bluuebunny/crossref_metadata_2025 huggingface dataset:
Model Non-Precious Metal Catalysts for Oxygen Reduction Reaction: A Bottom-up Approach
Authors: Martinez Ulises , Williamson Todd L , Artyushkova Kateryna , Hoffbauer Mark A , Purdy Geraldine M , Dumont Joseph H , Dattelbaum Andrew M , Mohite Aditya , Gupta Gautam , Zelenay Piotr
Published: February 2020

Further development of non-precious metal catalysts (NPMCs) synthesized from earth-abundant elements (C, N, transition metal) continues to be challenged by the lack of understanding of the origin of the oxygen reduction reaction (ORR) activity from such complex materials. Current state-of-the-art synthesis methods for NPMCs involve intricate pyrolysis steps producing highly heterogeneous catalytic systems (1, 2). Therefore, a systematic bottom-up approach using model carbon systems needs to be developed for the better understanding of the formation of active sites and the active site identification.

Recently, we have reported a novel approach for the incorporation of nitrogen heteroatoms into the graphitic carbon structure of liquid-phase exfoliated graphite (3). This approach utilizes high-flux energetic neutral atom beam technology (ENABLE) to incorporate nitrogen heteroatoms via direct chemical activation overcoming thermal activation barriers. Our preliminary results have identified a relationship between the type of nitrogen species doped and the substrate temperature (Figure 1). However, although improved onset potential for the ORR was observed from thin films doped with 13 at.% nitrogen (87% graphitic), the electrocatalytic activity in acid electrolyte is still poor. The work to be presented in this talk represents the continuation of our efforts to understand the role of each component in NPMCs, this time with the addition of transition metals, Fe and/or Co, prior to nitrogen doping. Electrochemical studies will be performed in both acid and alkaline electrolytes to better understand the different reaction mechanism in both environments.

References:

1. G. Wu, K. L. More, C. M. Johnston and P. Zelenay, Science (New York, N.Y.), 332, 443 (2011).

2. E. Proietti, F. Jaouen, M. Lefèvre, N. Larouche, J. Tian, J. Herranz and J.-P. Dodelet, Nature Communications, 2, 416 (2011).

3. U. Martinez, T. L. Williamson, K. Artyushkova, N. Mack, G. M. Purdy, J. H. Dumont, D. Kelly, W. Gao, A. M. Dattelbaum, A. Mohite, G. Gupta and P. Zelenay, ECS Transactions, 64, 293 (2014).

Figure 1
(Physical and Analytical Electrochemistry Division David C. Grahame Award) Kinetics of the Hydrogen Oxidation in Alkaline and Acid Electrolytes
Authors: Gasteiger Hubert A , Durst Julien , Herranz Juan , Siebel Armin , Hasché Frédéric , Rheinländer Philipp Jan , Simon Christoph
Published: February 2020

The development of fuel cells based on alkaline membranes (AMFCs) is one of the options to reduce the required amount of platinum, whereby the strong CO2sensitivity of alkaline membranes is a significant challenge.  However, while there are several non-noble metal catalysts for the oxygen reduction reaction in alkaline electrolytes which match the activity of platinum, the only currently known hydrogen oxidation catalysts are based on platinum or palladium.  Furthermore, the activity of platinum is orders of magnitude lower than in acidic electrolytes [1,2,3], so that ultra-low platinum loading anodes which can be used in acidic electrolytes (PEMFC) are not feasible in alkaline electrolytes.  Therefore, the challenge to catalysis research for alkaline membrane fuel cells is to develop more active hydrogen oxidation catalysts.

In our presentation, we will compare the kinetics of the H2 oxidation/evolution reaction (HOR/HER) on carbon supported platinum-group metal electrocatalysts in alkaline and acid electrolytes, determined by rotating disk electrode measurements in liquid electrolytes and hydrogen-pump measurements in fuel cells.  The so far proposed causes for the »100-fold lower HOR/HER kinetics in alkaline electrolyte are an increased H/metal bond strength [1,4], a change of the reaction mechanism from H+ to H2O activation requiring more oxophilic catalyst surfaces [5], and/or a change of the water configuration at the metal/electrolyte interface [6].  The consistency of these hypotheses with the HOR/HER kinetics on different metal electrodes will be discussed.

References:

[1]     J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz, H.A. Gasteiger, Energy Environ. Sci.
7(2014) 2255.

[2]     J. Durst, C. Simon, A. Siebel, P.J. Rheinländer, T. Schuler, M. Hanzlik, J. Herranz, F. Hasché, H.A. Gasteiger, ECS Trans. 64(3)(2014) 1069.

[3]     C.M. Zalitis, D. Kramer, A.R. Kucernak, Phys. Chem. Chem. Phys. 15 (2013) 4329.

[4]     Y. Wang, G. Wang., G. Li, B. Huang, J. Pan, Q. Liu, J. Han, L. Xiao, J. Lu, L. Zhuang, Energy Environ. Sci.(2014), DOI: 10.1039/c4ee02564d.

[5]     D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, D. Van der Vilet, A.P. Paulikas, V. Stamenkovic, N. Markovic, Nat. Chem. 5 (2013) 300.

[6]     J. Rossmeisl, K. Chan, R. Ahmed, V. Tripkovic, M. Bjorketun, Phys.
Chem. Chem. Phys. 15 (2013) 10321.
(Invited) A Central Aspect of Electrocatalysis: Generation of Active Sites By Potential-Driven Surface Processes (Part 2)
Authors: Gottesfeld Shimshon
Published: February 2020

This talk will open with presentation of a general aspect of electrocatalysis which has not been fully recognized, particularly so when it comes to theoretical derivations of the dependence of the rate of electrocatalystic processes on the electrode potential. Description of this prevalent and important pattern of potential-generated active sites in electrocatalysis,  will be followed by specific examples of ORR and HOR electrocatalysts in acid and in alkaline fuel cells , including the case of bifunctional HOR catalysts in alkaline membrane fuel cells.

 A wide variety of electrocatalytic processes taking place at either functionalized surfaces or “metal”  surfaces,  are all , in fact,  surface redox mediated . This means  that the electrode potential defines the steady state population of active sites and suggests that the role of the potential  in active site generation must  be incorporated in the pre-exponential factor of the overall rate expression.  In fact, the   potential driven active site generation serves to “ignite” the faradaic process.   This explains why the E0 
redoc
 
system  of M/Mox , or  MOX+n/MOX+n+m  surface couples , must be as close as possible to  E0
cell process , to enable high conversion efficiency as well as higher rates at low overpotentials.  

In acid systems, strong proximity of E0 
redoc
 
system  to E0
cell process , is difficult to implementfor the ORR , because the reduced form of the relevant redox mediator must also serve as stabilizer of the intermediate,OOHads, requiring significant oxygen affinity of the reduced form of the redox system ( e.g., Pt metal)    The coinage metals are active ORR catalysts at high pH apparently because a different early step in the faradaic process results in full highlighting of the benefit of active  site generation at the lowest possible  overpotential.

Bifunctional metal catalysts have been recognized as key to high HOR activity in alkaline membrane fuel cells. The last part of this talk will analyze this observation in terms of the wide principle of potential generated active sites.
(Invited) Water As Promoter and Catalyst in Dioxygen Electrochemistry at Aqueous and Organic Electrified Interfaces
Authors: Markovic Nenad M
Published: February 2020

Water and di-oxygen are the most important and pervasive chemicals that influence all areas of science, from physics to biology to chemistry, and are particularly important in governing phenomena occurring at solid-liquid interfaces in electrochemical environments. One property that sets aqueous-based electrochemical interfaces apart from all other interfaces is the unique arrangements of water molecules within the distinctive interactions between metal surfaces and hydrated ions. These interactions are complex, involving molecular and dissociative adsorption, as well as van der Waals forces both between water molecules and neighboring ions in the compact part of the double layer (i.e. solvation) and between water and covalently-bonded co-adsorbates (e.g. adsorbed hydroxyl species, OHad). Despite the enormous fundamental and technological significance in unfolding these complexities, previous work has treated the water molecule itself simply as a reactant needed to satisfy the stoichiometry of electrochemical reactions, rather than a vital hydrogen-/hydroxyl-donor molecule that can promote the rates of transformation of reaction intermediates to final products. The prime example of such an “incomplete” treatment of water is the oxygen reduction reaction (ORR) in “proton”-O2 fuel cell systems and in lithium-O2 battery systems. Current models guiding the development of new materials for these systems rely on a single descriptor - the binding energy of oxygen intermediates – that cannot explain many “anomalous” phenomena.

Here, we introduce a new model in which water itself plays a critical role in determining the reaction kinetics in dioxygen electrochemistry. The model is based on the formation of HOad···H2O (aqueous solutions), and LiO2···H2O (organic solvents) complexes that place water in a configurationally favorable position for proton transfer to weakly adsorbed intermediates. We found that water plays a dual role, acting as a key promoter in both environments as well as a catalyst in Li-O2 systems
(Invited) Investigation of Hydrogen Oxidation and Evolution Reaction Activity on Iridium Metal in Alkaline Electrolyte
Authors: Gorlin Yelena , Herranz Juan , Durst Julien , Rheinländer Philipp Jan , Gasteiger Hubert A
Published: February 2020

One of the challenges that currently impedes the commercialization of anion exchange membrane fuel cells (AEMFCs) is the development of suitable catalysts for the hydrogen oxidation reaction (HOR, H2 + 2 OH- → 2 H2O + 2 e-).(1) Because this challenge is unique to the alkaline environment of AEMFCs and is not present in the acidic environment of the proton exchange membrane fuel cells (PEMFCs), there has been renewed interest in quantifying hydrogen oxidation and evolution (HOR/HER) reaction kinetics and understanding the differences in activities of catalysts in acidic and alkaline environments. In these studies, a disagreement has emerged concerning the HOR/HER activity of iridium (Ir) metal in base, with researchers reporting that it is both higher(2, 3) and lower(4) than the corresponding activity of platinum (Pt) metal. In our study, we re-examine the electrochemical behavior of polycrystalline Ir in alkaline environment and find that the HOR activity of Ir depends on the electrochemical characterization procedure used in its quantification. In particular, we determine that subjecting the electrode to increasingly more cathodic potentials leads to a decrease in the HOR activity. Although this phenomenon could be argued to correspond to the adsorption of contaminants onto the catalyst surface, we demonstrate that the underlying reason for the drop in activity is likely not a surface contamination effect, but rather absorption of hydrogen into the sub-surface of the Ir electrode. Specifically, we find that exposure of the Ir surface to potentials that are lower than 0.10 V vs. the reversible hydrogen electrode (RHE) in H2-saturated environment leads to an appearance of an oxidation peak (Fig. 1) in a potential region in which surface contaminants are not expected to be oxidized (0.15-0.20 V vs. RHE), and that the size of this peak scales inversely with the HOR activity of the surface. Our results have important implications towards understanding of the HOR/HER kinetics and the development of improved catalysts for these reactions.

References

1. W. Sheng, H. A. Gasteiger and Y. Shao-Horn, J. Electrochem. Soc., 157, B1529 (2010).

2. N. Danilovic, R. Subbaraman, D. Strmcnik, K.-C. Chang, A. P. Paulikas, V. R. Stamenkovic and N. M. Markovic, Angewandte Chemie International Edition, 51, 12495 (2012).

3. D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, V. van der, A. P. Paulikas, V. R. Stamenkovic and N. M. Markovic, Nat Chem, 5, 300 (2013).

4. J. Durst, A. Siebel, C. Simon, F. Hasche, J. Herranz and H. A. Gasteiger, Energ. Environ. Sci., 7, 2255 (2014).

Figure 1
(invited) Spectroscopic Techniques for the Identification of Fe and Co Coordination Chemistries in Fe(Co)-N-C Catalysts : Pristine Versus Degraded Catalysts
Authors: Jaouen Frederic , Goellner Vincent , Sougrati Moulay-Tahar , Zitolo Andrea , Fonda Emiliano
Published: February 2020

While Proton Exchange Membrane Fuel Cells (PEMFCs) are already entering the portable sector and the market of materials handling vehicles, the long term economic growth of this technology remains subject to a further decrease in the platinum loading. Recent advances in non-precious metal catalysts for the oxygen reduction reaction (ORR) and synthesized from a transition metal (Fe, Co), a nitrogen and a carbon precursor are encouraging. The initial metal coordination in such catalysts is not yet fully understood, let alone that in the catalysts degraded in situ or ex situ.

 The initial metal coordination in Fe(Co)/N/C catalysts as well as coordination changes following accelerated degradation in PEMFC or accelerated ex situ degradation by H2O2 will be discussed, and compared to the parallel decrease in their ORR activity and other structural changes. In PEMFC, accelerated degradation was achieved by applying a set number of short potential steps up to 1.4 V vs. RHE, while the extent of ex situ H2O2 degradation was controlled through the amount of moles H2O2 contacted per gram of catalyst. The two different modes of degradation lead to two completely different set of changes in the metal contents, coordination and morphological changes in the catalysts.

 Coordination of the Fe atoms was experimentally investigated with both 57Fe Mössbauer and X-ray absorption spectroscopy while that of the Co atoms was investigated solely with X-ray absorption spectroscopy. These techniques are sufficiently sensitive to investigate powders with small metal contents (down to 0.1 wt %) or even initial and degraded electrodes with metal loadings of ca 50-150 mg cm-2. Full exploitation of these techniques and interpretation of the spectra is possible only when the pristine Fe(Co)/N/C catalysts are free of metallic, oxide or carbide by-products that are believed to be ORR inactive. If one or several of these phases are present, the spectroscopic signal related to the ORR active site(s) is obscured, which complicates or impedes analysis of the spectra. Catalysts free of such crystalline phases were obtained either by optimizing the metal content or the synthesis, allowing the recording of clean initial spectra and the tracking of coordinative changes occurring upon degradation. Furthermore, ab initio modeling of the X-ray absorption near edge structure spectra was performed and compared to experimental spectra, leading to a more precise concept of the metal coordination in Fe(Co)/N/C pyrolyzed catalysts.
Electrochemical Analysis and Density Functional Theory (DFT) Simulation to Investigate the Phosphoric Acid Adsorption on Pt3m (M = Fe, Co, Ni) Nanoparticles
Authors: Park Hee-Young , Lim Dong-Hee , Cha In Young , Chung Young-Hoon , Yoo Sung Jong , Kim Hyoung-Juhn , Henkensmeier Dirk , Kim Jin Young , Nam Suk Woo , Jang Jong Hyun
Published: February 2020

High temperature-polymer electrolyte membrane fuel cell (HT-PEMFC) utilizing phosphoric acid doped polybenzimidazol membrane is a promising power supply for a number of stationary applications. At high operating temperature, significant enhancement in oxygen reduction reaction (ORR) kinetics is expected. However, typically the cell performance of HT-PEMFC is lower than that of conventional Nafion-based PEMFCs. One of important reason is the strong adsorption of phosphoric acid or anions, so called ‘phosphoric acid poisoning’, which blocks the active sites on Pt/C.

Alloying with transition metals have been suggested for an efficient way to improve the performance of HT-PEMFC as the alloying may provide enhanced intrinsic ORR activity and improved tolerance against the phosphoric acid poisoning. Experimental observation and computational simulations revealed that lowered adsorption energy of OH on alloy of Pt and transition metal nanoparticle catalysts (PtM/C) provided the enhanced ORR activity1.

However, there were few reports investigating effect of transition metal alloying on the phosphoric acid tolerance. Recently, He et al. demonstrated improved tolerance against the phosphoric acid poisoning in bulk PtSn2 and PtNi nanoparticle3 alloy surfaces. They postulated that ligand effect or geometric effect may be responsible for the tolerance of alloy surfaces. As a theoretical investigation of the alloying effect, Savizi and Janik calculated potential dependence of phosphoric acid adsorption free energy4 on Pt(111) surfaces, using density functional theory (DFT) simulations. However, there has been no further study, including PtM/C electrocatalysts.

In this research, we investigated the effect of transition metal alloying on the phosphoric acid poisoning in Pt3M (where, M = Fe, Co, Ni) nanoparticle catalyst (Pt3M/C) surfaces. Using the cyclic voltammetry, adsorption strength of phosphoric acid on Pt3M/C was analyzed. Also, the effect of transition metal alloying on the adsorption strength of phosphoric acid in Pt3M/C was analyzed based on the DFT simulations. Combination of electrochemical analysis and DFT simulations allowed investigating systematically the effect of alloying on the phosphoric acid adsorption in Pt3M/C surfaces.

References

1. I.E.L. Stephens, A.S. Bondarenko, U. Gronbjerg, J. Rossmeisl, I. Chorkendorff, Energy Environ. Sci., 5, 6744 (2012).

2. Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Phys. chem. Chem. Phys., 12, 12544 (2010).

3. Q. He, B. Shyam, M. Nishijima, D. Ramaker, S. Mukerjee, J. Phys. Chem. C, 117, 4877 (2013).

4. I. S. P. Savizi, M. J. Janik, Electrochim. Acta 56, 3996 (2011).
High Electrocatalytic Activity of the Pt-Based Catalyst Supported on Carbon Prepared Using a Plasma Torch and Natural Gas
Authors: Ribeiro Josimar , Evangelista Tereza Cristina Santos , Paganoto Giordano Toscano
Published: February 2020

Physicochemical and electrochemical characterisations of Pt-based electrocatalysts supported on carbon (Vulcan® XC72, C1 and carbon produced using a plasma torch from natural gas vehicles, C2) toward ethanol electrooxidation were investigated. The Pt/C1 and Pt/C2 electrocatalysts were prepared by thermal decomposition of polymeric precursors at 350 ° C. The electrochemical and physicochemical characterisations of the electrocatalysts were performed by means of X-ray diffraction (XRD), Raman scattering, cyclic voltammetry and chronoamperometry tests. The XRD results show that the Pt-based electrocatalysts present platinum metallic which is face-centered cubic structure. The results indicate that the Pt/C1 electrocatalyst has a smaller particle size (10.1 – 6.9) compared with the Pt/C2 electrocatalyst; however, the Pt/C2 particle sizes are similar (12.8 – 10.4 nm) and almost independent of the reflection planes, which suggests that the Pt crystallites grow with a radial shape. Raman results showed that all the materials are composed of randomly oriented structural units varying from 50 to 80 Å in size. Cyclic voltammetry and chronoamperometry data obtained in this study indicate that the deposition of Pt on carbon plasma increases its electrocatalytic activity toward ethanol oxidation.

Acknowledgments

FAPES, CAPES, FINEP, PETROBRAS, LMC and CNPq.
Quantitative Study of Antioxidants and Their Reactivity in Various Tea
Authors: Perera Manori , Hocker Nathan , Rudd Lydia , Prochotsky Jennifer , Eppurath Atul
Published: February 2020

Tea is known as one of the most popular beverage throughout the world.  Lately it has also attracted consumers due to its health benefits through antioxidant properties.  Research shows different methods to identify and quantify these antioxidant-polyphenols.  But not much research has gone into (1) carefully quantifying what polyphenols are really active as antioxidants and (2) consumer products and their antioxidant content in consurmer products.  In this project, various tea ranging from lose leaf tea to already brewed bottled tea are used to identify and quantify the polyphenols and measure how reactive these are as antioxidants.  Polyphenol activity is measured using different potentiometric methods as well as a colorimetric method.  These results will enable us to understand what content of antioxidants are present is each tea and are all antioxidants are active in presence of radicals.
Electroactive Polymers Prepared By Vapour Phase Polymerisation
Authors: Brooke Robert , Crispin Xavier , Murphy Peter J , Evans Drew
Published: February 2020

Polymers are lightweight, flexible, solution-processible materials, which can possess insulating, semiconducting or metallic properties. Because of the high natural abundance of their constituting atoms, polymers are promising materials for low-cost printed electronics, mass produced and/or large-area applications. The conducting polymer poly(3,4-ethylenedioxythiophene), PEDOT, is one example material which displays (among others) high conductivity [1], and excellent thermoelectric properties [2].  Here, we report that when doped with tosylate and fabricated via vapour phase polymerization (VPP), the resulting PEDOT material is semi-metallic [2].  This material then forms the platform for a range of electrochromic applications. 

Through the use of variations to the VPP process, a range of electroactive thin films are prepared.  These cover complex multilayer structure, copolymerization of different conductive monomers, and spatial patterning.  Performance data on the switching of electrochromic devices based upon these polymer films show stability upwards of 10,000 switches.  Further enhancement of the electroactive polymers is achieved by incorporating within various 2D materials such as graphene [3].  In this extension, graphene- or MoS2-PEDOT-tosylate nanocomposite films, ca. 170 nm thick, have been prepared by dispersing sterically stabilised nanosheets throughout an oxidant solution containing a triblock copolymer, with the liquid-like properties of the oxidant film under typical VPP conditions transporting the 2D nanomaterials into the forming PEDOT-tosylate film. The resulting composite film of graphene-PEDOT-tosylate has a 65% larger in-plane modulus when compared to the polymer only film, and can be used to facilitate the oxygen reduction reaction, with efficiencies equivalent to or greater than that of Pt [3]. 

[1] M.V. Fabretto, D.R. Evans, M. Mueller, K. Zuber, P. Hojati-Talemi, R.D. Short, G.G. Wallace, P.J. Murphy, Polymeric material with metal-like conductivity for next generation organic electronic devices, Chem. Mater., 24, 3998-4003, 2012

[2] O. Bubnova, Z.U. Khan, H. Wang, S. Braun, D.R. Evans, M.V. Fabretto, P. Hojati-Talemi, D. Dagnelund, J.-B. Arlin, Y. Geerts, S. Desbief, D. Breiby, J.W. Andreasen, R. Lazzaroni, W. Chen, I. Zozoulenko, M. Fahlman, P.J. Murphy, M. Berggren, X. Crispin, Semi-metallic polymers for thermoelectricity, Nat. Mater., 13, 190-194, 2014

[3] N. Vucaj, M.D.J. Quinn, C. Baechler, S.M. Notley, P. Cottis, P. Hojati-Talemi, M.V. Fabretto, G.G. Wallace, P.J. Murphy, D.R. Evans, Vapor phase synthesis of conducting polymer nanocomposites incorporating 2D nanoparticles, Chem. Mater., 26, 4207-4213, 2014
Polymer Electrolytes for Electrochromic Devices
Authors: Silva M. M. , Leones R. , Alves R. , Pereira Rui F. P. , de Zea Bermudez V.
Published: February 2020

Polymer electrolytes are currently the focus of much attention as potential electrolytes in electrochemical devices such as batteries, display devices and sensors [1,2]. Generically, solid polymer electrolytes (SPEs) are mixtures of salts with soft polar polymers. SPEs have many advantages including high energy density, no risk of leakage, no issues related to the presence of solvent, wide electrochemical stability windows, simplified processability and light weight. With the goal of developing a new family of environmentally friendly multifunctional biohybrid materials displaying high ionic conductivity we have produced in the present work, flexible films based on different polymers or hybrids incorporating different salts.

The polymer electrolytes studied here have been characterized by means of Differential Scanning Calorimetry, Thermogravimetric Analysis, X-ray diffraction, Polarized Optical Microscopy, complex impedance spectroscopy and cyclic voltammetry. An evaluation of the performance of the sample with the highest conductivity as electrolyte in all solid-state ECDs was performed [3].

Acknowledgments:This work is funded by FCT- Fundação para a Ciência e a Tecnologia, project references Project Pest-C/QUI/UIO686/2013, PEst-OE/QUI/UI0616/2014, POPH/FSE for a grant (SFRH/BPD/87759/2012) (R.F.P.P.), POPH/FSE for a grant SRFH/BD/90366/2012 (R.L), grant POPH/FSE for a grant SFRH/BD/97232/2013 (R. A) and COST Action MP1202 ‘‘Rational design of hybrid organic–inorganic interfaces.” M. M. Silva acknowledges CNPq, for the mobility grant provided by this institution.

 

REFERENCES

[1] F.M. Gray, in Solid Polymer Electrolytes: Fundamentals and Technological Applications, VCH Publishers, Inc. (1991).

[2] J.R. MacCallum, C.A. Vincent, Polymer Electrolyte Reviews, vol. 1, Elsevier, London, 1987.

[3] S. C. Nunes, V. de Zea Bermudez, M. M. Silva, M. J. Smith, D. Ostrovskii, R. A. Sá Ferreira L.D. Carlos and J. Rocha, A. Gonçalves, E. Fortunato “Sol-gel derived potassium-based di-ureasils for smart windows”, Journal of Materials Chemistry 17 (2007) 4239-4248.
Electrochromic Devices Incorporating Conducting Polymer or Novel Viologens
Authors: Deepa Melepurath , Sydam Rambabu
Published: February 2020

Organic electrochromes such as conducting polymers and viologens (di-substituted-di-pyridinium salts) are attractive for electrochromic smart window applications due to high optical contrast, possibility of switching between multiple colors, ease of preparation and good write-erase efficiency. While conducting polymers are electrode bound species and undergo a color change via redox reactions at the electrode, viologens are typically colorless solution phase compounds, which form a reversible insoluble deeply colored film on the conducting electrode, upon application of an external bias (Figure 1). In this talk, the development of new viologen derivatives like the poly(cyclotriphosphazene-4,4′-bipyridinium) chloride, the effect of substituents on the electro-optical response, issues related to electrolytes and their compatibility with the electrochromic materials will be discussed. In the realm of conducting polymers, poly(3,4-ethylenedioxythiophene) (PEDOT), is a dual function material: it can serve as a transparent conducting electrode and a cathodically coloring electrochrome. In our lab, large area PEDOT films have been fabricated over plastic substrates and their ability to concurrently work as flexible conducting substrates while switching between the pale blue and dark blue hues is demonstrated. Concerns pertaining to scaling up of conducting polymer coatings and viologen based devices will also be discussed.

Figure 1
Progress in Electrochromics and Thermochromics: New Data on Oxide Films of W, Ni and V, and on Devices Based on These
Authors: Granqvist Claes-Goran
Published: February 2020

This paper surveys recent work on electrochromic and thermochromic materials and devices. The first part deals with electrochromic films based on of tungsten oxide and nickel oxide with emphasis on durability under extended cycling in different electrolytes, and the second part reports on thermochromic films based on vanadium oxide with focus on the role of nanostructure. Several new results will be discussed, including modelling of long-term cycling durability for electrochromic Ni oxide films and the growth of V oxide films on different substrates and in different gaseous ambients. Perspectives are given on device manufacturing.
Printed Flexible Solid State Electrochromic Devices Based on NiO/WO3 Complementary Electrodes
Authors: Cai Guofa , Darmawan Peter , Cui Mengqi , Lee Pooi See
Published: February 2020

In this paper, flexible solid state electrochromic devices based on NiO/WO3 complementary electrodes and gel polyelectrolyte was successfully prepared for transmissive electrochromic applications. The cathode of WO3 film and the anode of NiO film were prepared by inkjet printing, with gel polyelectrolyte as the Li+ion conductor layer. Inkjet printing is a low-cost and attractive technology for patterning electrochromic materials on various substrates and allows deposition of electrochromic materials on a specific location with simultaneous thickness control by the number of printed layers. The printing has been done on flexible transparent conductive electrodes such as indium tin oxide-(ITO) coated polyethylene terephthalate (PET), which overcomes the heavy and rigid drawbacks of ITO glass substrates. In addition, using a gel electrolyte avoids electrolyte leakage problem, allows the ease of handling reduces the cost of device packaging and attains greater reliability. The flexible device exhibits a large optical modulation, fast switching speed and high coloration efficiency.
An Electrostatically Strong Polyviologen-Reduced Graphene Composite Film for Highly Stable Electrochromic Systems
Authors: Gadgil Bhushan , Damlin Pia , Kvarnström Carita
Published: February 2020

Polyviologen (PV)-reduced graphene oxide (rGO) nanocomposite films were fabricated by simple, one step reductive electropolymerization of cyanopyridinium based precursor monomer in an aqueous dispersion of graphene oxide (GO). Since the polymer formation and reduction of GO occurs at the same potential window, electrocodeposition technique was chosen for obtaining nanostructured PV-rGO film. The cyclic voltammetry experiments of PV-rGO displayed two well resolved, highly stable one-electron redox processes typical of viologen. Being a redox polymer, incorporation of rGO further enhances the electroactivity of the PV in the composite films. FTIR, Raman, XRD and XPS analysis revealed structural changes occurred after composite formation.  The PV-rGO nanostructured film exhibits a conspicuous electrochromism with low driving voltage and striking color changes. It was found that the PV-rGO film exhibit high coloration efficiency, fast response times and better cycling stability compared to pristine PV thin film. This performance can be attributed to the high stability of the electrochrome in the composite assembly induced by electrostatically driven non-covalent interactions between redox PV and rGO, high electrical conductivity and enlarged surface area through reinforced nanostructured graphene sheets for tethering PV molecules.

Figure 1
Syntheses and Applications of Inorganic Electrochromic Materials and Devices
Authors: Wang Jinmin
Published: February 2020

Tungsten oxide (WO3) nanorods were synthesized by a hydrothermal process. Transparent film was fabricated by an aggregation-deposition process of WO3 nanorods on transparent conductive glass. The as-synthesized WO3 nanorods exhibit good electrochromic properties. WO3 nanopaltes were directly grown on transparent conductive glasses by a crystal-assisted hydrothermal process, showing enhanced response and coloration efficiency. These properties of WO3 nanostructures endow their promising application in large-area smart windows. Prussian blue films were fabricated and used in color-changeable betteries.

A bi-functional Prussian blue/Aluminium device has been demonstrated for self-powered electrochromic window and self-rechargeable transparent battery. Without applying any external bias, Prussian blue can be bleached to Prussian white by connecting the Prussian blue and Al electrodes. After bleaching, the blue colour of the device can be spontaneously recovered. In this regard, the designed device can be used as an energy-saving electrochromic smart window which requires no external power source. The as-prepared device can also be used as a battery with a high output voltage. Most importantly, after discharging, such a battery can automatically self-recharge. The as-prepared device exhibits promising applications in broad fields, for example, as a self-powered smart window to perform indoor light and heat management, and as a self-rechargeable transparent battery to power some delicate devices.
Conducting Polymers-Based Electrochromic Materials with Tunable Properties
Authors: Zhang Cheng
Published: February 2020

Conducting polymers-based electrochromic (EC) materials have attracted wide interests on the applications of smart window, display and rearview mirror due to their better processability, the ease of color control, fast switching and high coloration efficiency.1-3And for EC polymers, multi-color showing is one of the most important factors for commercial applications. Changing the structure of the EC polymers at the molecular level is an effective way to tune polymers’ colors, such as introducing functional groups, constructing D-A structure and copolymertization. Up to now, we have synthesized a series of conducting polymers base on thiophene, carbazole and triphenylamine derivatives. Among them, five different colors (including red, green and blue) could be realized, the higher optical contrast could reach to 76% and the switching time could be less than 1 s (about 0.6 s). The excellent properties have already meet the requirement of the materials for the practical applications. In addition, we investigated the influence of different donor (or accepter) units and multi-active position on the performance of EC polymers, which could give some reasonable conclusion and explanation.

References

1. H. K. Song, E. J. Lee , S. M. Oh, Chemistry of Materials, 17, 2232 (2005).

2. P. M. Beaujuge, J. R. Reynolds, Chemical Reviews, 110, 268 (2010)

3. G. E. Gunbas, A. Durmus, L. Toppare, Advanced Materials, 20, 691 (2008).

Fig.1
t
he electropolymerization route, spectroelectrochemical spectra and electrochromic properties

Figure 1
Tuning the Neutral State Color of Blue, Cyan and Green PI-Conjugated Copolymers By Jointly Playing the Acceptor Strength and the Steric Hindrance
Authors: Fagour Sébastien , Thirion Damien , Vacher Antoine , Sallenave Xavier , Sini Gjergji , Decarreau Jean-François , Aubert Pierre-Henri , Vidal Frédéric , Chevrot Claude
Published: February 2020

Due to their electronic structure, most of pi-conjugated polymers present visible coloration in their neutral state, hence possess a characteristic absorbance in the 400-800nm spectrum. Upon p-doping, this absorption shifts toward longer wavelengths leading to electrochromic properties. Among the colors accessible in the visible palette, the primary cyan is somewhat particular to obtain because two absorption bands are necessary, one around 400nm and a second near 670nm. This can be obtained by synthesizing donor-acceptor (D-A) pi-conjugated copolymers. Moreover during the switching of the material, these two bands have to be concomitantly shifted toward the infrared.1

In this presentation we will present the synthesis and characterizations of four pi-conjugated monomers having D-A-D structure (Scheme 1). The donating units are based on a fixed alkylated propylenedioxythiophenes and accepting units based on benzothiadiazole or quinoxaline units bearing variable substituents. The polymerization is conducted under mild conditions via oxidative coupling using iron III trichloride. The obtained copolymers have tunable optical properties that can be relied to the acceptor strength which control of D-A charge transfer (CT). The optical characterizations allow to extract the CIELAB colorimetric coordinates and experimental HOMO-LUMO energetic levels were obtained from electrochemical characterization. We also used computational chemistry (B3LYP and TD-B3LYP methods) to browse the structures of interesting candidates to achieve successful color control in D-A polymers using model compounds (monomers and trimers). Finally a color/structure relationships provides valuable insights on molecular design principles for this class of copolymers, putting forth the importance of jointly playing the steric hindrance factor and the electron-withdrawing/donating strength of carefully chosen substituents.

Figure 1
Solar-Powered Ambipolar Electrochromic Polyimidothioethers Via Perovskite Photovoltaics
Authors: Yen Hung-Ju , Tsai Hsinhan , Nie Wanyi , Liou Guey-Sheng , Wang Hsing-Lin
Published: February 2020

In this work, we demonstrate for the first time the novel electrochromic devices based on a series of ambipolar polyimidothioethers (PITEs) driven by state-of-the-art solution-processed perovskite solar cells. These devices with high color contrast and fast response time can have a low operating voltage, less than one volt. The electrochromic PITEs were prepared from new triphenylamine-based bismaleimides and commercial dithiols via Michael polyaddition. These polymers were readily soluble in various organic solvents and showed thermal stability associated with high glass-transition temperatures. The perovskite solar cell developed in our lab has a power conversion efficiency greater than 15% and open circuit voltage of 0.8-0.9 V, rivals the efficiency and cost of silicon solar cells in converting sunlight to electricity. Combined the innovative developments of both perovskite photovoltaics and ambipolar electrochromic materials, we have achieved a novel design of smart materials devices with strong commercial implications.
Multi-Color Electrochromic Devices Based on Phenyl and Heptyl Viologens Immobilized By an UV-Cured Polymer Electrolyte
Authors: Chang Ting-Hsiang , Kao Sheng-Yuan , Kung Chung-Wei , Lee Minhan , Lu Hsin-Che , Ho Kuo-Chuan
Published: February 2020

Over the last few decades, viologens have been applied for electrochromic devices (ECDs). However, viologens are soluble in water or polar organic solvent and solution-type viologens suffer from leakage problem. To tackle this issue, many strategies have been proposed for preparing immobile viologens. In this study, an UV-crosslinked ethoxylated trimethylolpropane triacrylate (ETPTA) polymer network and succinonitrile (SN) were employed to prepare a solid polymer composite electrolyte (PCE) matrix [1] at room temperature to immobilize heptyl viologen (HV) and phenyl viologen (PV) at the electrode surface. PV exhibits good EC property, while aggregation of PV occurs immediately utilizing conventional liquid or gel electrolyte due to strong π-π stacking. Herein, an all-solid-state ECD is proposed to solve aggregation issue of PV. Moreover, a multi-color ECD is fabricated by incorporating HV, PV, and PCE. By changing the operating potential, the ECD exhibits green, blue, gray color at 0.6 V, 0.8 V, and 1.0 V, respectively (Fig. 1). The first set of redox peaks in Fig. 1 is due to redox reaction of PV, and the second set of redox peaks is the overlap of first reduced state of HV and second reduced state of PV. Fig. 2 shows the dynamic transmittance change of the proposed ECD between 0 and 1 V. The increment in transmittance at 1 V is due to the second reduced state of PV and HV at 438 nm and 610 nm, respectively. The color-tuning of the proposed ECD is controlled by the ratio of HV and PV molecules immobilized on the electrode surface, which can be  explained by the coloration efficiency and cyclic voltammogram of the ECD.

Figure 1
Flexible, Low-Cost, Commercialized Smart Windows
Authors: Fan Jiangfeng
Published: February 2020

Smart windows modulating transmitted light and solar heat is a promising option for reduction of energy use of buildings. We are developing smart windows based on both inorganic and polymeric electrochromic materials. Revolutionary electrode materials are integrated in our products, endowing them with intriguing features including flexibility and low cost. Smart windows will be a shining star in the fields of buildings, transportations, furniture and wearable devices.
Surface Treatments for Electrochromic Glazing: Toward Reduced Costs and Optimal Performances through Ultrasonic Spray Pyrolysis
Authors: Maho Anthony , Denayer Jessica , Bister Geoffroy , Aubry Philippe , Colson Pierre , Henrist Catherine , Cloots Rudi
Published: February 2020

Research and industrial interests for electrochromic “smart” windows have considerably grown those recent years due to their potential use as an energy-saving material for buildings. Their CO2 emission can be significantly reduced by decreasing their energy consumption up to 30%.

The crucial issues of such devices are the coloration efficiency as well as the reversibility upon coloration and bleaching of the electrochromic layers. The combination of WO3 and Li-doped NiO surface films (separately as working and counter electrodes) affords a good coloration contrast between colored and bleached states of the device, since tungsten oxide colors upon electrons and ions insertion while nickel oxide gets colored after their extraction.

In order to improve the performances of those electrochromic films, we have studied the effects of a surfactant-assisted deposition process of both individual layers through Ultrasonic Spray Pyrolysis (USP). This technique indeed constitutes a low-cost alternative to industrial vacuum processes for manufacturing high quality thin films.

The crystallization and morphology of those films, as well as their optical, electrochromic and electrochemical properties have been investigated. The presence of surfactant in the precursor solution has led to improved wetting of liquid droplets sprayed on the heated FTO/glass substrate. The resulting films testify for a better homogeneity and a higher active surface, which also allows for enhanced reversibility and coloration contrast.
Enhanced Electrochromic Performance Based on Conducting Polymer/ZnO Nanocomposites
Authors: Lv Xiaojing , Zhang Cheng
Published: February 2020

Conducting polymers have been increasingly studied owing to their diverse colors, high optical contrast, fast switching speed and good processibility for various electrochromic (EC) applications, such as smart windows, reflecting mirrors and thin flat panel displays. However, practical applications need to meet several requirements, including a multicolor display, ultrafast switching speed and excellent long-term stability. Conducting polymer-inorganic nanocomposite has drawn more attention since they can combine the advantages of both components, and may offer special properties through the reinforcement or modification of each other.1-2 In this paper, conducting polymer/ZnO nanocomposites were fabricated via solvent thermal or electrodeposition combining with electropolymerization method. The effect of different ZnO nanostructures (such as nanoridges, nanorods, nanosheets) on the properties of electrochromic composites were investigated. The results demonstrate that the electrochromic performances of conducting polymers are significantly enhanced by incorporating with different ZnO nanostructures. Moreover, the possible mechanism for the enhanced properties is proposed that the introduction of ZnO nanostructures can shorten the diffusion distance and provide larger contact area, which facile the ion doping/dedoping and enhance the adhesion between the polymer and the electrode, resulting in higher optical contrast, faster switching speed and more excellent electrochemical stability.

References

1. K. Choi, S. J. Yoo, Y. E. Sung, R. Zentel, Chem. Mater.,
18
, 5823 (2006).

2. R. J. Mortimer, A. L. Dyer, J. R. Reynolds, Displays, 27, 2 (2006).

Figure. 1 SEM photos and the contrast of elelctrochromic properties between polymer and nanocomposite

Figure 1
in Situ Coherent Surface x-Ray Scattering Study of the Au (111) Surface Dynamics in Electrolytes: The Effect of Surface Reconstruction and Chloride Adsorption
Authors: Liu Yihua , Barbour Andi , Komanicky Vladimir , You Hoydoo
Published: February 2020

It has long been conceived that in equilibrium electrode surfaces in contact with electrolytes remain highly dynamic, exhibiting steady processes such as detachment and adsorption of surface atoms.  Importantly, some of those microstate fluctuations play an essential role on formation of surface structure and composition, and ultimately affect the functionality of electrodes.  Surface-sensitive techniques, like STM and surface x-ray scattering (SXS), have become invaluable to unraveling electrode surface structures under changing electrochemical environments.  Measurements on surface dynamics, however, remain challenging for electrochemical systems [[1]].  

In this talk, we will report on the study of Au (111) surface dynamics by coherent surface x-ray scattering (CSXS).  A brief introduction will be given for implementation of CSXS and ISXS for electrochemical studies. Time-resolved capability of CSXS will be highlighted.

To elucidate factors that could influence surface dynamics, Au (111) electrode surfaces are systemically tailored by varying electrochemical conditions.  Phase transition in Au (111) electrode surface had been well characterized by SXS, with structural changes that were shown to be both dependent on potentials and solution chemistry [[2]].  A sharp drop in x-ray scattering intensity around 0.12 V, shown in Fig. 1 (black curve), marks phase transition from (p x√3) to (1x1), which then can be reconstructed back to form a (p x√3) structure in a reverse potential scan.  A similar potential dependence is found with increasing chloride concentration as shown in Fig. 1 (red curve).  Careful comparison of the hysteresis loops, presented in Fig. 1, additionally reveals that chloride concentration influences the kinetics of phase transition in Au (111) surfaces.   

In additional to structural details, we have also attained some preliminary results on the dynamics of Au (111) surfaces from CSXS experiments.  In the present work, surface dynamics are quantified in terms of correlation time, a parameter that describes the temporal separation between two configurations that are no longer resemble each other due to microstate fluctuations.  Correlation time in relation to surface structure will be shown and discussed as a function of applied potential and chloride concentration. A comprehensive analysis on surface dynamics will be performed to help establish its relations with surface structure and solution chemistry.  

[1] M. Pierce, V. Komanicky, A. Barbour, D. C. Hennessy, C. Zhu, A. Sandy, H. You, Phys. Rev. B
86, 085410 (2012).

[2] J. Wang, B.M. Ocko, A. J. Davenport, H. S. Isaacs, Phys. Rev. B
46 10321 (1992).

Figure 1