bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomically Dispersed Transition Metal-Nitrogen-Carbon Electrocatalysts: Design, Synthesis, Characterization, Reactivity and Durability
Authors: Atanassov Plamen , Murphy Eamonn , Ly Alvin , Delafontaine Laurent , Wang Hanson , Khedekar Kaustubh , Huang Ying , Liu Yuanchao , Matanovic Ivana , Zenyuk Iryna
Published: September 2023

Platinum group metal-free (PGM-free) catalysts have been targeted as possible Earth Abundant Elements solution to many electrochemical energy conversion technologies. Special attention has been given to PGM-free electrocatalysis with atomically dispersed (AD) transition metal moieties decorated over nitrogen-doped carbonaceous materials (a.k.a. M-N-C catalysts). Major applications for M-N-Cs are in cathode catalysts for oxygen reduction reaction (ORR). 1 These materials are employed across the pH-range: in proton exchange membrane fuel cells (PEMFC), biological (microbial) fuel cells (MFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). We have successfully introduced M-N-C catalysts synthesized by sacrificial support method (SSM) as a hard template approach based on high temperature pyrolysis.2 In most cases a secondary pyrolysis is being performed to promote AD display of the transition metal.3

This talk will address structure-to-property correlations for M-N-C catalysts in ORR based on electrochemical activity obtained in rotating ring-disk electrodes (RRDE) with those spectroscopic and microscopic observations and density functional theory (DFT) calculations of oxygen binding on AD transition metal. We will discuss the role of the AD transition metal, participation of the surface N-groups as co-catalysts/alternative active sites and the possible role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor. M-N-C catalysts performance in single membrane electrode assembly (MEA) fuel cells will also be discussed in the context of its surface chemistry and materials structure/morphology. We will focus on local hydrophobicity of SSM-based M-N-C electrocatalystsand its impact on the MEA performance.

A broad spectrum of AD transition metal decorated MNCs have been synthesized and evaluated for catalytic activity in ORR (and other processes). The use of such materials as “active supports” for highly dispersed platinum or platinum alloy nanoparticles will be discussed. New developments in synthesis protocols enabling “green chemistry” scalable solutions will be discussed.

References:

T. Asset and P. Atanassov, Joule, 2020, 4, 33.

Y. Huang, Y. Chen, M. Xu, T. Asset, P. Tieu, A. Gili, D.S. Kulkarni, V. de Andrade, F. De Carlo, H.S. Barnard, A. Doran, D. Parkinson, X. Pan, P. Atanassov, and I.V. Zenyuk, Materials Today, 47 (2021) 53-68

Y. Chen, Y. Huang, M. Xu, T. Asset, X. Yan, K. Artyushkova, M. Kodali, E. Murphy, A. Ly, X. Pan, I.V. Zenyuk, and P. Atanassov, Materials Today, 53 (2022) 58-70
Elucidating Catalyst Degradation Mechanism of Non-Precious Metal Catalyst for Oxygen Reduction Reaction Using Electrochemical Tip-Enhanced Raman Spectroscopy
Authors: Chen Zhu , Jiang Song , Kang Gyeongwon , Schatz George
Published: September 2023

Identifying the chemical state and structure of electrocatalysts is critical for understanding the catalytic and degradation mechanisms in the oxygen reduction reaction. Tip-enhanced Raman spectroscopy (TERS) combines plasmonic enhancement of Raman scattering from surfaces and the high spatial resolution of scanning probe techniques to provide in situ chemical analysis at the nanoscale. We have employed electrochemical TERS (EC-TERS) to investigate the oxygen reduction reaction (ORR) catalyzed by transition metal phthalocyanine molecules under electrochemical conditions. Using EC-TERS, we have observed that the iron (II) phthalocyanine undergoes reversible and irreversible transformations during ORR. Combining Raman calculation and EC-TERS, we have identified that the irreversible transformation, which resulted in the formation of H2-phthalocyanine, is the primary degradation mechanism for iron (II) phthalocyanine in ORR. We have also extended the EC-TERS technique to investigate cobalt (II) phthalocyanine and identified its chemical state during ORR using the EC-TERS technique with multiple wavelength excitation.
(Invited) Electrocatalysis and Surface Chemistry in Lithium Sulfur Batteries
Authors: Wang Hailiang
Published: September 2023

This talk will focus on the application of electrocatalysis and surface/interface chemistry to solve the cycling stability problem of lithium sulfur batteries, which are a type of future high energy rechargeable battery that can deliver a few times more energy than the prevalent lithium ion batteries of the same mass. One critical problem is the adsorption of lithium polysulfides, the key reaction intermediates that control the electrochemical performance of the sulfur cathode. We find that 3d transition metal oxides effectively bind polysulfides via oxygen-lithium or metal-sulfur bonding, whereas metal phosphides and chalcogenides only do so with their oxidized surfaces. When the electrolyte/sulfur ratio is lowered for even higher energy density (lean electrolyte condition), we discover that catalysis is needed to overcome the potential limiting reaction barrier associated with the conversion of reaction intermediates. With this understanding, we have developed high capacity sulfur cathode materials achieving hundreds of stable charging-discharging cycles. This surface/interface chemistry approach also enables us to analyze the cycling behavior of the lithium/sodium metal anode and to develop electrode/electrolyte interphases for improving the charging-discharging efficiency and cycling stability, including lithium metal electrodes working with solid-state electrolyte.
Species Crossover in Electrochemical CO2 Reduction
Authors: Lou Kun , Hu Leiming , Wrubel Jacob A , Neyerlin K.C.
Published: September 2023

Catalyst studies have improved the overall CO2R (electrochemical CO2 reduction) faraday efficiency (FE)1, however, the experimental FE can be deteriorated by product crossover through the membrane in a practical electrochemical CO2R cell. The CO2R product molecules generated at the cathode are subject to oxidation at the anode if they permeate through the membrane, thus decreasing the practical CO2R product collection. The product loss at the anode also poses a challenge for quantification and study of the crossover behavior2–4. In this work, we will present experimental designs that effectively overcome the oxidation at the anode to reveal the CO2R product crossover.

The CO2R product crossover can be driven by electromigration and the concentration gradient across the membrane. Although the electromigration plays a significant role based on the current density of CO2R operation, the later can be varied by membrane design parameters. The membrane thickness and non-ionic reinforcement layers can effectively change the permeability of various CO2R product species. The CO2R product crossover measurements of commercially available anion exchange membranes will be presented.

From a fundamental perspective, CO2R product crossover is a reflection of membrane selectivity. We also extend the component study to the cell level where parameters like electrolyte concentration/conductivity and electrolyte/CO2 flow rate also affect the crossover. The species other than products in CO2R can have impact on both catalyst performance and crossover. We will discuss the crossover behavior in our standard CO2R setup5,6. Overall, we aim to address the CO2R product crossover by bridging the fundamental study of a component and CO2R integration efforts at NREL.

Ge, L. et al. Electrochemical CO2 reduction in membrane-electrode assemblies. Chem
8, 663–692 (2022).

McCallum, C. et al. Reducing the crossover of carbonate and liquid products during carbon dioxide electroreduction. Cell Rep. Phys. Sci.
2, 100522 (2021).

Wang, N. et al. Suppressing the liquid product crossover in electrochemical CO2 reduction. SmartMat
2, 12–16 (2021).

Zhang, J., Luo, W. & Züttel, A. Crossover of liquid products from electrochemical CO2 reduction through gas diffusion electrode and anion exchange membrane. J. Catal.
385, 140–145 (2020).

Chen, Y. et al. A Robust, Scalable Platform for the Electrochemical Conversion of CO2 to Formate: Identifying Pathways to Higher Energy Efficiencies. ACS Energy Lett.
5, 1825–1833 (2020).

Chen, Y. et al. The effect of catholyte and catalyst layer binders on CO2 electroreduction selectivity. Chem Catal.
2, 400–421 (2022).
Elucidating the Mechanisms of Oxygen Depolarized Cathode Catalyst Degradation
Authors: Yang Kevin , Kodali Mounika , Smeltz Andrew , Mukerjee Sanjeev
Published: September 2023

Fe-N-C has shown to be a viable low-cost, PGM-free catalyst to replace RhS/C for oxygen-depolarized cathode applications. Though it possesses high intrinsic ORR activity and relatively good immunity towards chloride ion poisoning, further studies must be conducted to explore the degradation pathways of Fe-N-C in a wide pH range to realize its capabilities in concentrated hydrochloric acid and Chlor-alkali electrolysis1.

Moreover, Fe-N-C has been shown to maintain performance after being in operation for more than one hour with three uncontrolled shutdowns, nearly matching RhS/C at a current density of 0.5 A/cm2 with a cell potential of 1.38 V1. Thus, we will perform long-term durability tests under Raman and X-ray absorption spectroscopy (XAS). Furthermore, a single electrochemical flow cell will be designed for both spectrochemical methods to characterize the interaction between the catalyst and the formation of products during the uncontrolled shutdown. Specifically, Raman spectroscopy will be utilized to detect changes in the catalyst structure if any Fe-N4 bonds are broken or changed due to chloride anions upon shutdown. XAS-Fe edge will be employed to elucidate the formation of Fe-Cl bonds due to crossover anions during operation and when the cell is removed from the power supply. By determining the degradation pathways or lack of, we can truly assess the viability of Fe-N-C as a replacement for RhS/C in hydrochloric acid and Chlor-alkali electrolysis. These techniques provide a platform to reduce experimental uncertainty and gain further insight into the degradation of both catalyst and membrane-electrode assembly performance.

References

[1] Jingkun Li, Qingying Jia, Shraboni Ghoshal, Wentao Liang, and Sanjeev Mukerjee Langmuir
2017
33 (37), 9246-9253
Towards Improved Cold-Start Capability of PEFCs: Patterned Gas Diffusion Layers
Authors: Liu Wenmei , Lee Jongmin , Schmidt Thomas J. , Boillat Pierre
Published: September 2023

Polymer electrolyte fuel cells (PEFCs) are electrochemical energy converters with high efficiency and zero pollutant emissions. The unassisted cold-start of PEFCs at -30 °C is one of the major challenges for automotive applications due to the freezing of supercooled water generated by the cathodic oxygen reduction reaction (ORR). Once triggered by the nucleus in cathode gas diffusion layers (GDLs), ice propagates through the active area, leading to oxidant gas blockage and cold-start failure1.

The cold-start capability of PEFCs can be improved by preventing ice propagation, especially in GDLs. In our previous work2,3, after the GDLs were segmented by polytetrafluoroethylene (PTFE) into two regions, the PEFC kept operating for another 30 minutes after the first freezing event in one region. Nevertheless, the PTFE barrier limited the active area as well as the heat and electric conductivity of PEFCs. In contrast, patterned GDLs allow water cluster separation without the abovementioned limitations. The improvement of water management and cell performance under technical operating conditions was demonstrated4. Yet, the cold-start capability with patterned GDL needs to be further investigated.

This work studies the effect of patterned GDLs on the water-ice phase transition and cold-start capability of PEFCs. First, non-isothermal differential scanning calorimetry (DSC) measurements were conducted to determine the onset freezing temperature distribution of supercooled water in patterned GDLs, taking into account various properties such as coating load and pattern size. It was observed that independent freezing events occurred in patterned GDLs in all cycles, as several freezing/exothermic peaks can be seen in Figure
1b. In contrast, ice propagated immediately in untreated GDL, as only one freezing peak was observed in all cycles (Figure 1d). By computing the integral of the heat flux curve, we obtained the corresponding cumulative icing ratio over 60 cycles, as presented in Figures 1a and 1c. The effective prevention of ice propagation is only observed in patterned GDLs. Second, to assess the cold-start capability, statistical isothermal cold-start measurements were conducted using a 4.4 cm2 differential cell, with the cell temperature held at -7.5 °C, -10 °C, -15 °C, and 20 °C. In summary, nonconcurrent freezing events in patterned GDLs indicate that the use of patterned GDLs significantly improved the cold-start capability of PEFCs under isothermal subfreezing conditions.

The findings of this work enhance the understanding of the cold-start dependence on the GDL and contribute to the development of unassisted freeze-start technology for PEFCs and the expansion of PEFCs applications.

Figure 1
Evaluation of Phosphoric Acid Leaching in PBI Membranes for High-Temperature PEM Fuel Cells By Ex-Situ and Operando Characterization Methods
Authors: Chen Jianuo , Perez-Page Maria , Holmes Stuart
Published: September 2023

High-Temperature PEM Fuel Cells (HT-PEMFCs) based on PA-doped-PBI membranes have become a promising sustainable power generation system due to their high proton conductivity, high tolerance to hydrogen impurities, thermal stability and high utilization of waste heat [1]. Unlike low-temperature fuel cells based on perfluorosulfonic acid polymers (Nafion), HT-PEMFCs do not need water to act as a proton conductor, instead a hydrogen-bonded matrix is established between PA and PBI, negating the need for humidification in the system. As a result, the proton conductivity of the PA-doped PBI membrane is related to its PA loading. When PA is added to the PBI membrane, each PBI repeat unit can only bond with two PA molecules, leading to higher doping levels due to PA distributed in the PBI matrix in a free state. This extra PA leaches from the membrane to the electrodes during cell operation [2] resulting in several problems, the reduction of the proton conductivity of the membrane, blocking of the pathway for the gases to and from catalytically active sites and drive the migration of Pt-based catalyst, resulting in an increase in both mass and charge transfer resistances [3].

To prevent acid leaching out of the membrane and the subsequent negative effects on the fuel cell performance, Single Layer Graphene (SLG) has been incorporated as barrier material between the PEM and cathode/anode. SLG acts as sieve material to block all atoms and molecules from passing through with the exception of protons improving the performance and the long-term of the HT-PEMFC [4]. However, although the electrochemical characterization proves this enhancement, the mechanism of the phosphoric acid migration and the effect of the SLG on the leaching is still unknown.

In this work, different techniques, X-rat CT [4, 5]y, Raman microscopy [5] and µ-XRF, have been used to evaluate the PA leaching under ex-situ and in-operando conditions to study the mechanism of the migration of the acid and to prove that the electrochemical improvement is due to SLG has a positive effect in the HT-PEMFC.

References:

[1] Y.-L. Ma, et al., Journal of the Electrochemical Society 151(1) (2003) A8.

[2] S. Galbiati, et. al., International journal of hydrogen energy 38(15) (2013) 6469-6480.

[3] S.H. Eberhardt,et al., Journal of the Electrochemical Society 162(3) (2015) F310.

[4] Chen, J, et al. Nano Energy, 93 (2022) 106829

[5] Bailey, J, et al. Journal of Power Sources 509 (2021) 230347.

Figure 1
Boron-Activating Ruthenium from Organic-Free Synthesis Process: A Hydrogen Oxidation Reaction Catalyst for Anion Exchange Membrane Fuel Cells
Authors: Cui Yingdan , Wang Yian , Liu Guimei , Yang Fei , Zhu Shangqian , Wu Hsiwen , Mustain William Earl , Shao Minhua
Published: September 2023

Using fossil fuels, power generation is always accompanied by environmental pollution. However, hydrogen-oxygen fuel cells, using H2 generated from renewable energy, can provide electricity with zero emissions, meeting the significant demands. Proton exchange membrane fuel cells (PEMFCs), though commercialized, are hindered by the high cost due to relying on expensive Pt. By contrast, as the potential alternative, anion exchange membrane fuel cells (AEMFCs), have attracted more and more attention as they can provide the benefit of using low-cost cathode catalysts while still having high power density. Although the oxygen reduction reaction (ORR) on the cathode can be well achieved by platinum group metal (PGM)-free catalysts in an alkaline environment, the high loading of Pt for the anode is still needed for high power output caused by the sluggish hydrogen oxidation reaction (HOR) kinetics. As the cheapest PGM, Ru with lower HOR activity is often added as an activity promoter to reduce the Pt loading. Recently, more efforts have been put into using exclusively Ru as the main catalysis active site, but the synthesis methods are often complex and involve toxic organics.

In this project, boron-activated Ru supported on carbon was developed for HOR catalysis in alkaline media. The B-Ru/C was synthesized by a simple organic-free method, making it possibly attractive for industrial application. This method adopted water as the only solvent and boric acid as the boron source to avoid the toxic problem and the tedious removal step of organics. It produced uniformly dispersed Ru nanoparticles in smaller particle sizes with a boron-rich environment verified by TEM and STEM images. Compared to Ru/C or Ru/BC, B-Ru/C not only has a higher electrochemical active surface area (ECSA) but also reached a much higher ECSA-normalized exchange current density which means boron does promote the activity of Ru. From the XPS spectra, the more significant peak shifts of Ru3p and B1s in B-Ru/C relative to Ru/C and BC indicate that the boron-ruthenium interaction is more robust in B-Ru/C than in Ru/BC. A theoretical simulation was conducted further to understand the mechanism of the HOR activity enhancement. From an electrochemical perspective, the B-Ru/C had a very high exchange current density in ex-situ tests and was also studied as an anode in operating AEMFCs. We believe this cost-effective Pt-free HOR catalyst with excellent performance prepared through an organic-free process can contribute to the industrial application of AEMFCs in the future.

Acknowledgments

This work is supported by the Research Grant Council (HKUST C6011-20G).
One-Dimensional, First-Row Transition Metal, Core-Shell Architectures as Multifunctional Electrocatalysts in Alkaline and Acidic Conditions
Authors: Koenigsmann Christopher
Published: September 2023

The development of practical electrocatalysts for fuel cells, electrochemical sensors, and batteries requires nanostructured architectures with high catalytic activity and good long-term durability. It is also essential that they have very low or even no platinum content. There has also been a recent emphasis on the importance of designing multifunctional catalysts with the ability to efficiently catalyze a wide-range of electrochemical reactions in both acidic and alkaline media. In light of these requirements, we have developed a solution-based synthetic method to prepare core-shell nanowires consisting of inexpensive and abundant first-row transition metals coated with precious metal shells. The core-shell motif enables a substantial quantity of platinum to be removed from the catalytically inactive core of the material, while also resulting in the ability to tune the activity of platinum through electronic and structural interactions between the two metals. The as-synthesized core-shell nanowires have a complex surface structure that brings together metal oxide and precious metal active sites that are active toward OER and result in a significant reduction in the overpotential for OER when compared with pure Pt and Co nanowires. In addition, we have developed an electrochemical process that selectively removes the metal oxide from the surface of the nanowires enabling the catalysts to be activated toward SOM oxidation in acidic media and ORR in alkaline media. For example, the activated core-shell nanowires display a 1.5-fold and a 4-fold increase in the specific activity and mass activity of methanol oxidation, respectively, relative to a pure platinum nanowire.
(Invited) Size, Composition Effects and Active State Formation of Nanostructured Cobalt and Iron-Cobalt Oxide-Based Catalysts during Oxygen Evolution Reaction
Authors: Roldan Cuenya Beatriz
Published: September 2023

The efficient water electrolysis is a key technology to establish a CO2-neutral, electrochemical (green) hydrogen production. Nonetheless, the electrocatalysts’ near-surface structure during the anodic oxygen evolution reaction (OER) is still largely unknown, which hampers knowledge-driven optimization. Here, we provide quantitative near-surface structural insights into oxygen-evolving CoOX(OH)Y nanoparticles by tracking their size-dependent catalytic activity down to 1 nm and their structural adaptation to OER conditions combining operando X-ray absorption spectroscopy and density functional theory calculations. We uncover a superior intrinsic OER activity of sub-5 nm nanoparticles and a size-dependent oxidation leading to a near-surface Co-O bond contraction and charge redistribution during OER.

I will also report on the role of Fe in the performance of Co-oxide-based electrocalysts. By comparing epitaxial Co3O4(111), Co1+δFe2-δO4(111) (|δ|<=0.2), and Fe3O4(111) thin film electrocatalysts combining quasi in-situ preparation and characterization in ultra-high vacuum (UHV) with electrochemistry experiments. Interestingly, Co1+δFe2-δ O4(111) was found to be up to five times more active than Co3O4(111) and Fe3O4(111) with the activity depending acutely on the Co/Fe concentration ratio. Under OER conditions, all three oxides are covered by oxyhydroxide but the characteristics of this overlayer, including its thickness, stability, structural and chemical evolution was found to depend on the Fe content.
High-Throughput Activity Screening of Oxygen Reduction and Oxygen Evolution Catalysts
Authors: Park Jaehyung , Myers Deborah J.
Published: September 2023

High-throughput techniques are being actively studied to expedite the evaluation of the electrocatalytic activity of newly developed materials. These techniques include the use of optical sensing or electrochemical array cells in stagnant or hydrodynamic aqueous electrolytes [1-2]. A new high-throughput electrochemical cell has been developed utilizing multiple glassy carbon working electrodes with dimensions comparable to those of a conventional ring-disk electrode (RDE) that are inserted into a channel flow cell (Figure 1) comprised of two PEEK blocks separated by a gasket that defines the electrolyte channel depth. This cell enables evaluation of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) activity as a function of the potential of multiple catalyst samples simultaneously that are deposited on the glassy carbon electrodes using standard methods used for RDE electrodes (e.g., using a hand-held micropipette). As shown in Figure 1, a common reference electrode is located in the lower cell block across an electrolyte channel from the working electrodes and a common counter electrode is located in the electrolyte outlet. Electrolyte flow has been simulated to ensure that the electrolyte is evenly distributed throughout the shallow flow channel with uniform laminar electrolyte flow and identical flow rate for all working electrodes. The new cell is coupled with a Bio-logic multichannel Potentiostat (VSP) that allows the use of multiple working electrodes simultaneously with a common counter electrode and common reference electrode. The catalyst activity and stability results obtained with the new cell have been verified by comparison with RDE measurements for the same catalysts.

Acknowledgments

This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

References

[1] Gregoire, J.M., et al., Scanning droplet cell for high throughput electrochemical and photoelectrochemical measurements. Review of Scientific Instruments, 2013. 84(2).

[2] Reddington, E., et al., Combinatorial electrochemistry: A highly parallel, optical screening method for discovery of better electrocatalysts. Science, 1998. 280(5370): p. 1735-1737.

Figure 1
Hydrogen Reconversion from Ammonia through Anion Exchange Membrane Electrolysis
Authors: Kanaan Riham , Affonso Nóbrega Pedro Henrique , Beauger Christian
Published: September 2023

Nitrogen-based compounds, especially ammonia, is a promising alternative for the storage and transport of renewable hydrogen over long distances [1]. Considering ammonia as a hydrogen carrier will require studying the conversion (ammonia to hydrogen) and reconversion steps (hydrogen to ammonia). The reconversion of ammonia can take place through electrolysis under alkaline conditions [2] and needs the development of more efficient catalysts. For this, we started studying the electro-oxidation of ammonia in an anion exchange membrane electrolyser over platinum-based and PGM free electrodes with KOH as electrolyte. We have prepared several catalysts, carbon supported platinum, platinum-iridium, and nickel nanoparticles using the polyol technique. Commercial carbon supported platinum nanoparticles was used as catalyst for the cathodes. Catalyst coated substrates (CCS) were then prepared by spraying a catalytic ink over stainless-steel fiber paper for the anode side. The formulation of the ink requires optimizing parameters such as the type of ionomer (nafion, sustanion) and the ratio of ionomer to carbon. Anodes obtained have been assembled with anion exchange membranes and commercial cathodes for ammonia electro-oxidation in single cell. We have compared the performance of these different membrane electrodes assemblies (MEAs) to commercially available ones integrating nickel-iron-cobalt based anodes. The performance of MEAs was analyzed based on polarization curves, cyclic voltammograms and impedance spectroscopy data. Different testing conditions were investigated by varying the ammonia concentration from 0.1 to 1 M, the temperature from 25 °C to 60°C, and the KOH concentration from 0.1 to 5 M.

References:

[1] N. Morlanés et al., “A technological roadmap to the ammonia energy economy: Current state and missing technologies,” Chem. Eng. J., vol. 408, 2021, doi: 10.1016/j.cej.2020.127310.

[2] N. M. Adli, H. Zhang, S. Mukherjee, and G. Wu, “Review—Ammonia Oxidation Electrocatalysis for Hydrogen Generation and Fuel Cells,” Journal of the Electrochemical Society, vol. 165, no. 15. pp. J3130–J3147, 2018, doi: 10.1149/2.0191815jes.
Mechanical Properties of PEMFC Electrodes According to Fabrication Methods
Authors: Ahn Kwang Ho , Kim Taek-Soo
Published: September 2023

Electrodes in a polymer electrolyte membrane fuel cell (PEMFC) are the crucial element performing electrochemical reactions and are the most vulnerable mechanically. Various operating conditions (freeze-thaw, start-up, shut down) generate buckling, cracks, and delamination in electrodes. These mechanical failures not only directly affect the performance of the PEMFC cell but also act as a fatal factor in shortening the lifespan. Therefore, understanding and improving the mechanical properties of electrodes is essential for designing high-durability PEMFCs. Furthermore, the fabrication method of electrodes is a factor that causes not only performance but also distinct mechanical property differences since it determines their internal structure and surface characteristics. However, evaluating the mechanical properties of electrodes has been challenging because they are fragile and hard to separate from substrates. Therefore, this study evaluated the intrinsic mechanical behaviors of the electrodes according to fabrication methods via a free-standing tensile test. The effect of fabrication methods was analyzed for blade coating and spray coating methods used universally from industry to laboratory. The difference in mechanical properties between the two methods was identified by analyzing the internal structure and distribution of ionomer agglomerate. For blade-coated electrodes, modulus (372.5 MPa) and elongation (2.44%) were 2-2.7 times higher than spray-coated electrodes (172.9 MPa,0.9%). The difference in mechanical properties originated from the electrodes’ surface and internal structures. Blade-coated electrodes were composed of smaller pores and volume than the spray coating using FIB-SEM. The modulus ratio according to the internal structure through finite element analysis (using ABAQUS software) was consistent with the actual experimental value. In addition, blade-coated electrodes have high elongation and strength because they enable uniform stress transmission with a smooth surface and uniform ionomer binder distribution (analyzed by HAADF-STEM and EDS). This study contributes to a better understanding of the mechanical properties of electrodes according to the fabrication methods and provides guidelines for mechanical improvement.

Figure 1
Impact of Aluminum Modification on the Dielectric Properties of Graphene Oxide Membrane: Different Al Source
Authors: Stehle Yijing Yin
Published: September 2023

The high dielectric constant and low dielectric loss of Graphene oxide (GO) membranes made them good dielectric separator membranes for both dielectric capacitors and planar micro-supercapacitors. A GO membrane, which is GO sheets laminated in the form of “brick-and-mortar” stacking configuration, is an orthotropic material. This means that GO will have different dielectric properties parallel to the GO sheets (in-plane) and perpendicular to the GO sheets (through-plane). Tailoring strategies applied to the membrane will impact its in-plane and through-plane dielectric property differently. Better understanding and ability to tailor the dielectric properties of the GO membrane is crucial for its dielectric applications. The Al3+ has the potential to interact with OFGs of GO sheets on the edge (carboxyl groups), which mainly impacts in-plane properties, or on the basal plane (hydroxyl, carbonyl, and carboxyl groups), which mainly impacts through-plane properties. The uneven interaction of Al3+ with the functional group on the edge and basal plane of GO sheets could lead to different modification effects of the in-plane and through-plane dielectric properties of the GO membrane. It was reported before that Al3+ from different sources will bond with the GO sheet differently, thus it has the potential to impact the through-plane and in-plane dielectric properties of the GO membrane differently. Here, the Al3+-modification to the GO membrane from three different Al source, Al metal foil, chloride salt, and alumina, were applied to tailor the through-plane and in-plane dielectric properties of as-fabricated GO membranes in the frequency range from 0.01 Hz to 105 Hz. Plane-to-plane and edge-to-edge coordination of Al3+ with the functional group on the basal plane or edge of the GO sheets were proposed to understand the different impact of Al3+ on the through-plane and in-plane dielectric properties of the GO membranes. This study provides a facile route to impact the dielectric property of GO membrane through interaction with the oxygenated functional group on the edge and basal plane of the GO sheet, and demonstrate the possibility of designing dielectric GO membrane with controllable dielectric performance.
Catalyst Layers with Blended Ionomer Using Short- and Long-Side Chain Dispersions
Authors: Kim Beom-Seok , Park Jong-Hyeok , Chae Soryong , Park Jin Soo
Published: September 2023

Hydrogen-based energy conversion technology is based on the membrane electrode assembly (MEA) comprising of an electrolyte and a pair of catalyst layers. It should have high efficiency and allow dynamic operation at low temperature. Electrochemical reactions for hydrogen oxidation reaction and oxygen reduction reaction occur in the catalyst layers in the MEA. Catalyst layers for MEA is prepared by catalyst inks comprising of electrocatalyst, ionomer dispersion and additional solvents. Ionomers plays an important roles for the formation of porous structure of catalyst layer for transportation of gas and reactant and for the ionic conduction. The ionomers are divided that long side chain (LSC) and short side chain (SSC) depending on the length of side chain. Long side chain (LSC) ionomers shows high performance at low temperatures and high humidity, while short side chain (SSC) ionomers shows high performance at high temperatures and low humidity. It has been reported that the properties of ionomer dispersions substantially influence the performance of catalyst layers due to the different interaction between electrocatalysts and ionomer. In this study, to investigate the effect of the properties of ionomer, various contents of blended ionomer dispersions were prepared. Properties of single and blended ionomers were characterized using catalysts layers in terms of I-V polarization, cyclic voltammetry, electrochemical impedance spectroscopy and microscopic evaluation such as porosimetry.

Acknowledgment

This research was supported in part by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning(NRF-2019M3E6A1063677) and by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520).
Valorization of Naturally Abundant Low-Value Peat into Highly Active Non-Platinum Group Metal Oxygen Reduction Catalysts
Authors: Teppor Patrick , Jäger Rutha , Nerut Jaak , Koppel Miriam , Aruväli Jaan , Volobujeva Olga , Lust Enn
Published: September 2023

As society continues to adopt an increasingly eco-friendly stance, the efficient usage of natural resources needs to be maximised. For instance, energy obtained from biomass covers roughly a tenth of the global demand. This biomass can instead be used as a carbon source to produce value-added materials such as tnon-platinum group metal (NPGM) oxygen reduction catalysts, which are desperately sought after as global demand for fuel cells continues to rise [1,2]. For example, peat is an extremely abundant biomass material in Estonia covering roughly 20% of the country [3]. Herein, the viability of using peat-based catalysts as oxygen reduction catalysts in alkaline media was investigated.

The peat sourced from a local peatland was processed and modified with inexpensive iron and nitrogen precursors through the common double-pyrolysis and acid washing synthesis procedure into peat-based NPGM catalysts. Additionally, zinc chloride was used as a pore forming agent. The influence of several principal synthesis parameters, e.g. precursor compound type and amount, on the physical and electrochemical properties of these materials was investigated using various characterization methods.

The NPGM catalysts obtained from naturally abundant peat were highly microporous systems due to the inclusion of zinc chloride in the synthesis mixture. High onset (~0.93 V vs RHE) and half-wave potential (~0.83 V vs RHE) values were obtained for most of the materials in activity screening experiments conducted with a rotating disc electrode setup using 0.1 M KOH. However, using an excessive amount of the nitrogen precursor in the synthesis proved to be detrimental to the obtained activity. The high activity of the obtained peat-derived catalysts was further investigated in a rotating ring disc electrode setup where the influence of the studied synthesis parameters on the oxygen reduction reaction selectivity was more evident.

Acknowledgments

This work was supported by the EU through the European Regional Development Fund under projects TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), NAMUR “Nanomaterials - research and applications” (3.2.0304.12-0397), NAMUR+ core facility funded by the Estonian Research Council (TT 13), PRG676 “Development of express analysis methods for micro-mesoporous materials for Estonian peat derived carbon supercapacitors” (01.01.2020–31.12.2024) and PUT1581 (1.01.2017–31.12.2020).

References

F. Jaouen, D. Jones, N. Coutard, V. Artero, P. Strasser, A. Kucernak, Johns. Matthey Technol Rev. 2018, 62, 231.

E4tech, 2022, The Fuel Cell Industry Review 2021.

M. Orru, H. Orru, Est. J. Earth Sci. 2008, 57, 87.
First-Row Transition Metal Nanowires As Electrocatalysts for the Oxygen Reduction and Oxygen Evolution Reactions
Authors: Doucette Brianna , Koenigsmann Christopher
Published: September 2023

Platinum is an effective catalyst for the electrochemical reactions in fuel cells and sensors but its high cost and low abundance has prevented the wide-spread commercial use of these devices. As a result, it is critical to develop electrocatalysts with other abundant and catalytically active transition metals. First-row transition metals represent a promising alternative because of their low cost and high abundance, however they are not sufficiently stable to act as catalysts in acidic media. Recent advancements in membrane technology have enabled the creation of electrochemical devices that can operate in alkaline conditions, where first row transition metals and their oxides are stable. In this project, we use a solution-based synthetic method to prepare metal nanowires consisting of two or more first-row transition metals, wherein the composition can be easily and predictably controlled. The nanowires are characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The resulting nanowires are catalytically active toward the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in alkaline media. Our results indicate that the catalytic activity is highly dependent on the composition of the nanowires and the activity can be tuned to increase the ORR activity significantly beyond that of nanowires consisting of only a single element. In addition, Pt-free transition metal alloy nanowires display significantly enhanced performance beyond that of pure Pt when used as catalysts for OER.
(Invited) Understanding Trends for Electrocatalytic and Catalytic Nitrate Reduction
Authors: Singh Nirala , Goldsmith Bryan R.
Published: September 2023

Fixation of nitrogen such as for ammonia production through the Haber-Bosch process is imperative for feeding the world’s population, but is causing an imbalance in the nitrogen cycle as oxidized nitrogen species such as nitrate builds up. This build up of nitrate pollution from agricultural and industrial waste poses an immediate threat to environmental and human health. While separation of this nitrate is a method to produce clean water, it does not chemically address the issue of oxidized nitrate. In addition, it does not form nitrogen species in a valuable form. One method is to use nitrate waste as a feedstock for production of fertilizers such as ammonia or ammonium nitrate. In this work we discuss the use of electrocatalysis to convert nitrate to ammonia, where renewable electricity can be used to drive the reaction, minimizing carbon dioxide emissions from current methods to produce ammonia. In this talk we will discuss (1) trends in electrocatalytic nitrate reduction, (2) similarities and differences in electrocatalytic nitrate reduction and catalytic nitrate reduction (i.e., using molecular H2 rather than an applied potential), and (3) practical challenges in systems to commercially convert nitrate. Through the use of kinetic studies, in situ spectroscopy, microkinetic modeling, and density functional theory calculations, we show how the adsorption energetics of nitrate and hydrogen are descriptors for nitrate reduction on metals and alloy surfaces. We will discuss the importance of operando spectroscopy to understand the catalyst under reaction conditions. We will show how alloying Pt with Ru to increase the nitrate adsorption energy shows an increase in the rates of nitrate reduction at low Ru content. We will also show that the nitrate reduction rate is decreased when the Ru content is too high, because nitrate binds to the catalyst too strongly. We will compare the electrocatalytic results to thermal nitrate catalytic and show that while there are numerous similarities between electrocatalysis and thermal catalysis, there are also factors unique to electrocatalysis that impact the rate of reaction. These differences motivate a greater understanding of electrochemical steps and the effect of the applied potential, solvent, and ions. We will discuss how the best performing catalysts in batch systems translate to flow reactors more amenable to commercialized processes and other challenges in realistic nitrate streams containing potential catalyst poisons such as chlorides.
(Invited) Electrocatalytic Synthesis of Ammonia and Urea
Authors: Costa Figueiredo Marta
Published: September 2023

Many industrial chemical processes involve a high-energy demand (often still derived from fossil fuels), toxic reactants, and the production of high amounts of waste. A good example is the production of ammonia and urea via the Haber-Bosh and Bosch-Meiser processes, respectively. These two nitrogen-containing compounds are mostly used in the fertilizer industry and with the increase in the world population, their production is expected to increase. Additionally, NH3 itself is responsible for 2% of the annual world energy consumption and has a carbon footprint of 1.5 tons of CO2 per ton of NH3 [1]. Therefore, the development of more efficient, less hazardous technologies that are based on renewable energies to produce valuable N- containing compounds, has become one of the most challenging topics for chemical synthesis. By using electrochemical methods for the synthesis of ammonia and urea, toxic and dangerous chemicals can be replaced with clean electrons. Furthermore, the efficiency and selectivity of the reactions can be tuned by the applied potential, and more importantly, the energy used can come from renewable sources like wind or solar [2].

In this talk, I will show the recent advances from our group in the development of catalysts for the electrocatalytic synthesis of ammonia and urea (as for example Cu2O and CuRh) and the reaction mechanism when using nitrate as a substrate [3].

References:

[1] S. Giddey, et al, Int. J. Hydrogen Energy, 38 (2013) 14576–14594

[2] Frontana-Uribe, B. A. et al; Green Chem. 2010, 12 (12) 2099– 2119

[3] D. Anastasiadou, Y. van Beek, M. C. Figueiredo, in preparation.
(Invited) Lithium-Mediated Ammonia Synthesis at Ambient Conditions
Authors: Manthiram Karthish
Published: September 2023

The Haber Bosch process has served as the dominant method of synthesizing ammonia over the last century. Ammonia produced through this route leads to a stoichiometric carbon dioxide footprint and also involves harsh conditions which limit modularity of the process. We are developing a continuous lithium-mediated approach through which nitrogen can be fixed at ambient conditions while eliminating the carbon dioxide footprint. We have elucidated the reaction network through which ammonia synthesis occurs in competition with hydrogen evolution. The coupling of kinetics and transport has a significant influence on the rates of ammonia synthesis, providing a means to improve selectivity of nitrogen fixation. By creating gas diffusion electrodes compatible with non-aqueous solvents, we have achieved high rates of ammonia synthesis at atmospheric pressure. The solid electrolyte interphase is found to be controlling of lithium-mediated nitrogen reduction rates and selectivities, as understood through cryogenic transmission electron microscopy.
Selective Separation between Ammonium and Potassium in a Membrane-Separated Magnesium-Based Electrochemical Process
Authors: Akbari Amir , Logan Bruce E. , Greenlee Lauren F
Published: September 2023

Increasing trends in global food and water demands alongside growing environmental concerns press the need for developing new wastewater management strategies. Modern wastewater treatment facilities should provide nutrient recovery and recycling, localized production capabilities, and low energy consumption. Magnesium-based electrochemical wastewater treatment processes are one technology option with the potential to address these needs by providing opportunities for simultaneous recovery of valuable resources from waste streams. In this system, phosphate and ammonium coprecipitate with the magnesium released from the sacrificial anode, producing struvite, NH4MgPO4, as a fertilizer. This technology also eliminates the disadvantages of the commonly used chemical precipitation method of struvite recovery, including magnesium salt dosing, and adding base to the system for pH control, due to in situ magnesium corrosion and hydroxide production at the magnesium anode surface.

In this presentation, we specifically focus on a membrane-separated electrochemical process with a solid magnesium electrode. A complex synthetic water matrix including key ions such as ammonium, potassium, and phosphorus with other background salts was made for the anodic chamber to simulate animal liquid manures. Sodium sulfate solution was used as the supporting electrolyte on the cathodic chamber. Two different cation exchange membranes (CEMs) were placed between the two compartments to separate the anolyte from the catholyte. All experiments were conducted under OCV (no external energy input), and ion concentrations in each chamber were tracked over time using ion chromatography to perform kinetic study. The produced precipitates from each experiment are collected and have been characterized by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) to identify the morphology and purity of the produced solid precipitates. Furthermore, X-ray diffraction (XRD) and Fourier-transform infrared spectrometry (FT-IR) were used to exactly identify the nature of the precipitates. Experimental results indicate that magnesium electrode corrosion under OCV in the anolyte will decrease ammonium separation through the CEM to the catholyte compared to potassium.