bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) The Implications of Cation Clustering in Anion Exchange Membranes on Conductivity and Mechanical Properties
Authors: Herring Andrew M , Coughlin E. Bryan , Liberatorre Mathew W. , Pandey Tara P , Sarode Himanshu N , Liu Ye , Di Noto Vito , Vezzù Keti
Published: February 2020

The potential of anion exchange membrane (AEM) fuel cells to provide inexpensive compact power from a wider variety of fuels than is possible with a proton exchange membrane (PEM) fuel cell, has continued to drive the research interest in this area. Alkaline catalysis in fuel cells has been demonstrated with non-precious metal catalysts, and with a variety of fuels beyond H2 and methanol. Alkaline fuel cells (AFCs), based on aqueous solutions of KOH, have serious drawbacks associated with system complexity and carbonate formation. Anion exchange membrane (AEMs) fuel cells have a number of advantages over both PEM fuel cells and traditional AFCs; however, although anionic conductivity in AEMs can be comparable to PEMs the chemical stability of membrane attached cations in hydroxide is still not always sufficient for practical applications. Recently, it has been recognized that a number of advanced cations, may give AEMs the needed chemical stability. In some circumstances simple trimethyl benzyl ammonium cations are stable up to 60oC allowing us to being to study hydroxide and water transport in these systems. We use in-plane conductivity and multi-nuclear PFGSE to measure self-diffusion coefficients of the water and where possible, the ion, i.e. F-, carbonate and bicarbonate. Together with temperature and RH dependent SAXS we couple this information with the morphological changes in the materails.

By their nature these organic cations form dipoles, which have a tendency to interact, see Figure below for a trimethylbenzyl cation with bromide for illustrative purposes. For maximum ion transport the cation should be distributed along the polymer chain, however, cation clustering is a common phenomena. It occurs in phase separated diblock polymers when an attempt is made to raise the IEC, no net increase is observed in ionic conductivity above a certain IEC. In many other less structured polymers it occurs in the fully humidified state when the distributed disordered cations order in agglomerates at a disorder/order Tδ. This Tδ is often observed in the operating temperature range expected for a device, in both DMA, DSC, and broadband electric spectroscopy. Interestingly, even though the SAXS clearly shows an agglomeration on the nano-scale, little difference is seen in the bulk conductivity with temperature. However, steric hindernce effects are expected to discourage aggregation, and may allow the cation to tune all properties of the AEM. As these phenomena are so prevalent in AEM materials the implications and science behind them are being investigated by us and will be discussed in this presentation. The implications of more complex cations proposed for stability in AEMs will be described.

Figure 1
NMR As a Tool for the Study and Rational Design of Aems
Authors: Elgammal Ramez Ahmed , Roy Asa Logan , Zawodzinski Thomas Anthony
Published: February 2020

The use of anion exchange membranes (AEMs) as separators in alkaline polymer electrolyte fuel cells (AFCs) has received considerable interest over the past decade. AFCs offer several advantages over more traditional PEM fuel cells, in particular operating at high pH enables the use of non-precious metal catalysts, drastically reducing the cost of the cells. However, widespread adoption of AEMs has been hampered due to poor stability, in part due to base-induced decomposition of the polymer backbone and cation group as well as conversion to carbonate form, all of which contribute to reduction of ion exchange capacity (IEC), conductivity, and mechanical strength. Furthermore, there is an insufficient understanding on how the polymer nanostructure and microstructure affects stability, transport, and cell performance.

Nuclear magnetic resonance (NMR) spectroscopy is well suited to investigate these issues. We will demonstrate how 1D and 2D NMR spectroscopy may be utilized to characterize the degradation of AEMs using both model cations and ex situ membranes. Measurements of relaxation, e.g. T1, for a series of AEMs will be correlated with ionic conductivity. We also have used pulsed-field gradient NMR experiments to measure water self-diffusion to assist in deconvoluting how tortuosity, connectivity, and the mobility of water in hydrophobic and hydrophilic domains are governed by the nature of the cation and polymer backbone. The ultimate goal of this work is to develop a structure-activity relationship to assist in the design of novel materials with desirable properties.
Anion Exchange Membrane for Fuel Cell: Multi-Scale Modeling Approach
Authors: Jang Seung Soon
Published: February 2020

It is required to form nanophase-segregated structures in anion exchange polymer electrolyte membrane to develop and enhance the ion transport. In this study, we employ multi-scale modeling method to investigate the correlation of the ion transport with the nanophase-segregation in anion exchange polymer electrolyte membrane. The atomistic force field is developed using density functional theory (DFT) method, and used for molecular dynamics (MD) simulations. The annealing procedure is applied to model the nanophase-segregation. The equilibration is achieved through NPT MD simulation, and the extent of nanophase-segregation is evaluated by the structure factor analysis. The ion transport is evaluated using mean-square displacement. The nanophase-segregated structures and the transport properties are compared to the proton exchange membrane consisting of the same polymer backbone except for the acidic functional group. The coarse-grained model is also constructed based on atomistic model. Using dissipative particle dynamics (DPD) simulation, the meso-scale structures are simulated to elucidate large-scale correlation in structure.
Electrochemical Behaviors of Directly Deposited Pt on Specific CNT As an Electrocatalyst for ORR
Authors: Yoshitake Masaru , Tanaka Yumi
Published: February 2020

Pt has been considered the best element for ORR in acidic condition in the point of activity, stability and power density. Pt catalysts for ORR have been often prepared using Pt compounds as starting material in aqueous solutions. The melting temperature, Tamman temperature and Huettig temperature of Pt are much higher than those of Pt compounds such as chlorides and oxides unlike Ni, Cu (1). It might be effective to deposit Pt metal directly on support to get better dispersed catalyst particles compared with the conventional methods. A liquid phase process and gas phase processes were found to be able to afford higher activity than conventional methods for various supporting materials. It was found that specific CV curves and extremely high mass activity in the case of CNT with low D/G as a catalyst support. as shown in Fig.1. The measurement condition was executed under the condition deciced based on the discussion with Y. Takasu and W. Sugimoto (2). It is very interesting that high ORR mass activity and the strong shift of HUPD to lower potential can be observed at the same time(3,4) in the electronic structure of Pt surface. We have started to discuss this behavior related with the surfacee electronic structure of Pt, the bonding between Pt and C, stability of the catalyst.  

References

1. J.A. Moulijn, B. Silberova, M. Makkee and F. Kapteijn, "Catalyst Deactivation and Process Design", 10th Internatinal Symposium on Catalyst Deactivation, February 5-8, 200 in Berlin/Germany.

2. Y. Takasu, W. Sugimoto, M. Yoshitake, "Examination of the Evaluation Method with the Common Catalysts for PEFC Cathode-3(Summary)", State-of-the-art Fuel Cells and Hydrogen Technology in Japan, - Collected from the 20th FCDIC Fuel Cell Symposium and the 1st FCV Forum, Fuel Cell Development Information Center, (2014).

3. M. Yoshitake et al, "Electrode material and method for producing same", WO2012053561 A1.

4. M. Yoshitake, "Development of PEFC at Asahi Glass Co., Ltd.", IUMRS-ICEM2010, Symposium H. Materials and Devices for FUel Cells, August 26,2010, Korea.

Figure 1
Electrospinning Strategies for PFSA/PVDF Nanofiber Composite Membrane Fabrication
Authors: Pintauro Peter N. , Park Jun-Woo , Rahmani Shahrzad , Powers Devon , Wycisk Ryszard , Nguyen Trung Van , Arefazarand Ahmad
Published: February 2020

Historically, the general strategy for developing new ion-exchange membranes focused almost exclusively on the synthesis of new polymers with a high IEC, where the ion-exchange groups are strongly dissociable. Unfortunately, the use of polymer chemistry alone has not been successful in achieving the performance goals of next-generation proton conducting membranes for fuel cells and redox flow batteries. For example, simply increasing the ion-exchange capacity of a polymer to improve conductivity has lead to polymers that are brittle when dry and swell excessively in water, with a loss in mechanical strength and counterion/coion selectivity. To overcome the problems with highly charged single polymer membrane systems, researchers have: (i) investigated block copolymers which self- assemble into separate phases, where one block provides selective transport pathways and the second block imparts mechanical strength, (ii) combined the desirable properties of two different polymers in a single membrane through blending, (iii) impregnated a functional polymer into a microporous inert support, where the support provides the requisite mechanical properties that the functional polymer lacks, and (iv) crosslinked the ionomer.

The present paper will focus on blended ion exchange membranes, composed of perfluorosulfonic acid (PFSA) and polyvinylidene fluoride (PVDF), where nanofiber electrospinning is used to control/alter the nano/micro distribution of PFSA and PVDF. Three membrane fabrication strategies will be presented, using 1100 and 825 EW PFSA and Kynar PVDF: (1) dual fiber electrospinning, where the final membrane morphology is an ionomer matrix with an embedded network of uncharged PVDF reinforcing nanofibers, (2) electrospinning of submicron fibers composed of a PFSA/PVDF polymer blend, followed by fiber mat processing to create a dense and defect-free film, where the morphology is that of randomly oriented bundles of PFSA and PVDF nanofibrils, and (3) core-shell single fiber electrospinning, where the core is PVDF and the shell is a mixture of PFSA and PVDF, followed by compaction and densification to create a dense membrane, where the final membrane structure is similar to that of (1). The methods for fiber electrospinning and follow-on mat processing will be described. Physical property data will be presented for the different fabrication schemes and for different PFSA/PVDF membrane compositions. The use of selected membranes in hydrogen/air and DMFC fuel cells and H2/Br2 redox flow cells will be discussed.
Multi-Layer Thin Film Coatings on Bipolar Metal Plates for PEMFC
Authors: Gath Kerrie K. , Ricketts Mark , Yang Jun , Xu Chunchuan , Hirano Shinichi
Published: February 2020

The proton exchange membrane fuel cell (PEMFC) offers the potential for an efficient, and reliable power source for vehicles. The bipolar plates are a key component in the stack providing mechanical support, supplying reactant gases to both anode and cathode, removing the reaction products, and providing electrical and thermal conductivity. [1] Bipolar plate materials are broadly divided into metallic and carbon-based materials. Carbon-based plate materials do well mechanically; still fabrication is difficult and costly. As a result, metallic bipolar plates are becoming increasingly popular.[2] Metal bipolar plates have all the necessary properties (including high thermal and electrical conductivity, low gas permeability, high manufacturability, and relatively low cost materials); however, chemical instability due to the highly corrosive environment of the PEMFC leads to the formation of a passive surface oxide layer.

Altering the surface by coating with a corrosion resistant material can be cost prohibitive when considering the amount of coating necessary to overcome the harsh conditions in a PEMFC, fabrication of the coating, and the number of plates in a stack. Less costly metals for coating, such as titanium, typically form an oxidative layer while non-corrosive metals can form pits where the underlying metal becomes exposed. Our multilayer technique combines both metal types for a corrosion resistant economical solution. [3] This design prevents oxide formation from percolating throughout the layered structure via thin films of non-corrosive layers alternated with thicker Ti layers. The specialized structure of multilayers of thin films (Au/Ti) allows the noncorrosive layer, the most costly, to be <1 nm while maintaining the viability and conductivity of the coating and the metal bipolar plate.

[1] H. Tsuchiya and O. Kobayashi, “Mass production cost of PEM fuel cell by learning curve,” International Journal of Hydrogen Energy, 29 (2004) 985–990

[2] K. RoBerg and V. Trapp, “Graphite-based bipolar plates,” in Handbook of Fuel Cells Fundamentals, Technology and Applications, W. Vielstich, A. Lamm, and H. A. Gasteiger, Eds., JohnWiley & Sons (2003) 308–314

[3] S Wang, J. Peng, W. Lui, and J. Zhang, Performance of the Gold-plated Titanium Bipolar Plates for the Light Weight PEM fuel cells,” Journal of Power Sources 162 (2006) 486–491  SHAPE  \* MERGEFORMAT

Figure 1. Multilayer design model.

Figure 1
Poly(2,6-dimethyl-1,4-phenylene oxide) Based Anion Exchange Membranes for Fuel Cell Applications
Authors: Sarode Himanshu N , Kuo Mei-Chen , Ferrari Paolo , Herring Andrew M
Published: February 2020

Anion exchange membranes are an integral part of a low temperature polymer electrolyte fuel cell. They serve the purpose of transporting hydroxide ions from cathode to anode while acting as a separator for fuel and air.

In this work we are focused on synthesis and device testing of some novel poly(2,6-dimethyl-1,4-phenylene oxide) based AEMs. The idea is to start with a polymer that is readily available in the market and synthesize large quantities of functionalized materials. Our work centers around attaching conventional quaternary ammonium cations as well as long spacer chain quaternary ammonium cations on the polymer backbone. We solvent cast and melt press the synthesized polymer to fabricate a membrane. Melt pressing crosslinks the membrane and adds the required mechanical and dimensional stability. We are able to achieve high degree of chlorination (~80%) of polyphenyle oxide and still maintain the swelling properties of the polymer because of crosslinking.

Our initial experiments show that the membrane has promising chloride conductivity, mechanical and dimensional stability thus making it suitable for fuel cell testing. We are also testing the device performance of these membranes using H2/O2fuel cell with Pt/C catalyst at various temperatures and different humidification levels to find the optimum operating conditions without causing significant degradation of the membrane.

Overall we are reporting a novel AEM material with simple chemistry which can be synthesized in large batches with ease and can serve as s good fuel cell membrane in the future.
Synthesis of Anion Exchange Membranes with Side-Chain-Type Benzylic Cationic Groups Using Chloromethylbenzoylation
Authors: Zhang Zhenghui , Wang Lihui , Ramani Vijay K
Published: February 2020

To circumvent the shortcomings of traditional synthetic routes relying on chloromethylation or bromination of benzylic methyl groups, a novel approach, chloromethylbenzoylation, has been proposed to synthesize commercially available poly(aryl ether)s (PAEs) with side-chain-type benzylic cationic groups for anion exchange membranes (AEMs). Previous works have demonstrated that adding alkyl side chain to PAE backbones can improve the alkaline stability of the AEMs. In this work, side-chain-type benzylchloride groups have been directly introduced onto poly resorcinol ketone (PRK) via an acylation reaction between 4-(chloromethyl)benzoic acid and PRK in P2O5/CH3SO3H at 60 oC. 1H NMR and GPC confirm that 100% substitution occurred, without side reactions such as crosslinking or degradation. Robust AEMs were then obtained through amination upon introduction of trimethylammonium (TMA+) groups. The chloride ionic conductivity of the AEM was 8.8 mS/cm at 30 °C, which is competitive with that of a commercial TokuyamaÒ A201 membrane at similar IEC values. In summary, this approach represents a simple and straightforward route capable of quantitative introduction of side-chain-type benzylchloride groups without using expensive or toxic reagents, with potential applications of the resultant AEMs in energy conversion and storage and other fields.
Evaluating Electrospun Polyacrylic Acid-Nafion Composite As Stable Catalyst Support for PEM Fuel Cell Electrodes
Authors: Kayarkatte Manoj Krishna , Delikaya Öznur , Roth Christina
Published: February 2020

Production of energy through renewable and sustainable processes are important goals for the future in the context of depleting fossil fuels and environmental pollution. In this regard fuel cell technology offers an attractive combination of highly efficient fuel utilization and environmentally friendly operation. For successful commercialization of low temperature proton exchange membrane (PEM) fuel cells, they should have a long life and a high performance.

Recently, high performance fuel cell electrodes were obtained by electrospinning a solution containing proton conducting Nafion and commercial platinum catalyst powder along with PAA as electrospinning polymer. Electrospinning of the catalyst together with Nafion ionomer resulted in enhanced triple phase boundaries which resulted in high fuel cell performance. Moreover, it was also found that the stability of the electrodes is significantly higher than the electrodes prepared from the same catalyst by conventional methods. However, carbon corrosion still ensued.

In this work, we demonstrate the stability of polyacrylic acid (PAA) - Nafion composite as a stable support due to which the Pt after the carbon corrosion does not come out of the system. On the contrary, it stays entrapped in the membrane electrode assembly giving significance performance even after the corrosion protocols/measurements. Here, we first produce Pt nanoparticles that are produced by a photochemical reaction of the precursor induced by UV light. To this, PAA and Nafion (1:2 by weight) were added and stirred overnight. The resulting solution was electrospun. (Small amount of carbon was added in some cases to get the desired conductivity) to get a Pt/PAA-Nafion catalyst as shown in transmission electron micrograph. The electrodes are first tested for electrochemical stability by potential cycling and then in the fuel cell test bench using the FCCJ recommended cell evaluation protocol.

Figure 1
Performance Evaluation on Hydrocarbon Polymer Electrolytes for PEFC Cathode
Authors: Matsuura Toyoaki , Ogu Kenichi , Rikukawa Masahiro
Published: February 2020

Cost reduction and performance improvements are still major issues for polymer electrolyte fuel cells (PEFCs). To solve these problems, the relationship between internal transport phenomena and performance in PEFCs are an essential factor.

 Particularly, the mass transport phenomena in the catalyst layer comprehends several unclear parts, which is desired to clarify. Evaluation of membrane electrode assemblies (MEAs) with different kind of ionomer materials under operating conditions are effective to clarify the impact of ionomer proton conductivity and gas diffusivity in the performance. However, these experiments are difficult due to less variety of ionomer materials.

We have already introduced poly (p-phenylene) based diblock hydrocarbon polymers has comparable properties to perfluorinated polymer electrolytes. Moreover, these materials can be used as model materials because their compositions and structures can easily be controlled. [1, 2] In this study, we synthesized several hydrocarbon polymer electrolytes for cathode ionomer, and the effect on the fuel cell performance was investigated.

The catalyst coated membranes (CCMs) were prepared for this study. Fig.1 shows the structure of hydrocarbon polymer electrolyte which was utilized for the cathode ionomer. It was synthesized by catalyst transfer polycondensation of the hydrophobic and hydrophilic monomers. The synthesized polymer electrolyte was dissolved in tetrahydrofuran (THF). Platinum supported on carbon black (Pt/C) catalyst (TEC10E50E, Tanaka Kikinzoku) and pure water were added to the solution, and the solution was mixed by a bead mill (BSG02, AIMEX). Nafion was utilized for the anode ionomer. Pt/C, isopropyl alcohol, and water were added to the Nafion solution (D2020, DuPont), and mixed by a bead mill. These catalyst inks were applied to polymer electrolyte membranes (NRE211, DuPont) by a pulse spray system (V5R02, Nordson).

A prepared CCM was installed in a single cell with two gas diffusion layers (SGL25BC, SGL). The single cell consists of separators with flow channels (1mm depth, 1mm width and 1mm rib), current correctors, and end-plates.

Electrochemical impedance spectroscopy (EIS) was performed by a potentio/galvanostat (HZ-7000, Hokutodenko). The cell temperature was remained at 80ºC, and 0.5 L/min hydrogen and 1.0L/min nitrogen were fed into the single cell. Both gases were humidified at 100%RH.

The cathode proton conductivity of the CCM with the hydrocarbon ionomer was close value of the CCM with Nafion ionomer. This result shows the hydrocarbon ionomer work well under practical operating conditions.

Details of their electrochemical activities and performance evaluation results are presented at the symposium.

Reference

[1] Umezawa, K., Oshima, T., Yoshizawa-Fujita, M., Takeoka, Y., & Rikukawa, M. (2012). ACS Macro Letters, 1 (8), 969-972.

[2] Takeoka, Y., Umezawa, K., Oshima, T., Yoshida, M., Yoshizawa-Fujita, M., & Rikukawa, M. (2014). Polymer Chemistry, 5 (13), 4132-4140.

Figure 1
Ionomer Fibers-Decorated Polymer Electrolyte Membrane for Low Pt-Loaded Fuel Cells
Authors: Choi Sungyu , Choo Min-Ju , Yuk Seongmin , Lee Dong Hyun , Doo Gisu , Kim Hee-Tak
Published: February 2020

Polymer electrolyte membrane fuel cell (PEMFC) technology faces considerable demands of cost competitiveness for mass commercialization of fuel cell electric vehicle. A significant challenge to the cost reduction is the reduction of Pt loading for membrane electrode assembly (MEA). Besides a lowered catalytic activity, low Pt-loaded catalyst layer (CL) suffers from large mass transports resistance, resulting in low power performance at high current densities. Such larger mass transport resistance at a lowered Pt loading can be attributed to a larger oxygen transport resistance from the ionomer film covering catalysts and more significant water flooding due to a lower amount of the pore volume in cathode CL. For conventional CL structure, gaseous oxygen and liquid water share the same network of meso-pores (< 50 nm) inside a flat CL for their transport, therefore, the water condensation in the pores inevitably causes a blocking of oxygen transport. In order to address this issue, an ionomer fiber-induced macro-porous CL is presented. It is fabricated via electrospinning of ionomer fibers onto the membrane, followed by spray-coating catalyst ink on the ionomer fiber-decorated membrane. The ionomer fiber deposition on the membrane induce a roughening of the membrane surface, which allows the formation of a CL, morphology of which dictates that of the ionomer fibers, and of micron-scale pores between the CL and gas diffusion layer. The new CL structure dramatically improves power performances at high current densities owing to an effective oxygen and water transport through the micron-scale mass transport pathway. From polarization curve and oxygen transport resistance analysis, and stability under constant current operation for various feeds, the efficacy of the unique CL morphology in enhancing power performances is demonstrated and understood. Also, the relationship between the macro-pore in CL and mass transport resistance is investigated with systematically varying the pore size and porosity.
Novel Non-Stoichiometric Tungsten Oxide Based Catalyst Support for the Increased CO Tolerance in PEMFC
Authors: Marceta Kaninski Milica P , Brkovic Snezana M , Perovic Ivana M , Lausevic Petar Z , Pasti Igor A , Saponjic Djordje P , Nikolic Vladimir M
Published: February 2020

Abstract

Cost and durability are two major factors that delay large-scale production and commercialization of PEMFC’s. One of the technologically ready application of the proton exchange membrane fuel cells (PEMFC) is in the combined heat and power systems (µCHP), which are used in the individual households or buildings. The performance of the µCHP systems greatly depends on the purity of the hydrogen stream, which is produced via methane reforming process. To overcome low CO tolerance of the commercially used Pt electrocatalyst and to lower the catalyst content we have prepared non-stoichiometric tungsten oxide as a Pt based catalyst support. We have prepared several catalysts designated as 10% Pt/WO3-C, 20% Pt/WO3-C, 40% Pt/WO3-C. The structure and morphology characteristics of the prepared catalysts were investigated using XRD, TEM and SEM/EDX techniques. Investigations concerning electroactivity of these catalysts towards the hydrogen oxidation reaction (HOR) were performed using cyclic voltammetry, linear sweep voltammetry, forming an ultra thin catalyst layer onto RDE. Mechanism and the kinetics of the prepared catalysts towards HOR were evaluated and if was found that increased mass activity of the 10% Pt/WO3-C could be attributed to the interactive naure of the WO3 catalyst support. Obtained results clearly show increased CO tolerance of Pt/WO3-C catalyst compared to commercial Pt/C, which was confirmed by lowering the stripping potential of the CO, adsorbed on the surface of the 10% Pt/WO3-C. catalyst is more facile than that on commercial 40% Pt/C. These catalysts were employed as anode catalyst in the MEA, and the performance of single cell PEMFC were compared to commercial catalyst.
Correlation Between Metal-Support Interaction and the Stability of Platinum Nanoparticles Supported on Heteroatom Doped Mesoporous Carbons for Oxygen Reduction Reaction
Authors: Kim Jae Hyung , Kim Jong Hoon , Park Jeong Young , Joo Sang Hoon
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have been regarded as a key element for the development of sustainable and renewable energy conversion devices, owing to their high efficiency and environmental benignity. In PEMFCs, carbon supported Pt-based catalysts (Pt/C) have shown the best activity, yet they are easily deteriorated via several degradation processes such as Pt particle detachment, Pt dissolution, and/or Ostwald ripening. Therefore, understanding and enhancing the durability of Pt catalysts is one of the major challenges for long-term operation of PEMFC. To improve the stability of Pt/C catalysts, recently, heteroatom-doped carbons have been exploited as support materials. In this work, we investigated the relationship between metal-support interaction and durability of Pt catalysts for the oxygen reduction reaction (ORR). For this purpose, three different types of heteroatom-doped ordered mesoporous carbon (OMC) supports, namely O-doped OMC (O-OMC), N,O-doped OMC (N,O-OMC), and S,O-doped OMC (S,O-OMC), were prepared and Pt nanoparticles were supported on these carbon supports. The interaction between Pt and doped OMC supports was investigated by using atomic force microscopy (AFM). It was revealed that the S,O-OMC exhibited the strongest adhesion with Pt, whereas the N,O-OMC showed the weakest adhesion. X-ray diffraction patterns and X-ray photoelectron spectroscopy corroborated the adhesion results. In accelerated degradation tests for the ORR, Pt/S,O-OMC exhibited the highest durability, followed by Pt/O-OMC and Pt/N,O-OMC. These results suggest that sulfur has the strong adhesive strength with Pt, thereby enhancing the durability, but nitrogen exert less adhesive force with Pt, undermining the durability.
NiMo As Non-Precious Metal Catalyst for Hydrogen Oxdiation Reaction in Alkaline Media
Authors: Kwon YongKeun , Kim MinJoong , Cho EunAe
Published: February 2020

Fuel cell is environment-friendly power source which has high efficiency in generating electricity. Polymer electrolyte fuel cell uses hydrogen as a fuel that only produces water as byproduct which does not cause any pollution. Currently, commercialized Nafion-based polymer electrolyte membrane fuel cell (PEMFC) applied Pt/C as both cathode and anode catalyst which cause cost inefficiency in manufacturing fuel cell stack.

Anion exchange membrane fuel cell (AEMFC) is being developed to combine advantages of both PEMFC and traditional alkaline fuel cell (AFC). By adopting solid membrane as electrolyte, leakage problem and insoluble salt precipitation could be solved. Furthermore, alkaline condition enhances oxygen reduction reaction (ORR) kinetics which obstructs cell power in PEMFC. However, stability of membrane is still in issue, and hydrogen oxidation reaction (HOR) kinetics are significantly diminished [1], which leads to higher Pt loading. This research is focusing at slow HOR kinetics and reducing catalyst cost by replacing Pt into non-precious metals such as transition metals.

One of the well-known HOR catalyst for alkaline fuel cell is nickel. Several studies show nickel has catalytic activity of hydrogen oxidation in alkaline media [2,3], but it’s not enough to overcome precious metals such as platinum. Therefore, diverse researches tried to enhance activity of nickel by expanding surface area or doping other elements [4]. However, these catalytic activities were only tested in 6 M KOH, 60~80 ℃ condition, which is identical to real cell operating condition.

NiMo catalyst was synthesized by electrodeposition method which is cost-effective way to produce. Nickel chloride is used for nickel source, and sodium molybdate worked as molybdenum source. Galvanostatic electrodeposition was applied to synthesize NiMo catalyst. Rotating disk electrode (RDE) was used to remove evolved hydrogen efficiently.

HOR activity was measured in hydrogen saturated 0.1 M KOH solution. RDE was used to control diffusion with 1600 rpm speed. Experiment was held at room temperature. To remove capacitive current, steady state polarization method was applied for measuring HOR activity.

Figure 1 shows HOR current of commercial Pt/C, electrodepositied NiMo, Ni. Adding small amount of Mo in Ni increases HOR current significantly. At overpotential of 20 mVRHE, Pt/C shows current density of 1.12 mA/cm2, where NiMo has 0.86 mA/cm2which is about 77% of Pt/C HOR activity.

Reference

[1] W. Sheng, et al., J. Electrochem. Soc. 157 (11), B1529 (2010)

[2] T. Tomida, et al., J. Electrochem. Soc. 136 (11), 3296 (1989)

[3] H. K. Lee, et al., Mat. Chem. Phys., 55, 89 (1998)

[4] J. A. Linnekoski, J. Fuel Cell Sci. Tech., 4, 45 (2007)

Figure 1
Structure of Anion-Conducting Polymers from x-Ray Scattering and MD Simulations
Authors: Schibli Eric Matthew , Frisken Barbara J
Published: February 2020

The structure of novel polymers for anion exchange membranes (AEMs) is investigated using small and wide angle X-ray scattering (SAXS & WAXS,) combined with molecular dynamics (MD) simulations using the CHARMM36 force field. The polymers studied are poly(benzimidazole) (PBI) derivatives including mesitylene-poly(benzimidazole) (mes-PBI), mesitylene poly(dimethylbenzimidazole) (mes-PDMBI), and hexamethyl-p-terphenylene poly(methylbenzimidazole). WAXS reveals an amorphous structure with two main length scales; SAXS shows no microphase separation. By comparing simulation results to scattering data, we attribute features observed in the scattering data to stacking between polymer chains, `kinked' monomer lengths, and chain-ion spacings. Overall, we are able to validate the interpretation of scattering data by combining MD simulations and scattering experiments and propose an interesting ion conduction mechanism.
Characterizing the Pt-Electrolyte Interface in PEM Fuel Cells
Authors: Garrick Taylor Reed , Moylan Thomas E , Yarlagadda Venkata , Kongkanand Anusorn
Published: February 2020

Much progress in reducing the platinum loading in proton exchange membrane (PEM) fuel cell cathodes to a target of 0.1 mg-Pt/cm2 has been made. However, large performance losses are observed at high current densities at low cathode platinum loadings. Recent studies have shown that the large losses are caused due to resistances at or near the catalyst-ionomer interface.[1] This resistance can be countered through the use of ionomers designed to interact with Pt in a way that does not limit the oxygen reduction reaction. However, the development of tools to quantify and characterize this resistance is needed to enhance our understanding of this resistance and correlate it with performance loss.

In the early 1990’s Feliu et al. developed a method for measuring adsorbed ion charges on Pt single crystals in an aqueous electrolyte.[1] We have validated this CO displacement method on polycrystalline Pt and carbon-supported Pt nanoparticles in an aqueous electrolyte and present here results from implementing this methodology in a fuel cell. Figure 1 illustrates the current transient measured during chronoamperometry as CO gas is introduced to the cathode of a fuel cell. The measured displacement charge at potentials less than 0.2 V represent a displacement of adsorbed protons, corresponding to a positive displacement current. At potentials greater than 0.3 V, a negative current is measured corresponding to the displacement of negatively charged adsorbed species. In the case of a fuel cell cathode, these negative species are the sulfonate group present in the ionomer. The adsorption charge can then be integrated to determine the amount of species adsorbed on the surface at each potential. Using this tool, ionomer adsorption for different ionomer types at different operating conditions can be examined.

[1] Kongkanand A, Mathias MF, J. Phys. Chem. Let. 7 (2016) 1127.

[2] Feliu JM, Orts JM, Gomez R, Aldaz A, Clavilier J. J. Electroanal. Chem. 372 (1994) 265.

Figure 1. Chronoamperometry at different potentials during CO Displacement. Introduction of CO to the cathode occurs at t=120s.

Figure 1
Development of a Portable Polymer Electrolyte Membrane Fuel Cell System Using Metal Hydride as the Hydrogen Storage Medium
Authors: Davids Moegamat Wafeeq , Tolj Ivan , Jao Ting-Chu , Lototskyy M , Pasupathi S , Sita C
Published: February 2020

This paper describes a Portable Polymer Electrolyte Membrane Fuel Cell (PEMFC) System developed at HySA Systems, UWC. The system has a rated maximum output power of 130 W at 240 VAC and 5 VDC USB output port. Hydrogen is supplied to the PEMFC using Metal Hydride (MH) on the basis of a multi-component AB2 – type hydrogen storage alloy (A=Ti,Zr; B=Mn,Fe,Cr,Ni; Ti:Zr=0.55:0.45). The stainless steel MH canister with external aluminium fins was developed in-house. The heat transfer performance was optimized by utilizing external fins and compacting thermal expanded graphite (TEG) with the MH powder to form pellets. The MH canister has a maximum hydrogen storage capacity of 90 NL H2.

It is well-known that the endothermic desorption of H2 from MH results in the significant cooling, which decrease H2 supply flow rate. To overcome this problem and improve the dynamic performance, the MH canister was placed in front of the fuel cell exhaust to utilise the waste heat generated by PEMFC. By utilisation of the PEMFC waste heat in combination with external fins and MH / TEG compacts, the MH canister allowed for >40 minutes-long stable operation at the stack power of 130 W (225 W/kg(MH)) with the utilisation of >90% of the stored H2. Figure 1 illustrates the MH storage unit integrated with 200 W PEMFC stack, Figure 2 shows the rated power of the PEMFC and temperature of the MH canister at different loads connected to the system.

Figure 1
A Study on Property and Performance According to the Pore Structure of Metallic Porous Separator for Fuel Cell Vehicle
Authors: Kim Myong-Hwan , Yoo Seung Eul , Goo Youngmo
Published: February 2020

In generally, Bipolar plate is vital component of PEM fuel cells, which supplies fuel and oxidant to reactive sites, removes reaction products, collects produced current and provides mechanical support for the cells in the stack. At the present, the bipolar plate for fuel cell vehicle is metallic separators formed of metallic materials such as stainless steel. The existing bipolar plate includes a land(contacting) portion directly bonded to the gas diffusion layer(GDL) and a channel portion that serves as a supply passage of reaction gases and an exhaust passage of water between land portions. In the typical separator, the land portion and the channel portion are disposed in a longitudinal direction and a flow field area in which the channel portion is formed both have a longitudinal structure. Also, the land portion and the channel portion are distinctly separated from each other.However, in the case of a typical separator, this non-uniformity causes a concentration difference between the area that the channel portion contacts and the area that the land portion contacts among the whole area of the MEA where the electrochemical reaction occurs and the performance of fuel cell is decreased.In this paper, a porous separator with various structures for a fuel cell, which causes the high diffusion of reactant gases was studied for increasing the performance of fuel cell. Also, we conducted an analysis of the properties(contact resistance, corrosion etc.), machinability(uniformity of thickness, change of hole structure etc.) and performance according to hole and pitch structure.In conclusions, the porous separator with optimum structure shows the performance above 200mA/cm2 at 0.6V in comparision with the typical separator. It is considered to be minimize concentration differences between area in a gas diffusion layer and achieve uniform electrochemical reaction and electricity generation over the whole reaction are, by improving the structure of a flow field in which reactant gases flow.
Diagnostic Analysis of the Oxygen Fraction at the Boundary Between Cathode Flowfield and Gas Diffusion Layer in the PEMFC
Authors: Hirano Shinichi , Chen Jixin , Shimpalee Sirivatch , Wang Chunmei , Saloka George
Published: February 2020

Enhancement of the fuel cell performance at higher current densities is important to improve the power density and reduce the cost of proton exchange membrane fuel cell (PEMFC) system. Mass transport overpotential is the major barrier to achieving high performance at high current density. The overpotential at the cathode is significantly large and the oxygen partial pressure in the oxygen reduction reaction (ORR) area is vital. Condensed water in the flowfield and the gas diffusion layer (GDL) reduces oxygen transport to the ORR area. Direct investigation of oxygen transport has been limited by an inability to resolve water saturation dependent properties. A novel diagnostic method to analyze the boundary between flowfield and GDL surface is required. A measurement of the oxygen partial pressure in the flowfield while the fuel cell is operating was introduced [1-3]. This method uses oxygen sensitive fluorophore materials whose fluorescent luminescence is a function of oxygen quenching as described by the Stern-Volmer equation. In the previous work, the oxygen quenching rate was modified in order to enable in-situ oxygen partial pressure measurement on the surface of the cathode GDL with typical operating conditions of an automotive PEMFC [3]. In this work, a computational fluid dynamic (CFD) based two-phase fuel cell model was newly developed to be validated with measured oxygen fractions. Figure 1 shows the geometric configuration of this tested single cell. Figure 2 shows that simulation of oxygen partial pressure distribution shows similarity to the previous experimental data. Figure 3 shows measured oxygen partial pressure on the cathode GDL surface along with fraction of flowfield channel length. This oxygen fraction is deviated from the average stoichiometric line. The spatial variability of current density, which is proportion to the oxygen consumption rate, is considered to be a large contributor. Combined empirical and modeling approaches enable to gain the mechanistic understanding of two-phase fluid flow in the flowfield and the surface of GDL, including water condensation and implication with the fuel cell operating conditions. Further analysis will be discussed.

 

References:

J. Inukai, et. al, Angewandte Chemie International Edition, 47(15):2792-2795

S. Hirano, et. al, ECS Trans. 58 (1) 1791-1797 (2013)

S. Hirano, et. al, ECS Trans. 2015 69(17): 1331-1339 (2015)

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Impact of Polymer Electrolyte Membrane Properties on Transport, Performance and Durability
Authors: Dutta Monica , Ghassemzadeh Lida , Young Alan P , Lauritzen Michael Victor , Knights Shanna
Published: February 2020

The structure and properties of the polymer electrolyte membrane has a major impact on the MEA performance and durability. Polymers with different chemical structures can propose different mechanisms for water and proton transport which lead to differences in performance and durability. For membranes with similar chemical structures, factors such as thickness and equivalent weight (EW) are crucial in transport and therefore could cause differences in the performance. The focus of this work was a closer look at the impact of these properties, and their changes due to degradation, on the performance and durability of the MEA and its components.

The impact of membrane thickness and equivalent weight was studied by comparing the water content of different PFSA membranes as a function of relative humidity (RH). The data was then used to further discuss the conductivity and hydrogen permeability of the membranes in different regimes of temperature and RH. The impact of membrane chemical degradation on transport property was studied by comparing the membrane conductivity, thickness, hydrogen permeability and performance before and after membrane degradation. To study the impact of membrane properties on cathode catalyst performance and degradation, the cathode degradation test was applied on MEAs with and without membrane degradation, and the results were compared.

The water content (Lambda) of all membranes showed a type II isotherm increase by increasing the relative humidity. Lambda was found to be independent of membrane thickness and equivalent weight, while, as expected, the absolute water content (g water/g membrane) showed a decrease at higher equivalent weights. Increasing the relative humidity and operational temperature showed an increase in membrane conductivity. Higher thickness or higher equivalent weight both resulted in higher membrane resistance; supporting a more general trend which is the linear increase of membrane conductivity with increase in the absolute water content.

Cathode degradation testing showed an impact on the ECSA loss and performance. The effect was more intense for thinner or lower EW membranes suggesting that membrane water content was the contributing factor. After the membrane degradation test, losses in membrane thickness, membrane conductivity, performance and ECSA were observed. In addition, the hydrogen crossover increased due to the membrane thinning. The membranes with pre-existing degradation showed less ECSA loss but increased performance losses. This trend was explained by the combination of higher catalyst layer ionomer resistance and platinum depletion which lead to higher catalyst layer ionic losses related to a reaction distribution shift further into the catalyst layer.

Acknowledgements: Funding was provided by Department of Energy EERE Hydrogen and Fuel Cell Technology Program (Project DE-EE0006375).
(Invited) High Performance Fe/N/C-Based ORR Electrocatalyst and Its Application in Alkaline Fuel Cell
Authors: Zhou Zhi-You , Chen Chi , Rauf Muhammad , Yang Xiao-Dong , Wang Yu-Cheng , Sun Shi-Gang
Published: February 2020

Fe/N/C is a promising electrocatalyst for oxygen reduction reaction (ORR). This type catalyst can perform in both acidic and alkaline media. In acidic media, the active sites of Fe/N/C can be corroded; however, in alkaline media, Fe/N/C can exhibit high stability. Therefore, it is promising to explore the applications of Fe/N/C catalyst in alkaline fuel cell. Herein, we will talk about our recent advances in preparation of Fe/N/C catalysts and the application of them in alkaline fuel cells: (1) By using 2-aminothiazole, a molecule containing both N and S atoms, we prepared S co-doped Fe/N/C catalyst with graphene nanosheets. In alkaline solution, this catalyst exhibited high ORR activity with half-wave potential of 0.926 V and mass activity of 0.56 A g-1 @ 1.0 V. Furthermore, the catalyst displayed excellent durability, and only lost 9% of initial activity after 100 h of durability test at 0.80 V. In alkaline anion exchange membrane fuel cell (AEMFC) test, the peak power density could reach 164 mW cm−2. (2) We used the unzipped carbon nanotubes as carbon support and melamine as nitrogen source, and prepared a Fe/N/C catalyst with high ORR activity in alkaline media. The edge sites of unzipped carbon nanotubes play a key role for high catalyst activity. (3) we explored a series of nitrogen source including binary polymer of melamine-terethalaldehyde, ternary polymer of cynuric acid, 2, 4-diamino-6-phenyl-1, 3, 5-triazine, and melamine. N-doped carbon nanotubes with encapsulated Fe nanoparticles were prepared. The catalyst exhibited considerably high ORR activity in alkaline solution. We further tested its performance in alkaline membrane direct ethanol fuel cell, and the peak power density was about 64 mW cm-2. These results demonstrated that Fe/N/C is a promising candidate for ORR electrocatalyst in alkaline fuel cell.

References

[1] C. Chen et al. Chem. Commun., 2015, 51, 17092-17095.
A Simple and Inexpensive Organometallic Compound Catalyzing Oxygen Reduction Reaction
Authors: Ramanujam Kothandaraman , Sheelam Anjaiah
Published: February 2020

One of the major obstacles in fuel cell commercialization is the cost of the precious metal catalysts used for oxygen reduction reaction (ORR) and hydrogen oxidation reaction(1). Recently, non-precious metal catalysts are mainly obtained by the pyrolysis of the transition metal, carbon and nitrogen sources together and these catalysts are viewed as potential alternative to the expensive platinum based catalysts(2). Pyrolysis step leads to formation of several nitrogen and transition metal based functionalities covalently embedded on the carbon surface(3). Hence, identifying the exact chemical structure of the ORR active site in the pyrolyzed catalyst remains elusive. Hence, designing a synthesis process (which includes pyrolysis) with an objective of maximizing the number of active sites is a work in progress. To avoid difficulties associated with such process, we propose a metalorganic complex capable of catalyzing ORR. As it is a molecular material, its characterization by single crystal XRD, 1H and 13C NMR unambiguously predicted the structure. In this study we report ORR on bis(2,2’-bipyridine-N,N’)carbonatocobalt(III)nitrate pentahydrate. The above said complex was immobilized on the Ketjenblack carbon and its ORR activity was measured in O2 saturated 0.1 N KOH solution (Figure (a)). This complex crystalizes in monoclinic (C 2/c) crystal structure and its crystal structure is shown in Figure (b).

Figure Shows (a) the cyclic voltamograms recorded at different rotation rate in O2-saturated (solid lines) and in N2-saturated (dash line) 0.1 N KOH electrolyte and (b) crystal structure of the metalorganic complex employed in this work.

References:

1. Y. Wang, K. S. Chen, J. Mishler, S. C. Cho and X. C. Adroher, Appl. Energy, 88, 981 (2011).

2. X. Li, H.-J. Zhang, H. Li, B. Zhao and J. Yang, J. Electrochem. Soc., 161, F925 (2014).

3. K. Artyushkova, A. Serov, S. Rojas-Carbonell and P. Atanassov, J. Phys. Chem. C, 119, 25917 (2015).

Figure 1