Synchrotron X-ray radiography was used to visualize the liquid water accumulation in polymer electrolyte membrane (PEM) fuel cells to compare the impact of carbon substrate thickness on water ...management. A differential fuel cell with an active area of 0.68cm2 and rib/channel width of 0.2mm was custom-made to provide 1-dimensional (1D) conditions over the active area. The fuel cell with the thin substrate (TGP-H-030) outperformed the fuel cell with the thick substrate (TGP-H-060). The fuel cell with the thinner substrate exhibited a higher limiting current density, less liquid water in the microporous layer (MPL)-substrate transition region, and reduced oxygen transport resistance measured through electrochemical impedance spectroscopy (EIS). The compression behaviour of each GDL was also investigated through two consecutive fuel cell assemblies. The pressure in the second assembly was lower than that for the initial assemblies for both GDLs, and this significant change in assembly pressure was more pronounced for the thinner GDL (TGP-H-030). The resulting interfacial contact between the catalyst layer and the GDL was degraded, which manifested in the microscale displacement of fuel cell materials during operation (detected as a negative liquid water thickness). While the thinner GDL provided superior performance, the long term effects of material deformation may exacerbate a heterogeneous distribution of liquid water that could also impact the performance.
In this study, X-ray Computed Tomography (X-CT) is used to study the structure of the bi-layered gas diffusion layer (GDL) of polymer electrolyte membrane (PEM) fuel cells. This work presents a ...unique, calibrated segmentation procedure developed in-house to identify the distinct components of the bi-layer GDL, isolating the carbon fibre, the microporous layer and the void regions as individual phases. The novel use of the areal mass and areal volume of the GDL facilitates calibrated, reliable and repeatable multi-component segmentation and removes the high degree of subjectivity that might otherwise be encountered in typical thresholding procedures. Samples with and without MPLs are studied for the impact of rib – channel compression on porosity profiles. Under the channel, the porosity profile is nearly identical to the uncompressed profile. Under the land region, there is a significant decrease in the GDL thickness. It is also observed that the majority of the compression is exhibited by the substrate region while the MPL undergoes significantly reduced compression.
•Novel segmentation methodology for X-ray computed tomographic images of gas diffusion layers.•Calibrated segmentation based on areal mass and areal volume of gas diffusion layers.•Channel compression has negligible impact on porosity distribution.•Rib compression results in fibrous substrate compression with negligible microporous layer compression.
Synchrotron X-ray radiography was utilized to visualize the liquid water distribution in a fuel cell with an active area of 0.48 cm2 with an effective spatial resolution of 10 μm. Water content was ...measured in the gas diffusion layers (GDLs), where microporous layer (MPL) thicknesses ranged between 0 and 150 μm. The distribution of liquid water in a substrate-free polymer electrolyte membrane (PEM) fuel cell with a 50 μm-thick MPL was also determined. It was observed that the presence of an MPL significantly reduced the water content at the interfacial region between the catalyst layer and GDL, and increasing the thickness of the MPL led to a reduction of liquid water accumulation at the interface between the substrate and MPL.
Synchrotron X-ray radiography and electrochemical impedance spectroscopy (EIS) were concurrently used to quantify the effects of varying MPL thickness on PEMFC performance. Increasing the MPL ...thickness from 30μm to 50μm was found to lower the liquid water volume by 8% in the cathode substrate, which resulted in a 50% decrease in the oxygen mass transport resistance at a current density of 2.0A/cm2. Increasing the MPL thickness beyond 50μm at the same current density did not lead to any further substantial reductions of the liquid water volume in the cathode substrate (2%); however, the ohmic resistance increases significantly (16%). Among the four MPL thicknesses studied, the 50μm-thick MPL provides an optimized trade-off between the hydration of the membrane and the liquid water content in the fibrous substrate. A key observation of this work is the significant influence that high current density operation has on the heat and water management of polymer electrolyte membrane fuel cells.
In this work, we present a feasibility study of the simultaneous use of electrochemical impedance spectroscopy (EIS) and synchrotron X-ray radiography in a polymer electrolyte membrane fuel cell ...(PEMFC) for studying the relationship between the presence of liquid water and cell performance. X-ray radiography was used to quantify liquid water in the anode and cathode fibrous carbon paper substrate and microporous layer (MPL). EIS was used as a complementary diagnostic tool to quantify the equivalent resistances of the fuel cell. Two fuel cell cases with varying MPL thicknesses were compared under constant current density operation. The fuel cell with a 150 μm-thick MPL resulted in an equivalent mass transport resistance that was 13% lower than the fuel cell with a 100 μm-thick MPL. This notable difference in mass transport resistance was attributed to the smaller quantity of liquid water in the cathode substrate, particularly in the transition region between the MPL and carbon paper.
•PEM Fuel cell performance with 100 and 150 μm-thick MPLs were compared.•EIS and synchrotron X-ray radiography were used in tandem to diagnose PEMFCs.•Effect of MPL thickness on liquid water was visualized with synchrotron X-rays.•Liquid water in the cathode substrate was correlated to mass transport resistance.
In this work, the in operando determinations of liquid water saturation and corresponding effective diffusivities were measured for polymer electrolyte membrane fuel cell gas diffusion layers (GDLs). ...Through-plane liquid water saturation profiles were obtained by combining liquid water thicknesses measured from in operando synchrotron X-ray radiography and the GDL porosity distributions from ex situ X-ray computed tomography. The effective diffusivity of these partially saturated GDLs were determined from electrochemical impedance spectroscopy (EIS) measurements combined with results from our one-dimensional fuel cell impedance model. The ratio of the effective diffusivity of the GDL to the oxygen bulk diffusivity was found to follow a power law relationship, (1−savg)2.80 which is in agreement with measurements typically reported in the literature from limiting current and three-dimensional mass transport models. The methodology presented in this paper provides a novel, in operando and complementary alternative technique for measuring the effective diffusivity of partially saturated GDLs.
Carbon nanotubes (CNTs) have shown great promise as sensing elements in nanoelectromechanical sensors. In this review paper, we discuss the electrical, mechanical, and electromechanical properties of ...CNTs that are used in such applications. This investigation indicates which nanotube properties should be carefully considered when designing nanotube-based sensors. We then present the primary techniques that have been used for the integration of nanotubes into devices and proceed to give a description of sensors that have been developed using CNTs as active sensing elements
Head injury occurs in up to 47% of skiing or snowboarding injuries and is the predominant cause of death in these sports. In most existing literature reporting injury type and prevalence, head injury ...mechanisms are underreported. Thus, protective equipment design relies on safety evaluation test protocols that are likely oversimplified. This study aims to characterize severity and mechanism of head injuries suffered while skiing and snowboarding in a form appropriate to supplement existing helmet evaluation methods.
A 6-year, multicentre, retrospective clinical record review used emergency databases from two major trauma centres and Coroner's reports to identify relevant cases which indicated head impact. Records were investigated to understand the relationships between helmet use, injury type and severity, and injury mechanism. Descriptive statistics and odds ratios aided interpretation of the data.
The snow sport head injury database included 766 cases. “Simple fall”, “jump impact” and “impact with object” were the most common injury mechanisms while concussion was observed to be the most common injury type. Compared to “edge catch”, moderate or serious head injury was more common for “fall from height” (OR = 4.69; 95% CI = 1.44–16.23; P = 0.05), “jump impact” (OR = 3.18; 95% CI = 1.48–7.26; P = 0.01) and “impact with object” (OR = 2.44; 95% CI = 1.14–5.56; P = 0.05). Occipital head impact was associated with increased odds of concussion (OR = 7.46; 95% CI = 4.55–12.56; P = 0.001).
Snow sport head injury mechanisms are complex and cannot be represented through a single impact scenario. By relating clinical data to injury mechanism, improved evaluation methods for protective measures and ultimately better protection can be achieved.
•Snow sport head injury cannot be represented by a single mechanism as practiced in safety standards.•Concussion is the most prevalent injury type of head injury for skiing and snowboarding.•A high prevalence of low energy injuries in contrast to high energy injuries suggests a need for better low energy protection.•Low and high velocity tests, as well as oblique tests, are necessary to best evaluate head protection.•These findings may aid in development of revised, more representative helmet certification testing protocols.
In this paper, the impact of dead-ended anode (DEA) operation on the liquid water management of polymer electrolyte membrane fuel cells (PEMFCs) was investigated using X-ray synchrotron radiography. ...The fuel cell voltage and concurrent through-plane liquid water saturations in anode and cathode gas diffusion layers (GDLs) were measured during DEA and open anode operation. It was observed that DEA operation led to significant increases in liquid water content in both anode and cathode GDLs, along with fuel cell power output degradation. A strong correlation was observed between the buildup of the liquid water in the anode and the cathode, and as a result, the liquid water transport in the cathode was also significantly impacted by this DEA operation.
•In situ liquid water thicknesses were measured by synchrotron X-ray radiography for a fuel cell operating in DEA.•Fuel cell voltage degradations were linked to both anode and cathode GDL flooding.•Strong correlations between anode and cathode liquid water content were observed.
Introduction: A significant gap exists between the number of people waiting for an organ and donors. There are currently 1,628 people awaiting organ donation in Ontario alone. In 2018 to date, 310 ...donors have donated 858 organs. The purpose of this study was to determine whether there were missed donors in the Emergency Department (ED) and by what percent those missed donors would increase organ donation overall. Methods: This was a health records and organ donation database review of all patients who died in the ED at a large academic tertiary care center with 2 campuses and 160,000 visits per year. Patients were included from November 1, 2014 – October 31, 2017. We collected data on demographics, cause of death, and suitability for organ donation. Data was cross-referenced between hospital records and the provincial organ procurement organization called Trillium Gift of Life Network (TGLN) to determine whether patients were appropriately referred for consideration of donation in a timely manner. Potential missed donors were manually screened for suitability according to TGLN criteria. We calculated simple descriptive statistics for demographic data and the primary outcome. The primary outcome was percentage of potential organ donors missed in the Emergency Department (ED). Results: There were 606 deaths in the ED from November 1, 2014 – October 31, 2017. Patients were an average of 71 years old, 353 (58%) were male, and 75 (12%) died of a traumatic cause. TGLN was not contacted in 12 (2%) of cases. During this period there were two donors from the ED and 92 from the ICU. There were ten missed potential donors. They were an average of 67 years, 7 (70%) were male, and 2 (20%) died of a traumatic cause. In all ten cases, patients had withdrawal of life sustaining measures for medical futility prior to TGLN being contacted for consideration of donation. There could have been an addition seven liver, six pancreatic islet, four small bowel, and seven kidney donors. The ten missed ED donors could have increased total donors by 11%. Conclusion: The ED is a significant source of missed organ donors. In all cases of missed organ donation, patients had withdrawal of life sustaining measures prior to TGLN being called. In the future, it is essential that all patients have an organ procurement organization such as TGLN called prior to withdrawal of life sustaining measures to ensure that no opportunity for consideration of organ donation is missed.
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