Cathode Catalyst Layer Research Articles

Optimizing catalyst layer composition of PEM fuel cell via machine learning: Insights from in-house experimental data

The catalyst layer (CL) is a pivotal component of Proton Exchange Membrane (PEM) fuel cells, exerting a significant impact on both performance and durability. Its ink composition can be succinctly characterized by platinum (Pt) loading, Pt/carbon ratio, and ionomer/carbon ratio. The amount of each substance within the CL must be meticulously balanced to achieve optimal operation. In this work, we apply an Artificial Neural Network (ANN) model to forecast the performance and durability of a PEM fuel cell based on its cathode CL composition. The model is trained and validated based on experimental data measured at our laboratories, which consist of data from 49 fuel cells, detailing their cathode CL composition, operating conditions, accelerated stress test conditions, polarization curves and ECSA measurements throughout their lifespan. The presented ANN model demonstrates exceptional reliability in predicting PEM fuel cell behavior for both beginning and end of life. This allows for a deeper understanding of the influence of each input on performance and durability. Furthermore, the model can be effectively applied to optimize the CL composition. This paper demonstrates the immense potential of AI, combined with a high-quality database, to advance fuel cell research.

Overcoming the Limitation of Ionomers on Mass Transport and Pt Activity to Achieve High-Performing Membrane Electrode Assembly.

The membrane electrode assembly (MEA) is one of the critical components in proton exchange membrane fuel cells (PEMFCs). However, the conventional MEA cathode with a covered-type catalyst/ionomer interfacial structure severely limits oxygen transport efficiency and Pt activity, hardly achieving the theoretical performance upper bound of PEMFCs. Here, we design a noncovered catalyst/ionomer interfacial structure with low proton transport resistance and high oxygen transport efficiency in the cathode catalyst layer (CL). This noncovered interfacial structure employs the ionomer cross-linked carbon particles as long-range and fast proton transport channels and prevents the ionomer from directly covering the Pt/C catalyst surface in the CL, freeing the oxygen diffusion process from passing through the dense ionomer covering layer to the Pt surface. Moreover, the structure improves oxygen transport within the pores of the CL and achieves more than 20% lower pressure-independent oxygen transport resistance compared to the covered-type structure. Fuel-cell diagnostics demonstrate that the noncovered catalyst/ionomer interfacial structure provides exceptional fuel-cell performance across the kinetic and mass transport-limited regions, with 77% and 67% higher peak power density than the covered-type interfacial structure under 0 kPagauge of oxygen and air conditions, respectively. This alternative interfacial structure provides a new direction for optimizing the electrode structure and improving mass-transport paths of MEA.

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.

Effect of Coupled Microstructural Characteristics of Catalyst Layer on High Temperature: Proton Exchange Membrane Fuel Cell Performance

Abstract The widespread adoption of High Temperature-Proton Exchange Membrane Fuel Cells (HT-PEMFC) in commercial applications is limited by their performance and durability compared to conventional energy sources. A key factor affecting these cells is the sluggish oxygen reduction reaction (ORR) at the cathode catalyst layer (CL). Optimizing the structural parameters of the cathode CL can enhance cell performance and longevity. Current research on these parameters is mostly descriptive, lacking numerical evidence to quantify their impact. This study develops a three-dimensional, non-isothermal HT-PEMFC numerical model to investigate the sensitivities of coupled structural parameters of the cathode CL, including Pt loading, CL thickness, and Pt particle diameter, at three levels. The orthogonal/Taguchi approach quantitatively assesses the impact of these parameters. The study reveals that Pt loading significantly affects cell voltage and cathode overpotential, while Pt diameter influences the homogeneity of overpotential distribution. The dominant impact of a single parameter decreases at higher current densities, necessitating careful analysis of trade-offs between different structural characteristics to maximize performance. These findings offer valuable insights for future experimental studies to enhance cell performance through adjustments to cathode catalyst characteristics.

An impedance spectroscopy study to unravel the effect of water on proton and oxygen transport in PEM fuel cells

A recent physics-based model for liquid and gaseous water transport in the cathode catalyst layer (CCL) is incorporated into our 1d ＋ 1d model for the PEM fuel cell impedance. The model includes parametric dependencies of the CCL oxygen diffusivity and proton conductivity on the liquid saturation. Fitting of the 1d ＋ 1d model to experimental impedance spectra of a PEM fuel cell reveals two intriguing effects. Contrary to common belief, the liquid water saturation in the CCL is nearly independent of cell current density due to the growing liquid pressure gradient that drives liquid water removal from the CCL. Further, the “dry” oxygen diffusivity of the catalyst layer increases with cell current density. Apparently, at small current density, electrochemical conversion proceeds primarily in narrow pores, where the Knudsen oxygen diffusivity is low. With growing current density, larger and better connected pores with higher oxygen diffusivity dominate in the current conversion, leading to increase in effective oxygen diffusivity observed in impedance spectroscopy data.

Dual functionality of cathode microporous layers: Reducing hydrogen permeation and enhancing performance in proton exchange membrane water electrolyzers

Hydrogen permeation and cell performance are critical factors for the safe and efficient operation of proton exchange membrane (PEM) water electrolysis. In this study, the effects of a cathode microporous layer (MPL) on water transport, hydrogen permeation, and cell performance in a proton exchange membrane water electrolyzer (PEMWE) were investigated. Results reveal that adding an MPL between the catalyst layer (CL) and the porous transport layer (PTL) at the cathode reduces interfacial contact resistance by approximately 60 % under 400 N cm−2, leading to superior performance. The wettability of the MPL plays a crucial role in water transport and hydrogen permeation in PEMWEs. The hydrophobic MPL-P-CB4, which uses polytetrafluoroethylene (PTFE) as a binder with a carbon black (CB) loading of 4 mgCB cm−2, enhances the crossover of water and hydrogen from the cathode to the anode through back diffusion, exceeding the technical safety criterion of 2 vol% H2 in the anode product gas (50 % lower explosion limit) at 2.0 A cm−2. However, the hydrophilic MPL with Nafion ionomers as binders (MPL-N-CB4) facilitates efficient removal of water and hydrogen from the cathode CL to the cathode flow field via capillary pressure, resulting in only 0.2 vol% H2 in O2 at 2.0 A cm−2. Consequently, a hydrophilic MPL is optimal for achieving superior performance and low-hydrogen-crossover in a PEMWE cathode. This study provides valuable insights for designing the PTL/CL interface in next-generation PEMWE cathodes.

In-Depth Analysis of the Impact of Ionomer Content on PEMFC Degradation By Combining Electrochemical Characterization Techniques and Transmission Line Modeling

This study analyzes the influence of the ionomer-to-carbon ratio (I/C) in cathode catalyst layers (CCL) on carbon corrosion behavior during high-potential cycling accelerated stress tests (ASTs). Membrane electrode assembly (MEA) samples with varying I/C ratios (0.5/0.85/1.2) were evaluated using polarization curve measurements and electrochemical impedance spectroscopy (EIS) under H2/air conditions. Analysis through the distribution of relaxation times (DRT) and equivalent circuit modeling revealed that the MEAs with a high I/C ratio (1.2) and a medium I/C ratio (0.85) exhibited the highest beginning of life (BoL) performance, attributed to their lower ionic resistances. Conversely, the MEA with a low I/C ratio (0.5) showed significant improvement during initial AST cycles and superior carbon degradation resistance, despite poor BoL performance. This study highlights the need for further investigation to fully understand the impact of the I/C ratio on electrode structure and carbon corrosion behavior. Furthermore, the combined results suggest that optimizing the I/C ratio could enhance the durability of PEMFC electrodes.

In-Depth Analysis of the Impact of Ionomer Content on PEMFC Degradation By Combining Electrochemical Characterization Techniques and Transmission Line Modeling

This study analyzes the influence of the ionomer-to-carbon ratio (I/C) in cathode catalyst layers (CCL) on carbon corrosion behavior during high-potential cycling accelerated stress tests (ASTs). Membrane electrode assembly (MEA) samples with varying I/C ratios (0.5/0.85/1.2) were evaluated using polarization curve measurements and electrochemical impedance spectroscopy (EIS) under H2/air conditions. Analysis through the distribution of relaxation times (DRT) and equivalent circuit modeling revealed that the MEAs with a high I/C ratio (1.2) and a medium I/C ratio (0.85) exhibited the highest beginning of life (BoL) performance, attributed to their lower ionic resistances. Conversely, the MEA with a low I/C ratio (0.5) showed significant improvement during initial AST cycles and superior carbon degradation resistance, despite poor BoL performance. This study highlights the need for further investigation to fully understand the impact of the I/C ratio on electrode structure and carbon corrosion behavior. Furthermore, the combined results suggest that optimizing the I/C ratio could enhance the durability of PEMFC electrodes.

A platinum degradation reaction model for the high-speed computation in the integrated fuel cell system simulator and its validation by the accelerated stress test data of the commercial fuel cells

A model to estimate the Pt degradation rate and the numerical methods for high-speed computation were developed for the year-long and system-scale durability simulation in an acceptable accuracy and computational time. The parameters in the model were determined to reproduce the published accelerated stress test (AST) data with the 1 cm2 MEA of 2nd-generation MIRAI (MIRAI-2), state-of-the-art commercial fuel cell electric vehicle. Accuracy of the simulation results was validated by the published data of the ASTs with the FC stack having 13 cells of MIRAI-2, which consists of the 30000 startup-shutdown cycles in 0–0.88 V and 73000 acceleration-deceleration cycles in 0.6–0.9 V. The experimental and simulation results of the residual fractions of the electrochemical surface area in the cathode catalyst layer after the ASTs were 68 and 69 %, respectively, and they agreed in an acceptable accuracy. It was confirmed from the AST simulation with the different initial particle size distributions that even the small number of the coarse particles significantly accelerated the Pt degradation. The developed model was integrated to the FC system simulator the current authors had presented and a remarkable computational speed for the year-long and system-scale durability simulation was demonstrated with a normal laptop computer.

A platinum degradation reaction model for the high-speed computation in the integrated fuel cell system simulator and its validation by the accelerated stress test data of the commercial fuel cells

A model to estimate the Pt degradation rate and the numerical methods for high-speed computation were developed for the year-long and system-scale durability simulation in an acceptable accuracy and computational time. The parameters in the model were determined to reproduce the published accelerated stress test (AST) data with the 1 cm2 MEA of 2nd-generation MIRAI (MIRAI-2), state-of-the-art commercial fuel cell electric vehicle. Accuracy of the simulation results was validated by the published data of the ASTs with the FC stack having 13 cells of MIRAI-2, which consists of the 30000 startup-shutdown cycles in 0–0.88 V and 73000 acceleration-deceleration cycles in 0.6–0.9 V. The experimental and simulation results of the residual fractions of the electrochemical surface area in the cathode catalyst layer after the ASTs were 68 and 69 %, respectively, and they agreed in an acceptable accuracy. It was confirmed from the AST simulation with the different initial particle size distributions that even the small number of the coarse particles significantly accelerated the Pt degradation. The developed model was integrated to the FC system simulator the current authors had presented and a remarkable computational speed for the year-long and system-scale durability simulation was demonstrated with a normal laptop computer.

Effects of Ionomer Film Thickness and Water Content on Oxygen Permeation Properties of PEFC Cathode Catalyst

In order to promote the widespread use of Polymer Electrolyte Fuel Cell (PEFC), enhancing cell performance is necessary. One significant factor affecting cell performance is the oxygen permeability in the ionomer, which depends on its nano-scale structure. In this study, to investigate the relationship between structures of catalyst layers and cell performances, we analyzed the effects of film thickness and water content on the oxygen permeation properties of ionomer in the cathode catalyst layer of PEFC using molecular dynamics simulations. We constructed a system in which oxygen molecules permeated ionomer on a platinum (Pt) surface. We found that sulfonic acid groups have a significant effect on oxygen permeation in low water content conditions.

Numerical Analysis on Influence of Double-Sided 3D-Patterned Cathode Catalyst Layers on Polymer Electrolyte Fuel Cell Performance

Abstract An optimized cathode catalyst layer (CCL) design can improve fuel cell performance. In this study, we tried to optimize the structure by investigating the electrochemical properties of ion and mass transport through various CCL structures with ionomer layer (IL) added using simulation numerical analysis. In the simulation, an electrochemical calculation was performed on the structure with polymer electrolyte membrane (PEM) and IL of CCL using multi-block model. The simulation was conducted by changing the aspect ratio (AR) structure of width and height of IL to five conditions so that IL is evenly distributed in catalyst layer (CL). The result confirmed that CL 3D IL AR 4.9 structure with the highest aspect ratio showed good performance. In addition, cell performance improved as the uniform reaction area with protons conducting through IL increased and the resistance of protons decreased. Finally, cell performance was predicted based on changes in oxygen concentration (OC), relative humidity (RH), and ionomer/carbon (I/C) ratio. This numerical analysis can show the reaction according to environmental and structural changes and design an optimized structure to improve cell performance.

A comprehensive modeling, analysis, and optimization of two phase, non–isobaric, and non–isothermal PEM fuel cell

This study models a non-isobaric, non-isothermal two-phase flow in a Polymer Electrolyte Membrane Fuel Cell (PEM-FC), focusing on conservation equations for mass, energy, and momentum across its components. Verification involves comparing PEM-FC performance and temperature distribution with experimental and literature data, showing consistent agreements. Results indicate that increasing cathode channel pressure enhances membrane moisture and reduces power loss. Higher oxygen partial pressure improves PEM-FC performance, whereas increased anode channel pressure heightens ohmic losses and lowers output voltage. Temperature distribution reveals highest temperatures near the cathode catalyst layer due to electrochemical reactions. Adjusting pressures in cathode and anode channels affects these temperatures accordingly. PEM-FC power density is optimized using various algorithms, with simulated annealing proving most effective. Optimal values for gas diffusion layer thickness, electrode porosity, and inlet humidity are determined. Under constant current density, power density increases by 6 % compared to baseline conditions, demonstrating effective parameter optimization for enhancing PEM-FC performance.

Novel design of a staggered-trap/block flow field for use in serpentine proton exchange membrane fuel cells

Enhancing the transverse velocity to the catalyst layer and exploiting the over-rib flow are two common methods of improving proton exchange membrane fuel cells (PEMFCs). The block flow field configuration significantly affects the augmentation of the transverse velocity to the catalyst layer, whereas the trap configuration significantly increases the molar concentration of O2 at the cathode catalyst layer without a pressure drop penalty. In this study, four-channel PEMFC models with different configurations were used, including the baseline and staggered-trap, -block, and -trap/block channels. The novel flow field with a combination of trap/block configurations exhibits a higher power output than those of the other designs. Furthermore, the novel staggered-trap/block channel induces a higher over-rib flow velocity than that of the baseline channel, leading to more uniform O2 and temperature distributions within the PEMFC. The optimal trap/block design increases the maximum net cell power by 8.04 % at V = 0.5 V.

3D carbon corrosion kinetic mechanism modeling study for proton exchange membrane fuel cells under localized flooding

Localized anode flooding often occurs in proton exchange membrane fuel cells (PEMFCs) during operation, which leads to localized H2 deficiency and triggers the carbon support corrosion in the catalyst layer, thus seriously weakening the performance and service life of PEMFCs. In this work, a 3D carbon corrosion kinetic mechanism model under localized anode flooding is developed to analyze in detail the multi-physics field distributions during carbon corrosion. The developed model is also coupled with a PEMFC performance model to focus on the carbon corrosion rate spatial distribution and its effect on the PEMFC performance. In addition, the effect of the cathode catalyst layer (CCL) added with oxygen evolution reaction (OER) catalyst on the carbon corrosion rate is analyzed in detail. Considering the particularly expensive OER catalysts and the non-uniform carbon corrosion distribution, a scheme of multi-area ordered adding with OER catalysts is further proposed to reduce the OER catalyst loading, and it is found that such a scheme can more effectively reduce the non-uniform carbon corrosion within the CCL. The electrochemical surface area loss is reduced by 7.38 % and the performance is improved by 5.69 % with scheme 2 compared to without the addition of OER catalyst.

Cathode catalyst layer aging of proton exchange membrane fuel cell during emulated start-up/shut-down phases

Start-up and Shut-down phases for Proton Exchange Membrane Fuel Cell stacks are known to damage the Cathode Catalyst Layer inducing an irreversible loss of performance. An original Accelerated Stress Test has been designed to mimic the Start-up phase in real-life system conditions. The impact of cathode potential on the degradation mechanisms of the Pt/C components within the Cathode Catalyst Layer by local electrochemical and physicochemical analyses provided a deep understanding of the cathode evolution. An unexpected cell performance improvement is observed between 1.0 and 1.2 V cathode potential, especially at high current density. A beneficial modification of the properties occurs suggesting that fresh Cathode Catalyst Layer exhibits non-optimized carbon support properties. However, a significant structure subsidence appears when the cathode potential is above 1.4 V. In this condition, modification/compaction of cathode layer due to carbon corrosion alters mass transport and empathizes water flooding through the electrode.

Effect of CO2 deficiency on the performance of membrane electrode CO2 electrolyzer

To mitigate greenhouse effects, carbon dioxide reduction reaction (CO2RR) has been used as an efficient means of carbon reduction. In CO2 electrolyzer, CO2 deficiency can happen and degrade the reaction efficiency. Herein, an efficient and long-lived formic acid three-cell electrolyzer is used to study the effect of CO2 deficiency, by operating the electrolyzer from full CO2 supply to CO2 deficiency. In addition, the effects of various CO2 fluxes and concentrations on the electrolyzer current, acid concentration and lifetime are investigated. This study quantitatively reveals the impact of CO2 deficiency on current density, product selectivity, and electrolyzer lifetime. The findings indicate that current density decreases by 12.74 %, while CO2 conversion efficiency drops by 92.5 %, demonstrating a significant reduction in the reactivity of CO2 conversion to formate ions. Conversely, the hydrogen evolution reaction is enhanced. Prolonged CO2 deficiency (below 13 ml/min) can also lead to catalyst degradation, including separation and dissolution within the cathode catalyst layer, ultimately diminishing overall performance. Compared with the CO2 flux, the CO2 concentration exerts a more pronounced influence. To ensure the electrolysis efficiency, the carbon dioxide concentration should not be less than 80 %.

Fabrication of high-performance gas diffusion electrode via microporous layer surface morphology control

Enhancing the performance of membrane electrode assemblies (MEAs) that utilize gas diffusion electrodes (GDEs) to match those based on catalyst coated membranes (CCMs) is critical for the widespread application of GDE-based technologies in proton exchange membrane fuel cells (PEMFCs). The inferior interfaces between the catalyst layers and the proton exchange membranes (PEMs) within GDE-based MEAs result in lower performance. In this study, the microporous layer (MPL) surface morphology control was achieved through hot pressing possessing the advantages of convenient implementation and avoiding excessive ionomer introduction. This approach produces smoother surfaces and higher peeling strengths between GDEs and PEMs, indicating enhanced interfacial contact. The ohmic resistance decreased from 0.056 to 0.033 Ω cm2, while the cathode catalyst layer proton resistance decreased from 0.124 to 0.059 Ω cm2, suggesting that the proton conductivity across the layers and within the catalyst layers were both increased. Moreover, the catalytic activity and gas transport capability within the catalyst layers are marginally improved. Following the MPL surface morphology control, the peak power density of GDE-based MEA was improved by 23 %, comparable to that of the CCM-based MEA. Nevertheless, excessive hot-pressing pressure might block the water transport path, resulting in poor performance at high current density.

Development of Multiple Electrospray Nozzles for Fabricating Catalyst Layers of Polymer Electrolyte Fuel Cells

The electrospray (ES) method can be used to make porous, high-performance and low-Pt-loading catalyst layers (CLs). In our group’s previous work, we succeeded in improving the cell performance in low-Pt-loading polymer electrolyte fuel cell cathode CLs by the use of a single-pin-nozzle ES method. However, the coating amount of the ES method is too low to be applied in mass production. In the present work, we have developed multi-pin nozzles. We started with the examination of two single-pin nozzles and confirmed that the ES method with plural nozzle pins was possible. We created a seven-pin nozzle as the first multi-pin nozzle. The uniformity of both the amount and scattering direction of the ink emission from that nozzle was deficient. We found that electrostatic-field control pins and plate were effective in correcting the behavior. Next, we created a 12-pin nozzle that was also equipped with electrostatic-field control pins and plate. We examined the length of the electrostatic-field control pins and the pin pitch with that nozzle. Finally, we increased the number of the nozzle pins to 72. The cathode CLs coated with that nozzle exhibited higher uniformity and cell performance in comparison with CLs coated by use of the pulse-swirl-spray method.

Modulating the electrode pore structure using the magnetic field for reduced local-oxygen transport resistance in polymer electrolyte membrane fuel cell

We utilize a magnetic field to align the pore structure of the PEMFC cathode catalyst layer in the direction of O2 infiltration. This alignment reduces the oxygen diffusion resistance within the catalyst layer, thereby augmenting the performance of the PEMFC. Membrane Electrode Assemblies (MEAs) with magnetically aligned cathodes demonstrate a 50% reduction in O2 transfer resistance compared to conventional MEAs, as verified through electrochemical experiments and it makes a performance enhancement in the I-V curve. Beyond electrochemical experimentation, electrode pore analysis utilizing 3D reconstruction and Lattice Boltzmann Direct Numerical simulation (LB-DNS) for internal flow field analysis within pores, reveals that alignment of the electrode structure in the through-plane direction enhanced pore continuity. This continuity and the resultant minimized proportion of dead pores are identified as the causative factors for the observed performance improvements.