bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of Advanced Pt-Ni Alloy Catalysts in Polymer-Electrolyte Fuel Cells
Authors: Perry Mike L. , Yang Zhiwei
Published: February 2020

The cost of a Polymer-Electrolyte Fuel Cells (PEFC) system is still the primary barrier to commercialization, although it has decreased significantly over the past decade. Platinum electrocatalysts are required due to the slow kinetics of the oxygen reduction reaction (ORR). To reduce electrocatalyst cost, platinum alloys with higher ORR mass activity are being developed.1,2 ORR activities exceeding DOE’s 2015 targets were reported by various research groups for carbon-supported Pt alloys and core-shell nanoparticles in rotating-disk electrode (RDE) tests.3,4 However, it can be challenging to achieve similarly high mass activities for these electrocatalysts in membrane-electrode assemblies (MEAs), as evidenced by in-cell performance at low current densities (kinetically-controlled) region, and it is even more challenging to achieve improved cell performance at higher current densities with these advanced alloy catalysts.5

United Technologies Research Center (UTRC) is a part of an on-going DOE-supported research project, led by Argonne National Laboratory (ANL), focused on improving the understanding, performance, and durability of advanced Pt-alloy catalysts operating in complete PEFCs. In the current study, advanced MEAs with high ORR activity Pt-Ni alloy catalysts are prepared by Johnson Matthey Fuel Cells (JMFC) and tested by UTRC in small PEFCs (12.5-cm2 active area). A variety of parameters, including: Pt-Ni catalyst composition and structure, catalyst-ink formulation, and MEA-fabrication procedures are being explored in order to develop MEAs with superior performance over the entire PEFC operating range relative to Pt-only MEAs. A comparison of Pt-only and Pt-Ni MEAs, which have similar catalyst particle size and the same carbon support and electrode composition, are shown in Figure 1. Results obtained from in-cell diagnostics will be used to explain the differences in the polarization curves, as well as project paths to future performance improvements. The impact of Pt:Ni ratio on ORR activity and cell performance will also be reported.

Acknowledgements

The authors gratefully acknowledge funding from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office (Nancy Garland, Technology Development Manager) under contract number DE-AC02-06CH11357. The authors would also like to thank their DOE project colleagues at ANL and at JMFC for both their support of this work and for helpful discussions.

References

S. C. Ball, S. L. Hudson, B. R. C. Theobald, and D. Thompsett, ECS Transactions, 11 (1), 1267-1278 (2007).

H. R. Colón-Mercado, and B. N. Popov, Journal of Power Sources, 155 (2), 253–263 (2006).

N. Markovic and V. Stamenkovic, DOE Hydrogen Program 2010 Annual Report (2010).

M. Shao, A. Peles, and K. Shoemaker, Nano Letters, 11 (9), 3714-3719 (2011).

K.C. Neyerlin, R. Srivastava, C.F. Yu, and P. Strasser, Journal of Power Sources, 186 (2), 261-267 (2009).
The Effect of Carbon Support Structure on Ionomer Distributions in PEM Fuel Cell Catalyst Layers
Authors: More Karren L. , Cullen David A , Reeves Kimberly Shawn
Published: February 2020

Ionomer thin films form the proton-conducting path within the catalyst layers (CL) of polymer electrolyte membrane fuel cells (PEMFCs) and the web-like ionomer network provides support for the porous CL structure. The recast ionomer is assumed to be relatively uniform in thickness, structure, and chemistry across the entire CL thickness, but there are numerous factors that can significantly influence the homogeneity and dispersion of the ionomer as well as its stability during electrochemical aging. These factors include (1) the type of carbon support material used, including the extent of graphitization (or lack thereof) and the presence of surface oxide functional groups, (2) the loading, dispersion, and size/shape of Pt-based electrocatalysts, and (3) the CL pore structure. Recently, extensive studies have been conducted to identify the optimum conditions for examining ionomer thin films using electron microscopy and spectroscopy techniques1 and molecular dynamics (MD) simulations have been performed to identify the structure and adhesion of ionomer thin films on carbon and Pt surfaces.2 The current work will expand on this microscopy research to apply specific microscopy methods, including high-resolution imaging and spectroscopy coupled with electron tomography, to identify the nature of ionomer film dispersions within CLs prepared with different carbon supports having varying degrees of graphitization (high surface area carbon, Vulcan, and fully graphitized low surface area carbon) and Pt loadings. Additionally, changes to these ionomer films within the different CLs during accelerated stress testing (AST), specifically the AST for carbon corrosion (1.2V hold for 100-400 hours), will be analyzed and compared in terms of changes to the ionomer distributions on the changing carbon surfaces. Microscopy observations will be coupled with MD simulations to better understand the correlations between ionomer dispersion and structure and the materials comprising the CLs.

References:

1. D.A. Cullen, et al., “Imaging and Microanalysis of Thin Ionomer Layers by Scanning Transmission Electron Microscopy,” in preparation.

2. Q. He, et al., “Structure of the Ionomer Film in Catalyst Layers of Proton Exchange Membrane Fuel Cells,” Journal of Physical Chemistry C
117 25305-25316 (2013).

Research sponsored by (1) the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and (2) through a user proposal at ORNL’s Center for Nanophase Materials Sciences, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
Pt-Decorated Non-Covalently Functionalized Carbon Graphitic Structures as Durable Catalyst for ORR
Authors: Negro Emanuela , Koper Ger , Baglio Vincenzo , Stassi Alessandro , Aricò Antonino S.
Published: February 2020

Carbon graphitic structures that differ in morphology, graphiticy and BET surface area were used as support for platinum for ORR reaction in low temperature fuel cells. Graphitic supports were first non-covalently functionalized with pyrene carboxylic acid (PCA) and subsequently platinum nanoparticles were nucleated on the surface following procedures found in previous studies. Non-covalently functionalization has been proven to be advantageous because it allows a better control of particle size and monodispersity, it prevents particle agglomeration since particles are bonded to the surface and it doesn’t affect the chemical and physical resistance of the support. Synthesized electrocatalysts were characterized by electrochemical half-cell studies, in order to evaluate electrochemically active surface area (ECSA), ORR activity, durability to potential cycling and corrosion resistance.
Pt/SnO2 Electrocatalysts on Conductive Fillers
Authors: Horiguchi Dai , Tsukatsune Takuya , Noda Zhiyun , Hayashi Akari , Sasaki Kazunari
Published: February 2020

For polymer electrolyte fuel cells (PEFCs), the electrocatalysts on which Pt nano-particles are homogeneously dispensed on carbon black (Pt/C) are widely used. However, during the fuel cell start-stop cycles, the potential of the cathode can reach up to ca. 1.5VRHE, resulting in a severe carbon corrosion. Tin oxide (SnO2) has been studied as an alternative support material because of its thermochemical stability. We have demonstrated negligible degradation within 60,000 cycles in a half-cell test [1-3], indicating that Pt/SnO2 electrocatalyst can exhibit considerable durability. However, relatively low electrical conductivity in such semiconducting oxides often leads to poor cell performance. Here, we aim to develop Pt/SnO2 electrocatalyst with both high durability and high activity, using conductive fillers as backbones of electrocatalysts.

We selected vapor grown carbon fibers (VGCF) and acetylene black (AB) as possible conductive fillers. SnO2/VGCF and SnO2/AB were synthesized via the ammonia co-precipitation method. Then, the impregnation of Pt particles was made using a Pt(acac)2 method to prepare both Pt/SnO2/VGCF and Pt/SnO2/AB. Nanostructure of electrocatalysts was observed by STEM. To evaluate the electrochemical activity of these electrocatalyst, electrochemical surface area (ECSA) was measured by cyclic voltammetry (CV). The durability of electrocatalysts under the cathode condition was evaluated, where the electrocatalysts were subjected to the potential cycles between 1.0 and 1.5 VRHE at a scan rate of 50 mV s-1 in the measurements.

Figure 1 shows the nanostructure of Pt/SnO2/VGCF, revealing the selective impregnation of Pt particles on SnO2 rather than the conductive fillers. Figure 2 shows the ECSA of various electrocatalysts as a function of the number of cycles. ECSA of Pt/SnO2/VGCF was about three times as large as that of Pt/SnO2 before CV cycles. After 60,000 cycles, the former is about five times as large as the latter. With respect to the retention of ECSA before and after the CV cycles, Pt/SnO2/VGCF kept 65.0% of the initial ECSA value and Pt/SnO2/AB kept 58.7%. These results indicate that electron-conductive fillers can be used as the conductive backbones of the PEFC electrocatalysts using semiconducting oxide supports.

Acknowledgement

Financial support by the Grant-in-Aid for Scientific Research (S) (No. 23226015), JSPS Japan, is gratefully acknowledged.

References

[1] A. Masao, S. Noda, F. Takasaki, K. Ito, and K. Sasaki, Electrochem. Solid-State Lett., 12 (9), B119 (2009).

[2] F. Takasaki, S. Matsuie, Y. Takabatake, Z. Noda, A. Hayashi, Y. Shiratori, K. Ito, and K. Sasaki, J. Electrochem. Soc., 158 (10), B1270 (2011).

[3] K. Kanda, Z. Noda, Y. Nagamatsu, T. Higashi, S. Taniguchi, S.M. Lyth, A. Hayashi, and K. Sasaki, ECS
Electrochem. Lett., 3 (4), F15-F18 (2014).

.
Synthesis of Pt@Ni Core-Shell Nanoparticles Using Mwcnt's Supported for Oxygen Reduction Reaction
Authors: Rosado Gabriel , Escobar Beatriz , Valenzuela-Muñiz Ana Maria , Barbosa Romeli , Verde Gomez Ysmael
Published: February 2020

Multi-walled carbon nanotubes (MWCNTs) are nanostructures with unique physicochemical properties. MWCNTs can be obtained using different catalytic agents, being the most common the organometallic materials based on Fe. In this work, MWCNTs were produced using thermal chemical vapor deposition; MWCNTs surface was modified by nitric acid to introduce functional groups which act as anchors for metallic nanoparticles. On the other hand, the oxygen reduction reaction (ORR) in a tends to be the slowest reaction in a fuel cells, being this important issue to solve. It has been demonstrated that bimetallic catalysts (e.g. PtRu, PtCo, PtNi, etc.) are a good option for the ORR. The effect of the second metal helps the Pt, generating an improvement in the activity. Pt@Ni core-shell nanoparticles with different Pt/Ni ratios have been prepared by chemical reduction, supported onto MWCNTs and used as electrocatalysts for PEMFC. Chemical reduction allows the production of a very narrow size distribution of metal particles, with an average size around the 10 nm. The morphology of the electrocatalyst was characterized by XRD and HRTEM. It was found that the Pt@NiMWCNTs catalyst exhibited a core-shell nanostructure. The ORR on Pt@Ni core shell was studied using the rotating disk electrode (RDE) technique in an O2-saturated acid solution. A normal three electrode cell was used with the Pt@Ni/MWCNT as working electrode (deposited in glassy carbon), Ag/AgCl (KCl Sat) as reference, a Pt wire as counter electrode, and 0.5M H2SO4 as electrolyte. The results and discussion of the electrochemical studies will be discussed.
Polydimethylsiloxane-Based Block Copolymer for Anion Exchange Membrane Fuel Cells (AEMFC)
Authors: Ghil Lee-Jin , Jun Mun-Suk , KIM Je-Deok
Published: February 2020

The anion exchange membrane fuel cells (AEMFCs) known as hydroxide ion (OH-) exchange fuel cells have evoked considerable attention due to their faster oxygen reduction reaction, lower fuel crossover, reduced CO poisoning, a wide choice of fuels (e. g. hydrogen, methanol, ethanol, hydrazine), and to the possibility of Pt-free catalysts. In the development of AEMFCs, anion exchange membranes (AEMs) play a critical role to make a breakthrough in AEMFC performance. Especially, alkaline stability and ion conductivity are key properties of AEMs. Although various AEMs were developed, there are still required new AEM with higher ion conductivity and stability. One of the attractive candidates is siloxane-based polymer substituted with anion exchangeable functional groups. In this study, we introduce the property of PDMS copolymer with quaternary ammonium groups.
On Power Density and Efficiency of H2/O2 Polymer Electrolyte Fuel Cell Systems
Authors: Büchi Felix N. , Hofer Marcel , Cabalzar Urs , Bernard Jérome , Hannesen Uwe , Closset Alexandre , Dietrich Philipp , Schmidt Thomas J.
Published: February 2020

When storing fluctuating renewable electricity by water electrolysis hydrogen and oxygen are obtained. Up to a scale in the order of Megawatt-hours the concurrent storage of oxygen and hydrogen gas is technically feasible. This opens up the possibility to use hydrogen/pure oxygen fuel cells for the efficient conversion of hydrogen back to electric power.

The oxygen reduction reaction is responsible for the largest voltage loss in the operation of polymer electrolyte fuel cells. The sluggish reaction rate of the four-electron reduction, even on the best platinum based catalysts, is aggravated by the low partial pressure of oxygen in air. When using pure oxygen the partial pressure can typically be increased by an order of magnitude.

On the cell level, not only the reduced electro catalytic loss but also voltage gain from lower transport overvoltage and reduced ohmic loss at same gas humidification as with air operation are observed. At the same time very high specific power densities of up to 2 W/cm2can be realized.

In addition to the advantages on the cell level, low parasitic power consumption in the balance of plant (no compressor/blower) also contributes to high system efficiencies of up to 69% (LHV).
Invited: Developing Alkaline Anion Exchanging Membrane Fuel Cells
Authors: Ren Xiaoming , Chu Deryn
Published: February 2020

To achieve sustainable development with limited natural resources and environmental concerns, fuel cells are expected to play an important role in providing clean power at high efficiency. After past decades of intensive development, the proton conducting polymer electrolyte membrane fuel cells (PEMFCs) have made substantial advancement in cost, performance and stability. As the results, some real commercial applications have been demonstrated around the world, such as in the combined heat and power generations, vehicle powers, stationary backup powers, and portable powers. Still, the high cost, scarceness and performance stability of the highly dispersed platinum catalysts in the strong acid environment under dynamic fuel cell operation conditions remain as the major challenges for the PEMFCs to reach widespread mass applications. To address these difficulties, alternative approach in developing alkaline anion exchanging membrane fuel cells (AEMFCs) has recently gained momentum. In this presentation, we report our efforts in developing AEMFCs at Army Research Laboratory. It covers our non-precious metal catalysts development, alkaline polymer electrolyte membrane characterization, fuel cell electrode optimization, and fuel cell tests. The results of this study illustrate some of the key factors affecting the current AEMFCs performance, and the remaining challenges.

Non-precious metal development was focused on producing high performance catalysts for oxygen reduction reaction (ORR) at low cost. Catalysts prepared with high temperature heat treatment of the transition metals embedded in nitrogen containing polymer matrix supported on carbon have demonstrated comparable mass activity to that of Pt-based catalysts, in addition to their superior performance stability and contamination tolerance under the alkaline conditions.

Some key properties of an anion exchanging polymer electrolyte membrane (AEPEM) measured include ion-exchanging capacity, water uptake, anion conductivity, electro-osmotic drag coefficient, methanol permeation rate, and CO2 permeation rate. These properties are compared to the proton exchanging membrane to illustrate the limitations of current AEPEM.

With current available AEPEM and ionomer materials, fuel cell electrode optimization was conducted by varying the ionomer content in the catalyst layer. Compared to Nafion ionomer used for PEMFCs, the current ionomer for the AEMFCs was made from hydrocarbon polymer, which has a lower ionic conductivity, a higher water uptake and a lower polymer density. All these properties limit the fuel cell electrode performance in term of catalyst layer ionic conductivity, catalyst utilization, and reactant gas mass transport. The optimized fuel cell performance has demonstrated to achieve a power density at 300 mW/cm2, which is still much lower than that achieved by PEMFCs. The performance in AEMFCs limitation could be overcome by developing a new generation ionomers with improved properties.
Methanol Oxidation on Pt/CNT Electrocatalysts Promoted with TiO2
Authors: Bedolla Zaira , Verde Gómez Ysmael , Gochi Yadira , Alonso Gabriel
Published: February 2020

Electrocatalytic materials are a major challenge for Direct Methanol Fuel Cells (DMFC) commercialization. To improve the properties of supported Pt electrocatalysts, various metal oxides are used to enhance the methanol oxidation performance [1-3]. Currently, titanium oxide is widely studied as electrocatalytic promoter due to its low cost and stability in acid media [1-3].

In this research, Pt-xTiO2/CNT electrocatalysts with various titanium oxide loadings (x= 5, 10 and 20 wt%) were prepared. In first instance, the titanium oxide was incorporated to CNT by a sonochemical method to obtain the system TiO2/CNT. Then, 10 wt% of Pt nanoparticles were incorporated to TiO2/CNT by sonochemical conditions using NaBH4 as a reducing agent.

The chemical composition of the systems was determinated by ICP analysis. The electrocatalysts structure was characterized by XRD diffraction and HRTEM. The nitrogen adsorption was performed to determinate the specific surface area by the BET method. The electrochemical study was performed by cyclic voltammetry in a three-electrode half-cell at room temperature.

Pt-xTiO2/CNT electrocatalysts were successfully synthesized by a short time synthesis method. The results of the cyclic voltammetry test for the methanol oxidation suggest that the incorporation of TiO2 improves the electrocatalytic activity of the synthesized materials, in comparing to the system Pt/CNT.

The authors acknowledge CONACyT project 174689 and PAPIIT IN104714.

References

[1]W. Xiuyu, Z. Jingchang, Z. Hong, Chin. J. Catal., 32 (2011), 74-79.

[2]W. Wang, H. Wang, J. Key, V. Link, et al., Ionics, 19 (2013), 529-534

[3] P. Kolla, A. Smirnova, Int. J. Hydrogen Energy, (2013), 1-8.
PTFE Distributions in Diffusion Media of PEFCs and Related Effects on Water Transport
Authors: Wargo Eric A. , Schulz Volker P , Kumbur Emin Caglan
Published: February 2020

The diffusion media (DM) of polymer electrolyte fuel cells (PEFCs) typically consists of a macro-substrate (or gas diffusion layer, GDL) coated with a micro-porous layer (MPL). The GDL portion is manufactured from carbon fibers/binder and is often treated with polytetrafluoroethylene (PTFE) to increase the hydrophobicity. Similarly, the MPL is manufactured from a slurry containing carbon nanoparticles and PTFE. While the distribution of PTFE undoubtedly influences water transport within the DM, the actual 3-D distribution of PTFE is extremely difficult to capture using a single, standalone device. Therefore, the objective of this work is to examine the impact of PTFE distribution on water transport by generating various PTFE distributions within the measured 3-D structures of DM materials.

A commercial DM sample was previously analyzed using X-ray computed tomography (XCT) and focused ion beam-scanning electron microscopy (FIB-SEM) to capture the 3-D structures of the GDL and MPL regions, respectively [1]. In this study, three different PTFE distribution cases are generated on the internal surface of the measured GDL structure: i) random PTFE surface pixels; ii) random PTFE surface clusters; and iii) wetting of PTFE into GDL crevices to mimic the PTFE treatment process used during manufacturing. Similarly, cases (i) and (ii) are generated in the measured MPL structure. In each case, PTFE is assigned to existing solid pixels so that the structure of the measured sample is preserved.

The well-established pore morphology or full morphology (FM) model [1,2], used for determining capillary pressure-saturation behavior in uniformly wetting pore structures, was recently extended to account for locally different wetting surfaces in a structure [3,4]. The extended-FM approach is applied here in 3-D to capture the impact of the PTFE distributions on water transport in the DM, by assuming one contact angle for the carbon fiber/binder surface and a different contact angle for the hydrophobic PTFE surface. Two uniform surface conditions (i.e., traditional FM approach) are also considered for comparison: one in which an average contact angle for carbon fiber/binder and PTFE is assumed, and another in which PTFE is neglected (i.e., untreated GDL sample). The capillary pressure-saturation results are compared with experimental and modeling studies available in literature.

References

[1] E. A. Wargo, V. P. Schulz, A. Cecen, S. R. Kalidindi, and E. C. Kumbur, Electrochimica Acta, 87, 201 (2013).

[2] V. P. Schulz, J. Becker, A. Wiegmann, P. P. Mukherjee, and C. Y. Wang, Journal of The Electrochemical Society, 154 (4), B419 (2007).

[3] F. Kraft, Programmierung eines effizienten Verfahrens zur Umsetzung eines Porenmorphologie-Modells, Student research project, Baden-Wuerttemberg Cooperative State University Mannheim, Germany (2014).

[4] V. P. Schulz, “Pore-morphology-based simulation of drainage in partially wetting porous media”, in preparation.
Degradation Mechanism of Membranes for Alkaline Membrane Fuel Cells
Authors: Choe Yoong-Kee , Henson Neil J. , Kim Yu Seung
Published: February 2020

Hydroxide-conducting alkaline membranes have received growing attention for alkaline membrane fuel cells (AMFCs) and solid-state alkaline water electrolysis. The harsh operating conditions of the alkaline electrochemical devices require high chemical stability of the membranes. Cation (such as alkylammonium) functionalized polyaromatic membranes have been employed for the above electrochemical devices while such a cation is known to degrade chemically due to the high reactivity of hydroxide anion. Recently, we and other groups reported that the backbone part of polyaromatic membranes is also a site that can react with hydroxide anion, resulting in cleavage of the backbone part of membranes. Such degradation obviously deteriorates the performance of membranes to a large extent. In order to design more robust membranes which is stable under high pH conditions, it is necessary to understand the degradation mechanism at an atomistic level. Mechanistic aspects of the backbone degradation, however, have not been well understood, of which situation calls for contribution from theory. In this presentation, we report results of density functional theory calculations carried out to investigate the mechanism of backbone degradation of polyaromatic membranes.
“Hybrid” Anion-Exchange-Membranes for Direct Ethanol Fuel Cells
Authors: Sun Lili , Guo Junsong , Chen Rongrong
Published: February 2020

In the past few years, we have developed novel anion-exchange-membranes (AEMs) based on block copolymers for H2/O2 fuel cell applications [1-2] and discovered that dimensional stability of an AEM is very critical for achieving optimal performance in the fuel cells. Since ethanol is a non-toxic bio-fuel with a rather high energy density, it has attracted great attentions to be fed directly into polymeric electrolyte fuel cells. Ethanol oxidation reaction (EOR) in an alkaline media is much faster than that in an acid media and can be catalyzed on non-Pt catalysts. In this work, we aim to develop AEMs suitable for direct ethanol fuel cell (DEFC) applications.

Four types of AEMs were prepared by varying "hybrid" SEBS-based copolymers. The swelling, water uptake, ionic conductivity, thermal stability and ion exchange capacity of the membranes were measured using the methods described in our previous work [1]. The impacts of ionic exchange capacity in the membranes on the performance of DEFCs were studied and compared with the commercial membrane (Tokuyama’s A201).

DEFCs performances of various "hybrid" types of QSEBS membranes (Type I, II, III and IV) and commercial membrane (A201) will be presented. The correlations of the swelling, water uptake, ionic conductivity, thermal stability and ion exchange capacity of the membranes with the performance of DEFCs will be established and discussed. The key factors for developing AEMs for DEFC applications will be identified.

References

[1] L. Sun, J. Guo, J. Zhou, Q. Xu, D. Chu, R. Chen, Journal of Power Sources 202 (2012) 70– 77.

[2] J. Zhou, J. Guo, D. Chu and R. Chen, Journal of power sources, 219 (2012) 272-279.
Detection of Dopamine Efflux in the Nucleus Accumbens caused by Electrical Stimulation of the Rat Fornix by Fast Scan Cyclic Voltammetry
Authors: Shin Hojin , Oh Yoonbae , Kim Dohyung , Jang Dong Pyo
Published: February 2020

Introduction: Deep Brain Stimulation (DBS) has been recently suggested as a potential therapy for improving memory functions in Alzheimer’s Disease, as the improvement of certain memory functions was shown when DBS on fornix, The goal of this study is to investigate the relationship between fornix stimulation and neurochemical change in rat brain.

Methods: We stereotactically implanted carbon fiber microelectrode (CFM) into nucleus accumbens of the rat to measure neurotransmitter changes during DBS of fornix using WINCS based fast scan cyclic voltammetry. DBS was applied with changes of stimulation amplitudes and frequencies under general anesthesia.

Results: Dopamine efflux change was measured in the core of nucleus accumbens, but not in the shell of nucleus accumbens. The dopamine changes became highest at 120Hz stimulating frequency and also get higher when increasing the stimulation amplitude.

Conclusion: In this study, the possible relationship between fornix and nuclueus accumbens was demonstrated with fast scan cyclic voltammetry. The dopamine releases in nucleus accumbens during fornix DBS could be utilized for explain the mechanism of the fornix DBS.
Effective Data Treatment for Impulse Chronopotentiometry
Authors: Sedov Andrey Vladimirovich , Lipkin Mikhail Semenovich , Lipkin Semen M.
Published: February 2020

Significant number of electrochemical and contiguous problems are studied and solved via chronopotentiometry. So in [1] it was used to define the solution composition. Expanding this application chronopotentiogram can serve as a source of information about metal alloy composition if small part of alloy sample is passed into solution in three-electrode cell.

According to this method alloy sample is attached to the cell as a working electrode and is oxidized by series of pulses of current. Parameters of these pulses are selected so that contents of elements in solution would be the same as in an alloy. This solution is later reduced by series of pulses of opposite polarity current. Thus, obtained chronopotentiogram Ej=[ej1,ej2...ejn]T
(fig. 1) consists of two stages: oxidation and reduction and its form depends on alloy composition.

However, as seen on fig. 1, obtained chronopotentiogram has a complex shape which doesn’t allow defining alloy composition directly by potential values of Ej
. Therefore chronopotentiometry data treatment comes down to extracting required information from potential values vector Ej
. This extraction is often based on mathematical model of used electrochemical process with models like Poisson-Nernst-Planck system [2] and convolutions [3] being used.

Proposed approach to chronopotentiometry data treatment is similar to convolutive modeling, except for weight functions V are defined not theoretically from analysis of used process but adaptively as eigenvectors of covariance matrix
K
of training set of chronopotentiograms
KV=VΛ

where
Λ
- diagonal matrix of eigenvalues
λi

of matrix
K
. Extraction is made via the following conversion:
Yj=VTEj

. And source chronopotentiogram can be recovered from
Yj

via the following:
Ej=ΣyjiVi+Qj

where
Qj

is constant bias vector.

As a result of application of this approach to chronopotentiograms of molybdenum alloys obtained potential values vectors Ej=[ej,1,ej,2...ej,728]T
were converted into vectors Yj=[yj,1,yj,2...yj,4]T
, i.e. chronopotentiograms dimension was 242 times reduced. In addition, this approach allows unification of chronopotentiometry data treatment independently from analyzed alloy composition.

van Leewen HP, Coulostatic pulse techniques. In: Bard AJ (ed), Electroanalytical chemistry, 1982, vol. 12, pp 157-238.

Nagai Junichi, Graham D. McMeeking, Modeling of electrochromic processes, Electrochimica Acta, 1999 Vol. 44, p. 219-229.

Peter J. Mahon, Keith B. Oldham, Incorporating electrode kinetics into the convolutive modeling of reactions at planar, cylindrical and spherical electrodes, Journal of Electroanalyrical Chemistry, 1998, Vol. 445.
Orientation-Controlled Single Molecule-Electrode Junctions
Authors: Borguet Eric
Published: February 2020

Molecular scale electronic devices usually are designed by wiring a single molecule between two metal electrodes via anchoring groups. Conventional single molecule conductance (SMC) studies focus on molecules with functional groups that provide efficient electronic coupling and bind the organic molecular backbone to the metal electrodes. However, conductance is sensitive to the atomic level details of the molecule-electrode contact so that the anchoring groups end up being resistive spacers between the molecule and the metal, decreasing the single molecule junction conductivity. Thus creating well-defined, highly conductive molecular junctions to minimize resistance introduced by chemical linkers is a challenging experimental problem especially under ambient conditions.

The conductivity of a single aromatic ring, perpendicular to its plane, is determined using a new strategy under ambient conditions and at room temperature using a combination of molecular assembly, Scanning Tunneling Microscopy (STM) imaging and STM break junction (STM-BJ) techniques. The construction of such molecular junctions exploits the formation of highly ordered structures of flat-oriented mesitylene on Au(111) to enable direct tip/π contacts, a result that is not possible via conventional methods. The measured conductance of sandwiched Au/π/Au junction is ~0.1Go, two orders of magnitude higher than the conductance of phenyl rings connected via standard anchoring groups. A comparison with other benzene derivatives, that do not display long-range ordered structure, suggests that such structures, which hold the aromatic ring in place and parallel to the surface, are essential to the increased probability of the formation of orientation-controlled “sandwiched” molecular junctions.
Glassy Carbon Electrodes Sequentially Modified by Thiol-Capped Gold Nanoparticles and Dendrimers for Detecting Uric Acid in Human Serum
Authors: Ramírez-Segovia Alejandra Sarahí , Banda-Alemán Jorge Alberto , Gutiérrez-Granados Silvia , Godínez Luis A. , Bustos Erika , Manríquez Juan
Published: February 2020

Glassy carbon electrodes (GCE) were sequentially modified by thiol-capped gold nanoparticles (AuNp@thiol) and dendrimers (GCE/AuNp@thiol/dendrimer), in order to explore their capabilities as electrochemical detectors of UA in human serum samples at pH 2. The results showed that concentrations of UA detected by amperometry with GCE/AuNp@thiol/dendrimer were comparable to those concentrations obtained using the uricase-based enzymatic-colorimetric method.
Effects of Surface Cathode Properties on Biopolymer Structuring via Electrochemical Deposition
Authors: Altomare Lina , Bernasconi Roberto , Magagnin Luca , Cigada Alberto , De Nardo Luigi
Published: February 2020

Electrochemical deposition is a versatile bottom up-approach for the realization of advanced surfaces in biomedical applications. Deposition of chitosan via cathodic polarization has been recently proposed as a simple, fast, and effective technique also for the preparation of cellular solids [1], by their peeling-off from the deposition substrate. Chitosan ((1,4)-linked 2-amino-2- deoxy-d-glucan) is a natural cationic polymer that has been widely applied in drug delivery and tissue engineering for its proven biocompatibility, biodegradability, and antibacterial properties. Its electrodeposition, based on transport phenomena and reduction reactions at the diffusion layer, offers a control of the process parameters through simple adjustment of processing time and applied potential. The morphology of the obtained structures, being in the range of interest for tissue engineering scaffolds, can be easily tuned by an appropriate selection of anionic species and their concentration. Here we show the effects of the selection of anionic species and the surface cathode properties on the morphology of deposited coatings in order to modulate the obtained porosity. Electrocoagulation processes strongly depend on local reduction at the cathode, in turn affected by the acid/base equilibrium in solution: we hence examined (i) different water-based acidic bath and (ii) surfaces with different overvoltages for the hydrogen evolution reaction. Different coating morphologies, in terms of pore size and interconnection, were obtained by modifying electrochemical bath composition and controlling the overvoltage for hydrogen evolution by selecting the proper substrate material and surface preparation. Gas evolution at the cathode surface determined the growth of pores in the deposit coatings and, depending on the process parameters, close vs. open porosities were observed. A mass increase of deposited chitosan by increasing pH was generally observed, even if this trend is not monotone by increasing the pH. An increase of film porosity has been, in fact, noticed by increasing the mass rate deposition and hydrogen evolution and entrapment in the deposited gels. The overall deposition process seems affected by different electrolytes mainly as a consequence of their acid/base equilibria. Porosity can also be tuned according to the surface properties of selected metallic substrates, based on the characteristic exchange current for hydrogen evolution reaction. An accurate control of this process, hence allows to modulate open vs. closed pore structures. The possibility of tuning surface morphology of this class of films paves the way for the design of a novel class of 3D structures supporting tissue engineering approach and advanced drug delivery.

[1] L. Altomare, L. Draghi, R. Chiesa, L. De Nardo, Materials Letters 78 (2012) 18.
Tenoxicam’s Electro-Analytical Determination with a b-Cyclodextrin Modified-Electrode
Authors: Guzmán-Hernández Dafne Sarahia , Ramirez-Silva Maria Teresa , Palomar-Pardavé Manuel , Corona-Avendaño Silvia , Romero-Romo Mario A.
Published: February 2020

An electrochemical study is presented of the analytical determination of the non-steroidal anti-inflammatory drug called tenoxicam. In this study the detection, quantification limit and sensibility obtained with different electrochemical techniques are presented, using a carbon paste electrode as working electrode, as well as the results obtained for the same study carried out with a b-cyclodetrin polymer-modified carbon paste electrode, which gave better analytic parameters for the determination, basically due to drug adsorption into the membrane of this electrode.
Laser Induced Natural Fiber Welding of Cellulosic Substrates
Authors: Brown E. Kathryn , Dennis Kathleen , Haverhals Luke M. , Sweely Kurt D. , De Long Hugh C. , Trulove Paul C.
Published: February 2020

As excellent solvents for cellulose and silk, certain ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium acetate (EMIAc),1,2 can be used for biopolymer modification and manipulation. Full dissolution and regeneration using IL solvents often results in biomaterials with inferior properties compared to the native material. When natural substrates are only partially dissolved and regenerated through a process we call Natural Fiber Welding (NFW), much of the native biomaterial structure can be maintained while still allowing for significant material modification. NFW enables the structural modification of the surface and incorporation of functional materials through the binding capability of the portion of dissolved biopolymer3-5.

In the present work we have employed a laser as the heat source to initiate partial dissolution of a cellulose substrate causing NFW in a spatially-specific manner. By using a non-solvent for cellulose (e.g., water) with the ionic liquid as a means of inhibiting the dissolution process, heat becomes the controlling factor necessary to obtain significant biopolymer dissolution and mobilization. A CO2 laser was used to raster a specific pattern onto a cellulosic paper substrate coated with IL solution. Raster power, concentration of the ionic liquid and the number of laser passes affect the amount of heat absorbed into the biopolymer and the level of NFW. Through tensile testing, confocal microscopy, ATR-IR, and SEM imaging, the resulting modification of the biopolymers was characterized.

References

Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am Chem Soc, 2002, 124, 4974.

Phillips, D. M.; Drummy, L. F.; Conrady, D. G.; Fox, D. M.; Naik, R. R.; Stone, M. O.; Trulove, P. C.; De Long, H. C.; Mantz, R. A. J Am Chem Soc., 2004, 126, 14350.

Haverhals, L. M.; Reichert, W. M.; De Long, H. C.; Trulove, P. C. Cellulose, 2010, 2985, 425.

Haverhals, L. M.; Sulpizio, H. M.; Fayos, Z. A.; Trulove, M. A.; Reichert, W. M.; Foley, M. P.; De Long, H. C.; Trulove, P. C.Cellulose, 2012, 19, 13.

Haverhals, L. M.; Nevin, L. M.; Foley, M. P.; Brown, E. K.; De Long, H. C.; Trulove, P. C. Chem.Commun., 2012, 48, 6417.
Porous Carbon Anodes for the Supply of Methane during Electrowinning of Aluminium
Authors: Khalaghi Babak , Mokkelbost Tommy , Kjos Ole Sigmund , Gudbrandsen Henrik , Haarberg Geir Martin
Published: February 2020

Currently consumable carbon anodes are utilized in the aluminium production process. The major drawback of this type of anodes is the high amount of CO2 emissions. Furthermore, due to the consumption of the anodes during the electrolysis it is necessary to adjust the anode – cathode distance continuously and finally replace the anode. Introduction of hydrogen or natural gas through the anode can decrease the CO2 emissions significantly and reduce the consumption of the anode. The use of inert porous anodes is interesting since the energy demand will be reduced due to natural gas/hydrogen participating in the anode reaction. However, due to unavailability of a sufficiently inert anode for aluminium electrolysis until now, carbon anodes seem to be more attractive. When natural gas/hydrogen is purged through the porous carbon anode, there will be competing anodic reactions depending on whether carbon from the anode or the CH4/H2 reacts with the oxygen ions from the bath. Previous studies using porous carbon anodes showed 0.3 V depolarization as well as 20% decrease in carbon anode consumption using methane compared to passing argon through the anode1. On the other hand, using CH4/H2 can lead to the formation and evolution of additional hydrogen fluoride. This was studied before and some ideas on how to deal with this extra HF evolution were presented2. In this study, further laboratory experiments were performed and the effect of carbon anodes with different porosities and designs were studied. Besides, off-gas analysis was performed and HF evolution will be discussed.

References:

S. Xiao, T. Mokkelbost, O. Paulsen, A.P. Ratvik, and G.M. Haarberg, Metallurgical and Materials Transactions, 44B, (2013) 1311.

T. Mokkelbost, O. Kjos, O. Paulsen, B. Øye, H. Gudbrandsen, A.P. Ratvik, and G.M. Haarberg, Light metals (2014), 756.
Catalysis of the Oxygen Reduction Reaction: Thin Layer Sonoelectrochemistry
Authors: Duda Chester G , Leddy Johna
Published: February 2020

The oxygen reduction reaction (ORR) is a multi-electron and -proton transfer mechanism. In acidic solution, the slow step is typically taken as the first electron transfer.

O2 + e + H+ ⇌HO2

Even with platinum electrocatalysts, ORR kinetics impose parasitic losses of ~30 % in proton exchange membrane (PEM) H2|O2 fuel cells. Because of poor O2 reduction kinetics, H2is generated by steam reforming of natural gas rather than by water electrolysis.

Typically, catalysis is achieved by chemical manipulation of the catalyst materials. Physical means, such as increased temperature and pressure, can also increase rates. One means to increase temperature and pressure is irradiation of a fluid with ultrasound so as to induce cavitation. Acoustic energy is carried by a wave that first compresses the fluid, then rarefies the fluid to form microscopic voids, and then compresses the fluid to collapse the voids. On collapse at the thin interface between the fluid and void, extreme temperature (T > 5000 K) and pressure (P > 103 atm) are generated.1

Ultrasound has been applied to electrochemical systems with the first studies undertaken by Coury, et. al.2 In these studies, cavitation was generated in a bulk electrolyte where electrodes were placed at a distance from a sonic horn or other ultrasound source. Large transport enhancements were observed, but effects on heterogeneous reactions were not observed. Bubbles introduced noise in the voltammetry and the distance between the ultrasound source and the electrodes allowed energy to dissipate. See Scheme 1.

Here, the ORR is investigated by sonoelectrochemistry undertaken in a thin layer electrochemical cell,3,4where:

Acoustic energy attenuates less in the thin layer and so impacts the electrode processes..

Acoustic energy is reflected back into the condensed phases rather than pass into the less dense air phase.

Frank cavitation is not observed and not necessary to the enhanced rate of the ORR.

ORR rate is increased to the mass transport limit.

As shown in Figure 1, on sonication in a thin layer, O2reduction proceeds at the mass transport limited rate. The experimental set up is shown in Figure 2.

In general, sonication in a thin layer increases interfacial rates without significant impact on transport3,4 and provides a general, physical means to effect catalysis.

References and Acknowledgments: Support of the National Science Foundation and the University of Iowa is gratefully acknowledged.

[1] K.S. Suslick, Y. Didenko, M.M. Fang, T. Hyeon, K.J. Kolbeck, M.M. Mdleleni, and M. Wong, Acoustic Cavitation, Phil. Trans. Royal Soc. A 1999.

[2] C.R.S Hagan R. S. and L.A. Coury Jr. Anal. Chem., 1994, 66(3), 399–405.

[3] Chester G. Duda, Ph.D. dissertation, University of Iowa, 2012.

[4] J. Leddy, C.G. Duda, and W.J. Leddy III, U.S. Patent application, 2013.
Synergy in the Hydrazine Assisted Electro-Oxidation of Formic Acid
Authors: Machado Eduardo Giangrossi , Varela Hamilton
Published: February 2020

In a recent paper, Schlogl have discussed thoroughly [1] the importance of chemistry on the energy scenario. It was pointed out that hydrogen could be an interesting source of energy, as long as storage problems could be fixed. Molecules such as formic acid and hydrazine are interesting hydrogen-carrier molecules, thus relevant in these energy-related systems. The mechanism by which the electro-oxidation of these molecules takes place was largely studied individually [2, 3]. However, few studies [4] have been done on the interaction present when these fuels are mixed. The present work aims at exploring the oscillatory instabilities present in the formic acid + hydrazine system to deepen the current understanding of surface reactions underlying these mixed fuels. The synergy in the electro-oxidation of mixtures of these two fuels is explored in this work. The electrochemical response obtained by the mixture is greater than the one obtained by the sum of the individual parts, as can be observed from the different oscillatory features in the separate and the complete system. The separate systems present limitations inherent to the characteristics of each fuel. For instance, formic acid has a self-poisoning process caused by the accumulation of oxygenated species that pulls the system away from the oscillatory condition in short times. On the other hand, hydrazine presents a deactivation of the electrode surface during time, as an effect of pH. When the two fuels are combined, long-last oscillations prevail, similarly to recently reported in our Group [5]. Additionally, the morphology of the time-series is different for the complete system comparing to the separate ones. Those evidences suggest that there is an intricate superficial interaction between the fuels, a synergy, to produce an unexpected oscillatory behavior.

Acknowledgements

EGM and HV acknowledge São Paulo Research Foundation (FAPESP) for financial support (grants #2009/07629-6, #2012/07313-1, #2012/24152-1, and # 12/21204-0). HV (#306151/2010-3) acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support.

References

1. Schlogl, R., The role of chemistry in the energy challenge. ChemSusChem, 2010. 3(2): p. 209-22.

2. Aldous, L. and R.G. Compton, The mechanism of hydrazine electro-oxidation revealed by platinum microelectrodes: role of residual oxides. Phys Chem Chem Phys, 2011. 13(12): p. 5279-87.

3. Joo, J., et al., Importance of acid-base equilibrium in electrocatalytic oxidation of formic acid on platinum. J Am Chem Soc, 2013. 135(27): p. 9991-4.

4. Aldous, L. and R.G. Compton, Towards Mixed Fuels: The Electrochemistry of Hydrazine in the Presence of Methanol and Formic Acid. ChemPhysChem, 2011. 12(7): p. 1280-1287.

5. Perini, N.B., B. C.; Angelo, A. C. D.; Epstein, I. R.; Varela, H., Long-lasting oscillations in the electro-oxidation of formic acid on PtSn intermetallic surfaces. ChemPhysChem - in press., 2014.