Fuel Cell Cathode Research Articles

MnO2 Nanowire Thin Mesh With Enhanced Mass Transfer as Hydroxide Exchange Membrane Fuel Cell Cathode

AbstractHydroxide exchange membrane fuel cells (HEMFCs) are promising due to the potential use of nonprecious metal catalysts. However, the performance of HEMFCs based on nonprecious catalysts is still unsatisfactory, and one reason for this is hindered mass transfer in the catalyst layer. In this study, we employ a hydrothermal method to grow in situ a MnO2 nanowire thin mesh (NTM) catalytic layer on the gas diffusion electrode. The HEMFC prepared with MnO2 NTM cathode achieves a peak power density of 425 mW cm−2, surpassing the performance of the HEMFC prepared using the traditional powder catalyst spraying method by four times. High‐frequency resistance and limiting current tests indicate that the MnO2 NTM reduces ohmic resistance and improves mass transfer, thereby enhancing the HEMFC performance. Furthermore, the peak power density of the HEMFC is increased to 626 mW cm−2 by depositing additional active Co3O4 nanoparticles on the MnO2 NTM. These findings demonstrate that an interconnected and porous catalyst layer structure is beneficial for improving mass transfer properties, which in turn enhances HEMFC performance.

Boosting the Durability of High-Pt-Content Fuel Cell Cathode Catalysts Through TaOx Decorating.

Enhancing the durability of carbon-supported platinum catalysts (Pt/C) for the oxygen reduction reaction remains a significant challenge in the field of proton exchange membrane fuel cells (PEMFCs), especially for catalysts with high-Pt contents. Herein, a TaOx decorating strategy that is capable of effectively boosting the durability of Pt/C catalysts even with a high-Pt content of 50 wt.% is introduced. This strategy involves introducing reducible Ta2O5 nanoparticles into carbon supports, depositing Pt nanoparticles, and finally conducting high-temperature H2 annealing to convert reducible Ta2O5 nanoparticles into amorphous TaOx decorating the Pt nanoparticles. The annealing temperature found in the Ta2O5 incorporation step is critical for the formation of reducible Ta2O5 nanoparticles, which, in turn, determines the continuity of the TaOx subsequently formed around the Pt nanoparticles. By controlling annealing temperature, the formation of a relatively continuous TaOx distribution on the Pt nanoparticle surface is achieved, thereby maximizing the interaction between Pt and TaOx and enhancing the electrochemical stability of Pt nanoparticles. Following the accelerated durability test, the resulting high-Pt-content catalyst demonstrates an array of exceptional durability metrics, including an electrochemical surface area loss of 30%, a mass activity loss of 35%, and a voltage loss of 22mV at 0.8 A cm‒2.

Seed-Mediated Synthesis of High Loading PtCo Intermetallic Compounds Enhanced Catalytic Efficacy and Long-Term Stability for Oxygen Reduction Reaction.

Atomically ordered intermetallic Pt-based nanoparticles, recognized as advanced electrocatalysts, exhibit superior activity for the oxygen reduction reaction (ORR) in fuel cell cathodes. Nevertheless, the formation of these ordered structures typically necessitates elevated annealing temperatures, which can accelerate particle growth and diminished reactivity. In this study, we synthesized carbon-supported platinum-cobalt intermetallic compounds (PtCo-IMCs) with sub-4 nm particle sizes and uniform distribution. These catalysts, characterized by high platinum content and exceptional ORR activity, are specifically tailored for heavy-duty vehicle (HDV) applications. The PtCo-IMCs exhibited significantly enhanced catalytic performance and durability compared to conventional Pt-based catalysts, utilizing platinum nanoparticles as nucleation sites to promote growth. This method effectively retained smaller particle sizes while achieving a higher degree of ordering and alloying during high-temperature annealing. Optimization of the annealing temperature resulted in peak activity and stability at 800 °C. The mass activity (MA) of the PtCo-800 catalyst was 2.7-fold and 1.8-fold that of the commercial Pt/C and disordered PtCo catalysts, respectively. Additionally, the single cell employing the PtCo-800 catalyst showed a minimal voltage loss of only 27 mV at a current density of 2 A cm-2 after 30,000 cycles of the accelerated durability test (ADT), underscoring its long-term stability.

Magic Angle Moiré Bilayer Graphene for Enhanced Electrochemical Oxygen Reduction Reaction in PGM-Free Catalysts

Tuning active site electronic structures is crucial to the efficient interconversion of electrochemical energy. The recent discovery of flat electronic bands in stacked atomically thin layers of graphene has sparked unprecedented interest in moiré superlattices with small twist angles (0.22º < theta < 5º).1 A recent work in electrocatalysis demonstrated enhancement of hydrogen evolution using Ru embedded in twisted bilayer graphene (TBG) nanosheets.2 In this talk, we explore moiré superlattice effects for applications in PGM-free fuel cell cathode catalysts, where molecular oxygen is electrochemically reduced at the catalyst-electrolyte interfaces (i.e., oxygen reduction reaction, ORR) to power polymer electrolyte fuel cells (PEFCs). The activity, stability, and affordability of catalysts are current bottlenecks at the materials level that prevent widespread adoption of PEFCs in the clean energy sector. Replacing rare and expensive Pt/C catalysts with graphene-based structures would greatly aid in addressing cost, but co-optimization in the activity and stability of such structures is required. We will discuss the theoretical and computational framework needed to unveil the mechanisms and merits of TBG as an effective material platform for realizing highly active and stable ORR precious metal free catalysts. This includes the feasibility of driving 4 electrons ORR pathways on TBG systems as a function of twist angle, which will provide us with an activity descriptor. For structures demonstrating feasible 4 electrons reduction pathway, we will further explore stability against metal dissolution. These efforts enable us to explore the existence of “magic angles” of TBG in ORR applications. This work will leverage our prior efforts in developing activity and stability descriptors for electrocatalyst and atomically dispersed systems.3–6 We will also combine uncertainty quantification approaches with multi-objective Bayesian optimization to navigate the TBG structural-chemical material space and suggest new synthesis target structures exhibiting both high activity and stability. References Y. Cao et al., Nature, 556, 43–50 (2018). J. Zhang et al., Angew Chem Int Ed, 61, e202116867 (2022). S. Li, G. S. Frankel, and C. Taylor, J. Electrochem. Soc. (2022) https://iopscience.iop.org/article/10.1149/1945-7111/ac86f8. E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020). H. Hafiz, P. Zelenay, and E. F. Holby, Applied Catalysis B: Environmental, 339, 123158 (2023). W. J. M. Kort-Kamp et al., Journal of Power Sources, 559, 232583 (2023).

La0.3Sr0.7Ti0.3Fe0.7O3-δ derived from Malaysian ilmenite and monazite for application of solid oxide fuel cell cathode

This study investigates the effect of using low-purity oxides in synthesizing lanthanum strontium titanate ferrite (LSTF) on its electrochemical performance as a solid oxide fuel cell (SOFC) cathode material. Lanthanum oxide at 30% and 60% purity is extracted from monazite, and iron oxide at 70% and 90% purity is extracted from ilmenite as the LSTF precursor. Symmetrical pellets are fabricated from yttria-stabilized zirconia (YSZ) as the electrolyte, samarium-doped ceria (SDC) as the buffer layer, and silver paste as the current-collecting layer (CCL). Results from electrochemical impedance spectroscopy (EIS) demonstrate that LSTF made from extracted lanthanum with low purity shows comparable electrical performance with a polarity resistance (Rp) of below 0.2 Ω at operational temperature of 800 °C compared to LSTF made from commercial ingredients, while LSTF made from extracted iron shows equal performance only with high-purity ingredients. LSTF made with extracted lanthanum and iron exhibits an Rp of 0.5 Ω and does not show comparable performance with LSTF made with commercial ingredients, likely due to a high variety of impurities. Based on this study, LSTFLa30 and LSTFFe90 show high potential for SOFC cathode applications at operating temperatures in the range of 700–800 °C.

Machine Learning‐Aided Discovery of Low‐Pt High Entropy Intermetallic Compounds for Electrochemical Oxygen Reduction Reaction

AbstractAdvancing the design of cathode catalysts to significantly maximize platinum utilization and augment the longevity has emerged as a formidable challenge in the field of fuel cells. Herein, we rationally design a high entropy intermetallic compound (HEIC, Pt(FeCoNiCu)3) for catalyzing oxygen reduction reaction (ORR) by an efficient machine learning stategy, where crystal graph convolutional neural networks are employed to expedite the multicomponent design. Based on a dataset generated from first‐principles calculations, the model can achieve a high prediction accuracy with mean absolute errors of 0.003 for surface strain and 0.011 eV atom−1 for formation energy. In addition, we identify two chemical features (atomic size difference and mixing enthalpy) as new descriptors to explore advanced ORR catalysts. The carbon supported Pt(FeCoNiCu)3 catalyst with small particle size is successfully synthesized by a freeze‐drying‐annealing technology, and exhibits ultrahigh mass activity (4.09 A mgPt−1) and specific activity (7.92 mA cm−2). Meanwhile, The catalyst also shows significantly enhanced electrochemical stability which can be ascribed to the sluggish diffussion effect in the HEIC structure. Beyond offering a promising low‐Pt electrocatalysts for fuel cell cathode, this work offers a new paradigm to rationally design advanced catalysts for energy storage and conversion devices.

Machine Learning-Aided Discovery of Low-Pt High Entropy Intermetallic Compounds for Electrochemical Oxygen Reduction Reaction.

Advancing the design of cathode catalysts to significantly maximize platinum utilization and augment the longevity has emerged as a formidable challenge in the field of fuel cells. Herein, we rationally design a high entropy intermetallic compound (HEIC, Pt(FeCoNiCu)3) for catalyzing oxygen reduction reaction (ORR) by an efficient machine learning stategy, where crystal graph convolutional neural networks are employed to expedite the multicomponent design. Based on a dataset generated from first-principles calculations, the model can achieve a high prediction accuracy with mean absolute errors of 0.003 for surface strain and 0.011 eV atom-1 for formation energy. In addition, we identify two chemical features (atomic size difference and mixing enthalpy) as new descriptors to explore advanced ORR catalysts. The carbon supported Pt(FeCoNiCu)3 catalyst with small particle size is successfully synthesized by a freeze-drying-annealing technology, and exhibits ultrahigh mass activity (4.09 A mgPt -1) and specific activity (7.92 mA cm-2). Meanwhile, The catalyst also shows significantly enhanced electrochemical stability which can be ascribed to the sluggish diffussion effect in the HEIC structure. Beyond offering a promising low-Pt electrocatalysts for fuel cell cathode, this work offers a new paradigm to rationally design advanced catalysts for energy storage and conversion devices.

Ni Nanoparticles Supported on Graphene-Based Materials as Highly Stable Catalysts for the Cathode of Alkaline Membrane Fuel Cells.

Ni nanoparticles supported on graphene-based materials were tested as catalysts for the oxygen reduction reaction (ORR) to be used in anion exchange membrane fuel cells (AEMFCs). The introduction of N into the graphene structure produced an enhancement of electrocatalytic activity by improving electron transfer and creating additional active sites for the ORR. Materials containing both N and S demonstrated the highest stability, showing only a 3% performance loss after a 10 h stability test and therefore achieving the best overall performance. This long-term durability is attributed to the synergetic effect of Ni nanoparticles and bi-doped (S/N)-reduced graphene oxide. The findings suggest that the strategic incorporation of both nitrogen and sulphur into the graphene structure plays a crucial role in optimising the electrocatalytic properties of Ni-based catalysts.

Engineering of a Coupled Nanocomposite as a High-Performance Protonic Ceramic Fuel Cell Cathode

Engineering of a Coupled Nanocomposite as a High-Performance Protonic Ceramic Fuel Cell Cathode

MOF-derived three-dimensional porous dodecahedral structured bimetallic Mn/Co-C-N composite for high-performance durable oxygen reduction reaction electrocatalysts

Investigating high-efficiency oxygen reduction reaction (ORR) catalysts is one of the most effective methods for addressing the sluggish kinetics at the fuel cell cathode. Bimetallic three-dimensional porous materials have garnered significant attention due to their diverse structures, large specific surface area and synergistic catalytic effects. Herein, we synthesized a bimetallic three-dimensional porous dodecahedral structure, Mn/Co-C-N, derived from MOF using a straightforward approach. Experimental reults confirm that the strategic incorporation of Mn enhances the electrocatalytic activity for ORR. Meanwhile, the synergistic effects of Mn and Co, as well as the advantages of the dodecahedral structure for expediting electron transfer, all contribute to the exceptional ORR performance. Arc testing in an alkaline electrolyte reveals that the initial potential (Eonset) and the half-wave potential (E1/2) are 0.89 V and 0.80 V, closely approximating those of commercial Pt/C (20 wt%). Following 10 000 stability test cycles, the half-wave potential exhibits a mere 8 mV change, confirming its remarkable stability.

Cobalt Nitride-Implanted PtCo Intermetallic Nanocatalysts for Ultrahigh Fuel Cell Cathode Performance.

Stable and active oxygen reduction electrocatalysts are essential for practical fuel cells. Herein, we report a novel class of highly ordered platinum-cobalt (Pt-Co) alloys embedded with cobalt nitride. The intermetallic core-shell catalyst demonstrates an initial mass activity of 0.88 A mgPt-1 at 0.9 V with 71% retention after 30,000 potential cycles of an aggressive square-wave accelerated durability test and loses only 9% of its electrochemical surface area, far exceeding the US Department of Energy 2025 targets, with unprecedented stability and only a minimal voltage loss under practical fuel cell operating conditions. We discover that regulating the atomic ordering in the core results in an optimal lattice configuration that accelerates the oxygen reduction kinetics. The presence of cobalt nitride decorated within PtCo superlattices guarantees a larger barrier to Co dissolution, leading to the excellent endurance of the electrocatalysts. This work brings up a transformative structural engineering strategy for rationally designing high-performing Pt-based catalysts with a unique atomic configuration for broad practical uses in energy conversion technology.

Recent Advances in Barium Cobaltite-Based Perovskite Oxides as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells.

Solid oxide fuel cells (SOFCs) are considered as advanced energy conversion technologies due to the high efficiency, fuel flexibility, and all-solid structure. Nevertheless, their widespread applications are strongly hindered by the high operational temperatures, limited material selection choices, inferior long-term stability, and relatively high costs. Therefore, reducing operational temperatures of SOFCs to intermediate-temperature (IT, 500-800°C) range can remarkably promote the practical applications by enabling the use of low-cost materials and enhancing the cell stability. Nevertheless, the conventional cathodes for high-temperature SOFCs display inferior electrocatalytic activity for oxygen reduction reaction (ORR) at reduced temperatures. Barium cobaltite (BaCoO3-δ)-based perovskite oxides are regarded as promising cathodes for IT-SOFCs because of the high free lattice volume and large oxygen vacancy content. However, BaCoO3-δ-based perovskite oxides suffer from poor structural stability, inferior thermal compatibility, and insufficient ionic conductivity. Herein, an in-time review about the recent advances in BaCoO3-δ-based cathodes for IT-SOFCs is presented by emphasizing the material design strategies including functional/selectively doping, deficiency control, and (nano)composite construction to enhance the ORR activity/durability and thermal compatibility. Finally, the currently existed challenges and future research trends are presented. This review will provide valuable insights for the development of BaCoO3-δ-based electrocatalysts for various energy conversion/storage technologies.

Integrating Hydrogenated TiO2-Modified Carbon-Supported PtRu Anodes and Fe–N–C Cathodes for High-Performance Direct Methanol Fuel Cells

Integrating Hydrogenated TiO₂-Modified Carbon-Supported PtRu Anodes and Fe–N–C Cathodes for High-Performance Direct Methanol Fuel Cells

Ruddlesden-Popper Perovskite Materials for Solid Oxide Fuel Cell Cathode: A Review

This review paper summarizes the recent findings on Ruddlesden-Popper (RP) phase materials for solid oxide fuel cell (SOFC) cathodes. These materials, known for their unique layered structure, show excellent performance in intermediate-temperature SOFCs due to their outstanding catalytic activity for the oxygen reduction reaction (ORR) and relatively high durability. RP perovskites are notable for their fast oxygen surface exchange rates and stability under operating conditions, making them suitable for both oxide ion and proton-conducting SOFCs. The paper examines the relationship between their crystal structure, physical properties, and the transport mechanisms of oxygen ions. Key strategies to enhance the properties of RP perovskites in SOFCs are discussed, including doping to optimize conductivity and thermal expansion coefficients, and creating composite cathodes to improve stability and performance. The paper also briefly covers the long-term stability of these materials with some examples. Finally, the review highlights the need for further research on the ORR kinetics of RP perovskites, especially in proton-conducting SOFCs, to fully realize their potential for efficient and durable energy conversion technologies.

Minimizing liquid/solid interfacial energy boosts Fe−N doping inside hollow carbon sphere for oxygen reduction in membrane-less direct formate fuel cell

Porous hollow carbon sphere (HCS) is an attractive catalyst support for oxygen reduction reaction (ORR) due to its large specific surface area for active site anchoring, porous and hollow structure for active site exposure and mass transfer. However, due to the high transfer resistance for exogenous heteroatoms into HCS, most of active sites are usually loaded on the outer surface of HCS, leading to the decrease of active site density and the aggregation of heteroatomic particles. In this work, we proposed that accompanied with the decrease of liquid/solid interfacial energy by changing solvent composition during impregnation, penetration of exogenous heteroatoms-containing solution was facilitated in HCS, resulting in increased density of uniformly-dispersed Fe−Nx active site by 58 %. Taking advantage of high-content and well-dispersed active site, structure-derived porosity for ion transfer and active site exposure, this HCS-derived catalyst (Fe-HCS@C2H5OH) exhibited positive onset and half-wave potentials of 0.953 V and 0.901 V (vs. RHE), as well as high power density of 20.17 ± 0.31 mW cm−2 when applied in membrane-less direct formate fuel cell cathode, surpassing those of commercial Pt/C and the state-of-the-art carbonaceous catalysts. This strategy of interfacial energy control provides a new stepping-stone for the synthesis of high-performance electrocatalysts.

Construction of more oxygen vacancies of BaCo0.4Fe0.4Zr0.2O3-δ for high-performance proton-conducting solid oxide fuel cell cathodes

The cathodic catalytic activity for the oxygen reduction reaction (ORR) plays a critical role in determining the performance of proton-conducting solid oxide fuel cells (P-SOFCs). BaCo0.4Fe0.4Zr0.2O3-δ (BCFZ) has emerged as a promising cathode for P-SOFCs due to its triple-phase conductivity. Nevertheless, its suboptimal proton conductivity and hydration ability at intermediate temperatures prevent it from achieving the anticipated ORR catalytic activity. To address these limitations, this study explores the enhancement of electrocatalytic activity in BCFZ through alkali metal doping and A-site defect construction. The effects of such modifications on oxygen surface exchange kinetics and ORR catalytic activity are systematically investigated. The findings reveal that BCFZ exhibits relatively low parameters in terms of electronic conductivity, oxygen ion conductivity, oxygen vacancy concentration, kchem, and Dchem. Conversely, these parameters are markedly improved in A-site deficient BCFZ (D-BCFZ) and Na/K-doped BCFZ. Consequently, the enhancement of these properties yields a significant increase in ORR catalytic activity, with D-BCFZ demonstrating the best electrochemical performance. Specifically, P-SOFC with D-BCFZ cathode achieves an Rp value of just 0.073 Ω cm2 and a Pmax value of 0.928 W cm−2 at 650 °C. This study provides theoretical insight into the mechanisms by how alkali metal doping and defect construction enhance the ORR catalytic activity of BCFZ. These findings offer valuable guidance for the development and optimization of high-performance P-SOFC cathodes.

Performance and biotoxicity of electro-Fenton treatment of bisphenol A: Evaluation of copper recovered from microbial fuel cell cathodes for subsequent catalytic applications

A three-tank microbial fuel cell (MFC) is successfully constructed to achieve electromigration and is used in the electro-Fenton process to treat bisphenol A (BPA). The MFC system exhibits excellent mobility and efficiently aggregates Cu+ to the cathode. Under optimal operating conditions, the MFC achieves a maximum power density of 31.4 mW/m2, which is a 3.4-fold increase over that at 0.5 kΩ. Increasing the external resistance increased the MFC power output (ca 1.5 times) and copper ion migration (ca 4.6 times) while reducing the internal resistance of the system (ca 25.3 %). Surface analysis of the cathode carbon cloth shows a 5.5-fold increase in copper content at 1 kΩ over that at 0.5 kΩ. This also increases the oxygen reduction reaction rate, thereby increasing the H2O2 yield by 1.5 times. The recovered copper cathode at 1 kΩ exhibits the best catalytic degradation of BPA, removing 99.7 % of BPA in 180 min, increasing 1.4 and 1.8 times that obtained at 1.5 and 0.5 kΩ, respectively. The optimal operating conditions significantly increased the abundance of electrochemically active bacteria (Azospirillaceae) (3.2 %−41.7 %), indicating that the optimized MFC is favorable for the rapid acclimatization of electrochemically active bacteria.

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.

Sr and Mn co-doping PrBaFe2O5+δ optimizes the electrochemical performance and stability of solid oxide fuel cell cathode

Developing cobalt-free cathode with high stability and high electrochemical activity is very important for constructing low-cost, high-performance solid oxide fuel cells. Layered perovskite PrBaFe2O5+δ (PBF) is known to ave important magnetic, oxygen exchange kinetic and electrochemical properties. In this study, Sr and Mn co-doping A-site and B-site of PrBa0.5Sr0.5Fe1.6Mn0.4O5+δ (PBSFM) electrode was synthesized and characterized its properties. The first-principles calculation shows that Sr and Mn co-doped PBSFM decreases the oxygen vacancy energy, improves the overlap of oxygen-metal bond hybridization and structural stability. The polarization resistance (Rp) of PBSFM decreases from 0.22 to 0.077 Ω cm2 at 700 °C. At 800 °C, the power density of fuel cell reaches 674 mW cm−2 using hydrogen as fuel. In addition, Sr and Mn co-doped PBSFM significantly improves impedance and single cell stability under operating conditions.

An enhanced salp swarm algorithm with chaotic mapping and dynamic learning for optimizing purge process of proton exchange membrane fuel cell systems

Swarm intelligence algorithm is now a research focus for the energy optimization of fuel cell systems to improve hydrogen utilization efficiency. However, conventional algorithms exhibit poor robustness and low execution efficiency since complex constraints are involved in the fuel cell cathode purge process. Given that, this paper innovatively introduces chaotic mapping and dynamic learning mechanisms into the Salp swarm algorithm to enhance the algorithm's global search and local exploitation capabilities under complex constraints. First, we developed a three-stage nonlinear cathode purge model to describe the different water transfer behaviors in the three purging stages. Then, an optimizing function is created under the complex staged constraints to accurately reveal the energy consumption mechanism. Finally, the enhanced Salp swarm algorithm enables the rapid and accurate determination of the three-stage dynamic purge flows based on minimizing energy consumption. Compared with the fixed flow purge scheme, we found that energy consumption is reduced by 3.6 %–8.2 % under various constraints. The enhanced Salp swarm algorithm proposed in this work demonstrates an outstanding performance in the energy consumption optimization of fuel cell systems.