Wettability of Nafion and Nafion/Vulcan carbon composite films

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

Protein Crystallization in a Microfluidic Contactor with Nafion®117 Membranes

Protein crystallization still remains mostly an empirical science, as the production of crystals with the required quality for X-ray analysis is dependent on the intensive screening of the best protein crystallization and crystal’s derivatization conditions. Herein, this demanding step was addressed by the development of a high-throughput and low-budget microfluidic platform consisting of an ion exchange membrane (117 Nafion^® membrane) sandwiched between a channel layer (stripping phase compartment) and a wells layer (feed phase compartment) forming 75 independent micro-contactors. This microfluidic device allows for a simultaneous and independent screening of multiple protein crystallization and crystal derivatization conditions, using Hen Egg White Lysozyme (HEWL) as the model protein and Hg²⁺ as the derivatizing agent. This microdevice offers well-regulated crystallization and subsequent crystal derivatization processes based on the controlled transport of water and ions provided by the 117 Nafion^® membrane. Diffusion coefficients of water and the derivatizing agent (Hg²⁺) were evaluated, showing the positive influence of the protein drop volume on the number of crystals and crystal size. This microfluidic system allowed for crystals with good structural stability and high X-ray diffraction quality and, thus, it is regarded as an efficient tool that may contribute to the enhancement of the proteins’ crystals structural resolution.

High Power Density Platinum Group Metal-free Cathodes for Polymer Electrolyte Fuel Cells

Low cost and high-performing platinum group metal-free (PGM-free) cathodes have the potential to transform the economics of polymer electrolyte fuel cell (PEFC) commercialization. Significant advancements have been made recently in terms of PGM-free catalyst activity and stability. However, before PGM-free catalysts become viable in PEFCs, several technical challenges must be addressed including cathode's fabrication, ionomer integration, and transport losses. Here, we present an integrated optimization of cathode performance that was achieved by simultaneously optimizing the catalyst morphology and electrode structure for high power density. The chemically doped metal-organic framework derived Fe-N-C catalyst we used allows precise tuning of the particle size over a wide range, enabling this unique study. Our results demonstrate the careful interplay between the catalyst primary particle size and the polymer electrolyte ionomer integration. The primary particles must be sufficiently large to permit uniform ionomer thin films throughout the surrounding pores, but not so large as to impact intraparticle transport to the active sites. The content of ionomer must be carefully balanced between sufficient loading for the complete catalyst coverage and adequate proton conductivity, while not being excessive and inducing large oxygen transport losses and liquid water flooding. With the optimal 100 nm size catalyst and ionomer loading, we achieved a high power density of 410 mW/cm² at a rated voltage and a peak power density of 610 mW/cm² in an automotive-relevant operating condition.

Surface Characteristics of Microporous and Mesoporous Carbons Functionalized with Pentafluorophenyl Groups

The in situ diazonium reduction reaction is a reliable and well-known approach for the surface modification of carbon materials for use in a range of applications, including in energy conversion, as chromatography supports, in sensors, etc. Here, this approach was used for the first time with mesoporous colloid-imprinted carbons (CICs), materials that contain ordered monodisperse pores (10-100 nm in diameter) and are inherently highly hydrophilic, using a common microporous carbon (Vulcan carbon (VC)), which is relatively more hydrophobic, for a comparison. The ultimate goal of this work was to modify the CIC wettability without altering its nanostructure and also to lower its susceptibility to oxidation, as required in fuel cell and battery electrodes, by the attachment of pentafluorophenyl (-PhF₅) groups onto their surfaces. This was shown to be successful for the CIC, with the -PhF₅ groups uniformly coating the inner pore walls at a surface coverage of ca. 90% and allowing full solution access to the mesopores, while the -PhF₅ groups deposited only on the outer VC surface, likely blocking its micropores. Contact angle kinetics measurements showed enhanced hydrophobicity, as anticipated, for both the -PhF₅ modified CIC and VC materials, even revealing superhydrophobicity at times for the CIC materials. In contrast, water vapor sorption and cyclic voltammetry suggested that the micropores remained hydrophilic, arising from the deposition of smaller N- and O-containing surface groups, caused by a side reaction during the in situ diazonium functionalization process.

Electrochemical performance and durability of carbon supported Pt catalyst in contact with aqueous and polymeric proton conductors

Significant differences in catalyst performance and durability are often observed between the use of a liquid electrolyte (e.g., sulfuric acid), and a solid polymer electrolyte (e.g., Nafion). To understand this phenomenon, we studied the electrochemical behavior of a commercially available carbon supported platinum catalyst in four different electrode structures: catalyst powder (CP), catalyst ionomer electrode (CIE), half membrane electrode assembly (HMEA), and full membrane electrode assembly (FMEA) in both ex situ and in situ experiments under a simulated start/stop cycle. We found that the catalyst performance and stability are very much influenced by the presence of the Nafion ionomers. The proton conducting phase provided by the ionomer and the self-assembled electrode structure render the catalysts a higher utilization and better stability. This is probably due to an enhanced dispersion, an improved proton-catalyst interface, the restriction of catalyst particle aggregation, and the improved stability of the ionomer phase especially after the lamination. Therefore, an innovative electrode HMEA design for ex-situ catalyst characterization is proposed. The electrode structure is identical to the one used in a real fuel cell, where the protons transport takes place solely through solid state proton conducting phase.