bluuebunny/crossref_metadata_2025 huggingface dataset:
3D CFD Modelling of Low Temperature Pemfcs
Authors: Klauber Daniel , Heinzmann Marcel , Magagnato Franco , Frohnapfel Bettina
Published: February 2020

Computational fluid dynamics (CFD) is becoming more and more an essential tool to gain deeper insight into the physics of proton exchange membrane fuel cells (PEMFCs). The goal is to achieve an optimized fuel cell design as a further step towards the commercialization of PEMFCs as an alternative to common automotive fuel engines. Nowadays a validated CFD model provides one means of improving the performance of fuel cells.

The open-source code of Beale et al. [1] is a generic framework for simulating different types of fuel cells. The authors extended it to a full three-dimensional model using additional model equations and modified source terms. According to the integrated cell concept used in the open-source code three additional so-called 'child' meshes are introduced to account for charge transport and water transport in the polymer electrolyte membrane.

The parameters of the Butler-Volmer equation (Figure 1, top), describing the electrochemical kinetics of the fuel cell, are used as fitting parameters in most existing literature. In this work the authors use a set of experimentally determined parameters in order to reduce the number of uncertain/fitting parameters.The method used to determine this set of parameters is electrochemical impedance spectroscopy whereby the data is analysed using the distribution function of relaxation times [2]. This method helps to separate the polarization processes contributing to the overall polarization loss in a clearer way. The numerical results of the model described above are compared to polarization curves measured by experiments. The results show good agreement (Figure 1, bottom) for two different humidifications (40% RH and 70% RH) in the activation and ohmic regions.

References

[1] S. B. Beale, H. Choi, J. G. Pharoah, H. K. Roth, H. Jasak, D. H. Jeon, Open-source computational model of a solid oxide fuel cell, Comput. Phys. Commun. 200 (2016) 15-26.

[2] H. Schichlein, A.C. Müller, M. Voigts, A. Krügel, E. Ivers-Tiffée, Deconvolution of electrochemical impedance spectra for the identification of electrode reaction mechanisms in solid oxide fuel cells, J. Appl. Electrochem. 32 (2002) 875–882.

Figure 1
Numerical Study of Liquid Water Saturation inside Gas Diffusion Layer and Micro Porous Layer during PEMFC Operations Using Multiscale and Multiphase Modeling Approach
Authors: Shimpalee Sirivatch , Satjaritanun Pongsarun , Weidner John W. , Hirano Shinichi
Published: February 2020

The objective of this study is to use multidimensional/multiscale/multiphase polymer electrolyte membrane fuel cell (PEMFC) model [1-10] to enhance understanding of water transport inside gas diffusion layer (GDL) and microporous layer (MPL) during fuel cell operations. The outcomes of this work will improve the development of a fuel cell stack and electrochemical cells with increasing in performance at high current densities. Experimental investigation of oxygen transport has been limited by an inability to resolve water saturation-dependent properties. This work also shows the successful in development of a multiscale calculation technique that incorporates detailed structure of each scale dimension in every component of a fuel cell and simultaneously performed a prediction. The effect of operating conditions and GDL/MPL properties on the transports including liquid water inside PEMFC will be the primary focus of this work.

Figure 1 shows an example of simulation works to predict the effect of MPL thermal properties on liquid water transport and performance of PEMFC. In this figure, three specific thermal conductivities were simulated. Figure 1 shows liquid distributions at cathode side of PEMFC using SGL 25BC GDLs. The amount of water condensation increases from low thermal conductivity to high thermal conductivity and the condensed water starts from the areas under the rib instead of the areas under the channels. This is because the areas under the rib has lower temperature than the areas under the channel. This figure also presents the local liquid saturation profiles inside GDL/MPL. The higher liquid saturation profiles are presented in MPL (Locations 5 and 6) than in GDL (Locations 1 to 4). In the particular operating condition, the performance increases when the thermal conductivity is higher. This simulation shows a possibility of model based engineering to optimize MPL thermal property and operating conditions.

References:

Shimpalee, D. Spuckler, and J. W. Van Zee J. Power Sources, 167 (2007) 130-138.

Shimpalee, M. Ohashi, C. Ziegler, C. Stoeckmann, C. Sadeler, C. Hebling, J. W. Van Zee, Electrochemica Acta, 54 (2009) 2899-2911.

Shimpalee, J. of Electrochem. Soc., 161 (2014) E3138-E3148.

Frisch, B. Hasslacher, Y. Pomeau, Physical review letters 56 (14) (1986) 1505-1508.

R. McNamara, G. Zanetti, Physical Review Letters 61 (1988) 2332-2335.

Satjaritanun et al., J. Electrochem. Soc. 164 (2017) E3359-E3371

Satjaritanun et al., ECS Transactions, 80 (2017) (8) 187-195

Hirano et al., Abstract# 1419, 232nd Electrochemical Society Meeting, October 1-5, 2017, National Harbor, Maryland.

Shimpalee et al., Abstract# 1418, 232nd Electrochemical Society Meeting, October 1-5, 2017, National Harbor, Maryland.

Satjaritanun et al., Abstract# 1373, 232nd Electrochemical Society Meeting, October 1-5, 2017, National Harbor, Maryland.

Figure 1
Characteristics of Water Droplet Release from Gas Diffusion Layers
Authors: Büchi Felix N , Mularczyk Adrian , Lamibrac Adrien , Marone Federica , Schmidt Thomas J. , Eller Jens
Published: February 2020

Droplet formation and detachment in the gas flow channel are important steps in the water management in polymer electrolyte fuel cells. Formation and detachment of the droplet are expected to cause changes in the local saturation in the GDL, which are important to understand the relevant forces determining formation and detachment.In order to control the two important boundary conditions of water feed rate and gas dynamics in the channel accurately, a non-operating set-up was developed. Water is injected through a 0.5 mm hole from the bottom into a SGL 25 BA gas diffusion layer (GDL) facing a gas flow channel on its top. The liquid water distribution in the GDL and the behaviour of droplet detachment at the GDL-gas channel interface are monitored using sub-second X-ray tomographic microscopy (XTM) with 0.75 s scan time and 2.55 s repeating frequency and fast X-ray 2D radiography (3 ms exposure time).

With the constant water injection rates, the droplet formation was found to be very periodic with droplet growth showing a repeating pattern. The droplet diameter evolution for two different injection rates is shown in Figure 1 (a). The final droplet volumes were found to be 17.6 nL at an injection rate of 350 nL/min and 10.3 nL at 1000 nL/min.Figure 1 (b) shows the water volume in the GDL. The liquid volume in near the inlet was found to be high and decreasing towards the gas channel, corresponding to a high saturation near the inlet and a low saturation near the gas channel. In the bulk of the GDL, no changes occurred at droplet detachment. But in the upper layers of the GDL, for the injection rate of 350 nL/min, a fluctuation of water volume caused by droplet detachment can be observed.

Figure 1
Wetting-Dependent Percolation through the Gas Diffusion Layer of PEM Fuel Cells
Authors: Herescu Alexandru
Published: February 2020

The percolation pressure through the porous gas diffusion layer (GDL) is known to depend on the pore size and geometry, as well as the wetting conditions within the material. It is less clear how the water-gas transport changes with the use of different materials and under varied fuel cell operating conditions. A major reason of discrepancy between models and experimental results is an inaccurate description of the interfacial behavior. Elementary simulations that capture the interface evolution as water breaks through a pore indicate that the process is more sensitive to mixed wetting conditions than to the geometry itself. The proposed model accounts for mixed wetting conditions by allowing for contact line slippage on non wetting surfaces while on wetting surfaces the contact line is pinned. The breakthrough pressure is found to be approximately 40% larger for the mixed wetting pore versus the wetting counterpart. Existing GDL experimental studies seem to indicate a change in the breakthrough pressure in the same ratio when surface wetting modifications are made which effectively create mixed-wetting pores.
Experimental Study on Ionic Conductivity of Carbon Support within Polymer Electrolyte Fuel Cell Catalyst Layers
Authors: Hu Leiming , Guo Yuqi , Litster Shawn
Published: February 2020

Conventional polymer electrolyte fuel cells (PEFCs) use carbon supported Platinum (Pt/C) as the catalyst. With decades of efforts, researchers have brought down the loading of Pt below 0.1 mg/cm2 on the anode and 0.4 mg/cm2 on the cathode. However, the high cost of Pt based catalyst still serves as a big barrier for PEFCs’ fully commercialization. Within the catalyst layer, polymer electrolyte ionomer (e.g. Nafion) is usually used as the proton conducting media. During the catalyst layer fabrication process, Pt/C particles are present as aggregates. Due to size exclusion, the polymer electrolyte mainly coats the large mesopores of the Pt/C aggregates, i.e. ionomer covers the secondary pores. In high surface area carbon supports, a significant amount of Pt exists within the smaller mesopores and micropores of the support, which is inaccessible to the ionomer. Although it is known that protons are able to reach Pt within the aggregates when those pores are filled with liquid water, the magnitude and mechanism of proton transport is largely unknown.

In past studies, the proton conductivity of continuous Pt surfaces have been studied (1), with hypothesis proposing that proton can transport through Pt surface by surface diffusion or through electric double layer (EDL) at the metal/water interface. It has also been reported that proton conductivity is severely hindered over extended glassy carbon surfaces (2). However, the widely used Pt/C catalyst doesn’t have continuous metal surface, and unlike glassy carbon, the carbon support used in the catalyst layer usually has a mixture of functional groups on the surface (e.g., carboxyl and sulfur species), which will alter the surface ionic conductivity through deprotonation. In this work, we measure the conductivity in ionomer free carbon (Vulcan XC72R) and ionomer free Pt/C (10 wt.% HiSPEC 2000) electrodes to better understand the conduction properties of ionomer-free carbon support surfaces. Our experiments evaluate the effects of both electrode potential and the relative humidity (RH) on the conductivity. Electrochemical impedance spectroscopy (EIS) and transmission line modeling show the proton conductivity of the ionomer-free electrode decreases as electrodes’ potential increase (see Figure 1). The potential dependence of the ionic conductivity is supported by a cyclic voltammetry (CV) analysis. Herein, we present several aspects related with the proton conductivity within the ionomer-free carbon domains of the catalyst layer and their effects on fuel cell performances.

Acknowledgement

This work was partially supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0007271.

References

E. L. Thompson and D. Baker, ECS Trans., 41, 709 (2011).

U. Paulus, Z. Veziridis, B. Schnyder, M. Kuhnke, G. Scherer and A. Wokaun, J. Electroanalytical Chemistry, 541, 77 (2003).

Figure 1
Polymer Electrolyte Membrane Fuel Cell Characterisation Based on Current Distribution Measurements
Authors: Chevalier Stephane , Olivier Jean-Christophe , Josset Christophe , Auvity Bruno
Published: February 2020

Polymer Electrolyte Membrane (PEM) fuel cells are considered as promising clean sources for automotive applications. A key challenge to reduce the cost of this technology is to increase the power density by operating PEM fuel cells at high current densities. Part of the research are focused in developing and designing new materials for this technology such as advanced catalyst layers (CL), new gas diffusion layers (GDL) structure, or innovative cell assembly conditions (clamping pressure, channel design…)[1]. To assess the performance of new materials, in situ characterisation techniques are required. Electrochemical impedance spectroscopy (EIS) is one of the most used technique to characterise the material impact onto the fuel cell mass/charge transfer, ohmic resistance and mass transport. However, due to the large number of parameters which has to be identified, inaccuracy in the identification process may arise leading to incorrect fuel cell material properties characterisation [2].

In authors’ recent work [3], it was shown that current density distributions can be used as a useful information to characterise fuel cell material properties. Thus, in this communication we will present a segmented cell designed and built to measure current density distribution along the channel while allowing optical access inside the channel to visualise the presence of liquid water. A range of fuel cell GDLs is characterised in situ in this cell for a range of operating conditions. The effective diffusivity of the GDLs is directly obtained from the current density distribution without any knowledge of the other fuel cell parameter (membrane ohmic resistance or CL kinetics). The values of effective diffusivity obtained using our methodology are compared to the ones obtained through EIS measurements, and their respective accuracy will be discussed. In addition, examples on the use of this characterisation cell to assess the performance of channel designs and fuel cell assembly conditions will be given. The results presented in this communication will introduce a novel fuel cell characterisation methodology which can strongly improve the development of more efficient fuel cell systems.

References

[1] T. Yoshida, K. Kojima, Toyota MIRAI Fuel Cell Vehicle and Progress Toward a Future Hydrogen Society, Interface Mag. 24 (2015) 45–49.

[2] S. Chevalier, D. Trichet, B. Auvity, J.C. Olivier, C. Josset, M. Machmoum, Multiphysics DC and AC models of a PEMFC for the detection of degraded cell parameters, Int. J. Hydrogen Energy. 38 (2013) 11609–11618.

[3] S. Chevalier, C. Josset, B. Auvity, Analytical solutions and dimensional analysis of pseudo 2D current density distribution model in PEM fuel cells, Renew. Energy. 125 (2018) 738–746.
Investigating Factors That Influence Conditioning Time of PEFCs
Authors: Rockward Tommy , Spears Andre , Garzon Fernando H , Martinez Ulises
Published: February 2020

The conditioning time required for PEFCs to reach either peak performance or system power requirement will have a definite impact on overall system cost. During the past decade, FC research and development has focused its efforts on overcoming several technical barriers (targets) that could compromise the viability of the technology. Performance, cost, and durability are three of the barriers in which a large portion of the efforts were placed. Consequently, this attention led to substantial improvements in the FC materials and components helping meet and or surpass technical targets. While these scientific advances were instrumental in the emergence of pilot Fuel Cell Electric Vehicles; it becomes critical that the conditioning time be minimal in order to produce affordable Fuel Cell systems for large scale production. We will present results on factors that influence the PEFC conditioning time.

The various aspects that can affect the conditioning time include:

MEA manufacturing processing conditions (pressing / drying conditions)

Electrode Morphology/Engineering (Ionomer/carbon ratio, catalyst and catalyst support materials, membrane (composition, thickness, radical scavenger additives),

Conditioning methodology (potential cycling versus steady state)

Operating conditions (Temp, relative humidity)
The Impact of Compression on PEM Fuel Cell Performance at High Power
Authors: Swider-Lyons Karen , Garsany Yannick , Netwall Christopher J. , Atkinson Robert W. , Gould Benjamin D. , Sassin Megan B.
Published: February 2020

The compression of PEM fuel cells has a significant impact on performance, particularly at high current densities where the ohmic contribution of mass transport and contact losses are major contributors. Compression, or more accurately the compressive stress on the fuel cell membrane electrode assembly (MEA), affects the mass transport of gases and water through the gas diffusion media (GDM). The transport of gases and water in turn affects the kinetics of the cells.

This talk will review our work toward better understanding how the compressive stress affects fuel cell performance. We observe that a break-in compression cycle decreases the contact or ohmic resistance between the GDM and metal bipolar plates when forming a high performance fuel cell stack, as the cycling appears to improve the interface between the porous GDM and roughness of the metal surface [1]. In a following effort to make laboratory-scale high performance MEAs, we observed that the compressive stress on the MEA was largely absorbed by the GDM, and the resulting porous structure of the compressed GDM had a large effect on overall performance at >0.2 A cm-2 due to the influence on both ohmic losses and transport effects [2]. We therefore recommended attention to compression of the MEA/GDM as a major influence in the performance of high performance fuel cells [3]. While a compression near 14% is recommended for paper-type GDM in laboratory cells that use rigid gaskets as compression stops [2,3], we see that much greater compression is desirable for fuel cells in “open air” configurations, for which the air is very dry [4]. Three-dimensional imaging of paper- and felt-type GDM with computed tomography shows a clear correlation between how the porosity of the GDM vs compression affects fuel cell performance, and that higher compressive stress is advantageous for fuel cells with felt-type GDM [5].

References

C. Netwall, B. D. Gould, J. A. Rodgers, N. J. Nasello, K. Swider-Lyons, J. Power Sources, 227, 137 (2013).

M. B. Sassin, Y. Garsany, B.D.Gould, K. Swider-Lyons, J. Electrochem. Soc., 163, F808 (2016).

M. B. Sassin, Y. Garsany, B.D. Gould, K. Swider-Lyons, Anal. Chem., 89(1), 511 (2017).

R. W. Atkinson III ,M. W. Hazard, J. A. Rodgers, R. O. Stroman, B. D. Gould, ECS Trans., 75(
14), 531 (2016).

R. W. Atkinson III, Y. Garsany, B. D. Gould, K. E. Swider-Lyons, I. V Zenyuk, ACS Appl. Energy Mater.,
1(1),
191 (2018).

Acknowledgements

We are grateful to the Office of Naval Research for their longstanding support of this research.
Advanced Core-Shell Nanostructures for Electrocatalytic Applications
Authors: Wang Chao
Published: February 2020

The electrocatalytic performance of Pt-bimetallic catalysts is usually limited by the lack of long-term durability, primarily due to leaching of the non-noble element under the harsh electrochemical conditions. We have recently developed cobalt-platinum core-shell nanostructures could sustain high catalytic activity for the oxygen reduction reaction, demonstrating 8 times of improvement in catalytic activity versus commercial Pt catalysts and no more than 13% of loss after 30,000 potential cycles. Furthermore, we have developed a series of core-shell nanostructures involving various transition metals, such as Co, Cu, Pd, Au, Ag, Rh and Pt. These materials have been found to exhibit superior catalytic performances in many electrochemical reactions, achieving enhanced catalytic activity and durability at reduced precious metal content. We have combined electron microscopic elemental mapping and electrochemical studies of CO stripping to follow the evolution of nanoscale and surface structures over the course of electrochemical reactions, which has allowed us to develop fundamental understanding of the interactions between the metals in the core-shell nanostructures.
Sustainable Synthesis of Bismuth-Based Core-Shell and De-Alloyed Nanoparticles As Electrocatalysts for Proton Exchange Membrane Fuel Cells
Authors: Angelopoulos Anastasios P.
Published: February 2020

The dissolution of base metal cores made of Ni, Fe, and Co in the hot, acidic environment of proton exchange membrane fuel cells (PEMFCs) has impeded the use of novel core-shell nanoparticles (NPs) where the precious metals Pt and Ru are confined to surface. Since electrocatalysis occurs on surfaces, a substantial reduction in precious metal use could be achieved with core-shell NPs relative to pure systems, as long as the core remains stable during use. Bi is an abundant earth metal with a low environmental and human toxicity and water stability across a wide pH range, particularly under the acidic conditions of a fuel cell environment. These characteristics make Bi an ideal candidate for use as a durable and inexpensive core material to minimize precious metal use in highly dispersed core-shell Bi-Pt nanoparticle (NP) electrocatalyst in PEMFCs. Bi has been found to substantially promote direct alcohol fuel cell (DAFC) efficiency relative to pure Pd by mitigating catalyst poisoning due to irreversibly bound reaction intermediates such as CO and acetaldehyde. Unfortunately, the formation of Bi NPs is difficult and currently based on unsustainable methods employing toxic organic solvents, expensive organic precursors, and dangerous reducing agents such as hydrazine and lithium that frequently yield highly non-uniform structures. In this work, we describe an inorganic ligand metal redox synthesis approach which is used to synthesize a variety of well-defined core-shell as well as Pt-Bi alloy nanoparticle structures under sustainable, all-aqueous conditions. The approach uses SnCl3- as both a reducing agent and inorganic stabilizing ligand to provide unprecedented control over the size and structure of these nanoparticles. Furthermore, the ligand itself exists in a variety of structures that can be used to control electrostatic assembly onto various substrates. The materials to be discussed in this presentation have never been previously reported and their synthesis is unexpected given both that pure Bi has well-known instability in high salt, low pH environment and that Bi-Sn ligand formation has not been previously recognized. The implications of such metal NP synthesis are transformative with respect to the practical realization and wide application of alternative energy technologies given its simplicity and sustainability. We will provide data showing that such structures can double the electrocatalytic oxygen reduction reaction mass activity and increase the specific activity by nearly an order of magnitude relative to pure systems (see graphic below). As important, we observe simultaneous mitigation of carbon monoxide poisoning due to the persistence of Bi and Sn on their surface. These observations are discussed relative to the surface distribution of active sites as characterized utilizing electrochemical adatom stripping.

Figure 1
Kinetic Analysis of Oxygen Transport Phenomena through Ionomer Thin Film on Pt Surface in PEFC
Authors: Kurihara Yuya , Mabuchi Takuya , Tokumasu Takashi
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) are expected as power sources because of their low emissions and high efficiencies. However, it is required to improve the power density at lower Pt loading to develop high power systems at a lower cost. It is known that the losses of the power density are caused by activation losses, ohmic losses, and mass transport losses, and that the mass transport losses are dominant at high current density. Moreover, it is suggested that one of the causes of the mass transport losses is the shortage of oxygen in the cathode side of PEFC. In the cathodic catalyst layer, there are Pt catalysts on supported carbon microparticles, and those particles are covered with ionomer thin films. The film has two properties for the water-generating reactions in the cathodic catalyst layer: the proton conductivity and the oxygen permeability. These two properties depend on the film thickness and water content in the film, however, as one of the problems, the dependence of the oxygen permeability on water content is required to be clarified.

In our previous research, we analyzed the oxygen transport properties—i.e., solubility, diffusivity, and permeability—in an ionomer thin film on a Pt surface based on the solution-diffusion theory using molecular dynamics (MD) simulations. As a result, the oxygen permeability decreased with increasing water content. The local oxygen permeability in each region was obtained, and it was found that the oxygen permeability in the ionomer/Pt interface is the lowest for all water contents. Moreover, compared with the oxygen diffusivity, the oxygen solubility has a larger contribution to the water content dependence of oxygen permeability. Then, the oxygen permeability of the film was obtained from the local oxygen permeability in each region of the film; however, the total permeability was not in good agreement with that estimated using the oxygen flux and the pressure differential. It is suggested as the causes that the local equilibrium condition at each boundary of the region is not satisfied in the non-equilibrium system for the oxygen permeation through the film.

In this study, therefore, without an assumption of the local equilibrium condition, a new theory was constructed to describe the oxygen transport phenomena in the film using the chemical potential distribution of oxygen in the system. In this theory, it is assumed that the oxygen flux is generated by the spatial gradient of the chemical potential in the thickness direction of the film. Based on the theory, the oxygen transport resistances in the film are discussed using the oxygen mobilities obtained by MD simulations. Moreover, since oxygen pathways in the film are found to be important to estimate the chemical potential distribution of oxygen, the structure of the film is also analyzed. Then, the relationship between the film structure and the oxygen transport properties is investigated.
Fuel Cell Testing of Intermetallic Catalysts
Authors: Spendelow Jacob S , Pan Yung-Tin , Kim Yu Seung , Li Junrui , Sun Shouheng , Cullen David A. , More Karren L.
Published: February 2020

Oxygen reduction catalysts based on alloys of Pt with base metals such as Fe, Co, and Ni have demonstrated high performance in ex situ aqueous studies and in situ fuel cell studies, but excessive rates of base metal leaching continue to hinder deployment of these catalysts. Recently, ordered intermetallic structures have been demonstrated to be less susceptible to base metal leaching. Results so far indicate that the degree of ordering is a critical parameter in determining intermetallic catalyst activity and durability, with fully-ordered face-centered tetragonal (fct) FePt catalysts exhibiting substantially improved activity and durability compared to partially ordered phases [1]. These tests have been confirmed with good durability in the fuel cell environment [2].

Several factors can affect base metal stability, including chemical nature of the base metal, degree of ordering, particle size, and Pt skin formation. By carefully tuning these parameters, extremely high durability can be achieved (Fig. 1 Top), with diffraction data demonstrating that high degrees of ordering can be maintained even after the DOE accelerated stress test (30,000 trapezoidal cycles between 0.6 and 0.95 V with 0.5 s rise time) (Fig. 1 Bottom). Ongoing work seeks to focus on optimizing the surface structure of fct-FePt and fct-CoPt intermetallic nanoparticle catalysts such that a synergistic effect between the surface and core can be established, i.e., a stable Pt surface that protects the fct-core that is thin enough to benefit from the geometric and electronic effects from the core.

Fig. 1 Top. Fuel cell polarization behavior of fct-CoPt/C before and after the 30,000 cycle AST. H2/air, 100%/20% RH, 80°C, 150 kPaabs, 0.1 mgPt/cm2.

Fig. 1 Bottom. X-ray diffraction of fct-CoPt/C before and after the 30,000 cycle AST.

References

Q. Li et al., "New Approach to Fully Ordered fct-FePt Nanoparticles for Much Enhanced Electrocatalysis in Acid," Nano Lett. 2015, 15, 2468−2473.

J. Li et al., “Fe Stabilization by Intermetallic L10-FePt and Pt Catalysis Enhancement in L10-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells,” JACS 2018, 140, 2926−2932.

Acknowledgements

This research is supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy.

Figure 1
N-Containing Carbon Nanospheres As PEFC Catalyst Support Prepared from Nature Inspired Precursor
Authors: Islam Muhammad Naoshad , Ozhukil Kollath Vinayaraj , Mayer Francis D , Baron Lukas , Secanell Marc , Karan Kunal
Published: February 2020

Apart from superior electrocatalytic activity for ORR, nitrogen containing carbon materials are also well-known for their ability to anchoring Pt nanoparticles. It was hypothesized that polydopamine (PDA), an intrinsically N-containing nature inspired polymer, may be able to stabilize platinum nanoclusters due to the binding ability between its amino and catechol groups with Pt precursor. In addition, the inherent fluorescence property of PDA makes it a suitable candidate to study catalyst layer micro-structure and pore size distribution by employing fluorescence microscopy. In this study, PDA was used as a precursor to synthesize ordered carbon nanospheres (100~150 nm) as a catalyst support for polymer electrolyte membrane fuel cells (PEFCs). Morphology of the catalyst was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy. TEM micrograph (Figure 1) indicated that well-dispersed and uniformly distributed Pt nanoparticles (2-3 nm) was deposited on the PDA based carbon nanospheres (cPDA) as theorized. Electrochemical activity including reaction kinetics of the catalyst was tested in both aqueous and polymer electrolyte (fuel cell condition) media. The performance of the catalyst in a fuel cell was studied at different operating conditions (temperature, relative humidity) and compared with that of the conventional vulcan carbon-based catalyst. Pt durability was assessed in both liquid electrolyte (0.5M H2SO4) and FC condition by conducting US department of energy (DOE) recommended accelerated stress test (AST) protocols. The presentation will share the details of catalyst synthesis and characterization as well as the results of its performance in a fuel cell.

Figure 1
Formation of Metal-Nitrogen Sites in Atomically-Dispersed Catalysts Observed By in Situ Microscopy
Authors: Cullen David A. , More Karren L. , Myers Deborah J , Wu Gang , Litster Shawn , Xu Hui , Chung Hoon T , Zelenay Piotr
Published: February 2020

Platinum group metal-free (PGM-free) catalysts are under intense development for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. Recent research efforts have focused on catalysts derived from metal organic frameworks doped with transition metals such as Fe, Ni, Co, and Mn. High temperature pyrolysis is a key synthesis step in the formation of the active catalyst, and aims to produce porous, mesographtic carbons with a high density of single transition metal atoms bound to nitrogen.

In this work, correlated in situ characterization techniques have been employed to explore the mechanisms that influence catalytic activity and provide guidance for synthesis protocols. The coordination of advanced synctrotron and electron microscopy methods provide new insight into the atomic-level transformations which occur during pyrolysis.

Micro-electro-mechanical system (MEMS)-based heating devices were utilized to directly observe transformations occurring at the atomic scale as the temperature was ramped to 1100oC within the electron microscope. It was observed that significant amounts of the transition metal and nitrogen were lost as the pyrolysis temperature increased from 900-1100oC, which could limit the active site density. However, rotating disk electrode measurements indicate that pyrolysis temperatures beyond 900oC appear to be required to maximize mass activity. As shown in Figure 1, low voltage scanning transmission electron microscopy observations indicated that the degree of carbon graphitization increased as the temperature was elevated 1100oC and nitrogen-bound transition metal sites were also more readily observed within the graphene lattice by electron energy loss spectroscopy. Consequently, approaches are being explored to maintain higher Fe and N content while also generating highly graphitized domains.

Beyond active site density, the microporosity of the support can also play a key role in the performance of the catalyst. Ongoing in situ studies will also aim to explore the mechanisms of microporosity formation within the MOF support and its subsequent influence on fuel cell performance.

Research sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy, as part of the ElectroCat Consortium, which is part of the Energy Materials Network. Microscopy performed as part of a user project at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility.

Figure 1
Electrocatalyst Performance for Selective Methanol Formation in Methane Electrolyzer
Authors: Fornaciari Julie , Primc Darinka , Weber Adam Z. , Bell Alexis T.
Published: February 2020

Methane’s abundance and low cost makes it an optimal raw material for chemical precursors and other energy dense fuels. Traditional methods of converting methane to methanol require large amounts of energy through thermal catalysis and high capital costs. However, electrochemical oxidation of methane is a cleaner and cheaper way to produce methanol, and a systematic study of an electrochemical cell could help assure selectivity over undesired products.

Electrochemical oxidation of methane is an underdeveloped field, but electrochemical cells have been employed with high selectivity towards methanol.[1,2] Promising transition state metal-oxide catalysts have shown activity towards the selectivity of methanol over other by products, such as carbon dioxide, carbon monoxide, formic acid, formaldehyde.[2, 3] Further investigation of single site metal oxide catalysts is required to improve conversion and activity, but system optimization is also required. Reports of electrolyzer and fuel cell systems show varying assemblies, ranging from various solid and liquid electrolytes, temperatures, pressures, and current densities. [1-3] Few reports have been consistent on the operating current density and potential windows of such systems. Little work has been done on understanding how various components for these systems and understanding the phenomena of creating methanol in this partial oxidation pathway.

In this study, we explore the activity, selectivity, efficiency of transition metal oxide catalyst in operation in an electrolyzer. The electrolyzer used was tested under a variety of relative humidity, operating temperatures, current densities, and membrane electrode assemblies. Through electrochemical and conductivity measurements, and gas phase analysis of the effluent, a better understanding of the partial electrochemical oxidation of methane to methanol is elucidated. The results of this study provide a systematic approach to this challenging problem and provide insights on new catalyst and electrochemistry pathways.

References:

Tomita, A., et. al., Direct Oxidation of Methane to Methanol at Low Temperature and Pressure in an Electrochemical Fuel Cell. Angewandte Chemie International Edition, 2008. 47: p. 1462–1464.

Lee, B., et. al., Direct oxidation of methane to methanol over proton conductor/metal mixed catalysts, Journal of Catalysis, 271(2): p. 195-200.

Rocha, R.S., et. al., Electrosynthesis of methanol from methane: The role of V2O5 in the reaction selectivity for methanol of a TiO2/RuO2/V2O5 gas diffusion electrode. Electrochimica Acta, 2013. 87: p. 606-610.
Electrocatalytic Performance of Palladium-Based Electrocatalysts Supported on Carbon Nanofibers for Formic Acid Oxidation
Authors: Palomar-Pardavé Manuel Eduardo , Juárez Marmolejo Leticia , Romero-Romo Mario Alberto , Montes de Oca-Yemha Maria Guadalupe , Ezeta-Mejía Araceli , Estrada-Arce Elsa Miriam , Pérez-Rodríguez Sara , Lázaro Maria Jesus
Published: February 2020

In the last decades, fuel cells have been considered as an alternative power source for electric portable devices. Direct formic acid fuel cells (DFAFC) have attracted particular interest, since formic acid is safe, environmentally-friendly and non toxic. Also, it exhibits high-energy density and fast oxidation kinetics compared with other fuels, such as methanol and ethanol [1]. Palladium electrocatalysts supported on different carbon materials have been widely used for the formic acid oxidation reaction (FAOR). However, further research is still necessary as Pd deactivates during the FAOR. In order to overcome this limitation, Pd-Metal alloys have been proposed [3-5]. Pd, and PdFe nanoparticles supported on the carbon nanofibers with and without functionalization (NFC and NFCox) have been used for the FAOR in acid media. Electrocatalysts were synthesized by the borohydride reduction method with a metal loading of 20 wt.%. The morphology, composition and structural properties of the electrocatalysts were studied by transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD). The ROAF was evaluated in acid media in a conventional three-electrode cell by means of cyclic voltammetry (VC) and chronoamperometry (CA). The electrochemical behavior of Pd-based electrocatalysts for the FAOR showed that the functionalization of carbon nanofibers (NFCox) increased the electrocatalytic activity of Pd and PdFe electrocatalysts compared with the same electrocatalysts supported on NFC, as shown in Figure 1.

X. Yu, P. Pickup, Journal of Power Sources,. 182(124-132) (2008)

K. Jiang, H. Xuan, S. Zou, W. Bin, Phys. Chem. Chem. Phys., 16(20360-20376) (2014)

H. Meng, F. Xie, J. Chen, P. Kang, Journal of Materials Chemistry., 21(11352-11358) (2011)

D. Morales, J. Ledesma, L. Godinez, H. Rodríguez, L. Álvarez, L. Arriaga, Journal of Power Sources., 195(461-465) (2010)

L. Zhang, L. Wan, Y. Ma, Y. Chen, Y. Zhou, Y. Tang, T. Lu, Applied Catalyst B: Environmental., 138-139(229-235) (2013).

Figure 1
2D Materials for the Electro Oxidation of Formic Acid
Authors: Gonzalez Rodriguez Romeo , Perez-page Maria , Holmes Stuart
Published: February 2020

In recent years Direct Formic Acid Fuel Cells (DFAFCs) have attracted interest as alternative energy sources. Formic acid is abundant as it is a by-product of multiple industrial processes and it can be obtained from the oxidation of biomass. In addition, due to the capacity to use high concentrations of fuel, DFAFCs are effective at room temperature which makes it an ideal candidate for portable energy applications and it has a low permeability, which clearly distinguishes it from other Proton Exchange Membrane Fuel Cells (PEMFCs). This allows it to generate higher power densities ~160 mW/cm2 at room temperature outperforming other liquid fuel cells such as Direct Methanol Fuel Cells (DMFCs) with power densities of ~50 mW/cm2. However, a few obstacles prevents its optimization, first the behaviour and loading of the catalytic material and second the proper selectivity of the proton exchange membrane. For this the synthesis of a new catalytic material has been carried out, by the deposition of palladium Nano-particles in graphene oxide and reduced graphene oxide, obtained by the electrochemical exfoliation of graphite in order to introduce doping agents in the graphene matrix such as nitrogen, sulphur and boron and with it improve its catalytically activity and reduce catalyst loadings in DFAFCs. To address the second obstacle hindering DFAFCs, a comparative analysis of proton exchange membranes of the Nafion family was carried out and the intrinsic conductivity, dimensional stability as well as its operational temperature was observed for its use in formic acid fuel cells. From the results obtained a high performance was observed using a polytetrafluoroethylene reinforce membrane (Nafion XL) at room temperature. The membrane displayed a higher resistance to dimensional change when exposed to a wide range of formic acid concentrations, showing a maximum increase of 10% of its planar dimension while other membranes such as Nafion 117,115 and 211 had a significantly higher increase up to 45%. Results indicated that a reinforced membrane could be more suitable for DFAFCs, not only by possessing a higher dimensional stability but also due to it having a higher hydrophobicity due to the reinforcement and the lower content of sulfonic groups present in the copolymer. These changes would address the dehydration of the membrane, a factor substantially affecting the performance of the cell.
Smooth and Fiber-Shaped Co Coatings Decorated with Pt Crystallites As the Anode Catalysts for Direct Borohydride-Hydrogen Peroxide Fuel Cells
Authors: Balčiūnaitė Aldona , Zabielaitė Aušrinė , Sukackienė Zita , Tamašauskaitė-Tamašiūnaitė Loreta , Norkus Eugenijus
Published: February 2020

In the present work, the smooth and fiber-shaped Co coatings decorated with Pt crystallites were investigated as the anode material in direct borohydride-hydrogen peroxide fuel cells (DBHPFCs). The Co sublayers, which have different structures, e.g. smooth and fiber-shaped, were used as a substrate for the depositing of Pt crystallites. The Co layer having smooth structure was deposited on the Cu surface (denoted as Cosmooth/Cu) via electroless deposition using morpholine borane as a reducing agent. Co layers, which have a fiber-shaped structure and the thickness of ~3 mm, were electroplated on the Cu surface (denoted as Cofiber/Cu) from the electrolyte containing CoSO4, NaOH and N-(2-Hydroxyethyl) ethylenediamine. The Pt crystallites were deposited on the Cosmooth/Cu and Cofiber/Cu electrodes by their immersion into a Pt(IV)-containing solution at a temperature of 25oC for different time periods. It has been determined that the Pt loadings were in the range from 10 to 14 µgPt cm–2 and 5 to 29 µgPt cm–2 in the PtCosmooth/Cu and PtCofiber/Cu catalysts, respectively.

The activity of the prepared PtCosmooth/Cu and PtCofiber/Cu catalysts for borohydride oxidation reaction (BOR) was evaluated using cyclic voltammetry and chronoamperometry. The performance of a DBHPFC operating with 1 M NaBH4 + 4 M NaOH as fuel and 5 M H2O2 + 1.5 M HCl as an oxidant, while employing Pt as the cathode catalyst and PtCosmooth/Cu and PtCofiber/Cu catalysts with different Pt loadings as the anodes were investigated.

It has been determined that the prepаred PtCosmooth/Cu and PtCofiber/Cu cаtаlysts hаve а higher аctivity аnd а better stаbility for the oxidаtion of BH4
- compаred to those of Cosmooth/Cu аnd Cofiber/Cu. The аssembled direct borohydride-hydrogen peroxide fuel cell with PtCosmooth/Cu and PtCofiber/Cu cаtаlysts as the anodes exhibited аn open circuit voltаge of cа. 1.9 V.

Acknowledgment

This research was funded by a grant (No. M-ERA.NET-1/2016) from the Research Council of Lithuania.
Electrocatalytic Effect of the Bimetallic Composition of PtxAuy in the Sorbitol Electro-Oxidation Reaction in Alkaline Medium
Authors: Torres-Pacheco Luis , Álvarez-Contreras Lorena , Guerra-Balcázar Minerva , Arjona Noé
Published: February 2020

Fuel cells has been developed as an alternative energy source, with the advantage of using renewable fuels like alcohols obtained from biomass. Among the 12 most important building blocks from biomass is sorbitol, capable of transferring up to 26 electrons in its complete electro-oxidation. The existing literature about the sorbitol electro-oxidation reaction (SOR) is few and mostly focused on platinum alone materials in acid medium, and the proposed SOR pathway leads to glucose and then follows the glucose electro-oxidation pathway. Since there is no report concerning the effect of bimetallic nanoparticles for the SOR, we decided to test the effect of the bimetallic composition of platinum-gold nanoparticles in alkaline medium, not only for sorbitol, but also for the reported by-products; gold was chosen due to its excellent electroactivity towards glucose oxidation. The highest current density was achieved by the catalysts Pt30Au70 with 2.16 mA/cm2, while the lowest peak potential was obtained by Pt alone at -0.03 V/NHE. The addition of gold to the bimetallic composition also change the electrochemical behavior, from various oxidation signals at low potentials for high Pt loadings to a single oxidation signal at higher potentials for low Pt loadings.

Figure 1
Electrolytic Solution of Anion Exchange Membrane Electrolyzer
Authors: Ito Hiroshi , Kawaguchi Natsuki , Someya Satoshi , Munakata Tetsuo
Published: February 2020

In the promotion of the use of renewable energy, the role of hydrogen (H2) as the energy carrier is a key for buffering the fluctuating and/or intermittent power from renewable energy sources. As the hydrogen production device from renewable energy, a water electrolyzer is the simplest and most realistic. Among several options, PEM water electrolysis is suitable for intermittent power input, and also capable of operation at higher current density (> 3 A cm-2). However, a major drawback of PEM electrolysis is its high capital cost per power input compared to conventional alkaline electrolysis. The acidic environment of PEM limits the type of material that can be used for cell components (i.e., bipolar plates and current collectors) to titanium (Ti) and that of the catalyst to platinum-group metals (PGMs). The use of these precious materials is a major reason for the high stack cost of a PEM electrolyzer. When a membrane performing under alkaline (basic) conditions is applied to the electrolyte, the material restriction for the cell components can be relaxed. In particular, the material Ti of the bipolar plates can replaced by a cheaper material such as stainless steel, which would significantly reduce the stack cost, because the cost share of Ti-bipolar plates is significant in the total stack cost of PEM electrolyzer. An alternative material for the electrolyte is an anion exchange membrane (AEM) that has high internal pH. When such an AEM is applied as the electrolyzer based on the same structure as the PEM electrolyzer, a low-capital-cost device is possible and still retain the advantages of PEM electrolysis.

In this study, in order to confirm the potential of AEM electrolysis under mild alkaline conditions (pH ≤ 12), the effect of species and concentration of electrolytic solution on the performance of AEM electrolysis was experimentally examined, where DI water, KOH (10mM), and K2CO3 of different concentrations (0.1, 1, and 10 wt. %) were applied for the electrolytic solution. In the cell, Pt/C was used as the cathode catalyst and CuCoOx as the anode catalyst. Furthermore, to examine the effect of structure of anode current collector (i.e., gas diffusion layer; GDL) on the performance, either nickel (Ni)-foam or Ni-felt was applied to the cell. In addition to current-voltage (i-V) characteristics, the Faraday (current) efficiency and hydrogen cross-permeation was also evaluated based on the experimental data.