bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin Films Deposition and Energy Storage Density in Lead-Free Ferroelectric Ba1-XSrxTiO3 Thin Film Capacitors (x = 0.1, 0.3, 0.7)
Authors: Castillo Ivan , Mishra Karuna K. , Katiyar Ram S.
Published: July 2022

Structure, phonon, and energy storage density in Sr2+-substituted lead-free ferroelectric Ba1-xSrxTiO3 (BSTX) thin films (x = 0.1, 0.3, and 0.7) were prepared using RF sputtering technique, and investigated using x-ray diffraction, Raman, and ferroelectric polarization measurements as a function of temperature. The thin film is tetragonal for x = 0.1 with large c/a ratio. The tetragonal anisotropy (c/a ratio) decreases upon increasing x and that turns cubic for x = 0.7. All these structural and ferroelectric properties change due to change in the c/a ratio. Temperature dependent phonon spectra analyses (80-500 K) indicate decrease in tetragonal to cubic phase transition temperature upon x due to reduction in anisotropy. Overdamping of ~90 cm-1 E soft phonon mode along with a dramatic decrease of intensity of ~160 cm-1 A-phonon mode was observed around the tetragonal ferroelectric to cubic paraelectric phase (< 300 K). The energy storage densities of these thin film capacitors (metal-insulator-metal) were estimated from the measured polarization hysteresis loops and were compared. For x = 0.1, a larger energy storage density (Ure) of ~29 J/cm3 with efficiency of ~48 % was estimated at an applied voltage of 1.1 MV/cm. Nearly room temperature transition temperature Tc, larger dielectric constant and encouraging energy density values of our lead-free BSTX thin film capacitors suggest their possible application in high energy storage and pulse power technology. These results will be presented in detail in the ECS meetings.
Electrocatalytic Hydrogen Evolution on Ferroelectric Perovskite Heterostructures
Authors: Abbasi Pedram , Fenning David P , Pascal Tod A
Published: July 2022

Ferroelectric perovskites have recently attracted interest for a wide range of photocatalytic and electrochemical applications1 due to their intrinsic properties for light adsorption2, electron–hole pair separation3–5 and a hypothesized enhancement of catalytic activity by polarization switching6–8. However, most of the well-known ferroelectric perovskites e.g., BaTiO3 and Pb (Zr, Ti)O3 are known to have limited activity toward electrocatalytic reactions e.g. hydrogen evolution (HER) and water splitting.2 In this work, we demonstrate that introducing only a few mono layers of SrRuO3, a metallic oxide from perovskite family, can significantly enhance the catalytic activity of BaTiO3 toward HER. Using a combination of first principle DFT+U calculations and experiments on thin films grown by molecular beam epitaxy, we investigated the activity of heterostructures of different thicknesses toward HER in an alkaline electrolyte. Computational results show that the Gibbs free energy barrier of H* adsorption on one monolayer of SrRuO3 atop ferroelectric BaTiO3 is at least two times smaller than BaTiO3, depending on the adsorption site or the direction of ferroelectric polarization. In line with the findings from our DFT calculations, our experimental results confirm significantly higher current density and lower charge transfer resistance toward hydrogen evolution for SrRuO3/BaTiO3 heterostructures compared to bare BaTiO3 surfaces. Harnessing oxide heterostructures, as demonstrated here, opens the door to leveraging the unique properties of ferroelectrics as supports to promote electrocatalytic activity.
Controllable Synthesis of N-Doped Single-Layer Graphene-Coated Cobalt Nanoparticles for Efficient Oxygen Evolution
Authors: Park Gisang , Shin Choel-Hwan , Kang Joonhee , Lee Kug-Seung , Zhang Chunfei , Yu Jong-Sung
Published: July 2022

Controllable synthesis of graphene-coated metal nanoparticles (NPs) presents a big challenge because the shell thickness plays a key role in activity of these catalysts. Herein, we use silica as a radical sieve to grow graphene over cobalt NPs via chemical vapor deposition. As-prepared single-layer graphene-coated cobalt NPs with and without N doping (Co@N-SG and Co@SG) exhibit noticeable oxygen evolution reaction (OER) activity of 316 and 334 mV, respectively at a current density of 10 mA cm-2. Furthermore, a magnet-assisted binder-free Co@N-SG electrode illustrates much improved OER activity and stability over conventional binder-assisted counterparts, suggesting this as an effective way to overcome the recognized issues of high electron transfer resistance and poor adhesion of binder-based electrodes in practical applications. Interestingly, the graphene shell possesses varying defects and major OER active sites are found around the defects in the shell. On the other hand, separately isolated Co@SG with a defect-free shell, despite exhibiting a slightly lower initial activity, illustrates a much-improved durable OER performance. The underlying Co affects the electron density of the graphene shell through dipole interaction and the electron density is optimized for adsorption of reaction intermediates, hence accelerating OER performance. This work will provide new clues to design efficient and durable electrocatalysts with further enhanced OER performance.
(Keynote) New Fabrication Methods and Cathode Designs for Nanofiber Electrode Fuel Cell MEAs
Authors: Fan Xiaozong , Kang Nalae , Wycisk Ryszard , Pintauro Peter N.
Published: July 2022

When fuel cell electrodes are prepared by a conventional spraying or slot-die coating method, there is little or no control over the multi-scale organization of catalyst particles and polymer binder. Electrode features such as particle and binder interconnectivity, macro-porosity, and micro-porosity are difficult to control, but are critically important when high-performance nanocatalysts are used in fuel cell electrodes. Consequently, the excellent oxygen reduction reaction activity observed in rotating disk experiments with next-generation catalysts does not usually translate into improved hydrogen/air fuel cell performance when such catalysts are incorporated in membrane-electrode-assemblies (MEAs). Nanofiber electrospinning is an electrode fabrication technique that can address fuel cell electrode morphology issues for next-generation MEAs. As a commercial fabrication method, electrospinning is scalable, robust, and cost-effective, especially for the creation of non-woven mats of sub-micron-diameter polymer fibers. In addition to the production of polymer nanofibers, electrospinning can also be used to prepare particle/polymer fiber networks with intra- and inter-fiber porosity. Such fiber mats have been used as the electrode material in Li-ion batteries and H2/air proton-exchange membrane fuel cells [1-4].

In this talk, new experimental results will be presented on nanofiber mat electrode MEAs with Pt/C and Pt-alloy catalysts at cathode loadings of 0.1 and 0.2 mgPt/cm2. Methods for electrospinning fibers with different ionomer binders will be described and new methods of incorporating particle/polymer nanofibers into MEAs will be discussed, with a focus on: (a) developing techniques that can be used with existing roll-to-roll MEA processing lines and (b) varying the electrode morphology at the nano and micron scales. Hydrogen/air fuel cell power output and durability results will be contrasted with data obtained for conventional electrode designs.

Acknowledgments

This work was funded by the U.S. Department of Energy’s Fuel Cell Consortium for Performance and Durability, DOE-EERE FC-PAD Project DE-EE0007653.

References

1. C. Self, M. Naguib, R. E. Ruther, E. C. McRen, R. Wycisk,G. Liu, J. Nanda,and P. N. Pintauro, ChemSusChem, 10, 1823 – 1831 (2017).

2. Brodt, T. Han, N. Dale, E. Niangar, R. Wycisk, and P. Pintauro, J. Electrochem. Soc., 162, F84-F91 (2015).

3. Brodt, R. Wycisk, N. Dale, and P. Pintauro, J. Electrochem. Soc., 163, F401-F410 (2016).

4. J. Slack, C. Gumeci, N. Dale, J. Parrondo, N. Macauley, R. Mukundan, D. Cullen, B. Sneed, K. More, P.N. Pintauro, J. Electrochem. Soc., 166, F3202-F3209 (2019).
Local Gas-Phase Current Contributions Influenced By Porous Media Properties and Geometric Features in PEM Electrolysis
Authors: Lopata Joseph Steven , Weidner John W. , Cho Hyun-Seok , Shimpalee Sirivatch
Published: July 2022

To expand the commercialization of polymer electrolyte membrane water electrolysis (PEMWE) devices, it is beneficial to understand how cell geometry and porous media properties can impact cell performance. Due to the use of precious materials in PEMWE, particularly with an acidic membrane, it is cost-effective to simulate cell performance using a number of proposed designs to limit the number of prototypes. The use of three-dimensional (3-D) computational fluid dynamics (CFD) to simulate PEMWE 1 and alkaline 2 electrolysis operation has been previously demonstrated. This analysis sheds additional light on evaporation and the important role that it plays in facilitating the anodic and cathodic reactions.

Evaporation rates in porous media vary immensely with changes in water content, which has been demonstrated experimentally. Zenyuk et al. 3 used computed tomography to quantify the liquid saturation and gas/liquid interfacial area inside a carbon gas diffusion layer. They linked these variables to evaporation rate using the injection feed pressure to adjust the liquid saturation. The authors determined that evaporation rates in fuel cells increase dramatically with a decrease in water content. Evaporation rate depends on the specific interfacial area (SIA). Measurements in porous media, namely sands and soils, have shown an increase in SIA with a decrease in liquid saturation. One may notice from Ouni et al. 4 that the SIA is indirectly proportional to liquid saturation when the maximum SIA is small and somewhat inversely proportional when the SIA is large. The nature of these relationships is considered in the present CFD model for evaporation in the porous transport layer (PTL) and catalyst layer.

This study explores the effects of manifold geometry, flow field geometry, and properties such as PTL porosity, permeability, interfacial area, and anisotropy on local current density. Special emphasis is given to the contribution of the gas phase to the overall current and the conditions under which the gas-phase reaction is favorable. Changes in operating conditions, such as the feed temperature, feed rate, and cell potential, and how they impact local void fraction, relative humidity, and temperature at the anode are also investigated. The sensitivity of overall performance to material properties was found to be dependent on these operating conditions, primarily the anode inlet feed rate.

References

J. Lopata, Z. Kang, J. Young, G. Bender, J. W. Weidner, H-S. Cho, and S. Shimpalee, J. Electrochem. Soc., 168, 054518 (2021).

J. S. Lopata, S-G. Kang, H-S. Cho, C-H. Kim, J. W. Weidner, S. Shimpalee, Electrochim. Acta, 390, 138802 (2021).

I. V. Zenyuk, A. Lamibrac, J. Eller, D. Y. Parkinson, F. Marone, F. N. Büchi, and A. Weber, J. Phys. Chem. C, 120, 28701-28711 (2016).

A. E. Ouni, B. Guo, H. Zhong, M. L. Brusseau, Chemosphere, 263, 128193 (2021).

Figure 1
(Invited) Electrocatalysts of Complex Oxides for Water Splitting
Authors: Yang Hong
Published: July 2022

Low temperature electrolysis plays a critical role in our effort for energy generation with net zero or negative carbon impacts. This process produces green hydrogen through catalytic splitting of water and requires the development of highly active and, perhaps more importantly, highly stable electrocatalysts for oxygen evolution reaction (OER). This presentation will focus on examining the structure-property relationship of complex oxides that are made of AxByOz, where A and B can be a single metal cation or mixed cations, respectively. Depending the compositions, perovskite, pyrochlore, and Ruddlesden-Popper (RP) phase solids all have been found to be highly active for OER in either acid or base conditions. Noticeably, structurally defective solid catalysts such as those observed in defect perovskite (J. Am. Chem. Soc., 2014, 136, 14646-14649) often possess high activity. I will review some of the latest advancements in understanding the mechanisms of OER and discuss the new results on regulating the cation sites and oxygen defect chemistry for enhancing the bond-stability of key catalytic constituents and surface structures for OER performance.
(Invited) Core-shell-structured Electrocatalysts for Oxygen Evolution Reaction in Water Electrolysis
Authors: Chen Shuo
Published: July 2022

Oxyhydroxide is widely reported as a low-cost and intrinsically active electrocatalyst to expedite oxygen evolution reaction (OER) in water electrolysis. For applications, it is important to further improve its specific activity (activity per atomic site) and maximize its number of active sites. An effective approach to realize the above strategy is using core-shell structures, where the core can introduce profound nucleation sites and modify the electronic structure of surface oxyhydroxide. In this talk, I will present our recent studies of CoPx@FeOOH electrocatalysts for OER. The structures were synthesized on highly-conductive nickel foams by hydrothermal and subsequent phosphidation at elevated temperatures. X-ray photoelectron spectroscopy indicates that the Fe peaks for CoPx@FeOOH are positively shifted to a higher oxidation state compared with that of pristine FeOOH, which is more favorable to catalyze OER. In addition, the electrochemically active surface area is also improved by approximately 2.5 times. As a result, it can drive an OER current density of 800 mV/cm2 at 303 mV overpotential in 1 M KOH solution, which is superior to pristine FeOOH and IrO2. Besides the performance in fresh water based electrolyte, I will also introduce its activity and stability in saline water as well as designing core-shell structures in other materials systems.
(Invited) Ionomer Design Aspects for AEM-Based Electrolyzers
Authors: Kim Yu Seung
Published: July 2022

Interest in advanced anion exchange membrane (AEM)-based electrolyzers is growing because of their ability to produce hydrogen using platinum group metal-free catalysts, less expensive anode flow fields, and bipolar plates. Quaternized ionomeric binders play a critical role in AEM electrolyzers in their performance. This presentation will focus on the ionomer design aspects of AEM-based electrolyzers. The performance of AEM-based electrolyzers will be demonstrated using several homemade ionomers to identify the performance-limiting factors. Then, I will discuss the chemical structural impact of ionomers in hydrogen and oxygen evolution reactions. The purpose of this presentation is to provide direction for long-lasting electrolyzers with highly efficient hydrogen production capabilities.
(Invited) Alkaline Membrane Electrolyzers: Catalysts, Degradation Mechanisms, and Materials Engineering for Performance and Durability
Authors: Boettcher Shannon W. , Lindquist Grace , Krivina Raina A
Published: July 2022

Commercialized membrane electrolyzers use acidic proton exchange membranes (PEMs). These systems offer high performance but require the use of expensive precious-metal catalysts such as IrO2 and Pt that are nominally stable under the locally acidic conditions of the ionomer. Alkaline-exchange-me mbrane (AEM) electrolyzers in principle offer the performance of commercialized proton-exchange-membrane electrolyzers with the ability to use earth-abundant catalysts and inexpensive bipolar plate materials. I will present our fundamental work in understanding earth-abundant water-oxidation catalysts, including the use of integrated reference-electrode device architectures and cross-sectional materials analysis, as well as progress in building high-performance AEM electrolyzers. To date, our baseline systems operate at 1 A·cm-2 in pure water feed at < 1.9 V at a moderate temperature of 69 °C. These devices, however, degrade rapidly (~ 1 mV/h) compared to PEM electrolyzers. I will show how we assess chemical changes to the anode and cathode catalyst and ionomer that are correlated with this performance loss, as well as present strategies we have developed to mitigate degradation.
High Performance AEM Water Electrolysis with Aemion® Membranes
Authors: Jansonius Ryan , Moreno Marta , Britton Benjamin
Published: July 2022

By 2030 up to 50% of energy is expected to be carried in the bonds of H2. Global electrolysis capacity must increase from the current 240 MW to an anticipated 300 GW in 2030 and 3500 GW in 2050 to enable this transition. Alkaline and PEM electrolyzers are commercially mature with the currently market share of new installations roughly an equal split between these technologies. However, each of these electrolyzers are associated with challenges – alkaline electrolyzers operate at low current density, and require high concentration electrolytes (30 wt% KOH) to conduct hydroxides through the porous electrode separator (I.e., Zirfon). PEM electrolyzers use a proton conductive membrane to enable high current densities, however, running the reaction in acidic electrolyte requires platinum group catalysts and component coatings that hinder scalability at 2050 targets.

AEM water electrolyzers address both of these challenges by pairing anion exchange membrane with alkaline electrolyte to enable high current density operation, at high pressure, without noble metal catalysts. These attributes enable the most cost-effective green hydrogen - bringing the DOE hydrogen shot target of $1/kg within reach.

Anion exchange membrane chemistries have previously hindered this type of electrolyzer – AEMs based on quaternary amines, or pendant imidazolium groups chemically degrade in concentrated alkaline electrolyte, and mechanically degrade (from swelling) in low concentration alkaline media. Ionomr’s Aemion+ membranes are based on a sterically-protected polybenzimidazole chemistry and are chemically robust (stable in up to 10 M KOH), and exhibit low swelling to enable operation in low concentration electrolytes. These membranes are an enabling technology for long duration water and CO2 electrolysis.

This talk highlights how Ionomr’s Aemion+ membranes enable performance in excess of 1 A/cm2 at 1.8 V with non-PGM catalysts and a variety of configurations, and >4000 hours of durability in continuous operation.

Figure 1
Probing the Effects of Defects in Ultrathin Oxide Overlayers on the Selectivity of Encapsulated Electrocatalysts
Authors: Stinson William D. H. , Esposito Daniel V.
Published: July 2022

Application of ultrathin oxide encapsulation layers on co-catalysts employed in z-scheme photocatalysis has the potential to increase overall efficiency through the prevention of undesirable back reactions and increased charge separation. [1,2] However, defects within the semipermeable oxide coatings – such as pinholes, cracks or particle protrusions – have been postulated to facilitate locally high rates of undesirable reactions by creating pathways for facile transport of undesired reactants to exposed active sites.[3] Local probe measurements, such as scanning electrochemical microscopy (SECM), can estimate the relative rates of production of product species generated from competing electrochemical reactions with high spatial resolution over the electrode. This can be leveraged to determine the influence of local defects on global performance metrics, such as the apparent permeability of the overlayer and selectivity of the electrode. In this presentation, we report the use of SECM to determine the influence of overlayer defects on the performance of a model silicon oxide (SiOx) -encapsulated Pt thin film electrocatalyst when operated under conditions where two competing reactions can occur. Motivated by Z-scheme photocatalysis, the hydrogen evolution reaction (HER) and Fe(III)/Fe(II) redox reaction were studied. After introducing new methodology to determine local selectivity towards HER using SECM tip current, the resulting selectivity maps are compared against defects seen in optical images, scanning electron micrographs, and atomic force microscopy images. This analysis reveals that that certain types of defects in the oxide overlayer can be responsible for a large percentage of the partial current density towards the undesired Fe(III) reduction reaction. Correcting for the defect contributions to the undesired reaction, it is determined that the true Fe(III) permeability values for the SiOx overlayers are almost two orders of magnitude lower than permeabilities determined from conventional analysis that ignored the presence of defects. Finally, different types of defects were studied revealing that the defect morphology can have varying influence on both the selectivity and calculated permeability. This work highlights the need for local measurements in addition to macroscopic measurements of oxide encapsulated catalysts as they are applied to more complex geometries such as particle photocatalysts.

References

[1] Qi, Y. et al. Applied Catalysis B: Environmental 224, 579–585 (2018).

[2] T. Zhao, et al., PNAS, 2021, 118 (7),

[3] N. Y. Labrador, et al.
,
ACS Catalysis, 2018, vol. 8, 1767–1778.
(Invited) Molecular Engineering of Ion-Conducting Polymer Membranes for Electrochemical Energy Storage and Conversion Technologies
Authors: Bae Chulsung
Published: July 2022

Anion exchange membranes (AEMs) based on hydroxide-conducting polymers are a key component for anion-based electrochemical energy technology such as fuel cells, electrolyzers, and advanced batteries. Although these alkaline electrochemical technologies offer a promising alternative to acidic proton exchange membrane electrochemical devices, the access to chemically stable, mechanically durable, high-performing polymer electrolyte materials has been bottleneck to advance electrochemical technologies for hydrogen and other green chemicals until now. Despite vigorous research of AEM polymer design, examples of high-performance polymers with good alkaline stability at an elevated temperature are uncommon. Traditional aromatic polymers used in AEM applications contain a heteroatomic backbone linkage which is prone to degradation via nucleophilic attack by hydroxide ion.

In this presentation, I will highlight recent progress at the Bae group of Rensselaer Polytechnic Institute in the development of advanced hydroxide-conducting polymers and membranes for AEM technology applications. We have developed a number of synthetic methodologies that produce polymer design made of all C−C bond backbones and a flexible chain-tethered quaternary ammonium group and that provide an effective solution to the problem of alkaline stability. The advantage of good solvent processability, synthetic versatility, and convenient scalability of the reaction process has generated considerable interest of these polymers, and they are considered leading candidates for commercial standard AEM. AEM fuel cells, electrolyzer, and redox flow battery tests of some of the developed polymer membranes showed excellent performance, suggesting that this new class of AEMs open a new avenue to electrochemical devices with real-world applications.
(Invited) Engineering Challenges in Green Hydrogen Production Systems
Authors: Tao Meng , Azzolini Joseph A
Published: July 2022

Today, hydrogen is overwhelmingly produced through natural gas reforming which involves significant carbon emissions. Green hydrogen production from water and renewable energy promises over 80% reduction in carbon emission, but the technology for large-scale (megawatt to gigawatt) solar- or wind-powered hydrogen production has yet to be developed. Technical barriers for green hydrogen production include engineering challenges associated with coupling direct-current (DC) solar power with DC electrolyzers as well as the low capacity factors due to intermittent solar and wind power. In this talk we will analyze three approaches for solar-powered electrolysis: 1) coupling a solar array and an electrolyzer through alternating current; 2) DC to DC coupling through a DC/DC power converter; and 3) direct DC to DC coupling without a power converter. We will also introduce the concept of maximum current point tracking (MCPT) and compare it with maximum power point tracking (MPPT) for solar-powered electrolysis. MPPT is practically used in all solar systems today except those direct-coupled systems, but MCPT is required to maximize the hydrogen output of a solar electrolyzer. We will also propose a solar + wind electrolytic hydrogen production system to improve the capacity factor of the electrolyzer to about 50% from 20% for a solar-only system.
(Invited) Durability of Electrolyte Supported Solid Oxide Cells for Steam Electrolysis: Results from Cell Testing in the 20,000 h to 50,000 Hours Range
Authors: Schefold Josef , Pöpke Hendrik
Published: July 2022

There is a current fast development of water/steam electrolysis for the production of hydrogen from renewable energy sources. (Multi) MW power demonstration units using the different (low and high temperature) technologies are, e.g., subject of the R&D project H2Giga funded by the German Federal Ministry of Education and Research /1/. Steam electrolysis with solid oxide cells (SOC) is characterised by a high energy-conversion efficiency, notably if steam is available, such as via a heat source of moderate temperature for steam generation. Approaches for a matching to a fluctuating load, important in the context of operation with renewable energy sources, are also under development with the SOC technology /2/.

For the SOC electrolysers, durability analysis of the cells in a time scale appropriate for application remains an important development step. Cell (or short stack) testing allows a rather precise control of the cell temperature which facilitates quantification of degradation for the practically required degradation rates well below 10 mV/1000 h (cf. /3/). In this contribution, our testing results will be updated, with up to about 50,000 h operation using electrolyte supported cells (ESC) with Ni/GDC hydrogen electrodes and different types of electrolyte (10Sc1CeSZ, 6Sc1CeSZ, 3YSZ). As reference for cell durability serves a 23,000 h steam electrolysis test with a cell with 6Sc1CeSZ electrolyte /4/. However, cells with the known robust 3YSZ electrolyte seem to yield a comparably low long-term degradation, together with better initial stability /5/. The use of an electrolyte of high ionic conductivity, 10Sc1CeSZ, allows a relatively low initial temperature (<800°C) for a cell voltage close to the thermal neutral voltage for 0.6 Acm-2 current density. This, in turn, leaves a wide temperature margin for compensation of voltage degradation via a temperature increase (cf. initial period of the test in /3/). The results from the durability tests serve as examples for a large degree of SOFC/SOEC reversibility achievable with the ESC. Moreover, the relatively thick electrolyte layer of the ESC with its large ohmic resistance comes along with a high ohmic contribution in the overall degradation in most tests. The different degradation contributions were separated with in-situ impedance spectroscopy without interrupting the DC current flow.

References:

/1/ www.wasserstoff-leitprojekte.de/leitprojekte/h2giga.

/2/ J. Schefold, A. Brisse, A. Surrey, C. Walter, Int. J. Hydrogen Energy, 45 (2020) 5143-54.

/3/ J. Schefold, H. Poepke, A. Brisse, ECS Transactions, 97 (7) (2020) 553-563.

/4/ J. Schefold, A. Brisse, H. Poepke, Int. J. Hydrogen Energy, 42 (2017) 13415-26.

/5/ A. Brisse, J. Schefold, C. Walter, Proceedings 14th European SOFC & SOE Forum, B0904, 20 - 23 October 2020, Lucerne (Switzerland), pp. 306-314.
Direct Measurements of Hydrogen Exchange and Diffusion Kinetics at Elevated Temperatures in Proton-Conducting Solid Oxide Materials
Authors: Yatoo Mudasir A , Skinner Stephen
Published: July 2022

Storage of purified hydrogen is one of the central challenges in addressing climate change and reducing our reliance on fossil fuels for energy conversion and storage, and therefore there is a global surge in research and development concerning hydrogen purification and storage. In this regard, we are studying proton conduction in solid oxide materials at elevated temperatures for applications in hydrogen separation and compression membranes. Hydrogen compression is the most recommended method to store hydrogen for automotive applications as it allows an increase in the hydrogen volumetric energy density.

Traditionally the protonic conductivity in these materials is measured by indirect methods. For example, conductivity measurements in mixed gas atmospheres, comparing for example dry N2 with humidified N2, thereby allowing the contribution of protons to be evaluated. In this study, we for the first time report the evaluation of protonic conductivity in BaZr1-xCexY0.2O3−δ (BZCY) and BaZr0.1Ce0.7Y0.2–xYbxO3–δ (BZCYYb) by direct measurements afforded by the Isotope Exchange Depth Profiling (IEDP) technique with deuterium labelling. We also report the kinetics of H/D transport through the bulk materials and across metal-ceramic interfaces with particular interest in the behaviour of the interface between the key Pd/Pd alloy catalyst component and the hydrogen transporting oxide ceramic material. The transport and interface behaviour information will be of significance in designing hydrogen separation and compression membranes.

Figure 1
Modeling Electrokinetics of Oxygen Electrodes in Solid Oxide Electrolyzer Cells
Authors: Jin Xinfang , Cook Korey , Wrubel Jacob A , Ma Zhiwen , Jayapragasam Puvikkarasan , Huang Kevin
Published: July 2022

High temperature solid oxide electrolyzers operated at >600oC are advantageous from a thermodynamic perspective since heat (TDS) can be converted into chemical energy (DH) [1]. This additional heat reduces the overall electrical power (DG) requirement, allowing an electrolysis cell to achieve ~100% efficient H2 production [1]. Since the thermal energy contribution to the electrolysis reaction can also be obtained from sensible Joule heating produced within the cell, the electrical energy demand is further reduced which decreases the H2 production price. The bulk of the heat can be provided by an external source such as nuclear power, solar thermal power, or waste heat from a chemical plant. Theoretically, there is no external heat requirement if the electrolyzers operate at the thermoneutral voltage. Due to the above advantages, the research and development on solid oxide-based water electrolyzers have received significant attention [1–6].

This work focuses on physics-based modeling of high temperature solid oxide electrolysis cells (SOEC). A microscale model is presented to simulate electrode kinetics of the oxygen electrode in a solid oxide electrolyzer cell (SOEC). Two mixed ionic/electronic conducting structures are examined for the oxygen producing electrode in this work: single layer porous lanthanum strontium cobalt ferrite (LSCF), and bilayer LSCF/SCT (strontium cobalt tantalum oxide) structures. An yttrium-stabilized zirconia (YSZ) electrolyte separates the hydrogen and oxygen electrodes, as well as a gadolinium doped-ceria (GDC) buffer layer on the oxygen electrode side. Electrochemical reactions [7-8] occurring at the two-phase boundaries (2PBs) and three-phase boundaries (3PBs) of single-layer LSCF and bilayer LSCF/SCT oxygen electrodes are modeled under various SOEC voltages with lattice oxygen stoichiometry as the key output. The results reveal that there exists a competition in electrode kinetics between 2PBs and 3PBs, but 3PBs are the primary reactive sites for single-layer LSCF oxygen electrode under high voltages. These locations experience the greatest oxygen stoichiometry variations and are therefore the most likely locations for dimensional changes. By applying an active SCT layer over LSCF, the 2PBs become activated to compete with the 3PBs, thus alleviating oxygen stoichiometry variations and reducing the likelihood of dimensional change. This strategy could reduce lattice structural expansion, proving to be valuable for electrode-electrolyte delamination prevention and will be the focus of future work.

Figure 1
Impact of Loading Displacements on the Degradation Behavior of Low-Load PEM Water Electrolysis Electrodes
Authors: Utsch Nikolai , Jain Mohit , Froning Dieter , Shviro Meital , Lehnert Werner
Published: July 2022

In advanced polymer electrolyte membrane water electrolysis, low-load membrane electrode assemblies will be used to meet the requirements associated with the intended large-scale deployment.1 In particular, the scarcity of iridium pressurizes the need to develop long-life, low-loaded iridium anodes without compromising performance.2 To obtain highly durable electrodes, the understanding of the impact of the electrode structure on the degradation mechanisms caused by intermittent and stationary operation is essential. By varying machine parameters of the spray coater, we were able to understand the interaction between the spray parameters and the morphology of the fabricated electrodes, while approaches for clustering and dimensionality reduction helped us to correlate surface properties with statistical image variables. This allowed us to design several reference electrodes (Figure 1) with different artefacts related to loadings displacement (MP1 to MP5), analyzed them with static and dynamic degradation protocols to evaluate the importance of basic electrode fabrication on their degradation pathway.

Acknowledgement

This project has received funding from the European Union's Horizon 2020 research and innovation programme under the PROMET-H2 grant agreement No 862253.

References

Z. Taie, X. Peng, D. Kulkarni, I. V. Zenyuk, A. Z. Weber, C. Hagen and N. Danilovic, ACS Appl Mater Interfaces, 2020, 12, 52701-52712.

S. M. Alia, S. Stariha and R. L. Borup, Journal of The Electrochemical Society, 2019, 166, F1164-F1172.

Figure 1
2D Model Porous Transport Layers for Interfacial Characterization in Polymer Electrolyte Water Electrolysis
Authors: Weber Carl Cesar , Gubler Lorenz , Buechi Felix N. , De Angelis Salvatore
Published: July 2022

Polymer electrolyte water electrolysis (PEWE) is a key technology in the realization of a future hydrogen economy. The thorough understanding and optimization of each of its components in a synergistic matter is essential in the advancement of this technology. In this study, we aim at understanding the role of the porous transport layer (PTL) interface in contact with the catalyst layer (CL) [1] and its impact on PEWE performance losses.

We addressed the PTL/CL interface by creating a matrix of well-defined two-dimensional PTL materials [2]. These 2D-PTLs are fabricated by precise laser drillings of varying sizes on thin Ti-sheets, allowing us to accurately control geometrical properties such as interfacial contact area, pore size, triple-phase boundaries (TPB), and surface roughness. This systematic approach, combined with in-depth electrochemical analysis, provides insights into how the interface parameters affect the catalyst layer utilization at different current densities leading to severe differences in mass transport losses. Furthermore, by combining operando X-ray tomographic microscopy [3] and electrochemical characterization under selective conditions, we were able to get insights into the water transport mechanism inside the CL as a function of the different interfacial regions at the PTL/CL interface.

The findings related to this work will potentially contribute to a future more rational design of PTL and CL structures.

[1] T. Schuler, T.J. Schmidt, F.N. Büchi, J. Electrochem. Soc. 166 (2019) F555–F565.

[2] Z. Kang, J. Mo, G. Yang, S.T. Retterer, D.A. Cullen, T.J. Toops, J.B. Green Jr, M.M. Mench, F.-Y. Zhang, Energy Environ. Sci. 10 (2017) 166–175.

[3] S. De Angelis, T. Schuler, M.A. Charalambous, F. Marone, T.J. Schmidt, F.N. Büchi, J. Mater. Chem. A 9 (2021) 22102–22113.

Figure 1
(Invited) Manufacturing Challenges, Opportunities, and Successes for PEM Electrolysis at Scale
Authors: Capuano Christopher , Ayers Katherine E. , Motz Andrew R , Keane Alex , Manco Judith , Errico Shaina
Published: July 2022

Hydrogen generation via electrolysis has gained much attention internationally as not only a sustainable source of fuel for the transportation, but as a carrier of energy to capture stranded renewable energy due to the carbon-free chemical cycle and response characteristics of the technology. The barrier to entry preventing this technology from being widely adopted is the overall cost associated with both the upfront capital expense as well as the operating cost incurred over the product life. The majority of this cost is driven by 1) low electrical efficiencies due to the high ohmic resistance of thicker membranes required by electrolysis systems to electrochemically compress generated hydrogen for storage and the overpotential associated with the water splitting oxygen evolution reaction (OER) catalysts typically used, 2) high cost of system and cell stack materials, which need to be durable for up to 100,000hrs at a potential of 2V in both reducing and oxidizing environments, and 3) the lack of a robust supply chain for high volume manufacturing to further drive down cost through economies of scale.

With 95% of hydrogen currently being produced through the reformation of cheap natural gas, significant cost reductions are necessary for electrolysis to become a viable alternative to the incumbent. Commercial proton exchange membrane (PEM)-based electrolysis has reached scales of several hundred kg/day, providing a relevant pathway for industrial scale hydrogen generation with tremendous opportunity for continuing cost reduction by leveraging system and manufacturing scaling laws and advancements in PEM fuel cell materials, manufacturing, and analysis tools. Order of magnitude improvements in some of the highest cost elements are easily achievable and with more research funding being directed towards hydrogen production, the realization of these reductions is occurring at a faster rate. While many improvements in stack design and materials of construction have been identified and implemented, there are still numerous opportunities to explore that would move electrolysis towards a viable, cost-effective alternative to natural gas reformation. This talk will describe some of the areas of success, where research is still needed, and ultimately how each of these improvements translate into cost and the path to reformation parity.
A Modular in-Situ Cell to Monitor Gas Diffusion Electrodes during ORR and CO2RR
Authors: Hoffmann Hendrik , Paulisch Melanie Cornelia , Osiewacz Jens , Manke Ingo , Turek Thomas , Roth Christina
Published: July 2022

Metal-based gas diffusion electrodes (GDE) are utilized to achieve high current densities during the reaction in energy conversion systems, such as chlor-alkali electrolysis or the electrochemical reduction of carbon dioxide. By intense contact between the liquid and the gas phase with the catalytically active surfaces within the metallic electrodes, industrially required current densities can be accomplished. Their almost bulk-like silver structures with the 3D porous design and the strong absorption of the extended material make radiographic measurements extremely demanding. To receive in-depth information on electrolyte intrusion into the electrode's porous structure and the distribution during electrochemical measurements, lab-based and synchrotron radiography allows for monitoring this process operando 1, 2
.

In this work, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the ORR and the CO2RR as exemplary and currently very relevant examples of gas-liquid reactions. The applied half-cell set-up designed for ORR allowed for operando synchrotron radiation measurements at electrochemically stable operation at viable industrial conditions and current densities to follow the electrolyte distribution within Ag-based GDE during chlor-alkali-electrolysis. By adding one additional electrolyte compartment, extending the X-ray window, and implementing an anion exchange membrane, the in-house built half-cell set-up designed for operando synchrotron radiation measurements of ORR, was converted into a full-cell set-up for imaging CO2RR of strongly absorbing metal-based GDEs. With the reported cell design, we were able to observe the electrolyte distribution within GDEs during cell operation at technically relevant current densities for CO2RR up to 300 mAcm-2 (Figure 1). By high-resolution synchrotron radiation operando measurements, we demonstrated crystallization of electrolyte caused by the hydrophobic character of the GDE. At high overpotentials, hydrogen evolution reaction caused blockade of the Ag-based GDE, resulting in declining current densities, which could be imaged and monitored during realistic potentiostatic operation.

M. C. Paulisch, M. Gebhard, D. Franzen, A. Hilger, M. Osenberg, S. Marathe, C. Rau, B. Ellendorff, T. Turek, C. Roth and I. Manke, ACS Appl. Energy Mater.,
4(8), 7497–7503 (2021).

M. Gebhard, M. Paulisch, A. Hilger, D. Franzen, B. Ellendorff, T. Turek, I. Manke and C. Roth, Materials (Basel, Switzerland),
12(8) (2019).

Figure 1
(Invited) Experimental Measurement of Spatial Activity on CO2 & CO Reduction Gas Diffusion Electrodes
Authors: Simonson Hunter , Kas Recep , Henckel Danielle Alexia , Van Cleve Tim , Neyerlin Kenneth C. , Smith Wilson
Published: July 2022

Over the past decade, the accessible current densities of electrochemical CO2 reduction (CO2R) and CO reduction (COR) systems have increased by orders of magnitude, following the adaptation of the Gas Diffusion Electrode (GDE) architecture. As GDEs increase in size from cm2 to m2, cell stability and performance can change due to physical and chemical spatial variations within the cell, which can be exacerbated by the chemical complexity of carbonaceous electrochemical systems. Here, we present two approaches to measuring spatial activity: testing iteratively larger electrodes and harmonizing those results with a multi-port sampling reactor capable of measuring product concentration along the length of the reactor. This dual-pronged approach allows for benchmarking of electrochemical performance and selectivity down the channel as reaction conditions vary. We examine selectivity changes through the lens of fundamental electrochemical properties and provide subsequent recommendations for device operation as devices approach > kW scale. Experimental results are aligned with a 2-D (path length and electrode thickness) transport model to compare physical simulations with measured electrochemical signatures. Feedback loops between experiment and simulation were developed to incorporate cell inhomogeneities into the transport model. We identify potential causes for poor catalyst utilization in large electrodes for both COR and CO2R and provide recommendations for translating bench-top scale results to pilot scale results.
Achieving High CO2 Electrocatalytic Activity By Tailoring Cation-Size Mismatch in Double Perovskite Oxides
Authors: Bae Kyung Taek , Lee Kang Taek
Published: July 2022

Conversion of CO2 into useful chemical products by solid oxide electrolysis cells (SOECs) is a promising technology capable of reducing CO2 concentration for a carbon-neutral society [1]. This electrochemical device has several advantages such as high-energy efficiency and fast electrode kinetics due to its high operating temperature. Conventionally, Ni/YSZ cermet has been widely used as the cathode material of CO2 electrolysis system. However, they are prone to degrade under CO2 atmosphere due to the oxidation of nickel, particle agglomeration, and carbon deposition. Therefore, the development of alternative cathode materials with high electrocatalytic activity and good long-term stability for CO2 reduction reaction (CO2RR) is highly needed.

The perovskite-type mixed ionic and electronic conducting (MIEC) oxides are widely investigated as the promising alternatives to the Ni/YSZ cermet cathode. Among them, double perovskite oxides PrBaCo2O5+d(PBCO) material is attracting attention because of high oxygen surface exchange, diffusion coefficients and adequate mixed ionic and electronic conductivity. However, this material is easily degraded in the presence of CO2 impurity, with the formation of BaCO3 nanoparticles [2]. To overcome this issue, doping the B-site Co cations with transition metals and tailoring the cation mismatch by controlling A-site dopant ratio in PBCO were selected as a novel strategy. As a result, it was proved that co-doping was an effective way to improve both electrochemical and surface chemical stability. Our design strategy could benefit the preparation of highly active and stable cathodes for direct CO2 reduction for SOECs.

References

[1] Lee, Seokhee, et al. Advanced Energy Materials (2021): 2100339.

[2] Zhu, Lin, et al. Applied Surface Science 416 (2017): 649-655.
Understanding the Temperature Effects on CO2 Electrolysis Performance at High Current Densities
Authors: Giron Rodriguez Carlos Andres , Moss Asger Barkholt , Garg Sahil , Chorkendorff Ib , Seger Brian
Published: July 2022

The CO2 electrolysis driven with renewable sources is a promising alternative to mitigate greenhouse gas emissions by converting CO2 into valuable feedstocks and storing renewable electrical energy 1. Membrane electrode assemblies (MEAs) equipped with gas diffusion electrodes (GDEs) have shown great potential to overcome the current limitation of aqueous-fed systems while bringing this technology to economically-competing levels 2. In the last decade, many studies have been devoted to developing efficient catalyst materials and reactor designs; however, the effect of operating conditions such as temperature has not been thoroughly studied3. Given that the temperature affects CO2 electrolysis in a complex way (simultaneous effects on the CO2 diffusivity, solubility, the ionic conductivity of the membrane, and surface wettability of the GDE4), a systematic investigation is necessary to determine temperature influence on the product distribution

In this study, we investigate the temperature effects on CO2 electrolysis of Cu-based GDEs in an MEA-based approach in a temperature range between 25 and 80˚C, to enhance the selectivity of C2+ products and the energy efficiency while suppressing the hydrogen evolution (HER) and the degradation of the GDE and the membrane. For this investigation, a robust system for controlling and measuring the temperature of all the system components was developed, and we simultaneously set up proper guidelines to perform these electrocatalytic temperature measurements in a consistent and reproducible way.

For evaluating the temperature influence on electrocatalytic performance, a series of electrochemical measurements such as linear sweep voltammetry (LSV), double-layer capacitance measurements (DLC), potentiostatic and galvanostatic experiments were performed. The obtained results provide insights into how CO2 diffusion, reaction kinetics, and CO2 mass transport vary with temperature and affect the overall performance. We observed improvement in reaction rates and a drop in cell voltages at higher temperatures due to the enhancement of membranes' ionic conductivity and water management. The experiments focused on selectivity and product crossover revealed a specific trend at temperatures above 60˚C for gas and liquid products, setting up the optimal conditions for a stable operation with higher faradaic efficiencies of carbon-based compounds.

1 A. Vasileff, Y. Zheng and S. Z. Qiao, Adv. Energy Mater., 2017, 7, 1–21.

2 T. Burdyny and W. A. Smith, Energy Environ. Sci., 2019, 12, 1442–1453.

3 B. Endrődi, G. Bencsik, F. Darvas, R. Jones, K. Rajeshwar and C. Janáky, Prog. Energy Combust. Sci., 2017, 62, 133–154.

4 A. Löwe, C. Rieg, T. Hierlemann, N. Salas, D. Kopljar, N. Wagner and E. Klemm, ChemElectroChem, 2019, 6, 4497–4506.