bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Conducting Tafel Analysis
Authors: Agbo Peter , Danilovic Nemanja
Published: May 2020

The application of linear, Tafel fitting procedures become problematic in the cases of experimental data featuring non-linearities in the Tafel (log(J)-V) response. This is especially difficult in low-overpotential regimes, where charge transfer kinetics generally control electrode behavior and Tafel analysis is expected to be most relevant. In response to this complication, and the qualitative forms of fitting that may arise from it, a methodology for the determination of Tafel slopes through a quantitative framework is presented. The efficacy of the method is tested using electrochemical measurements of well-characterized reactions for water splitting, hydrogen evolution and dioxygen reduction at iridium and platinum electrodes and shown to yield values consistent with literature reports of these catalysts. In addition, we show that the exchange currents extracted through this automated fitting procedure, used in conjunction with the Butler-Volmer model, are capable of reproducing the original electrochemical data in kinetically-controlled regimes for the cases of platinum-ORR and Iridium OER.
Measurement Drift in Electrochemical Impedance Spectroscopy
Authors: Halpern Jeffrey M , Ziino Emily , Marnoto Sabrina
Published: May 2020

Electrochemical impedance spectroscopy (EIS) is a powerful method that can be used to passively monitor disruptions on a surface. Yet, reproducibility issues associated with repeated impedance measurements using EIS is known.1,2 Often reproducibility issues are associated with differences in the initial state of the surface or quantifiable measurement drift of the EIS response. Measurement drift is of specific concern because it can result in mistaken interpretations of data.

We have been investigating the cause and potential reasons for the electrochemical drift that has been observed. We hypothesize that the charging state of the working electrode influences the observed impedance drift in EIS. We investigated multiple factors to look at the charged state of the working electrode, including removing the working electrode from the solution, reporting the open circuit potential, reporting the double layer capacitance and charge transfer resistance changes, varying the concentration of an electrochemical mediator, changing the ionic strength of the aqueous solution, and DC offset conditions. The run-to-run variation was controlled by waiting 10 min between each run over a period of 1 hour (6 runs in total). Total charge transfer resistance drift varied by over 500 Ohms in the worst conditions and as good as 5 Ohms at the best conditions over six runs, indicating improvements of 2 orders of magnitude. All experimental variable changes were run in triplicate to show experimental error and standard deviations of all runs. Taking these methods into account, the most reproducible model of repeated EIS impedance measurements will be discussed. Further, theories and data to indicate potential causes and solutions will be presented.

Acknowledgements: The authors would like to acknowledge the financial support from NIH (P20 GM113131) NSF (CBET 1638896), and the Hamel Center of Undergraduate Research at the University of New Hampshire. The authors also would like to acknowledge the assistance of Dr. Halpern’s laboratory.

References

1. M. E. Orazem, M. Durbha, C. Deslouis, H. Takenouti, and B. Tribollet, Electrochim. Acta, 44, 4403–4412 (1999).

2. A. Bogomolova et al., Anal. Chem (2009).
Application of Photoelectrochemical Technique for Photocatalysts’ Characterization
Authors: Han Qiaofeng , Li Shuzhen
Published: May 2020

Photocatalytic technology for hydrogen evolution and pollutants degradation may bring huge economic benefits due to its resolution for environmental pollution and energy shortage by utilizing natural solar light and thus attract more and more attention to materials researchers. However, up to now, it is still far away from practical application due to low photo quantum efficiency. The fast recombination of the photogenerated electrons and holes are key factors to influence potocatalytic efficiency. The separation and migration efficiency of photocatalysts are commonly characterized by electrochemical impedance spectra (EIS) and transient photocurrent responses. Yet, various plots have been presented especially in transient photocurrent responses spectra, such as spike peaks, negative peaks, exponential type peaks, and so on, which have not been fully explained. In our experiments, by changing the applied potentials, adding different hole scavengers, these phenomena could be avoided.
Glucose Sensor Using NAD-Dependent Glucose Dehydrogenase, Diaphorase, and Osmium Complex
Authors: Nam SangWook , Yang Haesik
Published: May 2020

It is still challenging to detect glucose selectively in serum and blood, and quickly using nicotinamide adenine dinucleotide (NAD-GDH). In this paper, we report a selective and rapid glucose sensor, based on electrochemical-enzymatic-enzymatic (ENN) redox cycling involving bis(2,2-bipyridyl)dichloroosmium(II)[Os(bpy)2Cl2], diaphorase (DI), NAD+, NAD-GDH, and glucose. DI and Os(bpy)2Cl2 are used to obtain fast mediated oxidation of NADH that is generated as a result of glucose oxidation by NAD-GDH. DI and NAD-GDH are co-immobilized via affinity binding on an avidin-modified indium tin oxide electrode to obtain fast and stable ENN redox cycling. Two enzymes (DI and NAD-GDH) and two electron mediators [Os(bpy)2Cl2 and NAD+] are efficient. The reason is that they are insensitive to oxygen. The applied potential (0.0 V vs Ag/AgCl) is low enough to minimize interfering electrochemical reactions, and the redox reactions of Os(bpy)2Cl2 with interfering species are slow. NAD-GDH is much less reactive to problematic monosaccharides such as xylose, fructose, galactose, and mannose than glucose. Artificial serum containing 5% (w/v) human serum albumin shows a similar electrochemical back-ground level in serum. All results enable us to obtain selective and reproducible glucose detection. The fast ENN redox cycling allows sensitive glucose detection with a wide range of concentrations in artificial serum with a short measuring time (5 s) without an incubation period.

Keywords: Glucose sensor, Glucose dehydrogenase, Diaphorase, Osmium complex
Visible-Light Photocatalytic Nitrogen Fixation and Electrons Transport in Bismuth Iron Molybdate
Authors: Liu Botong , Wu Nianqiang
Published: May 2020

The vast majority of semiconductors photocatalysts reported for artificial nitrogen fixation have a large bandgap at around 3.0 eV, thus photocatalytic nitrogen reduction is driven mainly by ultraviolet light. In contrast, this report demonstrates that bismuth iron molybdate (Bi3FeMo2O12) with a bandgap of 2.25 eV exhibits visible-light photocatalytic activity toward nitrogen conversion to ammonia. Furthermore, introduction of oxygen vacancy to this photocatalyst increases the ammonia production rate remarkably. The oxygen vacancies help adsorb and stabilize the N-H intermediate species and lower the energy barrier of intermediate reactions. Bi3FeMo2O12 has relatively narrow band gap and active sites for nitrogen fixation. However the ammonia production rate is low. Using photoelectrochemical system, surface photovoltage spectroscopy and simulation, we revealed that photoelectrons transport is constrained, which is attributed to the strong interaction between photoelectrons and lattice phonons.
Designing Nanoparticles for Optimized Pseudocapacitive Energy Storage
Authors: Foong Yee Wei , Bevan Kirk H
Published: May 2020

Power harvesting from intermittent renewable energy sources requires high charge storage capacity without compromising charging speed. These properties are achievable within hybrid capacitors by enhancing the pseudocapacitive (Faradaic) charge storage relative to the double-layer (non-Faradaic) charge storage, via the overlapping of equally-spaced redox reactions to reach a near ideal voltammetry profile. In this work, we examine how the structure of nanoparticles may be utilized to tune the pseudocapacitive response. This is accomplished by utilizing Gerischer-Hopfield electron transfer theory to capture the effects of redox species solvation through the solvent reorganization energy. Our model translates the total-energy picture by Marcus-Hush theory into single-particle picture for electron transfer in Faradaic charge storage processes, thereby arriving at a general phenomenological description of how pseudocapacitive properties can be engineered at the nanoscale. We also explore the design limitations of such nanoparticle-derived pseudocapacitance through a fundamental consideration of electron transfer energetics and kinetics. In general, our analysis is intended to aid the development enhanced pseudocapacitive properties in hybrid capacitor systems.
Low-Voltage STEM-Eels Quantification for Lithium Ion Battery Material Characterization
Authors: Dumaresq Nicolas , Gauvin Raynald , Zaghib Karim
Published: May 2020

In material sciences, in order to develop new compounds with different electrical, mechanical or optical properties we need to understand the link between these properties and the microstructure of the material. This apply also to understand the decrease of efficiency of a battery after multiple charge-discharge cycle where the structural changes need to be identify in order to prevent it. Scanning transmission electron microscopy (STEM) has been proven to be a powerful tool for the study of microstructure and morphology with a subnanometer resolution. Furthermore, a STEM paired with electron energy loss spectroscopy (EELS) can provide useful information on the specimen elemental composition. However, these technique are normally used with a high electron beam voltage (80-200 keV) and the high energy of the electron beam induce beam damage into low Z materials such as lithium compound. This becomes problematic when the microstructure of a LIB is observed since the change into the material cause by the beam damage is close to the changes cause by the use of batteries during cycling. To prevent beam damage such as knock-on damage, the electron beam voltage need to be reduce to relatively low kV. However, no work on low voltage EELS quantification has been reported.

This study will present the acquisition of EELS spectrum using a state-of-the-art dedicated transmission scanning electron microscope (Hitachi-SU9000EA) at 30 keV. Low-voltage EELS quantification on standard will be presented using the integration ratio method. Interesting results will be presented on the inelastic cross-section measurement at low-voltage with the combination of convergent beam electron diffraction(CBED) and EELS. Theses values will be compared with the cross-section obtain using computational calculation that are normally used for high voltage EELS quantification.
Imaging the Solution Phase Concentration Gradient in Li-Ion Battery Positive Electrodes with X-Ray Fluorescence
Authors: Dawkins Jeremy , Zamanzad Ghavidel Mohammedreza , Chhin Danny , Beaulieu Isabelle , Schougaard Steen Brian , Mauzeroll Janine
Published: May 2020

With the current climate crisis having no end in sight, communities worldwide are depending on new battery technology to store energy from intermittent sources of energy such as wind and solar. Li-ion batteries (LIBs) have presented themselves as a worthy candidate for the task given their high capacity for charge as well as their durability in terms of cycle life. LIB models have been developed extensively for the purpose of understanding current behaviour and predicting future performance. A limiting factor in LIBs is the rate at which they can be (dis)charged which can be extensively hindered by the formation of a concentration gradient of Li+ within the positive and negative electrodes. Although the models that exist can predict what these gradients should be within the electrodes, there has, as of yet, been no experimental data representing the concentration gradient formation within the electrode pores. Using X-ray fluorescence (XRF) in conjunction with a synchrotron light source allows the spatially resolved observation of the Li+ concentration profile. This work can validate the predictive power of established P2D models in order to improve their accuracy in addition to serving as a screening technique for new composite positive electrodes.

Figure 1
Prediction of Temperature in a Penetrated Lithium-Ion Pouch Cell Using a Multi-Physics Model
Authors: Lee Soon-Kyu , Choi Jin Hyeok , Kim Charn-Jung , Lee Kyu-Jin
Published: May 2020

Recently safety studies have been actively conducted for large capacity lithium-ion batteries (LIB) used in various industry fields, not only electric vehicle (EV) but energy storage system (ESS) and etc. However, these large LIB cells more can bring critically dangerous explosive accidents in larger scales than small LIB cells. Thermal runaway, the common event before the LIB explosion, is caused by many reasons such as overcharge, internal and external short circuits and self-reaction heating at high temperature.

Many numerical studies have been conducted to thermal behaviors of LIBs for safety. However, experimental tests of the safety incidents are usually hard to be reproduced and controllable so that experimental data has been lacked. In this situation, multi-physical models can produce electrochemical responses and electrical- thermal behaviors of LIBs which experience the safety problems. Using numerical models, thermal risks in various short-circuit circumstances can be predicted.

In this study, we will represent an electric- electrochemical-thermal (EECT) model to estimate thermal behaviors of LIB cells in internal short circuit situations. This multi- physics model considers charge conservation, thermal energy conservation in cell volumes and also calculates electrochemical reactions at active electrodes using the pseudo-2-dimension method (P2D). The model calculates electrical current paths through the nail penetrating the cell and Ohmic heat generated by the electric currents.

Using the EECT model, a large capacity LIB cell was simulated for a nail penetration case. The design of the cell was chosen to be similar to that of the cells in the industrial fields like energy storage system (ESS) or EV. The cell has about 20Ah capacity and graphite (LiC6) and layered nickel metal oxide (LiNi0.5Co0.2Mn0.3O2, NCM523). The size of the nail was 5mm by 5mm and made of still. Also, parametric studies about nail size, location, and state of charge (SOC) of the cell were conducted and the parametric data was used for providing the safety guidelines at the short-circuit situations.

Figure 1
Mechanisms of Stable Cycling 3D Structured Anodes for Lithium Metal Batteries
Authors: Zhang Rui , Shen Xin , Chen Xiao-Ru , Chen Xiang , Cheng Xin-Bing , Zhang Qiang
Published: May 2020

Lithium (Li) metal is among the most promising anode materials in next-generation high-energy-density energy-storage-systems due to its ultrahigh theoretical specific capacity of 3860 mAh g−1 and low negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode). However, Li dendrite growth, “dead Li” formation and unstable solid electrolyte interphase (SEI) have hindered its practical applications.

3D Structured lithium metal anodes, which possess customizable conductive framework for electron transfer and designable pore structures for ion transfer, have been widely proposed to settle these issues. We have constructed several carbon material based structured anodes to investigate the mechanisms in dendrite-free plating morphology, “dead Li”-free stripping morphology, and many other issues for achieving stable cycling 3D structured anodes. Based on the unstacked graphene framework, we found that the ultralow local current density induced by the high specific surface area of unstacked graphene can make great progress for stable and high-performance lithium metal anodes. Furthermore, with lithiophilic nitrogen-doped graphene framework, metallic Li nucleation can be regulated, then even plating morphology can be achieved. When apply the similar lithiophilic surface to a structural stable skeleton like carbon fibers, both Li dendrite growth and “dead Li” formation can be inhibited, and ultimately a high Coulombic efficiency can be achieved for high-capacity and high-rate Li metal batteries.

However, the mechanisms of stable cycling 3D structured anodes which can guide the design of lithium metal anodes are heavily lacking due to the grand challenges of current trial-and-error investigation based on complex materials innovation. If a quantitative theoretical analysis can be proposed, reliable lithium metal anodes with 3D host is highly expected. Thus, theoretical calculation such as phase field models are also employed to quantitatively describe the lithium plating and stripping process in various conductive structured lithium anodes. We found that structured lithium metal anodes with larger areal surface area and smaller pore-volumetric surface area can be much better for high rate and high capacity battery cycling.

Beyond the design and adjustment of lithium metal anodes, further experiments and simulations are required in revealing the mechanisms in lithium metal anodes, such as Li plating and stripping process, dendrite growth, SEI formation and its impact, etc., not only for 3D structured anodes. These mechanism investigations are promising for high-energy-density lithium metal batteries like Li–S and Li–O2 batteries.
Toward High Areal Capacity Lithium Batteries Via 3D Printing: From Liquid to Solid
Authors: Gao Xuejie , Sun Xueliang
Published: May 2020

3D-printing has found wide applications in numerous research fields, ranging from mechanical engineering, medicine, and material science to chemistry. Among them, it is capable of fabricating electrodes with high active material loading and improved ion/electron conductivity, and is thereby a promising method to improve the energy and power density of energy storage systems. And this technique offers a fresh viewpoint in designing high loading cathodes and will arise interest in other energy storage devices such as Li-ion batteries, Li-S batteries, and Li-Se batteries, etc. In this talk, I will talk about 3D-printed high active material loading cathode applied in batteries: from liquid to solid.

In the first part of this talk, I will introduce 3D-printed high S loading cathode applied in liquid-based Li-S batteries. Compared with conventional cathode fabrication method, a 3D-printed S cathode with grid structure, which could facilitate Li+/e- transport at the macro, micro and nano scale in Li-S batteries. Moreover, a thickness-independent S cathode structure is also proposed via converting thick electrode into thousands of vertically aligned thin electrode by 3D printing. And each thin electrode delivers a constant thickness of around 20 μm, which is not affected by the intrinsic thickness of electrode as well as sulfur loading. Compared with other high S loading Li-S batteries performace, this work demonstrate a similar electrochemical kinetics in spite of the total sulfur loading or thickness of the electrode. [1-2]

In the second part of this talk, I will talk about 3D-printed ultra-high Se loading cathode applied in solid-state Li-Se batteries. Compared with other Li-Se work, this work exhibits excellent cycling stability and remarkable rate performance with the highest reported Se loadings of 20 mg cm-2, and also delivers the highest reported areal capacity of 12.99 mA h cm-2 under a current density of 3 mA cm-2. The 3D-printed Se cathodes with grid structure provide large spaces for polymer electrolyte impregnation to further build interconnected Li+ transport channels in thick electrodes, enabling fast Li+ transport in solid-state Li-Se batteries. [3]

References

[1] X. Gao, X. Sun* et al,
Nano Energy
, 2019, 56, 595-603.

[2] X. Gao, X. Sun* et al,
Energy Storage Mater.
Doi.org/10.1016/j.ensm.2019.08.001.

[3] X. Gao, X. Sun* et al,
J. Mater. Chem. A
, under revision.

Figure 1
A Mechanistic Understanding of the Electrochemical Activity of Zinc Oxide in Alkaline Batteries
Authors: Hawkins Brendan E. , Turney Damon , Jadhav Ankur L. , Yadav Gautam Ganapati , Banerjee Sanjoy , Messinger Robert J.
Published: May 2020

Rechargeable zinc alkaline batteries are of great interest for stationary storage applications because they are inherently safe, energy dense, environmentally friendly, and low-cost. However, these batteries have not been commercialized on a large scale because of their low cycle life at high depths of discharge. One cause is the buildup of ZnO on the electrode. It has been shown recently that ZnO produced in zinc alkaline electrodes inserts protons and electrons and undergoes electrochromic color changes as a function of electrode potential. This dynamic behavior increases hydrogen catalysis, contributes capacity to the electrode, and changes oxide conductivity as a function of electrode potential. In this work we investigate the disorder and nonstoichiometry of ZnO that allow the material to become electrochemically active. We used 1H, 2H, and 67Zn solid-state MAS NMR to better understand structure, defects, order, and the hydrogen insertion mechanism of the ZnO. Understanding the physical properties of the ZnO will enable better design of electrodes and additives for zinc alkaline batteries in the future.
Understanding the Electrocatalytic Solid-Liquid Interface: The Early Years of the Więckowski University of Illinois Research Group
Authors: Myers Deborah J.
Published: May 2020

Andrzej Więckowski was an Assistant/Associate Professor of Chemistry at the University of Illinois Urbana-Champaign from 1985 to 1996 and a Full Professor from 1996 to 2012. Andrzej had a unique ability to attract students to his research group due to his infectious enthusiasm, boundless energy, and excitement for science and cutting-edge experimental approach. This talk will focus on the early years of Andrzej’s tenure at the University of Illinois and his pioneering research in probing the composition and structure of electrocatalytic solid-liquid interfaces using ultra-high vacuum techniques (Figure 1), radiochemistry, and electrochemical nuclear magnetic resonance spectroscopy.

Figure 1. (left) The first ultra-high vacuum instrument in the Andrzej Więckowski University of Illinois, Urbana-Champaign research group and (right) Andrzej, 1987.

Figure 1
Mixed-Metal-Oxide Based Hybrid Electrocatalytic Materials for Efficient Reduction of Carbon Dioxide
Authors: Kulesza Pawel J. , Rutkowska Iwona Agnieszka
Published: May 2020

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of catalytic sites (metal and metal oxide nanostructures, their stabilization and intentional activation, as well as organization into two-dimensional arrays, ultra-thin films or three-dimensional networks (e.g. through sequential deposition) on electrode surfaces. They can form nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties (e.g. toward reduction of CO2). We explore here the ability of polynuclear inorganic metal oxo systems to stabilize and functionalize metal (e.g. copper) nanostructures. Here certain nanostructured metal oxides of zirconium, titanium, zinc or tungsten have been demonstrated to influence supported metal centers in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Ag, Au, Pd, Ru) thus affecting their chemisorptive and catalytic properties. Metal oxide nanospecies can generate –OH groups at low potentials that induce proton mobility at the photo(electro)chemical interface.

Our research interests concern development of systems for the electrocatalytic reduction of carbon dioxide not only in neutral but also in acid media. For example, nanosized Cu or Ru naoparticles immobilized within ultra-thin films of tungsten oxide or zirconia have been considered. Selectivity of the catalytic systems largely depends on the activing adsorptive (CO2) phenomena and the affinity of catalytic centers to the adsorbed carbon monoxide (CO) type intermediates leading to their protonation or hydrogenation. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities relative to the competitive hydrogen evolution.
The Vanadium Redox Reactions – Electrocatalysis or Not?
Authors: Wang Jiabin , Stimming Ulrich
Published: May 2020

Catalytic effects of surface groups on porous carbon electrodes are claimed in literature for the redox reactions V(II)/V(III) and V(IV)/V(V). The literature is critically analysed also in relation to work of this group. A method on how to overcome the problem of assessing the electrochemically active surface area on porous electrodes is presented [1]. Applying this method, no catalytic effects for above reactions can be substantiated. It is further pointed out that the parameters electrochemical potential and temperature need to be used to assess electrocatalysis.

The main control parameter determining the rate of an electrochemical reaction is the Gibbs free enthalpy of activation, ΔG≠
, in contrast to ΔH≠
for e.g. a heterogeneous surface reaction. This would suggest to clearly define electrocatalysis as the “lowering the activation barrier, ΔG≠
, in an electrochemical reaction” where, in fact, the lowering of ΔG≠
can result from a change in ΔH≠
and/or ΔS≠
(∂
ΔG≠
/∂η=∂
ΔH≠
/∂η−T∂ΔS≠/∂η
, as in Figure1). Such a treatment of data of temperature dependent electrochemical reactions has been described in literatures [2,3]. An analysis according to the above-discussed procedures would pin down which quantity is responsible for the lowering of ΔG

≠
that may allow for a better interpretation of the electrocatalytic effect.

Using the example of the redox reactions V(II)/V(III) and V(IV)/V(V) the literature was analysed regarding possible catalytic effects of functional groups on carbon electrodes, as in Figure2. The conclusion was that no electrocatalysis of either of these reactions can be confirmed. Observed enhancements of currents can rather be attributed to a change in the effective surface area of the, usually, porous electrode. A method is suggested how such effects can be distinguished from electrocatalysis by using electrochemical impedance spectroscopy (EIS). Figure2 gives an example how EIS data are used for evaluation. In more general terms, the criteria for electrocatalysis were described. Experimentally, an investigation should contain both, measurements of the potential dependence and the temperature dependence since the main parameter in electrocatalysis is the lowering of ΔG≠
. Only then, the respective influence of ΔH≠
and ΔS≠
can be assessed.

Acknowledgments

This work was supported in part by Siemens AG through a research grant and by EPSRC through funding for the North East Centre of Energy Materials (NECEM) (EP/R021503/10).

References:

[1] U. Stimming, J. Wang, and A. Bund, ChemPhysChem, 2019, 20, 1-7.

[2] B. E. Conway, In Modern Electrochemistry, Vol. 16. New York: Plenum Press, 1987.

[3] Z. Borkowska, M. Cappadonia, and U. Stimming, Electrochim. Acta, 1992, 37(3), 565-568.

[4] J. Friedl, C. M. Bauer, A. Rinaldi, and U. Stimming, Carbon, 2013, 63, 228-239.

Figure 1
Synthesis and Electrochemical Study of Cobalt Based Nanostructured Catalysts for Energy Applications
Authors: Chen Aicheng , Sidhureddy Boopathi , Cirone Joseph , Prins Scott , Abner Sharon
Published: May 2020

The development of efficient electrocatalysts for the oxygen evolution reaction (OER) is an enduring challenge toward the commercialization of electrochemical technologies such as water electrolysis and solar to fuel production. Although noble metal based electrode materials (e.g., Pt, IrO2, and RuO2 etc.) are active catalysts for the OER, their cost-effectiveness, scarcity and long-term stability have hindered the development of electrochemical commercial applications. In addition, there is a great interest in the design of cost-effective and efficient catalysts for the oxygen reduction reaction (ORR) for the creation of clean energy technologies. In this presentation, we will report on the synthesis of one-dimensional Co3O4 nanorods, two-dimensional nanosheets, and three-dimensional nanocubes. The formed 1D, 2D, and 3D Co3O4 were systematically probed using a structure sensitive electrochemical OER, revealing that the 2D nanosheets exhibited higher catalytic activities in contrast to the 1D and 3D Co3O4, due to its high electrochemically active surface area and rich oxygen deficiencies. In addition, nanostructured nickel cobalt metal oxides with different composition were synthesized and studied for oxygen reduction. The effect of the composition, morphology, and active sites of the formed cobalt based nanomaterials on their catalytic activity will be discussed.
Exploring Fuel Cell Catalyst Layers at Multiple Scales
Authors: Zawodzinski Thomas A. , Subbaraman Ram
Published: May 2020

The catalyst layer used in a fuel cell is an archetype of multi-component composite materials used as electrodes in many electrochemical devices. In this talk, we will describe and link together a number of studies of the fuel cell catalyst layer that we have been carried out over the past 10 to 15 years. A major focus of the talk is work on a MURI project with Andrzej Wieckowski together with other ‘all-stars’ in the field. This project combined experiment and theory to evaluate electrocatalysis. We will discuss this effort and Andrzej’s critical role in some of the accomplishments of the team.

We will emphasize our work on describing the geometrically constrained limits on utilization of dispersed catalyst in the layer. To answer our original question, the catalyst components were broken down to constituents (Pt nanoparticles, carbon particles, ionomer) and interactions between components were used to build a hierarchical model of the catalyst layer. The interactions were defined in the context of colloidal interaction theory using descriptions of electronic properties of the constituents derived from experimental measurements of refractive index/dielectric properties across a wide range of frequencies. The model satisfactorily captured some aspects of the structure of the catalyst layer, e.g. the tendency toward segregation of components, and provides a good bound to the utilization of catalysts but failed to provide a quantitatively accurate description of certain transport-related physical properties.

Acknowledgement

We are humbled and honored to have enjoyed the collaboration and scientific spirit of Andrzej Wieckowski as well as his gracious support of our team effort. We gratefully acknowledge the support of this work by the US Army Research Office and the Naval Research Research Office. The significant contributions of Professor J. Adin Mann of Case Western Reserve university and Dr. Karren More of Oak Ridge National Lab are also appreciated.
Core-Shell Fe@Pt Nanoparticles Supported on MOx/C As Enhanced Electrocatalysts for Cathode of PEMFC
Authors: Park Ah-Hyeon , Kwon Young-Uk
Published: May 2020

For fuel cell electric vehicle (FCEV), the amount of platinum electrocatalyst is required around 10 g per fuel cell stack of 80 kW, and non- or low-platinum electrocatalysts needed to reduce the amount of platinum per vehicle considering the production cost. Therefore, a large-scale synthesis method for low-platinum electrocatalyst is necessary for the commercialization of FCEV. Ultrasound-assisted polyol synthesis (UPS) is a one-pot method for the preparation of small and uniform size core-shell nanoparticles on the support and is suitable for mass production of platinum shell electrocatalyst in this respect. Platinum(Ⅱ) acetylacetonate, Iron(Ⅲ) acetylacetonate, and carbon support were dispersed in ethylene glycol, which is reducing agent, and irradiated with ultrasound for 3 h to reduce to the metal nanoparticles, followed by washing and drying to obtain a powder. The characterization was observed by analysis such as solution color visualization, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrocatalytic performance. Also, the synthesized samples were calcined at various temperatures to cause the atomic rearrangement to the most stable arrangement. The atomic accumulation of boundary between each atom and compression of platinum lattice that affects activity or durability of electrocatalyst has changed at specific temperature. And both synthesized samples with optimized synthesis condition for mass production and samples with the heat-treatment process show improved electrochemically active surface area (ECSA) and Oxygen reduction reaction (ORR) catalytic activity in the half-cell test and durable catalytic activity in the performance evaluation of membrane-electrode assembly (MEA) compared to existing Platinum catalyst. As renewable energy conversion and storage system is one of the main challenges, FCEV is developed to solve pollution from CO2 emission and oil depletion issues. Our low-platinum nanoparticle with uniform distribution synthesized in a sonochemical method could replace precious metal catalysts used in fuel cells.
Oxygen Reduction Reaction Mechanism Study Via the Mean-Field Microkinetic Modeling and Uncertainty Quantification of Model Parameters
Authors: Kurilovich Aleksandr Andreevich , Stevenson Keith J.
Published: May 2020

Electrocatalytic oxygen reduction reaction (ORR) finds important applications as the cathodic reaction in hydrogen fuel cells or metal-air batteries. However, its slow kinetics even on the most active catalysts requires an understanding of the reaction mechanism for the cost-effective catalyst search.

The first insight into the reaction mechanism can be obtained via the rotation ring disk electrode experiment (RRDE), which can be used to extract information about the reaction kinetics. A substantial amount of experimental work has been carried out in this field with various reaction mechanisms proposed. In many cases, they show a similar level of agreement with the experimental data, because ORR is a complex reaction, while the only intermediate observed experimentally is H2O2 (HO2
- in alkali). More accurate results may be obtained within the mean-field microkinetic modeling approach (MF-MKM). It is built upon the Butler-Volmer formalism for the charge-transfer steps, the law of mass action for the chemical steps, mass transfer equations for the reaction intermediates in the electrolyte, and various interactions between the adsorbed species (Langmuir, Frumkin, and Temkin isotherms).

However, for the complex reactions, even the simplest numerical models have numerous parameters, such as forward/backward rate constants of the proposed reaction steps. They are usually adjusted manually, or fitted to the experimental data using the local optimization methods. The main drawback of both these approaches is that one should have prior knowledge of the approximate model parameters, i.e. guess the reaction pathway. While being successful for relatively simple models, it can be hardly done for the more complicated cases. Additionally, the uncertainty in the estimated model parameters is introduced from the errors in experimental data.

In this work, we describe the quantitative framework for the reaction mechanism selection based on model parameters uncertainty quantification via the Tree-Structured Parzen estimator algorithm and accuracy of fitting of available experimental data by the suggested reaction mechanism within the MF-MKM formalism. So it provides the elucidation of the reaction mechanism which can be considered based on the available experimental data and should be crucial to study the reaction mechanism of ORR and other sufficiently complex reactions.
Tuning Binding Energy in Nanoporous Core Shell Alloys of Palladium to Suppress CO Poisoning in Electrochemical Reduction of CO2
Authors: Chatterjee Swarnendu , Li Yawei , Snyder Joshua David
Published: May 2020

Electrochemical CO2 reduction reaction (CO2RR) has been extensively explored for conversion of dissolved CO2 into useful carbon based products e.g CO, formate/formic acid, alcohols etc. Formate/formic acid as a CO2RR product is drawing focus because of its high energy density and utility as a chemical precursor. Traditional formate producing metals e.g. Co, In, Bi, Sn etc. require high overpotentials, limiting their energy effectiveness. Pd on the other hand, originally known to produce CO at overpotentials above 600 mV RHE, has recently shown substantial formate FE’s at overpotentials below 200 mV. The gradual poisoning of Pd-based CO2RR electrocatalysts through the slow production of CO, even at near unity formate FEs, results in deactivation of the catalyst surface and limits the viability of Pd for sustained electrolysis.

Here, we report synthesis of core-shell nanoporous multimetallic Pd (np-PdX, where X = Co, Ni, Cu, Ag, Cu-Sn, Cu-Ti) alloys that show suppressed CO deactivation based on the subsurface composition of the alloy electrocatalysts. The Pd skinned nanoporous alloys have been obtained by electrochemical dealloying where the presence of less noble metal/alloy under the Pd shell changes the electronic structure of the Pd and consequently alters the CO adsorption strengths and subsequent catalyst deactivation. The tortuous pores (pore size: 5 – 10 nm) give rise to roughness factors above 200 which generates high geometric formate partial current densities (> 30 mA/cm2). Furthermore, the np-Pd electrodes are free standing and obviate the use of any binder and/or support which otherwise causes extra overpotential losses and morphological instability. The suppression of surface poisoning is explained on the basis of weakening of CO binding strengths due to electronic interactions of the alloying component that shifts the d-band center of Pd, as well as changes to the near surface hydrogen solubility which can also affect the adsorption strength of active/inactive intermediates and reaction selectivity.
Scanning Electrochemical Microscopy (SECM) for High-Throughput Screening of Tin Oxide Derived Catalyst Arrays for CO2 Electro-Reduction to Formate
Authors: Desilets Mayer Francis , Hosseini-Benhangi Pooya , Asselin Edouard , Gyenge Előd L.
Published: May 2020

Formate produced from the electro-reduction of CO2 has been proposed as a safe liquid alternative to hydrogen gas in renewable energy storage schemes1 . However, catalysts for electro-reduction of CO2 to formate reaction still suffer from poor stability and activity2,3. Furthermore, the CO2 electroreduction catalysis discovery and screening process is generally hampered by slow, one catalyst sample at a time, experimental procedures. Our overall objective is to develop SECM as a reliable high-throughput technique for screening of electrocatalyst arrays. Here, using SECM, we evaluated the activity of three different tin oxide derived catalysts arranged in an array. Tin(IV) dioxide, has been previously shown to be one of the most promising catalysts for formate generation, while also being thermodynamically reduced to metallic tin at the potential at which CO2RR happens in an aqueous medium4,5. We created two different tin oxide derived catalysts by subjecting mirror-polished native tin oxide to electro-reduction at a constant potentials prior to the CO2 reduction experiments. Electro-reduction of the native tin oxide surface at -3.00 V vs. Ag/AgCl yielded a tin(IV) dioxide deficient surface covered in nanospheres (≈70 um) while electro-reduction at -1.25 V vs. Ag/AgCl create a slightly porous surface exhibiting high proportion of tin(IV) dioxide. Fine tuning the SECM technique to analyze three samples (the two electroreduced and one native tin oxide surface) in an array, we demonstrate the successful evaluation of the electrocatalytic activities of these catalysts and we discuss the advantages and challenges of using SECM to screen catalysts for CO2 reduction.

1. S. Fukuzumi, Joule, 1, 689–738 (2017) https://doi.org/10.1016/j.joule.2017.07.007.

2. C. E. Moore and E. L. Gyenge, ChemSusChem, 10, 3512–3519 (2017) http://doi.wiley.com/10.1002/cssc.201700761.

3. B. Khezri, A. C. Fisher, and M. Pumera, J. Mater. Chem. A, 5, 8230–8246 (2017) http://xlink.rsc.org/?DOI=C6TA09875D.

4. A. Dutta, A. Kuzume, M. Rahaman, S. Vesztergom, and P. Broekmann, ACS Catal., 5, 7498–7502 (2015).

5. S. Geiger, O. Kasian, A. M. Mingers, K. J. J. Mayrhofer, and S. Cherevko, Sci. Rep. (2017).

Figure 1
Electrochemical Synthesis of C-N Organic Compound Via Direct Reduction of CO2 in Ionic Liquid
Authors: Ling Pinghua , Winchester Williams , Riley Kevin , Wang Zhe
Published: May 2020

The development of more efficient and sustainable methods for synthesizing C–N organic compound has always been a major focus of synthetic organic chemistry due to its critical roles natural environment and industries. Herein, we report a facile electrochemical approach to form C-N bonds form amines and CO2 in ionic liquid (IL) at room temperature under the metal-free condition. This reaction was carried out with very low potential under mild condition without adding any additives or tedious work-up. A broad range of amines could be catalyzed by active intermedia generated in a high efficient way, yielding the C-N bonds production selectively depended on the structure of amine and ionic liquid. This new strategy shows that a metal-free and friendly system could provide a platform not only to synthesize N-containing organic compounds with low-cost but also by efficient CO2 storage and utilization in an environmental friendly manner.
Atomistic Mechanisms of Single Atom Catalysis on Graphene for CO2 Reduction
Authors: Liu Yuanyue
Published: May 2020

Single metal atoms embedded in N doped graphene have attracted extensive interest as catalysts for carbon dioxide reduction. Although DFT calculations based on computational hydrogen electrode mode have been widely used to study the atomistic mechanisms, these calculations fail to reproduce/explain some of the important experimental observations/results. Consequently, it is unclear what is the atomic structure of the active site.

We show that these problems are due to the neglect of surface charge and water molecules in the modelling, which play important roles [1,2] in electrochemistry at solid-water interface. By including these into the simulations, we can explain the experiments and identify the active site [2]. The activity is further explained in a general picture of electronic structure. [3,4]

[1] D. Kim, J. Shi, Y. Liu, JACS, 2018, 140, 9127

[2] X. Zhao, Y. Liu, in preparation

[3] Y. Liu, J. Wu, K. P. Hackenberg et al, Nature Energy, 2017, 6, 17127

[4] Y. Liu, Y. M. Wang, B. I. Yakobson, B. C. Wood, Phys. Rev. Lett. 2014, 113, 028304
Electrocatalytical Performance of Au-Pd Cubic and Octahedral Core-Shell Nanostructures in the Formic Acid Oxidation Reaction
Authors: Romero Hernández Adrián , Estrada-Arce Elsa Miriam , Ezeta Araceli , Manriquez Ramirez Maria Elena
Published: May 2020

AuPd cubic and octahedral core-shell nanostructures were synthesized by seed growth method and its performance was evaluated in the formic acid oxidation reaction (FAOR). The core-shell nanostructure shapes were confirmed by SEM in Figure 1. The electrochemical surface areas were obtained by CO stripping. The electrocatalytic activity in the FAOR was evaluated in a 0.5 M HClO4 and 1 M HCOOH electrolyte by cyclic voltammetry in Figure 1. The cubic nanostructure showed the best current density for the direct route in the FAOR. The AuPd core-shell encouraged the FAOR direct or indirect route by the CO adsorption-desorption processes on the surface of each shape.

Figure 1
Unifying Concepts in (Electro)Catalysis for Understanding the Direct Synthesis of H2O2
Authors: Kromer Matthew , Adams Jason , Zhao Yuanya , Flaherty David , Rodriguez-Lopez Joaquin
Published: May 2020

Hydrogen peroxide (H2O2) is a sustainable and selective oxidant that is currently produced via the costly anthraquinone process from H2 and O2 gas.1,2 On-site production of H2O2 for various industrial applications would benefit from the direct synthesis of H2O2 using alternative highly selective and highly active catalysts. Recently, the mechanism of H2O2 production on metal catalysts was suggested to occur via an electron transfer between H2 and O2 mediated by individually addressable electrocatalytic steps.3 Understanding the manifestations of this electrocatalytic paradigm on (electro)catalysts would help design more selective and active H2O2 catalysts and create new opportunities for designing heterogeneous catalysts using electrochemical principles.

Here, we present an electrochemical model based on mixed potential theory for explaining and predicting the performance of H2O2 catalysts and its verification using high pressure electrochemistry, scanning electrochemical microscopy, rotating ring-disk electrode measurements, and matched electrochemical and heterogeneous catalysis reactor measurements. In our scheme, the H2 oxidation reaction (HOR) and the O2 reduction reaction (ORR) are treated as distinct half-cell reactions, allowing us to conveniently use electrochemical methods to determine reaction descriptors such as Tafel slopes and the number of electrons n transferred during the ORR. Several classes of catalysts were assessed towards their selectivity to form H2O2 via electrocatalysis and direct synthesis. Electrochemical kinetic parameters were used to obtain measures that relate the partial pressures of H2/O2 in direct synthesis to an equivalent operating potential. This operating potential was then used to predict the selectivity observed during thermochemical synthesis. We further generated guidelines to predict the characteristics of highly active catalysts.

Our model accurately predicted aspects of heterogeneous catalysis starting from purely electrochemical concepts. With the ability to directly predict H2O2 selectivities from electrochemical measurements, it is possible to rapidly screen materials to discover new low-cost and selective direct synthesis catalysts for H2O2 and for other reactions of interest. We hope the results presented here will seed new approaches for the discovery of heterogeneous catalysts using readily accessible electrochemical measurements.

1. Goor, G.; et al., 2007. Hydrogen Peroxide. Ullmann's Encyclopedia of Industrial Chemistry.

2. García-Serna, J.; et al.
Green Chem.
2014, 16, 2320–2343.

3. Wilson, N. M.; et al.
J. Am. Chem. Soc.
2016, 138, 574-586.