Cathode Catalysts For Fuel Cells Research Articles

Degradation Studies of Fuel Cell Cathode Catalyst Layers Using Machine Learning

Fuel cells are a promising technology that has the potential to significantly revolutionize the energy sector by providing clean and sustainable sources of power for transportation, aerospace, and electricity applications. However, optimizing the performance of these devices remains a significant challenge as it largely depends on the catalyst layer in the electrodes of these devices, composed of carbon-supported Pt nanoparticle catalyst (Pt/C), perflurosulfonic acid (PFSA), ionomer binder, and a solvent. The catalyst layer design and operation require extensive knowledge of complex physical and chemical processes especially when achieving a low (<0.1 mgcm-2) Pt loading.Furthermore, the degradation of fuel cells is usually associated with either mechanical and/or electrochemical processes of the catalyst layer during operations, ultimately resulting in performance loss. While combinations of factors are responsible for the degradation of the catalyst layer in the fuel cell electrodes, it is still challenging to evaluate which factor contributes the most to the degradation of the catalyst layer.Machine learning algorithms, being powerful tools for predicting and optimizing the behavior of systems can be used to model complex processes, identify optimal operating compositions, and conditions, and reduce the laborious time and cost required for experimentation. They can be used to analyze data obtained from various experiments to identify patterns, trends, and anomalies. In this study, machine learning algorithms are employed for the prediction of catalyst layer degradation. Furthermore, an assessment of feature importance is conducted, elucidating the relative contributions of individual features to the degradation of catalyst layers. Leveraging on machine learning, we can develop an efficient, reliable, and cost-effective fuel cell system.

(Invited) Next Generation Designer Carbon Supports for Durable Polymer Electrolyte Fuel Cell Cathode Catalysts

The implementation of polymer electrolyte membrane fuel cells (PEMFC) in medium- and heavy-duty vehicles is a promising strategy to eliminate greenhouse gas emissions as the only byproduct is water. However, the durability of PEMFC catalysts, especially for the kinetically sluggish oxygen reduction reaction (ORR) that occurs at the cathode, remains a significant obstacle. Current state-of-the-art electrocatalysts are comprised of platinum-based nanoparticles anchored on high surface area carbon black supports (Pt/C). While these catalysts meet the U.S. Department of Energy’s near-term activity benchmarks [2], they suffer heavily from degradation mechanisms that can lead to catastrophic failure of PEMFCs. Hence, carbon support materials that promote durability are crucial to further development of ORR catalysts. Here, we report on the physical and electrochemical characterization of next-generation commercial FCX carbon supports that aim to mitigate these degradation mechanisms.We synthesized Pt/C electrocatalysts by decorating FCX carbons with spherical Pt nanoparticles approximately 2-3 nanometers in diameter. The surface and pore structure of the supports were extensively probed to determine their effects on anchoring of Pt nanoparticles and ultimately catalytic activity. After physical and electrochemical characterization of the catalysts, structure-to-property relationships were established, leading to a schematic for an “ideal” Pt/C electrocatalyst as shown in Figure 1. The hierarchical pore structure is crucial for mass transport, and Pt nanoparticles are housed on the edges of stable graphitic carbon domains. Lastly, a promising alternative to the traditional Pt/C synthesis pathway is shown. As degradation is more pronounced on the catalyst’s exterior surfaces, this novel electrocatalyst contains Pt nanoparticles inside the support’s mesopores to mitigate the loss of electrochemically active surface area [3]. The insights gained from this work can be applied to optimizing carbon support morphology and chemistry for durable and highly active ORR electrocatalysts.[1] M. Rezaei Talarposhti, T. Asset, S. T. Garcia, Y. Chen, S. Herrera, S. Dai, E. J. Peterson, K. Artyushkova, I. Zenyuk, P. Atanassov, ChemPhysChem, 21 (2020) 1331-1339.[2] D.A. Cullen, K.C. Neyerlin, R.K. Ahluwalia, R. Mukundan, K.L. More, R.L Borup, A.Z. Weber, D.J. Myers, A. Kusoglu, Nature Energy, 6 (2021) 462–474.[3] G.S. Harzer, A. Orfanidi, H. El-Sayed, P. Madkikar, H.A. Gasteiger, J. Electrochem. Soc. 165 (2018) F770-F779. Figure 1

Long Time Dynamics for Platinum Surface Area Loss in PEM Fuel Cells

Proton exchange membrane (PEM) fuel cells may emerge as a dominant clean energy source for heavy duty transport vehicles. Amongst other considerations, the lifetime performance of the fuel cell cathode catalyst layer is a key component of their future viability and a focus in the development of many proposed membrane electrode assemblies (MEAs). Typical targets of the lifetime of a PEMFC stack are on the order of thousands of hours of operation. However, running degradation tests spanning those long timescales is often impractical; and consequently, extensive work has been done developing and implementing accelerated stress tests (AST's) in order to screen proposed cathode catalyst materials for fuel cells.Much value is obtained by accurate and robust lifetime prediction models which are able bridge the gap between degradation from AST's in differential cells, and degradation of the catalyst layer in a fuel cell stack under realistic operating conditions. In other words, by parameterizing a model on short-time, subscale ASTs and extrapolating to a stack after tens of thousands of hours of operation. Commonly in such models, the electrochemically active surface area (ECSA) of platinum is used as the primary state-of-health parameter and predicted using either data-driven models or physics-based models. On one hand, data-driven models may be well suited to utilize large sets of stack data, but offer weaker extrapolation potential, conversely fitting physics-based models on global measurements of stack data is rarely a well-conditioned inverse problem.In this talk we present a scaling law on the long-time behavior of the ECSA obtained from analysis of governing physics equations from the literature. It is assumed that the primary loss mechanism is the coarsening of platinum particles, and the chief technique used is the method of averaging, which allows for the separation of two timescales: the short timescale of platinum oxide formation and dissolution, and the longer timescale over which the particle size distribution changes and a performance loss can be detected. The physics-derived asymptote for the ECSA evolution is then applied to several experiments and found to be in good agreement, allowing for a simple, streamlined lifetime prediction method for PEM fuel cells.

Effect of Solvent Ratio (Ethylene Glycol/Water) in the Synthesis of Pt/C Cathode Catalysts on PEM Fuel Cell Performance

Abstract The ethylene glycol (EG)/water mixture composition of an alkaline one-step polyol synthesis for Pt/C catalysts was systematically investigated and optimized for a low ethylene glycol content with regards to resulting Pt particle size and electrochemical performance of membrane electrode assemblies tested as proton exchange membrane (PEM) fuel cell cathode catalysts. Beginning test fuel cell data show a possible reduction of the required EG amount per gram of synthesized catalyst by up to 98% without significantly compromising the initial electrochemical performance. Taking catalyst durability into account, a Pt/C catalyst synthesized with 40 vol% H2O and 32 mM Pt precursor concentration showed a decent initial electrochemical performance (716 mV at 1 A cm-2) as well as an accelerated stress test-derived stability similar to an internal reference catalyst, obtained with 100 vol% EG. In summary, our study shows that optimizing the amount of water and platinum precursor in the synthesis process can lead to catalysts with excellent performance for PEM fuel cells while contributing significantly to cost reduction by using less EG during synthesis.

Using the IL-TEM Technique to Understand the Mechanism and Improve the Durability of Platinum Cathode Catalysts for Proton-Exchange Membrane Fuel Cells.

Proton-exchange membrane fuel cells are one of the most promising energy conversion technologies for both automotive and stationary applications. Scientists are testing a number of solutions to increase the durability of cells, especially catalysts, which are the most expensive component. These solutions include, among others, the modification of the composition and morphology of supported nanoparticles, the platinum-support interface, and the support itself. A detailed understanding of the mechanism of platinum degradation and the subsequent improvement of the durability of the entire cell requires the development of methods for effectively monitoring the behavior of catalytic nanoparticles under various cell operating conditions. The Identical-Location Transmission Electron Microscopy (IL-TEM) method makes it possible to visually track structural and morphological changes in the catalyst directly. Because the tests are performed with a liquid electrolyte imitating a membrane, they provide better control of the degradation conditions and, consequently, facilitate the understanding of nanoparticle degradation processes in various operating conditions. This review is primarily intended to disseminate knowledge about this technique to scientists using electron microscopy in the study of energy materials and to draw attention to issues related to the characterization of the structure of carbon supports.

Laser-Induced Graphene as a Cathode Catalyst for Microbial Fuel Cell

Laser-Induced Graphene as a Cathode Catalyst for Microbial Fuel Cell

A review of fuel cell cathode catalysts based on hollow porous materials for improving oxygen reduction performance

Fuel cells are highly efficient green power generation devices that convert chemical energy into electricity.

Performance of a PEM fuel cell cathode catalyst layer under oscillating potential and oxygen supply

A model for impedance of a PEM fuel cell cathode catalyst layer under simultaneous application of potential and oxygen concentration harmonic perturbations is solved. The solution demonstrates strong lowering of the layer impedance under increase in the amplitude of oxygen concentration perturbation. Small in–phase oscillations of the overpotential and oxygen concentration lead to formation of a sub–layer with negligible oxygen transport loss. Working as an ideal non–polarizable electrode, this sub–layer dramatically reduces the system impedance.

Electrode Coating Process Impact on the Performance of Pt and PtCo Fuel Cell Cathode Catalysts

The polymer electrolyte membrane fuel cell (PEMFC) is one of the most promising energy sources for replacing fossil fuels in vehicles, as it does not produce greenhouse gas emissions during operation. As a key player in hydrogen mobility, SYMBIO is developing and producing PEMFC systems for a large field of applications. SYMBIO masters the electrochemical core (the Membrane Electrode Assembly - MEA), the complete stack (bipolar plate, stacking and housing) and the fuel cell system (Balance of Plant, operating conditions, control-command, packaging) [1].The widespread use of fuel cell vehicles is strongly linked to the price of the PEMFC system, in which the MEA as a high share. Decreasing the total PGM content, as well as moving to high-speed roll-to-roll production methods are important levers in the cost roadmap of MEAs. And from a performance point of view, systems for the heavy-duty market will need to show high efficiencies at low current densities (<1 A/cm2). Exploring the potential of highly active cathode catalyst is therefore mandatory for these applications.State of the art cathode catalyst layers consists in either Pt or PtCo-alloy supported on carbon material, the latter being more active for the ORR but also less resistant towards potential cycling. Regarding the ink formulation, the use of PtCo poses the challenge that Co atoms could dissolve, even if the catalyst has been previously acid leached, leading to the release of free Co2 +. These free ions will latter lower the catalytic activity and the transport of reactants (H+ and O2) to the active sites in the catalytic layer [2-3].The manufacturing of a catalyst coated membrane (CCM) can be done with different printing processes involving a catalytic ink and a substrate. Each coating process has different constraints (ink rheological behaviour, particle size) leading to optimisation of ink recipe (solvent matrix, solid content ...). The ink must also be compatible with the substrate that can be directly an MEA component such as the membrane (direct coating) or the GDL, or a decal-carrier substrate. All these parameters lead to catalyst layer structure differences that impact the MEA performance.In this study, the impact of three coating processes, hence three solvent systems for a same catalyst, ionomer, and I/C ratio, on the MEA performance is explored for commercial Pt and PtCo catalysts. The coating processes compared are direct coating on membrane via bar coater and spray coater and non-direct coating using decal method.The inks properties including the granulometry and the viscosity of different prepared inks were characterized before coating. Ex-situ techniques (SEM-EDX, TEM, N2 adsorption/desorption) were used to figure-out the impact of the coating process on the morphology and porosity of the cathodic catalyst layer. The influence of these parameters on the electrochemical performance was studied using H2-Air polarization curves, electrochemical impedance spectroscopy and the electrochemical surface area (ECSA).It will be highlighted how important the final PEMFC performance must be understood by taking into account the used ink system and coating process, as well as the intrinsic stability of catalyst, ionomer and membrane during these stages.

Operando x-Ray Absorption Spectroscopy Investigation of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction

Oxygen reduction reaction (ORR) plays a key role in the development of fuel cell technology, and great efforts have been made to reduce the amount of platinum, required to speed up this sluggish reaction, or, even more desirable, to use efficient electrocatalysts based on earth-abundant metals. To date, numerous single-atom catalysts in the form of metal-doped carbon-nitrogen materials (MNC) have proved to be a promising alternative to ORR Pt-based materials. [1-3]In this study we employed advanced spectroscopic techniques, namely Mössbauer spectroscopy and operando X-ray absorption (XAS) spectroscopy, to understand the structural and electronic factors underlying an increase in the catalytic turn over frequency (TOF) of bimetallic FeSnNC and FeCoNC catalysts, relative to the parent FeNC materials. In particular, 57Fe Mössbauer spectroscopy identified a larger ratio of D1/D2 species in both bimetallic catalysts, supporting a larger ratio of Fe(III)-Nx/Fe(II)-Nx sites. The combination of extended X-ray absorption fine structure (EXAFS) modeling, and the analysis of operando X-ray absorption near-edge spectroscopy (XANES) spectra revealed a disordered carbon structure around FeNx active sites, and variations in the iron oxidation state that can be linked to the enhanced intrinsic catalytic reactivity (TOF). This talk is therefore intended to draw attention to the potential of the XAS technique, especially when applied to in-situ/operando studies in the field of electrocatalysis. References F. Luo, A. Roy, L. Silvioli, D.A. Cullen, A. Zitolo, M.T. Sougrati, I.C. Oguz, T. Mineva, D. Teschner, S. Wagner, J. Wen, F. Dionigi, U.I. Kramm, J. Rossmeisl, F. Jaouen and P. Strasser. P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction. Nature Materials 2020, 19, 1215-1223A. Zitolo, N. Ranjbar, T. Mineva, J. Li, Q. Jia, S. Stamatin, G.F. Harrington, S.M. Lyth, P. Krtil, S. Mukerjee, E. Fonda, F. Jaouen. Identification of catalytic sites in cobalt-nitrogen-carbon materials for the oxygen reduction reaction. Nature Communications 2017, 8(1), 957A. Zitolo, V. Goellner, V. Armel, M. T. Sougrati, T. Mineva, L. Stievano, E. Fonda, F. Jaouen. Identification of catalytic sites for oxygen reduction in iron and nitrogen doped graphene materials. Nature Materials 2015, 14, 937-942

Heterogenous Degradation of Cathode Catalyst Layers: Influence of O2 Partial Pressure and Various Stressors Under Load Cycling Conditions

Proton exchange membrane fuel cells (PEMFCs) are an important technology to reduce greenhouse gas emissions in the heavy-duty vehicle automotive fleet. Of particular importance is achieving high performance and durability of the cathode catalyst layer (CCL) which uses platinum group metals (PGMs) to catalyze the kinetically sluggish oxygen reduction reaction (ORR).1 Understanding limits of performance under specific stressors and correlating stressors to changes in the microstructure of the membrane electrode assembly (MEA) and properties of the catalyst will enable better understanding of potential pathways to enhance durability of the PEMFCs.Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) studies have demonstrated through-plane differences in the local Pt content and nanoparticle size with regard to the gas diffusion layer (GDL)-catalyst layer interface, middle of the catalyst layer, and membrane (PEM)-catalyst layer interface.2,3 We have previously shown that there are spatial through-plane differences (e.g., F/Pt profile as a benchmark and nanoparticle size assessment) throughout the CCL depth of MEAs when ran under potential cycling accelerated stress test (AST) conditions under N2 with varied stressors (i.e., temperature, relative humidity, dwell time at upper and lower potential limits, etc.).3 It has also been demonstrated that adjusting these stressors can either mitigate or enhance the rate of degradation under potential cycling conditions.4 Historically, N2-based ASTs have been used, including in our past work, to characterize aging behavior in the CCL. Here, we present an analysis on the effect of oxygen presence in the cathode, more similar to real load/unload PEMFC operation. The elucidation of the through-plane spatial degradation with focus on influence of varied O2 partial pressure and comparison to lower temperature, relative humidity, and upper potential limit at 21% O2 will be discussed. More specifically, the differences in the F/Pt profile, nanoparticle size, depletion layer thickness, Pt band location within the membrane, etc. and its implications on real-world PEMFC testing will be presented.References(1) Cullen, D. A.; Neyerlin, K. C.; Ahluwalia, R. K.; Mukundan, R.; More, K. L.; Borup, R. L.; Weber, A. Z.; Myers, D. J.; Kusoglu, A. New Roads and Challenges for Fuel Cells in Heavy-Duty Transportation. Nat. Energy 2021, 6 (5), 462–474. https://doi.org/10.1038/s41560-021-00775-z.(2) Schneider, P.; Batool, M.; Godoy, A. O.; Singh, R.; Gerteisen, D.; Jankovic, J.; Zamel, N. Impact of Platinum Loading and Layer Thickness on Cathode Catalyst Degradation in PEM Fuel Cells. J. Electrochem. Soc. 2023, 170 (2), 024506. https://doi.org/10.1149/1945-7111/acb8df.(3) Coats, M.; Medina, S.; Braaten, J.; Cheng, L.; Craig, N.; Johnston, C.; Pylypenko, S. Quantitative Analysis of Fuel Cell Cathode Catalyst Layer Degradation Using Scanning Transmission Electron Microscopy and Energy Dispersive Spectroscopy. ECS Meet Abstr 2022, MA2022-02 1434. https://doi.org/10.1149/MA2022-02391434mtgabs.(4) Kneer, A.; Wagner, N. A Semi-Empirical Catalyst Degradation Model Based on Voltage Cycling under Automotive Operating Conditions in PEM Fuel Cells. J. Electrochem. Soc. 2019, 166 (2), F120–F127. https://doi.org/10.1149/2.0641902jes.

A New Catalyst System for the Oxygen Reduction Reaction (ORR) at Fuel Cell Cathodes: P-Block Precious Group Metal-Free Tin and Nitrogen-Doped Carbon (SnNC) Catalyst

The sluggish kinetics of the Oxygen Reduction Reaction (ORR) and the consequently large amount of platinum catalyst required for cathode material in Proton Exchange Membrane Fuel Cell (PEMFC) is today’s primary hurdle for commercializing fuel cell technology in automotive application.1 A class of carbon-doped with metal and nitrogen electrocatalysts (labelled MNC) is promising substitute for platinum-group metals (PGMs) in oxygen reduction reaction (ORR) in PEMFC.2 Particular attention was placed on a specific family of MNC catalysts derived from 3d transition metal precursors with FeNC and CoNC being the most promising for PEMFC applications requiring high power density.3-5 In the present contribution, we report on a new MNC catalyst system, different by its chemical nature from all others catalysts previously reported as ORR-active in acidic medium. The highlights of this work are the successful design and synthesis of SnNC as a non-noble metal catalyst for the first time, and the finding that SnNC hosts Sn-based active sites that can achieve the same turnover frequency as Fe-based active sites in FeNC, and much higher turnover frequency than Co-based active sites in CoNC. FeNC and CoNC materials have, until now, been the state-of-art PGM-free catalysts for ORR in acidic medium. The present SnNC material shows also high and similar selectivity for the four-electron ORR pathway as FeNC, much higher than CoNC materials. The prepared SnNC catalysts meet and exceed the FeNC catalysts in terms of hydrogen-air fuel cell power density. The SnNC-NH3 catalysts displayed a 40-50% higher current density than FeNC-NH3 at cell voltages below 0.7 V. Added benefits include a Fenton-inactive character of Sn. Among other techniques, density functional theory and 119Sn Mössbauer spectroscopy were used in combination to investigate SnNC, providing for the first time insights on the structure of its active sites, their rate-determining step for ORR and selectivity for the four-electron reduction pathway. References Holton, O. T.; Stevenson, J. W., The Role of Platinum in Proton Exchange Membrane Fuel Cells. Platinum Metals Review 2013, 57 (4), 259-271.Luo, F.; Wagner, S.; Ju, W.; Primbs, M.; Li, S.; Wang, H.; Kramm, U. I.; Strasser, P., Kinetic Diagnostics and Synthetic Design of Platinum Group Metal-Free Electrocatalysts for the Oxygen Reduction Reaction Using Reactivity Maps and Site Utilization Descriptors. Journal of the American Chemical Society 2022, 144 (30), 13487-13498.Zitolo, A.; Ranjbar-Sahraie, N.; Mineva, T.; Li, J.; Jia, Q.; Stamatin, S.; Harrington, G. F.; Lyth, S. M.; Krtil, P.; Mukerjee, S.; Fonda, E.; Jaouen, F., Identification of catalytic sites in cobalt-nitrogen-carbon materials for the oxygen reduction reaction. Nature Communications 2017, 8 (1), 957.Zitolo, A.; Goellner, V.; Armel, V.; Sougrati, M.-T.; Mineva, T.; Stievano, L.; Fonda, E.; Jaouen, F., Identification of catalytic sites for oxygen reduction in iron- and nitrogen-doped graphene materials. Nature materials 2015, 14 (9), 937-942.Luo, F.; Roy, A.; Silvioli, L.; Cullen, D. A.; Zitolo, A.; Sougrati, M. T.; Oguz, I. C.; Mineva, T.; Teschner, D.; Wagner, S.; Wen, J.; Dionigi, F.; Kramm, U. I.; Rossmeisl, J.; Jaouen, F.; Strasser, P., P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction. Nature materials 2020, 19 (11), 1215-1223.

Impact of polymer additives on crack mitigation of rod-coated fuel cell cathode catalyst layers

Cracks in catalyst layers (CLs) are a potential source of long-term failure in a fuel cell membrane electrode assembly (MEA). While modifications to the CL ink formulation can affect the degree of cracking, these changes may lead to lower initial performance than their cracked analogues due to the established link between formulation and performance. In this work, we explored the use of polymeric additives to mitigate CL cracks. Small quantities of poly (acrylic acid), poly (ethylene oxide), poly (methyl methacrylate), or poly (vinyl alcohol) – 5 wt% relative to ionomer mass – were added to the ink prior to its final mixing. Poly (vinyl alcohol) resulted in crack–free CLs, whereas the other polymers resulted in CLs with similar crack percentages as the control CL. Through a combination of transmission electron microscopy, X-ray computed tomography, and infrared spectroscopy, we ascribed the crack–mitigating mechanism of poly (vinyl alcohol) to its ability to hydrogen–bond with Nafion, the ion conducting polymer binder in the catalyst ink. Initial performance of this non–cracked electrode exhibited nearly identical electrochemical behavior to its cracked counterpart, demonstrating that PVA additives successfully reduce cracks while maintaining cell initial performance.

Single-Walled Carbon Nanotubes Supported Pt Electrocatalyst as a Cathode Catalyst of a Single Fuel Cell with High Durability against Start-up/Shut-down Potential Cycling

Single-Walled Carbon Nanotubes Supported Pt Electrocatalyst as a Cathode Catalyst of a Single Fuel Cell with High Durability against Start-up/Shut-down Potential Cycling

Improving oxygen reduction reaction by cobalt iron-layered double hydroxide layer on nickel-metal organic framework as cathode catalyst in microbial fuel cell

Cobalt Iron -layered double hydroxide (CoFe-LDH) nano sheets were attached to Nickel-metal organic frameworks (Ni-MOF) by utilizing hydrothermal reaction method, and CoFe-LDH@Ni-MOF was synthesized and worked as the cathode catalyst in microbial fuel cell. The surface of this composite material provided generous electrochemical active sites, consisting of wrinkled strips of CoFe-LDH adhering to a lamellar structure of Ni-MOF. In terms of the maximum output power density, CoFe-LDH@Ni-MOF as the catalyst was 211 mW/m2, 2.54 times higher than that of Ni-MOF (83 mW/m2), and it was stable at about 225 mV for 150 h. CoFe-LDH@Ni-MOF showed high oxygen reduction reaction capability and high specific surface area, and the electron transfer rate was accelerated. This work might set the stage for the development and utilization of fuel cell cathode catalysts.

(Invited) Catalysts, Inks and Electrodes for PEM Water Electrolysis: Scalable Approach for Highly Performed Catalyst Layer Fabrication

The majority of commercially available anodic electrocatalysts for Low Temperature PEM Water Electrolyzers are based on unsupported iridium-based materials. These electrocatalysts can be amorphous or crystalline metallic, oxidic, and/or hydroxide-derived compounds. The planned worldwide installations of electrolyzers (on the order of tens of Gigawatts per year) will require manufacturing of Membrane Electrode Assemblies (MEAs) via highly scalable methods, one of which is Roll-2-Roll production (R2R) [1, 2]. In contrast to spraying techniques, R2R requires the utilization of inks with a higher content of solids, which in the case of extremely dense Ir-based materials may cause a sedimentation of suspended electrocatalysts resulting in overall ink destabilization.In the presented work a systematic study of ink stability with commercial IrO2 catalysts over a period of 14 days was performed. During this period of time the minimal redispersion of slurries was done to mimic realistic conditions of inks aging. The inks were comprehensively characterized by rheological measurements, zeta potential, particle size distribution (Dynamic Light Scattering) and inks density. A series of decal electrodes was fabricated using Baker bar coating approach (a model of R2R production) and coatings were characterized by contact angle, X-Ray Photoelectron Spectroscopy and Transmission Electron Microscopy.Detailed electrochemical performance analysis including the separation of voltage losses [3] via Electrochemical Impedance Spectroscopy was performed to compare MEA performance with aging time. Acknowledgements and Statements. The authors acknowledge financial support from M2FCT and H2NEW consortia. References. [1] J. Sharma, X. Lyu, T. Reshetenko, G. Polizos, K. Livingston, J. Li, D. L. Wood, A. Serov "Catalyst layer formulations for slot-die coating of PEM fuel cell electrodes" Int. Journal of Hydrogen Energy 47 (2022) 35838-3585.[2] E. B. Creel, K. Tjiptowidjojo, J. A. Lee, K. M. Livingston, P. R. Schunk, N. S. Bell, A. Serov, D. L. Wood III "Slot-Die-Coating Operability Windows for Polymer Electrolyte Membrane Fuel Cell Cathode Catalyst Layers" J. of Colloid and Interface Science 610 (2022) 474-485.[3] A. Dizon et. al “Advanced Voltage Break Down Analysis by Statistical Open-Source Tool Case Study Based on Polymer Electrolyte Water Electrolysis”, ECS 242 (2022)

Optimal pore shape in a low‐Pt PEM fuel cell cathode catalyst layer

AbstractA model for performance of an axially symmetric pore with the curved generatrix is developed. Oxygen transport along the pore axis and in the radial direction through a thin ionomer film separating the pore volume from the Pt/C surface is taken into account. A performance functional is formulated, and the Euler–Lagrange equation is solved numerically for an optimal pore shape. This shape is close to a cubic paraboloid converging toward the membrane. Polarization curves show superior performance of the optimal pore over the cylindrical pore of the same active (side) surface area. The results suggest the shape of optimal ionomer loading for low‐Pt electrodes.

PtCoFe Intermetallic Alloy Catalyst Derived from PtFe@CoO with High Stability for Oxygen Reduction Reaction

AbstractPlatinum‐based ordered alloy catalysts possess higher intrinsic activity in oxygen reduction reactions (ORR). High‐temperature annealing during ordered alloy formation frequently results in larger nanoparticles, and the strategy for obtaining ordered alloys at 600 °C is still undefined. Herein, an ordered Fe‐doped PtCo catalyst (O‐PtCoFe/C) with a size of sub‐4 nm was prepared at 600 °C derived from PtFe@CoO. CoO can generate oxygen vacancies by H2 reduction, lowering the atomic migration barrier and serving as a protective layer to inhibit nanoparticle migration. Experimental analyses showed the formation of O‐PtCoFe/C and electron‐rich Pt atoms due to Pt, Co, and Fe, which was advantageous for ORR performance. The mass activity of the prepared catalyst for ORR was 382.8 mA mgPt−1, which is 5.4 times greater than Pt/C. After 10000 potential cycles, the half‐wave potential was only negatively shifted by 10 mV. In PEMFC (proton exchange membrane fuel cells) tests, the O‐PtCoFe/C showed only 3 % decay after 3000 cycles, whereas the Pt/C showed a significant loss (18.4 %). This work provides an effective method for preparing ordered PtCo alloys for fuel cell cathode catalysts at 600 °C.

Structure Dynamics of Carbon-Supported Platinum-Neodymium Nanoalloys during the Oxygen Reduction Reaction

Platinum-rare earth nanoalloys have been predicted to be promising proton exchange membrane fuel cell (PEMFC) electrocatalysts for the cathodic oxygen reduction reaction (ORR). However, their implementation in PEMFCs is limited by the challenge of their preparation as carbon-supported nanostructures. Consequently, the practical structure–activity–stability trends for this class of nanoalloys remain largely unexplored. Herein, carbon-supported Pt–Nd nanoalloys as ORR electrocatalysts are described. The physical chemistry of selected electrocatalysts was extensively investigated by means of combined ex situ and operando techniques, which reveal the unique structural dynamics of Pt–Nd nanoalloys in a simulated PEMFC cathode environment. The experimental observations, supported by theoretical calculations, indicate that after initial significant structural modification in the early stage of operation, the ORR activity is mediated in the longer term by surface compressive strain rather than charge transfer between Pt and Nd. Such key operando structure–activity–stability relations underpin further optimization of carbon-supported Pt-rare earth nanoalloys as fuel cell cathode catalysts.

Transition-Metal and Nitrogen-Doped Carbon Nanotube/Graphene Composites as Cathode Catalysts for Anion-Exchange Membrane Fuel Cells

Transition-metal and nitrogen-doped graphene-like material and carbon nanotube (M-N-Gra/CNT) composites are prepared, characterized, and used as cathode catalysts in anion-exchange membrane fuel cells (AEMFCs). Melamine as a nitrogen source and cheap iron and cobalt salts as metal precursors are used for doping via high-temperature pyrolysis. The success of doping is proven by several physicochemical analysis methods, and the catalyst materials possess rather similar textural properties. The initial assessment of the oxygen reduction reaction activity using the rotating disk electrode method shows that Fe-N-Gra/CNT, Co-N-Gra/CNT, and CoFe-N-Gra/CNT materials have very similar electrocatalytic performances in alkaline media as well as excellent short-term stability but a different yield of HO2– formation. The M-N-Gra/CNT materials as cathode catalysts together with the Aemion+ reinforced anion-exchange membrane exhibit very good AEMFC performance, especially CoFe-N-Gra/CNT, comparable to that of Pt/C, reaching a peak power density of 638 mW cm–2. Such an excellent fuel cell performance of the M-N-Gra/CNT catalyst materials is attributed to the presence of M–Nx sites, carbon-encapsulated transition-metal nanoparticles, and feasible nitrogen-containing moieties.