Electrodeposition-fabricated PtCu-alloy cathode catalysts for high-temperature proton exchange membrane fuel cells

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are interesting alternatives to fossil fuel-based technologies for power generation. Their higher operating temperature compared to classic low temperature (LT) PEMFCs is highly beneficial regarding the total system complexity and weight, especially for applications which cannot involve bulky/heavy cooling systems, like aeronautics. However, at the current state-of-art of the technology, the membrane electrode assembly performance in HT-PEMFC does not reach that of LT-PEMFCs and needs to be improved; this requires better catalyst material, catalyst layer structure and membrane doping [1], [2]. A given catalyst performance is largely influenced by phosphoric acid electrolyte poisoning [3], [4] and some studies have already evaluated such poisoning level on various catalysts toward oxygen reduction reaction [5], [6]. The current study further addresses this issue and specifically aims to understand the impact of various parameters which should impact the catalyst activity in H3PO4 electrolytes (loading, nano-particle size and shape, chemistry of the catalyst particles (Pt vs PtNi), density of aggregates, nature of the carbon support) and to evaluate the poisoning effect whether at low potential (anode) or at high potential (cathode).The effect of different parameters was unveiled thanks to a catalyst library (Figure a), analyzed comparatively in 1 M HClO4 and 1 M H3PO4 electrolytes at room temperature with a classic rotating disk electrode set-up and a gas diffusion electrode set-up. Pseudo CO-Stripping voltammetry, Hupd and CO-stripping voltammetry enable to shed light on the poisoning of the Pt surfaces: the electrochemical surface area (ECSA) is divided by a factor around 2 in H3PO4 electrolyte compared to HClO4 and varies according to the catalyst properties. The impact on hydrogen oxidation reaction is then noticeable. The poisoning at high potential (> 0.6 VvsRHE) was mainly evaluated thanks to the ORR activity (Figure b): the Pt nanoparticle size/shape, their loading on the carbon support and alloying with Ni do impact their ORR activity. All the catalysts exhibit significantly lower activity in H3PO4 than in HClO4 (by a factor ca 10). The mechanisms of H3PO4-induced poisoning and potential strategies to mitigate it will be detailed.[1] S. S. Araya et al., “A comprehensive review of PBI-based high temperature PEM fuel cells,” Int J Hydrogen Energy, vol. 41, no. 46, pp. 21310–21344, Dec. 2016, doi: 10.1016/j.ijhydene.2016.09.024.[2] R. E. Rosli et al., “A review of high-temperature proton exchange membrane fuel cell (HT-PEMFC) system,” Int J Hydrogen Energy, vol. 42, no. 14, pp. 9293–9314, Apr. 2017, doi: 10.1016/j.ijhydene.2016.06.211.[3] B. F. Gomes et al., “Effect of phosphoric acid purity on the electrochemically active surface area of Pt-based electrodes,” Journal of Electroanalytical Chemistry, vol. 918, Aug. 2022, doi: 10.1016/j.jelechem.2022.116450.[4] N. Sugishima et al., “Phosphorous Acid Impurities in Phosphoric Acid Fuel Cell Electrolytes: I . Voltammetric Study of Impurity Formation,” J Electrochem Soc, vol. 141, no. 12, pp. 3325–3331, Dec. 1994, doi: 10.1149/1.2059334.[5] Q. He et al, “Influence of phosphate anion adsorption on the kinetics of oxygen electroreduction on low index Pt(hkl) single crystals,” Physical Chemistry Chemical Physics, vol. 12, no. 39, pp. 12544–12555, Oct. 2010, doi: 10.1039/c0cp00433b.[6] K. ‐L. Hsueh et al, “Effects of Phosphoric Acid Concentration on Oxygen Reduction Kinetics at Platinum,” J Electrochem Soc, vol. 131, no. 4, pp. 823–828, Apr. 1984, doi: 10.1149/1.2115707. Figure 1

The aviation industry is facing one of its greatest challenges: how to reduce its CO2 emissions in the context of a constantly increasing air traffic. High Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFCs) technology is of great interest for aviation, due to its easier thermal management, a simplified water management system and lower weight. However, the current Membrane Electrode Assembly (MEA) of HT-PEMFCs operating at 160°C are not at the expected level of performance. In this context, the NIMPHEA project aims to develop a new generation of HT MEAs at temperatures above 120°C to meet the demanding requirements of aviation fuel cells. HT-PEMFCs typically use phosphoric acid doped polybenzimidazole (PA-PBI). However, PA-PBI-based fuel cells have limited stability in the presence of water or at higher operating temperatures. In fact, they suffer from phosphoric acid loss. Recently, HT-PEMFCs based on quaternary ammonium bisphosphate Ion-Pair coordination (Ion-Pair) have shown better phosphoric acid retention in the temperature range of 80-200°C than PBI ones. In the frame of NIMPHEA project, we worked on the development of MEA based on Advent's Ion-Pair membrane technology for HT-PEMFCs. After optimizing the composition of both the cathode and anode active layers and the gas diffusion layer, we obtained a fuel cell with a nominal power density of 0.8 W/cm² at 180°C under H2/Air at 1 bar exceeding the performance of standard PBI based HT-PEMCs based MEA. This project has received funding from the Clean Hydrogen Joint Undertaking under grant agreement No 101101407. This Joint Undertaking receives support from the European Union’s Horizon Europe research and innovation program and Hydrogen Europe and Hydrogen Europe Research. The authors also thanks Advent technologies for their participation . Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union. Neither the European Union nor the granting authority can be held responsible for them. Figure 1

High-Temperature Proton-Exchange Membrane Fuel Cells (HT-PEMFCs) represent a promising clean energy technology and are valued for their fuel flexibility and simplified balance of plant. Their commercialization, however, is critically hindered by the prohibitive cost and resource scarcity of platinum-group metal (PGM) catalysts. The challenge is amplified in the phosphoric acid (PA) electrolyte of HT-PEMFCs, where the severe anion poisoning of PGM active sites necessitates impractically high catalyst loadings. This review addresses the urgent need for cost-effective alternatives by providing a comprehensive assessment of recent advancements in non-precious metal (NPM) catalysts for the oxygen reduction reaction (ORR) in HT-PEMFCs. It systematically explores synthesis strategies and structure–performance relationships for emerging catalyst classes, including transition metal compounds, metal–nitrogen–carbon (M-N-C) materials, and metal-free heteroatom-doped carbons. A significant focus is placed on M-N-C catalysts, particularly those with atomically dispersed Fe-Nx active sites, which have emerged as the most viable replacements for platinum due to their high intrinsic activity and notable tolerance to phosphate poisoning. This review critically analyzes key challenges that impede practical application, such as the trade-off between catalyst activity and stability, mass transport limitations in thick electrodes, and long-term degradation in the harsh PA environment. Finally, it outlines future research directions, emphasizing the need for a synergistic approach that integrates computational modeling with advanced operando characterization to guide the rational design of durable, high-performance catalysts and electrode architectures, thereby accelerating the path to commercial viability for HT-PEMFC technology.

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

Experimental results have shown that palladium complexes with chelating aryl- and alkyl-substituted bis-NHC ligands, including [(H3C-Im)2CH2]PdBr2, [(C6H5-Im)2CH2]PdBr2, and [(H3CO-C6H4-Im)2CH2]PdBr2 are excellent catalysts for the Mizoroki-Heck reaction. To better understand and improve the catalysts, a density functional theory (DFT) study of the Heck reaction has been performed at the B3LYP/6-31G* level of theory, complemented by M06/def2-TZVP single-point calculations. Different mechanistic pathways have been investigated and compared to available experimental results. The most likely mechanism is a cationic catalytic cycle involving the palladium oxidation states 0 and +II. We also looked at other oxidation states, but on the basis of the calculated Gibbs free energy a +II/+IV mechanism can be excluded. Aryl substitution with electron-donating groups at the para position (e.g., the methoxy group in [(H3CO-C6H4-Im)2CH2]PdBr2) was found to reduce the reaction barrier of the rate-determining step. This is in agreement with the experimental findings for the catalysts. The experimentally observed cis selectivity could also be explained by the DFT study.

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) offer significant advantages for clean energy conversion. However, their performance is severely hindered by the dual role of phosphoric acid (PA), which serves as the proton conductor but also acts as a potent poison for platinum (Pt) catalysts, inhibiting the oxygen reduction reaction (ORR) and demanding high Pt loadings. This review provides a systematic analysis of the extensive efforts to mitigate PA poisoning. A diverse range of strategies is surveyed, including the development of poison-tolerant Pt-alloy catalysts (e.g., Pt–Ni, Pt–Co), the use of advanced carbon and metal oxide supports to leverage strong metal-support interactions, the design of protective surface modifications, the exploration of Pt-free catalysts like Fe–N–C, and the engineering of the catalyst layer with functional additives. Despite significant progress at the catalyst level, a critical performance gap persists between lab-scale tests and real-world membrane electrode assemblies (MEAs). This discrepancy arises because particle-centric approaches often neglect the severe mass transport limitations and low catalyst utilization within conventional, randomly structured electrodes flooded with viscous PA. To overcome these challenges, a paradigm shift is necessary. It is proposed that the future of HT-PEMFCs lies in a holistic approach that integrates advanced catalyst design with the fabrication of 3D ordered electrode architectures. These engineered structures create efficient transport pathways, maximize the functional triple-phase boundary, and can finally unlock the full potential of poison-tolerant catalysts, enabling high performance with drastically reduced Pt loadings. • Reviews diverse strategies against PA poisoning in HT-PEMFCs. • Summarizes catalyst-level strategies to mitigate PA poisoning. • Identifies RDE-to-MEA performance gap and its root causes. • Proposes integrating catalyst design with 3D ordered electrode architectures.

Recently, high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) have attracted much attention due to their tolerance to carbon monoxide and simple water management in the system level. HT-PEMFCs mostly use polybenzimidazole membrane doped with phosphoric acid (PA) as electrolyte. Therefore, uniform distribution of PA through a whole MEA plays a critical role in determining fuel cell performance. Distribution of PA in a MEA does not only depend only on properties of membrane such as a doping level of PA in membrane but also on gas diffusion layer(GDE) characteristics, especially the structure of the catalyst layer (CL). At present, the CL for HT-PEMFCs is typically composed of platinum catalyst and a polymeric binder. The polymeric binder maintaining the integrity of CL has an influence on mechanical stability of CL and the PA distribution within MEA. There have been many studies to explore the characteristics of different binders such as polytetrafluoroethylene(PTFE), polybenzimidazole(PBI) and polyvinylidenefluoride(PVDF). As previously described by Huaneng Su et al., PVDF has a good affinity with PA which leads to quick distribution of PA, on the other hand hydrophobic PTFE reduce PA leaching.[1] In this study, dual structured CLs with two different binders(PVDF and PTFE) by controlling the contents in catalyst layer are fabricated to investigate the influence of the wettability of CL surface in terms of fuel cell perfoemance. The properties of these CL were evaluated by structure characterization and electrochemical analysis. At ambient pressure and 150oC, the GDEs with PTFE binder exhibit the highest power density (383mW/cm2) with H2/air which may result from highly hydrophobic CL, leading to improved mass transport. It was suggested that the change in ratio of two binders with different wettabilities respectively had an impact on small arc on EIS. Keywords :high temperature proton exchange membrane fuel cell, catalyst layer, Membrane electrode assembly, poly(2,5-benzimidazole), hydrophobicity, Pt loading, gas diffusion electrode References S. Huaneng, J. Power Sources, 246, 63 (2014).

Ternary adsorption of Auramine-O, Rhodamine 6G, and Brilliant Green onto Arapaima gigas scales hydroxyapatite: Adsorption mechanism investigation using CCD and DFT studies

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have been considered as one of the most attractive power sources for portable devices, due to their high tolerance to CO, enhanced activity of the electrocatalysts and simplified water and heat managements. As the key component, high temperature proton exchange membranes (HT-PEMs) influence a lot on fuel cell performance and long term stability. In recent years, phosphoric acid (PA) doped HT-PEMs have been proved to be one of the most promising alternatives for HT-PEMFCs because of their high proton conductivity and great thermal stability. The major technical challenges of these PA doped HT-PEMs are that the increase of PA loading enhances proton conductivity while the mechanical properties significantly decrease and the PA leaching exacerbates, which limit their wide applicability in HT-PEMFCs. This monograph summarizes recent advances for PA doped HT-PEMs on the design of new polymer, physical modification, microstructure control and so on. These developments on fundamental theories and main technologies establish a good foundation for future research.

As a critical component for the oxygen reduction reaction (ORR), platinum (Pt) catalysts exhibit promising catalytic performance in High-temperature-proton exchange membrane fuel cells (HT-PEMFCs). Despite their success, HT-PEMFCs primarily utilize phosphoric acid-doped polybenzimidazole (PA-PBI) as the proton exchange membrane, and the phosphoric acid within the PBI matrix tends to leach onto the Pt-based layers, easily causing toxicity. Herein, we first propose UiO-66@Pt3Co1-T composites with precisely engineered interfacial structures. The UiO-66@Pt3Co1-T exhibits an octahedral porous framework with uniform structural dimensions and even distribution of surface nanoparticles, which demonstrate superior ORR performance compared to commercial Pt/C. The unique structure and morphology of the composites also exhibit a favorable half-wave potential in different concentrations of phosphoric acid electrolyte, regulated by the phosphoric acid adsorption site and intensity.This finding suggests that the incorporation of Co could effectively modulate the Pt d-band center, thereby enhancing the ORR performance. Furthermore, the selective adsorption of phosphoric acid by ZrO2 enables precise control over the phosphoric acid distribution. Notably, the retention of the octahedral framework post high-temperature treatment facilitates the establishment of dual transport pathways for gases and protons, leading to a stable and efficient triple-phase boundary.

In high‐temperature proton exchange membrane fuel cells (HT‐PEMFCs), the poisoning of Pt by phosphoric species severely affects the kinetics of the oxygen reduction reaction, which restricts their commercialized application. Herein, for the first time, the phosphate tolerance of PtFe ordered intermetallic alloys is enhanced by a doping‐modulated strain strategy via employing a low amount of Cu as a dopant to boost HT‐PEMFCs. This Cu doping facilitates the formation of compressive strain in PtFe crystals, consequently altering the electronic structure of electrocatalysts and then benefiting for weakening the adsorption energy between phosphoric acid and Pt surfaces. In addition, the high temperature phosphate adsorption tests also reveal that the dopant of Cu in Pt based electrocatalysts can improve the tolerance of phosphoric acid. The HT‐PEMFCs assembled by those cathodic electrocatalysts with the low‐Pt loading of 0.5 mgPt cm−2 achieve a preeminent peak power of 793.5 and 432.6 mW cm−2 under the condition of H2–O2 and H2–air atmosphere, respectively, or nearly 1.53 and 1.34 times higher as compared with commercial Pt/C electrocatalysts. Moreover, those electrocatalysts also exhibit robust stability under harsh condition in H2–O2 atmosphere with negligible activity loss for at least 100 h, exceeding most of other reported ORR electrocatalysts.

Employing the oxidative coupling of phenylacetylene with benzaldehyde as a model reaction, a density functional theory (DFT) study combined with extended X-ray absorption fine structure (EXAFS) experiment was carried out to reveal the difference between dinuclear and mononuclear zinc mediated nucleophilic addition. Newly reported DFT method M11-L computed results suggest that the mononuclear zinc mediated pathway, in which nucleophilic addition occurs via a four-membered ring transition state, is unfavourable both thermodynamically and kinetically. The dinuclear zinc mechanism, which appropriately explains the experimental observations, involves a six-membered ring transition state for nucleophilic addition. Subsequent in situ EXAFS experiment confirmed the existence of dinuclear zinc active species. Moreover, frontier molecular orbital (FMO) analysis and distortion-interaction energy analysis along the whole reaction pathways have provided interpretations for the advantage of dinuclear zinc mediated nucleophilic addition. Consequently, we believe this dinuclear zinc pathway will open up a general consideration of the dinuclear zinc mechanism for nucleophilic additions.

Cholesterol-based dimeric liquid crystals: synthesis, mesomorphic behaviour of frustrated phases and DFT study

Mineral chemistry of metal sulfides

We have performed a density functional theory (DFT) study of the electronic structure in ceria [Formula: see text] and gadolinium-doped ceria (GDC) system using VASP code in the generalized gradient approximation (GGA) with DFT[Formula: see text]+[Formula: see text]U. The band structures in GDC and thin film GDC are calculated and compared to that of bulk ceria. Doping of gadolinium significantly decreases the band gap of ceria, while the thin film structure of GDC raises the band gap greatly. The results help explain the electronic conductivity behavior of GDC and suggest that thin film-structured GDC could be used as a possible way to overcome the current leakage disadvantage of GDC.