Comprehensive experiments are carried out in order to gain insight into the effect of manganese contamination of the solid electrolyte interphase at the anode in Li-ion batteries. Electrochemistry shows that surface films contaminated with Mn are not passive toward electrolyte decomposition and are electroactive. Soft X-ray spectroscopy shows that the Mn is at +2 oxidation state in the film, just like Mn ions in the electrolyte. We believe Mn2 + from the electrolyte reduces to Mn0 at the electrode surface and Mn0 further reoxidizes by reacting with solvent molecules. Although not detected in soft X-ray spectra, it is possible that Mn0 is present in an amount high enough to allow for an electron leakage through the film, thereby suppressing passivation. Mn trapped in the film reversibly reacts with lithium according to a conversion reaction. It is a multiphase transformation yielding severe structural changes, hence the film undergoes severe morphological changes during cycling, thereby favoring electrolyte decomposition and further film growth. In this regard, Mn contamination of the SEI therefore promotes a larger cyclable lithium loss at the anode as compared to a Mn-free SEI, and thereby a persistent capacity loss of graphite/LMO cells.

Optimal water management in proton-exchange-membrane fuel cells at lower temperatures requires the efficient removal of liquid water from the cell. This pathway is intimately linked with liquid-water-droplet removal from the surface of the gas-diffusion layer (GDL) and into the flow channel. In this study, these liquid-water phenomena are investigated experimentally to improve the understanding of water transport through, and removal from, the GDL. Specifically, an experiment using a sliding-angle measurement is designed and used to quantify and measure directly the adhesion force for liquid-water droplets and to understand the droplets' growth and detachment from the GDL. The results show that unlike the static contact angle, the adhesion force, as measured by sliding angles, provides a good indicator of water-droplet removal as it is a direct measure of the dominating force that is holding a droplet on the GDL surface and preventing its detachment. It is also observed that injection through the GDL, as is representative of operating fuel cells, results in a higher adhesion force than a droplet placed on the top surface. Finally, it is shown that aged GDLs demonstrate higher adhesion forces, which dominate GDL degradation response and fuel-cell water holdup.

Catalyst layers (CLs) in proton-exchange-membrane fuel cells (PEMFCs) facilitate electrochemical reactions and therefore play a critical role in cell performance. Absorption and desorption of water into both the CL ionomer and the CL pore structure are integral aspects of PEMFC water management and performance. In this work, the water uptake from both the vapor and liquid phases is examined experimentally. Specifically, the dynamic water-uptake behavior of the CL ionomer is investigated as a function of relative humidity, temperature, Pt-loading and pretreatment. The water content of the ionomer in the CL, even after pretreatment, is found to be significantly lower than that for the bulk ionomer membrane, yet with similar sorption time constants. Thus, there is probably substantially slower transport into the ionomer which is likely due to its interfacial character. From the liquid phase, measured capillary pressure -saturation relationships show that the CL has an appreciably hydrophilicity that is strongly dependent on the existence of cracks. These findings are critical to the understanding and optimization of water management and transport phenomena within PEMFCs.