Start-stop Cycles Research Articles

Simultaneous accelerated stress testing of membrane electrode assembly components in polymer electrolyte fuel cells

The durability of polymer electrolyte fuel cells (PEFCs) in fuel cell electric vehicles is important for the shift from passenger cars to heavy-duty vehicles. The components of a PEFC, namely the proton exchange membrane (PEM), catalyst layer (CL), and gas diffusion layer (GDL), contribute to the degradation of the fuel cell performance. In this paper, we propose a method for simultaneously evaluating the degradation rates of these components by combining electrochemical characterization with operando synchrotron X-ray radiography. The open-circuit voltage, electrochemically active surface area (ECSA), and water saturation were used as the degradation indicators for the PEMs, CLs, and GDLs, respectively. The results of two accelerated stress tests (loading and start-stop cycles) after 10,000 cycles showed that the increase in water saturation owing to the loss of hydrophobicity due to carbon corrosion in the cathode GDL occurred on the same timescale as the degradation in the PEM and cathode CL. Specifically, during the load cycle AST, the cathode CL degraded with a 26% reduction in the ECSA along with the cathode GDL degradation with a 10% increase in water saturation. This suggests that more efforts should be devoted to studies on the durability of GDLs for heavy-duty applications.

Electrochemical Characteristics of Polymer Electrolyte Fuel Cells Using Pt-Ta-Co Electrocatalysts

Polymer electrolyte fuel cells for heavy-duty applications need highly active and durable electrocatalysts. For this purpose, electrocatalysts based on Pt-Ta-Co materials are here developed. This study evaluates the cell performance, the various overvoltages, start-stop and load cycling durability, and electrocatalyst layer microstructure under different fabrication conditions. Guidelines for higher power, higher performance, and higher durability of polymer electrolyte fuel cells are proposed. Using Pt7Ta2Co1/KB electrocatalysts, the initial catalytic activity, start-stop cycle durability, and load cycle durability were all significantly improved compared with a conventional Pt/C electrocatalyst.

Electrochemical Characteristics of Polymer Electrolyte Fuel Cells Using Pt-Ta-Co Electrocatalysts

Polymer electrolyte fuel cells for heavy-duty applications need highly active and durable electrocatalysts. For this purpose, electrocatalysts based on Pt-Ta-Co materials are here developed. This study evaluates the cell performance, the various overvoltages, start-stop and load cycling durability, and electrocatalyst layer microstructure under different fabrication conditions. Guidelines for higher power, higher performance, and higher durability of polymer electrolyte fuel cells are proposed. Using Pt7Ta2Co1/KB electrocatalysts, the initial catalytic activity, start-stop cycle durability, and load cycle durability were all significantly improved compared with a conventional Pt/C electrocatalyst.

PEFC Electrocatalysts using Highly-Graphitized Mesoporous Carbon Supports

The electrocatalysts used in polymer electrolyte fuel cells (PEFCs) are subject to oxidative corrosion of the carbon catalyst support due to start-stop cycling, as well as aggregation of Pt nanoparticles due to load fluctuations. The use of mesoporous carbon (MC) as a catalyst support has previously been shown to suppress aggregation. In this study, highly graphitized MC is prepared as a catalyst support to suppress both carbon corrosion and aggregation in Pt/MC electrocatalysts. The effect of graphitization temperature on the catalytic performance is evaluated, as well as the effect of pretreatment via either ball milling or pulverization to achieve suitable particle size. The results indicate that the initial activity of the electrocatalysts is improved by graphitization of the MC support after milling, and that the graphitization step improves the start-stop cycle durability.

A Tantalum-Rich Pt-Ta-Co Electrocatalyst for Polymer Electrolyte Fuel Cells

In polymer electrolyte fuel cells (PEFCs), Pt catalyst particle growth due to load fluctuation potential cycling, and oxidative corrosion of the carbon support due to start-stop potential cycling are important issues for cathode electrocatalysts affecting their durability. Here, we incorporate tantalum into the electrocatalyst to improve both the catalytic activity and durability. This is achieved via self-assembly of a nanocomposite electrocatalyst via dealloying to form Pt-Co alloy and TaOx support nanoparticles. Half-cell electrochemical measurements confirm that the catalytic activity and durability are significantly improved by the formation of this nanocomposite electrocatalyst.

Superior Electrochemical Performance and Rechargeability of Zinc Anodes Via Additive Manufacturing

Current roll-to-roll slurry-cast battery electrode manufacturing methods create serious restrictions for electrochemical energy storage, including: poor conductivity due to the presence of electrochemically inactive and electronically insulating binders, low energy density due to the need for foil current collectors, and limited form factors for electrode size/shape and cell design. Here, we report the benefits of advanced manufacturing methods for zinc anode rechargeability and performance.Zinc-based batteries pose an attractive alternative to lithium-ion (Li-ion) systems due to their excellent gravimetric and volumetric capacity, the increased safety and ionic conductivity of aqueous electrolytes, and the relative abundance and low price of zinc.Zinc metal is used as an anode in commercial alkaline batteries (i.e., Zn-MnO2) and other primary systems whose specific energies are comparable to (or higher than) Li-ion, such as Zn-Ag, Zn-Ni, and Zn-air, but which lack sufficient rechargeability to compete with Li-ion. Commercial zinc anodes comprise either zinc foil, which has high electronic conductivity but very low surface area, or zinc powders (i.e., zinc-binder powder composites or pastes), which have high surface area but poor inter-particle conductivity and long-range electrode connectivity; unfortunately, both of these form-factors significantly hinder zinc anode performance.One groundbreaking approach to overcome these problems utilized a monolithic 3D porous zinc “sponge” electrode architecture to produce high surface area and improved electronic conductivity [1]. These electrodes achieved ~ 90% zinc utilization when discharged in a primary Zn–air cell, and could be electrochemically cycled without macroscale dendrite formation in symmetric test cells (i.e., pure Zn sponge electrode vs. sponge electrode with Zn core/ZnO shell). Furthermore, nickel–zinc sponge alkaline cells achieved >100 high-rate cycles to 40% DODZn at lithium-ion-commensurate specific energy, and tens of thousands of cycles mimicking start-stop microhybrid vehicle duty cycles. The authors attributed this exceptional performance to architectural aspects of the electrodes, namely the interconnected porous voids and zinc domains. However, the authors acknowledged that the 3D porous “sponge” architecture could be improved through advanced manufacturing methods, such as laser powder bed fabrication (LPBF), which creates direct metallic connections between individual metal particles, without the need for solvents or non-conductive binders/surfactants. Additive manufacturing also provides exquisite control over electrode form factor, with high precision and resolution. Although porosity poses problems for the structural integrity of additively manufactured parts, the granular nature of sintered zinc powder has several potential benefits for electrochemical performance, including:(i) the direct, metallic connections between zinc particles are not degraded during charge/discharge, which preserves metallic conductivity throughout extended cycling;(ii) maximizing the total surface area of electrode in contact with the electrolyte.Another principal advantage of LPBF additive manufacturing is the ability to tune the density by adjusting the laser input to control the degree of melting. However, the main challenge for optimizing these additively fabricated samples is to create electrodes that are thin and porous enough to achieve complete zinc discharge and maximize the electrified electrode-electrolyte interfacial contact area without compromising the electrodes’ dimensional stability and integrity during extended charge/discharge cycling.Here, we present an electrochemical analysis of binder-free, pure zinc samples fabricated additively from zinc metal powder using LPBF. The manufacturability of thin-walled metallic deposits was demonstrated over a wide range of operating conditions, and the structures were characterized in terms of their thickness (200-500 µm), density (ρ=4-6.7 g/cm3) and roughness (Ra =10-15 µm).The electrodes provided a useful starting point for an evaluation of their electrochemical performance as anodes, and demonstrated facile electrochemical reversibility and extended cyclability, even without special electrolytes or electrode additives to improve electrochemical performance. The samples displayed stable and consistent cyclic voltammetry (CV) cycling at scan rates between 0.01 V s-1 and 1 V s-1, and completed multiple cycles at 50 mV/s without significant loss of capacity. Further, zinc-zinc symmetric cells containing additively manufactured anode and cathode displayed low overpotential (i.e., approximately 25 - 35 mV) and survived more than 2000 continuous hours of galvanostatic charge/discharge testing at 10 mAh cm-2. Full-cell galvanostatic charge/discharge testing is currently underway.This investigation provides a foundational starting point for further investigations of the benefits of additive manufacturing as a tool; for optimizing the architecture and structural features of zinc anodes. The results of our preliminary study portend well for our future efforts, which will focus on optimizing the thickness, density/porosity, geometric precision, and particle connectivity of additively manufactured zinc electrodes. REFERENCE [1] Parker JF, Chervin CN, Nelson ES, Rolison DR, LongJW.Wiring Zinc in Three Dimensions Re-Writes Battery Performance-Dendrite-Free Cycling. Energy Environ. Sci. 2014, 7, 1-3.

Tribo-Dynamic-Wear coupling analysis for Water-lubricated Bearings with journal surface imperfection under repeated start-stop cycles

Water-lubricated Bearings (WLBs) are the core transmission components of a ship propulsion system, and their wear behavior primarily occurs during the starting and stopping states. To characterize the wear behavior of WLBs, an equivalent experiment is conducted on bush material to obtain the relationship between dimensionless wear coefficient and sliding distance based on the Archard wear model. Then, an experimentally determined transient wear model is incorporated into a tribo-dynamic model to develop a fully coupled Tribo-Dynamic-Wear (TDW) model for the WLBs during repeated start-stop cycles. In this model, the 3D thermal effect, the transient bush worn surface and the geometric imperfection of the journal surface are considered. Numerical results show that the wear rate is more significant at the beginning of the start-up state and the end of the stopping state of the WLB. Meanwhile, it is found that compared to a perfect journal, a reasonable undulation number and undulated amplitude of the journal surface can improve the wear resistance performance of WLBs during repeated start-stop cycles. More specifically, a relatively lower undulation number leads to a smaller wear volume than the perfect journal, and the undulated journal surface has an optimal undulated amplitude that minimizes the wear volume.

Large-scale off-grid wind power hydrogen production multi-tank combination operation law and scheduling strategy taking into account alkaline electrolyzer characteristics

This paper proposes a multi-electrolyzer switching scheduling strategy based on the Pelican Optimization Algorithm (POA) to enhance the efficiency of large-scale wind power hydrogen production systems. To validate the effectiveness of the proposed strategy, we analyzed wind power data from three typical days in northern Hebei, China, with a 2.5 MW wind turbine output. We designed three strategies for comparative analysis: a simple start-stop strategy, a rule-based multi-electrolyzer switching strategy, and a POA-based multi-electrolyzer switching strategy. The study results demonstrate that the POA-based strategy exhibits higher hydrogen production efficiency and system stability under various wind conditions. Particularly, in extreme wind scenarios, this strategy significantly reduces the start-stop cycles of electrolyzers, thereby lowering operational costs and improving overall system performance. The main contribution of this study lies in the novel optimization algorithm and its validation through real-world data, demonstrating its effectiveness in large-scale wind power hydrogen production systems. Our findings provide new insights for enhancing the utilization of renewable energy and the economics of hydrogen production systems.

Predictive Set Point Modulation Control for Lithium-ion battery Management Systems with DC-DC Converters

Abstract Lithium-ion batteries, widely used in devices such as smartphones, remote controllers, and electric vehicles, often require adjustments to the output voltage to meet the varying demands of different devices. For instance, smartphones dynamically change the battery supply to enhance battery life, and electric vehicles necessitate different load voltages due to frequent start-stop cycles. This introduces the need for DC-DC converters to step up or step down the load voltage. However, this poses challenges to the stability of the bus voltage. In this study, we adopt a method for regulating the bus voltage reference value to predict and stabilize the voltage supplied by lithium-ion batteries. We first model the power supply system of lithium-ion batteries and then design a cascaded control framework for the voltage of DC bus. We introduce a predictive set-point control approach that eliminates the necessity to modify the energy storage system to mitigate voltage fluctuations. Simulation results illustrate that the proposed method effectively mitigates voltage overshoots in the DC bus.

Coordinated scheduling of wind-solar-hydrogen-battery storage system for techno-economic-environmental optimization of hydrogen production

Green hydrogen production powered by renewable energy emerges as a promising alternative to reduce emissions in the context of the global Net Zero target. Nevertheless, the inherent randomness and intermittency of renewables such as wind and solar cause prominent fluctuations in power supply to water electrolyzers, which pose challenges to their operational stability and efficiency, leading to decreased performance and shortened lifespan. To address these challenges, coordinated operation scheduling of the renewables-hydrogen system with multi-electrolyzers is investigated to enhance the system’s stability and efficiency while contributing to higher cost-effectiveness and sustainability. Meanwhile, the battery storage system is incorporated as a buffer to mitigate the variability of renewable power output and as a supplement to alkaline electrolyzers (AEL). This study also designs a dung beetle optimizer-gated recurrent unit (DBO-GRU) model for wind-solar power forecasting, offering guidance for more efficient and adaptive scheduling of AEL operations. To achieve multi-optimized scheduling of this integrated energy system, a refined rolling optimization strategy is developed, considering technical, economic, and environmental benefits to comprehensively improve green hydrogen production. Case studies using real-world scenarios validate its superiority across multiple time scales. For instance, compared with two other scheduling methods, the results show that the proposed strategy can respectively increase hydrogen production, reduce start-stop cycles, decrease LCOH, and lower carbon emissions by up to 4.19%, 25.40%, 7.98%, and 5.71% over a yearly-long operation. Therefore, the refined rolling optimization strategy simultaneously improves the overall system efficiency, operational cost-effectiveness, and sustainability of hydrogen production, underscoring its advantages and significance.

Pt-decorated tantalum oxide on mesoporous carbon supports for enhanced mass activity and start-stop and load cycling durability in PEFCs

Unique Pt/TaOx/MC cathode electrocatalysts for polymer electrolyte fuel cells (PEFCs) are developed using partially-reduced TaOx decorated on mesoporous carbon (MC). An initial mass activity (MA) of more than 500 A g−1 was observed for a TaOx/MC support heat treated at 700 °C in H2 or 1300 °C in Ar, more than double that of a conventional Pt/C electrocatalyst. The durability against start-stop and load potential cycling was successfully improved compared with the reference catalysts, as verified by half-cell voltammetry and full membrane-electrode-assembly (MEA) tests. Durability against start-stop cycling was attributed to the use of a thermochemically-stable TaOx support which prevents direct contact between Pt and MC, thus minimizing carbon corrosion. Durability against load cycling was mainly attributed to the mesoporous structure, preventing the agglomeration of Pt catalyst particles. As such, the Pt/TaOx/MC cathode electrocatalysts presented in this work have the potential to achieve both high durability and high power output, which is especially attractive for heavy-duty vehicular fuel cell applications.

Comparative analysis of degradation mechanisms in HT-PEM fuel cells under start–stop and load cycling with hydrogen and nitrogen-diluted feeds

The integration of reformers into high-temperature polymer electrolyte membrane (HT-PEM) fuel cells presents a significant opportunity to improve fuel flexibility and cost-effectiveness. To understand their degradation, we applied two start–stop cycling procedures: one with pure H2 and another with an 80 vol % H2 and 20 vol % N2 mix to simulate reformate gas. We also performed a load cycling test with H2 as anode gas. The results indicated that degradation rate of pure H2 start–stop cycling showed 306 μV h−1, while load cycling demonstrated a degradation rate of 19.7 μV h−1 for the current density of 0.2 A cm−2, and 88.2 μV h−1 for the current density of 0.4 A cm−2. Start–stop cycling with diluted gas resulted in a constant voltage drop with a degradation rate of 3.129 mV h−1. Electrochemical impedance spectroscopy (EIS) indicated an increased ohmic resistance during start–stop cycling and higher charge transfer (high-frequency) and mass transport (low-frequency) resistance with nitrogen introduction. Scanning electron microscope results confirmed MEA degradation. In conclusion, start–stop cycling and anode gas dilution are stressors that accelerate HT-PEM fuel cell degradation, reducing its lifetime.

Highly Hydrophilic Zirconia Composite Anion Exchange Membrane for Water Electrolysis and Fuel Cells.

To prepare anion exchange membranes with high water electrolysis and single fuel cell performance, an inorganic-organic composite (IOC) strategy with click cross-linked membranes coated with different contents of hydrophilic polar nanozirconia is proposed to fabricate composite membranes (CM) PBP-SH-Zrx. The performance test results showed that the CM PBP-SH-Zr4 not only has good through-plane ionic conductivity (167.7 mS cm-1, 80 °C), but also exhibits satisfactory dimensional stability (SR 16.5%, WU 206.4%, 80 °C), especially demonstrating excellent alkaline stability with only 16% degradation (2 M NaOH for 2200 h). In water electrolysis, the "microgap" between the membrane and catalyst layer (solid-solid interface) is alleviated, and the membrane electrode assembly (MEA) interfacial compatibility (liquid-solid-solid interface) is enhanced. The CM PBP-SH-Zr4 showed the lowest charge transfer resistance (Rct, 0.037 Ω cm2) and a high current density of 2.5 A cm-2 at 2.2 V, while the voltage drop was 0.361 mV h-1 after 360 h of endurance (six start-stop cycles) at 60 °C and 500 mA cm-2, proving a good water electrolysis durability. Moreover, an acceptable peak power density of 0.464 W cm-2 at 80 °C is achieved in a H2/O2 fuel cell with a PBP-SH-Zr4-AEM. Therefore, the IOC strategy can enhance the membrane's comprehensive performance and interface compatibility of MEA and may promote the development of anion exchange membranes (AEMs) for water electrolysis and fuel cells.

Ventilation control of road tunnels towards disturbance suppression

In recent years, research on ventilating tunnels has become increasingly important. However, the impact of external disturbances on ventilating systems has been largely ignored. To address this issue of frequent airflow fluctuations caused by external perturbations, which cannot be fully compensated using conventional control methods, this study proposes a perturbation-compensated ventilation control approach. A disturbance compensator is developed by incorporating the tunnel’s airflow velocity and the number of jet fan start-stop events as input parameters. By compensating for external disturbances, the disturbance to the system is reduced. The Simulink model of the tunnel controller was used for simulation experiments. The compensator demonstrated good tracking results in comparison experiments with different disturbances. The ventilation approach based on disturbance compensator is capable of regulating the fluctuation of CO concentration within a justifiable range compared to using PID control and ADRC. This not only improves the stability of the entire control system but also significantly prolongs the service life of the jet fan by reducing the frequency of start-stop cycles.

Investigation on the transient asperity contact behaviors of water-lubricated bearing under start-stop cycle

Investigation on the transient asperity contact behaviors of water-lubricated bearing under start-stop cycle

Highly Durable Membrane–Electrode-Assemblies Using High M w and Ether-Free Polyfluorene-Based Electrolytes for Anion Exchange Membrane Water Electrolyzer

Water electrolysis technology, which produces hydrogen through electrolysis of water using electricity derived from renewable energy, is attracting attention as a way to realize a carbon-neutral society. Among water electrolysis systems, anion exchange membrane water electrolysis (AEMWE) can achieve high energy conversion efficiency and quick response to fluctuating power supplies by using thin polymer electrolyte membranes, and operates in an alkaline environment, allowing the use of inexpensive non-precious metals for bipolar plates and electrodes. However, conventional AEMs and ionomers exhibit low durability in high-temperature and alkaline environments, which is a critical issue in realizing high-performance and highly durable membrane–electrode assemblies (MEAs) for AEMWE.Our group developed high-molecular-weight (M w) and ether-free, polyfluorene-based anion conducting polyelectrolyte (PFT-Cx-TMA, Cx represent the number of carbon atoms in the alkyl side chain) as shown in Fig. 1a.1 These polyelectrolytes show high OH− conductivity over 100 mS cm− 1, high chemical durability (stable in 8 M NaOH at 80 °C for 168 h), and high tensile strength (25–42 MPa, comparable to a Nafion membrane). This study applied PFT-Cx-TMA to AEMs and ionomers in MEAs to evaluate the durability against various AEMWE operations (constant current operation and start-stop operation in different voltage ranges), demonstrating MEAs with both high performance and high durability.Fig. 1b shows the constant current durability of the MEA with PFT-C8-TMA as AEM and ionomer.2 This test was performed at the constant current density of 0.2 A cm− 2 and 80 °C using a 1 M KOH aqueous solution fed to the anode. Here, to investigate the effects of AEMs and ionomers on MEA durability, conventional precious metal catalysts (anode: IrO2, cathode: Pt/C or PtRu/C) were used in the MEA. The MEA with PFT-C8-TMA exhibited a current density of 1.0 A cm− 2 at 1.79 V and there was almost no voltage change even after the constant current operation for over 100 h. It is noteworthy that the MEAs using PFT-C8-TMA and PFT-C10-TMA demonstrated high performance and high durability not only in the alkaline-fed operation but also in the pure-water-fed operation.Next, this study investigated the start-stop durability of MEAs using voltage cycles simulating the start-stop operation of water electrolyzer. Here, square-wave voltage cycling of holding at 1.8 V and 0.1 V for 1 min each was used for the start-stop test at 80 °C with a 1 M KOH solution fed to the anode. As a comparison, the MEA was prepared using a commercial AEM (Sustainion X37-50, 50 μm in thickness) and ionomer (Sustaionion XB-7). As shown in Fig. 1c, the MEA using a PFT-C10-TMA AEM (56 μm in thickness) and ionomer was highly durable in the start-stop test compared to the MEA using commercial Sustaionion. During the test, the elution of black solid particles from the catalyst layer and the increase in charge transfer resistance (Rct) were observed in the MEA with Sustaionion, whereas no elution of catalyst materials and no change in Rct were confirmed in the MEA with PFT-C10-TMA. These results suggest that nonlinear mechanical stress via rapid bubble formation and shutdown during start-stop cycles caused the leaching of catalysts, resulting in the performance loss of the MEA with Sustainion. The commercial ionomer (Sustainion XB-7) exhibits a large dimensional change (156%) compared to the PFT-C10-TMA membrane (34%) at 80 °C in a 1 M KOH aqueous solution. Catalyst particles covered with a highly swollen ionomer are easily detached from a catalyst layer by the nonlinear mechanical stress. On the other hand, the PFT-C10-TMA ionomer has a high molecular weight (M w = 240000 g mol−1), low swelling degree, and well-entangled polymer chains, hence preventing leaching of the catalyst particles.In summary, this study demonstrates that MEAs using high M w and ether-free polyfluorene-based electrolytes with both high chemical and mechanical durability have excellent durability for AEMWE operations including constant and dynamic (start-stop voltage cycling) operations. Acknowledgement This presentation is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References (1) S. Miyanishi and T. Yamaguchi, Polym. Chem., 2020, 11, 3812–3820.(2) R. Soni, S. Miyanishi, H. Kuroki, and T. Yamaguchi, ACS Appl. Energy Mater., 2021, 4, 1053–1058. Figure 1

Power Generation Charactristics of Polymer Electrolyte Fuel Cells with Electrocatalysts Supported on SnO2 in High Current Density Range

Introduction Considerable efforts have been made for FCEV commercialization, for which sufficient performance and durability have to be achieved1. SnO2-supported electrocatalysts with carbon backbone have a potential to achieve both high catalytic activity and high cycling durability2-3. However, it is necessary to further optimize cell performance up to high current densities for such alternative electrocatalysts. By controlling the thickness of the seal material and optimizing the Nafion content of the electrocatalyst layer, successful reduction of various overvoltages and improved power generation performance can be achieved, especially in the high current density region4. This study aims to further improve cell performance at high current densities by varying electrocatalyst layer fabrication conditions and selecting suitable settings for the MEAs. Experimental Using mesoporous carbon (MC) as a support backbone and SnO2 as a support surface layer on the cathode side5, membrane-electrode-assemblies (MEAs) with Pt/Sn0.92Nb0.08O2/MC electrocatalysts were fabricated. On the anode side, a standard Pt/C catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) was used. Cell performance and overvoltages up to high current densities were measured by varying the size of electrocatalyst particles. Start-stop cycle tests up to 60,000 cycles were also conducted. Results and discussion By ball milling before the Pt loading process in the preparation of the SnO2-supported electrocatalyst Pt/Sn0.98Nb0.02O2/MC, various overvoltages could be reduced, and cell performance became almost comparable to that of the standard Pt/C catalyst. Figure 1 shows the comparison of IV characteristics and Figure 2 shows the comparison of microstructures of electrocatalyst layers. Ball milling resulted in a more appropriate microstructure of the electrocatalyst layer due to the homogenization of the electrocatalyst particle size. As shown in Figure 3, the ECSA retention after 60,000 start-stop cycles was about 50%. Even when MC was used as the support framework, high durability could be achieved due to the presence of SnO2, which was further improved by ball milling. Without ball-milling, the retention was about 45%.In the future, we aim to further improve cell performance by controlling the porous microstructure and water management of the electrocatalysts layer. We will fabricate cells under various conditions, conduct performance tests, and analyze overvoltages. The start-stop and load cycle durability will also be evaluated. Based on these efforts, the latest results of cell performance and durability tests will be presented. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523 (2022).Nakazato, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, K. Sasaki, J. Electrochem. Soc., 165, F1154 (2018).Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, K. Sasaki, J. Electrochem. Soc., 165, F1164 (2018).Ogawa, Y. Inoue, K. Yamamoto, M. Yasutake, Z. Noda, S. M. Lyth, J. Matsuda, M. Nishihara, A. Hayashi, K. Sasaki, ECS Trans., 109 (9), 241 (2022).Inoue, M. Yasutake, Z. Noda, S. M. Lyth, M. Nishihara, A. Hayashi, J. Matsuda, K. Sasaki, ECS Trans., 109 (9), 413 (2022). Figure 1

PEFC Electrocatalysts Using Ta-Based Support on Mesoporous Carbon

Introduction Cathode catalysts of polymer electrolyte fuel cells (PEFCs) are subjected to a severe environment with strong acidity and high potential, leading to catalyst degradation[1]. In particular, the degradation of electrocatalysts in fuel cell vehicles is often caused by oxidative corrosion of their carbon support during start-stop cycles, and by dissolution and re-deposition of platinum during load cycles[2]. Our research group has developed electrocatalysts using Nb-doped SnO2 on carbon support, achieving high start-stop potential durability[3]. The use of Ti and Sn as metal supports instead of carbon has also been considered as a fundamental solution against start-stop related degradation[4]. However, catalytic activity has to be improved, compared to the standard Pt/C catalysts. Here in this study, catalysts using mesoporous carbon (MC) support are prepared using metallic Ta with a high melting point. Parameters such as loading and heat treatment conditions are varied to tailor higher performance and durability of PEFC electrocatalysts. Experimental Ta/MC supports were prepared by steam hydrolysis of an ethoxide reagent on mesoporous carbon (CNovel®, TOYO TANSO) with mesopores of 10 nmΦ. The Pt/Ta/MC catalysts was then prepared by decorating with Pt using the acetylacetonate (acac) method[5] . The microstructure of the prepared Ta/MC supports and the Pt/Ta/MC catalysts was observed using scanning transmission electron microscopy (SU9000, Hitachi High-Tech Corp., Japan). Electrochemical characterization of the catalysts was performed by half-cells: Pt electrochemical surface area (ECSA) was evaluated by cyclic voltammetry (CV), and oxygen reduction reaction activity (ORR activity) was evaluated from the activation-dominant current value by rotating disk electrode (RDE) measurements. The catalysts durability was evaluated by applying potential cycles simulating start-stop and load cycles. Results and discussion As shown in Fig. 1, microstructural observation of the catalyst supports by STEM confirmed that small Ta particles were uniformly supported, and that the Ta particles were impregnated into the mesopores of MCs. EDS elemental analysis was performed to calculate the residual oxygen content. It was found that the reduction of Ta2O5 to Ta proceeded by high-temperature heat treatment in an H2 atmosphere. The initial activity and durability of the prepared Pt/Ta/MC catalysts were evaluated by half-cell electrochemical measurements. ECSA and mass activity were 78.5 m2/g and 179.2 A/g, respectively, showing initial activity approaching that of the standard Pt/C catalyst. Regarding durability, high load cycle durability was confirmed. In this presentation, the microstructure and electrochemical properties of the Pt/Ta/MC catalysts will be presented as alternative cathode catalysts. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

(Poster Award - Honorable Mention) Ta2O5 Catalyst Support for Polymer Electrolyte Fuel Cells

Pt/C is widely used as polymer electrolyte fuel cells (PEFC) electrocatalysts. The cathodic environment of PEFC is prone to high acidity and high potential, which can degrade cell performance due to carbon corrosion 1. Therefore, electrocatalysts with oxide support such as SnO2 supported on carbon-based materials have been developed, achieving high durability. Further improvement of their catalytic performance is desirable, using a Pt-based alloy catalyst and a mesoporous carbon (MC) 2,3. However, studies using SnO2 as a support have suggested that the low melting point of Sn caused alloying of Pt and Sn and/or melting of metallic Sn, causing degradation of catalytic activity 3. From these reasons, here, we focus on tantalum (Ta) with much higher melting point to fabricate Ta2O5/MC electrocatalysts support, which can support Pt alloy catalysts to achieve both high durability and high activity. Ta2O5 was prepared by a sol-gel method using Ta-ethoxide, and Pt-Co alloy nano-particles were deposited via the acetylacetonate method 4. The amount of Ta2O5 on the MC was set to be 30 and 60 wt.%, and the durability was evaluated by varying the amount of Ta2O5. The molar ratio of Pt to Co was set at 3:1. The microstructure of the electrocatalyst was observed by field-emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM), and the alloy was evaluated by XRD measurements. Half-cell tests were made to evaluate electrochemical performance and durability (load cycle and start-stop cycle). From the XRD measurements, the Pt peaks were shifted and the Ta2O5 peaks were confirmed, indicating that Pt-Co alloys were formed without forming the alloy of Pt and Ta. FESEM observation revealed that Ta2O5 particles were impregnated with a diameter of about 5 nm, and Pt-Co alloy particles were impregnated with a diameter of 2 to 3 nm. Some of catalyst particles were found to be impregnated on Ta2O5, but no significant selectivity to Ta2O5 was observed. Both Pt effective surface area (ECSA) and oxygen reduction reaction (ORR) activity of the prepared catalysts were higher than of Pt/C, confirming the positive effect of Pt-Co alloy and MC on activity enhancement. Figure 1 shows that the load potential cycle durability was improved using MC, and the start-stop cycle durability was improved by using Ta2O5. In particular, the electrocatalysts with a lower loading of Ta2O5 exhibited higher durability under load potential cycling and subsequent higher ECSA compared to the Pt-Co/C electrocatalyst. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Ohma, K. Shinohara, A. Iiyama, T. Yoshida, and A. Daimaru, ECS Trans, 41(1), 775 (2011).Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K.Sasaki, J. Electrochem. Soc., 165 (14), F1164 (2018).Inoue, M. Yasutake, Z. Noda, S. M. Lyth, M. Nishihara, A. Hayashi, J. Matsuda, and K. Sasaki, ECS Trans., 109 (9), 413 (2022).Hayashi, H. Notsu, K. Kimijima, J. Miyamoto, and I. Yagi, Electrochem. Acta., 53, 6117 (2008). Figure 1

Performance and Durability of Carbon-Free Ionomer-Free PEFC Cathode Using Pt Nanosheet Catalyst

Polymer electrolyte fuel cells (PEFCs) have been attracting attention as highly efficient power sources and have been commercialized for use in residential power plants and automobiles. However, further widespread adoption requires the development of low-platinum catalysts. Additionally, for installation in heavy duty vehicles such as large trucks, high durability at high temperatures is necessary. Pt nanosheets (Pt(ns)), consisting of several atomic layers of Pt with a flat structure, possess high mass activity and durability due to the high specific surface area and low surface energy [1]. Conventional PEFC electrodes consisting of carbon-supported platinum (Pt/C) catalyst and ionomer suffer from degradation due to dissolution/redeposition, Ostwald ripening, and agglomeration of Pt, corrosion of the carbon support, and Pt poisoning by ionomer. Therefore, using unsupported Pt(ns) for an electrode that consists of neither carbon nor ionomer is expected to eliminate the degradation factors, resulting in a highly active and durable electrode. The purpose of this study is to develop highly active and durable electrodes by using Pt(ns) and eliminating degradation factors by making them carbon-free and ionomer-free.Polycrystalline Pt(ns) was synthesized by interlayer oxidation of graphene, as described elsewhere [2]. Catalyst ink was prepared, and cathode catalyst layers were created by dropping or spraying it onto carbon paper. A membrane-electrode assembly (MEA) was made by hot-pressing the cathode catalyst layer together with an anode made of Pt/C onto an electrolyte membrane. Power generation was conducted at 80˚C by supplying H2 to the anode and O2 or air to the cathode, each humidified under ambient pressure. Durability was evaluated by repeatedly applying cyclic potentials between 1.0 V and 1.5 V, supplying N2 to the anode and cathode, and examining changes in the cyclic voltammogram.The I-V curves of MEAs with ionomer-free carbon-free Pt(ns) cathodes fabricated using drop-coating and spray-coating methods and measured using air and oxygen as the cathode supply gases are shown in Fig. 1. As demonstrated in the figure, the activation overpotential at low current density was high, suggesting a low Pt utilization. The shape of the I-V curve of MEA using the spray method at high current density indicated that the concentration overpotential was suppressed under oxygen conditions but was high under air conditions. On the other hand, the concentration overpotential of the MEA using the drop method was high even under oxygen conditions. This may be attributed to the small spaces between the restacked nanosheets, which inhibited diffusion.A start-stop simulated potential cycle test was conducted for the MEA using ionomer-free carbon-free Pt(ns) cathode. The CV curves measured after a certain number of cycles are shown in Fig. 2. As shown in the figure, the change in the shape of the CV was small, and the ECSA remaining rate of the electrode was above 80% even after 8000 cycles, whereas that of the Pt/C cathode was less than 50% after 4000 cycles. This suggests that carbon-free ionomer-free Pt(ns) electrode has the potential as highly durable low Pt electrodes.AcknowledgementPart of this paper is based on results obtained from a project, JPNP20003, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).