Durability Test Protocol Research Articles

Development of Accelerated Durability Test Protocols for Polymer Electrolyte Membrane Fuel Cell Stacks Under Realistic Operating Conditions

ABSTRACTPolymer electrolyte membrane fuel cell durability is still a major challenge. To overcome time‐consuming durability tests, so‐called accelerated durability tests (ADTs) are of urgent need. This work presents our recent results in developing ADT protocols in the context of realistic operating conditions, especially voltage clipping at 0.85 V. A 5500 h long‐term test was carried out as a reference applying a realistic automotive drive cycle. Focusing on different stressors such as temperature, relative humidity (RH), and load profile four different ADT protocols of 1200 h duration were derived. Seven‐cell short stacks with 240 cm2 active area were used. Comparing cell voltage as a key indicator, an acceleration factor of 3–7 could be achieved. In‐situ characterization techniques such as spatially resolved current measurement, cyclic voltammetry, and electrochemical impedance spectra were employed to investigate the influences of individual stressors on specific degradation mechanisms and components. The highest acceleration was observed in the mass transport region of ADTs addressing RH as a stressor, suggesting that RH cycling leads to increased degradation of hydrophobic surfaces. Increased temperature was found to accelerate primarily carbon support degradation. Accelerated catalyst aging seems to be low, demonstrating the effectiveness of voltage‐clipping conditions. Our most promising ADT shows quite a homogeneous acceleration of voltage degradation across all current regions.

Potential-driven instability effect of carbon supports for Pt/C electrocatalysts

Proton exchange membrane fuel cell (PEMFC) technology is a crucial approach of achieving clean and efficient power generation. However, prior to its full commercialization, several pressing issues must be addressed, especially the dissolution/degradation of Pt-based electrocatalysts for the cathode oxygen reduction reaction (ORR). This degradation significantly reduces the electrocatalytic activity of the catalysts. In this work, the impact of solid carbon support (Vulcan XC-72 R) and porous carbon support (Ketjenblack EC-300) on the degradation process of Pt/C electrocatalysts was investigated. By utilizing various triangular-wave voltage cycles in accelerated durability testing (ADT) protocols, the experimental findings suggest that a lower upper potential limit (UPL) in ADT tends to promote Pt diffusion and further aggregation, while a higher UPL exacerbates the electrochemical dissolution of Pt. Furthermore, the results indicate that Ketjenblack is more proficient than Vulcan XC-72 R in facilitating Pt redeposition after dissolution, which helps to minimize the loss of Pt under standardized rotating disk-electrode (RDE) aqueous electrolyte ADT conditions.

Local ageing effects of polymer electrolyte fuel cell membrane electrode assemblies due to accelerated durability testing

AbstractAccelerated durability test (ADT) protocols are useful tools to reduce testing time and development costs of automotive polymer electrolyte fuel cell stacks. Established accelerated stress tests allow comparing individual cell components. However, such tests in general do not allow drawing reliable conclusions on the expected lifetime for a complete stack. In this work, we examine the influence of combined stressors on the ageing behavior of individual cell components operated on stack level. We combine known main stressors for mobile fuel‐cell operation such as dynamic load, temperature and humidity cycling or hydrogen/air fronts during start‐up to develop a new accelerated test protocol. It was applied to an automotive 5‐cell short stack for 460 operating hours (OpH). A second stack was operated in a reference long‐term test for 2300 OpH. Several in situ characterization techniques, such as cyclic voltammetry, and recording the local current density distribution were employed. In addition, post‐mortem analyses, such as focused ion beam scanning electron microscopy imaging, was applied in order to better understand the degradation mechanisms. The results presented here provide an excellent basis for the further development of a new ADT protocol, which will accelerate ageing processes in the fuel cell in a realistic way, i.e. leading to similar degradation characteristics as in long term testing.

The Influence of Stove Materials on the Combustion Performance of a Hybrid Draft Biomass Cookstove

ABSTRACT The cookstove requires various materials for different stove components, such as the combustion chamber, stove body, insulation, and other accessories, which have a significant impact on the overall combustion performance of the stove. In the present study, two hybrid draft biomass cookstove (HDBC) models with different combustion chamber materials (stainless steel and ceramic refractory cement) were developed and tested. Both stoves in combination with three different insulation materials (perlite, vermiculite, and ceramic wool) were tested using the modified Water Boiling Test (WBT-4.2.3) and Durability Test protocol to assess emissions, efficiency, and stove durability performance. According to the ISO 19867-3:2018 voluntary performance targets, both stainless steel and ceramic combustion chamber stoves with all three insulations met the targets of Tier 5, Tier 4, Tier 3 & 2 and Tier 5 in CO emission, PM2.5 emission, efficiency, and durability performance, respectively. Although there was no significant difference in CO emission, efficiency, modified combustion efficiency (MCE) and durability performance between the two stoves, the ceramic combustion chamber stove emits more PM2.5 than the stainless-steel combustion chamber stove. The combination of stainless-steel combustion chamber and perlite insulation performs overall better than the other combinations.

(Invited) Development of a Simple and Rapid Diagnostic for Redox-Flow-Battery Cells

Prof. Robert Savinell has made many important contributions to fuel-cell and flow-battery systems. Both of these systems utilize electrochemical flow cells to either generate or store electricity. Because of this commonality, one can leverage concepts used in one for adoption in the other. An important topic for any electrochemical system is durability. A considerable amount of work has been on this topic with polymer-electrolyte fuel cells (PEFCs); in fact, a textbook devoted to this topic was published over a decade ago [1]. However, despite a recent renaissance in redox-flow-battery (RFB) technologies, assessing the durability of RFB cells is a topic that has not received much attention in the open literature, to date, and further research is needed to better understand dominant degradation mechanisms [2, 3].A simple and fast diagnostic tool has been developed for analyzing polymer-electrolyte fuel-cell degradation [4, 5]. The tool is based on analyzing changes in polarization curves of a cell over its lifetime. Using the polarization-change curve methodology, the primary mechanism for degradation (kinetic, ohmic, and/or transport related) can be identified. This technique can also be applied to RFB cells, which will be the focus of this presentation. This diagnostic tool provides a simple method for rapid determination of primary degradation mechanisms. Areas for more detailed future investigations shall also be summarized. References Modern Topics in Polymer Electrolyte Fuel Cell Degradation, Mench, M.; Kumbur, E.; and Veziroglu, T.; Editors; Elsevier, Denmark (2011).Yuan, X.-Z.; Song, C.; Platt, A.; Zhao, N.; Wang, H.; Li, H.; Fatih, K.; Jang, D.; “A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies,” J. Energy Res., 43 (2019) 6599−6638.Yao, Y.; Lei, J.; Shi, Y.; Ai, F.; Lu, Y. C.; “Assessment methods and performance metrics for redox flow batteries,” Energy, 6 (2021) 582−588.L. Perry, R. Balliet, and R. Darling, “Experimental Diagnostics and Durability Testing Protocols,” a chapter in [1].M. Pant, Z. Yang, M. L. Perry, and A. Z. Weber, “Development of a Simple and Rapid Diagnostic Method for Polymer-Electrolyte Fuel Cells,” J. Electrochem. Soc., 165 (2018) F3007.

(Invited) Leak Current Analysis of Stop Operation and Its Modeling for the Development of Bipolar Alkaline Water Electrolyzer Electrodes

Introduction Water electrolysis is expected a key device to introduce large-scale renewable electricity under management of power grid and electrification of non-electric sector. While alkaline water electrolysis (AWE) systems are well-developed large system, degradation under fluctuated operation with start and stop operation is significant issue to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current, which is leak current through manifold of bipolar alkaline water electrolyzers, and electrode potential behavior of stop operation, and proposed accelerated durability test (ADT) protocol for start and stop operation. Experimental and modeling Figure 1 shows configuration of 4-cells bipolar alkaline water electrolyzer that was consisted with end plates of EP(-) and EP(+), bipolar plates of BP1 to BP3, anodes, separators, and cathodes with principle of reverse current. The end and bipolar plates were made of nickel. Anodes and cathodes were commercially available oxygen and hydrogen electrocatalyst coated nickel mesh electrodes (De Nora Permelec Ltd) with 27.8 cm2 of projected area. Zirfon Perl UTP500 (Agfa) was used for separators. Manifolds were made of Teflon tubes and 15 mL/min of 7 M (= mol/dm3) was circulated for each anolyte and catholyte chambers during measurements. An anode and a cathode set on a bipolar plate. During operation anodes and cathodes are oxidized and reduces, respectively. After stop, the anode and the cathode on a bipolar plate connects both electronically and ionically, so oxidized anode and reduced cathode surface discharges to same potential. In this study, we measured electrode potential and reverse current after 1 h water electrolysis of 80oC at 0.6 A/cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu).Reverse current behavior was analyzed with COMSOL Multiphysics version 5.5 based 2-dimensional model of stack and height direction using experimentally anode and cathode potentials as functions of discharge for anode and cathodes. Results and discussion Figure 2 shows cell performances in the stacks and a picture of the lab-scale zero-gap configuration electrolyzer. All cells in a stack showed almost the same performance. The cell voltage was 2 V at 400 mA/cm2 at 30oC and was 1.8 V at 500 mA/cm2 at 80oC. Therefore, we think all cells and parts work well.Figure 3 shows reverse currents and electrode potentials as a function of time after 1 h electrolysis under 600 mA/cm2 at 30 or 80 oC. Here, the dashed lines in Fig. 3-a) were simulated value and were almost same after 20 s. The measured reverse current increased around 20 s. At this moment, outlet manifolds filled with electrolyte to increase ionic conduction among the chambers, which was not considered in the simulation. After degassed of manifolds, the reverse current decreased with time with the largest reverse current for the BP2. The reverse current at 80oC was significantly larger than that at 30oC. This difference could be explained the dependence of ionic resistance of manifold on temperature. At same moment, anode and cathode potentials on the end plates were almost constant. The anode cathode potentials on the bipolar plates decreased and increased with time, respectively. Both anode and cathode showed significantly potential change region. The final potentials of all electrodes were around 0.9 V vs. RHE. The potential change regions of the electrodes on the BP2 were earlier than others. Here, the anode and cathode potentials as functions of discharge were almost same for the electrode on all bipolar plates. Therefore, the average discharge functions for anode and cathode were treated as characteristics of electrodes of this study. Using this function, reverse current as a function of time could be expressed accurately using the developed model. From this model, reverse current, and electrode potentials as a function of time would be expected with discharge function of each electrode and ionic resistance of manifold.Figure 4 shows that a start & stop operation simulated ADT protocol based on bipolar electrolyzer measurements. We propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Novel extraction method of working condition spectrum for the lifetime prediction and energy management strategy evaluation of automotive fuel cells

Lifetime is a major bottleneck for the commercialization of fuel cells. A quick evaluating method for fuel cell lifetime can assist in immediately assessing technology progress, predicting lifetime in real-time, and extending durability. Among the existing methods, the lifetime prediction method based on working conditions is a cost-effective, time-saving, and realistic method. However, there are no methods and clear standards for extracting the time and frequency of working conditions in test protocols used in this method. In this study, the working condition spectrum extraction method is proposed and used to extract the working condition spectra of commonly used durability test protocols. The lifetime prediction of fuel cells operating under different specific test protocols based on the working condition spectrum extraction method is performed and verified to demonstrate its reliability. Furthermore, the proposed method is used to extract the working condition spectra and predict the lifetime of fuel cells in hybrid power systems with different energy management strategies (EMSs). The results show that the extraction method can provide an evaluation method for developing EMSs of fuel cell hybrid power systems from the lifetime perspective, which is useful for fuel cell durability research.

Short pulse laser structuring as a scalable process to produce cathodes for large alkaline water electrolyzers

This paper presents a novel scalable electrode fabrication process suitable for large alkaline water electrolysers. Laser structuring technology is applied, and a large-scale development of active Ni-based cathodes is demonstrated. The most active electrode shows an overpotential of 104 mV at a current density of 300 mA cm−2 for the hydrogen evolution reaction at the end of the accelerated durability test protocol. Large 400 × 600 mm2 electrodes have been fabricated for the first time, and the electrodes thus fabricated are compared with state-of-the-art electrodes in an industrial alkaline electrolyzer. Within the test period, the laser-structured Ni electrodes significantly outperformed the comparison electrodes. This impressively high activity is attributed to the existence of Ni oxide adjacent to the metallic Ni reaction sites.

Accelerated Durability Testing of Fuel Cell Stacks for Commercial Automotive Applications: A Case Study

System durability is crucially important for the successful commercialization of fuel cell electric vehicles (FCEVs). Conventional accelerated durability testing protocols employ relatively high voltage to hasten carbon corrosion and/or platinum catalyst degradation. However, high voltages are strictly avoided in commercialized FCEVs such as the Toyota MIRAI to minimize these degradation modes. As such, conventional durability tests are not representative of real-world FCEV driving conditions. Here, modified start-stop and load cycle durability tests are conducted on prototype fuel cell stacks intended for incorporation into commercial FCEVs. Polarization curves are evaluated at beginning of test (BOT) and end of test (EOT), and the degradation mechanisms are elucidated by separating the overvoltages at both 0.2 and 2.2 A cm−2. Using our modified durability protocols with a maximum cell voltage of 0.9 V, the prototype fuel cell stacks easily meet durability targets for automotive applications, corresponding to 15-year operation and 200,000 km driving range. These findings have been applied successfully in the development of new fuel cell systems for FCEVs, in particular the second-generation Toyota MIRAI.

Quantification on degradation mechanisms of polymer exchange membrane fuel cell cathode catalyst layers during bus and stationary durability test protocols

Simulating bus and stationary protocols are designed to study the durability and degradation mechanisms of proton exchange membrane fuel cells. A quantitative method combined with characterization techniques, including electrochemical impedance spectroscopy, X-ray fluorescence spectroscopy and X-ray diffraction spectroscopy, is applied to distinguish performance degradation. Experimental results show that, for proton exchange membrane attenuation, chemical attenuation due to high cathode potential with long duration is more severe than mechanism attenuation due to dynamic load. For cathode catalyst layer decay, the principal reason under bus condition is particles growth (∼35%), followed by Pt dissolution (∼34%). In contrast,∼43% ECSA loss results from ionomer/catalyst interface loss under stationary condition. Such information indicates that the bus condition results in particles growth and Pt dissolution while the stationary condition induces ionomer/catalyst interface loss in the cathode catalyst layer. Combining more realistic protocols and quantitative analysis method can reveal the relationship between operating conditions of fuel cell in realistic road and MEA degradation. • Simulating stationary and bus protocols are used to study MEA degradation. • The attenuation mechanisms of MEA under these two protocols is proposed. • Chemical decay by durable high-potential affects severely PEM durability. • Particle growth and Pt dissolution cease CL decay under bus protocol. • Ionomer loss ceases CL degradation under stationary protocol.

(Invited) Electrocat 2.0: Accelerating PGM-Free Catalyst and Electrode Development

ElectroCat (The Electrocatalysis Consortium), formed by the U.S Department of Energy’s (DOE) Hydrogen and Fuel Cell Technologies Office (HFTO) as part of the Energy Materials Network (EMN), aims to accelerate the development of next-generation catalysts and electrodes that are free of the platinum group metals (PGM) currently required for good performance and durability. Given that polymer electrolyte membrane fuel cell (PEMFC) stack cost is dominated by the cost of the catalyst (>40% of stack cost), ElectroCat has focused its efforts on oxygen reduction reaction (ORR) catalysis for PEM fuel cells, in particular to improve catalyst activity. Over its first four years, this EMN Consortium has established a portfolio of unique experimental, analytical, and modeling capabilities; more than doubled the performance of PGM-free catalysts for PEMFCs; and developed and validated durability test protocols to be made available for use by the larger PGM-free catalyst community. Building on these successes, ElectroCat 2.0, which began this year, will increase focus on improving catalyst durability, investigating electrode engineering, and further advancing high throughput catalyst synthesis and characterization capabilities coupled with machine learning while still working to improve catalyst performance. Although the focus of ElectroCat 2.0 will remain on ORR for PEMFCs, the Consortium will expand its catalyst portfolio to include the development of PGM-free catalysts for low temperature electrolysis (LTE). ElectroCat 2.0 will continue the intent of the EMN strategy by focusing on a robust, materials discovery approach, with theory-guided and high-throughput components. In addition, like other EMN consortia, ElectroCat aligns R&D activities at national laboratories and, through DOE-funded projects, facilitates streamlined access of academic and industry partners to the world-class capabilities and expertise at the four core ElectroCat national labs (LANL, ANL, ORNL, NREL). The presentation will highlight recent R&D advancements, core national lab experimental and computational capabilities, as well as machine-learning approaches to expedite the development of PGM-free catalysts and electrodes.

A Durable Platinum Group Metal-Free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells

A Durable Platinum Group Metal-free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells Hanguang Zhang, Hoon T. Chung, Ulises Martinez, Edward F. Holby, and Piotr Zelenay Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Performance of platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), especially high-temperature metal-nitrogen-carbon (M-N-C) materials, has improved a lot in the last two decades,1, 2 however, their durability continues to present a big challenge. PGM-free catalysts typically suffer a 40-80% activity loss during the first 100 hours of operation in the low-temperature fuel cell cathode, which is way short of the 8,000-hour lifetime target for PEFCs.3, 4 Significant improvements to PGM-free catalyst performance durability are thus required before they can be considered for practical PEFCs.In this presentation, we will introduce a ‘dual-zone’ approach to high-temperature synthesis of PGM-free catalysts, which results in modifications to the catalyst surface and, ultimately, in very significant improvements to their durability. In H2-air fuel cell testing, the ‘dual-zone’ fuel cell catalyst has shown a minimal performance loss during up to 80,000 voltage cycles using standardized PGM-free durability test protocol developed in ElectroCat consortium and approved by DOE. The catalyst has also retained 70% of its initial activity in a 600-hour constant-voltage fuel cell test at 0.70 V.We will report fuel cell performance data in the first part of this presentation, followed by discussion of possible origins of the much improved performance durability imparted by the ‘dual-zone’ approach. Acknowledgement This research was supported by the U.S. DOE, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). References Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011, 332, 443-447.Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P., Direct atomic-level insight into the active sites of a high-performance PGM-free ORR catalyst. Science 2017, 357, 479-484.Shao, Y.; Dodelet, J.-P.; Wu, G.; Zelenay, P., PGM-Free Cathode Catalysts for PEM Fuel Cells: A Mini-Review on Stability Challenges. Mater. 2019, 31, 1807615.U.S. DRIVE Fuel Cell Technical Team Roadmap; Department of Energy, US, 2017.

Redox Durability of Ni-Co Alloy Cermet Anodes for SOFCs

Introduction Nickel (Ni) is commonly used as the anode material of SOFCs. However, in the power generation, as the oxygen partial pressure in the downstream of the SOFC systems increases, the metallic Ni can be oxidized to nickel oxide (NiO), causing volume expansion (1) This volume expansion and shrinkage in redox cycles cause irreversible degradation, by breaking electrode microstructure. Highly durable SOFC anodes using Ni-based alloy are therefore desirable (2). Here in this study, we focus on the Ni-Co alloy, by preparing a new Ni-Co-GDC cermet anode using the Ni-Co alloy, and evaluate the effects of cobalt addition on their redox durability. Experimental The cells were fabricated by screen-printing electrode paste on the electrolyte plate, followed by heat treatment. Scandia-Stabilized Zirconia (ScSZ, 10mol% Sc2O3-1mol% CeO2-89mol% ZrO2) was used as the solid electrolyte. Ni-Co-GDC cermet anodes were prepared by mixing Ni-Co-based oxide powder by ammonia co-precipitation with Ce0.9Gd0.1O2 (GDC) in a specific ratio by weight. La1-xSrxMnO3 (LSM) powder was used as the cathode material. The electrochemical characteristics of the cells, with the Ni-Co cermet anodes, were evaluated by measuring I-V measurements coupled with the current interruption method under the condition at 800oC, where 3%-humidified hydrogen fuel was supplied to the anode. Furthermore, the redox stability was evaluated using the durability test protocol simulating the fuel interruption (3). Anode microstructure was observed by a focused-ion beam system coupled with a scanning electron microscope (FIB-SEM). Results and discussion Figure 1 shows the I-V characteristics and overvoltages of the Ni-Co-GDC anode with various Co concentrations at 800oC with 3%-humidified hydrogen fuel. With increasing the Co content, the electrochemical performance decreased due to an increase in overvoltages. However, when the Co content was as low as 5 mol%, performance decrease was negligible. Figure 2 shows the redox stability of the Ni-Co-GDC anode evaluated by using the durability test protocol simulating the fuel interruption. With increasing the Co content, the redox stability was improved, associated with relatively-low ohmic losses. The microstructure of Ni-Co-GDC anodes will be reported and discussed. References Q. Fang et al., Int. J. Hydrogen Energy, 40, 1128 (2015).Y. Ishibashi et al., J. Electrochem. Soc., 167, 124517 (2020).M. Hanasaki et al., J. Electrochem. Soc., 161 (9), F850-60 (2014). Figure 1

Review of the Durability of Polymer Electrolyte Membrane Fuel Cell in Long-Term Operation: Main Influencing Parameters and Testing Protocols

Durability is the most pressing issue preventing the efficient commercialization of polymer electrolyte membrane fuel cell (PEMFC) stationary and transportation applications. A big barrier to overcoming the durability limitations is gaining a better understanding of failure modes for user profiles. In addition, durability test protocols for determining the lifetime of PEMFCs are important factors in the development of the technology. These methods are designed to gather enough data about the cell/stack to understand its efficiency and durability without causing it to fail. They also provide some indication of the cell/stack’s age in terms of changes in performance over time. Based on a study of the literature, the fundamental factors influencing PEMFC long-term durability and the durability test protocols for both PEMFC stationary and transportation applications were discussed and outlined in depth in this review. This brief analysis should provide engineers and researchers with a fast overview as well as a useful toolbox for investigating PEMFC durability issues.

Hydrophobicity of CO2 gas diffusion electrodes

In Nature Communications, Hu, Feng, and their colleagues present a scalable, facile method to tune the hydrophobicity of CO2 reduction gas diffusion electrodes by adding polytetrafluoroethylene (PTFE) nanopowder into the catalyst ink. For a copper catalyst CO2 reduction electrode, the additive significantly enhances CO2 reduction performance and imparts persistent hydrophobicity.

A New Accelerated Durability Test Protocol for Water Oxidation Electrocatalysts of Renewable Energy Powered Alkaline Water Electrolyzers

A New Accelerated Durability Test Protocol for Water Oxidation Electrocatalysts of Renewable Energy Powered Alkaline Water Electrolyzers

Insights on platinum-carbon catalyst degradation mechanism for oxygen reduction reaction in acidic and alkaline media

Developing durable electrocatalyst for oxygen reduction reaction (ORR) is essential for fuel cell commercialization. Herein, we perform a study of platinum-carbon (Pt/C) degradation mechanisms using potential cycling of accelerated durability testing protocols in acidic and alkaline media. Physicochemical results indicate that carbon surface oxides are formed after high-potential cycling in acid causing an increase in the double-layer capacitance and severe ORR activity loss due to Pt poisoning. Whereas, low-potential cycling in acid shows less ORR activity loss, mainly caused by Pt Ostwald ripening, and does not lead to a significant change in double-layer capacitance. In alkaline, the Pt/C catalyst after high-potential cycling shows a decrease of double-layer capacitance over time because of carbon layer dissolution. TEM images reveal larger Pt agglomerates in alkaline, due to high Pt mobility. These findings provide new insights into the role of catalyst and carbon support interface in developing mitigation strategies for stable fuel cell operation.

(Vittorio de Nora Award Address) Analysis of the Catalyst Requirements with Regards to Catalyst Structure and Catalyst Durability Studies for PEM Water Electrolysis

Proton exchange membrane (PEM) based water electrolyzers are a promising technology for the large-scale production of hydrogen from renewable energy. The most efficient and durable catalysts for PEM water electrolysis are platinum to catalyze the hydrogen evolution reaction (HER) and iridium oxide to catalyze the oxygen evolution reaction (OER). While the currently rather high noble metal loadings (≈0.3-0.5 mgPt/cm2 and ≈1-3 mgIr/cm2) have only a minor impact on the overall water electrolyzer system cost [1], the large-scale global implementation of PEM water electrolysis would require a substantial reduction of the noble metal loadings due to the limited availability of Pt and Ir. This is easy to achieve for the Pt cathode catalyst, owing to its fast HER kinetics and the fact that a high dispersion of Pt is readily achieved with carbon-supported Pt (Pt/C). However, lowering the Ir loading below ≈0.5 mgIr/cm2 is not possible with currently available Ir catalysts (Ir black, nano-IrO2, or IrO2 supported on a TiO2 substrate), as it results in too thin, non-contiguous electrode layers with poor in-plane conductivity, owing to their low iridium packing density of ≈2.3 gIr/cm3 electrode (this is in contrast to ≈0.05-0.10 gPt/cm3 electrode for a typical Pt/C catalyst) [2]. Thus, to reach the long-term target of an Ir-specific power density of ≤0.01 gIr/kW [2], novel catalysts with a lower iridium packing density are required, which could be achieved, e.g., by supporting iridium or iridium oxide nanoparticles on conductive supports or by other approaches [3]. A detailed analysis leading to this conclusion will be discussed in this presentation.The development and implementation of such novel catalysts also requires the evaluation of their long-term stability. Conventionally, this is either done by measurements in liquid electrolyte, typically using the rotating disk electrode (RDE) technique, or testing in an actual PEM electrolyzer. Unfortunately, recent studies revealed that the RDE based approach does not yield reliable catalyst durability data, since for yet unknown reasons, the catalyst life-times obtained by the RDE method are three to four orders of magnitude lower than what is observed in PEM electrolyzers [3, 4]. On the other hand, catalyst durability testing in a PEM electrolyzer requires very long measurement times, so that accelerated durability test protocols are necessary [5]. These aspects will also be discussed.

Electrochemical Characteristics of Ni-Co Alloy Cermet Anodes for SOFCs

Introduction Nickel (Ni) is widely used as the anode material for SOFCs. However, metallic Ni is oxidized to nickel oxide (NiO) in an oxidizing atmosphere at SOFC operational temperatures. Ni anode degradation occurs when the hydrogen-containing fuel supply is reduced in high fuel utilization operation or interrupted during the shutdown [1]. Due to the redox cycles, Ni volume expansion and shrinkage cause irreversible degradation, by breaking electrically-conducting pathways. Highly durable SOFC anodes using e.g. Ni-based alloy are therefore under development [2]. Here, in this study, we focus on the Ni-Co alloy, by preparing a new Ni-Co-GDC cermet anode using the Ni-Co alloy, and evaluate the effects of Cobalt addition on their electrode performance and durability. Experimental In this study, we prepared the Ni-alloy cermet by mixing the powder and the binder, preparing and printing electrode paste on the electrolyte plate, followed by heat treatment. Scandia-Stabilized Zirconia (ScSZ, 10mol% Sc2O3-1mol% CeO2-89mol% ZrO2) was used as the solid electrolyte. The powder prepared by mixing Ni-Co-based oxide powder prepared by ammonia co-precipitation with Ce0.9Gd0.1O2 (GDC) in a specific ratio by weight, was used as the anode material. La1-xSrxMnO3 (LSM) powder was used as the cathode material. The electrochemical characteristics of the cells, with the Ni-alloy cermet anodes, were evaluated by I-V measurements and the current interruption method under the condition at 800oC, and 3%-humidified hydrogen fuel was supplied to the anode. Furthermore, the redox stability was evaluated using the durability test protocol simulating the fuel interruption. Anode microstructural changes before and after the redox cycling tests were observed by a focused-ion beam system coupled with a scanning electron microscope (FIB-SEM). Results and discussion Ni-alloy GDC anode with x mol% of Co added to Ni, is denoted as Ni(100 – x)Cox -GDC anode. The anodes of x = 0, 5, 10, 20, and 30 were fabricated. The I-V characteristics and overvoltages, under the condition where the operating temperature was 800oC and 3%-humidified hydrogen fuel was supplied, are shown in Fig. 1 for different Co contents in the alloy. With increasing the Co content, the electrochemical performance decreases due to a gradual increase in overvoltages. However, when the Co content is as low as 5 mol%, performance decrease is negligible. The microstructure of the Ni95Co5-GDC anode shown in Fig. 2 also shows that the distribution of Ni and Co is overlapped, confirming that a Ni-Co alloy is actually formed. Electrochemical properties and durability of the cells with the Ni-Co alloy anodes with various Co concentrations will be reported and discussed.

(Invited) Reverse Current Behavior and ADT Protocol for Start & Stop Operation of Bipolar Alkaline Water Electrolyzer

Introduction Water electrolysis is expected a key energy conversion system to introduce large-scale renewable electricity under power grid management. Here, less expensive large system is needed. Alkaline water electrolysis (AWE) systems are well-developed large system to combine hydropower generation, but fluctuated operation with start and stop operation is not considered for conventional systems. Therefore, improvement of durability to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current behavior of bipolar alkaline water electrolyzers and proposes accelerated durability test (ADT) protocol. Theoretical and Experimental Figure 1 shows configuration of bipolar alkaline water electrolyzer, principle of reverse current. An equivalent circuit to analyze reverse current is also shown in the figure. During electrolysis, surface Ni of anode oxidizes to Ni(III) and that of cathode reduces to Ni(0). They electronically connect on a bipolar plate and ionically connect through manifold to distribute electrolyte. In the equivalent circuit, electrochemical potential difference between anode and cathode on a bipolar plate correspond to electromotive force of Uk(t). The R 1 and R 2 correspond ionic resistances of branch and communicating tubes, respectively. Relationship among these parameters can describe as eq. 1 in Fig. 1 based on the Kirchhoff's laws, so reverse current would be estimated. In this study, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using commercially available industrial anode and cathode (De Nora Permelec Ltd). The reverse current was measured ionic current through communicating tube with D. C. clamp meter.As bipolar electrolyzer evaluation, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using the commercially available anode and cathode. Effective electrode size was 27 cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu).As start & stop operation simulated ADT protocol, we propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Results and discussion Figure 2 shows the setup of lab-scale electrolyzer and cell performances in the stacks. All cells showed almost the same performance. Figure 3 shows reverse currents and electrode potentials as a function of time for 2 to 4 cells stack electrolyzer. The longer cell stack had lager reverse current at initial period of stop operation. As the potential difference between anode and cathode decreased, the reverse current decreased. The anode potential significantly decreased certain time, and that for longer cell stack was shorter. For the 4 cells stack, the time for the BP2 was shorter than that for the BP1 and BP3. Simultaneously, the I 2 was larger than the I 1 and I 3. These behaviors could be explained with eq. 1 in the Fig. 1 with the same electromotive force of the U(t=0)s for initial period and time function of U(t)s with same surface condition for all cells at the end of electrolysis. Remarkable point is that the cathode potential of BP2 was higher than the anode, which is impossible with discharge of BP2 itself. This opposite potential of the BP2 would be forced by electromotive force of the BP1 and BP3.Figure 4 shows the anode potential at 10 mAcm-2 (E @10mAcm-2) of oxygen evolution reaction (OER) current during the ADT protocol with various minimum potential: E min. The all anodes significantly degraded for around 3-days test protocol, although DN851 was developed as an active and durable anode for conventional OER electrode. The degradation increased with decreases of the E min. Above 0 V vs. RHE of the E min, The E @10mAcm-2 increased after ca. 800 cycles of introduction period and reached around 1.69 V vs. RHE after 1900 cycles, although it increased from initial period and the increase continued around 2000 cycles for -0.3 V vs. RHE of the E min. From these experimental results, the E min of between 0 to 0.3 V vs. RHE might be suitable for the ADT protocol because of rapid degradation with robustness to the E min. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1