bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Performance and Durability of a Solid Oxide Cell with Nanoparticles-Modified Electrodes for CO2 Electrolysis
Authors: Yu Miao , Tong Xiaofeng , Brodersen Karen , Chen Ming
Published: September 2023

Solid oxide electrolysis cell (SOEC) is one of the most effective technologies for converting carbon dioxide to carbon monoxide using renewable energy sources. Improving the electrode performance of an SOC by manufacturing nanocomposite electrodes via infiltration has attracted growing interest in recent years. This work investigated the electrochemical performance and long-term durability of a Ni/yttria-stabilized zirconia (YSZ)-supported planar-type SOEC cell (CGO@Ni/YSZ|YSZ|CGO|LSC/CGPO@CGO) infiltrated with nano-catalysts for CO2 electrolysis. The Ni/YSZ fuel electrode was infiltrated with Ce0.8Gd0.2O2−δ (CGO) solution, and the porous CGO scaffold was co-infiltrated with La0.6Sr0.4CoO3-δ (LSC) and Gd, Pr co-doped CeO2 (CGPO) nano-sized electrocatalysts. The cells were operated at 800 °C and -1 A/cm2 for 1548 h with a mixture of 24 L/h CO2/CO (83/17) supplied to the Ni/YSZ fuel electrode and pure O2 to the oxygen electrode. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis were conducted. Cell activation occurred at ⁓400 h of the durability testing due to the gas resupply from an unexpected power outage at ⁓360 h. During the durability testing period, the cell voltage increased from 1246 mV to 1400 mV with a degradation rate of 99.1 mV/kh (7.95%/kh). Furthermore, the cell showed a much lower degradation of ohmic resistance R
s (7.14 mΩ cm2/kh) compared to that of polarization resistance R
p (129.05 mΩ cm2/kh) after the gas resupply. DRT reveals that the degradation originates mainly from the Ni/YSZ fuel electrode during durability testing. Results from the current work demonstrate the potential of modifying SOECs for CO2 electrolysis at a high current density through the infiltration technique.
Development of Fuel Electrode Supported Solid Oxide Cell with Ni/CGO Active Layer
Authors: Klitkou Morten Phan , Lopez de Moragas Albert , Taubmann Julian , Khajavi Peyman , Pirou Stéven , Frandsen Henrik Lund , Hendriksen Peter Vang
Published: September 2023

Increasing the current density, at which substantial lifetime can be achieved, is one way to lower the cost of solid oxide electrolysis cell (SOEC) technology. Many state-of-the-art fuel electrode supported SOECs employ Ni/8YSZ fuel electrodes. These degrade at high current density because the increased fuel electrode overpotential accelerates Ni depletion/migration and loss of percolation in the Ni/8YSZ structure. This limits maximum current density. The stability for Ni/CGO (Ce0.9Gd0.1O1.95) fuel electrodes is not documented quite as well, but several reports show very stable fuel electrode performance for Ni/CGO in electrolyte supported cells. Good fuel electrode stability with Ni/CGO was also found in our tests at 750°C above -1.1 A/cm2 as shown in Figure b). To exploit this high current density performance stability at intermediate SOEC operating temperatures (~750ºC) we are working to incorporate Ni/CGO in a co-sintered thin electrolyte cell.

This contribution will give select results from our ongoing efforts to incorporate a Ni/CGO active layer into a fuel electrode supported SOEC consisting of a Ni/3YSZ support and a thin stabilized zirconia electrolyte. Half cells consisting of Ni/3YSZ support, Ni/CGO fuel electrode, zirconia electrolyte and CGO barrier layer have been successfully co-sintered, as shown in Figure a). Results from full cell tests based on these architectures will be reported.

To evaluate the general feasibility of the cell concept in parallel with cell manufacturing, supporting studies have been carried out. The chemical expansion of CGO caused by strongly reducing conditions at the fuel electrode is a potential mechanical threat to the cell concept. Initial modelling has shown a technologically relevant operating range with respect to gas composition, temperature and current density where the cell is predicted by modelling to stay intact. As shown in Figure c) thermoneutral operation falls well within the boundaries of mechanically safe operation. Subsequent experimental testing has even showed that the model gave a conservative estimate of the safe range, as we were unable to enforce a mechanical failure by testing under conditions of very strong chemical expansion (predicted expansion of 2%). In-situ XRD studies revealing strain levels and phases present have been performed to elucidate why mechanical failure does not occur, even under very strong reduction.

Beyond that, we are also testing the durability of Ni/CGO electrodes on commercial electrolyte supported cells to verify that stable electrode performance can be achieved under conditions relevant to fuel electrode supported SOECs with a thin electrolyte. So far these tests show no change in the polarization resistance contribution from the charge transfer reaction denoted Rp,lf, after operation at 0.5-1.3 A/cm2 regardless of current density.

Figure 1
Engineered Nanofunctional Thin Films as Interfacial Layers to Enhance Performance and Durability of SOFCs
Authors: Machado Marina , Baiutti Federico , Bernadet Lucile , Morata Alex , Nuñez Marc , Ouweltjes Jan Pieter , Fonseca Fabio Coral , Torrell Marc , Tarancón Albert
Published: September 2023

A strategy to improve the performance and durability of solid oxide fuel cells (SOFCs) is to increase the cathodic activity and decrease the interfacial resistance between the cathode and electrolyte. Pulsed laser deposition (PLD) has shown to be a promising method to engineer functional interlayers to enhance the cell's performance. In the present study, a bilayer consisting of Sm0.2Ce0.8O2-δ (SDC) barrier layer (BL) and a self-assembled nanocomposite consisting of SDC-La0.8Sr0.2MnO3-δ (SDC-LSM) employed as a cathode functional layer were deposited by PLD in an anode supported SOFC. The presented thin and dense layers are shown to be an effective strategy for the fabrication of high-performance fuel cells (power density of 1.0 W·cm−2 at 0.7 V and 750 °C). Durability tests carried out for up to 1500 h demonstrated the excellent stability of the fuel cell. Post-test analyses confirmed the stability of the microstructure of the developed bilayer.
Configurations and Operation Methods of Diesel-Based Solid Oxide Fuel Cell System
Authors: Lu Yang , Liu Yaodong , Han Minfang
Published: September 2023

Solid oxide fuel cell(SOFC) is a recently developed technology which has attracted increasing attention for its high efficiency and low emission. While the production and delivery of hydrogen still have giant obstacles, diesel will be a good substitute for its high heating value and low cost. However, it has not been widely used as the fuel for SOFC and researches on diesel-based SOFC system still remains to be further explored. In this work, a diesel steam reforming(SR)-SOFC system is studied. We proposed a series of system configurations of diesel-based SOFC and fitted key system units based on measured data of reforming and stack experiments. Moreover, the best system operation condition intervals were presented to achieve the maximize system efficiency and heat balance. The results suggest that a system with anode off-gas recirculation and electrodes off-gas mixture has the highest efficiency because it has higher syngas heat value and lower off-gas temperature; by adding a water condenser between reformer and SOFC stack, the system efficiency can be improved for higher percentage of H2 in syngas although the condenser will take away a part of the heat. Under this system configuration and the best system operation condition interval , the system efficiency can reach 58.2%(the stack efficiency is 45.8%), improving approximately 10% comparing with the system without anode off-gas recirculation. This research reveals the efficiency variance between different system configurations and gives a better system configuration as well as preferred operation methods, which lays a theoretical foundation for the upcoming design of a 100kw class physical system.

Keywords: solid oxide fuel cell, diesel reforming, system configurations, operation method
The Performance of Solid Oxide Fuel Cells Based on Methanol Solution
Authors: Yang Benrui , Liu Yaodong , Zhu Jianzhong , Han Minfang
Published: September 2023

The availability of hydrocarbon fuel is a unique advantage of solid oxide fuel cells (SOFCs). Methanol is one of the good choices for SOFC fuel because of its wide source, large output and easy storage and transportation. Methanol generally needs the steam reforming process before being used in SOFCs. In this paper, methanol reforming products under different steam-to-carbon ratio and temperature were tested on a commercial reforming equipment. Composition was compared with thermodynamic calculation results. The results show that when the temperature is below 700℃, a large deviation between components and thermodynamic calculation exists, indicating that methanol conversion is incomplete. When the temperature is above 700℃, methanol conversion is generally complete, and the temperature has little effect on the composition under this situation, while the steam-to-carbon ratio becomes the main influence factor. The hydrogen proportion in the products increases with the decrease of the steam-to-carbon ratio. A group of reforming products components were selected and tested on a commercial SOFC, and good performance was obtained, indicating the effectiveness of the optimization, which provides a research basis for the future application of methanol in SOFCs.
Improvement of the SOFC System by Anode Recirculation
Authors: Liu Yaodong , Han Minfang , Sun Kaihua , Li Qingxun
Published: September 2023

SOFC can utilize a variety of carbon-containing fuels stably and efficiently. Many studies have proved that anode recirculation can effectively improve the system fuel utilization, enhancing the system's electrical efficiency and lowering operating costs. More precisely, anode recirculation takes high power output, high efficiency, and high stability into account at the system level, while these three indexes are contradictory at the SOFC stack level. In this study, multiple SOFC system process models were built with MATLAB, which involved four anode recirculation modes, namely, "conventional low recirculating rate" mode, "conventional high recirculating rate" mode, "recirculation with water gas shift reaction reactor" mode and "recirculation with adiabatic reformer" mode. These modes were compared under different operating conditions. The key parameters that affect the system performance include fuel flow rate, recirculation rate, current per cell, and reformer temperature. Finally, the measured data of industrial-size fuel cells were used to make verification. It is found that the "recirculation with adiabatic reformer" mode can achieve high electrical efficiency while maintaining SOFC stacks working at low fuel utilization conditions. In other words, high power output, high electrical efficiency, and high stability are achieved at the same time. Moreover, it also has considerable feasibility in terms of system thermal balance. This study can provide powerful guidance for SOFC system design and construction.
Sulfur Impurities in COx Feed Gases of Solid Oxide Cells: Effect on Degradation and Removal Strategies
Authors: Riegraf Matthias , Bagarinao Katherine Develos , Biswas Indro , Costa Rémi
Published: September 2023

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies for carbon dioxide electrolysis. However, it is yet unclear which contaminant level in carbon monoxide and carbon dioxide feed gases are tolerable to achieve low degradation rates in commercial applications. In the present work, electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) fuel electrodes were exposed to CO/CO2 gas mixtures at open circuit voltage and in electrolysis operation. The resistance evolution over time was monitored by means of electrochemical impedance spectroscopy. With this approach it is shown that a severe reversible degradation over time periods of up to 72 h occurs. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that this degradation effect is related to sulfur impurities on the Ni surface. Inlet gas composition variations were carried out to show that sulfur impurities most likely in the low ppb level are present in both industrial CO and CO2 feed gases. The efficacy of different gas cleaning units at room temperature was investigated to identify a suitable desulfurization solution. The results demonstrate the importance of feed gas purity for the commercialization of high-temperature CO2 electrolysis.
Towards an Impedance-Based Analysis of SOFC-Stacks
Authors: Golani Sadhana , Bausinger Holger , Mai Andreas , Weber Andre
Published: September 2023

To understand the performance and durability limitations in SOFC stacks and systems, impedance spectroscopy is becoming increasingly important. However, in the analysis of entire stacks, gradients over the active cell area are averaged out, preventing access to local phenomena.

To get better insight into the spatial distribution of performance losses in a stack layer, incremental cells and repeat units with an active electrode area of 1 cm² are investigated in this study.

Impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation times (DRT) is applied to deconvolute the polarization processes in the Ni/CGO fuel electrode and the LSM air electrode of the investigated electrolyte supported cell. To ensure an appropriate deconvolution of air and fuel electrode processes, next to full cells symmetrical anode and cathode cells are applied. In case of Ni/CGO fuel electrodes charge transfer and gas diffusion overlap in the spectrum and the assignment has to be done indirectly using inert gas mixtures [1].

In Figure 1 impedance spectra and DRTs of fuel and air electrode obtained from symmetrical cells are compared with the full cell spectrum. This analysis enables a clear allocation of the processes in the single cell to Ni/CGO fuel electrode and LSM air electrode.

Next to the cell testing in an inert, ideal environment namely an Al2O3 flow field with gold and nickel contact grids respectively, the study is expanded to stack like conditions. The additional losses due to contact resistances and gas supply limitations are studied similar to Kornely et al. [2] for single repeat units (single cell + contact layer + metallic interconnects). In this contribution a physio-chemical equivalent circuit model based on these measurements will be presented and the complex impedance behavior of single cells and repeat units will be discussed.

References:

[1] C. Grosselindemann et al. 2021 J. Electrochem. Soc. 168 124506.

[2] M. Kornely et al., J. Power Sources, 196, 7209-7216 (2011).

Figure 1: Impedance spectra and related distributions of relaxation times (DRTs) of full cell, fuel electrode, air electrode and sum of the impedance of fuel and air electrode

Figure 1
Spatially Resolving Heterogeneous Chemistry on SOFC Electrodes with Operando Optical Methods
Authors: Walker Robert A. , Henning Tanner J. , Pomeroy Elias D , Owrutsky Jeffrey , Maza William A , Steinhurst Daniel
Published: September 2023

Carbon fouling (or coking) is one of the primary degradation mechanisms that leads to performance loss and eventual failure in high temperature, solid oxide electrochemical cells (SOCs). Accumulated carbon blocks electrocatalytic sites at three phase boundaries, impedes transport through porous electrode structures and can react with common electrode materials such as Ni to form carbides that disintegrate in a process described as metal dusting. Operando Raman studies examining carbon remediation through gasification showed surprising results. (J. Phys. Chem. C, 119 (2015) 7637.) When comparing carbon removal from Ni-YSZ cermet anodes at 750˚C by gas phase H2O, O2, and CO2, experiments measuring intensity of the carbon ‘G’ band, Raman studies showed that H2O was most effective, removing all observable carbon in a matter of seconds. Similar amounts of O2 required approximately one minute to remove detectable carbon, and CO2 required even longer and never removed all of the observable carbon. These results were supported by changes in the SOC open circuit potential. These Raman measurements, however, sampled only a single location on the anode. Work described in this presentation shows the anode surface chemistry to be considerably more heterogeneous than might be inferred from the Raman data. A combination of near-IR thermal imaging (NIRTI), Fourier transform IR emission spectroscopy (FTIRES), voltammetry and downstream mass spectrometry (MS) exhaust analysis have begun to spatially resolve processes associated with carbon gasification from coked Ni-cermet anodes at 800˚C, and show that carbon gasification proceeds through a sequence of steps involving both surface and gas phase reactions.
High Entropy Perovskite Electrolytes for Reversible Protonic Ceramic Electrochemical Cells
Authors: Oh Seeun , Kim Dongyeon , Lee Kang Taek
Published: September 2023

Reversible protonic ceramic electrochemical cells (R-PCECs) become cornerstones of low-temperature solid oxide electrochemical cells (SOCs) below 600 °C. Low activation energy and high energy conversion efficiency are primary significance of R-PCECs. However, electrolytes of high-performance R-PCECs still suffer from poor tolerance to complex operating conditions. To overcome their low stability and enhance proton conductivity, various cations have been doped into the Ba-based perovskite oxide electrolyte. Developing high entropy oxides by introducing multiple metal cations into A- or B- sites of the perovskite structure can be an effective solution for the structural stability. Due to the effect of the entropy-dominated stabilization in multi-doped perovskite oxides, the material can remain single phase under extreme temperatures and chemical environments. Promising high entropy stabilization concepts were adapted to electrolytes, and finally, durable proton-conducting perovskite oxide was designed. Here, we will present our recent progress on development of high entropy perovskite oxide electrolytes for R-PCECs.
Development of Long Duration Button Cell Test Stands and Testing Protocols
Authors: Hartvigsen Jeremy , Kane Nicholas , Casteel Micah , Gomez Joshua , Priest Cameron , Wang Lucun , White Casey , Boardman Richard , Ding Dong
Published: September 2023

In order to support the accelerated testing of the H2New consortium, long term repeatable cell testing is a necessary step. Cross-lab comparability and long duration tests are needed in order to establish a baseline degradation. The use of long-term testing with existing test stands and techniques that were developed primarily for material screening led to modifications to better suit long-term testing.

The stability of sealing of cells and operation of cells with the ability to endure a thermal cycle is a key point of interest in the long duration button cell testing. Cells with the ability to maintain performance unplanned power cycles are critical to the long-term understanding of button cells. System upgrades to improve long term button cell system reliability include the following: back-up power systems, thermal cycle stable glass, current collector attachment improvement, power monitoring, and in-operando cell leakage monitoring. The system modifications to identify and correct the most common causes of long-term button cell test failures are discussed. Discussions and lessons learned from cell test stand development and cell preparation protocols are presented.
Performance Analysis Method for PCFC Considering Leak Current and Application to 1000hr Endurance Test
Authors: Yoshikawa Masahiro , Tsuji Kentaro
Published: September 2023

We estimate the internal leakage current in PCFC mode, and report the results of a study on a performance analysis method that takes account of the leakage current. As results, the leak current increased with the supplied hydrogen, oxygen, and the water vapor concentration on the fuel electrode side, and the leak current tended to decrease only with the water vapor concentration on the air electrode side. Also, the higher the temperature, the more remarkable the change was observed in leakage current. Moreover, it was clarified that the cathode overvoltage greatly increases as the temperature decreases. From the result of 1000hr endurance test, it was revealed that the decrease output voltage was increase in the fuel electrode reaction resistance.
Effects of Transition Metal Elements on Ni Migration in Solid Oxide Cell Fuel Electrodes
Authors: Ouyang Zhufeng , Sciazko Anna , Komatsu Yosuke , Katsuhiko Nishimura , Shikazono Naoki
Published: September 2023

Solid oxide cells (SOCs), both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC), have emerged and attracted more and more attentions due to its high energy conversion efficiency and fuel flexibility. However, degradation of fuel electrodes after long-term operation remains as one of the main challenges for their commercial application. Two major types of microstructure evolution, nickel (Ni) migration and Ni coarsening in Ni - yttria-stabilized zirconia (Ni-YSZ) fuel electrodes have been widely reported, which have strong impacts on both cell performance and durability. Therefore, materials-driven research has focused on developing more robust fuel electrodes with good electrocatalytic ability. Utilization of Ni alloys has immersed as a promising concept to enhance the performance and robustness of conventional Ni/YSZ. In the present study, Ni-M (M = Fe, Cu) bimetallic fuel electrodes are applied to investigate the effects of transition metal elements on the morphological evolutions under SOFC and SOEC operations. Ni-Fe, Ni-Cu and pure Ni patterned fuel electrodes are sputtered on YSZ pellets. The electrochemical performance of these Ni-M bimetallic fuel electrodes decreases compared with pure Ni fuel electrode, while the performance degradation rate of Ni-Fe fuel electrodes is smaller than others. Besides, the spreading of Ni film on YSZ surface is observed for all samples under anodic polarization and such Ni migration is suppressed by Fe doping, whereas enhanced by Cu doping. On the other hand, the adhesion is weakened at the electrode / electrolyte interface for Ni-Cu and pure Ni fuel electrodes under cathodic polarization, while good adhesion at the interface is maintained for Ni-Fe, which correlates with the smaller performance degradation rate.
Experimental Investigation of Naphthalene Induced Degradation of Reversible Solid Oxide Cells Operated on Bio-Syngas
Authors: Steinrücken Benjamin , Herrmann Stephan , Feigl Karsten , Schwiers Alexander , Lenser Christian , Menzler Norbert H. , Spliethoff Hartmut
Published: September 2023

To tackle the demand for renewable alternatives to natural gas and for renewable energy, the operation of reversible solid oxide cells (rSOC) with syngas from biomass gasification is a highly efficient option. The fuel gas, produced close to carbon neutrality by the gasifier can be either converted to electrical power via the fuel cell mode or energetically upgraded via the electrolysis mode for e.g. utilization in chemical synthesis processes. Due to the reversible operation, a system based on an rSOC perfectly fits in an energy system with a high share of fluctuating renewable energy. However, impurities in fuel gas result in a fast degradation of the cells performance. This requires a comprehensive syngas cleaning to enable a stable operation of the cell. For the design of such a system, a deeper knowledge about the degradation processes is required. Especially the influence of tars is part of an ongoing research due to their ambivalent role as fuel and poison.

In this work, the model tar Naphthalene is used to experimentally investigate the influence of polycyclic aromatic components on the performance of 10 x 10 cm² fuel-electrode supported solid oxide cells operated at artificial bio-syngas under internal reforming conditions. Two different fuel electrodes based on yttrium-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) are investigated. A parameter study of the operational temperature and the operation mode is conducted with the YSZ based fuel electrode to quantify the effect on the degradation. The influence of the set-up is investigated by an experiment without the cell. The cell temperature distribution, the pressure drop and the fuel off-gas composition is measured. Electrochemical impedance spectroscopy is used to characterize the cell prior to the experiment and to monitor its performance during the poisoning and regeneration process. The measurements are interpreted via the distribution of relaxation times.

The electrolysis mode is observed to be more vulnerable towards poisoning with the tar than the fuel cell mode. The poisoning effects, whether it is a performance degradation or carbon deposition, are not only dependent on the tar but also on the operational conditions. The GDC fuel-electrode did not show the expected high robustness. The investigated cells are prototypes of an ongoing development process; hence a more detailed investigation is required when the development is finished.
Role of Operating Modes on the Performance Durability of Solid Oxide Cells: A Comparison between Potentiostatic and Galvanostatic Operations
Authors: Wang Yudong , Zhou Xiao-Dong
Published: September 2023

The commercialization of solid oxide cells for power generation or hydrogen production requires extended cell lifetime and durability. A solid oxide cell can operate either under a potentiostatic or a galvanostatic mode. It remains unclear what’s the role of those two operating modes on the performance durability of solid oxide cells, which limits our understanding and subsequently predicting service life and reliability of solid oxide cells.

It is known that many degradation phenomena in solid oxide cells can be accelerated by the electrochemical operations, which manifest various distributions of oxygen chemical potential (μO2) across a solid oxide cell. The variation in the local μO2 is a central driving force for the phase transformation, demixing, and microstructure evolution, leading to a higher resistance of the cell components and decreasing cell performance. As a response to the degradation, the μO2 redistributes across the cell and the driving force for the degradation changes. The μO2 distribution differs when a cell operates at a constant current or a constant voltage. The driving force with different extents of degradation under both operation modes is compared to establish the optimum operation approach, which can shed light on identifying mitigation strategies to improve performance durability with existing cell configurations and materials.

Acknowledgement

We greatly appreciate the support from U.S. Department of Energy’s Office of Fossil Energy and Carbon Management under DE-FE0032110. Part of this work is supported by U.S. National Science Foundation under NSF-2119688.
Influence of Process Parameters on SOEC Performance
Authors: Lee John-In , Ghosh Emily , Mulligan Jillian Rix , Akter Ayesha , Pal Uday , Basu Soumendra , Gopalan Srikanth
Published: September 2023

Solid oxide electrolysis cells (SOECs) are highlighted as futuristic Power-to-gas (P2G) devices that can provide reliable supply of hydrogen gas as a renewable energy carrier. Despite the great potential of SOECs there are many challenges facing their commercialization. In this work we investigated the influence of fuel electrode and process parameters on initial SOEC performance (500 hours). Electrolysis experiments were performed with both GDC (gadolinia doped ceria)-infiltrated and un-infiltrated Ni-YSZ fuel electrode under various hydrogen flow rates with different ratios of H2-H2O mix, and current density including open circuit conditions. All cells marginally improve in performance initially, then undergo a brief period of rapid decay followed by a stable performance. The observed three stages of variations in cell performance, in terms of length of time and rate of change, are dependent on the type of fuel electrode and experimental process parameters used. These are investigated employing I-V measurements, electrochemical impedance spectroscopy (EIS), distribution of relaxation time (DRT), and microstructural characterization. The role of GDC infiltration and process parameters driving these performance variations and efficiency of hydrogen generation is analyzed in this work.
Long-Term Stability of Perovskite-Based Fuel Electrode Material Sr2Fe2-XMoxO6-δ – GDC for Enhanced High-Temperature Steam and CO2 Electrolysis
Authors: Wolf Stephanie E. , Vibhu Vaibhav , Coll Carla L. , Eyckeler Niklas , Vinke Izaak C. , Eichel Rudiger-A , de Haart L.G.J. (Bert)
Published: September 2023

Solid oxide electrolysis cells (SOECs) have proven to be a highly efficient key technology to produce valuable gases (H2, CO). SOECs utilize renewably generated electricity at temperatures between 600 - 900 °C, thereby providing a carbon-neutral method for energy storage. However, the successful industrial implementation of this technology requires long-term stability of all system components and is mainly delayed by the degradation of the electrodes over time. The state-of-the-art Ni-YSZ fuel electrode has been extensively studied and exhibits severe performance loss due to Ni particle agglomeration and Ni migration away from the active sites at the electrolyte/electrode interface under real operating conditions [1]. To mitigate this issue, we have investigated the Ni-free perovskite Sr2Fe2-xMoxO6-δ + 30% GDC as fuel electrode material. As mixed ionic and electronic (MIEC) perovskite structured oxides, these materials have shown excellent short-term redox stability in oxidizing and reducing atmospheres in addition to high conductivity and outstanding coking resistance [2]. These characteristics meet exactly the targeted requirements for new solid oxide electrolyzer materials. We have compared the long-term degradation of an SFM fuel electrode to an electrode made of SFM-GDC (Figure 1). The degradation was less severe for the mixed electrode of SFM-GDC. Impedance and post-test SEM-EDX analysis clarified the main degradation mechanisms of SFM as well as SFM-GDC in steam and CO2 electrolysis. The tested button cells showed demixing of the SFM phase and particle aggomeration in the fuel electrode.

[1] S. E. Wolf, V. Vibhu, E. Tröster, I. C. Vinke, R.-A. Eichel and L. G. J. de Haart, Energies, 15(15), 5449 (2022).

[2] L. Bernadet, C. Moncasi, M. Torrell and A. Tarancón, Int. J. Hydrog. Energy, 45(28), 14208–14217 (2020).

Figure 1
Local Structure and Mixed Proton-Hole Conduction in Y and Al-Doped BaZrO3
Authors: Oikawa Itaru , Kimura Koya , Ishii Akihiro , Takamura Hitoshi
Published: September 2023

A mixed proton-hole conductor is expected to be an excellent cathode material for proton-conducting solid oxide fuel cells (PCFCs). Accepter-doped BaZrO3 has oxygen vacancies that can be either proton defects in wet or holes in oxidizing conditions. When both proton and hole concentrations are high enough, mixed proton-hole conduction is achieved. Our group has investigated the relationship between local structural distortion and hydration energy of accepter-doped BaZrO3. It was suggested that large Y3+ prefers the compensation by protonic defects; on the other hand, small Al3+ does holes or oxygen vacancies. Thus, by doping Y and Al into BaZrO3 simultaneously, high mixed proton-hole conduction is expected without transition metals. This study focuses on the local structure around dopants, especially around Al, which can be observed by nuclear magnetic resonance (NMR) spectroscopy. The coordination number of oxygen around Al can be converted to the number of oxygen vacancies. Based on the local structural analysis, the defect equilibrium and mixed conductivity of Y and Al co-doped BaZrO3 can be discussed. BaZr0.8Y0.2-xAlxO3-δ (BZYA) was prepared by solid-state reaction method. Proton concentration was evaluated by thermogravimetric analysis at 350 ºC. AC impedance measurement was performed to evaluate the electrical conductivity of BAYA in dry or wet Ar. The proton transport number was measured at 600 ºC using a water-vapor concentration cell. 27Al Magic-Angle Spinning (MAS) NMR was performed to investigate the configuration around Al. The proton concentration of BZY10A10 and BZY15A5 was 0.6 mol%, 1.8 mol%, respectively. These proton concentrations were much smaller than that of BZY20, 18.6 mol%. This indicates that Al substitution led to a decrease in proton concentration. Meanwhile, those BZYAs showed a relatively high proton transport number, 0.84. This was found to be due to the unique oxygen configuration around Al. The local structure around Al and its effect on proton concentration and mixed conduction will be discussed in the presentation.
Electrophoretically Deposited Protective Cu-Mn and Mn-Co Spinel Coatings for SOFC Interconnects
Authors: Basu Soumendra , Zhu Zhikuan , Mulligan J.R. , Pal Uday , Gopalan Srikanth , Abdul Jabbar Mohammed Hussain , Dale Nilesh , Fukuyama Yosuke , Miura Yohei , Miyoshi Yutaro
Published: September 2023

Stainless steel solid oxide fuel cell (SOFC) interconnects can lead to chromium poisoning of the cathode, necessitating the use of protective coatings. Electrophoretic deposition (EPD) is an efficient method to deposit coatings on substrates with complex microstructures. In this study, four spinel coatings; CuMn2O4, CuNi0.2Mn1.8O4, MnCo2O4, and MnFe0.34Co1.66O4, were electrophoretically deposited, and the coatings were evaluated on multiple criteria; including microstructural stability, conductivity, Cr gettering ability, and the ability to act as a diffusion barrier. The relative rankings of these measured properties for the four coatings will be discussed in this presentation.
Strategies to Improve the Effectiveness of the Thin Film Coated Interconnects
Authors: Reddy Mareddy Jayanth , Almyren Isak , Svensson Jan-Erik , Froitzheim Jan
Published: September 2023

Interconnects made of ferritic stainless steel (FSS) are used in solid oxide cells (SOC), both in fuel cells and electrolyzers, owing to a coefficient of thermal expansion similar to that of ceramic components, high oxidation resistance, good thermal conductivity, and adequate electrical conductivity of Cr2O3 scale at high temperatures. However, corrosion of the FSS interconnects at operating conditions between 600 – 900°C leads to high degradation rates and is a critical area for improving the SOC's performance.

The two significant issues with the FSS interconnects are 1. Chromia scale growth 2. Chromium evaporation. Protective chromia scale forms on the FSS upon exposure to high temperature, which grows continuously with time. The growing chromia scale increases the resistance across the cell, reducing cell efficiency. Additionally, the chromia scale reacts with oxygen in the presence of water vapour to form volatile Cr(VI) species such as CrO2(OH)2. These volatile Cr (VI) species interact with the cathode materials and get deposited at the triple-phase boundaries, hindering the oxygen electrochemical reaction on the cathode. This results in a decrease in the activity of the oxygen reduction reaction at the cathode referred to as cathode/ chromium poisoning.

Despite developing speciality steels like Crofer 22H and ZMG232, chromium evaporation is very high for the long-term performance of SOFC. Applying coatings is a widespread solution to suppress chromium evaporation. Manganese cobalt oxide (MCO) based coatings are extensively studied for this purpose. Physical vapour deposition deposited metallic Ce/Co coatings, which form MCO up oxidation, have been extensively studied for up to 38000 hours. Most of these studies were performed on as-received coatings, as opposed to the conditions in the stack. Commonly stacks are conditioned at high temperatures, usually 100-250 °C above the operating temperatures, to ensure gas-tightness in the stack.

To understand the influence of stack preheating on the coated interconnects, Ce/Co coated AISI 441 and Crofer 22 APU were pre-oxidized at 950 °C for 2 hours. After the pre/oxidation, the exposures were conducted in horizontal quartz tube reactors at 850oC for 1000 hours in air humidified with 3 % H2O. The oxidation kinetics of these coated steels was studied. Area-specific resistance (ASR) measurements were studied ex-situ after 1000 hours on these coated steels. The samples are characterized after pre/oxidation and exposure using scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). With the appropriate heat treatment, the interconnect lifetime can be increased by a factor of 5. The ASR of the pre-oxidized steels is lower than the as-received steels.
Metal-Supported Solid Oxide Cells for Energy Conversion, Electrolysis, and Chemical Synthesis
Authors: Tucker Mike C , Hu Boxun , Zhu Zhikuan , Welander Martha M , Shen Fengyu , Skafte Theis Løye , Lau Grace Y.
Published: September 2023

This talk will provide an overview and update of performance, durability, and applications of metal-supported solid oxide fuel cell (MS-SOFC) and electrolysis cell (MS-SOEC) technology developed at Lawrence Berkeley National Laboratory (LBNL). The unique LBNL symmetric cell architecture design, with thin zirconia ceramic backbones and electrolyte sandwiched between porous metal supports, offers a number of advantages over conventional all-ceramic cells, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. These features enable a wide variety of applications including vehicle range extenders, electrolysis for intermittent renewables, personal power generators, and distributed generation.

With infiltrated catalysts, the catalyst compositions can be easily tailored to a variety of reactions, without re-optimizing the entire cell. Recent efforts have developed catalysts for internal reforming of natural gas and ethanol, steam electrolysis to produce hydrogen, oxidative coupling of methane to synthesize ethylene, and oxygen generation from air. A recent focus is 1000+ hour continuous operation with detailed post-mortem analysis. Progress on cell performance and durability for each of these applications will be discussed.

Infiltrated catalysts, however, present a tradeoff between initial performance and long-term stability. Extremely high surface area promotes high electrochemical reaction rates, but also provides high surface energy leading to coarsening and facilitates Cr deposition. Recent approaches to mitigating catalyst coarsening and Cr deposition within the cathode include coatings to prevent Cr evaporation from the stainless steel components, and optimization of infiltrated catalyst processing to stabilize the microstructure during operation. The metal support structure has also been optimized for improved mass transport.
Influence of Temperature and Water Vapour on the High-Temperature Oxidation and Cr Evaporation Behaviour of High-Cr Alloys for SOFC Cathode Air Pre-Heaters
Authors: Zhang Kun , El-Kharouf Ahmad , Steinberger-Wilckens Robert
Published: September 2023

Chromium evaporation and oxide scale growth are among the key degradation mechanisms associated with Solid Oxide Fuel Cells (SOFCs). It is often underestimated how the cathode air pre-heater (CAPH) made of high Cr-containing alloys in SOFC systems can contribute to cathode degradation. This study examines the effect of exposure temperature and water content on both degradation mechanisms in Inconel 625, SS309 and AluChrom 318. For the influence of water content, samples of Inconel 625, SS309 and AluChrom 318 were isothermally exposed at 850°C in dry air and air containing 1%, 3% and 9% of H2O at a high flow rate for 168 hours. For the influence of temperature, samples of Inconel 625, SS309 and AluChrom 318 were isothermally exposed at 650°C, 750°C and 850°C in a 6.0 L/min air stream containing 3% H2O for 168 hours. The evaporated Cr (VI) species were collected using the denuder technique. The formed oxide scales were subsequently analysed using XRD and SEM/EDX. The results of the surface characterisation indicated that the oxide scales formed on Inconel 625, SS309 and AluChrom 318 at high temperatures were Cr2O3, (Cr,Mn)3O4 spinel and Al2O3, respectively.

The results of this study show that Cr evaporation and oxidation rates were dramatically reduced at the lower temperature used for Inconel 625 and SS309. AluChrom 318 exhibited an increased oxidation rate with increasing temperature, but it demonstrated a reverse trend to the temperature dependent Cr evaporation compared to Inconel 625 and SS309. It was also found that the amount of Cr evaporated from an alloy solely depended on the partial pressure of Cr presented on the oxide surface. At 850°C, the total mass of evaporated Cr(VI) species was found as follows: Cr2O3 (Inconel 625) > (Cr,Mn)3O4 spinel (SS309) >> Al2O3 (AluChrom 318). However, at 650 and 750°C, the total mass of evaporated Cr(VI) species was found to be: (Cr,Mn)3O4 spinel (SS309) > Cr2O3 (Inconel 625) > > Al2O3 (AluChrom 318). The significant effect of water vapour on the three tested materials appeared to be the further enhancement of Cr2O3 evaporation. At 850°C, the amount of evaporated Cr2O3 from the alloys exposed at the same humidity level corresponded to the Cr partial pressure on the surface, as follows: Cr2O3 (Inconel 625) > (Cr,Mn)3O4 spinel (SS309) > Al2O3 (AluChrom 318). The water vapour slightly increased the growth rate of Cr2O3 and (Cr,Mn)3O4 spinel formed on the Inconel 625 and SS309 surface, respectively. However, no evidence of change in the growth rate of the alumina on AluChrom 318 under the influence of water vapour in oxidising atmosphere was observed for the tested period in this study.

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Temperature-Dependent Sheet and Contact Resistivity Measurements on Ag and Ag-Ni Circuit Pastes
Authors: Bhatlawande Aishwarya , Hu Genzhi , Nicholas Jason , Hogan Timothy
Published: September 2023

The metal circuits and brazes used in electronic, energy conversion, and/or energy storage devices often have difficulty wetting and adhering to ceramic and/or ceramic-passivated metal substrates. Here, a novel Particle Interlayer Directed Wetting and Spreading (PIDWAS) technique is demonstrated that utilizes screen printing, the low wetting angle of silver on nickel, and the high work of adhesion between nickel and various ceramics to produce well-adhered, self-assembled silver patterns on ceramic and/or stainless-steel substrates not normally wet by silver. The resulting Ag-Ni circuits have higher sapphire adhesion strengths (up to 30 MPa on sapphire), higher densities (>97% on sapphire), and similar high-temperature electronic resistivities to those made using commercially-available Heraeus C8710 or DAD-87 silver circuit pastes. Similarly, Ag-Ni brazes between a variety of ceramic and/or stainless-steel substrates have better microstructural stability with rapid thermal cycling, reduction-oxidation cycling, and dual atmosphere isothermal aging than conventional Ag-CuO brazes. In addition, the residual Ni in these Ag-Ni circuits and brazes can be used to chemically getter surface segregated Al, ensuring low contact resistances on a variety of chromia- and/or alumina-passivated stainless steels.

Reference:

[1] Hu G, Zhou Q, Bhatlawande A, Park J, Termuhlen R, Ma Y, Bieler TR, Yu HC, Qi Y, Hogan T & Nicholas JD. Patterned Nickel Interlayers for Enhanced Silver Wetting, Spreading and Adhesion on Ceramic Substrates. Scripta Materialia, 2021; 196, 113767. 10.1016/j.scriptamat.2021.113767

[2] Park J, Phongpreecha T, Nicholas JD & Qi Y. Enhanced Liquid Metal Wetting on Oxide Surfaces via Patterned Particles. Acta Materialia, 2020; 199, 551-560. 10.1016/j.actamat.2020.08.037
Study of a Glass-Ceramic Seal Porosity
Authors: Moles Rémi , Laplace Annabelle , Begos Jean-Gabriel , Vallat Charlène , Regnier Elise , Schintu Lilou , Sierk Alexandre , Vulliez Karl
Published: September 2023

Sealing is a major issue in high temperature electrolyzers used for hydrogen production. The specifications that seals must meet are particularly demanding. In addition to sealing, the material must have mechanical, thermomechanical and chemical properties, as well as sufficient electrical resistivity. The geometries are complex and the lengths to be sealed are important. These numerous constraints lead to the use of glass powder suspended in organic solvents. This process allows the installation of the seal by deposition of the suspension on the areas to be sealed. Then, a heat treatment is applied to shape the material and ensure the sealing of the system. The use of a composition that tends to crystallize is implemented to improve, a priori, the thermal and mechanical properties.

The reference heat treatment consists in a first temperature rise followed by a crystallization stage. As the temperature rises, the organic solvents evaporate producing CO2 and gas present in the atmosphere of the furnace is trapped during sintering, which causes porosity to appear. Early surface crystallization can compete with the sintering phenomenon and prevent the maximum densification of the glass ceramic by freezing the structure. The objective of the study is to obtain a seal material with maximum density, thus minimum porosity, by controlling the removal of organic solvents, sintering and crystallization. Indeed, a large and interconnected porosity can create preferential leakage paths and decrease the sealing performances of the stack. Moreover, a dense material is known to be mechanically more resistant than a porous one. Indeed, a pore can initiate a crack that will eventually propagate through the seal.

This paper will present in particular the study of the material porosity. A quantification by SEM image analysis allows to determine the evolution of the porosity (percentage, size, number) as a function of time and temperature. Swelling, coalescence and rising of the pores are observed at high temperature. Glass powder and slurry are studied.

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Multi-Contaminant Getter for Trace Airborne Contaminant Capture in Elevated Temperature Electrochemical Systems
Authors: Belko Seraphim , Dubey Pawan Kumar Kumar , Lee Kevin X , Hong Junsung , Reisert Michael , Hu Boxun , Singh Prabhakar
Published: September 2023

Electrochemical systems operating at elevated temperatures such as solid oxide fuel cells (SOFC), solid oxide electrolysis cells (SOEC) and oxygen transport membranes (OTM) are susceptible to electrochemical performance degradation due to the presence of intrinsic and extrinsic contaminants in air stream. Intrinsic and extrinsic airborne contaminants include a wide range of gaseous compounds consisting of cations such as Cr, Si, and B, intrinsic impurities include SOx, NOx, VOC and PM’s. During high temperature exposure, the contaminants deposit and react with the cell components leading to both ohmic and non-ohmic polarization buildup. The use of a cost-effective, design-agnostic, passive “getter” system has been proposed for capturing trace contaminants. A number of getter formulations (containing alkaline earth, transition metal and lanthanide group elements) have been synthesized and experimentally tested. Results will be presented.