High surface area N-doped mesoporous carbon capsules with iron traces exhibit outstanding electrocatalytic activity for the oxygen reduction reaction (ORR) in both alkaline and acidic media. In alkaline conditions, they exhibit a more positive onset (0.94 V vs. RHE) and half-wave potentials (0.83 V vs. RHE) than commercial Pt/C, while in acidic media the onset potential is comparable to that of commercial Pt/C with a peroxide yield lower than 10 %. The Fe-N-doped carbon catalyst combines the high catalytic activity with remarkable performance stability (3500 cycles between 0.6 and 1.0 V vs. RHE), which stems from the fact that iron is coordinated to nitrogen. Additionally, the newly developed electrocatalyst is unaffected by the methanol cross-over effect in both acid and basic media, contrary to commercial Pt/C. The excellent catalytic behavior of the Fe-N-doped carbon, even in the more relevant acid medium, is attributable to the combination of chemical functions (N-pyridinic, N-quaternary and Fe-N coordination sites) and structural properties (large surface area, open mesoporous structure and short diffusion paths), which guarantees a large number of highly active and fully accessible catalytic sites and rapid masstransfer kinetics. Thereby, this catalyst represents an important step forward towards replacing Pt catalysts with cheaper alternatives. In this regard, an alkaline anion exchange membrane fuel cell was assembled with the Fe-Ndoped mesoporous carbon capsules as the cathode catalyst providing current and power densities matching those of a commercial Pt/C, which glimpses the practical applicability of the Fe-N-carbon catalyst.

A hybrid membrane of superacid sulfated Zr-MOF (SZM) and Nafion shows much superior performance to Nafion, particularly for fuel cell operating under low humidity. The Brønsted acidic sites in SZM networks retain an ample amount of water which facilitated proton conduction under low humidity. The water retention properties of Nafion-SZM hybrid membranes with 1 wt % loading of SZM increased at 35% relative humidity and outperformed commercial unfilled Nafion membrane. The proton conductivity increases by 23% for Nafion-SZM hybrid compared to unfilled Nafion membrane. The Nafion-SZM membrane also shows higher performance stability at 35% relative humidity than Nafion, as confirmed by close monitoring of the change of open circuit voltage for 24 h.

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The hot pressing process for fabricating membrane electrode assemblies (MEAs) has been widely adopted, yet little is known of its effects on the microstructural properties of the different components of the MEA. In particular, the interaction of the electrolyte, electrode and gas diffusion layer (GDL) due to lamination is difficult to probe as conventional imaging techniques cannot access the internal structure of the MEA. Here, a novel approach is used, which combines characterisation of hot-pressed membrane electrode assemblies using X-ray computed tomography, thermogravimetric analysis, differential scanning calorimetry and atomic force microscopy, with electrochemical performance measurements from polarisation curves and high-frequency impedance spectroscopy. Membrane electrode assemblies hot pressed at 100 o C, 130 o C and 170 o C reveal significant differences in microstructure, which has a consequence for the performance. When hot pressed at 100 o C, which is lower than the glass transition temperature of Nafion (123 o C), the catalyst only partially bonds with the Nafion membrane, leading to increased Ohmic resistance. At 170 o C, the Nafion membrane intrudes into the electrode, forming pinholes, degrading the catalyst layer and filling pores in the GDL. Finally, at 130 o C, the interfacial contact is optimum, with similar roughness factor between the catalyst and Nafion membrane surface, indicating effective lamination of layers.

Graphitic carbon nitrides are investigated for developing highly durable Pt electrocatalyst supports for polymer electrolyte fuel cells (PEFCs). Three different graphitic carbon nitride materials were synthesized with the aim to address the effect of crystallinity, porosity, and composition on the catalyst support properties: polymeric carbon nitride (gCNM), poly(triazine) imide carbon nitride (PTI/Li+Cl–), and boron-doped graphitic carbon nitride (B-gCNM). Following accelerated corrosion testing, all graphitic carbon nitride materials are found to be more electrochemically stable compared to conventional carbon black (Vulcan XC-72R) with B-gCNM support showing the best stability. For the supported catalysts, Pt/PTI-Li+Cl– catalyst exhibits better durability with only 19% electrochemical surface area (ECSA) loss versus 36% for Pt/Vulcan after 2000 scans. Superior methanol oxidation activity is observed for all graphitic carbon nitride supported Pt catalysts on the basis of the catalyst ECSA.

2 Highlights First description of in-plane water distribution using neutron imaging in an aircooled, open-cathode fuel cell. High water content identified under cathode land area, whereas anode water content is relatively homogeneous. Water distribution in anode GDL directly linked to dispersion of PTFE. Anode GDL composition shown to affect water content and distribution in cathode. Combined X-ray computed tomography, SEM/EDS and TGA used to characterise GDL structure and composition. AbstractIn-situ diagnostic techniques provide a means of understanding the internal workings of fuel cells under normal operating conditions so that improved designs and operating regimes can be identified. Here, an approach is used which combines exsitu characterisation of two anode gas diffusion / microporous layers (GDL-A and GDL-B) with X-ray computed tomography and in-situ analysis using neutron imaging of operating fuel cells. The combination of TGA, SEM and X-ray computed tomography reveals that GDL-A has a thin microporous layer with 26 % PTFE covering a thick diffusion layer composed of 'spaghetti' shaped fibres. GDL-B is covered by two microporous media (29 % and 6.5 % PTFE) penetrating deep within the linear fibre network. The neutron imaging reveals two pathways for water management underneath the cooling channel, either diffusing through the cathode GDL to the active channels, or diffusing through the membrane and towards the 3 anode. Here, these two behaviours are directly affected by the anode gas diffusion PTFE content and porosity. KeywordsGas diffusion layer; air-cooled open-cathode; X-ray computed tomography; neutron imaging; water management. IntroductionPolymer electrolyte fuel cells (PEFC) fuelled with hydrogen are among the most promising energy conversion technologies for a broad range of applications, including portable, stationary and automotive power delivery. However, understanding the cell water management is crucial for performance optimisation.Flooding impedes reactant transport (water mainly concentrating at the cathode) and reduces the surface area of the catalyst, causing significant if not catastrophic decay in cell performance, and dehydration can lead to cracks and irreversible damage [1][2][3]. The gas diffusion layer (GDL) provides a pathway for electron transport, ensures even reactant delivery and helps water management within each cell. The water balance between flooding and membrane dehydration is a function of the GDL's structure, porosity and PTFE (hydrophobic) content. Here, two commercial GDLs with microporous layers are characterised ex-situ by capturing the design and structure via X-ray computed tomography (CT), along with its polytetrafluoroethylene (PTFE) / carbon distribution via SEM/EDS analysis and thermogravimetric analysis (TGA); in-situ 'visualisation' of the water distribution in the in-plane orientation was performed using neutron radiography. These techniques can be correlated with one another to gain new insights into the water management role of the GDL in fuel c...

A novel PdIr/C supported alloy nanoparticle catalyst has been developed for use in the hydrogen oxidation reaction (HOR) at the anode of an Alkaline Anion Exchange Membrane (AAEM) fuel cell. The catalyst has been characterized using Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX) and Synchrotron X-ray Powder Diffraction (SXPD). Electrochemical testing suggests it has a comparable activity for HOR as Pt/C and is a good candidate for use on the anode of an AAEM fuel cell.

Text: Many electrochemical studies exist using the acidic ionomer Nafion ® as a binder in the ink formulation when operating in high pH systems. However, Nafion ® acts as an ionic insulator for OH-, and for reactions such as the hydrogen oxidation reaction, the transport of OHto the catalyst surface is of utmost importance when elucidating the performance of a catalyst. This work demonstrates that when using an alkaline polymer binder in the ink, the apparent activity of a commercially synthesised Pt/C catalyst is increased due to a lower diffusion resistance for the reaction. In order to obtain accurate values for kinetic data in alkaline media, the use of the acidic binder should be avoided.