As a part of an ongoing effort to study the continuum mechanics effects associated with cryopreservation, the current report focuses on fracture formation in vitrified thin films of cryoprotectant agents. The current study combines experimental observations with continuum mechanics analysis. Experimental results have been developed using a new imaging device, termed a "cryomacroscope", which has been recently presented by the current research team. A newly developed liquid nitrogen-based cooling stage is presented in this paper. The samples under investigation are 0.5 ml droplets of cryoprotective agents, having a characteristic diameter of 20 mm and a characteristic thickness of 1.5 mm. Tested samples included dimethyl sulfoxide (DMSO) in a concentration range from 6M to 8.4M, and the cryoprotectant cocktails VS55 and DP6. Some samples contained small bovine muscle segments, having a characteristic dimension of 1 mm, in order to study stress concentration effects. Experimental results show that the onset of fracturing in vitrified films of cryoprotectants is very consistent, occurring over a small temperature range. Fracture pattern, however, was affected by the cooling rate. The presence of tissue segments did not affect the onset temperature of fracture, but affected the fracture pattern. The continuum mechanics analysis solidified the hypothesis that fracture is driven by thermal stress, not by temperature per se, and allowed fracture strain to be inferred from observed fracture temperature. In conjunction with the current report, additional photos of fracture formation in thin films are available at

We report the development and use of a microstructured electrode scaffold (MES) to make spatially resolved, in situ, electrolyte potential measurements through the thickness of a polymer electrolyte fuel cell (PEFC) electrode. This new approach uses a microfabricated apparatus to analyze the coupled transport and electrochemical phenomena in porous electrodes at the microscale. In this study, the MES allows the fuel cell to run under near-standard operating conditions, while providing electrolyte potential measurements at discrete distances through the electrode's thickness. Here we use spatial distributions of electrolyte potential to evaluate the effects of Ohmic and mass transport resistances on the through-plane reaction distribution for various operating conditions. Additionally, we use the potential distributions to estimate the ionic conductivity of the electrode. Our results indicate the in situ conductivity is higher than typically estimated for PEFC electrodes based on bulk polymer electrolyte membrane (PEM) conductivity.

This paper presents a novel method for obtaining in situ, through-thickness measurements of potential, current, charging current, and charge stored or discharged across capacitor and battery electrodes. Here we apply the method to an electrochemical double layer capacitance (EDLC) negative electrode for an aqueous sodium hybrid battery. In this approach, an electrode scaffold (ES) is used to directly measure the electric potential at discrete distances through the electrode under charging and discharging conditions. Finite difference methods are used to calculated local current and charging/discharging rates. The distributions obtained from these measurements are used to show non-uniform charging across an ultra-thick electrode intended for high area-specific energy storage in grid-scale energy storage applications. Using the ES we are able to gain insight into several complex phenomena that cannot be directly observed by other methods. For instance, we identify the portions of the electrode that are underutilized as well as the location of stray, parasitic currents.

Transport limitations are a significant impediment to effective utilization of the costly Pt catalyst in polymer electrolyte fuel cells (PEFCs). We present a catalyst layer analysis framework to investigate the coupled catalyst layer properties that dictate performance, including the electrochemical reactions, electrode morphology, and transport phenomena. This framework combines 50 nm resolution X-ray computed tomography (nano-CT), spatially-resolved in-situ measurements with microstructured catalyst layer scaffold (MES) diagnostics, and porous electrode modeling. Together, these tools serve to identify limiting transport mechanisms and their relationship to catalyst layer architecture. In addition, this framework serves to identify limitations in PEFC catalyst layer models and to validate these models. Here, we apply the framework to ionic transport in the cathode catalyst layer. The results indicate the ionic conductivity is much higher than anticipated and typically specified in PEFC models. IntroductionTransport limitations are a significant impediment to effective utilization of the costly Pt catalyst in PEFCs. They result in voltage losses on the order of 100 mV per cell at moderate current densities and much more at higher currents. The effectiveness factor for catalyst utilization (ratio of the Faradaic current to that with infinitely fast transport) in current catalyst layers is estimated to be <30% due to transport losses (1, 2). These low effectiveness factors suggest much lower Pt loadings are feasible with improved transport. Figure 1 illustrates the framework we use here to analyze the coupled transport and electrochemical phenomena in PEFC catalyst layers. The three key aspects dictating the catalyst layer performance are the architecture, transport phenomena, and electrochemical reactions. The architecture incorporates the composition and organization of the catalyst layer materials, subsequently yielding the catalyst layer's transport properties and volumetric electrochemical activity. The transport phenomena and transport mechanisms determine the concentration and maximum rates at which reactants can reach catalyst sites. Finally, the kinetics of the electrochemical reactions at the catalyst surfaces couples with the architecture and transport phenomena to establish the overall catalyst layer performance. To address these three aspects, we use nano-CT imaging to resolve the architecture, MES diagnostics to elucidate the transport mechanisms, and porous electrode models to incorporate electrochemical reactions when evaluating the impacts of catalyst layer design on PEFC performance. 409 2 nm Reactions on catalyst nano-particles C O2 Dissolution Diffusion Electrochemical reactions Porous electrode models Transport phenomena Spatially resolved in-situ diagnostics Electrode architecture 50 nm resolution X-ray CT Porous electrode performance m m atalyst Figure 1. The porous electrode analysis framework used to study PEFC catalyst layers.As mentioned above, the electrode architecture plays an importa...

A micro-structured electrode scaffold (MES) was developed for performing in-situ measurements of through-plane oxygen partial pressure (OPP) distributions in the cathode of a polymer electrolyte membrane fuel cell (PEMFC). Alternating layers of insulating material and platinum are stacked and bonded, and surround a 100 micron diameter hole filled with catalyst layer material. The platinum layers serve as ultra-microelectrodes, allowing the measurement of local OPP at discrete intervals through the catalyst layer thickness. Following an investigation of ultra-microelectrode sensitivity and repeatability, pulsed amperometric detection was selected over potentiostatic operation as the most effective method for performing OPP measurements. Using calibration points at the full air and zero OPPs, the OPP distribution at a fuel cell current density of 450 mA cm-2 was measured.