bluuebunny/crossref_metadata_2025 huggingface dataset:
Palladium Alloy Based Nanocomposite as an Efficient Anode and Cathode Electrocatalyst for Polymer Electrolyte Membrane Fuel Cell
Authors: C Priji , S Ramaprabhu
Published: February 2020

Polymer electrolyte membrane fuel cell (PEMFC) has the capacity to efficiently convert chemical energy into electrical energy to meet the future energy requirements. High efficiency, zero pollution, low operating temperature and fast start-up time are the advantages of hydrogen based PEMFC, which makes it a promising candidate for transportation and portable applications. Platinum and platinum alloy based nanomaterials are the most commonly used electro-catalysts for both hydrogen oxidation reaction (HOR) as well as oxygen reduction reaction (ORR) in PEMFC due to its high catalytic activity and resistance to corrosion. However, the commercialization of PEMFC has been hindered by the high cost of platinum and less abundance. Hence, platinum free electrocatalysts with comparable activity have been widely investigated. Investigations of Palladium based electrocatalyst suggest that it is a good alternative for platinum based electrocatalyst. Further, the reduction in the cost of catalyst can be achieved by alloying palladium with transition metal. Furthermore, to achieve high catalytic activity, significant advances in catalyst support materials and proper utilization of catalysts are still needed. The complete utilization of the catalyst can be achieved by choosing a good support material with high surface area and good electrical conductivity. With the goal of reducing the cost of electrocatalyst with a good fuel cell performance, present work is focused on the preparation of palladium-transition metal (Pd-TM) alloy nanoparticles supported on partially exfoliated carbon nanotubes (PCNT) as an efficient anode as well as cathode electrocatalyst. PCNT has the combined structure of 1D multiwalled carbon nanotubes and 2D graphene and shows a synergistic effect of good conductivity and high surface area. The improvement in electrical conductivity helps in quick electron transport while enhancement in surface area provides the more anchoring sites to disperse catalyst nanoparticles. Figure 1 shows the TEM image of Pd-TM alloy nanoparticles supported on PCNT. It shows uniform dispersion of catalyst nanoparticles on the support material. Both half-cell and full cell measurements were carried out with this material and it showed significant performance. Pd-TM alloy/PCNT nanocomposite prepared in the present work exhibits good HOR and ORR activity and the work discusses the approach and the results.

Figure 1
Imidazolium-Functionalized Polymer Membranes for Fuel Cells and Electrolyzers
Authors: Pellerite Mark , Kaplun Marina , Hartmann-Thompson Claire , Lewinski Krzysztof A. , Kunz Nancy , Gregar Travis , Baetzold John , Lutz Dale , Quast Matthew , Liu Zengcai , Yang Hongzhou , Sajjad Syed D. , Gao Yan , Masel Rich
Published: February 2020

Imidazolium-functionalized styrenic copolymers have been widely studied as candidates for use as anion exchange membranes in carbon dioxide and water electrolysis systems. Recent new developments in catalytic electrode materials suggest that electrolyzers based on this technology will be commercially viable. Nevertheless, important aspects of the physicochemical behavior of these membrane materials, especially transformations occurring upon activation in strongly alkaline media, remain incompletely understood. We will discuss results from 1- and 2-D NMR, IR, IEC, and DSC studies of imidazolium-functional styrenic copolymer membrane materials recovered after activation by exposure to 1M KOH solution and reacidification in HCl. The work sheds some new light on such aspects as chemical reactions and polymer crosslinking processes occurring in strong base, although mechanistic questions remain.
Anion Conducting Block Copolymers with Partial Fluorination and Long Side Chains
Authors: Mandal Mrinmay , Liu Lisha , Ahlfield John M. , Kohl Paul A
Published: February 2020

Anion Exchange Membranes (AEM) can be used in fuel cells and electrolyzers. The benefits include lowering the amount of platinum catalysts, simplifying water management, and improving electrochemical kinetics at the air cathode. However, the performance of AEMs is not as high as that of proton exchange membranes partially because of factors such as low ionic conductivity, poor stability at high pH, and high water uptake.

A series of multiblock copolymers including poly(arylene ether)s and poly(norbornenes) with long head-group tethers were synthesized for use in AEM fuel cells and electrolyzers. In this study, the number of head-groups per block and resulting conductivity, domain size and water uptake was studied. The improvement in performance (increased conductivity and reduced water uptake) was correlated with domain size, bound and unbound water content, and ion channel configuration.

Financial support for L.L. and J.M.A. from US Office of the Deputy Assistant Secretary of the Army for Defense Exports and Cooperation (DASA-DE&C) is gratefully acknowledged. Financial support for M.M. from ARPA-E Ionics program is gratefully acknowledged.
Synthesis and Characterization of Perfluorinated Anion Exchange Membranes
Authors: Park Andrew Michael , Owczarczyk Zbyslaw R. , Garner L. E. , Yang-Neyerlin Ami C. , Long Hai , Antunes C. M. , Sturgeon Matthew R , Lindell M. J. , Hamrock Steven J , Yandrasits Michael , Pivovar Bryan S
Published: February 2020

The alkaline membrane fuel cell (AMFC) field continues to expand in interest. Membrane chemical stability is approaching the level required for commercial application (1), and membrane-electrode assembly (MEA) power output has reached and even surpassed 1 W/cm2 (2). In this presentation, work at NREL in the AMFC field regarding the synthesis of PFAEM and its implementation into MEAs will be summarized.

For example, our ‘Generation 2’ PFAEM, based on sulfonamide-linked hexyl trimethyl ammonium, retains greater than 90% of its ion exchange capacity (IEC) after 14 days of exposure to 2 M KOH at 80°C. Well over 200g of this material has been synthesized and is readily processed into solutions (for membrane fabrication) and dispersions (for electrode ionomer use). MEAs employing PFAEM membranes and ionomers outperform commercial AEM materials from Tokuyama with equivalent catalyst loadings (see figure). Further improvements have been attained with MEAs comprising PFAEM membranes and advanced electrodes where ~1 W/cm2 peak power and >500 hr durability in H2/O2 at 60°C were demonstrated. Performance and durability across different electrode architectures and compositions were studied via impedance, RH dependence, and cyclic voltammetry. Comparisons will be presented along with insights gained into the relative contributions of electrodes and membranes to durability and performance of AMFCs.

References

1. W.-H. Lee, Y. S. Kim and C. Bae, ACS Macro Lett., 4, 814 (2015).

2. L. Wang, E. Magliocca, E. L. Cunningham, W. E. Mustain, S. D. Poynton, R. Escudero-Cid, M. M. Nasef, J. Ponce-Gonzalez, R. Bance-Souahli, R. C. T. Slade, D. K. Whelligan and J. R. Varcoe, Green Chemistry, 19, 831 (2017).

Figure 1. Comparison between all-PFAEM and all-Tokuyama AMFC MEAs. Cell conditions comprised H2/O2 gas flows at 0.2 slpm, 60°C, 121 kpa absolute, and 100RH. Catalysts were 46% Pt/HSC for each electrode and loadings for all were 0.4 mg/cm2.

Figure 1
Quantification of Active Sites at Spinel Type Metal Oxide Catalysts by Surface Interrogation Scanning Electrochemical Microscopy
Authors: Behnken Julian , Deng Xiaohui , Tüysüz Harun , Dyck Alexander , Wittstock Gunther
Published: February 2020

Nanostructured spinel type metal oxides are promising catalysts for the oxygen reduction reaction (ORR) in fuel cells as well as for the oxygen evolution reaction (OER) in electrolysers under alkaline conditions [1]. For a more comprehensive understanding of the oxygen electrochemistry the enlightenment of the interaction between catalyst structure and occurring surface reaction will be a major step [2]. Therefore, new experimental approaches are needed to identify material patterns that determine the electrocatalytic activity. Especially, following the oxidation states of metal atoms as function of potential and time will provide new insights into the ORR and OER mechanisms.

A versatile and powerful method in the assessment of electrocatalysts is scanning electrochemical microscopy (SECM). The spatial activity and selectivity of a catalytic material is immediately visualized by analyzing the current response of a movable probe electrode [3]. Recently, Rodríguez-López et al. [4] described a surface interrogation mode of SECM that allows the detection of adsorbates depending on time and substrate potential. This method is based on a transient feedback of a redox mediator with which a coulometric titration is performed. By integrating the current response at the tip electrode the quantification of active catalytic sites is accessible.

In this study, we apply the surface interrogation mode to detect the amount of active sites at spinel type metal oxide catalyst under alkaline fuel cell conditions. Therefore, the catalyst powder is supplied in cavity-microelectrodes which were prepared by electrochemical etching of a metal wire [5]. Through the quantification of active sites and the examination of their reactivity new insights to the ORR of alkaline fuel cells are achieved. The results will be compared to a commercial carbon-supported platinum fuel cell catalyst.

1. X. Deng and H. Tüysüz, ACS Catal., 4, 3701 (2014).

2. I. Katsounaros, S. Cherevko, A. R. Zeradjanin and K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 53, 102 (2014).

3. G. Wittstock, M. Burchardt, S. E. Pust, Y. Shen and C. Zhao, Angew. Chem. Int. Ed., 46, 1584 (2007).

4. J. Rodríguez-López, M. A. Alpuche-Avilés and A. J. Bard, J. Am. Chem. Soc., 130, 16985 (2008).

5. A. Minguzzi, C. Locatelli, O. Lugaresi, A. Vertova and S. Rondinini, Electrochim. Acta, 114, 637 (2013).
Highly Stable and Methanol Tolerant RuTe2/C Electrocatalysts in Alkaline Media
Authors: Gong Qing , Zheng Jiwu , Wang Ye , Gong Shuiping , Yang Weifeng , Cheng Xuan
Published: February 2020

The carbon supported ruthenium tellurium (RuTe2/C) nanoparticles were synthesized through a simple microwave polyol method and heat treatment at 350℃. Effects of Ru/Te molar ratio on the crystal structure, surface morphology, microstructure, electrocatalytic activity and stability, as well as methanol tolerance in both acidic and alkaline solutions were systematically investigated. The orthorhombic RuTe2 and hexagonal Ru were formed. The catalyst nanoparticles were uniformly dispersed on carbon support and the average particle size ranged 5.0~8.6 nm. The best activities toward oxygen reduction reaction (ORR) were achieved with the RuTe2/C catalyst prepared at Ru/Te=1:1 in both acidic and alkaline media. The onset (Eonset
) and half-wave potentials (E1/2
) were 0.88 and 0.60 V in 0.1 mol/L HClO4, respectively, while 0.98 and 0.72 V in 0.1 mol/L KOH, respectively. The E1/2
values decreased by 5 mV after 1000 cycles in both acidic and alkaline electrolytes, while 20 mV and 7 mV in both acidic and alkaline electrolytes containing 2 mol/L methanol, respectively, suggesting the excellent stability and methanol tolerance.
Sodium Borohydride Oxidation on Pt and/or Pd-Based Electrodes in Hydrogen Peroxide Direct Borohydride Fuel Cells (H2O2-DBFCs)
Authors: Hjelm Rachel Marielle Emily , Garsany Yannick , Atkinson Robert W. , Stroman Richard O'Neil , Swider-Lyons Karen , Lafforgue Clémence , Chatenet Marian
Published: February 2020

Direct borohydride fuel cells (DBFCs) may offer high energy density due to the potential release of 8 electrons when borohydride (BH4
-) has been fully oxidized (overall reaction: BH4
- + 8OH- à BO2
- + 6H2O + 8e-). However, the borohydride oxidation reaction (BOR) is complex producing several reaction intermediates and solid borates1, and may compete with the heterogeneous hydrolysis of BH4
- to produce H2, which can be lost. In consequence, the full 8-electron oxidation reaction may be practically inaccessible. Incomplete BOR is largely due to transport of intermediate species away from the electrocatalyst before complete oxidation can occur. The escape of incompletely oxidized species leads to BH4
- and intermediate species concentrations (including H2) which vary as the fuel solution progresses through the fuel cell flow field 2. For this reason, the optimal catalyst layer composition and porosity are likely different at the fuel inlet vs outlet, making the catalyst layer and overall cell design a challenge.

In this study, the direct electrooxidation of sodium borohydride (NaBH4) is investigated within a liquid flow-through DBFC having a catalyst composition which varies from inlet to outlet. Electrochemical and spray coating deposition are used to form catalyst layers composed of a gradient of both thin-film and carbon-supported catalysts. The efficacy of the fuel cell design is evaluated electrochemically to understand which catalyst layer system maximizes fuel diffusion, minimizes hydroxide and hydrogen adsorption, and facilitates the removal of borate from the catalyst layer.

The characteristics of catalyst layer structure/composition before and after testing, and electrochemical efficiency for BOR are observed using several analytical techniques including scanning electron microscopy (SEM), X-Ray energy dispersive spectroscopy (X-EDS), Braunauer-Emmett-Teller sorptometry (BET), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS).

(1) Olu, P. Y.; Bonnefont, A.; Rouhet, M.; Bozdech, S.; Job, N.; Chatenet, M.; Savinova, E. Electrochim. Acta
2015, 179, 637.

(2) Stroman, R. O.; Jackson, G. S. J. Power Sources
2014, 247, 756.
Influence of SnO2 Orientation on Electrocatalytic Activities of Pt/SnO2 Model Electrodes for Methanol Oxidation
Authors: Miyazaki Kohei , Nagase Takahide , Fukutsuka Tomokazu , Abe Takeshi
Published: February 2020

As an electrocatalyst in fuel cells, carbon-supported platinum (Pt/C) catalysts are widely used, but there are some problems in the degradation of carbon support and CO poisoning of Pt surface. To mitigate these problems, oxides supports are considered to be an alternative support for Pt catalysts. Oxide supports have some advantages to improve the long-term stability and the CO tolerance of electrocatalysts, but the detailed mechanism of oxide supports has not yet been unveiled. In this study, we fabricated Pt/SnO2 model electrodes with controlling SnO2 crystalline orientation.

Pulsed laser deposition (PLD) technique was used for fabricating the SnO2 support oxides. Single crystals of aluminum and titanium oxides were used as a support for SnO2 thin film fabrication. Platinum nanoparticles were deposited on SnO2 film with the arc plasma deposition. Fabricated model electrodes were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Electrochemical measurements were performed in an aqueous solution with methanol and perchloric acid. CO stripping voltammetry was also carried out to investigate CO tolerance of model electrodes.

XRD patters show SnO2 thin films had surface orientation of (101), (100), and (110). XPS spectra also show the deposited Pt nanoparticles were metallic and had identical positive shift (~ 0.3 eV). The activities for methanol oxidation were in the following order: Pt/SnO2 (101) > Pt/SnO2 (100) > Pt/SnO2 (110). CO stripping voltammograms also showed similar activities for CO oxidation. Detailed influence and mechanism of surface orientation on catalytic activities will be discussed in the meeting.
Electrocatalysts for Ethanol and Methanol Oxidation Prepared by Ion Beam Assisted Deposition of Platinum and Rare Earths Metals on Carbon Fiber Paper Catalyst Carriers
Authors: Poplavsky Vasily , Dorozhko Alexandr , Matys Vladimir
Published: February 2020

Active layers of electrocatalysts were prepared by ion beam assisted deposition (IBAD) of platinum and one of rare earth metals (Ce, Gd, Dy, Yb) on the carbon based Toray Carbon Fiber Paper TGP-H-060 T (TorayCFP) and AVCarb® Carbon Fiber Paper Р50 (AVCarbCFP) catalysts carriers with the aim of electrocatalysts production for direct methanol and ethanol oxidation fuel cells (DMFC, DEFC) with polymer membrane electrolyte. Formation of layers in IBAD mode, by means of the deposition of metal and mixing of precipitating layer with the substrate by accelerated (U = 5 kV) ions of the same metal, was carried out. In this process, a neutral fraction of metal vapor and ionized plasma of vacuum pulsed electric arc discharge were used. According to scanning electron microscopy, electron probe microanalysis, X-ray fluorescence analysis and Rutherford backscattering spectrometry investigations atoms of deposited metals, carbon substrates, and oxygen as impurity enter into the composition of layers. The thickness of the prepared catalytic layers is ~30 nm; content of platinum atoms in the layers – ~2×1016 cm–2, or much less than 0.05 mgPt/cm2. Properties of the prepared electrocatalysts were investigated by cyclic voltammetry in 1M CH3OH + 0.5M H2SO4 and 1M C2H5OH + 0.5M H2SO4 solutions. It was established that the prepared electrocatalysts show activity in the processes of electrochemical oxidation of methanol and ethanol. The inclusion of the rare earth metal in the composition of formed layers enhances the activity of electrocatalysts in a multistage process of oxidation of alcohols. Moreover the activity of prepared electrocatalysts in the oxidation of more complex molecules of ethanol is higher than the activity in oxidation reaction of methanol. The advantages of proposed IBAD method are as follows: possibility of forming a cohesive catalytically active layer on a carbon substrate at low platinum consumption; one stage of deposition of each of metals a comparison against multistage traditional chemical methods of catalysts preparation.

Figure 1
Development of Stable Precious Metal-Free Cathodes in Alkaline Fuel Cells
Authors: Grimmer Ilena , Gebetsroither Florian , Pichler Birgit , Grandi Maximilian , Kalal Peter , Iseard Barry , Aronsson Robert , Schenk Alexander , Hacker Viktor
Published: February 2020

The Alkaline Fuel Cells (AFC) have been well developed in the 1960s for on-board power supply for Apollo missions to the moon. Later, in 1990s, the Polymer Electrolyte Membrane Fuel Cell (PEMFC) replaced the AFC due to their advantages such as a lighter and more compact system attributed to solid membranes as electrolyte. However, AFC systems have now reached new attention due to the necessity of using inexpensive non-precious metal catalysts, which is one of the greatest advantages of alkaline media.

In this work, precious metal-free oxide catalysts are investigated regarding their performance and long-term stability. Electrodes containing these precious metal-free catalysts are designed, manufactured and in-situ characterized in AFC half-cell tests and single-cell measurements.

The main focus lies on increasing the long-term stability of cathodes in alkaline media.

Cathodes are manufactured and tested in half-cells for 10,000 h. Tests are performed at different operating conditions: gases (O2, synthetic air, and ambient air), gas flow and temperature are varied. The influence of the operating conditions on the degradation rate and the stability of the cathodes are evaluated accordingly.

Furthermore, single cell tests are conducted with non-noble metal anodes, thereby achieving a precious metal-free AFC. Especially the activation processes are investigated.

In order to preserve cathode performance, the anode activation is performed separately. Afterwards, the two electrodes are assembled in a custom-made test cell and characterized in fuel cell operation.

For comparison of the performance of this precious metal-free AFC, single cells with platinum based catalysts are operated in parallel test cells. The results of the test series will be presented at the meeting.
(Invited) Probing the Activity of Transition Metal Oxide Nanoparticles Towards the Oxygen Reduction Reaction
Authors: Fermin David , Celorrio Veronica , Calvillo Laura , Russell Andrea E , Granozzi Gaetano
Published: February 2020

Complex transition metal oxides such as perovskites have been extensively investigated in the context of oxygen electrocatalysis.1,2 These materials represent a vast family of compounds with electronic properties sharply dependent on their composition, crystal phase and oxygen content. Consequently, the establishment of structure-activity relationships is of paramount importance in the search of highly active and chemically stable electrocatalysts for alkaline fuel cells. Indeed, the strongly correlated nature of electrons in these materials, as opposed to metallic phases, introduces a high degree of complexity for material screening from first-principle calculations. We have recently examined a range of lanthanide perovskites (LaBO3, with B: Co, Fe, Cr, Mn and Ni) synthesised by a versatile synthetic method capable of generating nanoparticles with a high degree of phase purity.3 We have shown that Mn based oxides show over two orders of magnitude higher activity than any other perovskite towards the 4-electron oxygen reduction reaction (ORR);3,4,5 a difference significantly larger than recognised in previous studies.2,6

In this contribution, we will investigate the origin of the exceptional activity of Mn based perovskites. Our key hypothesis centres around the fact that Mn sites undergo changes in their redox state at potentials close to the formal ORR potential. These redox transitions are key in the oxygen bond breaking step and the overall reactivity of the material. Our studies are underpinned by detailed analysis of the bulk and surface structure employing X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and in-operando X-ray absorption spectroscopy (XAS). We will also show that the intrinsic activity of these materials can be strongly affected by the nature of the A-site7 and the temperature of oxide phase formation.

References:

1- A. Grimaud et al. Nat. Mater. 2016, 15, 121

2- J. Suntivich et al. Nat. Chem. 2011, 3, 647

3- V. Celorrio et al. ChemElectroChem 2016, 3, 283

4- V. Celorrio et al. Catal. Sci. & Technol. 2016, 6, 7231

5- V. Celorrio et al. J. Phys. Chem. C. 2016, 120, 22291

6- K.A. Stoerzinger, ACS Catalysis 2015, 5, 6021

7- V. Celorrio, MRS Commun. 2017, DOI: 10.1557/mrc.2017.22
Effect of pH on the Activity of Hydrogen Oxidation Reaction/Hydrogen Evolution Reaction over PtRu Bimetallic Catalysts
Authors: Nash Jared , Zheng Jie , Xu Bingjun , Yan Yushan
Published: February 2020

Hydrogen proton exchange membrane fuel cell (PEMFC) powered automobiles have become commercially available, but are still too expensive. Hydroxide exchange membrane fuel cells (HEMFCs) offer the possibility of cheaper non-precious metal catalysts. However, the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) are significantly slower in base than in acid for Pt, Pd, Ir, and Rh1-4. PtRu shows higher HOR/HER activity than Pt5, 6, so understanding the mechanism of the HOR/HER on PtRu is key to developing non-precious metal catalysts for HEMFCs. Using the rotating disk electrode, bimetallic PtRu showed a minimum in the HOR/HER activity, pH relationship (Figure 1). The hydrogen binding energy and the hydroxide binding energy measured from the hydrogen underpotential desorption peak and the CO stripping peak, respectively, did not change significantly with pH. Leaching Ru from the catalyst, it was found that the HOR/HER activity of PtRu remains approximately constant while the Ru content is reduced. When a small amount of Ru is leached from the surface, the activity increases and only after a significant amount of Ru has been removed from the surface/near surface of the catalyst does the activity change. This suggests that the HOR mechanism is not the bifunctional mechanism. The charge transfer coefficient, α, decreases with the Ru content going from 0.8 to 0.5. Fitting the kinetic data with the dual pathway model7 shows that below pH 11, the Heyrovsky and Volmer reaction barriers are comparable and above pH 11, the Volmer step becomes rate determining. It is proposed that Ru can align more oxygen species on the surface giving water a more favorable orientation for the Volmer step to proceed, which results in an increase in activity.

References:

1. Sheng, W., et al., Nature communications
2015,
6.

2. Zheng, J., et al., Science Advances
2016,
2 (3).

3. Durst, J., et al., J Electrochem Soc
2015,
162 (1), F190-F203.

4. Sheng, W., et al., J Electrochem Soc
2010,
157 (11), B1529.

5. Wang, Y., et al., Energy Environ. Sci.
2014,
8 (1), 177-181.

6. Wang, J. X., et al., Scientific Reports
2015,
5, 12220.

7. Elbert, K., et al., ACS Catal
2015, 6764-6772.

Figure 1
FeNi2Se4 – Reduced Graphene Oxide Nanocomposite: Enhancing Electrocatalytic Activity for Water Oxidation through Synergistic Effects
Authors: Umapathi Siddesh , Masud Jahangir , Swesi Abdurazag T , Nath Manashi
Published: February 2020

Water splitting using earth abundant and environmentally benign catalyst is critical for renewable energy technologies. In spite of tremendous efforts to develop a catalyst with low cost, high activity and stability, it remains a challenge to match the performance of platinum group catalyst. In this presentation a hybrid material FeNi2Se4 supported on nitrogen doped reduced graphene oxide (FeNi2Se4-NrGO) nanoparticles as an efficient and dependable electrocatalyst for oxygen evolution reaction (OER) under alkaline conditions will be discussed. Fig. 1(a) shows the TEM image of catalyst where FeNi2Se4 is nicely distributed on NrGO matrix. The constructed hybrid catalyst is capable of catalyzing water oxidation at a small overpotential of 170 mV @ 10 mAcm-2, compared to FeNi2Se4 which has comparatively less catalytic activity (Fig. 1b). This study gives a new direction in the selenide based hybrid catalysts, which may be extended to prepare other ternary based selenide hybrids for a broad range of technological applications. The catalysts were characterized using TEM, SEM, EDX, XRD and XPS for structure, morphology, elemental compositions, and electronic states. Catalytic activity was studied from detailed electrochemical measurements including linear sweep voltammetry, chronopotentiometry and electrochemical surface area. The detailed results will be presented in the meeting.

Figure 1
Decoupling the Hydrogen Binding Energy to the Hydrogen Oxidation Reaction Kinetics in Alkaline Media
Authors: Li Jingkun , Ghoshal Shraboni , Bates Michael , Mukerjee Sanjeev , Jia Qingying
Published: February 2020

The slow rate of the hydrogen oxidation reaction (HOR) at high pH environments remains as a most fundamental conundrum in electrochemistry. It also offsets recent advancements in alkaline membranes with applications to alkaline fuel cells and electrolyzers. Herein we challenge the current prevailing hydrogen binding energy (HBE) mechanism for the HOR in alkaline media by decoupling the HBE with the HOR kinetics of monometallic and bimetallic catalytic systems. By studying various Pt-Ru systems and Ru/C system with combined electrochemical and in situ spectroscopic methods, we suggest that the desorption of Hads is facilitated by the reactive OHads species furnished by surface Ru oxides via the bifunctional mechanism. Our results verify that the availability of metal oxides plays a critical role for the HOR kinetics for catalytic surfaces with high oxophilic sites.

Figure 1
Morphological and Compositional Effects of Electrochemically Fabricated Cobalt Phosphide on Water Electrolysis
Authors: Kim Junhyeong , Kim Hyunki , Kim Jung Hwan , Ahn Sang Hyun
Published: February 2020

Recently, development of alternative energy for future has been under investigation to prevent environmental pollution caused by the huge use of fossil fuels. Among them, hydrogen is known as a clean energy source which does not emit pollutants. Effective hydrogen production using water electrolysis is one of the promising methods due to the simple procedure and high purity of product. However, its high cost limits the practical application of water electrolysis owing to the highly loaded platinum which is known as the best active catalyst for hydrogen evolution reaction (HER) To solve this problem, transition metals based compounds have been investigated as catalysts for HER.

In this study, the cobalt phosphide was fabricated on the carbon paper by using electrodeposition method. The morphology and composition of cobalt phosphide was controlled by bath composition and deposition potential/time. The morphology and composition of prepared CoPx catalyst was characterized by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Furthermore, transmission electron microscopy was utilized to examine the crystal structure and surface composition of CoPx catalyst at the surface. All electrochemical measurements to explore the HER activity were conducted by using conventional three electrodes cell system with N2-purged 0.5 M H2SO4 electrolyte. The HER catalytic activity and electrochemical surface area of CoPx was measured by using cyclic voltammetry. Especially, the electrochemical surface area was estimated by double layer capacitance measurement varying the scan rates. As a result, it was revealed that the intrinsic HER activity of prepared CoPx catalyst has significant relationship with their morphology and composition. Furthermore, the developed catalyst was adopted as hydrogen-evolving electrode for proton exchange membrane water electrolyzer (PEMWE).
Fern-like Nickel Cobalt Sulfide Electrocatalyst Prepared By Electrodeposition and Subsequent Sulfur Ion Exchange for Water Electrolysis
Authors: Kim Hyunki , Kim Junhyeong , Kim Jung Hwan , Ahn Sang Hyun
Published: February 2020

Recently, the attention on development of eco-friendly sustainable energy have been gradually increased, owing to the fossil fuel depletion and global warming. Among them, the utilization of hydrogen energy produced from water electrolysis is the one of the prominent methods to solve the problems due to the environmental-friendly characteristic of hydrogen energy. Representative study on water electrolysis is focusing on highly efficient and lower cost electrode development. It has been known that the Pt and IrO2 is the most activate catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. However, they are very rare and expensive, indicating that the severe cost problem is still remained for hydrogen production from water electrolysis. To solve the problem many efforts have been conducted to the development of non-noble metal based catalysts as comparably active as Pt for HER and IrO2 for OER. In particular, the researches on transition metal compounds: M-X (M=Ni, Co, Fe and X= S or P) catalysts have been dominative during the past few years. In this study, we have fabricated the fern-like NixCoyS1-x-y catalyst for water electrolysis. Firstly, NixCoyO1-x-y was electrodeposited on the carbon paper (CP) by two-step galvanostatic deposition. The morphology and composition of fern-like NixCoyO1-x-y were controlled by varying deposition conditions. Then, annealing process was conducted to further oxidization of NixCoyO1-x-y. As a last step, sulfur ion exchange was carried out on the NixCoyO1-x-y by changing dipping time in sodium sulfide solution at 90 °C. Through field emission scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction, formation of fern-like NixCoyS1-x-y was confirmed after the sufficient dipping time. Based on the electrochemical surface area, the intrinsic activity of NixCoyS1-x-y catalysts showed compositional dependence activity for water electrolysis.
A Novel Fabrication Technique for Electrodes of PEM Water Electrolyzers
Authors: Bühler Melanie , Klose Carolin , Hegge Friedemann , Lickert Thomas , Thiele Simon
Published: February 2020

State-of-the-art polymer electrolyte membrane water electrolyzers (PEMWEs) are assembled via sandwiching a catalyst coated membrane (CCM) between porous transport layers (PTLs). In this work we investigate electrodes deposited directly on PTLs. Together with the novel fabrication technique ‘direct membrane deposition’ (DMD, Fig 1a-c) - already successfully tested for PEM fuel cells [1,2] – this approach is supposed to lead to high performance MEAs for PEMWE. In DMD the fuel cell is assembled as two half-cells with the gas diffusion layers (GDLs) serving as the base for directly depositing the catalyst and the membrane layer. With this technique contact resistances and mass transport in PEM fuel cells were shown to be substantially improved and a reduction of the noble metal loading was enabled [3].However for the application of DMD a smooth and crack-free electrode surface is required [4]. Since state-of-the-art PTLs like Titanium fiber or powder sinter materials at the anodic side exhibit relatively large pores compared to the size of catalyst particles, the fabrication of a smooth catalyst layer on top of the PTL is the first step to establish the DMD method for PEMWEs (Fig. 1d). In this work we present our latest results on this novel topic and show current challenges and perspectives.

References

[1] M. Klingele et al.: Journal of Materials Chemistry A 3 (2015) 11239 - 11245.

[2] S. Vierrath et al.: Journal of Power Sources 326 (2016) 170 - 175.

[3] M. Breitwieser et al.: Electrochemistry Communications 60 (2015) 168 - 171.

[4] M. Breitwieser et al.: Journal of Power Sources 351 (2015) 145-150.

Figure 1
Activity-Stability Relationships on Cost-Effective Materials for Hydrogen Evolution Reaction
Authors: Lopes Pietro Papa , Martins Pedro F. B. D. , Stamenkovic Vojislav , Kanatzidis Mercouri G. , Markovic Nenad M
Published: February 2020

The successful deployment of alternative energy sources that are required to ensure a sustainable future based on clean energy production and consumption depends critically on the development of materials that can efficiently transform electrical energy in chemical bonds. Water electrolysis is a fundamental process to achieve abundant hydrogen production, but currently is highly dependent on precious metals as catalysts for the Hydrogen Evolution Reaction (HER). The use of cost-effective materials such as MoS2 and Mo-based chalcogels provide a unique catalytic opportunity to replace Pt, but that may suffer at the expense of lower conductivity and form the stability of their surfaces. Therefore, understanding the links between activity and stability on cost effective materials is critical to the development of more active and stable catalysts. In order to do so our approach employs the Stationary Probe Rotating Disk Electrode (SPRDE) connected to an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) that allows simultaneous measurement of dissolution of Mo and S atoms while HER is taking place. The insights gained with SPRDE-ICP-MS reveals an unexpected element dependent dissolution profile during HER that shed a different light on the nature of active sites and how stability plays a key role in it. The addition of dopant elements such as Ni, Co and Fe provide a framework on how all elements together alter the activity-stability relationships, guiding us on designing the next generation of catalysts.
Membrane Electrode Assembly Design with Various Bifunctional Catalysts in Reversible Anion Exchange Membrane Fuel Cells
Authors: Zhao Shuai , Gupta Shiva , Wu Gang , Xu Hui
Published: February 2020

Reversible anion exchange membrane fuel cells (AEMFCs) have been widely considered as both energy conversion and energy storage devices due to their low cost and high-energy storage capacity, especially when combined with renewable resources. The oxygen electrode reactions have long been one of the primary limiting factors of AEMFCs because of their sluggish kinetics and high overpotential. In our previous study, bifunctional non-platinum group metal (PGM) electrocatalysts for oxygen reduction and evolution reactions have been developed to lower the overpotential on the oxygen electrode, using hybrid structure of metal oxide supported on advance carbon nanotubes [1], transition metal derived graphene tubes [2] or structurally modified transition metal oxides. In this study, the membrane electrode assemblies (MEAs) of reversible AEMFCs using these non-PGM catalysts were designed exclusively, to be applied in real operating environment.

In addition to hardware and cell component down-selection, catalyst layer composition and distribution with different combination of anion exchange membranes and ionomers were optimized extensively by varying parameters including ionomer/catalyst ratio, catalyst ink solvent, mixing method, deposition method and annealing condition. Both catalyst-coated membrane (CCM) and gas diffusion layer (GDE) configurations were compared. Figure 1 shows the highlights of fuel cell and electrolyzer performance improvements. Fig. 1a indicates higher fuel cell internal resistance but better mass transfer in GDE configuration than that in CCM configuration. Fig. 1b demonstrates that electrolyzer performance was improved at elevated temperature through lowering the resistivity of membrane electrode. Fig. 1c provides the optimized ionomer/catalyst ratio for nickel cobalt oxide in electrolyzer mode. Fig. 1d presents the significant enhancement of anion conductivity in the electrolyzer cell with the assistance of KOH solution. This work may provide systematic design perspectives for bifunctional non-PGM catalyst-based MEA fabrication used for reversible AMFCs.

Figure 1. Fuel cell and electrolyzer performances of reversible AEMFC with under different configurations, temperatures, ionomer/catalyst ratios and electrolyte compositions.

Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.

References:

[1] Zhao, Shuai, et al. "Highly durable and active Co3O4 nanocrystals supported on carbon nanotubes as bifunctional electrocatalysts in alkaline media." Applied Catalysis B: Environmental 203 (2017): 138-145.

[2] Gupta, Shiva, et al. "Highly Active and Stable Graphene Tubes Decorated with FeCoNi Alloy Nanoparticles via a Template‐Free Graphitization for Bifunctional Oxygen Reduction and Evolution." Advanced Energy Materials 6.22 (2016).

Figure 1
AEM Electrolysis Progress and Impact on the Cost of Hydrogen
Authors: Ayers Katherine E , Capuano Christopher B , Wiles Luke
Published: February 2020

Membrane (PEM)-based electrolysis provides an ideal near-term technology to address the growing energy storage demands as intermittent renewable energy becomes more prevalent. While proton exchange membrane (PEM) systems are often viewed as preferred solutions to legacy KOH systems due to the lack of corrosive electrolyte, small footprint, and dynamic operating range due to the ability of the PEM systems to generate hydrogen at differential pressure, they still present capital cost challenges. In particular, the platinum group metal catalysts and valve metals for separator and flow field construction required for stability in the acidic environment become a significant cost driver at scale.

Alkaline exchange membrane (AEM)-based electrolysis is therefore viewed as a potential replacement to the current PEM systems as a means of driving down the high capital cost. This cost reduction is accomplished by replacing the typical high cost catalyst and materials of cell construction with lower cost metals that would corrode in the acidic PEM environments, but are stable in the alkaline chemistries. In theory, this approach is highly promising, but testing of the current state-of the art has shown the technology gaps between the two platforms in terms of stability, durability, and operating electrical efficiency. Modeling has shown that savings realized in capital cost are typically off-set by an increase in operating expense resulting from the lower activity of the non-PGM catalysts and poor conductivity of the AEM. Additionally, thermal instability of the AEMs require stacks to be operated at lower temperatures than a typical PEM system, impacting conductivity further and slowing kinetics.

The addition of liquid electrolyte to the water feed has been shown by some groups to be effective in reducing cell operating potentials and providing overall voltage stability. However, this solution adds management and additional maintenance of handling the caustics typically used. Efforts at Proton have shown significant improvements in operation under milder conditions, showing some potential to achieve targets required to compete with incumbent technology. In this talk, some of the advancements achieved and how these have impacted the cost of the hydrogen will be discussed. An example of this improvement is shown in the figure below, where collaborative ionomer research and partnering with a commercial entity for scale-up of catalyst synthesis have translated into an immediate improvement over targets previously established. Additionally, cost models will be compared to show the path needed to establish equivalence with current PEM systems and what is required to go beyond.

Figure 1
On the Effect of the Flow Field Plate’s Geometry on the Polymer Electrolyte Membrane Water Electrolysis Cell’s Performance
Authors: Al Shakhshir Saher , Kær Søren Knudsen
Published: February 2020

The key for successful commercialization of fuel cell products, such as Fuel Cell Vehicle, Hydrogen-Powered busses, and Hydrogen-Powered Passenger Train is compact, safe, reliable, rapid response, high hydrogen purity, dynamic operation, and high pressure system for hydrogen storage technology. These quality characteristics of hydrogen storage technology can be met by polymer electrolyte membrane water electrolysis (PEMWE) technology. Also the high compatibility of PEMWE technology with intermittent renewable energy sources leads to quicker commercialization of fuel cell products.

Flow field plates (FFPs) along with the current collectors represent 48% of the stack cost. Also, FFPs are responsible for distributing reactant water and removing the pure oxygen with unreacted water from the anode side and hydrogen with crossed over water from the cathode side. Thus, FFPs must be probably designed to distribute reactant water evenly resulting in more uniform electrochemical reaction over all the active area of the PEMWE cell. Uniform electrochemical reaction leads to uniform current and temperature distribution. Therefore, the cell performance might be developed and degradation rate might be reduced.

The present work presents the effect of the most common FFPs geometries; single serpentine, interdigitated, and parallel geometry on the polarization resistances using electrochemical impedance spectroscopy (EIS) measurements and on the whole cell performance using the IV curve measurements are experimentally demonstrated. Each anode FFP’s geometry is tested with three different cathode’s FEPs geometries. Thus, the effect 9 geometries combined between the anode and the cathode of a 50 cm2 PEMWE cell are presented in this work. All the geometries have the same inlet and outlet manifold design. Thus, the pressure drop between the inlet and the outlet of each FFP’s geometry is also presented in this work.
Challenging of Reducing Electrolysis Voltage by Superimposing Boiling on PEMWE–A Thermodynamic Coupling–
Authors: Ito Kohei , Terabaru Kenji , Li Hua , Inada Akiko , Nakajima Hironori
Published: February 2020

We challenge to reduce electrolysis voltage by thermodynamic coupling. When PEMWE reaches 100°C under atmospheric pressure, boiling progresses spontaneously and contributes to entropy generation. In principle, the entropy generation accelerates water electrolysis reaction through the thermodynamic coupling, resulting in reducing the electrolysis voltage of PEMWE.

In this study, we experimentally clarify whether electrolysis voltage drop at boiling temperature. The electrolysis voltage of a PEMFC is continuously measured while raising operation temperature from 80°C to 120°C under constant operation pressure (0.1 MPa) and electrolysis current (0.002 A/cm2). If the electrolysis voltage drops at boiling temperature, this matter becomes an evidence for the thermodynamic coupling between boiling and electrolysis. PEMWE used in this study embeds a CCM made with spray and hot-press method. Polymer electrolyte membrane (PEM) is Aquivion membrane. Catalyst layer formed on the membrane consists of IrO2 (1.5mg/cm2) for anode and PT/C (0.5mg/cm2) for cathode. The area of catalyst layer is 4 cm2.

Figure shows the electrolysis voltage and HFR (high frequency resistance, 1 kHz) to the change of temperature. The HFR approximately corresponds to proton resistance through PEM. The electrolysis voltage begins to abruptly decrease just over 100°C, and turns to increase at 105°C, showing a valley on the temperature-voltage characteristics. Each slope on the characteristic (dV/dT) near 80°C and 120°C closes to temperature dependence of water-electrolysis Gibbs free energy change (ΔG(T)) in the case of liquid and gas, respectively.

The electrolysis voltage drop appeared is analyzed based on overvoltage component. HFR began to increase just over boiling point, because water in cell evaporated, PEM dried up and the proton resistance rose. However, ohmic overvoltage change attributed to the rise of proton resistance is neglectable to the electrolysis voltage change. Concentration overvoltage also can not explain the electrolysis voltage drop, because the current is controlled to be small as 0.002 A/cm2. Thus, the voltage drop appeared near boiling point attributes to the effect of boiling on activation overvoltage and/or Nernst voltage.

To summarize, the electrolysis voltage in PEMWE shows the abrupt drop near 100°C under atmospheric pressure and and small electrolysis current (0.002 A/cm2) when temperature successively rises from 80°C to 120°C. Boiling imposed in the cell is thought to impact the electrolysis voltage drop through the thermodynamic coupling. The boiling, specifically, is considered to impact on activation overvoltage and/or Nernst voltage, leading to the voltage drop.

Figure 1