalysts that can facilitate the above multi-step reaction. Quantum chemical calculations and certain thermodynamic descriptors help in identifying electrochemical conditions at which catalysts participate in energetically efficient proton and electron transfers [1]. We discuss how Pourbaix diagrams can be useful descriptors to identify several organic molecules and inorganic compounds that electrochemically catalyze the conversion of CO2 [2-4]. We present our latest results on modeling CO2 electroreduction on tin oxide catalysts and our prediction of new dopants that result in lower overpotentials than undoped tin oxide [5]. References:

Keith, J. A. & Carter, E. A. Theoretical Insights into Pyridinium-Based Photoelectrocatalytic Reduction of CO2. J. Am. Chem. Soc.
134, 7580–7583 (2012).

Saravanan, K. & Keith, J. A. Standard redox potentials, pKas, and hydricities of inorganic complexes under electrochemical conditions and implications for CO2 reduction. Dalton Trans. 45, 15336–15341 (2016).

Groenenboom, M. C. et al. Structural and Substituent Group Effects on Multielectron Standard Reduction Potentials of Aromatic N-Heterocycles. J. Phys. Chem. A 120, 6888–6894 (2016).

Saravanan, K., Gottlieb, E. & Keith, J. A. Nitrogen-doped nanocarbon materials under electroreduction operating conditions and implications for electrocatalysis of CO2. Carbon 111, 859–866 (2017).

Saravanan, K., Basdogan, Y., Dean, J. & Keith, J. A. Computational investigation of CO2 electroreduction on tin oxide and predictions of Ti, V, Nb and Zr dopants for improved catalysis. J. Mater. Chem. A (2017). doi:10.1039/C7TA00405B
Analytical Models of Diffusive-Reactive Flow in 3-D Microstructural Networks to Guide the Design of Electrochemical Materials
Authors: Cocco Alex , Nakajo Arata , Chiu Wilson K. S. , Grew Kyle N.
Published: February 2020

In this work, we present a fully analytical, non-dimensional model to describe steady-state diffusive flow through a 3-D network. Through a combination of graph theory, linear algebra, and geometry, the model explicitly relates the network’s topology and the morphology of its channels to the material’s effective conductivity. The effective conductivity estimates calculated by the model exhibit good agreement with those from electrochemical fin theory and finite element analysis, but are computed 1.5 and 6 orders of magnitude faster, respectively. In addition, the theory explicitly relates a number of morphological and topological parameters directly to the conductivity, whereby the distributions that characterize the structure are readily available for further analysis, e.g., using network science. We then present an approach for extending the model to account for (1) n interacting flows and (2) for the single-flow case we demonstrate algorithmic approaches for (a) accounting for the influence of reactions at steady state and (b) examining the transient flow properties of the network. The non-dimensional metrics that follow from each model provide a means of comparing different materials and, furthermore, each extension, to a large extent, preserves the relative speed and ease-of-use inherent in the initial steady-state model, thus making them attractive for guiding transport-relevant hypotheses in materials design efforts.
Resistance Values of Aluminum Oxide Film in Situ during Anodization of Aluminum By Fabry-PéRot Interferometry
Authors: Habib Khaled
Published: February 2020

A combination of Fabry-Pérot interferometry and the DC electrochemical method have been used for the first time, in situ, to measure the resistance of aluminium oxide films in 2% sulfuric acid solution. Values of the corresponding resistance of the obtained Al2O3 film thickness were determined during anodization of aluminium (Al) in 2% H2SO4. The obtained resistance values were verified by electrochemical impedance spectroscopy (EIS) and holographic interferometry. The corresponding resistance (2.4 x109 Ohms) to the final thickness of the aluminum oxide film was found in an agreement with the resistance value that was measured by holographic interferometry, 2.54x109 Ohms, in 2% H2SO4. On the contrary, the corresponding resistance (2.4 x109 Ohms) to the final thickness of the aluminum oxide film was found twice the value of the resistance that was measured by the electrochemical impedance spectroscopy (EIS), 1.25x109 Ohms, in 2% H2SO4.

Keywords
. Aluminium, Thickness of Oxide Film, Fabry-Pérot interferometry, Holographic Interferometry, Electrochemical Impedance Spectroscopy (EIS), Resistance, and Sulfuric Acid.