bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Non-Monotonic Surface Charging Behavior of Platinum: Implications for Electrocatalysis in PEFC
Authors: Huang Jun , Zhang Jianbo , Eikerling Michael 
Published: February 2020

In electrochemical systems, metal surface charging phenomena dictate the strength of electrostatic interactions between the electrified electrode and ions in solution. Historically, the potential of zero charge (pzc) of the metal has been employed to parameterize the surface charging relation [1][2].
However, for a Pt electrode, classical radiotracer experiments of Frumkin and Petrii revealed a non-monotonic charging behavior upon increasing the metal phase potential, with consecutive transitions from a negative to a positive surface charging region and further to another negative surface charging region [3]. Garcia-Araez et al. later reported a similar ‘negative-positive-negative’ charging relation derived from laser-pulsed experiments [4]. This alternating charging behavior defies the role of the pzc as a sufficient descriptor of electrode charging phenomena. The situation calls for an overhaul of the charging relation that must be derived from first principles. This study presents a refined structural model for electrified interfaces, as shown on the left side of Figure 1. The model accounts explicitly for charging effects caused by the formation of a surface oxide layer and a layer of oriented water molecules. An analytical expression for the charging relation is derived.
The charging relation is parameterized using experimental data for a Pt surface as well as DFT calculations. It exhibits the three different charging regions observed in the experiments cited above. To illustrate the impact of the modified charging relation, it is employed to study the oxygen reduction reaction in nanoporous electrodes of polymer electrolyte fuel cells.
References
[1]. Frumkin, A.; Gorodetzkaya A. Z. Phys. Chem. 1928, 136, 451.
[2]. Petrii, O. A. Zero charge potentials of platinum metals and electron work functions (Review). Russ. J. Electrochem. 2013, 49, 401.
[3]. Frumkin, A. N.; Petrii, O. A. Potentials of zero total and zero free charge of platinum group metals. Electrochim. Acta. 1975, 20, 347.
[4]. Garcia-Araez, N.; Climent, V.; Feliu, J. Potential-dependent water orientation on Pt (111), Pt (100), and Pt (110), as inferred from laser-pulsed experiments. Electrostatic and chemical effects. J. Phys. Chem. C. 2009, 113, 9290.

Figure 1
Effect of Temperature on Platinum Dissolution from PEFC Catalysts
Authors: Wang Zhongqi , Tada Eiji , Nishikata Atsushi 
Published: February 2020

The durability of polymer electrolyte fuel cells (PEFCs) is a big concern for its applications like FCVs to be commercialized on a large scale. In particular, the instability of Pt-based cathode catalyst has been discussed intensively. Platinum (Pt) dissolution is recognized as one of the degradation mechanisms for carbon supported Pt catalysts (Pt/C) in PEFCs. It has been found that repeated potential cycles accelerate Pt dissolution.[1-3] Fundamental studies in aqueous media revealed preliminary behaviors of Pt dissolution during one potential cycle. The up-to-date data were mostly obtained near room temperature, and a dominant cathodic dissolution during reduction of Pt oxide was understood. As reported by Fuller et al.,[4] however, degradation of Pt/Cs at an elevated temperature near 60 to 80 °C, whereat a PEFC normally operates, was severer than that at room temperatures. Thus, it is necessary to evaluate Pt dissolution from Pt/Cs at such temperatures.
In prior studies,[5-6] we compared Pt dissolution at 25 °C and 65 °C by inductively coupled plasma mass spectrometry (ICP-MS) and a channel flow double electrode (CFDE). The experiments had some difficulties, but the results showed a ca. 5-time enhancement from 25 to 65 °C. The cathodic dissolution was enhanced because larger amount of Pt oxide was formed at 65 °C. The effect of temperature on the anodic dissolutions and the place exchange process remains unclear yet.
In this study, we evaluate Pt dissolution under temperatures ranging from 20 to 80 °C. We test a series of commercial Pt/C catalysts produced by TKK that have Pt loadings from 20 to 70 wt% and average Pt particle size from ca. 1.5 to 5 nm. We limited the potential region between 0.6 and 1.4 V, which is closely related to the operation region of a PEFC cathode. We use ICP-MS to evaluate to overall dissolutions and a CFDE to analyze the dissolution behavior in one potential cycle. The attached Figure showed a typical CFDE data presenting the current on a working electrode loading a 30wt% Pt/C (TEC10E30A) under potential cycling (I
WE) and the current recorded on a collector electrode (I
CE) at 80 °C in 0.5 M H2SO4. The I
CE helps to understand the dissolution of Pt4+ and Pt2+ complex during one potential cycle. Similar analysis will be discussed at other temperatures like 20, 40, and 80 °C in the presentation.

Reference

Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161, F380 (2014).

A.A. Topalov, S. Cherevko, A.R. Zeradjanin, J.C. Meier, I. Katsounaros, and K.J.J. Mayrhofer, Chem. Sci., 5, 631 (2014).

P. Jovanovič, A. Pavlišič, V.S. Šelih, M. Šala, N. Hodnik, M. Bele, S. Hočevar, and M. Gaberšček, ChemCatChem, 6, 449 (2014).

W. Bi and T.F. Fuller, J. Electrochem. Soc., 155, B215 (2008).

Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 163, F1-F3 (2016).

Z. Wang, E. Tada, and A. Nishikata, ECS Trans., 69, 255 (2015).

Figure 1
Direct Simulations of Coupled Transport and Reaction on Nano-Scale X-Ray Computed Tomography Images of Platinum Group Metal-Free Catalyst Cathodes
Authors: Ogawa Shohei , Komini Babu Siddharth , Chung Hoon T , Zelenay Piotr , Litster Shawn 
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) have been developed for automotive, residential, and portable power applications. Typically, PEFC stacks use platinum (Pt) or Pt alloys as the oxygen reduction reaction (ORR) catalyst in the cathode. Although Pt performs well, its raw material cost is significant and limits future cost reductions. As an alternative, platinum group metal-free (PGM-free) catalyst may have the potential to significantly reduce PEFC costs. Despite recent advances in PGM-free catalyst ORR activity,1 the volumetric activity remains well below that of Pt cathodes and results in thick electrodes with significant transport losses.
To advance PGM-free catalyst electrodes, it is important to understand the coupling between electrochemical reactions, transport phenomena, and microstructure in the catalyst layer. Here, we expand this understanding using a combination of nano-scale X-ray computed tomography (nano-CT) and direct simulations on the CT images. Nano-CT imaging was done for cyanamide-polyaniline-iron PGM-free catalyst cathodes with three different Nafion® loadings (35, 50 and 60 wt%). Using Zernike phase contrast we differentiated the solids (Nafion®, carbon, and iron) and the pore phase,2 and by staining the electrode with cesium, we distinguished the Nafion® phase by absorption contrast in a second scan. The two data sets were overlaid to complete the structure of the whole cathode.3 In other words, at each voxel we have the volume fractions of pore, Nafion®, and carbon catalyst phases. To illustrate, Figure 1a shows the Nafion® fraction over the simulation domain where the Nafion® had agglomerated and was heterogeneously distributed. The spatially-resolved volume fraction data is then input to the simulation of oxygen, proton, and electron transport as well as the local ORR volumetric current. Figure 1b shows the ionic potential and current streamlines in Nafion® phase resulting from the distributed reaction.

Acknowledgement

The authors gratefully acknowledge the support the support of the technology development manager Nancy Garland and funding from the US Department of Energy, the Office of Energy Efficiency and Renewable Energy, Office of Fuel Cell Technologies. The nano-CT instrument was acquired with the support of a Major Research Infrastructure award from the National Science Foundation under Grant No. 1229090.

References

1. G. Wu, K. L. More, C. M. Johnston, and P. Zelenay, Science, 332, 443–447 (2011).
2. S. Komini Babu, H. T. Chung, G. Wu, P. Zelenay, and S. Litster, ECS Trans., 64, 281–292 (2014).
3. S. Komini Babu, H. T. Chung, P. Zelenay, and S. Litster, ECS Trans., 69, 22–33 (2015).

Figure 1
Novel Electrocatalyst for Hydrogen Oxidation in Alkaline Media
Authors: Serov Alexey , Kim Yu Seung , Odgaard Madeleine , Halevi Barr , Atanassov Plamen 
Published: February 2020

Anion Exchange Membrane Fuel Cells (AEMFCs) are fast growing alternative to Proton Exchange Fuel Cell (PEMFC) technology. It was shown that several classes of non-platinum group metal (non-PGM) catalysts outperformed platinum in the oxygen reduction in alkaline media.[1] In contrast the published data on alternative to platinum anodes for hydrogen oxidation reaction in alkaline media is scarce.[2]One of the possible non-PGM catalysts for the HOR in alkaline media are Ni- and Pd-based materials. We have prepared Ni-Mo-Cu catalysts that shows HOR activities in the rotating disk electrode (Figure 1). The preliminary results on MEA tests show that the Ni-based alloys as an anode have shown extremely high open-circuit voltages (OCVs) in both oxygen and air (up to 1.1V), which is significantly higher compared to PGM-free anodes in PEMFCs. However, the effort in integration of those materials into MEA with most appropriate ionomer and MEA fabrication technique is needed. In this talk, we will discuss the preparation and characterization of the novel electrocatalysts for HOR in alkaline media.
Figure 1. HOR on Ni-Mo-Cu catalysts in 1M KOH saturated with H2, 1600RPM, 10 mV s-1.
Acknowledgements: Department of Energy, Hydrogen Oxidation Reaction in Alkaline Media, Control Number: 0966-1624, Award Number: DE-EE0006962 (PI A. Serov).

[1] M. H. Robson, A. Serov, K. Artyushkova, P. Atanassov, Electrochim. Acta, 90, 2013, 656–665.
[2] A. Serov, C. Kwak, Applied Catalysis B: Environmental, 91, 2009, 1–10.

Figure 1
Fine Tuning of the ORR Performance-Durability for Pt-Based Electrocatalysts
Authors: Lopes Pietro Papa , Li Dongguo , Lv Haifeng , Strmcnik Dusan , Paulikas Paul Arvydas , Markovic Nenad M , Stamenkovic Vojislav 
Published: February 2020

The progress in the ORR electrocatalysis over the last two decades has been achieved primarily through the fundamental understanding of processes that are taking place at well-defined surfaces. For instance, the nature of active sites is a common topic in the literature, however, despite decades of persistent studies aimed to reveal the fundamentals, insight at atomic level is still lacking. Properties such as surface crystallographic orientation, morphology, composition and defects are yet to be assigned to the correlation between the atomic structure and catalyst activity. For the first time, we report on the atomic structure that has been investigated in combination with durability. The ultimate precision that goes beyond a part per million of a single atomic layer has been achieved in determining electrocatalytic properties of the ORR catalysts. Obtained knowledge is of paramount importance in design of advanced highly functional nanoscale materials. Surfaces of Pt-based materials have been characterized by AES, LEED and UPS, which was followed by controlled transfer to electrochemical, in-situ FTIR and STM cells. These findings have been further used to optimize a unique RDE coupled ICP-MS system. Such effort has led towards the design and synthesis of nanoscale materials with superior electrocatalytic properties. Fine tuning of the surface properties induced unprecedented improvements in functionality of real world catalyst for the ORR in fuel cells that will be reported for the first time.
Development of Low Cost High-Temperature Polymer Electrolyte Fuel Cell Membrane-Electrode-Assemblies for Combined Heat and Power Plants in Single Family Homes
Authors: Schenk Alexander , Gamper Stefan , Grimmer Christoph , Pichler Birgit Elvira , Bodner Merit , Weinberger Stephan , Hacker Viktor 
Published: February 2020

High-temperature polymer electrolyte fuel cells (HT-PEFCs) are a suitable technology for decentralized small scale electricity and heat production. HT-PEFCs do not require hydrogen infrastructure and are characterized by a simpler and therefore less expensive system compared to available fuel cell systems. In combination with a reformer unit, HT-PEFC systems offer an efficiency gain over conventional combustion of hydrocarbons, such as natural gas. In near future, HT-PEFCs will be even more effective and efficient when renewable biofuels and hydrogen are widespread available.
We present an efficient HT-PEFC based combined heat and power (µ-CHP) system for the provision of electrical energy and hot water in single family households (see Table 1). Due to the optimized design and layout of the fuel cell based µ-CHP system and the respective manufacturing processes of the catalysts and the membrane electrode assemblies (MEA), the demand for cost effective and greenhouse gas efficient energy at customer level is addressed.
Major efforts were devoted to the establishment of scalable catalyst deposition methods, which enable a loss-free utilization of precious metals. By using appropriate multimetallic catalyst systems at anode and cathode, the precious metal loading was reduced by approx. 20% in comparison to commercially available electrodes without compromising performance (see Figure 1) [1]. Furthermore, by introducing post-preparation treatments, the stability of the catalysts was enhanced over commercial Pt/C. The activity and stability of the catalyst systems were evaluated ex situ by means of cyclic voltammetry and accelerated stress tests using a rotating disk electrode (RDE) setup. Furthermore, the catalyst systems were characterized in situ by means of polarization curves, continuous operation, accelerated stress tests and electrochemical impedance spectroscopy measurements at single cell, stack and at system level (see Figure 1).

Acknowledgment

Financial support was provided by The Climate and Energy Fund of the Austrian Federal Government and The Austrian Research Promotion Agency (FFG) through the program Energieforschung (e!Mission).
[1] A. Schenk, C. Grimmer, M. Perchthaler, S. Weinberger, B. Pichler, C. Heinzl, C. Scheu, F.-A. Mautner, B. Bitschnau, V. Hacker, Platinum–cobalt catalysts for the oxygen reduction reaction in high temperature proton exchange membrane fuel cells – Long term behavior under ex-situ and in-situ conditions, J. Power Sources. 266 (2014) 313–322.

Figure 1
Measurement of Local Electrode Potentials in an Operating PEMFC Exposed to Contaminants
Authors: Spendelow Jacob S , Castanheira Luis , Hinds Gareth , Rockward Tommy , Langlois David A. , Mukundan Rangachary , Borup Rod L. 
Published: February 2020

The use of a three-electrode cell, in which the potential of a working electrode can be accurately measured vs. a reference electrode (RE), is a standard practice in liquid-phase electrochemical experiments. However, the geometric constraints of a working PEMFC make use of a RE challenging. Incorporation of a RE into an operating PEMFC typically requires experimental compromises that prevent precise and accurate measurements from being obtained, and do not allow accurate spatial resolution of potential variation along the electrodes. As a result, PEMFC experiments are often performed using the PEMFC anode, which remains within a few mV of 0 V vs RHE during typical operation, as a pseudo RE.
Recently, the National Physical Laboratory (NPL) developed an effective technique for accurate in situ monitoring of local electrode potentials in a PEMFC. By inserting REs from the back side of the MEA, the NPL configuration eliminates the edge effects, lack of anode vs. cathode specificity, Ohmic losses, and current density distribution disruptions that have compromised previous fuel cell RE experiments.
We report here on the use of this RE technique to monitor local electrode potentials in an operating PEMFC during exposure to CO gas (Figure 1). CO is a common impurity in H2 gas and is known to poison Pt-based anodes. Levels of CO present in H2 fuel are expected to be in the ppb range for cells operating on pure H2 and the ppm range or higher for cells operating on reformate. Use of an RE can reveal the distribution of CO losses, and can also enable losses on the anode to be distinguished from those on the cathode. The results of this work demonstrate a new diagnostic capability that enables improved understanding of local conditions during PEMFC operation during transient or steady state operation.
Figure 1. Cell voltage (orange) and anode potential (blue) of a MEA operating at 1 A/cm2 with anode exposed to 20 ppm CO. CO was removed from the anode feed at t = 47 min. Gore MEA, with anode/cathode loading of 0.4/0.1 mg/cm2, 80°C, 100% RH, 100 kPaabs.

Figure 1
Bipolar Membrane Design for Hybrid PEM/AEM Fuel Cells
Authors: Ahlfield John M. , Liu Lisha , Chu Deryn , Kohl Paul A 
Published: February 2020

Bipolar membranes fuel cells utilizing both anion and cation conductive materials have several advantages compared to their purely acidic or alkaline counterparts. The potential advantages include improved water management through self-hydration and facile electrode kinetics. Material transport properties play an important role in determining viability of membrane and ionomer materials. In addition, the cation-anion junction itself is a critical element in determining device performance because it must be sufficiently conductive to ionic species and mechanically stable to withstand the internal pressure from water formation. A series of electrochemical devices using different bipolar membranes have been fabricated for use in direct methanol and hydrogen fuel cells. This study examines both single- and two-membrane systems containing cation-anion junctions. These fuel cells were characterized by performance metrics and electrochemical impedance spectroscopy to determine specific areas for improvement in the bipolar devices. Operation under varying humidity was studied in order to understand water management necessary for bipolar fuel cells. These results will be used in the future optimization of bipolar devices.
Financial support from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged.
CNTs Grown on Al2O3 Spheres As an Efficient Catalyst Support for High Performance MEA in PEM Fuel Cells
Authors: Lim Eun Ja , Chang Kwang Hyun , Cho Seonghun , Park Seok-Hee , PARK Gu-Gon , Yim Sung-Dae 
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have been widely accepted as a clean energy device because of its capability of generating high energy density and only water as a product via direct converting of the chemical energy into the electrical energy. However, durability problems originating from the carbon corrosion and Pt agglomeration have been one of the major issues for practical applications. The high potentials formed in a cell during the fuel cell operations lead to serious carbon corrosion in catalyst layers, which causes the decrease of cell performance. To resolve the carbon corrosion, highly durable carbon materials such as carbon nanotubes (CNTs) have been intensively studied. Although the corrosion-resistant characteristics of CNTs were efficient to utilize as an electrocatalyst support for PEMFCs, the difficulty in processing the CNTs mainly due to poor dispersibility and easy bundle formation in a catalyst ink limited their practical applications. In this respect, vertically aligned carbon nanotubes (VACNTs) have been tried and showed promising results in a PEMFC MEA. However, VACNTs need complex process to make MEAs, remaining the issues of mass production.
In this work, we report CNTs grown on Al2O3 (Al2O3-CNT) as an efficient support material for PEMFC MEAs. The catalyst support was designed to utilize durable CNT properties while resolving the CNT bundling problems. The catalyst was characterized by transmission electron microscope (TEM), field emission scanning spectroscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) in order to investigate structural and electronic properties. The kinetics of O2 reduction is examined with the rotating disk electrode (RDE) technique. A potential cycling test was applied to evaluate durability of the catalyst. The electrochemical surface area (ECSA) of Pt/Al2O3-CNT slightly decreased (17 %), while Pt/C loses nearly 46 % of its ECSA of its initial value over repeated cycling test under carbon corrosion potential range, representing more durable properties of CNTs. The single cell test was also performed with Pt/Al2O3-CNT and Pt/C after fabricating the catalysts to MEAs. The performance of the Pt/Al2O3-CNT was comparable to that of Pt/C and showed better performance at high current density regions. Furthermore, after the accelerated stress test (AST), the Pt/Al2O3-CNT also showed approximately 2 times higher stability than Pt/C in a single cell test.
Synthesis of Highly Crosslinked Polymer/Inorganic Membranes and Discussion of the Resulting High Proton Conductivity and Chemical Stability
Authors: Motz Andrew R , Horan James L , Kuo Mei-Chen , Herring Andrew M 
Published: February 2020

Heteropoly acids (HPA)s are a large class of inorganic acids that are known to have extremely high proton conductivities.[1] It has been demonstrated that doping perfluorinated sulfonic acid and hydrocarbon-based membranes with HPA is able to improve protonic conductivity, particularly under reduced humidity and elevated temperatures, but this method suffers from a lack of stability to water.[2,3] Even when the cesium salt (water-insoluble) is used, it is likely that agglomeration will occur overtime, as the HPA is not truly immobilized. Silicotungstic acid (SiW12O40
-4) is of particular interest for use in a fuel cell because it has been shown to be stable under relevant conditions.[4]
In an effort to mitigate agglomeration and water instabilities that plague most HPA containing films, we have covalently attached silicotungstic to 3M FC-2145 (polyvinylidene-co-hexafluoropropylene), forming a highly crosslinked polymer/hybrid network. First, phenol phosphonic acid (PPA) side chains are attached to FC-2145, and then two PPA groups react with a single, mono-lucunary silicotungstic acid (SiW11O39
-8), thus forming covalent crosslinks. This synthesis produces materials that have loadings of HPA, stable to boiling, in excess of 60wt%. The resulting material has high proton conductivity (>200 mS/cm at 90°C/95%RH) under humidified conditions as well as relatively high proton conductivity (>30mS/cm at 110°C/50%RH) under lower humidity conditions. This talk will include discussion on synthesis, transport properties, and preliminary chemical stability.

References:

[1] Nakamura, O.; Kodama, T.; Ogino, I.; Miyake, Y., High-Conductivity Solid Proton Conductors - Dodecamolybdophosphoric Acid and Dodecatungstophosphoric Acid Crystals. Chemistry Letters 1979, 17-18.
[2] Meng, F.; Aieta, N. V.; Dec, S. F.; Horan, J. L.; Williamson, D.; Frey, M. H.; Pham, P.; Turner, J. A.; Yandrasits, M. A.; Hamrock, S. J.; Herring, A. M., Structural and transport effects of doping perfluorosulfonic acid polymers with the heteropoly acids, H3PW12O40 or H4SiW12O40. Electrochimica Acta 2007, 53, 1372-1378.
[3] Wang, Z.; Ni, H.; Zhao, C.; Li, X.; Fu, T.; Na, H., Investigation of sulfonated poly(ether ether ketone sulfone)/heteropolyacid composite membranes for high temperature fuel cell applications. Journal of Polymer Science Part B: Polymer Physics 2006, 44, 1967-1978.
[4] Sweikart, M. A.; Herring, A. M.; Turner, J. A.; Williamson, D. L.; McCloskey, B. D.; Boonrueng, S. R.; Sanchez, M., 12-Tungstophosphoric Acid Composites with Sulfonated or Unsulfonated Epoxies for High-Temperature PEMFCs. Journal of The Electrochemical Society 2005, 152, A98.