High Current Density Operation Research Articles

Progress on Coherent Perovskites Emitters: From Light‐Emitting Diodes under High Current Density Operation to Laser Diodes

Progress on Coherent Perovskites Emitters: From Light‐Emitting Diodes under High Current Density Operation to Laser Diodes

High Current Density Operation of a Proton Exchange Membrane Fuel Cell with Varying Inlet Relative Humidity—A Modeling Study

This paper focuses on proton exchange membrane fuel cell (PEMFC) operation at current densities in the order of 6 A/cm2. Such high current densities are conceivable when the traditional carbon fiber papers are replaced with perforated metal plates as the gas diffusion layer to enhance waste heat removal, and at the same time the relative humidity inside the fuel cell is kept below 100% by applying appropriate operating conditions as was found in previous one-dimensional modeling work. In the current paper, we applied a three-dimensional, multi-phase computational fluid dynamics model based on Ansys-CFX to obtain additional insight into the underlying physics. The calculated pressure drops are in very good agreement with previous one-dimensional modeling work, and the current densities in all case studies are in the order of 5–6 A/cm2, but different from the previous one-dimensional study, the results suggest that the relative humidity is very close to 100% throughout the entire channel length when the inlet relative humidity is 100%, ensuring best hydration cell conditions and hence best performance. Importantly, the model results suggest that fuel cell performance at a high current density in conjunction with relatively low stoichiometric flow ratios around 1.5–2 is possible.

Novel Ru-Based PEM Electrolysis Catalyst – Development from the Nano- to the Industrial-Scale

For the de-fossilization of sectors like chemicals, steel, and transportation, green H2 generated via water electrolysis provides a path towards net-zero. The broad use of H2 across hard-to-abate sectors confirms the urgent need for green hydrogen at scale.Within water electrolysis, there are several competing technologies: the so-called solid oxide electrolysis cell (SOEC), alkaline water electrolysis (AEL) and polymer electrolyte membrane electrolysis (PEM EL). Here, the latter shows significant benefits, such as high current density operation (> 2 A/cm2) and thus a smaller footprint, highly dynamic operation mode, high gas purity, and generation of pressurized hydrogen. However, at present, PEM EL requires precious metal catalysts; in particular, the O2 evolution on the anode currently relies on iridium, a metal which is rather scarce and expensive [1].To meet the demand of iridium with respect to the announced increase in electrolyzer capacities in the multi-GW range, material innovation to reduce the use of this precious metal must be implemented. Successful catalyst and electrode developments have already been demonstrated in the BMBF funded project Kopernikus P2X, whereby loadings of approx. 0.3 mg/cm2 (< 0.1 g/kW1) have been achieved without any significant losses in activity over time [2, 3].Here, we present a material innovation in the form of Ru-based electrocatalysts with a significantly reduced Ir content. This ruthenium-iridium oxide can be adjusted in a wide range of Ir content down to less than 15 wt.% (Ir). Consequently, iridium-based electrode loadings of less than 0.1 mg/cm2 and mass activities of about 3,500 A/g are feasible. Moreover, in accelerated degradation tests those mixed-oxides have demonstrated the often-missing stability by showing low degradation rates, similar to that of pure IrO2, in up to 30,000 potential-induced stress cycles.This achievement stems from a remarkable screening approach that combines synthesis, characterization and testing at the nanoscale at Mattiq, and on industrial scale in the multi-gram range at Heraeus Precious Metals GmbH & Co. KG. Remarkably the alignment of degradation testing on both scales showcases the power of the applied method, providing a blueprint for high throughput screening for future material developments, both within water electrolysis and beyond.

Modulating *OOH Adsorption on RuO2 for Efficient and Durable Acidic Water Oxidation Electrocatalysis.

Acidic water electrolysis is of considerable interest due to its higher current density operation and energy conversion efficiency, but its real industrial application is highly limited by the shortage of efficient, stable, and cost-effective acidic oxygen evolution reaction (OER) electrocatalysts. Here,an electrocatalyst consisting of Ni-implanted RuO2 supported is reported on α-MnO2 (MnO2/RuO2-Ni) that shows high activity and remarkable durability in acidic OER. Precisely, the MnO2/RuO2-Ni catalyst shows an overpotential of 198mV at a current density of 10mA cm-2 and can operate continuously and stably for 400h (j = 10mA cm-2) without any obvious attenuation of activity, making it one of the best-performing acid-stable OER catalysts. Experimental results, in conjunction with density functional theory calculations, demonstrate that the interface electron transfer effect from RuO2 to MnO2, further enhanced by Ni incorporation, effectively modulates the adsorption of OOH* and significantly reduces the overpotential, thereby enhancing catalytic activity and durability.

Effect of gas diffusion layer surface property on platinum nanowire array electrode performance in proton exchange membrane fuel cells

3D-ordered catalyst electrodes have been recognized as one effective strategy to reach high current density operation for proton exchange membrane fuel cell (PEMFC) applications. Gas diffusion electrodes (GDEs) with platinum nanowire arrays in-situ grown on gas diffusion layer (GDL) surface is an important contribution in this area, but the performance is highly dependent on the GDL surface properties. In this study, the GDLs available in the market are systematically investigated, with a focus on the influence of the GDL surface properties on the in-situ growth of Pt nanowire arrays to fabricate GDEs as cathodes for PEMFCs. The experimental results indicate that mesopores especially micropores play a key role. They enable a hydrophilic surface for the isopropanol pretreated GDL, facilitating the in-situ growth of Pt nanowires to form a uniform array with a large electrochemical surface area (ECSA), finally leading to a high-power density. With Freudenberg H24CX483 carbon paper GDL, the highest power density of 0.9 W cm−2 is achieved. The understanding achieved here could be further used to develop novel GDLs for fabricating the next generation of electrodes for large current density operations.

Progress on Coherent Perovskites Emitters: From Light‐Emitting Diodes under High Current Density Operation to Laser Diodes

Perovskites exhibit appealing optical and electrical properties, making them attractive candidates for efficient luminescent materials with low‐cost and straightforward fabrication processes. Their versatility is highlighted by the ability to deposit perovskite thin films on various substrates, including silicon, glass, sapphire, and flexible substrates, enabling potential monolithic integration on silicon for applications such as photonic integrated circuits, high‐speed communication. Extensive studies on perovskite light‐emitting diodes have shown external quantum efficiencies exceeding 20% across a wide spectral range from deep blue to near‐infrared, with chirality. Additionally, perovskite‐based lasing action has been achieved under pulsed optical excitation and continuous‐wave operation, as well as in functional diode structures. However, realizing electrically driven perovskite laser diodes for practical applications requires the injection of intense current densities. This review provides a comprehensive overview of the historical progress in perovskite lasers and light‐emitting didoes, along with important design considerations essential for their development.

Efficient oxygen reduction to alkaline peroxide at current densities up to 500 mA cm−2 on a gas diffusion electrode with hydrophobic carbon microporous layer: Influence of fluid dynamics and reactor operation on scale-up

The two-electron electrochemical O2 reduction reaction (2e-ORR) on a gas diffusion electrode (GDE) using clean electricity is an attractive process for generating the green oxidant hydrogen peroxide (H2O2). Electrolyte flooding through the porous catalyst and diffusion layers is one of the major factors inhibiting the operational stability and longevity under industrially relevant current densities (>100 mA cm−2). This study reports for the first time that optimizing the two-phase flow and the mode of reactor operation brings about a remarkable improvement in the high current density operation (up to 500 mA cm−2) on a scalable (20 cm2 geometric area) and commercially available Sigracet 39BB GDE with the microporous carbon layer (MPL) acting as the catalyst layer. The interacting effects of current density, gas and liquid flow rates and the flooding threshold limit for the differential liquid/gas pressure were determined. While high peroxide Faradaic efficiency (FE > 95 %) was attained in a gas flow-by mode during short-term experiments, long-term stability was only established when the gas was switched to the flow-through or quasi-flow-through mode of operation. Under the latter conditions, at 500 mA cm−2 operational stability of more than 20 h was demonstrated with a peak FE of 97 % in 1.0 M KOH, at 293 K, 1 atm. It was found that optimizing the reactor operation has a profound effect during scale-up, and developing novel catalytic materials for 2e-ORR to alkaline peroxide is not warranted since a low-cost microporous carbon-based GDE is sufficient for stable and efficient operation.

Effects of temperature and pressure on the limiting current density of PEM electrolysis cells based on a theoretical prediction model and experiments

Operation at high current density of polymer electrolyte membrane electrolysis cell (PEMEC) can reduce its electrode area and capital expense. The high current density operation is limited by the limiting current density (LCD), where electrolysis voltage abruptly increases. Effects of operating temperature and pressure on the LCD were evaluated in a lab-scale PEMEC within a range from 70 to 90 °C and from 0.1 to 0.3 MPa. Also, a theoretical model was developed to predict the LCD, and to clarify what determines LCD and how the operating conditions influence the LCD. The theoretical analysis suggests that when current density is close to the LCD, water mass transport at anode reaches a limitation, which indicates that water saturation reaches almost zero at anodic catalyst layer. The analysis also finds that lower operating temperature and higher operating pressure can reduce oxygen gas saturation and raise the water saturation in porous transport layer at anode, and finally enlarge the LCD.

Thermoelectric Limitations of Graphene Nanodevices at Ultrahigh Current Densities.

Graphene is atomically thin, possesses excellent thermal conductivity, and is able to withstand high current densities, making it attractive for many nanoscale applications such as field-effect transistors, interconnects, and thermal management layers. Enabling integration of graphene into such devices requires nanostructuring, which can have a drastic impact on the self-heating properties, in particular at high current densities. Here, we use a combination of scanning thermal microscopy, finite element thermal analysis, and operando scanning transmission electron microscopy techniques to observe prototype graphene devices in operation and gain a deeper understanding of the role of geometry and interfaces during high current density operation. We find that Peltier effects significantly influence the operational limit due to local electrical and thermal interfacial effects, causing asymmetric temperature distribution in the device. Thus, our results indicate that a proper understanding and design of graphene devices must include consideration of the surrounding materials, interfaces, and geometry. Leveraging these aspects provides opportunities for engineered extreme operation devices.

Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

AbstractPorous transport layers (PTL) and their surface properties have the potential to improve the performance of proton exchange membrane water electrolyzers (PEMWE), which is imperative to reduce feedstock costs and lead to their widespread implementation. This work introduces a novel generation of titanium microporous layers (MPLs) with ultra‐low thicknesses of ≈20 µm which reduces raw material costs. They also feature advanced interfacial properties tailored to maximize catalyst utilization at low Ir‐loadings. The bulk morphology and surface properties of the hierarchically structured PTLs are assessed by X‐ray tomographic microscopy. The low surface roughness of the MPL allows the use of thinner membranes since it minimizes possible deformations in the membrane. Cells containing the MPLs outperformed those containing state‐of‐the‐art commercially available PTL materials by up to 100 mV at 7 A cm−2 in combination with low‐loaded catalyst‐coated membranes of 0.4 mgIr cm−2. Hydrogen crossover is also reduced, especially at low current densities, leading to a larger turndown ratio which can enable more cost‐effective operating strategies. Finally, these rationally designed MPLs also lead to high catalyst utilization by overcoming the naturally occurring high in‐plane resistance of low‐loaded catalyst layers.

Extended power to hydrogen operations for enhanced grid flexibility in low carbon systems

Power-to-hydrogen (P2H) systems are increasingly recognized as a promising solution to expedite the integration of Renewable Energy (RE) in various energy sectors. P2H in Hydrogen Consuming Industries (HCIs) can serve hydrogen demands and the much-needed flexibility for power system operations. However, consideration of these systems for significant industrial and power sector use cases requires modelling fidelities for exact operational and economic reflections. P2H operational modelling for flexibility focuses on excess renewable energy evacuation and storage only while often oversimplifying their models by using constant efficiency models or neglecting specific Hydrogen Electrolyzer (HE) overvoltage components. Under variable operations and downstream HCI demands, this can lead to inaccurate assessments, undermining existing flexibility quantum from HCIs. Another prevalent issue with P2H adoption is its costs, which are directly linked with P2H operating ranges. These systems are presently modelled with constrained operations, leading to increased costs and limited ability to provide grid services. Therefore, appropriate modelling of HCIs considering P2H device working characteristics and its inherent flexibilities is essential. It can allow cost-effective operations and the exchange of accurate flexible margins with electrical grids. In this regard, this work proposes a comprehensive extended electro-chemical HE model for HCIs allowing high current density working through the extended operation of P2H. The considered model inherits intrinsic working characteristics of electrolyser operation, i.e., variable current, nonlinear efficiency, and loading, to cater to the hydrogen demands of HCI. The effect of high current density operations is elucidated through device operations under reaction kinetics. The results highlight that the proposed model integrated with the electrical grid provides actual operational costs and flexibility margins. A comparison of various modelling approaches and their effect on adjustable margins demonstrates a considerable difference in P2H loading, working efficiency, operating costs, and adjustable margins with the proposed model.

Enhanced Water Management in Fuel Cell Cathodes by the Application of Superhydrophobic Fluorinated Carbon Microporous Layers

Under high current density operation, the efficiency of polymer electrolyte fuel cells (PEFCs) can dramatically decrease. This is due to water accumulation at the cathode side, preventing oxygen diffusion to the electrocatalyst. As such, effective water management is of vital importance by use of a suitable gas diffusion layer (GDL) and/or microporous layer (MPL). MPLs generally consist of carbon black as the porous electron conducting phase, and polytetrafluoroethylene (PTFE) as a hydrophobic binder. Here, we instead use superhydrophobic fluorinated carbon powder in the MPL as a novel material to decrease the required PTFE content. It is confirmed that the water contact angle of the MPL can be increased from 131° to 151° by using fluorinated carbon. Moreover, the fluorinated carbon MPL shows lower oxygen transport resistance at high humidity. Furthermore, in single fuel cell tests at various temperatures and relative humidity values, the I–V performance is significantly and consistently better than for the conventional MPL. These results confirm that fluorinated carbon is a promising new material for water management in the MPLs of PEFCs.This paper is based on results obtained from project JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).1. Tailored Wettability in Fluorinated Carbon Nanoparticles Synthesized from Fluorotelomer Alcohols, E. Can, M. Nishihara, K. Sasaki, S. M. Lyth, Applied Surface Science, 157136 (2023)2. Superhydrophobic Fluorinated Carbon Powders for Prevention of Flooding in PEFCs, E. M. Can, A. Mufundirwa, T. Kitahara, M. Nishihara, K. Sasaki, S. M. Lyth, Journal of Power Sources, 548, 232098 (2022)3. Solvothermal Synthesis of Superhydrophobic Hollow Carbon Nanoparticles from Fluorinated Alcohol, S. M. Lyth, W. Ma, J. Liu, T. Daio, K. Sasaki, A. Takahara, and B. Ameduri, Nanoscale, 7, 16087 (2015)

Effect of Operating Temperature and Pressure on the Limiting Current Density of PEM Electrolysis Cell Based on Theoretical Prediction Model and Experiments

Introduction The PEM electrolysis cell (PEMEC) exhibits great potential to produce hydrogen gas. However, the high cost associated with cell components, such as the iridium oxide catalyst and titanium porous transport layer, poses a challenge to the commercialization of PEMEC. So, continued research is needed to improve the cost-effectiveness of PEMEC. Operation at high current densities can minimize the electrode area and reduce capital expenses. However, high current density operation is limited by limiting current density (LCD), which causes a sharp increase in electrolysis voltage. At high current densities, the generation of oxygen gas bubbles creates additional flow restrictions to the water supply and increase overvoltage. Although previous studies have achieved relatively high current densities [1-2], the limit of operating current density and its mechanism still remain unknown.In this study, it reveals the impact of operating temperature and pressure on LCD of a lab-scale PEMEC. The experiments are conducted over a range of temperatures from 80 to 90 ℃ and pressures from 0.1 to 0.3 MPa. In conjunction with experiments, a mathematical model is developed to analyze the mechanism of LCD. The model includes mass and momentum equations for liquid water and oxygen gas through the porous transport layer. And the model also involves electrochemical equations to study overvoltages associated with mass transport. By combining experimental and theoretical analysis, this study provides valuable insights into the factors affecting LCD of PEMECs and facilitates the optimization of high-performance operation. Experimental apparatus The specifications of crucial components such as membrane (PEM), catalyst layer (CL), porous transport layer (PTL) is listed in Table.1 . Nafion NR212 is used as PEM, and the thickness is 51 μm. The catalyst is contained on CL, and its loading amount are 1.5 mg/cm2 IrO2 on anode and 0.5 mg/cm2 Pt on cathode, respectively. The anodic PTL is a Titanium mesh plated by Pt (Nikko Techno, NKT-1803-03), and the carbon paper (SGL 38BA) is used as cathodic GDL. For separators, the anode separator is fabricated from titanium, and the cathode separator is carbon. The anodic and cathodic flow pattern is designed as single-serpentine channels, and the channel depth, channel width, and rib width are 1 mm ×1 mm ×1 mm, respectively. Results and discussions Fig.1 shows the theoretical and experimental I-V curves. In Fig.1, the electrolysis voltage in both experiment and simulation raises abruptly, which is corresponding to LCD. The experimental LCD is 11.6 A/cm2 as indicated by the black circle, and the predicted LCD is 10.1 A/cm2. Although the prediction of LCD is qualitative, simulation could follow the IV characteristics obtained by experiment before LCD.Fig.2 and Fig.3 shows the effect of operating temperature and pressure on LCD. The electrolysis voltage “E” is experimentally determined, while the gas saturation at interface of PTL-CH “Sg” is obtained through simulation. As shown in Fig.2, the lower operation temperature enlarges the LCD, the experimental LCD increases 8% from 90 ℃ to 80 ℃. Theoretically, high operating temperature increases oxygen bubbles and then rises the gas saturation S g at the anode CL. So, the water supply flowing to CL is insufficient, and the electrochemical performance also decrease. Therefore, the overvoltages caused by mass transport becomes larger in higher operating temperature. As shown in Fig.3, higher operating pressure shrinks the volume of oxygen gas and enhance the water supply from CH to CL, leading to a larger LCD. Under 80 ℃, the experimental LCD rises by 17 % from 0.1 MPa to 0.3 MPa.Although the theoretical analysis reproduced the experimental results in a qualitative manner, the theoretical analysis suggests that, when electrolysis current density is quite close to the LCD, water mass transport at anode reaches a limitation, indicating that water saturation drops to zero at anodic catalyst layer. References Lee J K, et al. Cell Reports Physical Science, 2020:100147.A Zinser, et al. International Journal of Hydrogen Energy, 2019, 44(52): 28077-28087. Figure 1

Oxygen Evolution Reaction Activity of Iridium Oxide with Strange Structure, Its Toward PEM Water Electrolysis

Water electrolysis is a promising approach of hydrogen mass production.PEM water electrolysis has advantages such as high current density operation and quick response against input electricity.From these advantages, PEM water electrolysis is adequate to the hydrogen mass production system adopted the renewable energy.Iridium oxide shows good oxygen evolution reaction(OER) activity and durability for PEM water electrolysis anode catalyst, but there are material supply and cost issues as it is precious metal.To solve these issues, a number of studies have been conducted to improve OER activity of Iridium oxide.In this work, the crystal structure of iridium oxide is focused in order to improve OER activity.As a result of several synthesis survey, we have synthesized iridium oxide with unique structure and it shows more than four times OER activity compared to commercial catalysts in RDE.The mechanism for the high OER activity would be discussed based on the results of electrochemical properties, spectroscopy, and structural analysis.

Striking a Balance between Carbon Mediated Cathode Degradation and SEI Engineering Towards Stable High-Performance Solid-State Batteries

Solid-state batteries (SSBs) can render a paradigm shift in battery safety and energy density. The promise hinges on integrating high-capacity alkali metal electrodes with state-of-the-art inorganic solid electrolytes and high-energy Li-ion cathodes. However, the development has been restricted, mainly owing to the limited understanding and partial overcoming of the interfacial electro-chemo-mechanical issues at the electrode-electrolyte interfaces, leading to inferior power capability, energy efficiency, and long-term stability of the cell.1 Sulfide-type solid electrolytes (SEs) like Li6PS5Cl, Li10GeP2S12, and Li3PS4 are promising for commercial SSB development, but they seem to suffer from interfacial stability issues with the high-energy NMC (LiNixCoyMnzO2) cathodes, particularly when a conductive carbon additive is employed, which is required for improved capacity and high current density operations. Earlier reports suggest that the carbon enables a faster electronic percolation pathway, leading to a quicker NMC-SE interfacial degradation over cycling. Parallelly, the reactive functional groups on the carbon surface may aggravate the decomposition pathway by reacting with the thiophosphate SEs.2–4 , 5 To shut down this conductive additive-led decomposition and to stabilize NMC-sulfide SE-based SSBs, often a protective coating of LiNbO3, LiZrO3, Li3PO4, etc., is applied on the NMC particles in addition to avoiding the use of carbon in the cathode composite. Relatively lesser-known approaches looked into the effect of modifying the conductive additive surface itself with a non-conductive polymer or insulator-type material to tame the degradation mechanism led by the electron percolation pathway.1,6–9 In this context, by thorough experimentation, we have established an in-depth understanding of carbon’s role in the NMC performance degradation process. This led to the reckoning that one of the insulating degradation products can be in situ generated with functionalized carbon as the conducting additive, rendering stable solid electrolyte interphase (SEI) during electrochemical cycling. We found that the controlled degradation kinetics with an optimally functionalized carbon material help achieve the required conductivity (low impedance) at the cathode for improved energy and power densities and a stable cathode SEI for durable SSB cycling. In conclusion, we present a novel and facile idea of engineering the conductive carbon additive for achieving high-capacity, long-life NMC-based SSBs without the complication of expensive coating strategies.Reference: Ding, Z., Li, J., Li, J. & An, C. Review-Interfaces: Key Issue to Be Solved for All-Solid-State Lithium Battery Technologies. (2020)Koerver, R. et al. Redox-active cathode interphases in solid-state batteries. J. Mater. Chem. A 5, 22750–22760 (2017).Walther, F. et al. Influence of Carbon Additives on the Decomposition Pathways in Cathodes of Lithium Thiophosphate-Based All-Solid-State Batteries. Chem. Mater. 32, 6123–6136 (2020).Walther, F. et al. Visualization of the Interfacial Decomposition of Composite Cathodes in Argyrodite-Based All-Solid-State Batteries Using Time-of-Flight Secondary-Ion Mass Spectrometry. Chem. Mater. (2019)Park, S. W. et al. Graphitic Hollow Nanocarbon as a Promising Conducting Agent for Solid-State Lithium Batteries. Small 15, (2019).Takada, K. et al. Interfacial modification for high-power solid-state lithium batteries. Solid State Ionics 179, 1333–1337 (2008).Banerjee, A., Wang, X., Fang, C., Wu, E. A. & Meng, Y. S. Interfaces and Interphases in All-Solid-State Batteries with Inorganic Solid Electrolytes. Chem. Rev. 120, 6878–6933 (2020).Zhang, Y. et al. Direct Visualization of the Interfacial Degradation of Cathode Coatings in Solid State Batteries: A Combined Experimental and Computational Study. Adv. Energy Mater. 10, 1903778 (2020).Randau, S. et al. On the Additive Microstructure in Composite Cathodes and Alumina-Coated Carbon Microwires for Improved All-Solid-State Batteries. Chem. Mater. 33, 1380–1393 (2021). Figure 1

On the Importance of MPL Structural Characteristics for PEM Fuel Cell Performance

Gas diffusions layers (GDLs) constitute vital subcomponents of proton exchange membrane fuel cells (PEMFCs) since they participate in all relevant transport processes (gases, vapor, liquid water, electricity and heat).Meanwhile, state-of-the-art GDLs are produced on commercial scale using high volume reel-to-reel (R2R) processes. In almost any case, GDLs are designed as dual-layer structures with a macro-porous carbon fiber-based substrate (backing) and a micro-porous layer (MPL) consisting of carbon particulates bonded with polytetrafluoroethylene (PTFE) binder. A body of scientific work has verified that different aspects of the MPL microstructure and the MPL/macroporous substrate interface play a substantial role in the water management of PEMFCs [1-6].A systematic study was performed based on a singular backing using different MPL types and penetration levels.A simple method to estimate the micro-porous layer penetration in gas diffusion layers based on data obtained from force-deflection behavior of backings and MPL-coated GDLs is proposed. Comparison with SEM and previously published tomographic studies shows that a good estimate for the extent of MPL intrusion into the backing is obtained.MPL loading and penetration is shown to affect different ex-situ GDL properties (in-plane gas permeability, electrical and thermal conductivity) as well as the GDL single cell performance characteristics with respect to humification and high current density operation.Keywords: Gas diffusion layers, Microporous Layer, PEMFC fuel cells Weber, and J. Newman, “Effects of microporous layers in polymer electrolyte fuel cells”, J. Electrochem. Soc. 152, A677-A688 (2005).Lee, R. Yip, P. Antonacci, N. Ge, T. Kotaka, Y. Tabuchi, and A. Bazylak, Synchrotron investigation of microporous layer thickness on liquid water distribution in a PEM fuel cell, J. Electrochem. Soc. 162, F669-F676 (2015).Zhou, S. Shukla, A. Putz, and M. Secanell, “Analysis of the role of the microporous layer in improving polymer electrolyte fuel cell performance”, Electrochim. Acta. 268, 366-382 (2018).Cho, J. Park, H. Oh, K. Min, E. Lee, and J.Y. Jyoung, “Analysis of the transient response and durability characteristics of a proton exchange membrane fuel cell with different micro-porous layer penetration thicknesses”, Appl. Energy 111, 300-309 (2013).T. Gostick, M. A. Ioannidis, M. W. Fowler, and M. D. Pritzker, “On the role of the microporous layer in PEMFC operation.”, Electrochem. Comm. 11, 576-579 (2009).P. Ramasamy, E. C. Kumbur, M. M. Mench, W. Liu, D. Moore, and M. Murthy, “Investigation of macro- and micro-porous layer interaction in polymer electrolyte fuel cells”, Int. J. Hydrogen Energy 33, 3351-3367 (2008).

Challenges of Pt-Ni Aerogel PEMFC-Cathode Catalyst Layers Under Automotive-Relevant Conditions

Proton exchange membrane fuel cells (PEMFCs) constitute an emerging technology for the decarbonization of the transportation sector. However, in order for the price of fuel cell electric vehicles (FCEVs) to be comparable to that of internal combustion engine cars, the manufacturing costs of PEMFCs, must be significantly reduced. These costs are mainly related to the Pt-based catalysts used in PEMFCs’ anode and cathode electrodes and, as a result, extended FCEV-commercialization passes by decreasing these Pt loading to a value of 0.06-0.11 mgPt cm-2. Moreover, the automotive PEMFCs suffer from an insufficient durability that is partially due to the corrosion of the carbon support used in state-of-the-art Pt-catalysts, which is in turn induced by the high cathode potentials (> 1.5 V vs. the reversible hydrogen electrode) reached upon PEMFC start-up and/or shutdown.To tackle both these needs, in our previous work we introduced a novel catalyst layer (CL) based on a carbon-free bimetallic Pt-Ni alloy nanochain network (referred to as “aerogel”) which featured an excellent performance and start-up/shutdown durability upon PEMFC operation [1]. In a more recent work, the synthesis of this Pt-Ni aerogel was up-scaled (as to yield ≈ 120 mg of material per batch) and catalyst-coated membrane (CCM) processing methods were adapted and optimized using an automated spray-coating machine that yielded homogenous and high-performing aerogel CLs with a Pt-loading of ≈ 0.3 mgPt cm-2.The decrease of the above loading to the needed values of ≤ 0.1 mgPt cm-2 discussed above is expected to pose a challenge in terms of high current density operation due to limitation in the transport of reactants (oxygen and protons) to such a reduced catalyst area[2]. Part of this performance loss includes the transport of O2 through the ionomer film that generally covers the Pt nanoparticles in the cathode CL. This O2 transport resistance can be quantified via O2 limiting current measurements through which the non-Fickian, Knudsen diffusion through the CL can be quantified[3]. Thus, in this work we present our results in the manufacture and PEMFC-testing of low loading Pt-Ni aerogel CLs, which we tackled with and without the use of an ionomer and benchmarked against equivalently -loaded CLs prepared with a commercial Pt/C catalyst. Our results unveil a relation between ionomer presence/absence, non-Fickian oxygen transport resistance and roughness factor that is comparable to that reported by Kongkanand and Mathias for unsupported, Pt-based nanostructured thin films[4].In addition to this, aerogel electrodes feature a reduced thickness (≈ 5 μm/(mgPt∙cm− 2) that is likely to result in water flooding and ice accumulation at low temperatures and during cold-starts (< 0˚C), respectively. Under the latter, extreme conditions, the water produced by the reduction of oxygen can form ice, which is expected to accumulate within the cathode pore volume and lead to a high oxygen transport resistance[5]. Moreover, the lack of hydrophobicity and of storage capacity (i.e. void volume) within the catalyst layer is susceptible to cause water flooding and/or ice formation, ultimately leading to cell failure[6]. Thus, this contribution will also showcase our results under such low temperature and cold start conditions (in the latter case, at − 10 °C), and do so while considering the combinations of low vs. high aerogel loadings and presence vs. absence of ionomer discussed above. In doing so, this work will provide a holistic picture of the mass-transport effects determining the performance of these aerogel CLs under automotive-relevant conditions.

A nonlinear contraction channel design inspired by typical mathematical curves: Boosting net power and water discharge of PEM fuel cells

The next-generation fuel cell needs to fit high current density operating conditions, necessitating improved flow fields with superior capabilities in mass transfer and drainage. This study introduces four innovative nonlinear contraction channels aimed at enhancing net power and mitigating waterflooding under high current density. This design draws inspiration from classical mathematical curves, which can provide targeted mass transfer enhancement contingent upon species distribution. Multiple quantitative indicators are employed to evaluate the efficacy of nonlinear structures in cross-scale mass transfer, drainage, temperature uniformity, and power consumption. Numerical results indicate that the exponential-like curve channel exhibits notably superior overall performance. Its nonlinear contraction region induces purge airflow at the tail of channel, facilitating drainage and boosting the local mass transfer flux in oxygen-starved region by 48.75%. The utilization of nonlinear contraction structures alters the diffusion-convection distribution mechanism and increases the convective mass transfer proportion. Under conditions of high current density, there is a noticeable rise in the Peclet number. Considering the pumping power loss, the hyperbolic tangent, quarter-ellipse, parabolic, and exponential-like curve flow channels can enhance the net power by 3.10%, 6.82%, 8.57%, and 10.04% over straight channels. Additionally, the exponential-like curve channel enhances temperature uniformity in the catalyst layer under rated working conditions, whereas the hyperbolic tangent flow channel demonstrates superior uniformity in higher current density.

Hybrid Anode Design of Polymer Electrolyte Membrane Water Electrolysis Cells for Ultra-High Current Density Operation with Low Platinum Group Metal Loading

Reducing platinum group metal (PGM) loading and high current density operation are both essential for minimizing the capital expenditure (CAPEX) of polymer electrolyte membrane (PEM) electrolyzers. Catalyst-integrated porous transport electrodes (PTEs) in which iridium acts as both a catalyst and a conductive coating on porous transport layer (PTL) surfaces, enable the preparation of Pt-coating-free PTLs, but can also result in relatively high activation and ohmic overvoltages. Here, a novel hybrid anode design combining an intermediate catalyst layer and a catalyst-integrated PTE is developed. This hybrid anode demonstrates that Ir on PTL can contribute to the oxygen evolution reaction (OER) and exhibits comparable electrolysis performance to a conventional anode consisting of Pt-coated PTL with the same Ir loadings despite Pt-coating-free on the PTL of the hybrid anode. This novel anode eliminates the need for a Pt coating whilst also enabling ultra-high current density operations up to 20 A cm−2 with a total PGM loading of only around 0.6 mg cm−2 on the anode side. This paper proposes a next-generation anode structure with new functions of PTLs for ultra-high current density operation with low PGM loading to significantly reduce green hydrogen costs.

Robust CoP@NiFe LDH/Ni heterostructured electrodes for efficient overall water splitting with high current density

Alkaline water electrolysis techniques have enormous potential for industrial-scale hydrogen generation, but a lack of effective and low-cost bifunctional electrocatalysts capable of steady high-current density operation has hampered progress. Layered double hydroxides (LDHs) have been considered promising OER electrocatalysts, but their poor electrical conductivity impedes hydrogen evolution reaction (HER) activity. Integrating LDHs with transition metal phosphides (TMPs) can potentially achieve bifunctional capability by overcoming individual limitations. Herein, CoP@NiFe LDH/Ni heterostructured catalyst was rapidly synthesized by a scalable two-step electrodeposition method. The integration of NiFe LDH with CoP enhanced its electrical conductivity. Meanwhile, electron transfer occurred from the metal atoms to the more electronegative phosphorus, facilitating phosphorus to act as a proton acceptor and expedite the HER process. Benefiting from the synergistic integration and optimized electronic structure, CoP@NiFe LDH/Ni exhibited excellent alkaline water-splitting performances with low overpotentials of 260 mV for HER and 351 mV for OER at 400 mA/cm2. The CoP@NiFe LDH/Ni two-electrode-based alkaline electrolyzer displayed a cell voltage of 2.13 V and stable operation for 100 h at a high current density of 1000 mA/cm2. This work elucidates a strategy to tackle critical challenges impeding the design and preparation of high-current-density tolerant bifunctional electrocatalysts.