Enhancement of Mass Transport in Catalyst Layers of HT-PEMFC with Tetrafluorophenyl Phosphonic Acid Binder.

The design and development of new and efficient catalyst binder materials are important for improving cell performance in high-temperature proton-exchange membrane fuel cells (HT-PEMFCs). In this study, a series of tetrafluorophenyl phosphonic acid-based binder materials (PF-y-P, y = 1, 0.83, and 0.67) with rigid structures and controllable degrees of phosphonation were prepared and used in HT-PEMFCs using the ultra-strong acid-catalyzed Friedel-Crafts reaction and the combined Michaelis-Arbuzov reaction. The samples exhibited high stability, low water uptake, superior proton conductivity, and cell performance. In addition, the oxygen mass transport properties of the PF-1-P binder were investigated using high-temperature microelectrode electrochemical testing techniques. Compared with the phosphoric acid-doped polybenzimidazole (PBI) binder, the O2 solubility of PF-1-P binder material increased by 30% (5.36 × 10-6 mol cm-3) and the PF-1-P binder material exhibited better cell stability in HT-PEMFCs. After 10.5 h of discharge at a constant current of 0.12 A cm-2, the MEA voltage decreased by 7.1% and 20.8% in case of the PF-1-P and PBI binders, respectively.

Deciphering Single-Bacterium Adhesion Behavior Modulated by Extracellular Electron Transfer.

For bacterial adhesion and biofilm formation, a thorough understanding of the mechanism and effective modulating is lacking due to the complex extracellular electron transfer (EET) at bacteria-surface interfaces. Here, we explore the adhesion behavior of a model electroactive bacteria under various metabolic conditions by an integrated electrochemical single-cell force microscopy system. A nonlinear model between bacterial adhesion force and electric field intensity is established, which provides a theoretical foundation for precise tuning of bacterial adhesion strength by the surface potential and the direction and flux of electron flow. In particular, based on quantitative analyses with equivalent charge distribution modeling and wormlike chain numerical simulations, it is demonstrated that the chain conformation and unfolding events of outer membrane appendages are dominantly impacted by the dynamic bacterial EET processes. This reveals how the anisotropy of bacterial conductive structure can translate into the desired adhesion behavior in different scenarios.

Localized Electrochemical Impedance Measurements on Nafion Membranes: Observation and Analysis of Spatially Diverse Proton Transport Using Atomic Force Microscopy.

The distribution of ion conductive channels on the Nafion membrane surface, which determines the formation of the three-phase boundary, plays a very important role in improving the performance of proton-exchange membrane fuel cells. Therefore, understanding the microstructures at the catalyst layer/membrane interfaces of proton-exchange membranes is essential. Although current-sensing atomic force microscopy (AFM) can present some surface conductance data, localized impedance measurement providing more accurate proton-transport information is desirable. To obtain this information, in our study, localized electrochemical impedance spectroscopy was measured automatically with a home-built AFM-electrochemical impedance spectroscopy setup in which AFM was coupled with an impedance tester by a customized procedure. By this method, the localized proton-transport resistance at different humidities was observed in spatially diverse locations, and the value decreased as the membrane became hydrated. Furthermore, the microstructure of the Nafion membrane was numerically reconstructed at different hydration levels to examine the relationship between the membrane microstructural morphology and proton-transport resistance. The results showed that the spatial diversity of proton-transport resistance arose from the variable concentration of hydrophilic groups at the contact location of the AFM tip and the membrane, and from the heterogeneity of dry sulfonic acid groups in the membrane that creates local variation in water content.