Sang Young Son

Pore-Water Morphological Transitions in Polymer Electrolyte of a Fuel Cell

We show a criticality of three water morphological transitions on pore-water transport and proton conductivity in Nafion of a polymer electrolyte membrane fuel cell, addressing its pore-size distribution and the Schroder paradox. The first transition leads to the onset of proton conductivity; the second allows for the onset of the capillary percolation channels and proton conductivity jump at a low water content λ im ,H 2 O = 5. Using this as immobile saturation, the predicted water distribution and cell performance are in reasonable agreement with the available experiments. The third (the paradox, postulating further capillary advancing) bounds the maximum water content on the cathode side of Nafion, which is also supported by the proposed adsorption isobar (thermodynamic equilibrium limit). These transitions appear in the available pore-size experiments which show capillary percolation channel sizes. In addition, the optimal Nafion pore-water content is between the second and third transitions.

X-ray tomography of morphological changes after freeze/thaw in gas diffusion layers.

Liquid water produced in a polymer electrolyte membrane fuel cell experiences a freeze/thaw cycle when the cell is switched off and on while operating at ambient temperatures below freezing. This freeze/thaw cycle permanently deforms the polymer electrolyte membrane fuel cell capillary structures and reduces both the cell life and its ability to generate electric power. The X-ray tomography facility at the Pohang Accelerator Laboratory was used to observe the freeze/thaw effects on the gas diffusion layer (GDL), which is the thickest capillary layer in the cell. Morphological changes in the GDL under a water freeze/thaw cycle were observed. A scenario in which freeze/thaw cycles affect fuel cell performance is suggested based on images from X-ray tomography.

Analytical Performance Issues: Exploring a Novel Ultrafine Particle Counter for Utilization in Respiratory Protection Studies

Correspondence to: Sergey Grinshpun, University of Cincinnati, Environmental Health, 3223 Eden Ave., P.O. 670056, Cincinnati, OH 45267; e-mail: sergey. grinshpun@uc.edu. Exposure to ultrafine (≤0.1 μm) particles is widespread at various workplaces. Several studies have revealed associations between ultrafine particle exposures and adverse health effects, including respiratory problems, impairment of cardiovascular function, and others.(1–3) Condensation particle counters (CPCs) are conventionally deployed to measure the ultrafine particle concentrations in real time. For example, the P-Trak (Model 3007, TSI Inc., Shoreview, Minn.) is the most commonly used CPC in occupational environments. However, commercially available CPCs are typically too bulky to serve as workers’ personal exposure monitors; furthermore, their performance is generally affected by their orientation. Several attempts have been made recently to design a better instrument for real-time personal exposure assessment, including a novel ultrafine particle counter (prototype) developed at the University of Cincinnati (UC UFP counter, Figure 1).(4,5) The operation principle of this device, like any CPC, involves condensation on nuclei; however, the novelty of this instrument is that the condensation takes place on nano-materials entering through the input channel. After passing a PM filter (cyclone), the particles enter a non-wetting, porous evaporationcondensation tube. Enlarged due to condensation growth, they are detected with an optical laser counter. Capillary force spontaneously generated on the surface of the non-wetting tube prevents flooding regardless of orientation and movement. This makes the instrument particularly advantageous for field applications. In addition, its time of response to a change in aerosol concentration is as low as approximately 0.3 sec. The detection particle size range is 4.5 nm to >1.0 μm that, in contrast to conventional CPCs, includes a low nano-scale. The present prototype of the UC UFP counter is portable; however, it is undergoing additional miniaturization to make the device wearable. In this study, we examined the feasibility of using the UC UFP counter for measuring the aerosol particle penetration through an elastomeric half-mask respirator donned on a breathing manikin.(6,7) Elastomeric respirators are commonly used by firefighters and first responders. The UC UFP counter was tested against the TSI Model 3007 CPC operating side by side. Combustion particles (generated by burning wood, paper, or plastic) were used as challenge aerosols. Exposures to combustion aerosols at various workplace environments have been associated with adverse health outcomes.(2,3) More than 70% (by number) of particles in a firegenerated smoke are ultrafine.(8) The penetration values were obtained by measuring the aerosol concentrations inside and outside the respirator. The sampled airflow was split with 0.3 L/min directed to the UC UFP counter and 0.7 L/min to the TSI CPC. Measurements were conducted for four respirator sealing conditions (unsealed, sealed at the nose area, sealed at chin and nose, fully sealed) and for three cyclic breathing flow rates (mean inspiratory flow = 30, 85, and 135 L/min) and one constant flow rate (30 L/min).

Analytical Performance Issues

Correspondence to: Sergey Grinshpun, University of Cincinnati, Environmental Health, 3223 Eden Ave., P.O. 670056, Cincinnati, OH 45267; e-mail: sergey. grinshpun@uc.edu. Exposure to ultrafine (≤0.1 μm) particles is widespread at various workplaces. Several studies have revealed associations between ultrafine particle exposures and adverse health effects, including respiratory problems, impairment of cardiovascular function, and others.(1–3) Condensation particle counters (CPCs) are conventionally deployed to measure the ultrafine particle concentrations in real time. For example, the P-Trak (Model 3007, TSI Inc., Shoreview, Minn.) is the most commonly used CPC in occupational environments. However, commercially available CPCs are typically too bulky to serve as workers’ personal exposure monitors; furthermore, their performance is generally affected by their orientation. Several attempts have been made recently to design a better instrument for real-time personal exposure assessment, including a novel ultrafine particle counter (prototype) developed at the University of Cincinnati (UC UFP counter, Figure 1).(4,5) The operation principle of this device, like any CPC, involves condensation on nuclei; however, the novelty of this instrument is that the condensation takes place on nano-materials entering through the input channel. After passing a PM filter (cyclone), the particles enter a non-wetting, porous evaporationcondensation tube. Enlarged due to condensation growth, they are detected with an optical laser counter. Capillary force spontaneously generated on the surface of the non-wetting tube prevents flooding regardless of orientation and movement. This makes the instrument particularly advantageous for field applications. In addition, its time of response to a change in aerosol concentration is as low as approximately 0.3 sec. The detection particle size range is 4.5 nm to >1.0 μm that, in contrast to conventional CPCs, includes a low nano-scale. The present prototype of the UC UFP counter is portable; however, it is undergoing additional miniaturization to make the device wearable. In this study, we examined the feasibility of using the UC UFP counter for measuring the aerosol particle penetration through an elastomeric half-mask respirator donned on a breathing manikin.(6,7) Elastomeric respirators are commonly used by firefighters and first responders. The UC UFP counter was tested against the TSI Model 3007 CPC operating side by side. Combustion particles (generated by burning wood, paper, or plastic) were used as challenge aerosols. Exposures to combustion aerosols at various workplace environments have been associated with adverse health outcomes.(2,3) More than 70% (by number) of particles in a firegenerated smoke are ultrafine.(8) The penetration values were obtained by measuring the aerosol concentrations inside and outside the respirator. The sampled airflow was split with 0.3 L/min directed to the UC UFP counter and 0.7 L/min to the TSI CPC. Measurements were conducted for four respirator sealing conditions (unsealed, sealed at the nose area, sealed at chin and nose, fully sealed) and for three cyclic breathing flow rates (mean inspiratory flow = 30, 85, and 135 L/min) and one constant flow rate (30 L/min).

Exploring a novel ultrafine particle counter for utilization in respiratory protection studies.

Correspondence to: Sergey Grinshpun, University of Cincinnati, Environmental Health, 3223 Eden Ave., P.O. 670056, Cincinnati, OH 45267; e-mail: sergey. grinshpun@uc.edu. Exposure to ultrafine (≤0.1 μm) particles is widespread at various workplaces. Several studies have revealed associations between ultrafine particle exposures and adverse health effects, including respiratory problems, impairment of cardiovascular function, and others.(1–3) Condensation particle counters (CPCs) are conventionally deployed to measure the ultrafine particle concentrations in real time. For example, the P-Trak (Model 3007, TSI Inc., Shoreview, Minn.) is the most commonly used CPC in occupational environments. However, commercially available CPCs are typically too bulky to serve as workers’ personal exposure monitors; furthermore, their performance is generally affected by their orientation. Several attempts have been made recently to design a better instrument for real-time personal exposure assessment, including a novel ultrafine particle counter (prototype) developed at the University of Cincinnati (UC UFP counter, Figure 1).(4,5) The operation principle of this device, like any CPC, involves condensation on nuclei; however, the novelty of this instrument is that the condensation takes place on nano-materials entering through the input channel. After passing a PM filter (cyclone), the particles enter a non-wetting, porous evaporationcondensation tube. Enlarged due to condensation growth, they are detected with an optical laser counter. Capillary force spontaneously generated on the surface of the non-wetting tube prevents flooding regardless of orientation and movement. This makes the instrument particularly advantageous for field applications. In addition, its time of response to a change in aerosol concentration is as low as approximately 0.3 sec. The detection particle size range is 4.5 nm to >1.0 μm that, in contrast to conventional CPCs, includes a low nano-scale. The present prototype of the UC UFP counter is portable; however, it is undergoing additional miniaturization to make the device wearable. In this study, we examined the feasibility of using the UC UFP counter for measuring the aerosol particle penetration through an elastomeric half-mask respirator donned on a breathing manikin.(6,7) Elastomeric respirators are commonly used by firefighters and first responders. The UC UFP counter was tested against the TSI Model 3007 CPC operating side by side. Combustion particles (generated by burning wood, paper, or plastic) were used as challenge aerosols. Exposures to combustion aerosols at various workplace environments have been associated with adverse health outcomes.(2,3) More than 70% (by number) of particles in a firegenerated smoke are ultrafine.(8) The penetration values were obtained by measuring the aerosol concentrations inside and outside the respirator. The sampled airflow was split with 0.3 L/min directed to the UC UFP counter and 0.7 L/min to the TSI CPC. Measurements were conducted for four respirator sealing conditions (unsealed, sealed at the nose area, sealed at chin and nose, fully sealed) and for three cyclic breathing flow rates (mean inspiratory flow = 30, 85, and 135 L/min) and one constant flow rate (30 L/min).

Development of System for Measuring Evaporation Rate through Porous Medium in Fuel Cells

Removing residual water in a fuel cell is a critical operational process for managing its performance and controlling its lifetime. Understanding the mechanism of water transport in fuel cells is essential for the design of the water removal process. In this study, an experimental method for measuring the water evaporation rate through a gas diffusion layer, which is a porous medium, under steady-state conditions was developed. Experimental bench tests were conducted to apply the developed method. Then, the effects of various parameters of the drying gas and the gas diffusion layer were experimentally measured. The water evaporation rate increased as the humidity of the drying gas decreased and the flow rate of the drying gas increased. In addition, a thinner gas diffusion layer yielded a higher water evaporation rate.

Visualization of water on through‐plane direction of GDL using X‐ray radiography

In this investigation, we visualized water distribution and behavior of water on through plane direction of GDL (Gas Diffusion Layer), which is one of components of PEMFC, using X‐ray radiography. In order to investigate water distribution and behavior at GDL of PEMFC, the facilities was set up at the 7B2 beam line in Pohang Accelerator Laboratory. The phenomena of cathode side GDL is more important because the cathode side GDL has more water than the anode side. For this reason, the cathode side GDL was targeted and test section (Figure 1) was made to make similar boundary condition with a cathode side GDL of operating PEMFC. GDL faced two single channels. One is air channel as cathode gas channel of PEMFC and the other is liquid channel as cathode catalyst layer. Water is produced in cathode catalyst layer and almost of this water transport through cathode GDL. Because of this, liquid channel was adopted as catalyst layer. Images of water distribution were recorded per 4 second under various liquid pressure conditions. Water content was calculated from these images using mathematic process.

Visualization of water distribution in operating PEMFC using x-ray microscopy

In this investigation, X-ray microscopy (7B2) in Pohang Accelerator Laboratory was employed to visualize the water distribution in operating PEMFC which had 2cm × 2cm active area. This X-ray microscopy has 1μm spatial resolution with 1.5mm × 1.2mm view area. Each image spent about 1.3 second, 0.65 second for exposure and about 0.6 second for data read out. The resistance of the electric loader was changed and electric current and voltage was measured during images were recorded. The water distribution in PEMFC was analyzed with this I-V curve. Water distribution was depend on current density and aggregated on interfaces of layers (GDL, MPL, MEA).Copyright