Water management in anion-exchange membrane water electrolyzers under dry cathode operation.

Dry cathode operation is a desired operation mode in anion-exchange membrane water electrolyzers to minimize contamination of the generated hydrogen. However, water management under such operation conditions makes it challenging to maintain reliable performance and durability. Here, we utilize high-resolution in situ neutron imaging (∼6 µm effective resolution) to analyze the water content inside the membrane-electrode-assembly of an anion-exchange membrane water electrolyzer. The ion-exchange capacity (IEC) and thus hydrophilicity of the polymer binder in the cathode catalyst layer is varied to study the influence on water content in the anode (mid IEC, 1.8-2.2 meq. g-1 and high IEC, 2.3-2.6 meq. g-1). The neutron radiographies show that a higher ion-exchange capacity binder allows improved water retention, which reduces the drying-out of the cathode at high current densities. Electrochemical measurements confirm a generally better efficiency for a high IEC cell above 600 mA cm-2. At 1.5 A cm-2 the high IEC has a 100 mV lower overpotential (2.1 V vs. 2.2 V) and a lower high frequency resistance (210 mΩ cm-2 vs. 255 mΩ cm-2), which is believed to be linked to the improved cathode water retention and membrane humidification. As a consequence, the performance stability of the high IEC cell at 1 A cm-2 is also significantly better than that of the mid IEC cell (45 mV h-1 vs. 75 mV h-1).

Single-Color Barcoding for Multiplexed Hydrogel Bead-Based Immunoassays.

Current developments in precision medicine require the simultaneous detection of an increasing number of biomarkers in heterogeneous, complex solutions, such as blood samples. To meet this need, immunoassays on barcoded hydrogel beads have been proposed, although the encoding and decoding of these barcodes is usually complex and/or resource-intensive. Herein, an efficient method for the fabrication of barcoded, functionalized hydrogel beads is presented. The hydrogel beads are generated using droplet-based microfluidics in combination with photochemically induced C-H insertion reactions, allowing photo-crosslinking, (bio-) functionalization, and barcode integration to be performed in a single step. The generated functionalized beads carry single-color barcodes consisting of green-fluorescent particles of different sizes and concentrations, allowing simple and simultaneous readout with a standard plate reader. As a test example, the performance of barcoded hydrogel beads (3 × 3 matrix) functionalized with capture molecules of interest (e.g., antigens) is investigated for the detection of Lyme-disease-specific antibodies in patient sera. The described barcoding strategy for hydrogel beads does not interfere with the bioanalytical process and captivates by its simplicity and versatility, making it an attractive candidate for multiplex bioanalytical processes.

Breaking the Interface: Efficient Extraction of Magnetic Beads from Nanoliter Droplets for Automated Sequential Immunoassays.

Droplet-based microfluidic systems offer a high potential for miniaturization and automation. Therefore, they are becoming an increasingly important tool in analytical chemistry, biosciences, and medicine. Heterogeneous assays commonly utilize magnetic beads as a solid phase. However, the sensitivity of state of the art microfluidic systems is limited by the high bead concentrations required for efficient extraction across the water-oil interface. Furthermore, current systems suffer from a lack of technical solutions for sequential measurements of multiple samples, limiting their throughput and capacity for automation. Taking advantage of the different wetting properties of hydrophilic and hydrophobic areas in the channels, we improve the extraction efficiency of magnetic beads from aqueous nanoliter-sized droplets by 2 orders of magnitude to the low µg/mL range. Furthermore, the introduction of a switchable magnetic trap enables repetitive capture and release of magnetic particles for sequential analysis of multiple samples, enhancing the throughput. In comparison to conventional ELISA-based sandwich immunoassays on microtiter plates, our microfluidic setup offers a 25-50-fold reduction of sample and reagent consumption with up to 50 technical replicates per sample. The enhanced sensitivity and throughput of this system open avenues for the development of automated detection of biomolecules at the nanoliter scale.

Highly Stable, Low Gas Crossover, Proton-Conducting Phenylated Polyphenylenes.

Two classes of novel sulfonated phenylated polyphenylene ionomers are investigated as polyaromatic-based proton exchange membranes. Both types of ionomer possess high ion exchange capacities yet are insoluble in water at elevated temperatures. They exhibit high proton conductivity under both fully hydrated conditions and reduced relative humidity, and are markedly resilient to free radical attack. Fuel cells constructed with membrane-electrode assemblies containing each ionomer membrane yield high in situ proton conductivity and peak power densities that are greater than obtained using Nafion reference membranes. In situ chemical stability accelerated stress tests reveal that this class of the polyaromatic membranes allow significantly lower gas crossover and lower rates of degradation than Nafion benchmark systems. These results point to a promising future for molecularly designed sulfonated phenylated polyphenylenes as proton-conducting media in electrochemical technologies.