bluuebunny/crossref_metadata_2025_split huggingface dataset:
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).
.
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.
“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.
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.
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.