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A spectrum of selenium-doped Fe–N–C catalysts is prepared and scrutinized for acidic oxygen reduction reactions to understand the impact of the presence and amount of chalcogen dopants on the catalytic performance as cathode catalyst layers (CCLs) for H 2 –O 2 and H 2 –air polymer electrolyte membrane fuel cells (PEMFCs). While for a high initial content of Se, all available iron is bonded into iron selenides, a low amount of Se doping yields Fe–N–C catalysts of extensive microporosity, increased nitrogen content, and iron occurring predominantly in the Fe-N x coordination state. The chemistry of the iron-carbon-selenium (Fe–C–Se) system is studied in detail to elucidate the impact of Se on Fe–N–C catalyst formation during pyrolysis. The performance of the Se-doped platinum group metal-free Fe–N–C catalysts in PEMFCs is compared with their commercially available counterpart. The effect of the catalysts' morphology alternation by ball-milling on their performance is also studied. It is concluded that chalcogen doping (either S or Se doping) indirectly impacts Fe–N–C catalyst activity by controlling carbon scaffold properties, while the idea of a direct impact of chalcogen atoms on the Fe-N x catalytic centers is challenged. [Display omitted] • Se-doped Fe–N–C catalysts are studied as CCLs in H 2 –O 2 and H 2 –air PEMFCs. • Se-content is varied in a wide range, yielding a large family of Se-doped Fe–N–C. • Se doping grants enhanced microporosity and formation of Fe–N x sites. • Common characteristics of chalcogen-doped Fe–N–C catalysts are identified. • Ball-milling alters catalysts' morphology, thus improving their activity. [ABSTRACT FROM AUTHOR]

A method for stopping work of a polymer electrolyte membrane fuel cell (PEMFC) fueled with a gaseous fuel such as hydrogen has been elaborated that allows to instantly fill the anodic compartment of the fuel cell with air. The method utilizes three elements of proceeding: (i) isolation of hydrogen with opening of the PEMFC's anodic compartment to the external atmosphere, (ii) stopping the flow of air through the PEMFC's cathodic compartment, and (iii) electrically loading the PEMFC with a large load. It is shown that only the combination of all these three elements is effective in reducing corrosive catalyst degradation typically occurring when the PEMFC is stopped for a longer period of time. [ABSTRACT FROM AUTHOR]

Abstract: Proton-exchange membrane fuel cell (PEMFC) testing of Pt–Ru catalysts supported on differently prepared multiwall carbon nanotube (MCNT) supports was performed to elucidate the influence of the different supports on the operating characteristics of the catalysts under real direct methanol fuel cell (DMFC) anode and H2-PEMFC anode conditions. The MCNTs were either thin, entangled or thick, disentangled. Pretreatment of the MCNTs was also done and it was either high-temperature KOH etching or annealing (graphitization). The performance of the catalysts was compared against the performance of a commercial Pt–Ru catalyst supported on a high-surface-area carbon black. Among the different MCNT supports, the graphitized, entangled support offered the best performance in all tests, which was equal to the performance of the commercial catalyst, despite the MCNT catalyst layer was ca. 2.2 times thicker than the carbon black catalyst layer. Even for an MCNT catalyst layer, which was almost 7 times thicker than the carbon black catalyst layer, the transport limitations were not prohibitive. This confirmed the expected potential of nanotube supports for providing superior reactant transport properties of the PEMFC catalyst layers. [Copyright &y& Elsevier]

The fuel cell operation is associated with significant current density and durability problems, among other anode collectors. We used a numerical model based on flows with chemical reactions in a porous medium to solve these problems. We tested four variants of the anode channels. In the shape of the anode channel, we introduced changes to improve the current density. We also examined the influence of the channel shape on the stress field and rheological processes in the casing material. We verified the numerical model on the experimental data. Furthermore, we corrected the amount of the hydrogen stream and the produced water in the whole range of the cell's operation. The test results show that it is possible to increase the current density in all operating fields of the fuel cell while maintaining a low mechanical load on graphite elements and their safe operation time. [ABSTRACT FROM AUTHOR]

The operation of a fuel cell (PEMFC) is associated with severe problems related to individual components' local power density and durability. The problem arises from the unsatisfactory distribution of the H2 and O 2 reaction components and the high flow resistance. To find an answer to the problem posed, we tested nine variants of open anode/cathode channels dedicated to subsequent 3D printing. We have compared the obtained current-voltage characteristic curves with the experimental data of the fuel cell for which the new channels were dedicated. Each of the newly designed open flow channels had better current characteristics. Subsequently, we have compared selected cell properties between the best variants from the section. The final shape of the open channel ensured a high value of the current flux and local power density in the entire operating range of the fuel cell. Also, it generated low flow resistance allows for building a stack of cells. [Display omitted] • The size of the mesh determines the value of current-voltage characteristics. • The open porous channel was dedicated to the PEM fuel cell. • The complicated shape of the channel made it difficult to distribute the fluid. • A better distribution of the fluid components increased the current density. [ABSTRACT FROM AUTHOR]

Phloroglucinol/2-pyrrolaldehyde porous organic polymer impregnated with FeCl 3 was utilized to produce pyrolyzed iron-nitrogen-carbon (Fe−N−C) electrocatalysts for oxygen reduction reaction. The influence of the iron precursor content, addition of phenanthroline and pyrolysis temperature on the final Fe−N−C catalyst properties and activity were studied. The performance of the electrocatalysts obtained was additionally studied in a H 2 ‒air single-cell polymer electrolyte fuel cell (PEFC) with a ⁓4 mg (Fe−N−C) cm−2 cathode (5 cm2 membrane electrode assembly) and a Pt-based anode. The carbon gel-derived platinum group metal-free catalysts perform well in the PEFC achieving 0.2 W cm−2 and 0.37 A cm−2 at 0.5 V. The durability of the obtained Fe−N−C catalysts was also examined. [Display omitted] • Pyrolyzed Fe−N−C catalysts are produced from porous organic polymers (organic gels) • Pyrolysis at temperatures ≥850 °C yields catalysts with high activities • 3D architecture of Fe–N–C exhibits good transport properties in a H 2 −air fuel cell • Phenanthroline addition yields materials with enhanced graphitization and better durability • Fe–N–C catalysts achieve ⁓0.2 W cm−2 and 0.37 A cm−2 at 0.5 V in a H 2 −air fuel cell [ABSTRACT FROM AUTHOR]

[Display omitted] • PGM-free Fe−N−C catalysts are produced from N or N/S co-doped porous organic gels. • S-doping alters fundamental properties of carbon materials vs S-free counterparts. • S co-doping induces extensive ultramicroporosity (pores of ∼0.6 nm) • Ultramicropores could enhance ORR via their strong adsorption potential. • S co-doped Fe−N−C catalysts achieve ∼0.15 W cm−2 peak power density in a H 2 –air FC. • Morphology dominates other Fe−N−C characteristics and determines FC performance. Fe−N−C electrocatalysts were obtained via pyrolysis of N- or N/S co-doped synthetic polymers impregnated with FeCl 3. The influence of the presence/absence of sulfur co-doping, the initial FeCl 3 content and phenanthroline addition on the Fe−N−C–based cathode catalyst layers (CCLs) performance in H 2 -air PEM fuel cells was studied. To this end the Fe−N−C materials were first characterized concerning their chemical composition, surface chemistry, porosity and morphology. Sulfur and phenanthroline additions strongly affect these characteristics of Fe−N−C materials. This in turn determines (to various extents) the electrochemical properties as measured with a rotating ring-disk electrode and upon infusion in the cathode catalyst layer in H 2 -air PEM fuel cells. While simultaneous sulfur and phenanthroline addition yields Fe−N−C catalysts with high N-content and specific surface area, this does not translate into good electrochemical performance. We discuss the multitude of factors determining the catalysts' and the final CCLs' performances and conclude that the specific micro-colloidal morphology of the carbon gel-based materials dominates other Fe−N−C characteristics and determines overall FC performance. The best performing CCL provided peak power density of ∼0.15 W⋅cm−2 in a H 2 -air PEMFC. [ABSTRACT FROM AUTHOR]