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Membrane electrode assemblies (MEAs) for anion exchange membrane fuel cells (AEMFCs) were manufactured from commercial materials: Pt/C catalyst, A201 AEM and AS4 ionomer by using an industrial mass-production digital printing method. The MEA designs selected are close to those recommended by US Department of Energy, including low loading of platinum on the cathode side (0.2 mg cm −2 ). Polarization curves and electrochemical impedance spectroscopy (EIS) were applied for MEA evaluation in fuel cell conditions with variation of gas humidification and oxygen partial pressure (air vs oxygen). The typical impedance curves recorded at H 2 /O 2 gas configuration consist of high- and medium-frequency arcs responsible for hydrogen oxidation and oxygen reduction, respectively. Operation with air as a cathode feed gas resulted in a decrease in AEMFC performance due to possible CO 2 poisoning and mass transfer losses. At the same time, EIS demonstrated formation of a low frequency loop due to diffusion limitations. Despite the low loading of platinum on the cathode (0.2 mg cm −2 ), a peak power density of ∼330 mW cm −2 was achieved (at 50/50% of RH on anode and cathode), which is substantially higher performance than for AEMFC MEAs tested at similar conditions. [ABSTRACT FROM AUTHOR]

The design of cathodic catalysts layer (CCL) consisted of Platinum Group Metal-free (PGM-free) electrocatalysts was done by catalyst coated membrane approach. Three different Fe-Mn-N-C compounds were synthesized with Fe:Mn ratio of 1:1, 2:1 and 2:1 with modified heat treatment profile. The catalysts were characterized by X-ray photoelectron spectroscopy, X-ray powder diffraction, pore and particle size distribution, zeta potential and transmission electron microscopy. Electrocatalysts were integrated into membrane electrode assembly and evaluated by electrochemical methods. Electrochemical impedance spectroscopy in combination with modeling were used for estimation of proton conductivity of CCL and its oxygen diffusivity. It was found that all CCLs possess extremely high proton conductivity, which was demonstrated for the first time for these types of PGM-free catalysts. The observed ORR mechanism was predominantly 4e- due to peroxide/radicals scavenging effect of Mn. [Display omitted] • Bi-metallic Fe-Mn-N-C PGM-free catalysts were synthesized. • Highly performed, industrial quality MEAs were fabricated. • Detailed electrochemical fuel cell evaluation was combined with EIS modeling. • The proton conductivity in catalyst layer was improved 5 times vs literature data. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a study of multi-phase flow through the cathode side of a polymer electrolyte membrane fuel cell employing an interdigitated flow field plate. A previously published model has been extended in order to account for phase change kinetics, and a comparison between the interdigitated flow field design and a conventional straight channel design has been conducted. It is found that the parasitic pressure drop in the interdigitated design is in the range of a few thousand Pa and could be reduced to a few hundred Pa by choosing diffusion media with high in-plane permeability. The additional compressor work due to the increased pressure loss will only slightly increase, and this may be offset by operating at lower stoichiometries as the interdigitated design is less mass transfer controlled, which means that the overall efficiency of the interdigitated arrangement will be higher. In the interdigitated design more product water is carried out of the cell in the vapor phase compared to the straight channel design which indicates that liquid water management might be less problematic. This effect also leads to the finding that in the interdigitated design more waste heat is carried out of the cell in the form of latent heat which reduces the load on the coolant. Finally we see that the micro-porous layer might help keep the gas diffusion layer substrate dry due to a potentially higher evaporation rate caused by a combination of the Kelvin effect and a larger specific surface area compared to the diffusion layer substrate. [Copyright &y& Elsevier]

Abstract: The permeability of carbon dioxide and oxygen in Nafion® 1100 EW membrane has been studied as function of the relative humidity or water content using a mass spectrometer equipped with a membrane inlet. The rate of permeation of CO2 was found to depend strongly on the water content of the membrane. It was similar to the oxygen permeation rate for the dry membrane but an order of magnitude higher for the fully humidified membrane. The data were used to correct the estimated methanol crossover rate and fuel efficiency in a commercial DMFC using Nafion® 117 as electrolyte by subtracting the contribution from the CO2 permeation to the CO2 flux from the cathode. The contribution varied between 4.5% and 12% of the flux depending on the mode of operation. In an operating DMFC the electrolyte/anode interface will be saturated with CO2. For very efficient anodes (almost complete methanol conversion at the electrode/electrolyte interface) and the use of thin electrolyte membranes negligence of the CO2 permeation contribution may thus lead to misleading conclusions regarding the magnitude of methanol crossover. [Copyright &y& Elsevier]

Proton Exchange Membrane (PEM) fuel cell electrodes with different ionomer contents were studied with various microscopic techniques. The morphology and surface potential were examined by Atomic Force Microscopy (AFM) and Kelvin Probe Microscopy (KPM), respectively. The particulate nature of the electrode was well displayed in the topography and phase images. The particle and pore size (Z) distributions showed the most frequent values at 30–40 nm and 20–30 nm, respectively. The particle size corresponds to the size of the carbon support for the platinum catalyst. Catalyst agglomeration was observed in high ionomer content electrodes. The surface potential images showed distinct difference to the topography images. The overall grain size was seen to increase, the pore volume to decrease, the surface roughness to decrease, and the surface potential variation to increase with the increase of ionomer content in the catalyst layer. Transmission electron microscopy (TEM) was carried out on selective electrodes to provide additional information and confirmed with the AFM results. Cyclic voltammetry (CV) showed that the electrode containing 30 wt.% ionomer has maximum catalyst utilization. [ABSTRACT FROM AUTHOR]

• A method for measurement of PEM fuel cell cathode electron and proton conductivity is developed. • The method is based on fitting of recent impedance model to the spectra measured in N2/H2 regime of cell operation. • The method is demonstrated using Fe-N-C-based PEM fuel cells. • The electron and proton conductivity of Fe-N-C cathodes are close to these parameters of Pt/C cathodes. • The method could be used for in-situ control of carbon corrosion in long-term cell operation. Impedance spectra of a PEM fuel cell with three Fe-N-C cathodes have been measured under the H 2 /N 2 testing regime. The spectra have been fitted using a recently developed physics-based impedance model, which takes into account finite proton (σ p) and electron (σ e) conductivity of the oxygen-free cathode catalyst layer. Fitting allowed to extract numerical data for σ p , σ e , the double layer capacitance, and the inductance of cables used for measuring impedance spectra. The values of σ p and σ e are close to what previously found for standard Pt/C electrodes, which is found for the first time using PGM-free catalysts. The method enables simultaneous measurement of reference proton and electron conductivity of PEMFC cathode. [ABSTRACT FROM AUTHOR]

A family of novel carbon materials with intermediate surface area and varying morphology and surface chemistry were used to prepare Pt/C catalysts by two different preparation procedures; a chemical impregnation method and a microwave-assisted polyol method. The catalysts were thoroughly characterized, and their electrochemical performance and stability were investigated with rotating disc electrode (RDE) cyclic voltammetric (CV) measurements. The intermediate-surface-area carbon supports gave catalysts with much greater support stability than a widely used standard catalyst. The novel catalysts had lower electrochemical surface area than the reference, but their specific electrocatalytic activity towards the oxygen-reduction reaction (ORR) was much higher, and some of them also featured higher mass-specific ORR activity than the reference. The series of catalysts prepared by the microwave-assisted polyol method featured smaller Pt nanoparticles and higher activities than those prepared by impregnation. On the other hand, the impregnated catalysts showed better durability of the Pt particles. The most promising catalysts were selected and elaborated in further optimized preparation procedures to obtain quantities sufficient for their use in proton-exchange membrane fuel cells (PEMFCs). [ABSTRACT FROM AUTHOR]

Carbon-based catalyst support and Pt catalysts are commonly used in polymer electrolyte fuel cells (PEFCs). During cell start-up and shutdown processes, carbon support oxidation occurs, which leads to losses of electrochemical performance. In this work, carbon corrosion accelerated stress tests (ASTs) were performed and lifetimes of high surface area carbon (HSAC) and graphitized carbon (GrC) supports were investigated. 1000 AST cycles were conducted on Pt/HSAC while 10000 AST cycles were conducted on Pt/GrC due to different carbon corrosion rates, and both Pt/HSAC and Pt/GrC showed rapid decrease of performance at end of life (EOL). Detailed comparisons of electrochemical characterizations were also conducted between Pt/HSAC and Pt/GrC. Electrochemical surface area (ECSA) loss in different levels was found for both Pt/HSAC and Pt/GrC due to Pt loss, Pt detachment and particles coalescence, which also resulted in reduction of S O 3 − group coverage and more tortuous H + transportation, leading to decreased catalyst layer ionic conductivity. For Pt/HSAC after 1000 AST cycles, more than 2 times higher ECSA loss but with only 50% greater particle size growth and similar Pt loss strongly suggested that a greater Pt detachment occurred on HSAC support during the AST cycles. Apart from that, it was found that after 1000 AST cycles, graphitized carbon support was much more robust compared to HSAC support, and it showed 2 times less ECSA reduction, 2.5 times less catalyst layer ionic conductivity reduction and 4 times less S O 3 − group coverage reduction. Double layer capacitances increased for both carbon supports after AST at their EOLs, as more disordered carbon contacts were formed, which created more contacts between solid and ionic materials. This study shows a possibility of Pt/GrC catalysts to meet the Department of Energy (DOE) target of 5000 AST carbon cycles, as the Pt/GrC cell met the target of ≤ 40% ECSA loss of initial area. • Carbon corrosion tests are performed for two supports for fuel cells. • Graphitized support maintained high surface area after 5000 cycles. • High surface area carbon support layer lost most of its thickness after 1000 cycles. [ABSTRACT FROM AUTHOR]

A commercial high surface area carbon black (808 m 2 g −1 ), low surface area carbon black (226 m 2 g −1 ) and an experimental grade medium surface area carbon black (ExpCB, 384 m 2 g −1 ) were studied as supports for platinum deposition: (i) from true solutions of H 2 PtCl 6 , Pt(C 5 H 7 O 2 ) 2 , Pt(NH 3 ) 4 (NO 3 ) 2 , or Pt(NH 3 ) 2 (NO 2 ) 2 , and (ii) from fine slurries of Pt(C 5 H 7 O 2 ) 2 or PtO 2 to achieve high Pt loadings of 60 wt.%. Temperature programmed reduction (TPR) revealed that PtO 2 , H 2 PtCl 6 , Pt(C 5 H 7 O 2 ) 2 , Pt(NH 3 ) 4 (NO 3 ) 2 , and Pt(NH 3 ) 2 (NO 2 ) 2 deposited on carbon blacks were reduced to metallic Pt at 0, 70, 120, 140, 150 °C, respectively. Cyclic voltammetry (CV) was carried out on electrodes prepared from selected catalyst materials on a rotating-disc electrode (RDE). The electrochemically active surface area (ESA) of the platinum and electrocatalytic activities towards the oxygen-reduction reaction (ORR) were evaluated from the RDE measurements, in which also the stability towards electrochemical ageing was investigated. These analyses indicated that impregnation by H 2 PtCl 6 is the most suitable of the studied catalyst synthesis methods. Mass-specific ORR activities similar to that of commercial reference catalyst are obtained. Catalysts prepared on carbon ExpCB showed greater stability than those based on 350G. Further increase in stability results from dechlorination of the catalyst. [ABSTRACT FROM AUTHOR]

A new platinum group metal (PGM)-free proton exchange membrane fuel cell (PEMFC) cathode catalyst materials, synthesized using the VariPore™ method by Pajarito Powder, LLC, are characterized for their structure and activity. The physico-chemical analysis of the iron-nitrogen-carbon (Fe-N-C) electrocatalysts show mesoporous carbon material effectively doped with iron and nitrogen. The materials have an average pore size of 7–8 nm and high specific surface area. The Fe-N-C catalysts exhibit good oxygen reduction reaction (ORR) activity in 0.5 M H 2 SO 4 electrolyte with high half-wave potential and sustainable electrochemical stability over 10,000 repeated potential cycles with insignificant losses in their activities. As cathode catalysts in a PEMFC, the Fe-N-C materials deliver remarkably good fuel cell performance at low overpotential approaching that of the commercial Pt catalyst. The high ORR electrocatalytic activity of these Fe-N-C catalysts is credited to the synergy between nitrogen-moieties, specifically pyrrolic-N, pyridinic-N, and graphitic-N, and iron in addition to the high mesoporosity that facilitate an effective reaction path in boosting the electrocatalytic activity and stability. [Display omitted] • State-of-the-art commercial PGM-free catalysts for ORR were characterized and evaluated. • Was shown that active centres are atomically dispersed. • Performance of electrocatalysts was evaluated in industrially manufactured MEA form-factor. • The fuel cell performance is close to the state-of-the-art R&D PGM-free catalysts. [ABSTRACT FROM AUTHOR]

To elucidate the evolution of ionomer-Pt and ionomer-carbon interfaces during life cycle of polymer electrolyte fuel cells (PEFCs), electrodes with high surface area (HSA) and durable carbon supports underwent catalyst and carbon corrosion accelerated stress tests (ASTs) under stoichiometric and sub-stoichiometric gas flow conditions. Electrochemical characterizations, as well as X-ray photoelectron spectroscopy (XPS) were utilized to assess degree of components degradation. Catalyst AST results revealed that Pt nanoparticles dispersed within the micro- and meso-pores and not in contact with ionomer are the main contributor to the 50% electrochemical surface area (ECSA) loss observed after 30k cycles resulting in significant polarization loss, which is much more notable in the case of sub-stoichiometric operating condition. Support AST results for HSA carbon showed severe ionomer degradation and 55% ECSA loss within the first 100 cycles, while cell with durable support exhibited negligible polarization and ECSA decay during the first 2500 cycles attributed to higher ionomer coverage, preservation of proton pathways preventing Pt from detachment. [Display omitted] • Interfaces evolution are evaluated during accelerated stress tests (ASTs) for fuel cells. • Pt that is not in contact with ionomer degrades the most for catalyst AST. • Ionomer degradation is observed for all ASTs. • Graphitized carbon supports mitigate corrosion and Pt loss. [ABSTRACT FROM AUTHOR]