bluuebunny/crossref_metadata_2025 huggingface dataset:
Porous Graphene Layers on Pt Catalyst for Long-Term Stability of Fuel Cell Electrode
Authors: Kim Heeyeon , Robertson Alex W , Warner Jamie H , Kim Sang Ouk
Published: February 2020

With the development of various energy technologies, much interest is focused on the feasibility and efficiency study of energy devices such as fuel cells, batteries, supercapacitors and water electrolysis systems. Among them, polymer electrolyte fuel cell (PEFC), which convert hydrogen into electric energy with zero emission of pollutants, is one of the most promising environmentally friendly technologies. Despite innumerable studies for more than half a century, degradation of the key component, membrane electrode assembly (MEA), is still a big obstacle for the commercialization of PEFC system.

For the high performance and long-term stability of Pt/C electrode catalyst, the agglomeration of Pt particles and dissolution or detachment of Pt particles from carbon support have to be improved. For this purpose, we adopted a new shape of nano-carbon material for the surface modification of Pt catalyst.

Graphene has been an attractive two-dimensional carbon allotrope having large surface area and electronic conductivity. Graphene also shows high flexibility and mechanical strength so that it can be used for large number of applications such as flexible display or printable electronics, etc [1-2]. In most cases, people need large-area graphene films with little or no defect for high thermal and electronic conductivity. Also, people need to transfer the as-prepared graphene film for each application. All of these processes are not easy or simple, and they are also labor-intensive processes. However, in the case of catalysis, porous graphene films can be synthesized via very simple one-step process and can be used as effective protective layers for Pt catalysts.

In this study, we developed porous graphene films in order to improve the long-term stability of Pt catalysts maintaining the high performance of them. The graphene films were synthesized by single-step vaporization process, where the number of graphene layers and the defects in their structure are manipulated by temperature and composition of the precursors. In this process, the amounts of structural defects, pyridine was simultaneously introduced to the vaporization process, which is much easier and cost-effective compared to the conventional NH3-treatment at high temp [3].

Consequently, our Pt/C catalysts coated with porous graphene films showed similar initial activity compared with the commercial catalysts (Pt 40wt%, Johnson Matthey) showing more than 150% higher long-term stability [4].

 [1] A.K. Geim and K. S. Novoselov, Nature Mater. 6 (2007) 183.

[2] X. L. Li, G. Y. Zhang, X. D. Bai, X. M. Sun, X. R. Wang, E. Wang and H. J. Dai, Nature Nanotech. 3 (2008) 538.

[3] Y. Wang, Y. Shao, D. W. Matson, J. Li and Y. Lin, ACS nano 4(4) (2010) 1790.

[4] H. Kim, A. Robertson, S. O. Kim, J. M. Kim and J. H. Warner, ACS nano 9(6) (2015) 5947.
Comparison of the Stability of Niobium and Antimony Doped Tin Oxide Supports on in Situ Load and Stop/Start Cycling of Pt/Nb-SnO2 and Pt/Sb-SnO2
Authors: Jimenez Morales Ignacio , Dupont Marc , Cavaliere Sara , Jones Deborah J. , Rozière Jacques
Published: February 2020

Nanofibre antimony and niobium doped tin oxides (Sb-SnO2, Nb-SnO2) were prepared by electrospinning and calcination, and were functionalised by depositing platinum nanoparticles prepared by a microwave-assisted polyol method. Catalysts inks of Pt/Sb-SnO2 and Pt/Nb-SnO2 were used to prepare cathodes that were assembled with a commercial anode and membrane into MEAs. These MEAs were submitted to voltage cycling between 0.9 and 1.5 V, and to stop/start cycling. I-V characteristics recorded at the beginning and end of the accelerated stress test protocols. The relative stability of Pt/Sb-SnO2, Pt/Nb-SnO2 under these conditions, and the results of probe spectroscopic methods used to investigate ageing mechanisms in doped tin oxides, will be described.
Development of Nitrogen-Doped Titanium Oxide Electrocatalysts for PEFCs
Authors: Yamato Yoshinori , Lee Kunchan , Wang Hailin , Imai Takuya , Ishihara Akimitsu , Ota Kenichiro
Published: February 2020

With their efficiency, high power density, and low/zero emissions, polymer electrolyte fuel cells (PEFCs) are recognized as promising energy converting system. However, high cost and insufficient durability currently hinder their commercialization. Especially, one of the major barriers is the high cost and low stability of platinum (Pt)-based catalysts 1). Thus, developing alternative catalysts with low cost and high stability has been strongly required for the commercialization of PEFCs.

In the effort to reduce the cost of PEFCs, we have been developing nitrogen doped titanium oxide (N- TiO2) as a non-noble metal electrocatalyst in NEDO (New Energy and Industrial Technology Development Organization, Japan) project. In this paper, we introduce a new and convenient synthesis method of N-doped TiO2electrocatalysts and their catalytic activities for oxygen reduction reaction (ORR).

In this study, we used phthalocyanine (Pc) as nitrogen source in order to dope nitrogen into TiO2. For the high surface area of electrocatalyst, TiO2 nanoparticles were deposited on high surface area carbon supports (C). The carbon supported TiO2 (TiO2/C) and phthalocyanine (Pc) were mixed and heat-treated at 900oC in inert gas atmosphere containing a small amount of hydrogen (H2) and oxygen (O2) in order to finally obtain N-TiO2/C electrocatalysts.

TiO2 nanoparticles of ca. 20 nm size deposited on the carbon supports were observed by transmission electron microscope (TEM), indicating that the synthesized N-TiO2/C may have considerably high surface areas. In X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) studies, it was found that the XPS core-level peaks of Ti was very similar to that of Ti-N binding energy and the XRD peak of TiO2 shifted to higher angles, respectively. These results well explain that the nitrogen was successfully doped into TiO2 nanoparticles by our synthesis process. Fig. 1 compares the ORR catalytic activities of the synthesized N-TiO2/C and TiO2/C. The synthesized N-TiO2/C electrocatalyst shows significantly higher ORR catalytic activity than that of TiO2/C. It is believed that the enhanced catalytic activity of N-TiO2/C is due to the doping effect of nitrogen into TiO2.

 

Acknowledgements

The authors wish to thank NEDO (New Energy and Industrial Technology Development Organization) for financial support.

 

References

Ken-ichiro Ota, Yoshiro Ohgi, Kyung-Don Nam, Koichi Matsuzawa, Shigenori Mitsushima, Akimitsu Ishihara, J. Power. Sources.,

196, 5256, ( 2011).

Figure 1
Electrochemical Decontamination of Platinum Nanocrystals and Its Electrocatalytic Performances for Methanol
Authors: Lu Leilei , Du Baozhong
Published: February 2020

Platinum is the most widely used catalyst for fuel cells. The morphology of platinum has great influences on its catalytic activity and selectivity. Thus, the morphology controlled synthesis of platinum nanocrystals is attracting more and more attention in recent years [1-3]. Polyvinylpyrrolidone (PVP) is one of the most commonly used surface active agent for the morphology control of platinum nanocrystal. However, since PVP could strongly adsorb on the platinum surface and was difficult to remove thoroughly, the platinum surface couldn’t be utilized effectively and thus its catalytic activity will be reduced to a certain extent.

This work focused on the decontamination of PVP on platinum by electrochemical treatment. Platinum nanocrystals was synthesized by colloidal method using chloroplatinic acid as the metal precursor and PVP K30 as a stabilizer. Spherical, cubic, octahedral and truncated octahedral platinum nanocrystals were obtained by adding different concentrations of silver nitrate to the above colloidal solution. The morphology of platinum nanocrystals was characterized by transmission electron microscope (TEM). It was found that the as-preparation platinum nanocrystals were well dispersed with a narrow size distribution. Electrochemical decontamination was applied to the platinum nanocrystals by short pulse potential step before electrocatalytic performance measurements. Repeating potential steps were set up between high voltage and low voltage. As the potential step proceeding, more and more surface sites were exposed, which could be confirmed from the more and more clear hydrogen and oxygen adsorption/desorption peak of the cyclic voltammograms (CV) (as shown in Fig. 1A). The CV curves stabilized eventually. The electrocatalytic activity of the electrochemical cleaned platinum nanocrystals was characterized by CV (as shown in Fig. 1B) and chronoamperometry measurements. It was found that truncated octahedral platinum nanocrystals showed the best catalytic activity for metha nol electrooxidation in 0.5 mol·L-1 H2SO4 + 0.5 mol·L-1 CH3OH solution. The methanol electrooxidation peak current was much higher than the current on platinum nanocrystals with other morphology. This study put forward a simple and effective electrochemical decontamination method of the platinum surfaces capped by PVP.

Figure 1
The Effect of Hydrogen Containing NH3 on Aemfc Performance
Authors: Kikkawa Yuki , Negishi Takayuki , Isomura Takenori
Published: February 2020

Hydrogen is the most popular fuel source for fuel cell applications due to fast electrocatalytic reaction and very high energy to weight ratio. But its storage and distribution are still major issues. To solve these problems, it is necessary to use alternative other materials as hydrogen source.

Ammonia has attracted attention as one of the candidate hydrogen carrier materials1-3). Ammonia has following features.

-CO2-free energy carrier

-Simple storage as liquid

-High storage density at low pressure

-Essentially non-flammable, non-explosive

-Easy and efficient to crack to hydrogen

-Well-established transport and storage infrastructure already in place

Generally, a few ppm ammonia remains in ammonia cracking to hydrogen3). In case of this ammonia cracked hydrogen for proton exchange membrane fuel cells (PEMFC), significant performance loss will happen because of the decreased conductivity caused by the conducting ions’ convert to NH4
+ from H+ 4). On the other hand, it has been expected that this fuel can be used for anion exchange membrane fuel cells (AEMFC), because its conducting species is OH- and will not be substituted by NH4
+. However, there is little study dealing the effect of ammonia on AEMFC until today.

 In this study, we operated AEMFC with hydrogen with different amount of NH3. As the results, we could confirm that their performance would not be affected by the existence of NH3 in hydrogen up to around 20%. We succeeded in demonstrating that AEMFC has the good adaptability of NH3-H2fuel compared to PEMFC.

This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST).

References

1. K. Kordesch, V. Hacker, J. Gsellmann, M. Cifrain, G. Faleschini, P. Enzinger, R. Franlhauser, M. Ortner, M. Muhr, R. Aronson, J. Power Sources, 86, 162 (2000)

2. W. Wang, J. M. Herreros, A. Tsolakis, A. P.E. York, Int. J. Hydrogen Enegy, 38, 9907 (2013)

3. A. Klerke, C.H. Christensen, J.K. Nrslov, T. Vegge, J. Mater. Chem. 18, 2304 (2008)

4. F.A. Uribe, S. Gottesfeld, T.A. Zawodzinski, J. Electrochem. Soc. 149, A293 (2002)
Platinum Thin Catalyst Layer for Proton Exchange Membrane Fuel Cell
Authors: Kim Youngkwang , Kim Jiyong , Kwon Oh Joong
Published: February 2020

As one of the renewable energy, polymer electrolyte membrane fuel cell (PEMFC) is a promising candidate because of its good performance efficiency and environment-friendly technique. However, high cost and poor durability of Pt catalys are main obstacles to a commercialization of PEMFC. As a solution for the problems, some researchers have focused on thin film catalyst layer instead of Pt/C catalyst for reducing the amount of platinum use and for enhancing performance at high current density. For example, NSTF (nanostructured thin film) catalyst layer and inverse opal structured catalyst layer were studied for improving mass-transfer and enhancing durability and stability of catalyst.[1-2]

In this study, we used ultrasound to form a thin catalyst layer. By using ultrasound, we synthesized Pt nanoparticle and coated it on MPL (microporous layer), simultaneously. It has being revealed that ultrasound is an effective way to create metal nanoparticle because of ultrasound’s cavitation effect.[3] Bang et al explained about cavitation effect. Bubble explosion provides huge pressure and energy for a chemical reaction if the bubble size reached the critical point under ultrasound irradiation.[4] In addition, ultrasound has a micro jet effect, which has ability to clean a substrate and coat nanoparticles on it.[5] In our study, ultrasound applied to form a catalyst layer and the we adopted it for fabricating MEA (Membrane Electrode Assembly) of single cell. The MEAs were compared with MEA fabricated by a conventional method with Pt/C catalyst.

To verify a formation of nanoparticle via a cavitation effect of ultrasound, we used UV-visible spectroscopy and observed spectrum change nearby 450 nm which is known for Pt4+ after ultrasound’s irradiation.[6] To coat Pt nanoparticles on the carbon paper, we prepared carbon papers fixed at an acrylic frame in platinum precursor solution with reducing agent. Ultrasound was irradiated at various conditions. For example, time and power of irradiation, concentrations of the precursor and the reducing agent were changed to find an optimum condition for a sonochemical coating. As shown in Figure 1, images of the carbon papers acquired by FE-SEM (Field Emission Scanning Electron Microscope) and EDS (Energy Dispersive Spectroscopy) were used for checking platinum distribution. Cathode’s catalyst layer of MEAs was prepared by sonochemical method and anode’s catalyst layer was formed by spraying Pt/C on carbon paper. The MEAs were fabricated using hot-pressing without ionomer. Figure 2 shows I-V curve of the MEAs made at the 12 W of ultrasound power for 120 min and 90 min. To figure out experiment condition effect, we are still carrying out single tests and perform a characterization of MEA to elucidate the difference between MEAs. All the results investigated in the study will be presented with in-depth discussion.

Figure 1
Water Transport Simulation in a Gas Diffusion Layer of PEMFC Using Lattice Boltzmann Method
Authors: Jeon Dong Hyup , Song Jung-Hoon
Published: February 2020

The water transport in a gas diffusion layer (GDL) has been investigated using two-dimensional lattice Boltzmann (LB) simulation. The LB model is developed to simulate the dynamic behavior of liquid water and enables to visualize the water-invasion process through micro-pores in GDL. To investigate the effect of rib structure on water invasion process in GDL, two different cases (i.e., with and without rib structure) are compared. The numerical model is verified by the comparison of the flow permeabilities in GDL. The validation result indicates that the LB model can properly predict the permeability of GDL and enables to simulate the water transport behavior in the GDL. The reconstruction of GDL is established by randomly placing the particles in GDL and ignoring the GDL deformation due to clamping force. The results of LB simulation confirm that the liquid water transport inside GDL is strongly governed by capillary force and the rib structure greatly impacts on the water transport behavior. The rib structure influences on the location of water breakthrough by comparing the simulation results of two different cases. This is due to the higher resistance force underneath the rib, resulting in the change of flow path which preferentially selects the lower resistance force. The water saturation level under the channel is higher than that under the rib caused by the suppression of growth of water cluster. After water breakthrough, the liquid water distribution under the channel has little change, whereas that under the rib keeps stretching for a while. The result indicates that a careful control of rib structure would enhance the water removal from the GDL. Therefore further studies for the optimum design of rib structure are needed. In an operating PEMFCs, the mechanism of water transport and wetting characteristics play an important role on flooding behavior. Therefore the results of the present study would contribute to the novel design for better water removal and flooding alleviation from the GDL.
CFD Analysis of a Fuel Cell Stack Package Using LNG for a Ship
Authors: Roh Gill-Tae , Ahn Jong-Woo , Song Jong-Chun , Lee Jae-Hoon
Published: February 2020

One of the key issues to ensure the safety of a ship in the case of a gas leakage is the condition of air flow inside a fuel cell stack package. Unstable air flow increases the explosion risk by allowing the accumulation of leaked gas in one place. Therefore, a place for installing a ventilating fan and its capacity should be properly selected in order to make the air flow smoothly inside the package. Furthermore, an alarm unit and gas detector should be installed at the proper place for detecting leaked gas.

This paper studied the characteristics of air flow inside the stack package using CFD techniques (FLUENT flow analysis) in order to ensure safety in the case of a gas leak for the 300kW MCFC stack package model for ships. The analysis of a leaked gas accumulation is to decide for the installing sites of the alarm unit, gas detector, and ventilating fan, as well as its capacity. As a subsequent, a model for flow field including a fuel cell stack module, BOP and various pipes was prepared.

 With the developed stack package model, a temperature flow analyzation was performed for the heating conditions of each component or pipe to study where the temperature was evenly distributed inside the package and the temperature rise at the outlet of the model. Using the analytical model for the gas leakage that may occur in the valve, analysis of the gas distribution inside the package was also conducted.
Durablility of Methane Steam Reforming Catalysts Prepared By Exsolution and Infiltration
Authors: Lim Ye Sol , Bang Wan-Keun , Hwang Hae Jin
Published: February 2020

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems.

In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern.

In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes.
Numerical Simulation of PEMFC Performance Considering Striped Wettability Distribution of GDL
Authors: Takaya Koji , Araki Takuto
Published: February 2020

For optimizing the performance of proton exchange membrane fuel cells (PEMFCs), proper water management in the cell is one of the most important issues because liquid water in PEMFCs have a significant impact on the cell performance. If excessive water accumulate in the cell, including that produced by chemical reactions and the humidification of supplied gases, power generation performance will decrease since the transport of the fuel gas will be blocked by the liquid water that has accumulated in the void of a gas diffusion layer (GDL) or a gas flow channel. On the other hand, the drying of the polymer electrolyte membrane (PEM) causes not only a performance decrement due to an increased proton transport resistance, but also a degradation of membrane. Therefore it is very important to understand the water transport in PEMFCs. Some researchers have investigated the water transport phenomena and mass transfer characteristics in the GDL. Utaka and Koresawa have been proposed a novel GDL (Hybrid type GDL, Fig. 1) which has two different wettability to improve the oxygen diffusivity by controlling the water distributions and movement in the GDL, and have examined the effects of the wettability distribution and PTFE content in the hydrophobic region of the GDL on efficient oxygen diffusivity [1]. Additionally, they also have been proposed a novel gas channel with micro-grooves [2]. The cell performance of PEMFC that combined the hybrid GDL and the gas channel with micro-grooves were experimentally investigated in an attempt to improve the power generation of PEMFC. Figure 2 shows the effects of hybrid GDL and novel gas channel on cell performance, and from this figure, the PEMFC combined the hybrid GDL and gas channel with micro-grooves could enhanced the performance under high current density.

A three-dimensional numerical model, which includes the gas channels with micro-grooves, GDLs, catalyst layers in both cathode and anode side and PEM, has been developed to investigate the water transport and power generating characteristics. In addition, we investigate the effectiveness of the hybrid GDL to mitigate liquid water saturation under flooding conditions by using our comprehensive model, and compared with experimental results.

Numerical result of liquid water distribution at two different wettability region in GDL shown in Fig. 3. Liquid water distribution biased to hydrophilic regions due to the drawing the water from the hydrophobic region into the hydrophilic region. Furthermore, the performance of PEMFC improved by combined the hybrid GDL and novel gas channel with micro-grooves, and discussed quantitatively.

Reference

[1] R. Koreaswa and Y. Utaka, J. Power Sources, 271, 16 (2014).

[2] Y. Utaka, A. Okabe and Y. Omori, J. Power Sources, 279, 533 (2015).

Figure 1
Preferential Horizontal Growth of WS2 Nanoplate on Porous Carbon: A Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction
Authors: Seo Bora , Jung Gwan Yeong , Kim Jae Hyung , Kwak Sang Kyu , Joo Sang Hoon
Published: February 2020

Two-dimensional layered transition metal dichalcogenides (2D TMDs) have been of tremendous recent interests. Understanding their growth behavior on specific substrate or support can provide critical insights for designing the TMDs with desirable structure and functionality for targeted applications. Particularly for the electrocatalytic hydrogen evolution reaction (HER), where porous carbons are predominantly used as conductive supports, revealing the growth behavior of TMDs on porous carbon materials can suggest rational design concept for the TMD-based HER catalysts. With an aim to investigate the growth orientation on porous carbon support, we synthesized MS2 (M = W or Mo) nanoplates embedded on porous carbon nanorod arrays by limiting their growth space at the nanoscale. We found that the horizontal growth is preferred in WS2 giving rise to monolayer nanoplates, which is contrast to the growth of MoS2 that favors vertical stacking to generate multilayer structure. Density functional theory calculations of adhesion energy of TMDs on porous carbons and their stacking energies revealed that WS2 favor the basal plane bonding with carbon support and horizontal growth, wheareas the edge bonding and vertical growth is favored for MoS2, supporting experimental results. The orientation-controlled WS2 monolayer NPs embedded in mesoporous carbon exhibited highly efficient electrocatalytic activity for the HER with a low overpotential of 179 mV (vs RHE) at ‒10 mA cm-2 and low Tafel slope of 63 mV sec-1.
Electrochemical Fabrication of Ag and Au Foams for Electrochemical Conversion of CO2
Authors: Lee Hyunju , Kim Hoyoung , Park Hyanjoo , Kim Junhyeong , Kim Hyunki , Hwang Eunkyoung , Kim Soo-Kil , Ahn Sang Hyun
Published: February 2020

In recent, huge efforts have been conducted to relieve the global warming problem by the electrochemical conversion of CO2 into useful chemicals. Particularly, it has been reported that the Ag and Au are highly active materials to produce the CO with high selectivity. However, the cost problem originated from use of noble metal catalysts limits their practical applications.

 In this study, the Ag and Au foam structures were electrochemically fabricated as a catalyst for CO2 reduction to produce CO. As a first step, the Cu foam was prepared on Ti foil substrate by galvanostatic pulse deposition which consisted of low current for continuous Cu film and following high current for porous Cu. The pore size (22 ~ 56 μm) and wall thickness (14 ~ 42 μm) were controlled by concentration of Cu precursor and applied deposition currents. Then, the Cu foams were immersed in the electrolyte which contained noble metal precursors and additives, in order to minimize the noble metal usage as well as to increase the electrochemical surface area. The coverage and morphology of noble metals on the surface of Cu form were affected by the precursor and additives concentrations in displacement step. The catalytic activity of fabricated noble metal foams were examined for electrochemical CO2 reduction. As a result, it was revealed that the CO Faradaic efficiency was significantly related to the morphology and composition of noble metal foams.
Mechanical Response of Thin Nafion Films during Hydration Cycles
Authors: Frieberg Bradley R. , Graybill Joshua R. , Page Kirt A. , Stafford Gery R. , Soles Christopher L. , Stafford Christopher M.
Published: February 2020

Proton exchange membrane (PEM)-based fuel cells are being aggressively targeted as an alternative energy source for transportation and stationary power due to their high charge density and low operating temperatures. While the structure, transport and mechanical properties of bulk PEMs have been extensively studied, there is increasing interest on the behavior of these materials at interfaces and under confinement, since there exist many heterogeneous interfaces within an actual fuel cell assembly. One could argue that the performance and ultimate failure of the membrane electrode assembly is greatly impacted by the structure and transport of ionomers confined to extremely small length-scales.

At the heart of the PEM fuel cell is the polymer membrane that must transport protons but not electrons, while also acting as a barrier to the reactant gases (H2 and O2). The most widely studied material for this purpose is perfluorosulfonic acid (PFSA) ionomers such as Nafion. Over its service life, the polymer membrane undergoes hundreds if not thousands of cycles between wet and dry conditions, which leads to swelling and shrinking of the membrane material. This can ultimately lead to mechanical failure in the membrane. This mechanical fatigue is of particular importance in the catalyst layer where the PFSA ionomers, often used as an ionically conductive binder, are confined in domains on the order of tens of nanometers in thickness. A further understanding of the swelling-induced stresses experienced in both the catalyst layer as well as the PEM is necessary.

In this talk, we will describe our efforts to develop and implement a cantilever bending technique1 in order to investigate the swelling induced stresses in Nafion thin films. By monitoring the deflection of a cantilever beam coated with a thin Nafion film as it is exposed to varying humidity environments, the swelling induced stresses of the polymer film can be measured. Using this technique, we have measured the mechanical response to humidity cycling of thin Nafion films as a function of film thickness and thermal annealing, as well as hygrothermal aging.

K. A. Page, J. W. Shin, S. A. Eastman, B. W. Rowe, S. Kim, A. Kusoglu, K. G. Yager, and G. R. Stafford. In Situ Method for Measuring the Mechanical Properties of Nafion Thin Films during Hydration Cycles, ACS Applied Materials and Interfaces, 7, 17874-17883 (2015).
Identification of Iron Nanoparticles As Active Species for Oxygen Reduction in Non-Precious Metal Catalysts
Authors: Gewirth Andrew A , Varnell Jason A.
Published: February 2020

The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction (ORR). Fe-based non-precious metal (NPM) catalysts exhibit promising activity and stability as an alternative to state-of-the-art Pt catalysts. However, the identity of the active species in NPM catalysts remains elusive, impeding the development of new catalysts. For the first time, we report the identification the catalytic species in an active NPM catalyst using Cl2 and H2 treatments to decrease heterogeneity. Additionally, we demonstrate the reversible deactivation and reactivation of the catalyst using the Cl2 and H2 treatments. Mössbauer and X-ray absorption spectra reveal that carbon-encapsulated Fe nanoparticles present in the as-prepared and H2-treated catalyst, but absent in the Cl2-treated catalyst are responsible for the observed ORR activity and stability of the catalyst. These findings suggest a new direction for the design and synthesis of enhanced NPM ORR catalysts.
Pyrolyzed Stable Ferrocene-Co-Corrole N4 As a Promising Non-Precious Electrocatalyst for Oxygen Reduction Reaction
Authors: Samireddi Satyanarayana , Shown Indrajit , Wong Ken-Tsung , Chen Li-Chyong , Chen Kuei-Hsien
Published: February 2020

The limited natural abundance, high cost and carbon monoxide deactivation of Pt and other noble metals possess a major barrier in its applications for hydrogen or methanol fuel cells and therefore; development of alternative electrocatalytic materials based on non-precious metal-N4 is a key challenge in the current growing demand for the clean-energy fuel cell research. In this regard, in our group, a new cobalt-corrole molecule functionalized with ferrocene has been successfully synthesized and its structural characterization was done by UV-Vis, NMR and HR-Mass spectroscopic studies. The molecular structure of the complex was also confirmed by single crystal X-ray diffraction and explained with structural orientation of the atoms and attached moieties. Furthermore, this molecule mixed with activated carbon was pyrolyzed at different temperatures and among the resulting electrocatalysts, particularly at 500 °C was shown to be performed as promising ORR active catalyst for the PEM Fuel-Cell application. The unique Co-corrole integrated with mono substituted peripheral Fe complex with its pyrolyzed form of low symmetric structure provides a bimetallic (Co and Fe) active centre and facilitates the oxygen reduction reaction (ORR) via a 4-electron pathway. The prepared carbon black supported catalyst at 500 °C pyrolyzed temperature exhibits higher electron transfer number 3.96 for ORR in acidic medium with better stability, which is superior to the previously reported pyrolyzed Co-corroles. The enhancement of the ORR activity of the well characterized Co-corrole with peripheral Fe-metallocene bimetallic N4 macrocyclic complex provides a new prospect for the next-generation of non-precious metal-N4 electrocatalysts for fuel cell application. In this presentation, I will talk more in details of the electrochemical experimental process of the catalyst and its characterization using different analytical techniques.

Key words: N4-macrocyclic, corrole, oxygen reduction reaction, electrocatalysts, fuel cell
Enhanced Performance of Pristine Au Catalysts in the Presence of Ag for Alcohol Electrooxidation
Authors: M S Brahma Teja , R S Sai Siddhardha , R Sai Saihish , B Sai Siva Kumar
Published: February 2020

In the present study, we demonstrate a one-pot capping agent free synthesis of metal nanoparticles deposited on low dimensional carbon supports. A laser ablation mediated synthesis (LAMS) of gold-silver on graphene and/or carbon nanotube composite is reported here. We aim to remove the use of surfactants, which are known to mask the performance of the catalyst. The composite materials have been well characterized morphologically as well as, functionally using microscopic and spectroscopic techniques. It has been observed that the introduction of Ag into the bimetallic catalyst has made the electro-oxidation of ethylene glycol and glycerol more facile. The synergistic influence of the two metal nanoparticles, with the added advantage of its pristine surface, pose an enhanced catalytic effect for alcohol electrooxidation. In addition, the onset potential for the reaction has been found to be more negative that translates to its plausible application in Direct Alcohol Fuel Cells.

Figure 1
Power Generation Characteristics of the Direct Formic Acid Fuel Cell Using Silica Containing Carbon Nanofiber as the Anode Supports
Authors: Tsujiguchi Takuya , Mohamed Aslam Norraihanah , Onishi Ryo , Matsuoka Fumihiko , Yamazaki Nozomi , Osaka Yugo , Kodama Akio
Published: February 2020

Direct formic acid fuel cells, DFAFCs, have received considerable attention due to their higher power density in the direct liquid fuel cells. Recently, 550 mW/cm2 of power density at 30 oC was reported by Chan et al. using Pd–Ni2 P/C catalyst for DFAFC anode [1]. In order to obtain the higher power density, the operation temperature of DFAFC should be elevated since anode and cathode reaction kinetics increases with the increasing operation temperature, however, it has been known that the power density of DFAFC above 50 oC showed plateau with the increasing temperature. As a reason of the plateau in the power desnity above 50 oC, the increase of the mass transport loss was considered [2]. Therefore, controlling the mass transport in the catalyst layer is one of the key factor to obtain high power density. In this context, the silica embedded carbon nanofiber, SECNF, support for DFAFC anode have been suggested in this study. By using SECNF as a catalyst support, both of the high porosity catalyst layer which can enhance the mass transport rate in the catalyst layer and the high catalystic activity due to the support metal effect of the silica have been expected. It was found that the formic acid oxidation reaction activity significantly increased by using SECNF as a support of Pd comparing to conventional Pd/CNF and Pd/C due to the support effect of the SiO2. Moreover, the high porosity anode electrode could be successfully fabricated by using Pd/SECNF. On the other hand, the power density of DFAFC was not enhanced due to thick catalyst layer. In the presentation, the effect of the porosity and thickness of catalyst layer on the anode mass transport loss and power generation characteristics will be discussed in detail.

Reference

[1] J. Chang, L. Feng, C. Liu, W. Xing, and X. Hu, Angew. Chemie Int. Ed., 53, 122–126 (2014).

[2] T. Tsujiguchi, F. Matsuoka, Y. Hokari, Y. Osaka, and A. Kodama, Electrochim. Acta, 197, 32–38 (2016)
Novel Highly Acidic Mixed-Metal (W, Zr) Catalytic Matrices for Dispersed Noble Metal Nanoparticles: Electrooxidation of Hydrogen and Small Organic Molecules
Authors: Kulesza Pawel J , Rutkowska Iwona Agnieszka
Published: February 2020

Application of metal oxides as active matrices in electrocatalysis is particular importance. The hydrous behavior, which favors proton mobility and affects overall reactivity, reflects not only the oxide’s chemical properties but its texture and morphology as well. What is of importance to electrochemical science and technology, certain nonstoichiometric mixed-valence oxides could exhibit pseudo-metallic conductivity and possess appreciable catalytic activity.

Recently, mixed oxide systems stabilized through Zr-O-W bonds have been demonstrated to be very attractive acid catalysts exhibiting high catalytic activities and good stabilities in many demanding industrial reactions. For electrocatalytic applications, mixed-valent tungsten(VI,V) oxide and zirconium(IV) oxide have been sequentially deposited and integrated through voltammetric potential cycling to form sub-microstructured films on glassy carbon electrode. The mixed WO3/ZrO2 systems are characterized by fast charge (electron, proton) propagation during the system’s redox transitions. By dispersing metallic Pt and bimetallic platinum-ruthenium (PtRu) electrocatalytic nanoparticles over such active WO3/ZrO2 supports, the electrocatalytic activities of the respective systems toward the oxidation of hydrogen and small organic molecules (formic acid, methanol, ethanol or dimethyl ether) have been enhanced even at decreased loadings of noble metal nanostructures (for hydrogen oxidation) as well as in terms of both increasing the electrocatalytic currents and lowering the onset potentials of organic fuels’ reactions. The enhancement effects should be attributed to features of the mixed metal oxide support such as porosity and high population of hydroxyl groups (due to presence of ZrO2), high Broensted acidity of sites formed on mixed WO3/ZrO2, fast electron transfers coupled to unimpeded proton displacements (e.g. in HxWO3), as well as strong metal-support interactions between nanosized noble metals (Pt, Pd or PtRu) and metal oxo species. The fact that WO3/ZrO2 nanostructures are in immediate contact with the metallic catalytic sites leads to the competitive interactions (via the surface hydroxyl groups) with undesirable reaction intermediates (including CO adsorbates). Thus their desorption (“third body effect”) or even oxidative removal (e.g. of CO to CO2) are feasible.

 Furthermore, during oxidation of ethanol, when rhodium nanoparticles have been dispersed in between WO3 and ZrO2 layers (toward formation of the nanoreactor system), significant electrocatalytic current enhancements are observed. The result can be rationalized in terms of the formation of sub-microstructured nano-reactors in which Rh induces splitting of C-C bonds in C2H5OH molecules toward CHx/CH4 and CO adsorbate species, or even methanol-type intermediates, that could be further electrooxidized at PtRu catalytic centers. Further mechanistic studies along this line are planned.
Graphitic Carbon Nitride-Graphene Hybrid Nanostructure as a Catalyst Support for Polymer Electrolyte Membrane Fuel Cells
Authors: Mansor Noramalina , Jia Jingjing , Miller Tom , Suter Theo , Belen Jorge Ana , Gibbs Christopher , Shearing Paul R. , McMillan Paul F. , Mattevi Cecilia , Shaffer Milo , Brett Daniel J.L.
Published: February 2020

Graphitic carbon nitride is a new class of semiconducting graphene-like polymeric material with visible light absorption and photocatalytic properties. In addition to high nitrogen content and tunable structure, it was shown that graphitic carbon nitride based on polytrazine imide (PTI) sheets exhibit excellent anti-corrosion ability in ex-situ fuel cell environment.1 However, in bulk form, their low surface area and poor conductivity limits their applications in fuel cells.

In this work, an exfoliation route was established to produce PTI ink containing single to few-layer nanosheets. The ink was then processed to produce 3D networks of carbon nitride nanosheets/reduced graphene oxide (rGO-PTI) hybrid nanostructure with large interconnecting pores for fast mass transport of reactants (Figure 1a) and high surface area. The material was decorated with low loadings of platinum which also acts as spacers to prevent the restacking of the nanosheets, and then investigated for its electrochemical properties and applications as a durable catalyst support for PEM fuel cells. Initial results show that the cathode catalytic activity of Pt/rGO-PTI hybrid is significantly improved in comparison to Pt/PTI or Pt/rGO (Figure 1b), and long-term potential cycling shows that it is more durable than commercial Pt/C. The work is now being extended to develop high-performance and stable membrane electrode assemblies (MEA) for PEM fuel cells.

N. Mansor, A. Belen Jorge, F. Corà, C. Gibbs, R. Jervis, P. F. McMillan, X. Wang, D. J. L. Brett, J. Phys. Chem. C 2014,
118 (13), 6831-6838

Figure 1
The Challenges to Ultra-Low-Platinum PEMFC Cathode and the Electrocatalyst Design Thereof
Authors: Zhang Junliang , Shen Shuiyun , Zhu Fengjuan , Wang Chao , Luo Liuxuan
Published: February 2020

Polymer electrolyte membrane fuel cell (PEMFC) has been extensively studied because of its many desirable qualities for the automotive application, including high power density, low operating temperature (~80 oC) as well as quick start-up and match-up to the power demand. Although appealing, a challenge caused by the high Pt loading in the cathode should be addressed before the mass production of fuel cell vehicles. In this regard, the research topic is now urgently focused on to use ultra-low Pt loading (≦0.1 gPt/kW) in the cathode of PEMFCs. It is noted that both the electrode kinetics of oxygen reduction reaction (ORR) [1] and mass transport for conventional cathodes with low Pt loading do not apply to the cathodes with ultra-low Pt loading, especially for the local mass transport surrounding Pt particles in the catalyst layer [2]. Herein, the challenges in the ultra-low Pt cathode in terms of ORR kinetics and local transport resistance will be clarified and the corresponding solution in terms of the electrocatalyst design will be provided. How the ORR kinetics on the cathode changes with the Pt loading decreasing will be examined in detail and the difference in the transport resistance in each component (Figure 1), especially the O2local transport between the ultra-low Pt cathode and high Pt cathode will be elucidated. The effects of catalyst type, specific activity, Pt loading as well as the cathode structure on the cell performance will be discussed, thus providing a solid scientific guideline for developing cathodes with ultra-low Pt loading and accelerating the commercialization of PEMFCs using cathodes with ultra-low Pt loading.

Acknowledgements

This work was supported in part by National Natural Science Foundation of China (Grant No. 21373135 and 21533005) and Science Foundation of Ministry of Education of China ( Grant No. 413064).

References

[1] Y. Huang, J.L. Zhang, A. Kongkanand, F.T. Wagner, J.C.M. Li, J. Jorné, Transient platinum oxide formation and oxygen reduction on carbon-supported platinum and platinum-cobalt alloy electrocatalysts, J. Electrochem. Soc., 2014, 161 (1): F10-F15.

[2] Y. Ono, T. Mashio, S. Takaichi, A. Ohma, H. Kanesaka, K. Shinohara, The analysis of performance loss with low platinum loaded cathode catalyst layers, ECS Transactions, 2010, 28 (27) 69-78.

Figure 1
Facile Synthesis of High Performance Platinum-Cerium Oxide Nanocatalysts for Methanol Oxidation
Authors: Valk Peeter , Nerut Jaak , Kanarbik Rait , Lust Enn
Published: February 2020

Electrooxidation of methanol has been studied intensively in the scientific community, and various catalysts have been developed for direct methanol fuel cells.

In this study, platinum-cerium oxide nanoparticles have been synthesised, exhibiting high activity towards methanol electrooxidation. The materials were electrochemically characterised using rotating disk electrode, cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy methods. Scanning electron microscopy, X-Ray diffraction, inductively coupled plasma mass spectrometry and BET surface area mesurements were performed to characterise the physical properties of the synthesised materials.

The methodology of the synthesis of the materials was straightforward and resource efficient. The synthesised nanocatalysts have a very uniform dispersion on the catalyst support material, and a narrow size distribution.

Even at low platinum loadings, the materials have a lower overpotential towards methanol oxidation than commercial Pt-Vulcan catalysts. Based on cyclic voltammetry measurement data, the peak potential for the synthesised materials was 40 mV more negative than for the commercial material in the anodic potential scan, and 60 mV more negative in the cathodic potential scan.

In addition to the high currents for methanol oxidation, extremely high currents were achieved in the cathodic potential sweep, in the region attributable to the oxidation of carbon monoxide. Methanol and carbon monoxide poisoning of the nanocatalysts was unnoticeable during the experiments.

The results of the study lay a promising foundation for the investigation of nanocatalysts containing other rare earth metal oxides, as well as to the investigation of the electrooxidation of ethanol or other organic fuels on composite catalysts.

Acknowlegements

The authors wish to thank P. Paiste for ICP-MS measurements and J. Aruväli for XRD measurements

This work was supported by the EU through the European Regional Development Fund TK141, the institutional research funding project IUT20-13 of the Estonian Ministry of Education and Research, the Estonian Energy Technology Program Project No. SLOKT10209T, Estonian Materials Technology project 3.2.1101.12-0019, Estonian Center of Excellence in Science Project TK117T, grant ETF9352 and PUT55.
Electrical Conductivity and Defect Equilibria of MoO3-d, a Catalyst for Biofuel Upgrading
Authors: Bishop Sean R. , Mortola Vanessa , Shetty Manish , Roman Yuriy , Tuller Harry L.
Published: February 2020

The transportation sector currently relies heavily on non-renewable fossil-based fuels to meet its energy requirements. Alternative energy sources need to be developed to meet the projected energy demand in the future in a sustainable and environmentally conscious manner. Bio-oils, generated via biomass fast pyrolysis, represent an attractive avenue for the production of renewable fuels and chemicals. We are investigating MoO3-δ, a promising catalyst for bio-oil upgrading, that selectively transforms various phenolic compounds into aromatic hydrocarbons with high yields using low H2 pressures by hydrodeoxygenation (HDO). While it is widely suggested that both ionic (oxygen vacancies) and electronic defects (e.g. Mo5+/3+), in both the oxide catalyst and oxide support (e.g. TiO2, ZrO2 and Al2O3), play controlling roles in the catalytic reactions, surprising little is known about how operating conditions (temperature, dopants/impurities, and atmosphere (pO2, pH2O, pH2, carbon activity, etc.)) impact the concentration or the diffusivities of these key defects, nor how they influence the reaction kinetics. In this presentation, we discuss our efforts to combine catalysis with defect chemical and impedance spectroscopic approaches to achieving a deeper understanding of the role that defects in metal oxide catalysts and supports play in influencing catalytic selectivity, efficiency, stability and reaction rates. The relationship between the defect equilibria and electrical conductivity is reported for a range of oxygen partial pressures (10-5 - 1 atm O2) and temperatures (300 – 600 oC). Relevant energetics of defect formation and transport are extracted, and their relationships to relevant catalysis processes are discussed.