Hydrogen produced by hydrocarbon reforming typically contains trace amounts of CO, which severely poison anode catalysts in PEMFCs. In this work, Pd was chemically deposited on a support consisting of mesoporous 10 mol% W-doped SnO2 (Sn10W) and graphene nanoplatelets (GNP). Black Pearls 2000 carbon (BP) was subsequently introduced by mechanical mixing to obtain the final Pd/Sn10W-GNP-BP electrode for HOR in acidic media. The surface chemistry investigations by XPS highlighted the presence of Sn2+ and W4+ oxidation states, in addition to Sn4+ and W6+/5+, after Pd deposition, as well as the oxygen bound in residual W=O groups and a highly hydroxylated Pd/Sn10W-GNP surface. SEM showed that Pd nanoparticles were preferentially located on defect-rich oxide regions and at or near the edges of GNP flakes. Electrochemical measurements confirmed HOR activity in acidic media, with BP improving electronic connectivity and Pd utilization. More importantly, Pd/Sn10W-GNP-BP showed remarkable CO tolerance, with CO oxidation starting at ~50 mV and the main oxidation peak at ~415 mV, both markedly lower than for commercial PtRu/C. Based on XPS results correlated with Raman spectroscopy, revealing multivalent W and Sn species, abundant OHads groups, oxygen vacancies and W-related surface defects, a bifunctional mechanism can explain the enhanced CO tolerance.

The commercialization of proton exchange membrane hydrogen-air fuel cells (PEM-HA-FCs) necessitates the development of durable, high-performance PEMs capable of efficient operation under low relative humidity (RH) conditions. In this work, amino-functionalized tungsten oxide was employed as an inorganic filler to enhance the proton conductivity of Nafion membranes at reduced RH. The amino functionalization was achieved through a silanization process utilizing (3-aminopropyl)triethoxysilane (3-APTES) as the precursor. XRD, FTIR, and TGA analyses confirmed the successful functionalization. The structural, morphological, thermo-mechanical properties, along with the physicochemical and electrochemical characteristics of both Nafion/amino-WO3 composite membranes and recast Nafion membranes were systematically investigated. The amino-WO3 composite membrane achieved an outstanding proton conductivity of 0.0196 S cm(-1), approximately 2.5-fold higher than the unmodified Nafion membrane under conditions of 20% RH and 80 degrees C. Beyond enhanced proton conductivity, membrane electrode assemblies (MEAs) fabricated with Nafion/amino-WO3 composite membranes demonstrated satisfactory current density at 0.6 V, achieving 0.4 A cm(-2) and 0.305 W cm(-2) power density when operated at merely 20% RH and 80 degrees C. Furthermore, the membrane containing 0.5% filler exhibited approximately 6-fold improved chemical durability and 62% reduced H2 crossover relative to the recast Nafion membrane.

Laboratory-scale fuel cell testers typically regulate cell temperature via endplate heating cartridges. In practical stack applications, however, temperature control is achieved by cooling systems, making uniform temperature distribution a critical factor in system design and scale-up. To investigate these thermal effects under realistic conditions, autothermal activation and autothermal polarization experiments were conducted. Membrane electrode assemblies (MEAs) were polarized according to the New European Driving Cycle protocol, while galvanostatic electrochemical impedance spectroscopy (GEIS) measurements were performed in parallel to determine R1, R2, and C2 parameters in situ. Three MEA configurations differing catalyst layers were tested: C-60-Pt, C-40-Pt, and C-60-Pt (0.13 mg Pt/cm2), all with symmetrical Pt loadings. A custom-developed spray-gun robot was used for gas diffusion electrode fabrication. Among the samples, the C-40-Pt MEA demonstrated a pronounced break-in effect after 4 h of autothermal activation and achieved the highest current density. While the low-Pt MEA exhibited the lowest performance, it also showed the largest temperature rise during autothermal polarization. Impedance data confirmed that despite similar series resistance, the C-40-Pt MEA had lower internal resistance, while the more porous C-60-Pt showed increased R1. More consistent curve shapes during autothermal conditions compared to fixed-temperature GEIS indicate that temperature adaptability enhances measurement reproducibility.

Novel blend membranes containing S-PVA and PEBAX 1657 at a blend ratio of 8:2 were doped with varying amounts of titanium dioxide phosphate (TiO2PO4) as a nanoparticle filler at concentrations of 0, 3, 5, and 7 wt%. The membranes were fabricated using the solution-casting technique. The effect of the TiO2PO4 nanofiller on the polymer matrix was thoroughly investigated. Our aim was to investigate how the incorporation of TiO2PO4 nanofillers into non-fluorinated SPP-based membranes affects their structural, physicochemical, and electrochemical properties for application in fuel cells. Crystallinity of the samples was checked by means of X-ray diffraction (XRD), while FTIR was used to investigate the contact between the nanofiller and the polymers. The good compatibility resulted in strong interactions between the constituents and led to increased crystallinity of the membrane as well. Furthermore, SEM images confirmed the uniform distribution of the nanofiller. These structural features led to good thermal stability, as evidenced by thermogravimetric analysis (TGA), and good mechanical strength, as proved by tensile tests. Among the samples investigated, the highest water uptake of 51.70% was achieved on the composite membrane containing 3 wt% TiO2PO4, which also showed the highest ion exchange capacity at room temperature, reaching 1.13 meq/g. In line with these properties, among the synthesized membranes, the membrane labeled SPP 3% TiO2PO4 has the highest current density and power density, with values of 175.5 mA/cm2 and 61.52 mW/cm2, respectively.

Sn-doped TiO2-carbon composites were identified as promising multifunctional supports for Pt electrocatalysts, in which the oxide component enhances resistance against corrosion and strong metal-support interactions at the Pt-oxide boundary ensure high stability for the Pt nanoparticles. This work is devoted to the study of the influence of preliminary functionalization of the carbon on the properties of Pt/Ti0.9Sn0.1O2-C catalysts. The structural, compositional and morphological differences between the samples prepared using functionalized or unmodified carbon, as well as the effect of carbon pre-modification on the electrocatalytic behavior of the synthesized Pt catalysts, were investigated using TEM, XRD, XPS, nitrogen adsorption and electrochemical measurements. The presence of oxygen-containing functional groups on carbon treated with HNO3 and glucose leads to the formation of a homogeneous coating of the carbon with dispersed crystallites of mixed oxide. Elemental mapping revealed the proximity of Sn species with highly dispersed (2-3 nm) Pt particles. Notably, the electrochemical results indicated enhanced activity in CO electrooxidation for both functionalized and unmodified carbon-containing catalysts. An improvement in the 10,000-cycle long-term stability of the catalyst prepared using functionalized carbon was evident compared to the catalyst with untreated carbon or reference Pt/C.

The lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is significantly influenced by the degradation of their catalysts. A composite-type electrocatalyst support with the formula Ti(1−x)MoxO2-C (x: 0–0.2, C: carbon) has been found to provide higher stability for the Pt active metal than carbon alone. Non-traditional carbon materials such as graphene nanoplatelets (GNPs) and graphite oxide (GO) offer new possibilities for supports. This work aims to explore whether it is possible to combine the advantageous properties of GNP and GO in composite-supported Pt electrocatalysts. Composites prepared using the modified sol–gel method and Pt catalysts supported on them were characterized by physicochemical methods. Electrochemical behavior in terms of CO tolerance, activity and stability was studied. Although GO transformed into a mainly graphitic material during composite synthesis, its addition still increased the functional group content of the carbonaceous backbone. The electrical conductivity was significantly higher when GNPs-GO mixtures were used as the starting carbon material compared to the use of pure GNPs. Increased CO oxidation activity was achieved due to the incorporated Mo. Stability of the composite-supported Pt catalyst was significantly higher than that of commercial Pt/C. Increased stability of the GNPs-GO-derived catalyst compared to the GNP-derived one was obtained.

Hydrogen and fuel cell technologies are accepted by consensus as being part of the future energy system, especially in hard-to-abate segments where electrification is not an efficient solution [...]

Development of strong metal-support interaction (SMSI) and its influence on the catalytic performance of the Pt/Ti0.8Mo0.2O2-C system, a representative of the mixed oxide-carbon composite supported Pt electrocatalyst family, were investigated. Structural, surface chemical and electrochemical properties of the as-prepared Pt/Ti0.8Mo0.2O2-C catalyst and its counterparts reduced in the 150-450 degrees C temperature range were compared. TEM elemental mapping confirmed the widespread formation of Pt-oxide-C triple junctions in all catalysts. XPS revealed electronic interaction between the Pt particles and the oxide both in the as-prepared and the reduced catalysts, moreover, demonstrated that transport of Mo to the surface of Pt is initiated by reduction in the 150-250 degrees C range. Electrochemical measurements pointed out the durability of these Pt-bound Mo species, which also enhance the oxygen reduction activity of the catalyst. Based on the results of 10,000-cycle stability tests, reductive pretreatment between 250-350 degrees C is recommended for enhancing the properties of Pt/Ti0.8Mo0.2O2-C catalysts by SMSI.

Composite types of supports made of TiO2 and carbonaceous materials provide higher stability for the Pt electrocatalysts under the working conditions of polymer electrolyte membrane fuel cells than the traditional carbon supports. We have demonstrated in our previous work that composites with general formula of 75 wt.% Ti(1-x)MoxO2-25 wt.% C (x = 0-0.2; C = traditional Black Pearls (BP) carbon) were promising supports which provided increased stability for the Pt electrocatalysts. In this study, the effect of nitrogen doping of the carbonaceous component of the composite was explored. 75 wt.% TiO2-25 wt.% carbon composite supports were prepared using graphite oxide (GO), N-doped GO and N-doped multilayer graphene. Electrocatalysts were made by loading the supports with 20 wt.% Pt. The systems were compared based on their physicochemical properties determined by low-temperature nitrogen adsorption, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and conductivity measurements. The activity of the catalysts was investigated by conventional methods in a 3-electrode electrochemical cell. The results of various characterization methods contributed to the understanding of the difference in the electrochemical properties of N-free and N-containing catalyst samples. While GO was favorable for this composite supported catalyst, its N-doping strongly influenced the growth of TiO2, forming an almost continuous coating of small TiO2 crystals. This quasi-insulating TiO2 layer between the Pt catalytic sites and the conductive part of the composite resulted in poor electrochemical activity. Mixing the sample with carbon improved its conductivity, which resulted in a significant increase in the oxygen reduction activity.

Novel composite membranes employing a poly(ether-block-amide) (PEBAX) copolymer and sulfonated montmorillonite (S-MMT) as a filler were developed. The ratio of polyether to polyamide blocks was investigated using PEBAX 2533 and PEBAX 4533 based on the membrane properties and performance. Additionally, the effect of the changing filler ratio was monitored. The interaction between the S-MMT as nanofiller and the polymer matrix of PEBAX2533 and PEBAX4533 as well as the crystalline nature and thermal and mechanical stability of the composite membranes were evaluated using Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and tensile test. The composite membrane with 7 wt.% S-MMT showed the highest water uptake of 21% and 16% and an acceptable swelling degree of 16% and 9% for PEBAX 2533 and PEBAX 4533 composite membranes, respectively. In terms of water uptake and ion exchange capacity at room temperature, the new un-protonated membranes are superior to un-protonated Nafion. Meanwhile, with the same S-MMT content, the ion conductivity of PEBAX 2533 and PEBAX 4533 composite membranes is 2 and 1.6 mS/cm, and their ion exchange capacity is 0.9 and 1.10 meq/g.

Design of composite support materials based on Sn-doped TiO2 and carbon is one of the strategies to develop corrosion-resistant and CO-tolerant Pt electrocatalysts for polymer electrolyte membrane (PEM) fuel cells. As the synthesis methodology may have crucial influence on the structural and functional properties of the composites, different preparation routes for the novel support materials are explored and compared. Ti(1-x)SnxO2–C (x: 0.1-0.3) composites with different mixed oxide/carbon ratios were prepared by two sol-gel-based synthesis routes, namely (i) the introduction of a Sn precursor after the formation of the TiO2-rutile nuclei on the carbon backbone (route A), and (ii) simultaneous introduction of Ti and Sn precursors, resulting in good mixing of the Sn- and Ti-sol before the addition of the carbon (route B). The bulk and surface microstructure of the composites and the electrocatalysts obtained by their Pt-loading were investigated in detail. The incorporation of tin into the TiO2-rutile unit cell was confirmed by X-ray powder diffraction and Raman spectroscopy; the results indicated doping levels in good accordance with the amount of tin precursor. The advantages of composites and Pt electrocatalysts obtained via synthesis route B were that they do not contain segregated Sn0 or SnO2 phases, have a more homogeneous/uniform mixed oxide distribution over the carbon backbone, and the electrochemically active surface area values (~60-80 m2/gPt) are twice as high as those of catalysts with similar compositions synthesized by method A. A common feature of the composites prepared by routes A and B was the presence of a tin oxide-rich overlayer identified by X-ray photoelectron spectroscopy. As a consequence, the electrocatalytic behavior of the catalysts was not influenced by the Ti/Sn ratio and was mainly dependent on the synthesis method used in the preparation of composite support materials. Elemental maps confirmed the formation of areas where Pt and the Sn doping element were in atomic proximity to each other, which means a favorable interaction either for the bifunctional mechanism or the electronic ligand effect. An increase in carbon content in composite materials led to an increase in both catalytic activity and long-term stability. The results of electrochemical studies showed that Sn-containing Pt catalysts with a high carbon content (75wt.%) are the most promising for potential use both as an anode and a cathode for PEM fuel cells.

Novel blend membranes containing S-PVA and PEBAX 1657 with a blend ratio of 8:2 (referred to as SPP) were prepared using a solution-casting technique. In the manufacturing process, sulfonated montmorillonite (S-MMT) in ratios of 0%, 3%, 5%, and 7% was used as a filler. The crystallinity of composite membranes has been investigated by X-ray diffraction (XRD), while the interaction between the components was evaluated using Fourier-transform infrared spectroscopy (FT-IR). With increasing filler content, good compatibility between the components due to hydrogen bonds was established, which ultimately resulted in improved tensile strength and chemical stability. In addition, due to the sulfonated moieties of S-MMT, the highest ion exchange capacity (0.46 meq/g) and water uptake (51.61%) can be achieved at the highest filler content with an acceptable swelling degree of 22.65%. The composite membrane with 7% S-MMT appears to be suitable for application in proton exchange membrane fuel cells (PEMFCs). Amongst the membranes studied, this membrane achieved the highest current density and power density in fuel cell tests, which were 149.5 mA/cm2 and 49.51 mW/cm2. Our fluorine-free composite membranes can become a promising new membrane family in PEMFC applications, offering an alternative to Nafion membranes.

TiO2-based mixed oxide–carbon composite support for Pt electrocatalysts provides higher stability and CO tolerance under the working conditions of polymer electrolyte membrane fuel cells compared to traditional carbon supports. Non-traditional carbon materials like graphene nanoplatelets and graphite oxide used as the carbonaceous component of the composite can contribute to its affordability and/or functionality. Ti(1−x)MoxO2-C composites involving these carbon materials were prepared through a sol–gel route; the effect of the extension of the procedure through a solvothermal treatment step was assessed. Both supports and supported Pt catalysts were characterized by physicochemical methods. Electrochemical behavior of the catalysts in terms of stability, activity, and CO tolerance was studied. Solvothermal treatment decreased the fracture of graphite oxide plates and enhanced the formation of a reduced graphene oxide-like structure, resulting in an electrically more conductive and more stable catalyst. In parallel, solvothermal treatment enhanced the growth of mixed oxide crystallites, decreasing the chance of formation of Pt–oxide–carbon triple junctions, resulting in somewhat less CO tolerance. The electrocatalyst containing graphene nanoplatelets, along with good stability, has the highest activity in oxygen reduction reaction compared to the other composite-supported catalysts.

The composites of transition metal-doped titania and carbon have emerged as promising supports for Pt electrocatalysts in PEM fuel cells. In these multifunctional supports, the oxide component stabilizes the Pt particles, while the dopant provides a co-catalytic function. Among other elements, Sn is a valuable additive. Stong metal-support interaction (SMSI), i.e., the migration of a partially reduced oxide species from the support to the surface of Pt during reductive treatment is a general feature of TiO2-supported Pt catalysts. In order to explore the influence of SMSI on the stability and performance of Pt/Ti0.8Sn0.2O2-C catalysts, the structural and catalytic properties of the as prepared samples measured using XRD, TEM, XPS and electrochemical investigations were compared to those obtained from catalysts reduced in hydrogen at elevated temperatures. According to the observations, the uniform oxide coverage of the carbon backbone facilitated the formation of Pt-oxide-C triple junctions at a high density. The electrocatalytic behavior of the as prepared catalysts was determined by the atomic closeness of Sn to Pt, while even a low temperature reductive treatment resulted in Sn-Pt alloying. The segregation of tin oxide on the surface of the alloy particles, a characteristic material transport process in Sn-Pt alloys after oxygen exposure, contributed to a better stability of the reduced catalysts.

Herein, a new direct synthesis route leading to a mesoporous NiWO4 with crystalline framework and NiWO4 -graphene nanoplatelets (GNP) composite is reported. Ni and W assembled into a mesoporous tungstate type of symmetry by co-precipitation synthesis route and its composite with GNP were used as supports for electrocatalysts, with reduced Pt content (8 wt.%), in oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) in acidic medium. A comprehensive assessment of the modifications related to the crystalline and porous structures, morphological aspects as well as the surface chemistry aiming to explain the electrochemical properties was performed. It was found that the presence of GNP during the synthesis process leads, mainly, to the enhanced growth of NiWO4 nanocrystallites, as well as induces changes in the surface chemistry. The elec-trochemical results show that the introduction of GNPs into the NiWO4 composite support leads to a significant improvement in the activity of the Pt electrocatalyst in ORR and HOR compared to both initial NiWO4 and Pt/NiWO4 samples, as well as mechanical mixtures of these catalysts with carbon. Mass activity for hydrogen oxidation, determined in a mixed kinetic-diffusion controlled region, obtained on the 8 wt.% Pt/NiWO4-GNP catalyst was significantly higher compared to the commercial 20 wt.% Pt/C Quintech catalyst. Our comprehensive structural and surface chemistry assessments indicate this composite material as a viable electrocatalyst for PEMFCs using a broader type of fuels.& COPY; 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Comparison of physicochemical properties and electrocatalytic behavior of different N-doped carbonaceous materials as potential catalysts for oxygen reduction reaction (ORR) was attended. Ball-milling of graphite with melamine and solvothermal treatment of graphite oxide, graphene nanoplatelets (GNP) with ammonia were used as preparation methods. Elemental analysis and N 2 physisorption measurements revealed the synthesis of N-doped materials with strongly different morphological parameters. Contact angle measurements proved that all three samples had good wettability properties. According to analysis of XRD data and Raman spectra a higher nitrogen concentration corresponded to a smaller size of crystallites of the N-doped carbonaceous material. Surface total N content determined by XPS and bulk N content assessed by elemental analysis were close, indicating homogenous inclusion of N in all samples. Rotating disc electrode tests showed that these N-doped materials weremuch less active in acidic medium than in an alkaline environment. Although the presence of in-plane N species is regarded to be advantageous for the ORR activity, no particular correlation was found in these systems with any type of N species. According to Koutecky–Levich analysis, both the N-containing carbonaceous materials and the reference Pt/C catalyst displayed a typical one-step, four-electron ORR route. Both ball-milled sample with high N-content but with low SSA and solvothermally synthesized N-GNP with high SSA but low N content showed significant ORR activity. It could be concluded that beside the total N content other parameters such as SSA, pore structure, structural defects, wettability were also essential for achieving high ORR activity.

The proton exchange membrane (PEM) represents a pivotal material and a key challenge in developing fuel cell science and hydrogen technology. Nafion is the most promising polymer which will lead to its commercialisation. Hybrid membranes of nanosized tungsten oxide (WO3) and Nafion were fabricated, characterised, and tested in a single cell. The incorporation of 10 wt% WO3 resulted in 21% higher water uptake, 11.7% lower swelling ratio, almost doubling the hydration degree, and 13% higher mechanical stability of the hybrid membrane compared to the Nafion XL. Compared to commercial Nafion XL, the rNF–WO-10 hybrid membrane showed an 8.8% and 20% increase in current density of the cell at 0.4 V operating at 80 and 95 °C with 1.89 and 2.29 A/cm2, respectively. The maximum power density has increased by 9% (0.76 W/cm2) and 19.9% (0.922 W/cm2) when operating at the same temperatures compared to the commercial Nafion XL membrane. Generally, considering the particular structure of Nafion XL, our Nafion-based membrane with 10 wt% WO3 (rNF–WO-10) is a suitable PEM with a comparable performance at different operating conditions.

TiO2-based mixed oxide–carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti1−xMoxO2–C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky–Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H2O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability.

Perfluorosulfonic acid (PFSA) polymers such as Nafion are the most frequently used Proton Exchange Membrane (PEM) in PEM fuel cells. Nafion XL is one of the most recently developed membranes designed to enhance performance by employing a mechanically reinforced layer in the architecture and a chemical stabilizer. The influence of the water and acid pre-treatment process on the physicochemical properties of Nafion XL membrane and Membrane Electrode Assembly (MEA) was investigated. The obtained results indicate that the pre-treated membranes have higher water uptake and dimensional swelling ratios, i.e., higher hydrophilicity, while the untreated membrane demonstrated a higher ionic exchange capacity. Furthermore, the conductivity of the acid pre-treated Nafion XL membrane was ~ 9.7% higher compared to the untreated membrane. Additionally, the maximum power densities obtained at 80 °C using acid pre-treatment were ~ 0.8 and 0.93 W/cm2 for re-cast Nafion and Nafion XL, respectively. However, the maximum generated powers for untreated membranes at the same condition were 0.36 and 0.66 W/cm2 for re-cast Nafion and Nafion XL, respectively. The overall results indicated that the PEM’s pre-treatment process is essential to enhance performance.