A highly active NiMo electrocatalyst for HOR in alkaline media with power density at 0.5 V higher than 100 mW cm−2 (peak value of 120 mW cm−2), which is similar to palladium was synthesized and comprehensively studied.

No abstract

No abstract

Optimizing electrode morphology with a more uniform ionomer distribution is key to reducing ohmic losses and increasing electrocatalyst utilization in polymer electrolyte fuel cells (PEFCs). Inherent ionomer conductivity, volume fraction and tortuosity determine effective ionic conductivity. We use hydrogen pump (HP) method to measure effective ionic conductivity of a pseudo catalyst layer (PCL) comprised of Vulcan XC-72 carbon black and 3M 825 EW ionomer with ionomer to carbon (I/C) ratios of 0.6, 1 and 1.4 and relative humidity (RH) range of 50 to 120%. These direct current (DC) experiments are then compared with electrochemical impedance spectroscopy (EIS). Both DC and EIS methods show good agreement, indicating that EIS can be used as an alternative to DC method in HP experiment. Ionic conductivity for PCL with I/C of 1 and 1.4 was found to be about one order of magnitude higher than I/C of 0.6 for most of the RH range. At 90% RH tortuosities for I/C = 1 and 1.4 were close to 1, whereas tortuosity for I/C = 0.6 was 3. With decrease in relative humidity tortuosities increased linearly and at 50% relative humidity a PCL with I/C = 0.6 had the highest tortuosity of 6.1.

Metal-Nitrogen-Carbon catalysts have emerged as the most promising platinum group metal-free catalysts toward oxygen reduction reaction for proton exchange membrane fuel cell (PEMFC) applications. However, their large-scale implementation in H 2 /air PEMFCs is still hindered by the low density of active sites in such materials, implying the need for thick active layers with inferior mass-transport properties. In this work, the co-electrospinning of nano-ZIF-8 (a zeolitic imidazolate framework) and polyacrylonitrile results in anisotropic and microporous FeNC fibers, offering an effective approach towards active layers with hierarchical micro-, meso-and macroporosity. X-ray computed tomography performed on the cathode ex situ reveals enhanced macroporosity of fibrous FeNC layers compared to a non-fibrous one derived from nano-ZIF-8.Applied in operando in a PEMFC, X-ray tomography showed abundant water-free macroporous voids in the fibrous FeNC layer, beneficial for the transport of reactants and products toward and away from the active sites. The combination of the Fe precursor in the electrospun solution and the high voltage applied during electrospinning is however also shown to enhance the formation of metallic Fe particles after pyrolysis, which is detrimental to the density of atomicallydispersed FeN x active sites. FeNC fibrous morphology with higher density of FeN x active sites, obtained with a modified electrospinning process or other techniques, holds therefore great potential to replace Pt/C with MNC cathodes in H 2 /air PEMFCs.

A systematic analysis, both experimental and model-assisted, has been performed over three main configurations of platinum group metal-free (PGM-free) electrodes in polymer electrolyte fuel cells (PEFCs): catalyst-coated membrane CCM technology is being compared to the gas-diffusion electrode (GDE) method of electrode fabrication and juxtaposed to a hybrid/combined GDE-CCM method of membrane-electrode assembly (MEA) fabrication. The corresponding electrodes were evaluated for their electrochemical performance, modeled, and studied with in situ and operando X-ray computed tomography (X-ray CT). The study establishes that through-thickness inhomogeneities play the most important role in water withdrawal/water management and affect most significantly PGM-free PEFC performance. The catalyst integration technique results in formation of interfacial regions with increased porosity and surface roughness. These regions form critical interfaces de facto responsible for flooding type behavior of the PEFC as shown for a first time by operando X-ray CT. The computational model shows that the PEFC performance critically depends on liquid water formation and transport at cold and wet conditions.

The side reactions during long-term operation of vanadium redox flow batteries (VRFBs) increase the average oxidation state of the electrolyte and associated equilibrium potential of the positive half-cell. This consequently initiates the corrosion reactions at the positive side as the half-cell potential passes the critical limit. In this study, an ex-situ accelerated electrochemical corrosion protocol is performed on the carbon paper electrode to investigate the effects of corrosion conditions induced by extended cycling on electrode morphology and VRFB system performance. In terms of morphological changes of corroded electrodes, only minor mechanical degradation is observed, including disappearance of binder material and reduced mechanical properties. With regards to the cell performance, the flow cell with the corroded electrode demonstrates notably higher charge and discharge capacities which can be attributed to the enhanced active surface area of the electrode. Furthermore, the corroded case exhibits an improved capacity retention during extended cycling which can be related to the improved redox activity caused by the increased carboxyl groups and wettability. This study shows that even at these fairly aggressive corrosion conditions, the process behaves as a treatment method, which oxidizes surface functional groups, increases active surface area, and hydrophilicity, and subsequently enhances VRFB performance.

Fuel cells are, to date, on the verge of large-scale commercialization. Still, long-term stability is of concern, especially in the automotive field, mainly because of the cathodic catalyst support. In fact, carbonaceous materials, the state of the art to date, suffer from severe corrosion phenomena during discontinuous operation. In the effort to replace carbon as Pt support and develop a nanoengineered architecture for the fuel cell electrodes, we report here the concept of a hierarchical TiN nanostructured thin film (HTNTF) electrode, in which Pt is deposited on an array of quasi-1D TiN nanostructures with good conductivity, high roughness factor, tunable porosity, and outstanding chemical stability. The HTNTF is grown by self-assembly from the gas phase by means of a one-step, template-free, room-temperature process, namely, pulsed laser–scattered ballistic deposition, PL–SBD. The activity of the nanostructured thin film electrode is assessed toward the oxygen reduction reaction and its stability evaluated according to DOE accelerated stress test (AST) standard protocols, revealing an electrochemical surface area (ECSA) loss as low as 7% with respect to the 40% goal. Moreover, a proof-of-concept cell has been realized to demonstrate the applicability of our supports to the device scale. Despite the fact that further optimization is needed to achieve high performances, this new class of electrodes has clear potential in terms of stability with respect to the state of the art, overcoming carbon corrosion by simply removing it from direct contact with the Pt electrocatalyst.