bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Interaction Mechanisms of Metal Reducing Bacteria with Functionalized Gold Surfaces during Initial Attachment and in Artificial Biofilms
Authors: Kastania Eleni , Ozcan Ozlem
Published: February 2020

Bacterial biofilms represent a ubiquitous form of microbial life on Earth. Due to an evolved armory of protean biological responses to external stimuli, bacteria are able to adhere to, colonize and thrive on virtually all surfaces, whether natural or synthetic, even in challenging environmental conditions. In addition to significant health risks, biofilms are among the salient contributors to the deterioration of metals and their alloys, thereby causing safety risks for technical equipment. Hence, understanding the interaction mechanisms of electroactive sessile bacteria with metal surfaces is vital for facilitating the development of efficient control strategies and novel anti-fouling surfaces in various industries and technologies.

The present study focuses on a combined spectroelectrochemical approach, melding methods of surface enhanced Raman spectroscopy (SERS) and electrochemical techniques, to investigate the chemical characteristics and redox activities of electroactive bacteria during the initial stages of biofilm formation. Gold has been selected as a model substrate due to its inert character, considerably high surface enhancement factor, as well as its capability to allow surface chemistry modifications and substrate polarization in order to precisely control the surface charge. Square wave voltammetry (SWV) and cyclic voltammetry (CV) studies have been performed for quantitative determination of flavin concentration and electrochemical impedance spectroscopy (EIS) has been utilized to study the changes in electrochemical processes within biofilms during different stages of growth. Shewanellasp. have been chosen as microorganisms within this work due to their versatile exoelectrogenic respiratory behavior and their distinct ability to reduce metals via extracellular electron transfer mechanisms involving self-secreted electron shuttle redox molecules such as flavins. To further explicate the process of diffusion of flavins within biofilms, a model system has been developed to simulate the structural features of the bacterial extracellular polymeric substances typically found in biofilms. This has been achieved by creating hydrogel films comprised of calcium-cross-linked alginate. The results demonstrate an interplay of factors contributing to the initial phases of bacterial settlement and biofilm formation as a function of environmental parameters. Furthermore, the results allow insight into the diffusion of flavins, much like they would in a natural biofilm, and how their redox behavior affects the biofilm development.
Analysis of Water-Assisted Crystallization Process in Anodically Grown Titania Nanotube Arrays
Authors: Ahiabu Ivy Berlinda , Paulose Maggie , Varghese Oomman K
Published: February 2020

Titania nanotube arrays grown using anodic oxidation have exhibited enormous potential as a semiconductor nanoarchitecture beneficial for a wide range of applications including solar energy conversion and storage. High degree of crystallinity is a pre-requisite for several of these applications. While conventional furnace annealing has long been identified as an effective method to crystallize the amorphous as-prepared nanotubes, recent research efforts to reduce the thermal budget revealed that titania nanotube arrays could be crystallized using water at or near room temperature. Crystallization and phase transformation was, however, accompanied by morphological changes. Although several reports on the topic appeared after this finding, most of these papers presented conflicting information on the mechanism of crystallization at room temperature and performance of this material when used for applications such as photocatalysis that exploit semiconducting properties. While some groups believed water as responsible for the crystallization, some others attributed it to electrolyte species such as fluorine. We performed a comprehensive investigation on water-assisted crystallization of nanotubes prepared under different conditions and our study revealed the true process behind crystallization. The quantum efficiency measurements on solar photoelectrochemical fuel generation cells fabricated using the room-temperature water crystallized nanotubes showed almost no improvement in the photocatalytic properties despite having the phase transition from amorphous to anatase. We will discuss the details of our findings in this presentation.
(Invited) TiO2 Nanotubes in Photocatalysis
Authors: Schmuki Patrik
Published: February 2020

TiO2 nanotubes in photocatalysis

Ning Liu, Anca Mazare, Patrik Schmuki

Department of Materials Science WW-4, LKO, University of Erlangen-Nuremberg, Martensstrasse 7, 91058 Erlangen, Germany

In the past decade, anodically formed self-organized TiO2 nanotube layers attracted considerable scientific interest (see e.g. reviews [1,2]). This is mainly due to the fact that these layers combine the defined nanotubular geometry with a broad range of functional features inherent to TiO2. Particularly in photoelectrochemical and photocatalytic applications nanotubular layers have shown remarkable results. The presentation will first give an overview of the most promising features of classic nanotube layers for photocatalysis and then focus on TiO2 nanotube (NT) arrays, converted by a high pressure H2 treatment to anatase-like "black titania"[3,4]. This modification shows a remarkable high open-circuit photocatalytic hydrogen production rate without the presence of any cocatalyst. We will discuss the main effects caused by the high H2pressure annealing and the origin of this outstanding activity of black titania.

REFERENCES

P. Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904

K. Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385

N. Liu, P. Schmuki et.al. Nano Letters, 14 (2014) 3309

N. Liu, P. Schmuki et.al. 53 (2014) 14201
(Invited) Probing Local, Hybrid Perovskite Photophysics through Spatially- and Temporally-Resolved Absorption/Emission Microscopy
Authors: Kuno Masaru , Draguta Sergiu
Published: February 2020

The presentation will describe recent work conducted to investigate local hybrid perovskitephotophysics through spatially-resolved optical measurements.In particualar, by conducting local emission intensity (Iem
) versus excitation intensity (Iexc
) measurements, we have established the existence of optical response variations due to electronic disorder stemming from the presence of nonuniform trap densities. Regions of solution-processed MAPbI3 films exhibit effective free carrier recombination while others exhibit emission dynamics strongly influenced by trap states. Through appropriate kinetic modeling of the data, quantitative estimates of local trap densities (Nt
) have been made. What results are Nt
values between Nt
~1015-1017 cm-3. We have additionally found that spatially-varying trap densities impact MAPbI3 radiative recombination efficiencies, resulting in local emission quantum yields that range from 5% to ~7% at 1 sun. To link the above conclusions with corresponding solar cell performance, we have begun to correlate optical response to local solar cell efficiencies. These measurements have entailed Iem
versus Iexc
, emission lifetime, and photocurrent measurements on planar (FTO/compact-TiO2/MAPbI3/Spiro-MeOTAD/Au) ~17% efficiency solar cells. Obtained results confirm that photogenerated electrons are the charge species being trapped in MAPbI3. The fraction of trapped electrons is small and is on the order of 2-3%. An even smaller (~0.2%) fraction undergoes radiative recombination. What remains available for current generation is ~97-98% of the initially photogenerated carriers. Unfortunately, interface recombination at electron/hole transporting layers significantly suppresses this value, resulting in net power conversion efficiencies below the Shockley limit. Subsequent spatially-resolved measurements (conducted on planar as well as on analogous planar-inverted and mesoporous solar cells) link local power conversion efficiencies to underlying charge trapping/charge injection efficiencies.
(Invited) The Bright Future for Electrode Materials─Highly Conductive Porous Na-Embedded Carbon Nanowalls for Energy Conversion and Storage
Authors: Hu Yun Hang
Published: February 2020

Although doping alkali metals into carbon materials was demonstrated to create highly conductive carbon materials in 1991, the dopants were located on the carbon surface and could be easily oxidized, leading to a great loss in conductivity. As an ideal material, alkali metal atoms must be completely surrounded by carbon atoms to form alkali-metal-embedded carbon material. Such a hypothetical material is totally different from widely used intercalation carbon compounds, in which alkali ions are inserted into spaces between graphite layers. However, the alkali-metal-embedded carbon material has not yet been successfully synthesized for 25 years. In this presentation, I will talk about our recent success of synthesizing highly-conductive porous Na-embedded carbon nano-wall materials (with large accessible surface areas) using an original reaction between liquid Na and CO gas. The novel materials solve the critical issue “the contradiction between high electrical conductivity and large accessible surface area” in current electrode materials. Furthermore, the synthesized materials were tested as electrodes for (1) dye-sensitized solar cells (DSSCs), energy devices, leading to high power conversion efficiency up to 11.03% and (2) supercapacitors, resulting in ultrahigh areal capacitance of 1.14 F/cm2 and a wide operating temperature range.
(Invited) Development of Plasmonic Nanostructures for Plasmon-Enhanced Photocatalysis
Authors: Ma Dongling
Published: February 2020

With unique surface plasmon resonance and high potential for many important applications, plasmonic nanostructures are attracting more and more attention in the past decade. In addition to ever increasing research interest in realizing precise control over their structure (such as size, shape, aspect ratio and uniformity), plasmon enhanced catalysis represents a highly promising research area. In this presentation, the development of several types of plasmonic nanostructures by wet chemical method or pulsed laser ablation will be introduced first. Their interesting optical properties and their applications in photocatalysis will then be presented and discussed.
(Invited) Nanophotonic Structures for Solar Light Harvesting and the Generation of Hot Plasmonic Electrons
Authors: Wiederrecht Gary
Published: February 2020

Future nanophotonic architectures for optical energy conversion and photocatalysis will require nanostructures with roles that work together cooperatively, such as structures with a large absorption cross section combined with features that enable guiding, propagating, and converting energy. Ultrafast optical responses in nanostructures are potentially important for modulating energy flow and also for characterizing and minimizing energy dissipation pathways in nanophotonic structures. Also, ultrafast extraction of hot plasmonic electrons from metal nanostructures is an important opportunity for increasing efficiency of solar energy conversion and photocatalysis. Efforts to greatly improve the efficiency of hot electron generation through plasmonic metamaterials, and characterization of hot electron dissipation pathways are described. I further describe efforts to induced long-range energy propagation in nanostructures. Nanostructured materials inspired by natural photosynthetic membranes represent an opportunity for efficient and directional energy transport. In natural photosystems, light harvesting complexes can transport excitons to the reaction center core with near unity conversion of absorbed photons to separated charge. A key to this process is the high rate of exciton hopping and the directionality of exciton flow due to an energy level waterfall effect of excitons in complexes as the reaction center core is approached. Efforts to induce similar behavior in biomimetically inspired nanostructures are described. Finally efforts to image exciton flow in light harvesting nanoscale materials are introduced. Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
(Invited) Correlation of Charge Carrier Behaviors with Band Structure of Semiconductor-Based Photocatalysts
Authors: Wu Nianqiang (Nick)
Published: February 2020

This presentation will discuss the correlation of band structure with charge separation, charge migration and charge recombination in the semiconductor-based photocatalysts. Doping elements into the semiconductor could alter the electronic band structure, which will change the charge separation and charge recombination processes, leading to modulation of photocatalytic activity. When two materials are formed to a heterojunction, the band alignment and the interfacial defects in the heterojunction have significant effects on the charge separation, charge migration and charge recombination processes.
(Invited) Chemical and Electronic Surface Structure of Compound Semiconductors for Solar Water Splitting
Authors: Heske Clemens
Published: February 2020

The purpose of this talk is to utilize a tool chest of soft x-ray and electron spectroscopies (in particular using high-brilliance synchrotron radiation) to gain insights into the electronic and chemical surface properties of candidate materials for solar water splitting. Focus will be placed on GaInP2- and Cu(In,Ga)(S,Se)2-based material systems, and how ambient conditions and deliberate tailoring can modify and impact the surface of such materials. It will be shown that photoelectron spectroscopy (PES), x-ray-excited Auger electron spectroscopy (XAES), inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive band edge positions, band gaps, electronic level alignment, and insights into chemical stability, both with experiments in ultra-high vacuum, as well as under in situ and operando conditions.
(Invited) Visible Light CO2 Reduction and Water Oxidation on Modified Semiconductor Photocatalysts
Authors: Maeda Kazuhiko
Published: February 2020

CO2 reduction and water oxidation on semiconductor photocatalysts are of great importance from the viewpoint of solar-to-fuel energy conversion toward artificial photosynthesis. In this presentation, recent progress on the development of new photocatalysts will be given. In particular, surface modification techniques developed by our group to construct active sites and light-absorbing centers will be presented.

It is known that certain metal complexes based on rhenium or ruthenium catalyze CO2 reduction into CO or HCOOH photocatalytically with high selectivity and quantum yields. However, the oxidation ability of metal complex photocatalysts is generally low, requiring a strong electron donor for operation. On the other hand, semiconductors have high activity and stability for oxidation reactions, although the selectivity to CO2 reduction is low. Here we developed a new system for CO2 reduction using a visible-light-responsive semiconductor and a binuclear metal complex having a redox photosensitizer and a catalytic unit. In this reaction scheme, both the semiconductor and the photosensitizer unit of the metal complex undergo photoexcitation. The conduction band electrons in the semiconductor move to the excited state of the sensitizer unit, producing a one-electron reduced species. After subsequent intermolecular electron transfer from the one-electron-reduced species to the catalyst unit, CO2 is reduced into HCOOH (or CO), while holes left in the valence band of the semiconductor participate in the oxidation reactions. Because of the electron transfer pathway, this is called “Z-scheme” CO2 reduction system. We found that TaON, CaTaO2N, Y2Ta2O5N2, and C3N4 became active component for the Z-scheme system driven by visible light (> 400 nm) in combination with a suitable binuclear metal complex.

As the component of water oxidation half cycle, we developed a new powdered photocatalyst consisting of Co(OH)2 and TiO2. TiO2 is known to be an active photocatalyst, but only works under UV irradiation. By contrast, the Co(OH)2/TiO2 hybrid photocatalyst is capable of absorbing visible light with wavelengths of up to 850 nm and oxidizing water into oxygen gas, even though it consists of only earth-abundant elements only. To our knowledge, this system provides the first demonstration of a photocatalytic material capable of water oxidation upon excitation by visible light up to such a long wavelength.
On the Control of Electron Transfer Rates through the Morphology of Nanoparticles
Authors: Spitler Mark
Published: February 2020

It will be shown how the morphology and dimension of inorganic nanostructures in a solution should affect the rates of outer sphere electron transfer for nearby redox ions much differently than is predicted for a macroscopic planar interface. Simple Marcus theory and electrostatic evaluations of the self-energy of the ions near these nanostructures are used to calculate this effect, which is controlled by the degree to which the environment about the ion is the high dielectric permittivity of the solid rather than solution. A higher degree results in a lower reorganization energy for the ion and a smaller activation energy for electron transfer. The extreme of interest to this discussion is that of a redox ion within a spherical or cylindrical nanocavity of an inorganic solid.

It has long been known how simple Marcus theory predicts electron transfer rates for donor and acceptor couples as a function of the difference in the free energy of the reaction and experimentation1 has confirmed the predicted parabolic form of transfer rates and the “inverted region,” where rates slow down. Variations in the outer sphere reorganization energies of donor-acceptor couples also result in changes of charge transfer rates predicted by this theory and also indicate this decrease in transfer rates.2 Recently, it has been demonstrated how the temperature dependence of electron transfer rates for a specific donor-acceptor couples also describes this parabolic behavior according to theory.3 This presentation on nanostructures and outer sphere electron transfer explores how the dielectric permittivity within Marcus theory may be an additional variable to control rates of electron transfer reactions.

Geometric configurations will be examined in this work in the limits where the radius of the nanocavity of the solid varies from large compared to that of the redox ion within it to where it approaches the size of the redox ion. The electron transfer will be calculated as a self-exchange rate for reduced and oxidized forms of a redox couple to avoid considerations of electron exchange with the solid. To illustrate the principles involved, the solution will be taken as acetonitrile and the solid as ZnO. Spherical nanoshells will also be considered to illustrate how the same redox ion can have an accelerated electron transfer rate within the cavity while its rate for ions outside the shell slows down.4

References:

1. Closs, G.L.; Miller, J.R. Science
1988, 240, 440-447.

2. Kuss-Petermann, M.; Wenger, O.S. J. Am.
Chem. Soc.
2016, 138, 1349-1358.

3. Waskasi, M. M. et al., J. Am. Chem. Soc.,
2016, 138, 9251-9257.

4. Spitler, M.T. Electrochim. Acta, 2007, 52, 2294-2301.
A Physics-Based Model to Investigate Degradation-Related Performance Loss in Photoelectrochemical Devices
Authors: Nandjou Fredy , Haussener Sophia
Published: February 2020

Understanding and mitigating performance loss in photoelectrochemical devices are key factors for advancing their large-scale implementation and industrialization. Performance loss is caused not only by the degradation of single components (semiconductor, catalyst and electrolyte), but also by the interplay between the operating conditions and the various degradation phenomena. While the catalyst and electrolyte degradations are considerable challenges for long-term durability, the short-term durability mainly depends on the semiconductor material and its interface with the electrolyte [1]. Semiconductors with good photoabsorption behavior and interesting band alignments are inherently non-stable, and therefore degrade within hours due to photocorrosion.

Usually, photocorrosion is interpreted on the basis of energy schemes, comparing the quasi-Fermi levels of minority carriers to the corrosion potentials of the photoelectrode [2]. However, the competition between the pure redox process of water splitting and photoelectrode dissolution/passivation is mainly determined by kinetic parameters [3].

In this study, we use a physics-based model to quantify the effect of photocorrosion phenomenon on the global performance loss of the photoelectrochemical device. The studied device is composed of different catalyst covered semiconductors, immersed in a liquid electrolyte. The catalyst layer is considered a nanoporous media, the solid phase being composed of a supporting structure and catalyst particles.

The simulation results highlight the practical limitation of using thermodynamic calculations for the investigation of photoelectrochemical devices durability, and how irradiation, mass transport, and kinetic properties can impact the stability of the photoelectrode/electrolyte interface.

[1] F. Nandjou and S. Haussener. Degradation in photoelectrochemical devices: Review with an illustrative case study. J. Phys. D: Appl. Phys. 50 (2017) 124002.

[2] H. Gerischer et al. Report EUR 9531 EN (1984), Commission of the European Communities.

[2] R. Memming. The Role of Energy Levels in Semiconductor
‐
Electrolyte Solar Cells. J. Electrochem. Soc. 125 (1978) 117.
Evaluating Losses Associated with Single Hydrogen Bubbles on Photoelectrode Performance
Authors: Dorfi Anna Elisabeth , Esposito Daniel V , West Alan C
Published: February 2020

Photoelectrochemical cells (PECs) are integrated devices that offer an attractive approach to converting solar energy into storable chemical energy, such as hydrogen. In PEC-driven water electrolysis, the product species, hydrogen and oxygen, are first evolved as gas bubbles at the surface of the electrode. However, these gas bubbles can lead to significant efficiency losses, due to increasing electrode surface coverage by gas bubbles that block active material and reactants from reaching the photoelectrode surface. It is known that when gas bubbles are attached to the surface of a photoelectrode, they can induce a variety of loss mechanisms, however, these bubble losses are difficult to quantifiably measure and still not completely understood. Therefore, it is desirable to study the gas evolution dynamics on these photoelectrodes so that systems can be designed to minimize efficiency losses. In this study, in situ scanning photocurrent microscopy (SPCM) is used, for the first time, to investigate the local photocurrent losses associated with isolated hydrogen bubbles attached to the surface of a photoelectrode. By measuring the change in photocurrent response of an area of interest, we can quantify and determine local optical bubble-induced photocurrent losses on a photoelectrode at the sub-bubble level. Silicon-based photocathodes based on a metal-insulator-semiconductor (MIS) architecture containing a continuous 3 nm metal layer, are used for this work. SPCM is used to systematically investigate the influence of varying bubble size on the performance of these photoelectrodes under varied experimental conditions. The quantitative SPCM measurements are combined with optical modeling based on Snell’s Law. Comparisons between the experimentally determined losses and those predicted with the optical model are used to elucidate relationships between local photocurrent losses and bubble size. Significant increases in optical losses for larger bubbles (diameter > 150 μm) are seen, due to regions of total internal reflection that are not present for the small bubbles studied. Finally, the knowledge gained from the SPCM single-bubble measurements are applied to a large photoelectrode surface under uniform AM1.5 illumination. Using these measurements, we can model the current-time profile associated with multiple bubble evolution off of a fully-illuminated photoelectrode surface. Overall, this study sets the stage for quantitatively modeling bubble-related losses for various photoelectrode geometries and operating conditions. We have also provided valuable insight into the optical losses associated with having a single surface bound gas bubbles on a photoelectrode surface.
(Invited) Surface Chemistry of Gap in Solar-Driven Pyridine-Catalyzed CO2 Reduction
Authors: Chen Zhu , Kronawitter Coleman X. , Koel Bruce E.
Published: February 2020

Atypical high selectivity for the conversion of CO2 to methanol has been reported when pyridine is dissolved in the electrolyte of a photoelectrochemical cell employing a p-type gallium phosphide (GaP) photocathode.[1] Despite considerable electrochemical characterization and theoretical consideration, there is no consensus on the mechanism by which pyridine catalyzes CO2-to-methanol conversion. A fundamental understanding of the origin of high selectivity in this system is important for continued optimization of solar-driven CO2 reduction. Our research combines a surface science approach with in situ and operando spectroscopy to investigate GaP surface chemistry and determine the role of heterogeneous processes in this catalysis.

Ambient pressure photoemission spectroscopy (APPES) was used to study the adsorption of H2O [2] on GaP(110) and pyridine (Py) on clean and hydrided GaP(110). The stable adsorption of both H and pyridine on GaP(110) characterizes the precursor state for the formation of adsorbed dihydropyridine (DHP), which could be a key hydride-shuttling catalyst for heterogeneous CO2 reduction. Using APPES we also observed dissociative adsorption of methanol on GaP(111), which leads to the formation of surface-bound methoxy (CH3O) species, while simultaneous formation of surface-bound formate (HCOO) and methoxy occurs on the more reactive GaP(110) surface. Low temperature scanning tunneling microscopy (LT-STM) was used to observe orbital-resolved bonding of adsorbed pyridine on the GaP(110) surface.[3] By examining the distribution of unoccupied molecular orbitals with high spatial and energy resolution, we have identified the sites on pyridine susceptible to nucleophilic attack that lead to the formation of hydrogenated species such as dihydropyridine. O
perando FTIR studies of pyridine hydrogenation at a Pt electrode under relevant electrochemical conditions was used to observe the formation of a hydrogenated piperidinium (PyH7
+) near-surface species, which implies that dihydropyridinium (PyH3
+), the protonated form of dihydropyridine, must exist transiently during CO2 reduction.[4]

1. Barton, E. E.; Rampulla, D. M.; Bocarsly, A. B., J. Am. Chem. Soc.
130, 6342 (2008)

2. Kronawitter, C. X.; Lessio, M.; Zhao, P.; Riplinger, C.; Boscoboinik, A.; Starr, D. E.; Sutter, P.; Carter, E. A.; Koel, B. E., J. Phys. Chem. C
119, 17762 (2015)

3. Kronawitter, C. X.; Lessio, M.; Zahl, P.; Muñoz-García, A. B.; Sutter, P.; Carter, E. A.; Koel, B. E., J. Phys. Chem.
C
119, 28917 (2015)

4. Kronawitter, C.; Chen, Z.; Zhao, P.; Yang, X.; Koel, B. E., Catal. Sci. Tech., 7, 831 (2017)
(Invited) Solar-Driven Electrochemical Conversion of Carbon Dioxide to Hydrocarbons and Oxygenates
Authors: Ager Joel W.
Published: February 2020

Sustainable solar to fuel conversion could provide an alternative to mankind’s currently unsustainable use of fossil fuels [1]. Solar fuel generation by photoelectrochemical (PEC) and electrochemical methods is a potentially promising approach to address this fundamental challenge. To date, solar to fuel research efforts have been mostly focused on solar water splitting, which produces hydrogen [2]. In contrast, the conversion of CO2 to hydrocarbons that could displace currently used fossil fuels is considerably less well developed [3].

Achieving a viable solar-driven EC CO2 reduction energy conversion efficiency requires minimizing potential losses in all aspects of the device including the cathode, anode, electrolyte, and membrane. Achieving selective products requires management of multi-electron transfer reactions [4]. Strategies to optimize each component (anode, cathode, electrolyte, cell design) of our CO2 electrolyzer cell to obtain high selectivity and energy conversion efficiency at low overpotential will be described. An overall cell design which has efficient gas to liquid mass transfer of CO2 is employed [5]. Use of a CsHCO3 buffered electrolyte increases selectivity to C2+ products such as ethylene and ethanol [6]. A nanostructured anode is used which shows superior stability and high performance for oxygen evolution in the pH range of interest for CO2 reduction. Finally, a cathode design has been developed which enables selectivity to hydrocarbons and oxygenates over a wide range of pH and cell voltage conditions.

Solar-driven CO2 reduction is accomplished by coupling the optimized electrolysis device to solar cells. 1 sun efficiencies of over 4% for the production of hydrocarbons and oxygenates are achieved. Notably, the overall system also functions at >1% conversion efficiency at illumination intensities down to 0.3 suns.

Chu, S.; Cui, Y.; Liu, N. The Path towards Sustainable Energy. Nat. Mater.
2016, 16, 16–22.

Ager, J. W.; Shaner, M. R.; Walczak, K. A.; Sharp, I. D.; Ardo, S. Experimental Demonstrations of Spontaneous, Solar-Driven Photoelectrochemical Water Splitting. Energy Environ. Sci. 2015, 8, 2811–2824.

Goeppert, A.; Czaun, M.; Jones, J.-P.; Surya Prakash, G. K.; Olah, G. A. Recycling of Carbon Dioxide to Methanol and Derived Products – Closing the Loop. Chem. Soc. Rev.
2014, 43, 7995–8048.

Y. Hori, in Mod. Asp. Electrochem., (Springer New York, New York, NY, 2008), pp. 89–189.

Lobaccaro, P.; Singh, M. R.; Clark, E. L.; Kwon, Y.; Bell, A. T.; Ager, J. W. Effects of Temperature and Gas–liquid Mass Transfer on the Operation of Small Electrochemical Cells for the Quantitative Evaluation of CO 2 Reduction Electrocatalysts. Phys. Chem. Chem. Phys.
2016, 18, 26777–26785.

Singh, M. R.; Kwon, Y.; Lum, Y.; Ager, J. W.; Bell, A. T. Hydrolysis of Electrolyte Cations Enhances the Electrochemical Reduction of CO2 over Ag and Cu. J. Am. Chem. Soc.
2016, 138, 13006–13012.
Efficient Electrochemical Reduction of CO2 to Ethylene
Authors: Kenis Paul J.A. , Gewirth Andrew A
Published: February 2020

A significant reduction in atmospheric carbon dioxide (CO2) emissions as well as in the development of alternative energy sources will be critical to curb the unwanted effects of climate change (e.g., global warming, erratic weather patterns) and to reduce our dependence on fossil fuels. A number of strategies will need to be pursued simultaneously to indeed reduce anthropogenic CO2 emissions. One such strategy is the use of CO2 as a feedstock for the production of useful chemicals (formic acid, carbon monoxide, hydrocarbons, or alcohols) via electrochemical reduction. This type of electrolysis processes can be driven in a cost effective and sustainable manner if otherwise-wasted renewable energy produced in excess of grid demand is used.

Over the past decade, significant advances have been made in the efficient electrocatalytic conversion of CO2 to carbon monoxide (to be used for dense energy carrier production) with scale up and commercialization activities now ongoing. The production of other interesting chemicals such as methanol and ethylene via electroreduction of CO2 has been lagging.

This presentation will report on our recent progress to in developing ever more active and especially selective catalysts for the production of ethylene and ethanol. Many researchers are pursuing Cu-based catalysts for this task. While reasonable conversion rates can be achieved (overall current densities exceeding 100 mA/cm2), the main challenge has been achieving selectivity for the desired products of ethylene and ethanol. Typically, other gaseous products such as CO, hydrogen and methane are formed in significant amounts, in addition to ethylene and ethanol. Here we will report our work on the development of Cu-based catalysts that produce 70-80% ethylene and ethanol, at a combined rate exceeding 170 mA/cm2. The presentation will also include an analysis of economic feasibility for the production of ethylene from CO2.
Advanced Biowaste-Based Flexible Photocatalytic Fuel Cell As a Green Wearable Power Generator
Authors: Lui Gregory , Jiang Gaopeng , Lenos Jared , Lin Edric , Fowler Michael , Yu Aiping , Chen Zhongwei
Published: February 2020

This study designs a wearable power generator from a flexible, photocatalytic fuel cell (fPFC) using various biowaste sources (lactic acid, ethanol, methanol, urea, glycerol, and glucose) as fuel. The fPFC uses light irradiation and the decomposition of biowaste to generate electrical power under both flat and bending (r = 3 cm) conditions. When employed as a sweat band, the fPFC generates a maximum power 4.0 mW cm−2 g−1 from human sweat. The wearable fPFC is able to overcome many of the disadvantages of wearable microbial and enzymatic cells while providing comparable if not superior power density.
Low Noble Metal Content Oxygen Evolution Reaction Catalyst for Solar Water Splitting
Authors: Koonce Jonathan G
Published: February 2020

Water splitting for hydrogen production requires catalysts that are active for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). OER kinetics typically limit the efficiency of electrolysis, so improved OER catalysts are needed. This research has found an iridium doped nickel-iron based catalyst that is effective even at extremely low loadings. This low loading also allows the films to be transparent. This work shows an analysis of thin, transparent films of this catalyst. The stability, OER activity, transparency, loadings, composition, and efficiency in a solar water splitting device are all analyzed.
Eutectic Ionic Liquid Mixture for Lithium Batteries
Authors: Huang Qianwen , Gurkan Burcu
Published: February 2020

Lithium-ion batteries (LIBs) are widely used in portable electronic devices. However, LIBs are reaching their fundamental limits and new battery chemistries become essential for wider applications. Lithium metal batteries offer an order of magnitude increase in energy density in theory, compared to LIBs. However, the high reactivity and the related safety hazard of the metallic lithium hinder its application in electrochemical energy storage devices. Ionic liquid (IL) electrolytes due to their unique properties including lack of flammability, negligible volatility, wide electrochemical window and high thermal stability are capable of resolving safety and stability issues in lithium metal batteries, thus enabling high-energy storage devices. The ionic conductivity of ILs, however, need to be improved to achieve practical charge/discharge rates in batteries. We investigate the non-idealities in physical and electrochemical properties of eutectic ILs and their lithium salt mixtures. Here, we will present the ionic interactions that can lead to increased conduction pathways for lithium ion in eutectic mixtures.

ILs consist of ions and their interactions with small charged ions such as Li+ create heterogeneities in the solvation shell of these solutes. Eutectic IL mixtures including the [PYR13][TFSI] with high electrochemical stability, and imidazolium and sulfonium based ILs with low viscosities but lower stabilities were studied. Improved conductivities were obtained for the eutectic IL mixtures, compared to the parent ILs. When examined on a Walden plot, the eutectic IL electrolyte demonstrate moderate ionicity. Surface Enhanced Raman Spectroscopy (SERS) was used to investigate the Li+ interaction and coordination in the bulk and near electrode surface via confocal capability of SERS. Li+ coordination is observed to increase with increasing lithium salt concentration in the range of 0 – 1 M, as expected. Increasing the concentration further to 2 M, however, shows no further changes in coordination suggesting that there are free Li+. Our in-situ electrochemical SERS indicate that the coordination condition did not completely reverse to initial state after polarization. Measured electrochemical windows, thermal analysis results and conductivities will be presented for the eutectic systems studied. Further performance analysis of these electrolytes are being conducted for lithium metal batteries.
(Invited) Ion Transport in Polymerized Ionic Liquids: Structure-Morphology-Property Relationships
Authors: Sangoro Joshua R , Heres Maximilian Ferdinand , Liu Hongjun , Paddison Stephen , Strehmel Veronika
Published: February 2020

Polymerized ionic liquids (PolyILs) are a novel class of functional polymers that combine the unique physicochemical properties of molecular ionic liquids with the outstanding mechanical characteristics of polymers. This special mix of features might help to circumvent the key limitations of low molecular weight ionic liquids, namely, leakage and poor mechanical properties while utilizing their outstanding characteristics such as low vapor pressures, wide liquidus ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. PolyILs have shown remarkable advantages when employed in electrochemical devices such as dye-sensitized solar cells, lithium batteries, actuators, field-effect transistors, light emitting electrochemical cells, and electrochromic devices, among others. Despite their promising prospects as ideal polymer electrolytes, the role of molecular structure, morphology, and polymer dynamics on charge transport in PolyILs remains poorly understood. According to classical theories, the self-diffusion and ion transport in electrolytes are controlled by structural relaxation. These approaches predict similar temperature dependence for the dc conductivity and structural dynamics. Although this prediction has been shown to hold reasonably well for low molecular weight aprotic ionic liquids, it fails for PolyILs. In addition, the impact of morphology on charge transport is not considered within the framework of these theories.

This talk will focus on new insights obtained from experimental studies employing broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, rheology, and scattering techniques to elucidate the impact of morphology on charge transport and structural dynamics in systematic series of polymerized ammonium- and imidazolium- based ionic liquids. Detailed analyses reveal strong decoupling of these processes in the PolyILs, implying the limitation of the classical theories in describing charge transport and molecular dynamics in these materials, in contrast to low molecular weight systems. In addition, the strong correlation observed between ionic conductivity from dielectric experiments and morphologies from scattering and computational studies will be discussed.
Morphology of Polymerized Ionic Liquids from X-Ray and Neutron Scattering: An Atomistic Simulation Perspective
Authors: Liu Hongjun , Paddison Stephen
Published: February 2020

The design of solid-state electrolytes for electrochemical applications that utilize polymerized ionic liquids (polyILs) would greatly benefit from a molecular-level understanding of structure-property relationships. We herein use atomistic molecular dynamics simulations to investigate the structural properties of a homologous series of poly(n-alkyl-vinylimidzolium bistrifluoromethylsulfonylimide) poly(CnVim Tf2N) and present the first direct comparison of the structure factors obtained from scattering and simulations. Excellent agreement is found in terms of peak position and shape. Specifically, three characteristic peaks can be identified: low-q backbone-to-backbone peak or polarity peak, immediate ionic peak or charge peak and high-q pendant-to-pendant peak or adjacency peak. As the alkyl chain length increases, the backbone-to-backbone peak becomes stronger, moving to larger distance, the anion-to-anion separation slightly increases with weaker intensity, and the pendant-to-pendant or close contact peak remains essentially intact. The longer alkyl chains lead to the longer backbone-to-backbone separation and the larger nonpolar nanodomains. The quantitative cluster analysis along with color-coded snapshots vividly demonstrates that discrete nonpolar islands first form within the continuous polar network, then nonpolar domains grow beyond the percolation threshold, finally interconnect with the polar network into a bicontinuous ‘sponge-like’ nanostructure. Moreover, we exploit the selective labeling technique of neutron scattering using hydrogen/deuterium substitution to afford further insight into the morphology of poly(CnVim Tf2N). The neutron scattering profiles markedly depend on the isotopic substitution pattern. The total neutron structure factors of the backbone deuterated samples reveal the most noticeable low-q peak and are much more intense than those observed in single isotope neutron scattering. Our results strongly suggest that the X-ray scattering and distinct isotopic labeled neutron scattering data do not necessarily give rise to the same positioned scattering peaks. We hope these insights will lead to a fundamental understanding in structure and morphology of polyILs and pave a path forward towards the rational design of future polyILs for electrochemical devices.
Charge Transport and Dynamics of 2D-Confined Polymerized Ionic Liquids
Authors: Kinsey Thomas , Cosby James Tyler , Glynn Kaitlin , Yolit Katherine , Sangoro Joshua R
Published: February 2020

Polymerized ionic liquids are advantageous for numerous applications such as batteries, dye- sensitized solar cells, and fuel cells. The combination of thermal and electrochemical stability, non- flammability, and ionic conductivity of ionic liquids; the mechanical properties of polymers; and also the decoupling of ionic and segmental dynamics make polymerized ionic liquids promising alternatives to traditional polymer electrolyte solutions. However, their intrinsic ionic conductivities are typically too low for many applications. This shortfall may be improved with proper chemical design of the polymer backbone and ionic groups as well as nanoscale confinement of the polymer chains, which has been hypothesized to increase the free volume of the diffusing ion. This study investigates the confinement effects of poly(1-ethyl-3-vinylimidazolium) bis(trifluoromethylsulfonyl)imide polymerized ionic liquid within mesoporous silica membranes using broadband spectroscopy to probe charge transport and polymer dynamics. Confinement is achieved by in situ free-radical polymerization of the vinyl- imidazolium monomer within the various sized pores. The progression of monomer conversion and polymerization kinetics is observed as a function of pore diameter and thermolytic initiator concentration using Fourier transform infrared spectroscopy. The interplay of the nanoscale confinement and ionic conductivity are discussed in terms of the current understanding of charge transport and dynamics in confined polymerized ionic liquids.
(Invited) Monitoring Endogenous Opioid Neuropeptide Dynamics in Real Time Using Multiple Scan Rate Voltammetry Coupled with Carbon Nanotube Yarn Microelectrodes
Authors: Sombers Leslie A , Lee Christie A , Calhoun Sarah E , Meunier Carl J , Smith Samantha K , McCarty Gregory S
Published: February 2020

Opioid peptides are critically involved in a variety of physiological functions necessary for adaptation and survival, and as such they show tremendous promise as therapeutic targets. However there is a critical gap in understanding when and where these molecules are released, because there is a paucity of detection methods for monitoring opioid peptides in the extracellular space. We have designed a novel waveform that employs two distinct scan rates in each voltammetric sweep to detect enkephalin dynamics in live tissue with sub-second temporal resolution using carbon fiber microelectrodes. Combining two scan rates in a single voltammetric scan is unprecedented in molecular monitoring. It exploits fundamental principles to offer a combination of temporal and spatial resolution, sensitivity, and chemical selectivity that has the potential to advance the voltammetric detection of many classes of molecules. Electrochemical detection is further enhanced by combining this approach with a microelectrode sensing substrate engineered entirely of multi-walled carbon nanotubes spun into a yarn, replacing the standard carbon fiber altogether. The high aspect ratio and distinct electronic properties of the nanotubes result in markedly improved selectivity, sensitivity, and spatial resolution, as well as faster electron transfer kinetics that are manifested as sharper voltammetric peaks when compared to conventional carbon-fiber microelectrodes. By combining a groundbreaking voltammetric approach with a novel tool engineered from nanoscale materials, we are enabling a shift from interferential measures of endogenous opioid activity to direct molecular measurements.
An Ultrasensitive and Incubation-Free Electrochemical Immunosensor Using Outer-Sphere-Reaction-Philic and Inner-Sphere-Reaction-Philic Species
Authors: Fang Chiew San , HA Jin Nyeong , Yang Haesik
Published: February 2020

This communication reports a new nanocatalytic scheme based on the facts that the redox reaction between a highly outer-spherereaction-philic (OSR-philic) species and a highly inner-spherereaction-philic (ISR-philic) species is slow and that an OSR- and ISRphilic Au-nanocatalyst label can mediate the two different types of redox species. This scheme allows highly sensitive and incubation free detection of creatine kinase-MB. Using outer-sphere to inner-sphere ENc redox cycling that allows high signal amplification. When the ENc redox cycling was applied to a sandwich-type immunosensor for the detection of CK-MB, the calculated detection limit was approximately 20 fg mL1 , indicating that the immunosensor is highly sensitive. The results for clinical serum samples showed that the immunosensor is practically appealing.