bluuebunny/crossref_metadata_2025 huggingface dataset:
Colossal Pseudocapacitance in a High Functionality - High Surface Area Carbon Anode Doubles the Energy of an Asymmetric Supercapacitor
Authors: Mitlin David
Published: February 2020

Here we demonstrate a facile template-free synthesis route to create macroscopically monolithic carbons that are both highly nitrogen rich (4.1-7.6 wt.%) and highly microporous (SA up to 1405 m2 g-1, 88vol% micropores). While such materials, which are derived from common chicken egg whites, are expected to be useful in a variety of applications, they are extremely promising for electrochemical capacitors based on aqueous electrolytes.  The Highly Functionalized Activated Carbons (HFACs) demonstrate a specific capacitance > 550 F g-1 at 0.25A g-1 and > 350 F g-1 at 10 A g-1 in their optimized state. These are among the highest values reported in literature for carbon-based electrodes, including for systems such as templated carbons and doped graphene. We show that HFACs serve as ideal negative electrodes in asymmetric supercapacitors, where historically the specific capacitance of the oxide-based positive electrode was mismatched to the much lower specific capacitance of the opposing AC. An asymmetric cell employing HFACs demonstrates a 2X higher specific energy as compared to the one employing a state-of-the-art commercial AC. With 3.5 mg cm-2 of HFAC opposing 5.0 mg cm-2 of NiCo2O4/graphene, specific energies (active mass normalized) of 50 Wh kg-1 at 230 W kg-1 and 28 Wh kg-1 at 1900 W kg-1 are achieved. In terms of volumetric energy density, the improvement is 4X, with the energy density of an asymmetric cell being 76.3 Wh L-1 versus 18.3 Wh L-1 of the symmetric cell. The asymmetric cell performance is among the best in literature for hybrid aqueous systems, and actually rivals cells operating with a much wider voltage window in organic electrolytes.
Understanding and Controlling of Solution Chemistry of Lithium Polysulfide to Enable High Energy Li-S Redox Flow Battery
Authors: Pan Huilin , Wei Xiaoliang , Henderson Wesley A , Chen Junzheng , Shao Yuyan , Xiao Jie , Liu Jun
Published: February 2020

Large-scale energy storage has become an important topic for the modern life. The identification of high energy and low cost energy storage and conversion technologies for stationary applications has gained intensive research interest in recent years. Lithium sulfur (Li-S) redox flow battery is one of the most promising candidates. Fundamental understanding and controlling of polysulfide chemistry were explored to enable high energy Li-S redox flow cells. Different from static Li-S batteries targeting for vehicle electrification, high solubility of all lithium polysulfide generated at different depth of discharge and state of charge is preferred in flow battery in order to take full advantage of multiple electron transitions between S and Li2S. A new kind of DMSO based electrolyte was first proposed for Li-S redox flow batteries, which not only enable high solubility lithium polysulfide species, especially for the short-chain species, but also stabilize excellent cycling with high Coulombic efficiency. Challenges and opportunities existing in the Li-S redox flow concept have also been discussed in detail.
(Invited) Recent Progress in the Study of Single Molecule Electrochemistry Using Surface-Enhanced and Tip-Enhanced Raman Spectroscopy
Authors: Van Duyne Richard P
Published: February 2020

During the last few years, there has been an explosion of interest and activity in the field of plasmonics. The goal of plasmonics is to control and manipulate light on the nanometer length scale using the properties of the collective electronic excitations in noble metal films or nanoparticles, known as surface plasmons. An improved understanding of the interactions between adsorbed molecules and plasmonic nanostructures (i.e., molecular plasmonics) is having a significant impact in a number of research areas including electrochemistry, surface science, catalysis for energy conversion and storage, the materials science of nanoparticles, biomedical diagnostics, art conservation science, and nanolithography.

            In the first part of this lecture, I will provide some background material on the basic physical concepts underlying molecular plasmonics with an emphasis on surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR) spectroscopy, and tip-enhanced Raman spectroscopy (TERS).

            In the second part of this lecture, I will focus in on our most recent work in studying single molecule electrochemistry using surface-enhanced and tip-enhanced Raman spectroscopy. I will first describe the development of an instrument that has the capability of combining tip-enhanced Raman spectroscopy at the solid/liquid interface with scanning electrochemical microscopy (SECM). Next the single molecule Raman spectroelectrochemistry of Rhodamine 6G (R6G) at acetonitrile/Ag interface will be discussed. Finally, I will discuss the path forward toward the goal of understanding heterogeneous electron transfer at the single molecule level.
(Invited) Bioelectrocatalytic Oxidation of Sucrose with an Enzyme Cascade Assembled on a DNA Scaffold
Authors: Minteer Shelley D.
Published: February 2020

Over the last decade, there has been substantial research focused on multi-enzyme cascades as anodic catalysts to improve the performance of enzymatic biofuel cells, as it allows for the conversion of more chemical energy stored in complex fuels. However, the performance of these enzyme systems is often limited by the mass transport of intermediate substrates between enzymes. Nature addresses this issue by organizing metabolic enzymes in a sequential and proximal manner to enhance the efficiency of metabolic pathways. In this work, we investigate the utilization of DNA as a structural scaffold for the assembly of the invertase/glucose oxidase enzymatic supercomplex to improve sucrose bioelectrocatalytic activity. It has been found that the DNA-assembled enzyme cascade has higher activity than the free cascade, both in solution and in the immobilized state on a bioanode surface. The organization of the enzyme cascade on the DNA scaffold leads to a 100% increase in the current density in amperometric measurements for a sucrose biosensor and a 75% increase in the power density of the biofuel cell. This is the first evidence of the advantages of utilizing DNA scaffords for improved bioelectrocatalysis.
Contact Lens Biofuel Cell Tested in Conditions Similar to Human Eyes
Authors: Reid Russell C , Minteer Shelley D. , Gale Bruce K.
Published: February 2020

Researchers in recent years have begun developing “smart” contact lenses for biomedical applications or for wearable electronic displays. Most of these devices require an external power source, which can be cumbersome, especially to people with an active lifestyle. In this work, we describe a biofuel cell contact lens prototype, which could someday replace external power sources for contact lens devices. Our first-generation prototype consisted of buckypaper electrodes with a poly(methylene green)/NAD+/lactate dehydrogenase anode and a bilirubin oxidase cathode (Fig. 1). These electrodes were molded into a silicone elastomer contact lens, and the prototype was tested in synthetic tears, both in vitro and on a test stand that mimicked eye conditions. The open circuit voltage was 0.413 ± 0.06 V and the maximum current and power density were 61.3 ± 2.9 µA cm-2 and 8.01 ± 1.4 µW cm-2, respectively. A COMSOL model was created and subsequently used to determine better electrode size and arrangement. These model results guided the design and fabrication of a second-generation contact lens biofuel cell, which showed improved performance compared to the first-generation lens.

Fig. 1. Contact lens biofuel cell prototype. Modified buckypaper electrodes were integrated into a silicone elastomer lens. Connecting leads can be seen extending to the right.

Figure 1
Mixed Ionic / Electronic Conductivity of Electrolyte-Modified Carbon/Zirconia Composites
Authors: Shetzline Jamie A , Creager Stephen
Published: February 2020

A recently developed method for independently obtaining electronic and ionic contributions to electrical conductivity was used to study conductivity in thin-film samples of carbon/zirconia nanocomposite materials for which molecular and polymer electrolytes were covalently grafted onto the carbon/zirconia particle surfaces. The method relies upon careful control of the nature of the contact between the sample and the current-carrying electrodes. Electronic conductivities are derived from currents obtained when using electronically-conductive glassy carbon electrodes to contact the sample, whereas ionic conductivities are derived from currents obtained when using ionically-conductive Nafion electrodes to contact the sample. Carbon / zirconia samples were prepared from zirconia sol precursors combined with RF carbon aerogels and also with carbon black to produce carbon containing integrated zirconia.  Solution-phase treatment with molecular electrolytes containing organo-phosphonate groups resulted in electrolyte attachment via zirconia-phosphonate binding.  Thin-film samples of the resulting electrolytes were prepared and their mixed electronic and ionic conductivity studied as functions of temperature and relative humidity
Accumulation of Naturally-Occurring Radionuclide Polonium-210 By Phytoplankton in Urban Sea Bays
Authors: Peydus Daniel , Lazorenko Galyna Evdokymovna , Mychanov Vladimir Sergeevich
Published: February 2020

Polonium-210 (210Po) is most available naturally occurring isotope of the polonium radionuclide with the half-life time of about 138 days. It forms in the result of 238U-226Ra decay series is 100% alpha-radioactive. These make 210Po convenient for research purposes. Polonium is an extremely toxic element. Because of its self-heating and subsequent transformation into aerosol forms, it is dangerous even at distances far exceeding the range of alpha-particles. Therefore, understanding of 210Po distributions in populated areas is an important environmental topic.

Polonium finds its path into sea basins from the atmosphere and various water systems. In the marine environment it connects with the organic matters and eventually enters into seafood chains. First organisms accumulating polonium relate to phytoplankton.

The present paper reports 210Po distributions have been studied in the Sebastopol bay of the Black sea. The water samples were collected using phytoplankton nets from surface levels of water in the bay. The collection was conducted at three fixed stations and on board of a research vessel at different locations.

The obtained water samples were filtered through the nitro cellular membranes “Sartorius” with the pore diameter 1.2 um. The membranes were dried and the mass of phytoplankton was measured. Polonium was extracted from phytoplankton radiochemical means. Then polonium was deposited on disks made of silver foils. 210Po concentrations were measured using an alpha-spectrometer.
Electrochemical Properties of Bi(111)|1-Ethyl-3-Methylimidazolium Tetracyanoborate and 1-Ethyl-3-Methylimidazolium Iodide Interface
Authors: Siimenson Carolin , Siinor Liis , Lust Enn
Published: February 2020

Room temperature ionic liquids (RTILs) can sustain substantially higher cell potentials (ΔE) in electrochemical cells without decomposing. For electrochemical double layer capacitors (EDLCs) the widening of the cell potential increases exponentially the energy and power densities. RTILs can be use as electrolytes in modern electrochemical energy devices, such as capacitors, solar cells, batteries and fuel-cells. 1–4

In this work the cyclic voltammetry and electrochemical impedance spectroscopy methods have been applied to investigate the electrical double layer formation and adsorption kinetics parameters of iodide anions at the electrochemically polished Bi(111) electrode surface. The ionic liquid solution was prepared in order to increase the differential capacitance of the system. Therefore 1 wt% 1-ethyl-3-methylimidazolimu iodide (EMImI) was added to 1-ethyl-3-methylimidazolium tetracyanoborate (EMImTCB).

Analysis of current density (j) vs. electrode potential (E) dependencies shows that the Bi(111) electrode is ideally polarizable within the potential range from -1.0 to -0.2 V for 1 wt% vs. Ag| AgCl.

The measured ideal polarizability region is in a good agreement with impedance data. The mixed kinetic processes take place on both systems (Bi(111)|EMImTCB and Bi(111)|EMImTCB + 1%EMImI). Higher capacitance values were obtained for the Bi(111)|EMImTCB + 1%EMImI system. Our recent studies have shown that the addition of specifically adsorbed iodide ions strongly influence the electrochemical characteristics of RTILs systems. 1

Acknowledgments: This study was partially funded by the Estonian Science Foundation Grants 7791, 8357 and 8786, Estonian Energy Technology Program project SLOKT10209T, Estonian Basic Research project SF0180002s08 and Estonian Centers of Excellence in Science project: High-technology Materials for Sustainable Development TK117

References:

1. C. Siimenson, L. Siinor, K. Lust, and E. Lust, J. Electroanal. Chem., 730, 59–64 (2014).

2. T. Tooming et al., J. Electrochem. Soc., 161, A222–A227 (2014).

3. L. Siinor, J. Poom, C. Siimenson, K. Lust, and E. Lust, J. Electroanal. Chem., 719, 133–137 (2014).

4. L. Siinor, K. Lust, and E. Lust, Electrochem. Commun., 12, 1058–1061 (2010).
Electrochemical Activity of Titanium Dioxide Toward Oxygen Reduction and Evolution Reactions
Authors: Tavassol Hadi , Haile Sossina M
Published: February 2020

We report on the electrochemical activity of TiO2 polymorphs toward oxygen reduction and evolution reactions in a CsH2PO4 solid acid electrochemical system. Oxygen reduction and evolution are catalytically challenging reactions relevant to the fuel cell and water splitting applications. Because of the strong O=O bond, oxygen reduction is a slow reaction even on a Pt surface. In fuel cells, the oxygen reduction reaction (ORR) requires high loadings of the precious Pt catalyst. Even at the operating temperature of the super-protonic CsH2PO4 solid acid, ca. 240 °C, the ORR remains sluggish.

Titanium dioxide has been studied extensively as a promising, low cost (photo)catalyst for water splitting. TiO2 activity toward oxygen led us to examine its catalytic performance for the oxygen reactions in the CsH2PO4 electrochemical system. Solid state TiO2 catalysts on carbon based supports show a range of activity depending on the relative ratio of the rutile to anatase polymorphs. Rutile phase exhibits a lower overpotential for the ORR. The activity of the catalysts are also controlled by the type of the carbon based interconnects used in the fabrication of the composite electrodes. Interconnects facilitate the interaction between CsH2PO4 and TiO2 particles. Catalysis only occurs on TiO2 particles that are connected to the CsH2PO4 electrolyte, and are also accessible to the O2 gas. We will discuss the selective activity of pure and mixed phases of TiO2 rutile and anatase polymorphs toward oxygen reduction and evolution reactions.
Enhancement of Water Oxidation at Tungsten Oxide Photoanodes Doped with Borotungstate-Polyanion Modified-Hematite
Authors: Miecznikowski Krzysztof , Ramirez-Caro Alejandra , Fiechter Sebastian , Kulesza Pawel J
Published: February 2020

A procedure based on sol-gel aggregation for the fabrication of mesoporous WO3 photoanaodes was adopted to produce the doped oxide films by admixing the tungstic acid sol with Keggin-type borotungstic acid (H5BW12O40) or the borotungstic acid–stabilized hematite (Fe2O3).  Such physicochemical properties as structure, morphology and spectroscopic identity of the resulting hybrid (doped) WO3 films were assessed using X-ray diffraction, scanning electron microscopy, as well as UV-Vis and Raman spectrocopies.  When using a solar cell system operating in 0.5 mol dm-3 H2SO4 in the three-electrode configuration, the doped WO3 films acting as photoanodes yielded (following illumination with visible light) significantly (up to 80%) larger water oxidation photocurrents (at potentials higher than 0.75 V vs. RHE), in comparison to the analogous undoped mesoporous tungsten oxide films. The effect was the most pronounced in a case of the WO3 film doped with borotungstic acid–stabilized hematite.  The observed enhancement effects could be rationalized either in terms of appearance of new conduction band structures in doped WO3 films or a marked increase in the degree of hydration of the doped oxide structures regardless annealing at high temperatures (450 oC). Judging from our experiments in 0.5 mol dm-3 NaCl, the systems are also applicable in the sea-water-type environments.  Present results are consistent with the view that the doped tungsten oxide structures do not exhibit significant undesirable electron-hole recombination effects. Optimization of the system is underway aiming at further improvement of the photocurrent efficiency and the systems' utility under different conditions. Any increase in the photoelectrochemical efficiency of WO3–based films is of importance to the development of photoanodes for the visible-light driven water splitting.
Physical-Chemical Properties of the Naf-AlF3-Sc2O3-Al2O3 Molten System
Authors: Tkacheva Olga , Kataev Alexander , Redkin Alexander , Zaikov Yurii
Published: February 2020

The Al-Sc alloys are typically obtained by aluminothermy method.  However, the high alloy’s price is defined by the cost of a scandium-containing substance (such as ScF3 or Sc, etc.) prepared from its raw material (Sc2O3) for the reaction with aluminum. Expenses for a multistage scandium extraction process are also substantial. Another way for producing the Al-Sc alloys can be the electrochemical co-reduction of Al and Sc from their oxides dissolved in a cryolite (NaF-AlF3) melt. To develop the electrolysis process and to determine its operating parameters it is necessary to know some basic physical-chemical properties of the NaF-AlF3-Sc2O3-Al2O3 molten system, such as liquidus temperature, Sc2O3 solubility in cryolite including a cross impact  of both Sc2O3 and Al2O3 oxides on their solubility and electrical conductivity of molten mixture. A thermo analysis (TA)  was used for liquidus temperature measurements. An oxide solubility was determined by the TA along with isothermic saturation method. An electrical conductivity was measured in the capillary (BN) cell  and in the cell with parallel Mo-electrodes using an impedance technique. The obtained results testified that the Sc2O3 behaved similar to the Al2O3. Its additions to the molten cryolite decreased the liquidus temperature and the electrical conductivity. The Sc2O3 solubility in the NaF-AlF3 melt with molar ratio of NaF/AlF3=2.3 was found to be about 10 wt% at 980 ᵒC.  The Al2O3 solubility in the scandium-containing cryolite decreased with the Sc2O3 concentration rise.  The total solubility of both oxides, in controversial to known data, was determined to be slightly higher than the solubility of each separate oxide in the NaF-AlF3 melt.
NaCl Augmented Phase Transformation in Interfacial Water Under Quasistatic-Loading Conditions
Authors: Khan Shah Haidar , Hoffmann Peter Manfred
Published: February 2020

From clay swelling to geological transformations, from the structure to functioning of living organism, and from metallic corrosion to the recovery of oil from deeply lying pores, the presence of ions in water at the interface plays an important role. Many studies have been performed to understand the role of ions in water at the interface between solid to solid, solid to liquid and soft matter to liquid media. However, the dynamics and mechanical properties of electrolytic water at the interface have not been completely understood as evident by controversial results and sometime contradictory explanations. Here we present a study of the effects of concentration of NaCl on the stiffness and damping properties of interfacial water confined between mica substrate and an oxidized silicon cantilever. We have used a home-built Scanning Probe Microscope (SPM), based on Fabry-Perot interferometer principle, to monitor the amplitude and phase of the cantilever with <0.1 Å precision. Here we present the behavior of electrolytic water of various NaCl concentrations (0.001-1M) near the interface under different dynamical conditions. We have observed that even under near to ideal static condition (a compression rate of 2 Angstrom per second), the presence of NaCl introduces peaks in the relaxation time not seen in the case of pure water suggesting a phase transformation of the electrolytic water  from a liquid-like to more solid-like behavior near the interface. The critical concentration of NaCl suggesting the phase transformation seems to be lying around 0.1 M NaCl. Our detailed and systemic study of the effects of NaCl containing water as compared with pure water under different dynamical conditions may contribute to better understanding of the role of electrolyte in interfacial water as well as help clear some of the underlying controversies in its physics and chemistry.
Investigation of Quantum Confinement in Lead Sulfide Quantum Dots, through Cyclic Voltammetry
Authors: Haram Santosh K , Gujarathi Yogini D
Published: February 2020

Due to the large Bohr radius (18nm) and formation of the multi-excitons per photon, lead sulfide quantum dots (Q-PbS) have been viewed as an important material in the light harvesting devices. A performance of these devices however is greatly relying on the formation of hetero-junctions for which the knowledge of relative band positions of the components is desirable. These values are normally estimated by ultra-violate photoelectron spectroscopy (UV-PES) and scanning tunneling spectroscopy (STS). In both the cases one need special sample preparation protocols and involved instrumentation. Here, we demonstrated that these parameters can readily be gauged by electrochemical technique such as Cyclic Voltammetry.  For that, Q-PbS in the size-range 3-5nm  have been prepared by solvo-thermal method and cyclic voltammograms were recorded on their dispersions in dichloromethane.  Distinct cathodic and anodic peaks observed in CV have been co-related to the electron transfer, mediated through the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the Q-dots, respectively. Systematic correlation was observed between the size of Q-dots and the position of HOMO and LUMO which is attributed to the quantum confinement of the charge pairs. The results were found to be matched very well with the one reported with PES in air.
Continuum Models for High Molarity Electrolyte Solutions
Authors: Promislow Keith , Gavish Nir
Published: February 2020

Differential capacitance data is one of the most widely used experimental quantities for characterizing the structure of electrolyte solutions near charged interfaces. Many studies have attempted to fit differential capacitance data to generalized Poisson-Boltzmann models, particularly to account for finite-volume, ion-crowding effects. We consider the inverse problem: the derivation of generalized Poisson-Boltzmann type free energies from prescribed differential capacitance data. The method is applied to differential capacitance data obtained from experiments and from theoretical models typically found in the literature. In particular, we show that differential capacitance data can not uniquely determine finite volume effects, and provide examples for models which give rise to the same differential capacitance data but characterize solutions with very different qualitative features. Further, we show that uniqueness within the class of generalized Poisson-Boltzmann free energies requires knowledge of the excess chemical potential of the system in the bulk (spatially uniform) state.  We discuss applications of the derived free energies to models of pore formation within ionomer membranes.
Formic Acid Electrochemical Oxidation on Au25 and Pt@Au24 Nanocatalysts: A DFT Approach
Authors: Clayborne Andre , Chen Wei
Published: February 2020

Electrooxidation of formic acid has been the focus of intensive investigations due to its importance in the development of low temperature fuel cells. In this work, first principles density functional theoretical calculations were carried out to examine the reaction path for the electrocatalytic oxidation of formic acid on the monolayer-protected Au25 and Pt@Au24 nanoclusters. The Au25-nanocluster oxidizes HCOOH via an indirect pathway; first, forming CO, which can then be reoxidized to form CO2.  On the Pt@Au24 nanocluster, it proceeds either through a formate and/or direct path at lower onset potentials than Au25.  The calculations present a mechanism for electrochemical experimental observations for formic acid oxidation on monolayer-protected cluster nanocatalysts.
Predicting Transport Properties at Electrode/SEI/Electrolyte Interfaces in Li Ion Batteries
Authors: Qi Yue
Published: February 2020

The electrode/solid-electrolyte-interphase (SEI)/electrolyte interface is rather complex and critially important in Li-ion battereis. Improving Li transport and preventing electron leakage through the solid electrolyte interphase (SEI) are critical to Li-ion batteries capacity drop and power loss.  Identification of the dominant diffusion carriers and their diffusion pathways in main components of SEI is a necessary step to understand the functionality of SEI before tailoring its properties. Therefore, dominant Li diffusion carriers and the ionic conductivity in perfect SEI components (such as Li2CO3 and LiF) were predicted with density functional theory (DFT) over a broad voltage range of the electrode materials that the SEI component covers. It was predicted that the main diffusion carriers in Li2CO3 on anode are excess Li ion interstitials (Li
i

+), however, above 3.98V, Li ion vacancies (V
Li
-) become the dominant. In contrast, the main diffusion carriers in LiF was predicted to be Schottky pairs (V
Li
-  and V
F
+), agreeing with experimental observations. While the V
Li
- diffuses through direct hopping, the Li
i

+ diffuses by knocking off the Li+ ion from a lattice. Meso-scale Li+ ion diffusion equations were then formulated based on the diffusion mechanisms discovered by DFT and the boundary conditions of isotope exchange experiments in order to make direct comparison with TOF-SIMS measurements. Furthermore, by studying the point defect formation and diffusion, it is proposed that electron or polaron hopping can be facilitated by the diffusion of point defects, such as Li
i

0 interstitial, when the SEI is thicker than electron tunneling length. Ab initio molecular dynamics of electrode/SEI/electrolyte interface simulations further demonstrated that when a Li
i

0 interstitial transports into the electrolyte, ethylene carbonate (EC) reduction is observed immediately. This is a possible mechanism to explain electron leakage through thick SEI films into the electrolyte.
Multiscale Modeling of a Proton Exchange Membrane Fuel Cell: Atomistic Fuel Cell Model
Authors: Castañeda Ramírez Sergio , Pérez Mendoza Alejandro Esteban , Carmona Juan , Ribadeneira Paz Rafael Esteban
Published: February 2020

Proton Exchange Membrane Fuel Cells (PEMFCs) are very promising to generate electric energy for transport and electronic devices because they produce minimal pollutant emissions and can operate at low temperature [1]⁠. Despite of enormous progresses made to date, this technology has to reach all technical requirements in order to be competitive.

In this sense, the research of the physicochemical processes in PEMFCs is primordial to characterize and to understand the operation of these devices, aiming to suggest strategies to enhance their performance. Numerical simulations are able to provide detail of quantities that are difficult to measure experimentally, thus they can complement the experimental approaches allowing a comprehensive understanding of the PEMFCs operation [2]⁠.

Several processes on different scales occur in the PEMFC components. The most important processes include the electrochemical reactions in the catalytic layers, ion transport in the electrolyte membrane, and mass transport in all regions of the PEMFC. Different simulation approaches study these processes [3–6]⁠, but these models describe the electrochemical reactions using Butler-Volmer equations with empirical parameters, which rely on operation conditions.

Furthermore, the oxygen reduction reaction (ORR) is fundamental in the development of fuel cells, and it is required a deeper understanding of these macroscopic parameters relating to chemical and structural properties of the catalyst, in order to enhance catalysts and catalytic layers used in this technology. Thus, in this work, it is shown an atomistic approximation using density functional theory (DFT) to describe the reaction processes in the kinetic section of a PEMFC model, which includes transport phenomena at the electrolyte membrane.

It is considered a dissociative mechanism to describe ORR in the cathode of the cell. DFT calculations of a Pt model surface with adsorbed species are carried out to determine activation energies of each elemental step and hence the kinetic parameters are estimated applying the transition state theory.

The kinetic modeling based on DFT calculations enables further insight into reaction mechanisms and deeper understanding of the ORR .

References:

[1] Y. Wang, K.S. Chen, J. Mishler, S.C. Cho, X.C. Adroher, Appl. Energy 88 (2011) 981.

[2] A. A. Shah, K.H. Luo, T.R. Ralph, F.C. Walsh, Electrochim. Acta 56 (2011) 3731.

[3] A.Z. Weber, J. Newman, J. Electrochem. Soc. 151 (2004) A311.

[4] A.Z. Weber, R.L. Borup, R.M. Darling, P.K. Das, T.J. Dursch, W. Gu, D. Harvey, A. Kusoglu, S. Litster, M.M. Mench, R. Mukundan, J.P. Owejan, J.G. Pharoah, M. Secanell, I. V. Zenyuk, J. Electrochem. Soc. 161 (2014) F1254.

[5] P.K. Das, X. Li, Z.-S. Liu, J. Electroanal. Chem. 604 (2007) 72.

[6] W. Sun, B. A. Peppley, K. Karan, Electrochim. Acta 50 (2005) 3359.
Design of Novel Electrochemical Materials from Data-Driven First-Principles Calculations
Authors: Persson Kristin Aslaug
Published: February 2020

In spirit of Materials Genome Initiative, the Materials Project (http://www.materialsproject.org) aims to leverage the information age for materials design. The goal of the Materials Project is to accelerate materials discovery and education through advanced scientific computing and innovative design methods, scale those computations to inorganic compounds and beyond, and disseminate that information and design tools to the larger materials community. The Project was launched online in October 2011 and since then we have computed and imported > 60,000 inorganic compounds into the database, which can now be freely accessed and searched over through the web interface for many materials properties such as structure, local environments and coordination, XRD, electronic structure, battery electrode properties, elastic tensors, reaction energies and more. In this talk we will highlight some of our results in utilizing the Materials Project infrastructure and wealth of data to understand the limitation of current materials and subsequent design novel materials for electrochemical systems.

Examples will be given on the design of materials for technologies relevant for electrochemical energy storage and harnessing such as Li-ion electrode materials, novel materials for multi-valent intercalation electrodes, electrolytes for multi-valent systems, and transition metal oxide compounds for solar water splitting applications.
Modeling Oxide Formation and Reduction on Platinum
Authors: Eikerling Michael
Published: February 2020

The formation and reduction of surface oxide species determine both the electrocatalytic activity of Pt towards the oxygen reduction reaction as well as the rate of corrosive Pt dissolution [1]. We perform theory and modeling work to rationalize the various stages of oxide formation and reduction at Pt and, subsequently, use it to explore mechanisms of Pt dissolution. Mechanistic models developed through this work strive to establish relations between metal phase potential and surface oxidation state that govern the transient current response of the electrode. The first part focuses on a recently developed kinetic model for oxide formation and reduction at Pt in the voltage range of 0.65–1.15 V [2]. The model is evaluated against electrochemical [3], spectroscopic [4] and computational studies [5]. The second part presents a kinetic model of oxide growth on platinum in the high voltage regime, above 1.15 V. The governing equations of the oxide growth model account for mass and charge conservation, species migration, and electric field effects. The model is expected to provide insights into different oxide growth mechanisms and to rationalize various growth laws that have been found experimentally. Results will be compared to experimental cyclic voltammetry data to extract rates of kinetic and transport processes. In an ensuing step, platinum dissolution kinetics will be incorporated and linked dynamically to oxide growth and reduction. It is thus expected that the model will be able to explain the dramatically enhanced rate of Pt dissolution that was found in recent experimental studies, when the electrode voltage was cycled through the high voltage regime [6,7,8]. The detailed mechanistic understanding of oxide growth and reduction on platinum will thus complete our theory of platinum dissolution in catalyst layers for polymer electrolyte fuel cells [9].

References

[1] A. Seyeux, V. Maurice, and P. Marcus, J. Electrochem. Soc.
160, C189 (2013).  

[2] S. G. Rinaldo, W. Lee, J. Stumper, and M. Eikerling, Electrocatalysis
5, 262 (2014).

[3] A.M. Gómez-Marín, J. Clavilier, J.M. Feliu, J. Electroanal. Chem.
688, 360 (2013)

[4] M. Wakisaka, H. Suzuki, S. Mitsui, H. Uchida, M. Watanabe, Langmuir
25, 1897 (2009)

[5] L. Wang, A. Roudgar, M. Eikerling, J. Phys. Chem.
C
113, 17989 (2009)

[6] S. G. Rinaldo, P. Urchaga, J. Hu, W. Lee, J. Stumper, C. Rice, and M. Eikerling, Phys. Chem. Chem. Phys., in press.

[7] A. A. Topalov, S. Cherevko, A. R. Zeradjanin, J. C. Meier, I. Katsounaros, and K. J. J. Mayrhofer, Chemical Science
5, 631 (2014).

[8] L. Xing, M. A. Hossain, M. Tian, D. Beauchemin, K. T. Adjemian, and G. Jerkiewicz, Electrocatalysis
5, 96 (2014).

[9] S. G. Rinaldo, W. Lee, J. Stumper, and M. Eikerling, Physical Review E
86, 041601 (2012).
Theoretical Study to Improve O → OH Reactions in the Fuel Cell ORR
Authors: Yu Ted H. , Torres Randy , Goddard William A
Published: February 2020

Using density functional theory (DFT), Pt sandwich catalysts1 are studied to improve the oxygen reduction reaction (ORR) in fuel cells.  The ORR can occur through six different reactions, in which the oxygen hydration2 (Oad + H2Oad → 2OHad) reaction was determined to be the rate determining step.  A sandwich catalyst consists of Pt on the surface layer, a different metal in the second, and Pt in the bulk.  The catalysts have been shown to display unique properties that improve the sluggish ORR in fuel cells. 

     Twenty-eight different transition metals were tested as the middle sandwich layer.  We found that the correlation of these special catalysts with the electronic d-band center is different from what was previously thought.  For the 28 catalysts tested, the d-band center fits best linearly with a new index that measures non-correlated binding energy of Oad and OHad.  This value is related to the exothermicity of a reaction with Oad as reactant and OHad as product.  Thus, Pt sandwich catalysts with large d-band centers calculated using nudged elastic band (NEB) perform exceptionally well for reactions that convert Oad to OHad.

     Breaking down the ORR into three basic steps, we categorize the catalytic property that can best improve each step:

Step I)  O2Activation:  High O binding Energy.

Step II)  OH Formation:  High Index

Step III)  OH Consumption:  Low OH binding Energy.

     While previous models based on binding energy can predict relatively well a catalystic reaction for Step I and Step III, improving Step II of the ORR was difficult to characterize due to the correlated binding energy of O and OH.  Improving this new index was found to be a new strategy to improve Step II ORR reactions.  Studying the density of state, we explain why the d-band center is related to this index in Pt sandwich catalysts to give theoretical insights.

Figure 1:  Binding energy of 28 different Pt sandwich catalysts.  The line in the middle describes the general correlated binding energy of pure metal catalysts between O and OH.  The perpendicular distance for each catalyst from the middle line is the new index, in which, Pt-W-Pt is the highest, while Pt-Ag-Pt is the lowest.

References:

1.         C. A. Menning, H. H. Hwu and J. G. G. Chen, J Phys Chem B 110(31), 15471-15477 (2006).

2.         Y. Sha, T. H. Yu, B. V. Merinov, P. Shirvanian and W. A. Goddard, Journal of Physical Chemistry Letters 2 (6), 572-576 (2011).

Figure 1
Mechanistic Study of Palladium Based Electrocatalysts for Direct Borohydride Oxidation
Authors: Grimmer Christoph , Grandi Maximilian , Zacharias Robert , Friedrich Theo , Woisetschläger Dieter , Mayer Nicole , Koncar Michael , Kalb Roland , Hacker Viktor
Published: February 2020

The direct borohydride fuel cell (DBFC) is one of several promising direct liquid fuel cells due to easy fuel handling and high energy storage density [1]. DBFCs are still in an early stage of development and further improvements of anode catalyst materials and MEA design are necessary for widespread application.

Herein we present an extensive study of Palladium based catalysts for the anode reaction of DBFCs (see reaction 1) including several electrochemical experiments supported by 11B-NMR and FTIR measurements.

BH4
- + 8OH-  →  BO2
- + 6H2O + 8e-                                              (1)

(E0 = -1.24 V vs. SHE)

Palladium based electrocatalysts nanodispersed on high surface area carbon are prepared by reduction of precursor salts in an aqueous dispersion of the support material. The catalyst is characterized by transition electron microscopy (TEM).

Rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) experiments with subsequent analysis of reaction products by 11B-NMR are conducted. Fig. 1 shows a typical result of Pd/C on a RDE with a borohydride concentration of 5 mM. Additionally mechanistic aspects on Palladium are investigated employing in-situ FTIR spectroscopy [2].

By combining all results obtained from the experiments mentioned above a substantial proposition of ongoing mechanisms of BH4
--electrooxidation on Palladium is presented.

[1]       J. Ma, N. a. Choudhury, Y. Sahai, Renew. Sustain. Energy Rev. 14 (2010) 183.

[2]       B.M. Concha, M. Chatenet, C. Coutanceau, F. Hahn, Electrochem. Commun. 11 (2009) 223.

Caption Figure 1:

RDE experiments of Pd/C catalyst at rotation rates of 0-2000 rpm (anodic sweeps) in 1M NaOH with 5 mM NaBH4, insert: according Levich-plot at 0.830 V.

Figure 1
Enhancement of the Oxygen Reduction on Nitride Stabilized Pt-M (M = Fe, Co and Ni) Core-Shell Nanoparticle Electrocatalysts
Authors: Kuttiyiel Kurian A , Sasaki Kotaro , Park Gu-Gon , Choi YongMan , Hwang Sun-Mi , Yang Tae-Hyun , Su Dong , Liu Ping , Adzic Radoslav
Published: February 2020

Given the harsh operating conditions in hydrogen/oxygen fuel cells, there has been considerable efforts to make Pt(M) alloy nanoparticles as a stable oxygen reduction reaction (ORR) catalyst that have had a marginal success.  Core-shell catalysts have unique properties of reducing the precious metal for the reaction and at the same time increasing the ORR activity by combined geometrical and electronic effects. Multiple mechanism has been proposed to explain the enhanced ORR activity of Pt(M) alloys. Watanabe et al. had explained the enhanced ORR activity based on the lattice parameter changes by alloying non-precious metals to Pt. Their results showed that the ORR activity increased in the order of PtFe/C > PtCo/C > PtNi/C, whereas the calculated lattice parameter decreased in the order of PtFe/C < PtCo/C < PtNi/C. Mukerjee et al. investigated the enhancement mechanism on some PtM alloys for the ORR by using XANES and EXAFS.  Based on the d-band calculations that decreased in the order of PtFe/C < PtCo/C < PtNi/C, the ORR activity increased in the order of PtFe/C > PtCo/C > PtNi/C. So overall the trend in ORR activity for Pt(M) alloy nanoparticles have been in the order of PtFe/C > PtCo/C > PtNi/C.

Here we report on a new class of catalyst consisting of nitride metal cores enclosed by thin Pt shells that can be easily synthesized. Our theoretical analysis and the experimental data indicate that metal nitride nanoparticle cores could significantly enhance the ORR activity as well as the durability of the core-shell catalysts as a consequence of combined geometrical, electronic and segregation effects on the Pt shells.   Adding nitride metal in the core increases the ORR activity in the order of PtNiN/C > PtFeN/C > PtCoN/C. DFT calculations have shown a volcano type behavior with PtNiN/C at the top of the curve revealing the fact that, among the catalysts investigated, it has the best combination of both the surface strain and d-band center shifts.

Figure 1
Understanding the Superior ORR Activity of the Fe-N2+2 to That of the Fe-N4 Site
Authors: Jia Qingying , Strickland Kara , Hafiz Hasnain , Bernardo Barbiellini-Amidei , Mukerjee Sanjeev , Ramaswamy Nagappan , Tylus Urszula
Published: February 2020

Despite recent progress made in the development of M–Nx–C catalysts, the exact nature of the active sites formed during pyrolysis, as well as the reaction mechanisms remains unclear. Herein, in situ
x-ray absorption spectroscopy (XAS) measurements were performed on representative iron–based catalysts [1-3] to identify the nature of the active sites in these catalysts. XAS offers unique insights into electrode processes by providing simultaneous electronic and structural information on the electrode materials under actual in situ cell operating conditions [4]. In particular, Δμ technique, which has evolved into a powerful tool for elucidating surface adsorbed species in  electrocatalysis, was utilized to probe the local structure of the active sites and their interactions with reaction intermediates [3-5]. In addition, density function theory calculations were conducted to correlate the structure to the ORR activity.

We showed that the original macrocycle (denoted as Fe-N4), in which the N is pyrolylic type can be differentiated from the active sites formed upon high temperature pyrolysis (denoted as Fe–N2+2), in which the N is pyridinic type by using Δµ. Combined EXAFS and XANES showed that the central Fe in Fe–N2+2 is off the N4–plane and in high spin state, whereas the central Fe in Fe–N4 is precisely in the N4-plane and in intermediate spin state. Upon the adsorption of ORR intermediates at high potential region, the displacement, the oxidation state, and the spin state of the central Fe change in different ways between Fe–N4 and Fe–N2+2 sites. DFT calculations showed that this different Fe–N switching behavior accounts for the superior ORR activity of Fe–N2+2 to Fe–N4.

Acknowledgements:

The PANI-derived catalysts were prepared and provided by Gang Wu and Piotr Zelenay (Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545). Use of the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL), was supported by the U.S. Department of Energy, Office of Basic Energy Sciences. This publication was made possible by the Center for Synchrotron Biosciences grant, P30-EB-009998, from the National Institute of Biomedical Imaging and Bioengineering (NBIB). Support from beamline personnel Dr. Erik Farquhar and Mark Chance (X3B) are gratefully acknowledged.

References

(1) Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P. Science
2011, 332, 443-447.

(2) Tylus, U.; Ramaswamy, N.; Jia, Q.; Mukerjee, S. Meeting Abstracts
2012, 225-225.

(3) Ramaswamy, N.; Mukerjee, S. Advances in Physical Chemistry
2012, 2012, 17.

(4) Roth, C.; Benker, N.; Buhrmester, T.; Mazurek, M.; Loster, M.; Fuess, H.; Koningsberger, D. C.; Ramaker, D. E. J. Am. Chem. Soc.
2005, 127, 14607-14615.

(5) Jia, Q.; Ramaker, D. E.; Ziegelbauer, J. M.; Ramaswamy, N.; Halder, A.; Mukerjee, S. The Journal of

Physical Chemistry C
2013, 117, 4585-4596.
Study of Non-PGM ORR Catalyst Degradation Using Synchrotron Techniques
Authors: Tylus Urszula , Chung Hoon T , Higgins Drew C , Myers Deborah J , Nordlund Dennis , Segre Carlo U , Zelenay Piotr
Published: February 2020

Several recent reports on the development of oxygen reduction reaction (ORR) non-platinum group metal (non-PGM) catalysts have shown an impressive progress towards high ORR activity [1-2]. By now, in RDE testing, these catalysts are quite routinely reaching E½
values of 0.8 V versus reversed hydrogen electrode [1]. The high initial performance notwithstanding, truly durable non-PGM catalysts, capable of maintaining ORR activity for hundreds or thousands of hours at low pH values of the polymer electrolyte fuel cell (PEFC), are yet to be developed. The development of such catalysts must involve a carefully thought-out experimental design and the use of reliable multiple techniques to provide answers to the quarter-of-a-century-old questions about the structure of the ORR active site(s) in metal-nitrogen-carbon (M-N-C) catalysts.

According to some previous in-situ XAS studies [3-4], a vast majority of non-PGM catalysts consist of two forms of transition metal, iron coordinated by nitrogen species (Fe-Nx) and non-coordinated iron nanoparticles (FeNP). While the existence of these species has been detected using different methods, the in-situ XAS reviled a specific redox behavior accompanied with spin switching behavior of the Fe-Nx species when subjected to potential bias simulating PEFC environment [2-4]. There is still a large ambiguity, however, about the actual nature of the M-N-C active sites and their degradation modes. Among many challenges facing this research, it is important to take a closer look at other elements present in such catalysts, such as nitrogen and carbon. This is especially needed for non-PGM catalysts without nitrogen-coordinated Fe (e.g. FeNP) with very high activity [5].

Herein, we present a study of a Fe-based non-PGM catalyst derived from multiple nitrogen precursors. The study has been performed using synchrotron X-ray absorption techniques coupled with standard electrochemical methods, including RRDE and MEA testing. We look at the structures involving all elements in the catalyst by employing high-energy photons at Argonne National Laboratory (to monitor in-situ Fe-containing species) and low-energy photons at Stanford Synchrotron Lightsource to monitor carbon and nitrogen species (C and N K-edge), claimed to play an important part in the ORR active site sites. With better understanding of the structure-to-function relationship in Fe-N-C species as the main objective, we study the effect of durability cycling (Figure1) on the catalyst performance and structural changes involving all elements in Fe-N-C species.

Figure 1