In this work, we demonstrate gravure coating as a highly relevant technology for the production of roll-to-roll coated catalyst layers. Our results showed gravure coating is capable of coating ...multi-meter lengths of platinum on carbon catalyst layers at industrially-relevant loadings. Multiple characterization methods were used to examine the microscale and macroscale morphology of the coated layer. Using full-web inspection it was shown that gravure coating produced uniform films in both the cross-web and down-web directions. Using electron microscopy, it was observed that gravure coating produced catalyst layers with larger pores than catalyst layers produced by ultrasonic spray coating. In situ performance testing of the gravure-coated electrodes showed promising results, though additional modifications to the catalyst layer ink and/or drying process are needed to match the catalytic activity of spray-coated catalyst layers. This study lays the foundation for future process science studies to understand the science of scale up.
Surface chemical treatments impact the nucleation and uniformity of growth of Pt catalysts fabricated into carbon nanotube arrays by atomic layer deposition. The carbon functionalizations and their ...impacts on the growth of the Pt catalyst films are characterized and the electrochemical performance of the most promising fabrication routes are demonstrated. Display omitted
► Surface functionalization of CNT surfaces influences the growth of Pt by ALD inside aligned CNT arrays. ► Pt density and uniformity inside arrays depends strongly on the gasses used for functionalization. ► Ar plasma blocks nucleation, O2 plasma and trimethylaluminum treatments enhance uniformity. ► Generation/reduction of oxygen rich defect sites is the key to promote/block Pt ALD nucleation.
Uniform metal deposition onto high surface area supports is a key challenge of developing successful efficient catalyst materials. Atomic layer deposition (ALD) circumvents permeation difficulties, but relies on gas-surface reactions to initiate growth. Our work demonstrates that modified surfaces within vertically aligned carbon nanotube (CNT) arrays, from plasma and molecular precursor treatments, can lead to improved catalyst deposition. Gas phase functionalization influences the number of ALD nucleation sites and the onset of ALD growth and, in turn, affects the uniformity of the coating along the length of the CNTs within the aligned arrays. The induced chemical changes for each functionalization route are identified by X-ray photoelectron and Raman spectroscopies. The most effective functionalization routes increase the prevalence of oxygen moieties at defect sites on the carbon surfaces. The striking effects of the functionalization are demonstrated with ALD Pt growth as a function of surface treatment and ALD cycles examined by electron microscopy of the arrays and the individual CNTs. Finally, we demonstrate applicability of these materials as fuel cell electrocatalysts and show that surface functionalization affects their performance towards oxygen reduction reaction.
This work demonstrated a robust, scalable cell architecture for electroreduction of CO2 (CO2R). An up to 90% faradaic efficiency for the conversion of CO2R to formate at 500 mA/cm2 was realized at a ...25 cm2 gas diffusion electrode (GDE) with a carbon-supported SnO2 electrocatalyst. Furthermore, a 1.27 mm thick catholyte was used between the bipolar membrane and cathode GDE, which could be further reduced to tens of micrometers upon refinement. The deconvolution of the potential drop from each individual component/process guides the pathways to higher energy efficiencies of CO2R at this platform. Significant changes in the agglomerate size and aspect ratio on the electrode before and after an 11 h test were revealed by nano-CT, suggesting reduced CO2 accessibility from electrode degradation. The versatility of this CO2R testing platform enables the ability to assess materials, components, and interactions at scales more in line with future devices.
The development of novel platinum group metal (PGM)-free catalysts is a challenging task, particularly when coupled with the integration into a cathode catalyst layer (CCL). The optimization of such ...PGM-free electrode structures is often non-linear and iterative, making it a demanding task due to the high number of parameters that affect performance. To accelerate both materials discovery and electrode development, this work demonstrates the application of a high-resolution segmented cell (SC) with 121 segments of 0.413 cm2 size for combinatorial high-throughput PGM-free catalyst screening and CCL optimization. The approach utilizes three flow-field strips with active areas of 4.45 cm2 each, distributed over 11 segments. Electrodes with identical catalyst material and fabrication method result in reproducible data with typically less than 10% variation between each segment and match in performance with differential single cell data. High throughput testing of combinatorial sample sets, with varied PGM-free electrocatalyst materials or electrode composition, demonstrated the ability to rapidly discern high performing outliers, and establish or confirm trends in electrode optimization. The results indicated significant performance benefits of electrodes with ionomer content of 45 wt% over lower values, and of water rich inks with 82% water content over those with 50%.
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•High spatial resolution segmented cell with 50 cm2 area divided in 121 segments.•Spatially resolved study on combinatorial PGM-free electrode samples.•Conditioning behavior varied significantly between different PGM-free electrodes.•High throughput method detects performance changes due to fabrication parameters.•Segmented cell is a valuable tool for optimization of PGM-free electrodes.
Bipolar membranes (BPMs) are the enabling component of many promising electrochemical devices used for separation and energy conversion. Here, we describe the development of high-performance BPMs, ...including two-dimensional BPMs (2D BPMs) prepared by hot-pressing two preformed membranes and three-dimensional BPMs (3D BPMs) prepared by electrospinning ionomer solutions and polyethylene oxide. Graphene oxide (GO x ) was introduced into the BPM junction as a water-dissociation catalyst. We assessed electrochemical performance of the prepared BPMs by voltage–current (V–I) curves and galvanostatic electrochemical impedance spectroscopy. We found the optimal GO x loading in 2D BPMs to be 100 μg cm–2, which led to complete coverage of GO x at the interface. The integration of GO x beyond this loading moderately improved electrochemical performance but significantly compromised mechanical strength. GO x -catalyzed 2D BPMs showed comparable performance with a commercially available Fumasep BPM at current densities up to 500 mA cm–2. The 3D BPMs exhibited even better performance: lower resistance and higher efficiency for water dissociation and substantially higher stability under repeated cycling up to high current densities. The improved electrochemical performance and mechanical stability of the 3D BPMs make them suitable for incorporation into CO2 electrolysis devices where high current densities are necessary.
This study focuses on determining fabrication conditions to create high-performance roll-to-roll-coated (R2R-coated) gas-diffusion electrodes (GDEs) for proton-exchange-membrane fuel cells (PEMFCs). ...Here, we examine how process conditions influence the distribution of ionomer in the electrode, which is shown to be critical for high performance. Using a combination of Kelvin probe, X-ray photoelectron spectroscopy, and nano-scale X-ray computed tomography we show that formation of an ionomer-rich surface is promoted by using a higher drying rate. We show that R2R-coated GDEs have higher surface ionomer concentration than spray-coated GDEs, which enables these R2R-coated GDEs to not need an additional ionomer overlayer, as is typically the case for spray-coated GDEs. This will reduce the number of processing steps and lower material costs in a manufacturing setting. This work shows that with the appropriate selection of materials, ink formulation, and processing conditions, direct-coated GDEs are a viable pathway for fuel cell manufacturing.
•Method to make high-performance roll-to-roll coated GDEs developed.•Rapid drying of catalyst layer found to enrich ionomer at top surface.•Ionomer-rich catalyst layer surface forms low-resistance interface with membrane.•Roll-to-roll coated GDEs perform as well as spray-coated GDEs.
This work utilizes EIS to elucidate the impact of catalyst–ionomer interactions and cathode hydroxide ion transport resistance (R CL,OH– ) on cell voltage and product selectivity for the ...electrochemical conversion of CO to ethylene. When using the same Cu catalyst and a Nafion ionomer, varying ink dispersion and electrode deposition methods results in a change of 2 orders of magnitude for R CL,OH– and ca. a 25% change in electrode porosity. Decreasing R CL,OH– results in improved ethylene Faradaic efficiency (FE), up to ∼57%, decrease in hydrogen FE, by ∼36%, and reduction in cell voltage by up to 1 V at 700 mA/cm2. Through the optimization of electrode fabrication conditions, we achieve a maximum of 48% ethylene with >90% FE for non-hydrogen products in a 25 cm2 membrane electrode assembly at 700 mA/cm2 and <3 V. Additionally, the implications of optimizing R CL,OH– is translated to other material requirements, such as anode porosity. We find that the best performing electrodes use ink dispersion and deposition techniques that project well into roll-to-roll processes, demonstrating the scalability of the optimized process.
This work investigates how local ionomer/platinum (Pt) interactions and ionomer distribution in electrospun Pt/Vulcan nanofiber electrodes impact ionomer coverage, proton accessibility, and oxygen ...reduction reaction (ORR) performance in proton-exchange membrane fuel cells. Insights from various in situ electrochemical diagnostics were utilized in conjunction with ex situ microscopic characterization to understand how the electrode microstructureboth at the aggregate level and near the ionomer/platinum interfaceis affected by electrospinning in comparison to ultrasonic spraying. The effect of the carrier polymer poly(acrylic acid) (PAA) concentration from 5–20 wt % (with respect to total ink solids) on the resulting nanofiber morphology is discussed. Electron microscopy observations and CO displacement measurements indicated that Pt/Vulcan nanofibers prepared with a higher PAA concentration (15 wt %) were conformally coated with a film of ionomer on the exterior of the fiber, which resulted in an overall lower ionomer coverage on both Pt and carbon throughout the fiber diameter. In contrast, 10 wt % PAA leads to a uniform intrafiber distribution of the ionomer within the fibers, increasing the overall ionomer coverage and proton accessibility under both wet and dry conditions. These differences in the local ionomer coverage on Pt between 10 and 15 wt % PAA were also attributed to differences in the adsorption/interaction affinities between PAA and the ionomer onto the catalyst surface in the ink using zeta potential measurements. Additional fuel cell electrochemical tests on the electrospun electrodes show improvements in ORR kinetics and high-current-density H2/air performance compared to the ultrasonically sprayed electrodes.
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