Cathode Flooding Research Articles

Analysis and optimization of dynamic response during the startup process of proton exchange membrane fuel cell

Proton Exchange Membrane Fuel Cell (PEMFC) is a prominent application of hydrogen energy in fields such as mobile devices, vehicles and small-scale energy systems. This study experimentally investigates transient response of the automotive PEMFC when starting with different load under various operating conditions, which significantly influences durability. The key finding is that dynamic behavior follows a “two-stage” response mode under drier conditions. The first stage is related to the diffusion processes of cathode gas and the second stage is determined by the membrane rehydration process. Under wetter conditions, dynamic behavior exhibits a “three-stage” response mode with a larger voltage fluctuation and longer startup time. The contributors to the first two stages are the same as the “two-stage” response mode and the third stage is determined by the degree of cathode flooding. Results indicate that increasing cathode stoichiometry, cathode humidity, and temperature obviously enables PEMFC to startup more stable and faster and with a higher load. Besides, a step loading strategy with a gradually reducing magnitude achieves an optimal balance between response time and voltage fluctuation at the target load, with a moderate startup time of 9.6 s and minimal voltage fluctuation of 0.009 V.

Development of Large-Sized CO2 Electrolyzer Producing CO for Industrial Applications

Utilization of carbon dioxide (CO2) as a feedstock of valuable chemicals is necessary to achieve carbon neutrality. CO2 electrolysis producing valuable organic molecules such as carbon monoxide (CO) is one of the most promising methods. To implement this technology in society, a large-sized electrolyzer that can convert a huge amount of CO2 are required. Toshiba is developing a low-temperature zero-gap type CO2 electrolysis cell/stacks with 400 cm2 electrodes to produce CO [1,2], which can be converted into chemicals and fuels by catalytic reactions with hydrogen. With properly designed gas flow plates and optimal operation conditions, CO faradaic efficiency of the 400cm2 single cell were comparable to that of a smaller cell with 4 cm2 electrode [3]. Another problem to be solved is low durability of the electrolyzer. During continuous operation of the electrolyzer, several failure modes such as cathode flooding, salt precipitation, diaphragm degradation, corrosion of flow plates, and catalyst dissolution often occur. By resolving each of these failure modes, stable performance over 500 h was achieved. Additionally, in this presentation, we report the results of electrolysis tests using CO2 gas containing impurities that are expected to be contaminated in an actual environment, and the results of electrolysis tests to confirm effects of a ripple current generated from AC/DC converter on the efficiency of CO2 electrolyzer. Part of this work is commissioned by Ministry of the Environment, Government of Japan. [1] Y. Kofuji, A. Ono, Y. Sugano, A. Motoshige, Y. Kudo, M. Yamagiwa, J. Tamura, S. Mikoshiba, and R. Kitagawa, Chem. Lett., 50, 482-484 (2021). [2] Y. Kiyota, Y. Kofuji, A. Ono, S. Mikoshiba, and R. Kitagawa, 242nd ECS Meeting, I05, 1942, (2022). [3] Naoya Fujiwara, Yusuke Kofuji, Satoshi Mikoshiba, Ryota Kitagawa, Atsushi Matsunaga, Isamu Kikuchi, Soichiro Shimotori, 244th ECS Meeting, I05, 2328, (2023).

Impact of cell design and conditioning on polymer electrolyte membrane water electrolyzer operation

Integration of polymer electrolyte membrane water electrolyzers (PEMWEs) for clean hydrogen generation requires a robust understanding of the impact cell designs and conditioning protocols have on operation and stability. Here, catalyst-coated electrode and catalyst-coated membrane cells employing Pt/C cathode catalyst layer, an IrO2 anode catalyst layer, with a platinized titanium mesh or a carbon paper with a microporous layer as the porous transport layer were developed. The impact of cell conditioning above and below 0.25 A cm−2 was investigated using advanced electrochemical impedance spectroscopy analyses and microscopic imaging, with the electrochemical response related to physicochemical processes. Operation below 0.25 A cm−2 prior to operation above 0.25 A cm−2 resulted in anode corrosion and titanium cation contamination, increasing the cell voltage at 1 A cm−2 by 200 mV compared to uncontaminated cells. Conditioning above 0.25 A cm−2 led to non-negligible hydrogen transport resistances due to cathode flooding that resulted in a ca. 50 mV contribution at 1 A cm−2 and convoluted with the anode impedance response. The presence of a microporous layer increased catalyst utilization but increased the cell voltage by 300 mV at 1 A cm−2 due to increased anodic mass transport resistances. These results yield critical insights into the impact of PEMWE cell design and operation on corresponding cell performance and stability while highlighting the need for application dependent standardized operating protocols and operational windows.

CO2 Loss into Solution: An Experimental Investigation of CO2 Electrolysis with a Membrane Electrode Assembly Cell.

In pursuit of commercial viability for carbon dioxide (CO2) electrolysis, this study investigates the operational challenges associated with membrane electrode assembly (MEA)-type CO2 electrolyzers, with a focus on CO2 loss into the solution phase through bicarbonate (HCO3 -) and carbonate (CO3 2-) ion formation. Utilizing a silver electrode known for selectively facilitating CO2 to CO conversion, the molar production of CO2, CO, and H2 is measured across a range of current densities from 0 to 600 mA/cm2, while maintaining a constant CO2 inlet flow rate of 58 mL/min. The dynamics of CO2 loss are monitored through measurements of pH changes in the electrolyte and carbon elemental balance analysis. Employing the concept of conservation of elemental carbon, a chemical reaction analysis is conducted, identifying the critical role of the hydroxide (OH-) ion. At lower current densities below 125 mA/cm2, where CO2 reduction predominates, it is observed that CO2 loss is proportional to current density, reaching up to 0.18 mmol/min, and directly correlates with the rate of OH- ion production, indicative of HCO3 -/CO3 2- ion formation. Conversely, at higher current densities above 450 mA/cm2, where hydrogen evolution is the dominant process, CO2 loss is shown to decouple from the OH- ion production rate with a constant limit condition of 0.12 mmol/min, regardless of the current density. This suggests that electrolyte-induced cathode flooding restricts CO2 access to cathode sites. Additionally, pH change in the electrolyte during the electrolysis further infers differing ion populations in the CO2 reduction and hydrogen evolution regimes, and their movement across the membrane. Continued monitoring of the pH change after the cessation of electricity offers insights into the accumulation of HCO3 -/CO3 2- ion at the cathode, influencing salt formation.

Cation‐Infused Bilayer Ionomer Coating Enables High Partial Current Density Toward Multi Carbon Products in CO2 Electrolysis

AbstractElectrochemical CO2 reduction (eCO2R) stands as a pivotal technology for carbon recycling by converting CO2 into value‐added products. While significant strides have been made in generating multi‐carbon (C2+) products like ethylene (C2H4) and ethanol (C2H5OH) at industrial‐scale current densities with high Faradaic efficiency (FE), cathode flooding and (bi)carbonate salt accumulation remain a fundamental concern in an alkaline electrolyte. In this work, ion‐conducting polymers are used to tailor the micro‐environment mitigating cathode flooding and salt precipitation and thus, enhancing the local CO2 availability. The impact of cation and anion exchange ionomer layers, specifically Nafion and Sustainion XA‐9 are examined on overall eCO2R performance. The use of an ultra‐thin bilayer configuration significantly reduces cathode flooding and salt accumulation by ≈58% compared to commercial anion exchange membrane (AEM). Alongside, cation infusion improves the C─C bond formation inducing a favorable micro‐environment for selective C2+ formation. This cation‐infused bilayer ionomer (CIBLI) achieves a high partial current density of ≈284 mA cm−2 toward C2+ products maintaining a stable eCO2R performance for 24 hours (h). This scalable approach of directly deposited ultra‐thin CIBLI offers a minimal conversion energy of 117 GJ/ ton C2+ products with an energy efficiency (EE) of 29% at 350 mA cm−2 current density in one‐step CO2 conversion.

Extrinsic hydrophobicity-controlled silver nanoparticles as efficient and stable catalysts for CO2 electrolysis.

To realize economically feasible electrochemical CO2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm‒2), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO2RR instead of HER. We analyze catalyst degradation and cathode flooding during CO2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO2 electrolysis.

Porous Electrode Optimization for PEMFCs Using 3D Printing Technology

Proton Exchange Membrane Fuel Cells (PEMFCs) represent a class of fuel cells that transform the chemical energy of fuels, ideally hydrogen and oxygen, into electrical power. Utilized in diverse applications, PEMFCs power vehicles and supply backup energy to buildings. The core of a PEMFC is the membrane electrode assembly (MEA), composed of a polymer electrolyte membrane, an anode, and a cathode. Oxygen, protons, and electrons merge at the cathode, forming water. One challenge PEMFCs face is water-induced cathode flooding at low temperatures, a consequence of the electrochemical reaction's water accumulation. This reduces the oxygen supply, potentially leading to decreased cell performance or even failure. This issue can have substantial undesired consequences, as PEMFCs depend on oxygen availability at the cathode to generate electricity.Gas Diffusion Layers (GDLs) serve as critical PEMFC components, providing porous structures that facilitate reactant access to the catalyst layer and enabling electron flow through the external circuit. GDLs also offer structural support and promote reactant distribution across the membrane surface. Water accumulation in the cathode may cause pore clogging within the GDL, restricting reactant flow, and reducing cell performance. Additionally, water build-up increases pressure drop across the GDL, hindering reactant access to the catalyst layer and diminishing fuel cell efficiency.Three-dimensional (3D) printing has emerged as a potential technique for fabricating GDLs in PEMFCs. 3D printing enables the creation of GDLs with ordered pore size structures, offering a more uniform surface than traditional GDLs with randomly oriented fibres. This uniformity enhances reactant distribution across the membrane surface and mitigates water accumulation risks. In addition, to prevent cathode flooding, 3D printed GDLs are immersed in PTFE solution to increase hydrophobicity.This talk delves into the creation and evaluation of 3D printed carbonized GDLs for PEMFC implementation. A desktop 3D printer constructed a polymer framework, which was subsequently carbonized in a high-temperature tube furnace. Isothermal thermogravimetric analysis (TGA) tests were performed to identify weight change across a temperature range of 30-900 °C under an N2 atmosphere, optimizing the carbonization step to reduce structural distortion and increase electrical conductivity.The 3D printed GDLs displayed pore size diameters spanning 80 to 120 μm and fibre radii of 20-30 μm. The 3D printing technique produced GDLs characterized by a consistent, planar structure without blocked pores that are normally caused by excess resin residue. Electrical conductivity assessments were conducted on the carbonized specimens, and tensile and compression tests measured their mechanical properties.GDLs possessing minimal pore sizes and thicknesses were integrated into membrane electrode assemblies (MEAs) and examined in low-temperature PEMFCs. Diverse spraying methodologies were investigated, involving either the catalyst being sprayed onto the 3D printed GDL or the membrane receiving a catalyst coating. Commercial MEAs, comprising Nafion membranes and platinum electrodes, acted as benchmarks for MEAs featuring 3D printed GDLs. Furthermore, the current challenges facing 3D printed GDLs, including material selection, production consistency, compatibility with other PEMFC components, costs, and scaling up are highlighted in the talk.These findings underscore the promise of 3D printed carbonized GDLs in boosting PEMFC performance, showing their potential as a cost-effective and proficient substitute for conventional carbon paper based GDLs. Figure 1

Development of Durable Large-Sized CO2 Electrolysis Cells for Industrial Applications

Utilization of carbon dioxide (CO2) as a feedstock of valuable chemicals is necessary to achieve carbon neutrality. Toshiba is developing the low-temperature zero-gap type CO2 electrolysis cells to produce carbon monoxide (CO) [1,2]. CO can further be converted into various chemicals and fuels by catalytic reactions with hydrogen. To make the CO2 electrolysis technology industrially feasible, it is necessary to establish high-throughput system by expanding the electrode area and stacking the cells. Large-sized cells and stacks often suffer from low Faradaic efficiency for the CO production, which is related to insufficient and nonuniform supply of reactant CO2 gas to the cathode reaction sites. This time we focused on the development of large-sized single cells and fabricated an electrolysis cell with 400 cm2 electrodes. With properly designed gas flow plates and gaskets, the cell voltage and the CO Faradaic efficiency of the fabricated cell at a current density of 400 mA cm-2 were comparable to those of the previously developed smaller cells with 4 cm2 electrodes. The CO concentration in the cathode outlet gas reached ca. 80% by controlling the inlet CO2 flow rate. Stability is another essential property of CO2 electrolysis cells required for the industrial application. Cathode flooding and salt precipitation are major stability issues characteristic of relatively short-term operations, whose detailed mechanism is still in debate [3]. To mitigate those stability issues, we focused on the cathode inlet humidity and the pressure difference between the cathode and the anode. The former is related to the salt concentration in electrolyte solution around the cathode reaction sites, and the latter is related to the convection of electrolyte from the anode side to the cathode side. By controlling those parameters, stable performance over 100 h was achieved.Part of this work was commissioned by Ministry of the Environment, Government of Japan.[1] Y. Kofuji, A. Ono, Y. Sugano, A. Motoshige, Y. Kudo, M. Yamagiwa, J. Tamura, S. Mikoshiba, and R. Kitagawa, Chem. Lett., 50, 482-484 (2021).[2] Y. Kiyota, Y. Kofuji, A. Ono, S. Mikoshiba, and R. Kitagawa, 242nd ECS Meeting, I05-1942 (2022).[3] M. Sassenburg, M. Kelly, S. Subramanian, W. A. Smith, and T. Burdyny, ACS Energy Lett., 8, 321-331 (2023).

Pressure and Impedance Based in Situ Diagnostic Methods for Water Management in Proton Exchange Membrane Fuel Cells Applications

Recent advancements in proton exchange membrane fuel cells (PEMFCs) have led to significant developments in low-carbon transport technology, enabling the generation of clean, efficient electricity with minimal noise and toxic emissions for heavy-duty applications. However, effective water management remains a critical challenge in PEMFCs due to the intricate phase changes and liquid-gas transport processes within key components, which significantly impact cell performance and longevity in industrial applications. Given the rapid dynamics of water activities and material responses within cells, in situ diagnostic techniques for water management in PEMFCs are essential for optimizing cell performance and extending the lifespan of fuel cell stack and system.Water, electrochemically produced on the cathode side, can cause potential flooding in key components including the catalyst layer (CL) and gas diffusion layers (GDLs), impeding air/oxygen supply to the cathode side. To characterize the performance loss induced by water flooding, Electrochemical Impedance Spectroscopy (EIS) is commonly employed as a fuel cell diagnostic tool. EIS records the contributions of different polarization processes to the global impedance with individual time constants during operation. However, the interpretation of complex EIS spectra can be very challenging, as polarization processes may overlap in frequency and be difficult to identify. To address this issue, Distribution of Relaxation Times (DRT) analysis is implemented as a powerful tool that allows for a clear separation and quantification of the polarization processes showing as peaks in a frequency domain [1]. Thus, we utilize EIS-based DRT analysis as an in-situ diagnostic tool to detect cathode flooding during cell operation. To validate this approach, we have conducted tests on a 300 cm2 low temperature PEMFC, varying one operation parameter at a time and evaluating its effects on cathode flooding by studying the frequency and height evolution of DRT peaks.Nevertheless, water flooding is not confined to the cathode side, as water can also permeate through the proton exchange membrane (PEM) and reach the anode side, resulting in potential fuel starvation on the cathode's counterpart and subsequent degradation of carbon-based materials. To address the sensitivity limitation of the EIS-based DRT method in detecting anode flooding, we employ an in-house developed pressure drop indicator (PDI) tool, as a non-invasive and real-time approach for diagnosing water flooding in the anode. The PDI tool assesses the pressure drop across anode channels, which is a function of the liquid water contents in bipolar plates considering the pressure reduction mainly caused by the frictional drag [2]. The effectiveness of the PDI tool is validated through cell testing at different water flooding levels by varying relative humidity and pressure conditions. This technique offers timely and sensitive detection of anode water flooding in PEMFCs, which is crucial for alarming irreversible material degradation in the electrode and facilitating appropriate follow-up actions.To conclude, we have developed and employed in situ PDI and EIS-based DRT methods within our water management framework for diagnosing water flooding in both the anode and cathode of PEMFCs in industrial applications. The combination of these techniques offers real-time and accurate assessments on water management conditions, which is crucial for optimizing overall performance and longevity of PEMFC stacks and systems.[1] Heinzmann, M., Weber, A., Ivers-Tiffée, E. (2018). Advanced impedance study of polymer electrolyte membrane single cells by means of distribution of relaxation times. Journal of Power Sources, 402, 24-33.[2] Barbir, F., Gorgun, H., & Wang, X. (2005). Relationship between pressure drop and cell resistance as a diagnostic tool for PEM fuel cells. Journal of Power Sources, 141(1), 96-101. Figure 1

(Digital Presentation) Modeling the Effect of Membrane Electrode Assembly Microstructure on Thermal and Water Transport in Polymer Electrolyte Fuel Cells

The effect of water management on oxygen transport plays a critical role in the design of high-performance polymer electrolyte fuel cells (PEFCs) for the automotive industry, especially at low cathode platinum loading [1,2]. In this regard, optimizing the hierarchical pore structure of the membrane electrode assembly (MEA) is crucial to alleviate cathode flooding while ensuring good membrane hydration [3]. However, this task is complicated due to the small dimensions involved in the problem. Mathematical modeling has turned out to be a key tool to understand transport in the thin layered assembly used in PEFCs, including the catalyst layer (CL), microporous layer (MPL) and gas diffusion layer (GDL).In this work, oxygen, heat and two-phase water transport in the MEA are examined by means of a 1-dimension continuum bundle of capillary tubes model. Experimental pore size distributions (PSDs) are considered for the GDL/MPL/CL assembly. The model takes especial care in analyzing thermal and water behavior in catalyst layer by considering micro (< 20 nm of pore radius), meso (between 20 and 300 nm) and macroscale (> 300 nm) structures as different interconnected domains, each with their own effective thermal conductivity and water saturation. In this aspect, taking into account pore hydrophilicity or hydrophobicity is determinant as water behavior is extremely different.The model predictions are validated against previous experimental data for various operating conditions and pore structures (Figure 1a). The results offer precise information on the coupling between heat and water transport in both liquid and gas phases, and the impact of operating conditions and transport properties on the saturation distribution through the MEA layers (Figure 1b). Then the continuum bundle of capillary tubes model is also used to run a parametric analysis centered on the obtention of optimal PSD-dependent effective transport properties to produce improved MEA microstructures.[1] A. Sánchez-Ramos, J.T. Gostick, P.A. García-Salaberri, Modeling the Effect of Low Pt loading Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells: Part I. Model Formulation and Validation, Journal of the Electrochemical Society 168 (2021) 124514.[2] A. Sánchez-Ramos, J.T. Gostick, P.A. García-Salaberri, Modeling the Effect of Low Pt loading Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells: Part II. Parametric Analysis, Journal of the Electrochemical Society 169 (2022) 074503.[3] M. Gomaa, A. Sánchez-Ramos, N. Ureña, M.T. Pérez-Prior, B. Levenfeld, P.A. García-Salaberri, M. Rabeh, Characterization and modelling of free volume and ionic conduction in copolymer proton exchange membranes, Polymers 14(9) (2022) 1688. Figure 1

Mass Transport Impedance in a PEMFC with Superhydrophobic Catalyst Layers

Electrosprayed catalyst layers improve liquid water management in PEMFCs thanks to their superhydrophobic character [1]. Using appropriate parameters, the electrospray deposition of a suspension of Pt/C powder and ionomer (Nafion solution) gives rise to a macroporous layer with superhydrophobic pores. Under current generation in a PEMFC, superhydrophobicity of the cathodic catalyst layer minimizes water interaction with pores walls, and enhances water transport towards the anode. As a consequence, water distribution inside the cell is more homogeneous, which makes cathode flooding less severe and improves anode humidification. PEMFCs with cathodic electrosprayed catalyst layer have shown higher power production rate at intermediate and high current densities, with peak power densities above 20%-25% compared with conventional, more hydrophilic, catalyst layer under standard testing conditions. We have studied in previous works the transport properties of electrosprayed catalyst layers with a number of techniques, like polarization curves, electrochemical impedance spectroscopy, and hydrogen transport.In this communication, catalyst layer transport properties in a PEMFC with electrosprayed electrodes are studied with 'Current Modulated Hydrogen Flow Rate Spectroscopy' (CH2S) [2], which is a transport impedance technique relating hydrogen flow rate with faradaic current. With this aim, PEMFCs have been mounted with electrosprayed catalyts layers in anode and in cathode. When in anode, the electrosprayed catalyst layer gives rise to significant differences in the CH2S Nyquist plots and dependent on cell humidification (Fig. 1). The CH2S signals resolve transport kinetics having different characteristic times, that can be assigned to transport in different parts of the anode, like flow-field, gas diffusion layer, microporous layer and catalyst layer. The study is completed with CH2S measurements on PEMFCs with different configurations, having electrosprayed electrodes in anode and cathode. It is concluded that CH2S provides new insights into mass transport properties of gas diffusion electrodes.AcknowledgementsFunding by PORHYDRO2 project (TED2021-131620B-C22, ‘Preparation and characterisation of catalyst layers fabricated by electrospray for proton exchange fuel cells with passive gas feed’) by the Spanish Ministry of Science and Innovation.[1] M.A. Folgado, J.J. Conde, P. Ferreira-Aparicio, A.M. Chaparro, Single Cell Study of Water Transport in PEMFCs with Electrosprayed Catalyst Layers, Fuel Cells. 18 (2018) 602–612. https://doi.org/10.1002/fuce.201700217.[2] L. Duque, A. Molinero, J.C. Oller, J.M. Barcala, M.A. Folgado, A.M. Chaparro, Analysis of Hydrogen Feeding to the Anode of a PEMFC By a Transport Impedance Technique, ECS Meet. Abstr. MA2022-02 (2022) 1406–1406. https://doi.org/10.1149/ma2022-02391406mtgabs. Figure 1

Degradation Processes in Bipolar Membrane CO2-Electrolysis Studied by Time-Resolved X-Ray Tomography

Electrochemical reduction of carbon dioxide via CO2 co-electrolysis (CO2ELY) is an essential process to produce non-fossil chemical feedstock acting as CO2 sink. The required electrical energy can be harvested from temporal surplus of renewable energy sources like solar or wind. Employing a bipolar electrolyte membrane (BPM) in forward-bias is a promising approach to mitigate fundamental problems of the current technological fore-runner design that employs an anion exchange membrane (AEM). We employed synchrotron time-resolved X-ray tomographic microscopy (XTM) to study degradation processes in BPM CO2ELY.In forward-bias BPM co-electrolysis, the cation exchange layer (CEL) faces the anode to provide favorable acidic conditions for the oxygen evolution reaction. Such acidic anode allows using pure water as electrolyte eliminating the salt precipitation at the cathode observed for AEM CO2ELY. As the second major issue in AEM CO2ELY, (bi)carbonate ions formed at the cathode are transported to the anode presenting a major obstacle for high CO2 conversion efficiency. The then required effort to separate CO2 from the electrolyte further reduces the overall energy efficiency. Employing a BPM and introducing the CEL prevents (bi)carbonate ions reaching the anode. BPM CO2ELY retains at the same time the advantages of AEM CO2ELY of performing CO2 reduction under alkaline conditions with the anion exchange layer (AEL) of the BPM facing the cathode.However, BPM CO2ELY suffers from low current density and poor stability in the range of only a few hours. Current limiting factors and degradation processes as well as the affected components are rarely investigated and poorly understood. Processes that have been brought forward are cathode flooding similar to fuel cells or catalyst poisoning. We employ synchrotron XTM to investigate structural dynamics in CO2ELY during operation. The brilliant synchrotron source allows us to acquire one full high-quality scan with a voxel size of 2.75 um in 1 s. We acquired one scan every minute for one hour during electrochemical operation.The image data reveals the formation of gas bubbles at the AEL-CEL junction and ultimately delamination of the BPM. We explain the gas formation as the recombination of (bi)carbonate ions with hydrogen ions at the junction producing gaseous CO2. This CO2 additionally reaches the anode by diffusion causing partial delamination of the anode catalyst layer. CO2 escaping from the AEL surface at the anode forms high-pressure gas bubbles that break the water wet catalyst layer. A diffusive model considering the transport of ions and neutral CO2 is able to capture the mechanism.Our imaging experiments provide insights not attainable by other diagnostic methods and highlight the need for fundamental research on forward-bias BPM CO2ELY. Knowledge based on AEM CO2ELY and fuel cells is not necessarily directly applicable and specific studies on BPM CO2ELY are required to increase performance and stability.We gratefully acknowledge provision of beamtime at TOMCAT, SLS, Paul Scherrer Insititut, Villigen PSI, Switzerland.Figure 1: Tomographic slice of CO2-electrolyser (cathode to the left) a) before operation and running water through anode b) after 23 minutes operation at 3.5V constant potential showing liquid water dynamics at cathode, membrane swelling, gas formation within the membrane and anode catalyst layer disintegration. Figure 1

Critical analysis for evaluating maximum power point tracking strategy in photovoltaics and fuel cells using key performance metrics

This study performs detailed analyses to investigate and justify the utilization of maximum power point tracking (MPPT) algorithm in photovoltaics (PV) and fuel cells. Two devices are parallelly analyzed to establish a comparative and contrasting study on the performance of the two technologies at MPP regime for a given operational condition. Direct methanol fuel cell (DMFC) is chosen as a representative of the hydrogen fuel cells family. The operational variables affecting the electrical power in the devices, including temperature (for both devices), solar irradiance (for PV cells), and methanol concentration (for DMFC) are discussed, along with their similarities and differences. Voltage losses are addressed to gain insights into the electrical quality of each device at MPP regimes. Due to their pivotal role, fuel availability and cost, energy losses, overall efficiency, and cathode flooding are selected as crucial performance metrics to compare the two technologies at MPP. The results demonstrate that PV cells have a good voltage quality at MPP with an average retention of 87% from open-circuit voltage VOC, whereas DMFC performance deteriorates at MPP, resulting in a significant decline with a loss of 61% from VOC . Consistent with voltage loss results, fill factor analysis at MPP zones lead to the same conclusion wherein photovoltaics offer high fill factor of approximately 82%, whereas DMFC has lesser values that are below 40%. The maximum overall efficiency of PV cells is attained at the MPP zones, whereas optimal efficiencies do not match the MPP loci in fuel cells. Simulations show that DMFC is extremely prone to cathode flooding at MPP zones, where approximately 90% of pore spaces in the liquid distribution layer are occupied with water. Conversely, PV cells are completely free from such issues. Some recommendations for further advancement and investigation on the use of MPPT in both technologies are provided.

Understanding the Role of Cu Electocatalyst, Binder, and Membrane Interfaces in CO2 Electrolyzer Durability

Carbon dioxide electrolyzers capable of maintaining stable performance for thousands of hours are necessary for commercial electrochemical reduction of CO2 to two-carbon products such as ethanol and ethylene. Currently, most studies containing CO2 reduction to two-carbon products have been for durations of under 20h. Only a few (<5) instances of CO2 reduction to two-carbon products at durations over 100h have been reported. Common cell failure mechanisms, such as carbonate salt precipitation and cathode flooding, can be mitigated by tuning the operating conditions of the reactor. Beyond these modes of failure, there are practical limitations related to materials' durabilities and long-term stabilities, including ionomeric membranes' operating lifetimes, gas diffusion cathodes, anodes, and other MEA components.In this presentation, we explore the role of CO2, water, and ion transport on cell performance over extended periods of operation. The polymeric anion exchange membrane and conductive binder have been identified as crucial components in tuning the transport properties of electrolyzer systems and, thus, will be the focus of this study. We consider several types of anion exchange membranes (e.g., imidazolium, ammonium, piperindinium) and conductive binders (e.g., Nafion, PVDF, PTFE, PSMIM) for use in the direct reduction of CO2 to two-carbon products at nanoscale Cu electrodes (150mA/cm2, 0.01M KHCO3 anolyte). This work improves upon previous analysis of membrane and binder transport properties by testing a wider variety of materials for >100h durations and reporting specific cell failure times and causes. We will discuss the balances between carbonate precipitation, flooding, and other membrane or electrode failures as a function of materials, MEA preparation, and operating conditions. A comprehensive set of failure standards based on electrolyzer performance (pressure, outlet mass flow, two-carbon product Faradaic efficiencies, energy efficiency, carbon efficiency) is introduced, and electrolyzer configurations are tested in triplicate to produce statistically significant failure data. Overall, this provides insight into CO2, ion, and water transport's role in electrolyzer cell performance and failure mechanisms. Figure 1

Experimental investigation on PEM fuel cell flooding mitigation under heavy loading condition

Water flooding is a crucial factor affecting the lifetime of a proton exchange membrane (PEM) fuel cell. In this paper, A laboratory-scale (25 cm2) single PEM fuel cell was tested to investigate the characteristics of fuel cell under a load shedding process with various air flow rates. The performance was assessed using output power and electrochemical impedance spectroscopy, while the cathode flooding was identified using voltage and cathode pressure drop. The results show that reducing the load within a specific range can lower the impedance and lessen floods. The results also demonstrate that there is an optimal inlet flow rate interval considering its effect on system efficiency, durability, and water flooding. In addition, a stepped load shedding pattern was proposed to solve the flooding problem of a fuel cell while taking the power demand into account. The effect of load shedding cycle and air inlet flow rate on flooding was evaluated by comparing the flooding severity coefficient and output power. The results prove that a longer current reduction cycle is more favorable in alleviating flooding problems. The optimal mode for the fuel cell in this paper was determined according to the flooding situation and power variation. Finally, the approach to obtaining the optimal load shedding pattern for other PEM fuel cells system was summarized. The flooding mitigation approach proposed in this paper can be utilized as a guide for developing strategies to extend the life of PEM fuel cells.

Directly‐Deposited Ultrathin Solid Polymer Electrolyte for Enhanced CO2 Electrolysis

AbstractThe economic viability of carbon dioxide electroreduction (CO2R) relies on improved performance accompanied by scalable system design. Membranes are commonly used for the separation of reduction and oxidation products as well as to provide a suitable micro‐environment for CO2R. Commercial membranes often address only one of the key challenges in CO2R: either they offer a suitable micro‐environment for CO2R (e.g., anion exchange membrane) or suppress carbonate cross‐over (e.g., cation exchange membrane and bipolar membrane). This work presents a cation‐infused ultrathin (≈3 µm) solid polymer electrolyte (CISPE) that concomitantly addresses both challenges via a bidirectional ion transport mechanism and suppressed cathode flooding. This directly‐deposited CISPE (that substitutes the commonly used pre‐made membrane) enables record high full‐cell energy efficiency of 28% at 100 mA cm−2 for one‐step CO2 electrolysis to ethylene (C2H4) with ≈110 h of stable operation. This translates into a record low energy cost of 290 GJ per ton C2H4 for the end‐to‐end process (i.e., CO2 capture and electroreduction, carbonate regeneration, CO2 separation from anode and cathode streams) in a membrane electrode assembly CO2R. The present work offers a versatile design paradigm for functional polymer electrolytes, opening the door to stable, and efficient electrolysis of high‐value feedstock chemicals and fuels using low‐cost catalysts.

Water Management for μDMFC with Foamed Stainless Steel Cathode Current Collector.

For micro direct methanol fuel cell (μDMFC), water flooding on the cathode seriously affects the performance stability. Additionally, the effect of material and wettability of the cathode current collector (CCC) on the drainage capacity is studied to improve the μDMFC’s performance. To this end, a CCC with foamed stainless steel was prepared to assemble the μDMFC due to its absorbency. Further, based on analyzing the gas–liquid two-phase flow characteristics of the μDMFC cathode, it was found that the gradient wettability CCC could accelerate the discharge of cathode water. Hence, the foam stainless steel CCC was partially immersed in a KOH solution to complete the gradient corrosion using its capillary force. Then, four different types of gradient wettability CCC were prepared by controlling the time of chemical corrosion. Finally, the performance of the μDMFC with different gradient wettability CCC was tested at room temperature using electrochemical impedance spectroscopy (EIS) and discharge voltage. The experimental results show that the gradient wettability CCC can improve the performance of the μDMFC by slowing down the rate of cathode flooding. The optimum corrosion time is 5 min at a concentration of 1 mol/L. Under these conditions, the CCC has the best gradient wettability, and the μDMFC has the lowest total impedance. The discharge voltage of the μDMFC with corroded CCC is increased by 33.33% compared to the uncorroded CCC μDMFC. The gradient wettability CCC designed in this study is economical, convenient, and practical for water management of the μDMFC.

Effects of Oversaturated Cathode Humidity Conditions on the Performance Degradation of PEMFCs and Diagnostic Signals of Warburg Impedance under Low Humidity Conditions

A proton exchange membrane fuel cell (PEMFC) inevitably experiences performance degradation during long-term operation under various corrosive conditions. In particular, cell operation under cathode flooding conditions results in severe cell degradation through sequential processes that induce the degradation of each component in the membrane electrode assembly (MEA). Furthermore, an excessive amount of water remaining at the cathode can diffuse into the anode side (back diffusion of water), and repeated instances can cause anode flooding (leading to fuel starvation). Herein, we focus on the collateral anode degradation of a stationary PEMFC operating under cathode flooding conditions with an oversaturated cathode in terms of relative humidity (RH, 150% RH). We suggest low-humidity electrochemical impedance spectroscopy (EIS-RH30) as a fault identification method to detect the degradation of the MEA, including the anode, before severe cell deterioration. Specifically, the EIS-RH30 analysis enables the detection of the malfunctioning anode reaction by limiting the hydrogen oxidation reaction (HOR) and proton conductivity, through which the phase difference between transporting protons from the anode to the cathode can be reflected as the horizontal aspect of the Warburg impedance. A generalized finite-length Warburg is introduced to understand the variation in the Warburg impedance spectra, and its numerical analysis can act as a diagnosable signal to monitor the sequential degradation of an MEA. A feasibility study of EIS-RH30 on actual degradation behavior that occurs under cathode flooding conditions was performed along with a microstructural investigation inside the MEA.

Progress and challenges: Review for direct liquid fuel cell

Direct liquid fuel cell (DLFC) is one of the leading fuel cell types due to their great features of superior energy density, modest configuration, small size in fuel container, immediate boosting, and effortless storage and carriage. Commercially used liquid fuel types are prepared using alcohols, such as methanol or ethanol, glycol, and acids. DLFCs face great challenges although they are potentially far-reaching depending on the expensive catalysts and the use of high-loading catalyst. More questions that should be addressed to ensure excellent DLFC performance include cathode flooding, fuel crossover, numerous side yield production, fuel security, and unverified elongated-duration robustness. Further studies need to be carried out to ensure the continuous improvement of the quality of DLFCs' performance and their penetration in the commercial market. To date, direct liquid fuel cells made of methanol and ethanol have been successfully produced in commercial scale, but other types of DLFCs are still under study. In this review, introduction to DLFC will be discussed by covering work and commercialization as well as recent progress and challenges encountered.

A Study on the Electrochemical Impedance Analysis of PEMFC Under the Low Humidity Condition

Polymer electrolyte membrane fuel cells (PEMFC) have received much attention as a next generation energy conversion system due to the pollutant-free byproduct (water), and high efficiency. PEMFC fundamentally consists of many components such as membrane electrode assembly (MEA) gas diffusion layers (GDLs), and bipolar plates (GDLs). Among them, MEA is directly correlated to the performance and durability of PEMFC since the MEA components such as catalyst materials, supporting carbon, and an ionomer (binder) can be degraded under corrosive environment during operating Hence, it is important to develop the meticulous analysis method to diagnose the degraded condition of PEMFC; thus, fault detection have to be properly identified before severe deterioration of MEA happens. Among an in situ diagnosis tool to investigate the degraded components of MEA, the electrochemical impedance spectroscopy (EIS) technique is well-known electrochemical method to classify each resistance such as high frequency resistance (HFR, Ohmic resistance), charge transfer resistance, and Warburg impedance, separately; thus, it makes it possible to trace the degraded components of MEA. Among them, the performance of PEMFC is closely related to the activity of catalyst that is reflected as a charge transfer resistance, and therefore, usual impedance studies are mostly focused on the catalyst [1]. In fact, however, the degradation behavior of a fuel cell system is very complicated since it originated from a complex chain and combination of corrosion issues [2], such as ionomer degradation, membrane thinning, corrosion of the supporting carbon, and Pt corrosion, which are the crucial degradation factors that affect both performance and durability of PEMFC. Hence, to elaborate the impedance measurement, it is necessary to focus on the inherent properties of all components of MEA.In this context, we performed the impedance measurements under low humidity (RH 30 %) condition to emphasize the ionic resistance during PEMFC operation. By deliberately limiting the ionic conductivity, the dehydrated ionomer accentuated the influence of ionic resistance among various resistance components inside the MEA, and thus the degraded MEA can be analyzed with respect to the ionomer surrounding catalyst layer (CL), as shown in Figure 1. Moreover, the complex capacitance adopting transmission line model (TLM) circuit under non-faradaic process facilitates to investigate the double layer capacitance (EDLC) of degrading CL [3, 4] as shown in Figure 2. To verify the feasibility of this approach, we studied degradation mechanism of MEA under dehydration and cathode flooding condition, respectively, since these problems related to water management are typical issues to be solved in systemic point of view [5].As a result, under the dehydration degradation, the increase of gas permeation induced the mixed potential formation at the anode, causing the cathode CL deterioration with surface variation of cathode CL. It could be monitored though the volume fraction of supporting carbon and ionomer. In addition, under the flooding degradation, the unbalanced current distribution caused the irregular anode deterioration, and phase differences between transported protons were reflected at horizontal aspect at low frequency region in Warburg impedance spectra. The detailed mechanism based on the aforementioned EIS measurement will be discussed in this presentation.