bluuebunny/crossref_metadata_2025 huggingface dataset:
Impedance of Mediated Electrochemical Processes: Fenton Reaction
Authors: Polczynski Piotr , Jurczakowski Rafal Robert
Published: February 2020

Impedance is a powerful technique that provides a deep insight into the mechanism, kinetics, and thermodynamics of various physicochemical processes. Impedance of electrochemical systems coupled with homogeneous chemical reactions is seldom reported. Catalytic processes governed by the EC′ mechanism are of particular relevance since these processes are widely employed for mediated electrochemical oxidation of persistent environmental pollutants, gas sensing, catalytic hydrogen evolution, carbon dioxide electroreduction, enzyme oxidation, electrochemistry of nucleic acids, amino acids, as well as for numerous other bioanalytical applications. These system has been investigated almost exclusively by using classical transient electrochemical methods.

Recently we have developed an analytical expressions describing the faradaic impedance of the catalytic processes governed by (pseudo) first-order chemical kinetics. The solution was obtained in the rigorous treatment and it is applicable to the analysis of the experimental EC’ systems regardless the kinetics of the homogeneous and electrochemical steps.1 We have found that unequal diffusivities of the oxidized and reduced forms of the redox mediator have a strong effect on the impedance characteristics of the catalytic EC’ systems. This behavior is related to the novel impedance element, which reduces to the Gerischer impedance when both diffusion coefficients are equal.1

In this study we demonstrate how to fully characterize EC’ type processes by using impedance spectroscopy and our model. Provided equivalent circuit together with potential dependence of all impedance parameters allow for a rapid and precise determination of all kinetic and thermodynamic parameters of EC’ type reactions. For Fenton reaction, the formal potential, E
0’, heterogeneous, k
0, and homogeneous, k, rate constants, electron transfer coefficients, α, β, and both diffusion coefficient of the redox mediator D
ox, D
red were precisely determined. Greater part of these parameters have been determined here for the first time while the other are in good agreement with the previous literature reports.  

[1] R. Jurczakowski and P. Polczynski, J Phys. Chem. C, 2014, 118, 7980-7988.
Novel Methanol-Tolerant Metal Selenide Based Chalcogenide Electrocatalysts for Oxygen Reduction in Alkaline Solution
Authors: Masud Jahangir , Swesi Abdurazag , Nath Manashi
Published: February 2020

Direct methanol fuel cells (DMFCs) have been studied as an alternatives of conventional energy-generating devices due to their high energy density and low-to-zero emissions. Although significant advancements have been achieved for DMFCs in recent years, unremitting efforts are still needed to make them commercially applicable. The methanol “cross-over” phenomenon, the permeation of alcohol through the membrane, remains as one of the major problems for the widespread commercialization.1 In order to overcome this drawbacks, efforts are focused in the development of a new cathode electrocatalysts that do not adsorb methanol while maintaining an excellent activity for the oxygen reduction reaction. Here, we demonstrate transition metal  selenide, Mx
Sey (M = Co, Ni) based electrocatalysts for oxygen reduction reaction (ORR) in alkaline solution which also exhibit high methanol tolerance.

Electrocatalysts were prepared by electrodeposition on GC electrodes. These catalysts exhibited excellent ORR activity in presence of methanol in 0.1 M KOH solution. The onset potentials for ORR in 0.1M KOH solution were found to be 0.85 and 0.9 V (vs. RHE) for NixSey and CoxSey, respectively, which even didn't change in presence of methanol. The catalysts were characterized using TEM, SEM, EDX, XRD and XPS for morphology, elemental chemical compositions, phases and electronic states. Figure 1 shows SEM images of the catalysts (NixSey and CoxSey). The detailed electrochemical studies along with catalytic activities will be presented in the meeting.

Reference:

N. Jung, Y. H. Cho, M. Ahn, J. W. Lim, Y. S. Kang, D. Y. Chung, J. Kim, Y.H. Cho, Y.E. Sung, International J. of Hydrogen Energy, 2011, 36, 15731.

Figure 1
Influence of Temperature on the Shape Evolution of IrO2-SiO2 coating and Its Electrochemical Activity for Oxygen Evolution
Authors: Wang Qingfa , Zhang Xiangwen , Wang Li , Yangzhang Ruoping
Published: February 2020

The surface structure of IrO2-SiO2/Ti anode was modified by thermal decomposition of non-aqueous solution of iridium chloride (IrCl3) and tetraethoxysilane (TEOS) with different calcination temperatures. The surface morphology and microstructure of these anodes were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray-photoelectron spectroscopy (XPS). At low calcination temperature, the surface was dominated by biphase solid solution, in which the IrO2-rich phase, spiculate IrO2-SiO2 crystal, was encircled by the SiO2-rich phase, the amorphous SiO2­-IrO2 solution. As the calcination temperature increase, more amorphous IrO2 from the SiO2-rich phase converted into rutile nanothorn, then into nanoparticle composed by fine crystallites nanosheet aggregated on the surface of coatings and grew larger constantly. The electrochemical behaviors of the oxygen evolution reaction (OER) were evaluated by cyclic voltammetry (CV) and quasi steady-state polarization. The results showed that the electrocatalytic activities and the electrochemically active sites on the surface of the oxide electrodes for OER decreased with the increase of calcination temperature. This could be explained by the decrease of amorphous IrO2 and the surface active sites, such as surface OH groups and crystal edges. The onset potentials of IrO2-SiO2/Ti anode were significantly affected by the calcinations temperature. The onset potential of amorphous film was shifted toward the negative side from that of the crystalline ones. The Tafel slopes indicated that the electron charge transfer process is the rate determining step of IrO2-SiO2/Ti electrodes for the OER.
Electron Transfer Studies Between New Fad-Dependent Glucose Dehydrogenase and Different Osmium Polymers (Applications in Biosensors and Biofuel Cells)
Authors: Aslam Iqra , Zafar Muhammad Nadeem , Ludwig Roland , Leech Dónal , Gorton Lo
Published: February 2020

A new extracellular flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase from Glomerella cingulata (GcGDH) was electrochemically studied as a recognition element in glucose biosensors. The redox enzyme was recombinantly produced in Pichia pastoris, homogeneously purified and its glucose oxidizing properties on spectrographic graphite electrodes were investigated. Six different Os-polymers, the redox potentials of which ranging in a broad potential window between +15 and +489 mV vs. NHE, were used to immobilize and “wire” GcGDH to the spectrographic graphite electrode’s surface. The GcGDH/Os-polymer modified electrodes were evaluated by chronoamperometry using flow injection analysis.  The current response was investigated using a step-wisely increased applied potential. It was observed that the ratio of GcGDH:Os-polymer and the overall loading of the enzyme electrode significantly affect the performance of the enzyme electrode for glucose oxidation. The best suited Os-polymer [Os(4,4¢-dimethyl-2,2¢-bipyridine)2(PVI)Cl]+ had a potential of +309 mV vs. NHE and the optimum GcGDH:Os-polymer ratio was 1:2 yielding a maximum current density of 493 µAcm-2at a 30 mM glucose concentration.

Key words: Glucose dehydrogenase, FAD, Os-polymers, glucose biosensor, chronoamperometry, oxygen reactivity.
Empirical Insights into the CO2 Reduction Reaction Mechanism: A Study of the Reduction of CO2, CO and Formaldehyde on Cu Electrodes By Differential Electrochemical Mass Spectrometry
Authors: Javier Alnald , Chmielowiec Brian , Sanabria-Chinchilla Jean , Kim Youn-Geun , Baricuatro Jack Hess , Soriaga Manuel P
Published: February 2020

This work describes results from a first-ever attempt to employ differential electrochemical mass spectrometry (DEMS) of selectively pre-adsorbed reactants and (postulated) intermediates as a supplementary experimental approach in the study of electrocatalytic reaction mechanisms. For the specific case of the Cu-catalyzed electrochemical reduction of CO2, dilute solutions of CO2, CO and HCHO in aqueous KHCO3 were placed separately in a DEMS stationary thin-layer electrochemical cell in contact with a Cu electrode. Simultaneous faradaic-current (CV) and mass-spectrometric-current (MSCV) voltammograms were then obtained for each solution. The only reduction products detected by mass spectrometry were H2, CH4, H2C=CH2 and CH3CH2OH; CO was also assayed but only from the reduction of CO2.

The results prompt the following empirical inferences: (i) The slight but not imperceptible drop in the hydrogen-evolution current may not be caused by CO poisoning. It also exists for HCHO, a more feeble adsorbate, in the absence of the monoxide. In addition, the adsorption strength of H2 is four times greater than that of CO. (ii) CO is the first product of CO2 reduction, as well as the first intermediate in more advanced reactions that include formation of pure and oxygenated hydrocarbons; this is in conformity with the (almost) unanimously held view. (iii) HCHO is not a precursor for C=C double-bond formation. (iv) HCHO is a secondary intermediate for the production of methane and ethanol. (v) The generation of CH4 and CH3CH2OH from adsorbed CO occurs via two pathways: one requires a theoretically postulated surface species, CO protonated on the C atom, and the other involves adsorbed HCHO, constituted after the rate-limiting protonation step. (vi) The generation of CH4 and CH3CH2OH from CO has a much higher activation barrier than conversions from HCHO; not unexpected since the reactions transpire after the slow Cu–OCH+ formation and, consequently, are not highly activated.
Determination of Battery Stability with Advanced Diagnostics
Authors: Lamb Joshua , Orendorff Christopher J , Christophersen Jon
Published: February 2020

The increasing demand of lithium ion batteries for vehicle electrification is changing the typical use conditions that batteries may see. Over time, batteries may develop defects that are difficult to detect with traditional measurements. It is also possible that batteries may be left in an unknown state after failure of the monitoring system, loss of communication, or a potentially damaging event (such as an auto accident). It is therefore useful to explore other monitoring and interrogation methods that can better determine the stability of a battery in an unknown state. This work explores the use of electrochemical impedance spectroscopy as a method to determine the stability of batteries by observing changes in the complex impedance measurement as the cell is exposed to abusive conditions. Very dramatic changes to the internal resistance were observed when single cells were exposed to abusive conditions, suggesting that even single frequency impedance measurements could be effective with single cells. However tests on three cell series and parallel strings yielded smaller changes, primarily to the charge transfer resistance, showing that complex impedance measurements are more appropriate as the system increases in complexity. A rapid impedance tool developed at Idaho National Laboratory was tested and compared to traditional potentiostat tools as well. This was shown to yield similar data to the traditional tools, providing a potential method for continuous monitoring of a battery system. It was observed, however, that shifts in the data are difficult to detect in very transient systems.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Numerically Characterizing Nail Penetration Testing for Safety Evaluation of Li-Ion Cells
Authors: Yang Chuanbo , Kim Gi-Heon , Keyser Matthew , Pesaran Ahmad
Published: February 2020

Multi-physics modeling was performed for better understanding the nature of nail penetration testing. Nail penetration test is a mechanical abuse technique used to evaluate battery safety performance by inducing battery internal short circuits (ISC).  With specified battery chemistries and form factors, it has shown nail penetration results are affected by a number of test parameters, including battery sizes, short resistances caused by mechanical failure, nail penetration locations, speeds, depths, nail materials and diameters etc.  Due to the lack of sufficient understanding of relationships between testing parameters and outcomes, nail penetration test could give inconsistent results and is not able to provide desired reliability.

3D multi-physics modeling of nail penetration process was carried out to quantify testing parameter influence.  This objective is not feasible to be achieved by testing approaches, not only since nail penetration is a high dynamic process involving multi-physical behaviors, but measurement data is insufficient.  The model applied in this study is able to estimate battery dynamic responses under nail penetration tests by integrating a series of physical-based sub-models. The initial consequence of nail punch damage, short circuits, was addressed as an input variable.

Utilizing this model, outcome difference between a nail penetration test and a real ISC case scenario was identified. Simultaneous battery behaviors along nail movement in the battery were captured.  Parameter studies were conducted to quantify the effect of selected testing parameters, e.g. nail penetration speeds, depths and locations. The numerical results provide in-depth insights for understanding the nature of nail penetration testing and improve safety testing reliabilities.
Improve Battery Safety for Hybrid Electric Vehicles through Multi-Objective Optimization of Battery Design and Hybridization Level
Authors: Liu Changhong , Liu Lin
Published: February 2020

Balancing fuel consumption and battery safety is critical for hybrid electric vehicles (HEVs). Both hybrid power control strategies and battery design parameters can significantly affect battery degradation. Battery degradation is caused by the irreversible side reactions, which can lead to further safety issues. This paper aims to reduce battery degradation for HEVs through multi-objective optimization. The proposed approach adopts our reduced order electrochemical battery model to predict battery degradation (e.g, SEI layer growth and capacity loss) and estimate the battery state (e.g., State of charge and State of Health). Hysteresis phenomenon and temperature dependence are also considered in the battery model so as to predict heat generation and dynamic voltage response. Battery degradation is complicated and can be affected by various factors. Different battery design parameters (e.g., electrode thickness, particle size, and electrode porosity) have influence on battery degradation, energy density, and power density. In addition, hybrid power control strategy affects the hybrid power output from power sources i.e., hybridization level. Various strategies of using battery power can also influence battery degradation. Therefore, optimization of battery design parameters and hybridization level in HEVs are able to be mitigate battery degradation and improve battery safety. In this paper, a HEV is simulated under a standard driving cycle (e.g., FTP-72). Fuel consumption, vehicle drivability, and battery degradation are set as control objectives. In order to optimize the hybrid system, battery design parameters and hybridization level are iterated after each simulation until minimized battery degradation is found. Then, the corresponding design parameters and hybridization level are considered as the optimal results for battery design and power control strategy. Furthermore, optimal results under different driving cycles are investigated. The results of battery degradation and fuel consumption are also analyzed to show the overall optimization outcome for improving battery safety.
(Invited) Understanding the Role of Organic Alloys in Polymer-Fullerene Solar Cells
Authors: Thompson Barry C
Published: February 2020

While the efficiency of organic solar cells increases beyond 10%, it is still clear that there is much room for improvement in efficiency, lifetime, and cost-effective synthetic and fabrication approaches. We are investigating ternary blend solar cells based on two donor components and one acceptor component (or one donor and two acceptors), which have been recognized as a potential route to increase the absorption breadth of a solar cell and consequently the short-circuit current density. Recently, using a three-component system, we demonstrated for the first time that the open-circuit voltage of ternary blend solar cells is composition dependent and can be tuned across the full range defined by the corresponding limiting binary blends without negatively impacting the fill factor or the short circuit current. As a result, with judicious choice of components, the attainable product of short circuit current and open circuit voltage (and by extension the efficiency) in a single-layer ternary blend solar cell could be higher than is achievable with a standard binary blend solar cell. We have successfully demonstrated higher efficiencies in ternary blends based on two donor polymers and one fullerene acceptor than could be achieved in either of the limiting binary blends. It has become apparent in the systems we have investigated that the formation of so-called organic alloys is critical to the synergistic function of components in these ternary blends. Here, the electronic and physical structure of these organic alloys will be presented and the broader ramifications of organic alloys will be discussed. Efforts toward developing a deeper understanding of the mechanism of operation in these ternary blends will also be discussed.
Formic Acid Oxidation on Platinum- a Simple Mechanistic Study
Authors: Schwarz Kathleen , Sundararaman Ravishankar , Moffat Thomas , Allison Thomas
Published: February 2020

The oxidation of small organic acids on noble metal surfaces under electrocatalytic conditions is important in industrial processes and of scientific interest, but the basic reaction mechanisms continue to be a matter of debate.  Formic acid oxidation on platinum is one of the simplest of these reactions, yet even this model system remains poorly understood.  Historically, proposed mechanisms for the oxidation of formic acid involve the acid molecule as a reactant, but recent studies suggest that the formate anion is the key reactant instead. Ab initio studies of this reaction do not address formate as a possible reactant, due to the difficulty of calculating a charged species near a solvated surface under potential control.  Using the recently-developed Joint Density Functional Theory (JDFT) framework for electrochemistry, we perform ab initio calculations of this reaction on a Pt(111) surface to explore this reaction and help resolve the debate.  When a formate anion approaches the platinum surface with H pointing towards the surface, it reacts to form CO2 and adsorbed H with no barrier on a clean Pt surface at relevant voltages.  This mechanism explains the elusiveness of an active surface intermediate and leads to a reaction rate proportional to formate concentration and number of available platinum sites.  Additionally, high coverages of adsorbates lead to large reaction barriers, and consequently, we expect availability of pristine metal sites to limit the experimentally observed reaction rate.
Nano-Impact Electrochemistry for Assessing the Chemical Reactivity of Nanoparticles
Authors: Karimi Anahita , Andreescu Daniel , Andreescu Silvana
Published: February 2020

The electrochemical study of particle impacts on electrode is a rapidly developing field which provides the extensive capabilities of nanoparticle detection and characterization. It has demonstrated significant promise for quantification of nanoparticles and characterization in terms of nanoparticle coatings and catalytic activity. In this presentation, we describe the development of an electroanalytical collision technique to characterize the fundamental surface properties, functionalization and redox reactivity of metal and metal oxide nanoparticles by nano-impact electrochemistry.  We will demonstrate the potential of this method: (1) as a screening tool of particle reactivity, (2) study of the adsorption/desorption of environmental contaminants with single particle resolution, and (3) extract mechanistic information that would be predictive of the chemical reactivity of nanoparticles for various applications. We will discuss the potential of this approach to complement or replace costly characterization techniques and enable routine study of nanoparticles and their reactivity.
Towards Efficient and Acidically Stable Dye-Sensitized Photocathodes for Solar Fuels
Authors: Wu Yiying
Published: February 2020

Photocatalytic water splitting is an attractive approach for converting intermittent solar energy into clean fuels. Tandem dye-sensitized photoelectrichemical cells mimic the Z-scheme in photosynthesis by integrating a dye-sensitized photoanode (DSPA) with a dye-sensitized photocathode (DSPC). However, the tandem design is limited by two main factors: efficiency mismatch between DSPA and DSPC, and electrode instability under long-term operation. In this talk, I will talk about our recent progress in the design of dye and molecular catalysts towards efficient and acidically stable DSPC for photocatalytic water reduction into hydrogen. With our newly developed molecules, we have demonstrated an increase of photocurrent by ~2 orders of magnitude and stable operation in aqueous solutions with pH down to zero.
Efficient Solar-to-Hydrogen Production Materials and Devices
Authors: Wang Heli , Ager Joel W. , Gaillard Nicolas , Miller Eric Lars
Published: February 2020

Renewable hydrogen production via water splitting needs to tackle the challenges of high solar-to-hydrogen (STH) efficiency and high stability of the materials and devices. For photoelectrochemical (PEC) water splitting, semiconductor materials’ band gap, band edge, optoelectronic efficiency, and stability must be satisfied simultaneously to tackle the challenge.

With over five decades of research, different materials and devices have been studied and explored. STH efficiencies of metal oxides have been limited by issues related to the wide band gap, absorption, charge mobility, recombination, interfacial kinetics, etc., those the material class may be stable. Thin films (like III-V and CIGS) offer alternative pathways to efficient STH conversion, with stability remains an issue.

On the other hand, structures and configurations have been developed for unbiased PEC water splitting, mostly in laboratory scale. This presentation will address semiconductor materials, structures and devices developed for solar hydrogen production.
Photoelectrochemical Solar Energy Conversion and Electrocatalysis Using Earth-Abundant Nanomaterials
Authors: Jin Song
Published: February 2020

The scale of renewable energy challenge not only calls for highly efficient technologies but also abundant, inexpensive, and robust materials. Nanomaterials can help to mitigate the poor properties of earth-abundant semiconductors and catalysts to enhance solar energy conversion. We have controlled the nanostructures and polymorphs of layered MS2 (M = Mo, W) materials and other earth-abundant metal chalcogenides, such as metallic cobalt pyrite (CoS2), to significantly enhance their catalytic activity in hydrogen evolution reaction (HER). We further establish ternary pyrite-type cobalt phosphosulfide (CoPS) as a high-performance earth-abundant HER catalyst that achieves geometrical catalytic current density of 10 mA/cm2 at overpotentials as low as 48 mV with outstanding long-term operation stability. These earth-abundant catalysts and semiconductors have been integrated to enable efficient solar energy conversion. Integrated photocathodes of the novel earth-abundant catalysts on n
+-p-p
+ silicon micropyramids achieved high photocurrents up to 35 mA/cm2 and onset photovoltages as high as 450 mV vs RHE, and 5-6% solar-to-hydrogen conversion efficiency.
(Europe Section Heinz Gerischer Award) A Perspective of Photoelectrochemistry: Past Expectations and Present Realities
Authors: Heller Adam
Published: February 2020

It was Heinz Gerischer who got me interested in and taught me semiconductor electrochemistry when he visited me just after the Oil Crisis of 1973. He, I and later many others dreamed of a world powered by semiconductor-liquid junction solar cells, hoping that that these would be simpler and cheaper than the silicon p-n junction solar cells that powered at the time communication satellites, remote terrestrial communication relays, wristwatches, calculators and other portable electronic devices.  By 1981 research on the semiconductor -liquid junctions led to the uncovering of truths of nature and to 12 % solar conversion efficiencies, both to electrical power and in the generation of hydrogen. However, I did not see how efficient photo-electrochemical conversion  could provide a technological edge over all-solid silicon and thin-film solar converters, because their packaging cost were lower and their stability was superior.  After 34 years of fine research leading to solar conversion efficiency now at 20 %, packaging cost and stability still prevent photo-electrochemical solar converters from being preferred over all solid solar cells.

In the absence of technologically relevant semiconductor-liquid junction based solar converters we joined Akira Fujishima and Kazuhito Hashimoto in their quest for technologically relevant photo-catalytic surfaces that clean themselves of accumulating organic grime by catalyzing its air oxidation. On the fundamental side, the truth that Heinz Gerischer and I uncovered during his repeated stays at the University of Texas in Austin has been that the rate of the n-TiO2 –photo-catalyzed O2 oxidation of organic matter was not controlled by the rate of photo-generation of holes, but by the rate of reduction of adsorbed O2 by trapped electrons.  On the practical side, we developed photo-stable binders that allowed the incorporation of photo-catalytic n-TiO2 in coatings; and a method of producing self-cleaning window glass.
Surface Chemistry of Electrocatalysts for CO2 Reduction to Fuels
Authors: Kronawitter Coleman X. , Chen Zhu , Zhao Peng , Koel Bruce E.
Published: February 2020

The surface chemistry of electrocatalysts for the production of fuels by CO2 reduction was explored by surface science model studies using high-resolution spectroscopy and atomic scale imaging, as well as by electrochemical analysis of active electrodes. Using an experimental surface science approach, ultrahigh vacuum conditions were used to facilitate the fabrication of highly characterizable electrode-adsorbate systems. We have utilized a range of techniques for surface analysis to determine the structure and properties of single-crystal surfaces and unique alloys formed by vapor deposition under controlled conditions. Specifically, XPS, LEIS, LEED and STM were used to characterize the composition and structure of III-V semiconductors and bimetallic model catalysts. TPD, UPS, and vibrational spectrocopy using HREELS and IRAS were used to study the binding and electronic structure of adsorbates.

Many of our experiments are designed to explain the role of the electrode surface in the high selectivity observed in pyridine and other N-heterocycle-catalyzed CO2 reduction systems. We examined the preferential adsorption sites, bonding interactions, and reactivities of these molecular catalysts and other relevant adsorbates on the surfaces of photoactive electrode materials. Ambient pressure photoemission spectroscopy (APPES), STM, and vibrational spectroscopies were used to study the interaction of water and CO2 reduction catalysts with the surfaces of III-V semiconductors.

We have applied these techniques to also study bimetallic alloy electrocatalysts.  Bimetallic alloys have been shown to exhibit lower overpotentials for CO2 reduction to fuels when compared to their metal constituents.  By tuning the composition of the alloys, one can influence the binding of adsorbates and therefore reaction selectivity.  We synthesized bimetallic surface alloys in controlled UHV environments to investigate the relationship between surface composition and electronic structure.  We studied the interaction of relevant adsorbed species with the bimetallic alloy surfaces using TPD, IRAS, HREELS, and UPS to begin to understand the surface chemistry of these electrodes.

In parallel to these surface science investigations, we studied the electrochemical behavior of single crystals and bimetallic alloys.  The purpose of these studies is to correlate CO2 reduction product selectivity to the quantitative measurements of surface chemistry made in UHV discussed above.  Specifically we examined the relationship between electrochemical activity, surface composition, and the binding strengths of intermediates along CO2 reduction pathways. This work aids development of a molecular-level understanding of the heterogeneous processes involved the reaction mechanisms of efficient electrocatalytic fuel generation.

This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012455.
Photocatalytic Coversion of CO2 By H2o As an Electron Donor Using Various Solid-State Photocatalysts
Authors: Teramura Kentaro
Published: February 2020

The use of heterogeneous photocatalysts to reduce CO2 into storable feedstock is of particular interest because of its simplicity and low cost of operation. We have reported that CO as a main product is obtained for the photocatalytic conversion of CO2 in the presence of H2 over ZrO2, MgO, ATaO3 (A = Li, Na, and K), and Ga2O3, of which Ga2O3 exhibited the highest conversion of CO2: 7.8% over 48 h of photoirradiation. Unfortunately, these bare metal oxides function as photocatalysts in the presence of H2O not for reduction of CO2 but for overall water splitting. As of late, we found that Zn-doped, Ag-modified Ga2O3 exhibits higher formation rate of CO and selectivity toward CO evolution than bare, Ag-modified Ga2O3 for the photocatalytic conversion of CO2 by H2O as an electron donor.  An isotope experiment using 13CO2 and mass spectrometry clarified that the carbon source of the evolved CO is not the residual carbon species on the photocatalyst surface, but the CO2 introduced in the gas phase. In addition, stoichiometric amounts of evolved O2 were generated together with CO. Only in recent years, XAFS measurement identified that ZnGa2O4 is generated on the surface of Ga2O3; therefore, it suppresses the evolution of H2, which results in the higher selectivity toward CO evolution.
Mathematical Modeling of Solar-Fuel Generators
Authors: Stevens John , Xiang Chengxiang , Singh Meenesh , Chen Yikai , Weber Adam Z
Published: February 2020

A solar-fuel generator is a multicomponent device composed of light absorbers, electrocatalysts, membranes, and electrolytes in a specific system geometry.  The overall solar-to-fuel conversion efficiency of such a system depends on the performance and materials properties of the individual components as well as the design of the system. In this talk, efforts in the Joint Center for Artificial Photosynthesis (JCAP) aimed at the continuum-scale modeling of these various components will be presented. In particular, the tradeoffs between the transport phenomena, kinetics, and photon capture will be detailed for different geometries and conditions. For example, the use of optically concentrating lenses can result in efficiency gains and lower cost systems, although the increased temperatures have both beneficial (e.g., transport properties and kinetics) and detrimental (light absorber efficiency and solvent stability) impacts that are ideally optimized through modeling. In addition, applications of the modeling framework to both hydrogen generation via water splitting and fuel formation via carbon reduction will be discussed, where the product distribution of the latter is heavily influenced by the local electrode overpotential.
SnO2 and F:SnO2 Inverse Opal Based Photoelectrochemcial Water Splitting
Authors: Kang Soon Hyung
Published: February 2020

Nowadays, the exploration of new photoelectrode architectures to improve the light-harvesting and charge-collection properties of photoelectrochemical cells and related devices have been regarded as a challenging work. Here, we synthesized the inverse opal SnO2 for photoelectrochemical water splitting by the spin-coating method exploring the polystyrene beads with a size of approximately 350 nm. The SnO2 inverse opal structure shows the photonic crystal effect with a well-ordered hexagonal structure packing. Upon this film, the photoactive TiO2 layer with various thicknesses from 10 nm to 40 nm was deposited by atomic layer deposition. Herein, it is expected that an optimal TiO2 layer takes part in a role as a photoactive material. Adding to these results, the F doping on the SnO2 inverse opal film was also examined with the TiO2layers. These results were confirmed using Field-emission scanning electron microscopy, X-ray diffraction and ultraviolet-visible spectrophotometer. Detail results and discussion would be presented.

Figure 1
Guiding Practical Pathways for Photo-Electrochemical Solar-Hydrogen Generation
Authors: Haussener Sophia , Dumortier Mikael
Published: February 2020

Photo-electrochemical electrolysis of water provides a direct pathway for the conversion of solar energy into an energy-dense, storable and transportable fuel. The practical implementation of photo-electrochemical approaches requires focusing simultaneously on four key developmental concerns: device and system i) efficiency, ii) durability and reliability, iii) environmental sustainability, and iv) scalability with economic viability.

We developed a techno-economic model and coupled it to a life cycle assessment (LCA) in order to jointly assess efficiency, hydrogen cost, energy input, and lifetime/degradation of photo-electrochemical devices. The model we used accounted for optical losses in the concentrator, recombination and resistive losses in the photoabsorbers, overpotentials in the electrocatalysts (including mass transport limitations, relevant at high irradiation concentrations), as well as photoabsorber and electrocatalytic degradation. The sustainability assessment accounted for the energy input required for material mining and manufacturing of the device components, as well as operation. The cost assessment accounted for material and component cost and manufacturing. The model was used to investigate and compare a class of 16 devices: combinations of devices using i) concentrated or non-concentrated irradiation (irradiation concentration, C), ii) low quality Si-based or high quality III-V-based photoabsorbers, iii) earth abundant or rare electrocatalysts, and iv) integrated photoabsorber and electrocatalyst with the same or different absorber and electrolysis area (current concentration, F).  

The results predict that maximum efficiency does not guarantee minimum hydrogen price or minimum energy demand, as depicted in figure 1 for a selection of devices. Devices using large irradiation concentration and III-V-based photoabsorbers showed low hydrogen prices and best efficiencies while non-concentrating devices using Si-based photoabsorbers and rare electrocatalysts showed slightly higher energy demand and hydrogen price. An increase in the component’s lifetime was generally beneficial to efficiency, cost, and energy demand. Degradation significantly influenced all three characteristics, and the calculations provided guidance for the most suitable exchange time of individual components – keeping overall device efficiency high while reducing energy and cost resulting from component exchange – during the lifetime of the complete device.

The coupled techno-economic-ecologic approach provides quantitative design guidelines for photo-electrochemical devices and can support decision-making for the implementation of large-scale, sustainable and competitive solar hydrogen production.

Figure 1
Benchmarking Nanoparticulate Metal Oxides for the Alkaline Water Oxidation
Authors: Jung Suho , McCrory Charles C L , Peters Jonas C , Jaramillo Thomas F
Published: February 2020

Nanoparticulate metal-oxide catalysts are among the most prevalent systems for alkaline water oxidation. However, comparisons of the electrochemical performance of these materials has been challenging due to the numerous methods of attachment and catalyst loadings used in the literature.  Herein, we have identified a conventional drop-casting method that ensures adhesion of the catalysts and consistently applied to a variety of metal oxides for water oxidation reactions in alkaline condition.  The nanoparticulate materials were characterized using XRD, XPS, BET, and SEM.  The activity and Tafel slopes of the nanoparticulate catalysts attached by this method have been compared directly to similar systems synthesized by different methods such as electrodeposition, sputtering, etc.  A brief discussion of the differences and similarities in the surface area as measured by BET and determined from the double-layer capacitance of the system is also provided.
Enhanced Production of Solar-Fuels By Plasmonic Metal/Semiconductor Photocatalyst Heterostructures
Authors: Bright Joeseph , Li Jiangtian , Cushing Scott Kevin , Chu Deryn , Wu Nianqiang
Published: February 2020

Earth’s dependence on fossil fuels for providing the majority of the world’s energy is problematic due to the finite nature of fossil fuels and the release of greenhouse gases and other pollutants during their combustion. As such, sustainable, carbon-neutral fuels are needed as a long-term replacement for fossil fuels. One promising approach is direct solar energy-to-chemical fuel conversion by photocatalysis. Examples of fuels produced include H2 from photocatalytic water splitting or photocatalytic reduction of CO2 to methanol or methane. However, current photocatalyst materials suffer from a combination of problems such as poor charge carrier lifetimes and mobility, poor photostability in water, wide bandgaps that allow only UV light absorption, and/or an inactive surface for carrying out redox reactions. Forming heterostructures made of plasmonic metals (i.e. Au, Ag, or Cu) and semiconductor photocatalyst materials can serve to enhance overall photocatalytic performance versus the photocatalyst alone. This enhancement comes from photonic mechanisms like visible or NIR light absorption or scattering by plasmonic metal nanostructures and plasmonic enhancement mechanisms of direct transfer of “hot” electrons from the plasmonic metal to the photocatalyst and plasmon-induced resonant energy transfer from plasmonic metal to photocatalyst through dipole-dipole interactions. This poster summarizes our latest research on determining the nature of these enhancement mechanisms and progress towards high efficiency photocatalytic production of solar-fuels.
Sol Gel Dip Coated Yb and Tm Doped Indium Oxide Dye Sensitizrd Solar Cells
Authors: Murali Kollegal Ramakrishna
Published: February 2020

In2O3 thin films were deposited by the sol gel dip coating method adopting the following procedure. Clean ITO substrates were used for the deposition of the films. 10 ml of 0.33 M solution of Indium (III) nitrate was taken in a clean glass beaker. The solution was heated to 70˚C and the pH was brought to 9 by the addition of ammonia, then 1 gm of Acrylamide was added followed by the addition of 0.25 gm of N,N,bis methylene acrylamide. After 20 min, 5 mg ammonium persulphate initiator was added to  this mixture. The solution became viscous. Cleaned microglass slides (2.5 cm x 7.5 cm) were immersed into the viscous solution and withdrawn at the rate of 1cm min-1. The film formed on the surface was dried in an air oven for about 15 min followed by annealing in air at different temperatures in the range of 350 - 500˚C for different durations in the range of 15 min to 90 min. Doping with Tm and Yb was done by adding 0.1 g of Yb(NO3)3 and 0.1 g of Tm(NO3)3 to the Indium nitrate solution before gelling. The doped and undoped films were dipped in N719 dye for 24 hours. a sandwich structure was formed by bonding the FTO substrate with dye coated In2O3 and a Pt counter electrode together through a hot-melt spacer, and a drop of electrolyte (0.60 M 1-butyl-3-methylimidazolium iodide (BMII), 0.03 M I2 was injected into the device through predrilled holes on the Pt counter electrode. DSSCs based on In2O3:Yb and In2O3:Tm were also fabricated via the same process.

The XRD patterns of the In2O3, In2O3:Tm and In2O3:Yb. . All the patterns can be assigned to cubic phase standard card (JCPDS 06-0416) without any additional diffraction peaks. The UV–vis absorption spectra of the doped and undoped In2O3 exhibit the absorption peak of the pure In2O3 about 3.85 eV, which is consistent with the results published, and it icreases to 3.93 eV and 4.00 eV respectively as Tm and Yb are doped into In2O3.

            The J-V characteristics of the doped and undoped Indium oxide films indiacted that the Voc increased from 410 mV for undoped films increased to 530 mV and 630 mV for Tm and Yb doped films respectively. The Jsc increased from 2.45 mA cm-2 for the undoped films increased to 3.50 mA cm-2 and 4.25 mA cm-2 for Tm and Yb doping respectively.IPCE measurements indicated that for doped films the PCE was higher than that of undoped films. The fill factor of the films increased by doping with Tm and Yb. The larger Voc obtained with Yb doping can be explained on theb basis that the conduction band edge of Yb doped films is higher than that of undoped and Tm doped Indium oxide.
Electroreduction of CO2 to Synthesis Gas and Hydrocarbons on Doped Carbons
Authors: Varela Ana Sofia , Strasser Peter
Published: February 2020

Strategies to close the anthropogenic carbon cycle through a renewable energy-driven efficient chemical conversion of CO2 into usable chemical feeds have become a scientific priority. Conversion of CO2 rich streams from steel mills, concrete- or coal-fired power plants, into syn-gas alcohols or hydrocarbons is of tremendous interest for industry. Of all chemical ways to convert CO2 into hydrocarbons, the electrocatalytic coupling of water splitting and CO2 reduction appears attractive, as it is  a one-step process step, occurs at ambient  temperature and pressures, involves solely water and CO2 as reactants, and may involve renewable electricity from wind, solar or hydro power plants.

CO2 electroreduction is typically carried out on the surface of metal catalysts. Cu catalysts generate various gas products such as H2, CO, methane and ethylene, while Au and Ag are the catalysts of choice for the selective electroreduction of CO2 into CO/H2 synthesis gas mixtures. On all metal catalysts the CO2 electroreduction suffers from prohibitively high kinetic overpotentials and limited product selectivity. This is why the identification of new catalysts or new catalyst formats, such as nanoparticles or core shell architectures, with reduced overpotentials combined with the exploration of new strategies to control and improve product selectivities has become the two key goals for CO2 reduction.

In this contribution, we share recent work on the electroreduction of CO2. In particular, we discuss a family of heteroatom-doped carbon catalysts for the generation of synthesis gas. We show evidence that carbon catalysts meet and exceed the activity and selectivity of traditional Au catalysts providing an intriguing cost-effective alternative.
Fully Integrated Stand-Alone Device for Gas-Phase CO2 Reduction Using Sunlight: Proof of Concept
Authors: Arab Mobin , Church Tamara L. , Li Xiaobo , Maschmeyer Thomas , Minett Andrew I.
Published: February 2020

The conversion of CO2 to fuels can be a promising pathway to reduce the carbon intensity of the economy, if the energy required for its conversion is supplied from renewable sources. We showcase a fully integrated, wireless, stand-alone unbiased photoelectrochemical cell (PEC) for the conversion of CO2 and H2O to chemicals and fuels in gas phase. Simulated sunlight at 1 Sun intensity is used to drive the conversion reaction. Proof-of-concept experiments show that the device is operational in dilute CO2 streams (10% CO2, 2% H2O, Ar balance) as well as in concentrated CO2 streams (98% CO2, 2% H2O). With a Cu sheet as the cathode catalyst, the device offers a CO2 reduction selectivity of ~50%; when Cu2O nanorods are employed, the selectivity toward CO2 reduction increases to ~90%. Experiments related to improving the performance of the device, testing other catalyst materials, and detecting the products is ongoing. The cell is lightweight, built of earth-abundant materials, and easy to assemble and scale. Further, it operates in dilute CO2 streams and the gas-phase operation facilitates the separation of liquid products. Thus the device represents a promising avenue toward the direct conversion of CO2 from flue gas or even air, without the need to first capture the CO2.

Figure 1- Chronoamperometry experiments when the device is under interval illumination with difference cathode materials; a) Cu2O Nanorods, b) Cu sheet.

Figure 1